Method of manufacturing a semiconductor device with leveling of a surface of a semiconductor film through irradiation Number:6,803,296 from the United States Patent and Trademark Office (PTO) owispatent To obtain a TFT, in which an off-current value is low and the fluctuation is suppressed, and an electronic equipment provided with the TFT. A film deposition temperature is set to substantially the same between a base insulating film and an amorphous semiconductor film to improve flatness of the semiconductor film. Then, laser light irradiation is conducted.<H semiconductor, manufacturing, Method, of, manuf, 6803296.html, Patent, pto, 6803296

Title: Method of manufacturing a semiconductor device with leveling of a surface of a semiconductor film through irradiation

Abstract: To obtain a TFT, in which an off-current value is low and the fluctuation is suppressed, and an electronic equipment provided with the TFT. A film deposition temperature is set to substantially the same between a base insulating film and an amorphous semiconductor film to improve flatness of the semiconductor film. Then, laser light irradiation is conducted.

Patent Number: 6,803,296 Issued on 10/12/2004 to Miyairi

Inventors: Miyairi; Hidekazu (Kanagawa, JP)
Assignee: Semiconductor Energy Laboratory Co., Ltd. (Kanagawa-Ken, JP)

Appl. No.: 10/157,233

Filed: May 30, 2002

Foreign Application Priority Data


Jun 01, 2001 [JP]			2001-166642

Current U.S. Class: 438/486 ; 257/E21.413; 257/E21.703; 257/E27.111; 257/E29.275; 257/E29.278; 257/E29.293; 438/487; 438/509

Field of Search: 257/66,347,352,353 438/149,150,160,166,486,487,488,502,509

References Cited [Referenced By]

U.S. Patent Documents


5693541	December 1997	Yamazaki et al.
6225197	May 2001	Maekawa
6455360	September 2002	Miyasaka
6559036	May 2003	Ohtani et al.
2001/0034088	October 2001	Nakamura et al.

Foreign Patent Documents


8-78329	Mar., 1996	JP
2001-60551	Mar., 2001	JP

Primary Examiner: Pham; Long
Assistant Examiner: Pham; Hoai
Attorney, Agent or Firm: Fish & Richardson P.C.

Claims

What is claimed is:

1. A method of manufacturing a semiconductor device, comprising: forming a base insulating film on an insulating surface; forming an amorphous semiconductor film on the base insulating film; doping the amorphous semiconductor film with a metal element; performing heat treatment to the amorphous semiconductor film; irradiating the amorphous semiconductor film with a first laser light to form a semiconductor film having a crystalline structure and an oxide film thereon; removing the oxide film; and irradiating the semiconductor film having the crystalline structure with a second laser light in an inert gas atmosphere or in a vacuum to level the surface of the semiconductor film having the crystalline structure.

2. A method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is a heating process or a process of irradiating a strong light.

3. A method of manufacturing a semiconductor device according to claim 2, wherein the strong light is a light emitted from one selected from the group consisting of a halogen lamp, a metal halide lamp, a xenon-arc lamp, a carbon-arc lamp, a high-pressure sodium lamp and a high-pressure mercury lamp.

4. A method of manufacturing a semiconductor device according to claim 1, wherein the metal element is one or a plurality of elements selected from the group consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.

5. A method of manufacturing a semiconductor device according to claim 1, wherein each of the first and second laser lights is a laser light emitted from an excimer laser, a YAG laser, a YVO.sub.4 laser or a YLF laser.

6. A method of manufacturing a semiconductor device according to claim 1, wherein the inert gas atmosphere is a nitrogen atmosphere.

7. A method of manufacturing a semiconductor device according to claim 1, wherein the second laser light is a continuous oscillation laser.

8. A method of manufacturing a semiconductor device, comprising: forming a base insulating film on an insulating surface; forming an amorphous semiconductor film on the base insulating film; doping the amorphous semiconductor film with a metal element; performing heat treatment to the amorphous semiconductor film; irradiating the amorphous semiconductor film with a first laser light to form a semiconductor film having a crystalline structure and an oxide film thereon; removing the oxide film; and irradiating the semiconductor film having the crystalline structure with a second laser light in an inert gas atmosphere or in a vacuum to level the surface of the semiconductor film having the crystalline structure, wherein the first laser light is a continuous oscillation laser.

9. A method of manufacturing a semiconductor device, comprising: forming a base insulating film on an insulating surface; forming an amorphous semiconductor film on the base insulating film; doping the amorphous semiconductor film with a metal element; performing heat treatment to the amorphous semiconductor film; irradiating the amorphous semiconductor film with a first laser light to form a semiconductor film having a crystalline structure and an oxide film thereon; removing the oxide film; irradiating the semiconductor film having the crystalline structure with a second laser light in an inert gas atmosphere or in a vacuum to level the surface of the semiconductor film having the crystalline structure; forming a semiconductor film comprising a noble gas element over the semiconductor film having the crystalline structure; and gettering the metal element to the semiconductor film comprising the noble gas element to reduce the metal element in the semiconductor film having the crystalline structure.

10. A method of manufacturing a semiconductor device, comprising: forming a base insulating film on an insulating surface; forming an amorphous semiconductor film on the base insulating film; doping the amorphous semiconductor film with a metal element; performing heat treatment to the amorphous semiconductor film; irradiating the amorphous semiconductor film with a first laser light to form a semiconductor film having a crystalline structure and an oxide film thereon; removing the oxide film; irradiating the semiconductor film having the crystalline structure with a second laser light in an inert gas atmosphere or in a vacuum to level the surface of the semiconductor film having the crystalline structure, forming a barrier layer by oxidizing the surface of the semiconductor film having the crystalline structure; forming a semiconductor film comprising a noble gas element on the barrier layer; and gettering the metal element to the semiconductor film comprising the noble gas element to reduce the metal element in the semiconductor film having the crystalline structure.

11. A method of manufacturing a semiconductor device, comprising: forming a base insulating film on an insulating surface; forming an amorphous semiconductor film on the base insulating film; doping the amorphous semiconductor film with a metal element; performing heat treatment to the amorphous semiconductor film; irradiating the amorphous semiconductor film with a first laser light to form a semiconductor film having a crystalline structure and an oxide film thereon; removing the oxide film; irradiating the semiconductor film having the crystalline structure with a second laser light in an inert gas atmosphere or in a vacuum to level the surface of the semiconductor film having the crystalline structure; patterning the semiconductor film having the crystalline structure; forming a gate insulating film over the patterned semiconductor film having the crystalline structure; forming a gate electrode over the gate insulating film.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having a circuit composed of thin film transistors (hereinafter, referred to as TFTs) and a method of manufacturing the semiconductor device. For example, the present invention relates to an electro-optical device typified by a liquid crystal display panel and an electronic equipment mounted with the electro-optical device as a component.

Note that the term semiconductor device in this specification indicates devices in general capable of functioning with the use of semiconductor characteristics, and electro-optical devices, light emitting devices provided with EL elements and the like, semiconductor circuits and electronic equipment are all included in the category of the semiconductor device.

2. Description of the Related Art

In recent years, a technique of constituting a thin film transistor (TFT) by using a semiconductor thin film (with a thickness of approximately several to several hundred of nm) formed on a substrate having an insulating surface has attracted attention. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device, and needs to be developed promptly as, in particular, a switching element of an image display device.

An active matrix liquid crystal module, an EL module, and a contact image sensor are known as typical examples of the thin film transistors. Particularly, a TFT having a silicon film having a crystalline structure (typically, polysilicon film) as an active layer (hereafter, referred to as polysilicon TFT) has high filed effect mobility, and thus a circuit with various functions can be formed by using the TFT.

For example, in a liquid crystal module mounted to a liquid crystal display device, a pixel portion for performing image display for each functional block and a driver circuit for controlling the pixel portion, such as a shift register circuit, a level shifter circuit, a buffer circuit or a sampling circuit, which is based on a CMOS circuit are formed on one substrate.

Further, TFTs (pixel TFTs) are respectively arranged in several tens to several million of pixels in the pixel portion of the active matrix liquid crystal module, and pixel electrodes are provided to the respective pixel TFTs. Opposing electrodes are provided in an opposing substrate sandwiching liquid crystal with a substrate, and a sort of capacitor with the liquid crystal as dielectric is formed. A voltage applied to the respective pixels is controlled with a switching function of the TFT to control charge to the capacitor to thereby drive the liquid crystal. Thus, a light transmission amount is controlled, thereby displaying an image.

The pixel TFT consists of an n-channel TFT, and applies a voltage to the liquid crystal to drive it as a switching element. Since the liquid crystal is driven by an alternating current, a system called frame inversion driving is often adopted. In this system, in order to suppress power consumption at a low level, it is important to sufficiently lower an off-current value (drain current that flows at the time of off-operation of the TFT) for a characteristic required for the pixel TFT.

Further, in order to manufacture a TFT having superior electrical characteristics at lower cost, a laser annealing technique that enables processing for a short period of time has been essential.

Laser annealing is generally used for a process of crystallizing an amorphous semiconductor film, a process of improving crystallinity, and the like. Note that a laser often used for laser annealing is an excimer laser. A method of conducting laser annealing in which: a laser beam emitted from a pulse oscillation laser with large output is processed by an optical system so as to have a shape of a square spot several by several centimeters or a linear shape with a length of, for example, 10 cm or more on an irradiation surface; and an irradiation position of the laser beam is scanned relative to the irradiation surface, is preferably used since the method provides high productivity and is superior in mass-production. Particularly, when a laser beam having a linear shape (hereinafter referred to as linear beam) is used on the irradiation surface, differently from the case where a spot laser beam, which needs scanning in back and forth directions and right and left directions, is used, the laser beam can be irradiated over the irradiation surface only with the scanning in a direction perpendicular to a line direction of the linear beam, which provides high productivity. The reason the scanning is performed in the direction perpendicular to the line direction is that the perpendicular direction is the most effective scanning direction. Due to the high productivity, the use of the linear beam from a large-output laser, which is processed by an appropriate optical system, is becoming the main stream in laser annealing. Further, the linear beam is irradiated in an overlapping manner while gradually shifting in a short direction, whereby laser annealing is conducted to the entire surface of an amorphous silicon film to crystallize the film or improve the crystallinity.

Further, in order to manufacture a TFT at lower cost, it has been essential to manufacture the TFT on a glass substrate which is cheaper than a semiconductor substrate or a quartz substrate and which can attain a large surface area thereof.

In case of using the glass substrate, in order to prevent alkaline metal contained in the glass substrate from diffusing, a base insulating film comprised of an insulating film containing silicon as its main constituent (silicon oxide film, silicon nitride film, silicon oxynitride film, or the like) is provided, an amorphous silicon film is formed on the film, and then, laser light irradiation is conducted.

The present inventors found a large number of minute holes in the surface of the silicon film that has undergone laser irradiation through many experiments and studies. The minute hole is very small, and a photograph of the hole in SEM (magnification of 35 thousand) observation is shown in FIG. 26. The present inventors found that variation is caused among a large number of TFTs formed on a substrate with the cause of unevenness of the surface of a semiconductor film due to the minute hole. In the case where the active layer of the TFT is formed at the position of the minute hole, the TFT has the poor electrical characteristics in comparison with other TFTs manufactured on the same substrate.

Further, the minute hole often occurs in the case where laser light is irradiated with a relatively high energy density or a relatively high overlap ratio. In particular, there is a tendency that the minute hole appears remarkably in the case where laser light is irradiated in a nitrogen atmosphere or a vacuum.

Moreover, the minute hole occurs in the case where the amorphous silicon film is formed on the base insulating film, but does not occur in the case where the amorphous silicon film is formed contacting the substrate without forming the base insulating film.

Based on the above, the present inventors made many experiments and studies from various angles in order to pinpoint the cause of occurrence of the minute hole. As a result, they further found that minute convex portions were formed in the surface of the amorphous silicon film before laser light irradiation. This minute convex portion is also very small (typically, with a diameter of 1 .mu.m or less and a height of 0.05 .mu.m or less), and a photograph of the convex portion in SEM (magnification of 50 thousand) observation is shown in FIG. 25. Note that when the minute convex portion and the vicinity thereof are measured by EDX analysis, it is confirmed that the convex portion is not impurities such as dust.

When the minute convex portion is irradiated with laser light, the minute hole is easy to occur. The present inventors found that the minute convex portion is the cause of occurrence of the minute hole.

The minute convex portion is formed at the step of forming the amorphous silicon film on the base insulating film, and can be observed as an extremely small luminous point by microscopic observation in a dark-field reflection mode with magnification of 500.

Means can be adopted in which the base insulating film is not formed. However, the base insulating film is provided in order that impurity ions such as alkaline metal contained in the glass substrate do not diffuse into a semiconductor film formed above the base insulating film, and is indispensable for manufacture of the TFT at lower cost.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an object of the present invention is therefore to form a base insulating film and an amorphous semiconductor film in lamination on an inexpensive substrate (glass substrate or the like) and to suppress occurrence of a minute convex portion and of a minute hole due to the convex portion even with laser light irradiation. That is to say, an object of the present invention is to obtain an amorphous semiconductor film having an excellent surface in flatness on a base insulating film.

In order to solve the above-mentioned problems, many experiments and studies were made from various angles. As a result, a film deposition temperature of the base insulating film and a film deposition temperature of the amorphous semiconductor film are made substantially equal to each other, whereby the amorphous semiconductor film having a surface which does not have the minute convex portion and which is excellent in flatness can be obtained. Thus, the occurrence of the minute hole can be suppressed even with laser light irradiation.

Note that "film deposition temperatures are made substantially equal to each other"indicates that the ratio of the film deposition temperature of the amorphous semiconductor film to the film deposition temperature of the base insulating film is 0.8 to 1.2, preferably that the difference between the base insulating film and the amorphous semiconductor film in film deposition temperature is in a range of .+-.50.degree. C.

According to a first structure of the present invention disclosed in this specification, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming an amorphous semiconductor film on the base insulating film; and a third step of performing crystallization by irradiation of laser light to the amorphous semiconductor film, thereby forming a semiconductor film having a crystalline structure, characterized in that a film deposition temperature of the base insulating film is the same as a film deposition temperature of the amorphous semiconductor film.

According to a second structure of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming an amorphous semiconductor film on the base insulating film; and a third step of performing crystallization by irradiation of laser light to the amorphous semiconductor film, thereby forming a semiconductor film having a crystalline structure, characterized in that a difference in film deposition temperature between the base insulting film and the amorphous semiconductor film is in a range of .+-.50.degree. C.

The film deposition temperature of the base insulating film and the film deposition temperature of the amorphous semiconductor film are made substantially the same, whereby the semiconductor film surface with high flatness can be obtained. By using the semiconductor film with high flatness in the active layer of the TFT, the withstand voltage is raised. Thus, the reliability of the TFT is improved.

Further, the present invention is applicable to not only laser light irradiation in crystallization but also a process with laser light used in the manufacturing process of the semiconductor device, for example, laser annealing used for the improvement of film quality and for the activation of the impurity element.

According to a third structure of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming an amorphous semiconductor film on the base insulating film; and a third step of performing laser light irradiation to the amorphous semiconductor film, characterized in that a difference in film deposition temperature between the base insulting film and the amorphous semiconductor film is in a range of .+-.50.degree. C.

Further, in prior art, as a leveling process, there are given an etchback method, in which etching is performed to attain leveling after the formation of an application film, a mechanical chemical polishing (CMP) method, and the like. However, in the present invention, it is only necessary that the film deposition temperature is made the same between the base insulating film and the amorphous semiconductor film, and the reduction in the film thickness due to leveling and the increase in the number of steps are not effected.

Further, the present invention is particularly effective in the case where the base insulating film is required as in case of the glass substrate.

According to a fourth structure of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming an amorphous semiconductor film on the base insulating film; a third step of performing crystallization by irradiation of laser light to the amorphous semiconductor film, thereby forming a semiconductor film having a crystalline structure and an oxide film on the semiconductor film, a fourth step of removing the oxide film; and a fifth step of performing laser light irradiation in an inert gas atmosphere or in a vacuum, thereby leveling the surface of the semiconductor film, characterized in that a difference in film deposition temperature between the base insulting film and the amorphous semiconductor film is in a range of .+-.50.degree. C.

Further, the present invention is particularly effective since minute holes are easy to occur in the case where laser light is irradiated to the semiconductor film in a vacuum or in an inert gas atmosphere.

Further, in the fourth structure, it is characterized in that energy density of the laser light in the fifth step is higher than energy density of the laser light in the third step.

Further, in the fourth structure, it is characterized in that an overlap ratio of the laser light in the fifth step is lower than an overlap ratio of the laser light in the third step.

According to a fifth structure of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming an amorphous semiconductor film on the base insulating film; a third step of doping the amorphous semiconductor film with a metal element; a fourth step of performing heat treatment to the semiconductor film and then performing laser light irradiation, thereby forming a semiconductor film having a crystalline structure and an oxide film on the semiconductor film; a fifth step of removing the oxide film; and a sixth step of performing laser light irradiation in an inert gas atmosphere or in a vacuum, thereby leveling the surface of the semiconductor film, characterized in that a difference in film deposition temperature between the base insulting film and the amorphous semiconductor film is in a range of .+-.50.degree. C.

According to a sixth structure of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first step of forming a base insulating film on an insulating surface; a second step of forming a first semiconductor film having an amorphous structure on the base insulating film; a third step of doping the first semiconductor film having an amorphous structure with a metal element; a fourth step of performing heat treatment to the first semiconductor film and then performing laser light irradiation, thereby forming a first semiconductor film having a crystalline structure and an oxide film on the first semiconductor film; a fifth step of removing the oxide film; a sixth step of performing laser light irradiation in an inert gas atmosphere or in a vacuum, thereby leveling the surface of the first semiconductor film; a seventh step of oxidizing the surface of the semiconductor film having a crystalline structure with a solution containing ozone, thereby forming a barrier layer; an eighth step of forming a second semiconductor film containing a noble gas element on the barrier layer; a ninth step of gettering the metal element to the second semiconductor film, thereby removing or reducing the metal element in the first semiconductor film having a crystalline structure; and a tenth step of removing the second semiconductor film and the barrier layer, characterized in that a difference in film deposition temperature between the base insulting film and the first semiconductor film having an amorphous structure is in a range of .+-.50.degree. C.

Further, in the sixth structure, it is characterized in that the noble gas element is one or a plurality of elements selected from the group consisting of He, Ne, Ar, Kr and Xe.

Further, in the sixth structure, it is characterized in that the second semiconductor film is formed by sputtering with semiconductor as a target in an atmosphere containing the noble gas element.

Further, in the fifth structure or the sixth structure, it is characterized in that the heat treatment in the fourth step is a heating process or a process of irradiating a strong light. The strong light is a light emitted from one selected from the group consisting of a halogen lamp, a metal halide lamp, a xenon-arc lamp, a carbon-arc lamp, a high-pressure sodium lamp and a high-pressure mercury lamp.

Further, in the fifth structure or the sixth structure, the metal element is one or a plurality of elements selected from the group consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au, which are elements that accelerate crystallization of silicon.

Further, in each of the above-described structures, the laser light is emitted from an excimer laser, an Ar laser or a Kr laser of continuous oscillation or pulse oscillation type, or a YAG laser, a YVO.sub.4 laser, a YLF laser, a YAlO.sub.3 laser, a glass laser, a ruby laser, an alexandrite laser, or a Ti:sapphire laser of continuous oscillation or pulse oscillation type.

Further, in the fourth structure, the fifth structure or the sixth structure, the inert gas atmosphere is a nitrogen atmosphere.

Further, in the fourth structure, the fifth structure or the sixth structure, the second laser light irradiation is a leveling process performed in a vacuum or in an inert gas atmosphere, and the surface of the semiconductor film is further leveled. Particularly in the case where the gate insulating film is thin, for example, the gate insulating film has a thickness of 100 nm or less, the present invention is very effective.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1E are views according to the present invention (Embodiment Mode 1);

FIGS. 2A to 2G are views according to the present invention (Embodiment Mode 2);

FIGS. 3A to 3G are views according to the present invention (Embodiment Mode 3);

FIGS. 4A to 4E are views according to the present invention (Embodiment Mode 3);

FIGS. 5A to 5D are views of a manufacturing process of an active matrix substrate;

FIGS. 6A to 6C are views of the active matrix substrate;

FIG. 7 is a view of the active matrix substrate;

FIG. 8 is a photograph of a vicinity of a gate electrode in observation with TEM;

FIGS. 9A and 9B are graphs showing deterioration rates in a TFT (a gate insulating film with a thickness of 115 nm);

FIGS. 10A and 10B are graphs showing deterioration rates in a TFT (a gate insulating film with a thickness of 80 nm);

FIGS. 11A and 11B are graphs showing deterioration rates in a TFT (a gate insulating film with a thickness of 60 nm);

FIG. 12 is a graph showing an off-current value in a TFT (a gate insulating film with a thickness of 115 nm) with L/W=2/8;

FIG. 13 is a graph showing an off-current value in a TFT (a gate insulating film with a thickness of 80 nm) with L/W=2/8;

FIG. 14 is a graph showing an off-current value in a TFT (a gate insulating film with a thickness of 60 nm) with L/W=2/8;

FIG. 15 is a graph showing an off-current value in a TFT (a gate insulating film with a thickness of 60 nm) with L/W=7/40;

FIG. 16 is a view of an outer appearance of an AM-LCD

FIG. 17 is a view of one example of a sectional view of a liquid crystal display device (Embodiment 4);

FIGS. 18A and 18B are a top view and a sectional view of an EL module (Embodiment 5);

FIG. 19 is a sectional view of the EL module (Embodiment 5);

FIGS. 20A and 20B are views of examples of TFTs (Embodiment 6);

FIG. 21 is a view of a laser device (Embodiment 7);

FIGS. 22A to 22F show examples of electronic equipment;

FIGS. 23A to 23D show examples of electronic equipment;

FIGS. 24A to 24C show examples of electronic equipment;

FIG. 25 is a photograph of a minute convex portion in observation with SEM (magnification of 50 thousand); and

FIG. 26 is a photograph of a minute hole in observation with SEM (magnification of 35 thousand).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment modes of the present invention will be described below.

In the present invention, at least a process of forming a base insulating film on an arbitrary insulating surface with a large area, a process of forming a semiconductor film on the base insulating film at the same film deposition temperature as that of the base insulating film, and a process of irradiating laser light to the semiconductor film are provided.

By adopting the same film deposition temperature, a flat semiconductor film surface with no minute convex portion can be obtained at the stage before irradiation of laser light. When laser light irradiation is conducted to the semiconductor film having the flat surface to manufacture a TFT, satisfactory electrical characteristics can be obtained.

Hereinafter, a manufacturing procedure of a typical TFT according to the present invention is simply shown with reference to FIGS. 1A to 4E.

Embodiment Mode 1

Here, an example in which the present invention is applied to a technique of crystallizing an amorphous semiconductor film by laser light irradiation is shown.

In FIG. 1A, reference numeral 10 indicates a substrate having an insulating surface, and reference numeral 11 indicates a base insulating film that becomes a blocking layer.

In FIG. 1A, a glass substrate, a quartz substrate, a ceramic substrate or the like can be used as the substrate 10. Further, a silicon substrate, a metal substrate or a stainless substrate having an insulating film on its surface may also be used. Also, a plastic substrate having heat-resistance that withstands a process temperature in this embodiment mode may be used.

As for the substrate 10, a glass substrate is particularly preferable in a point that the substrate is inexpensive, is easy of supply of a large area substrate, and is suitable for mass-production.

First, the base insulating film 11 is formed on the substrate. As the base insulating film 11, an insulating film of a single layer or a lamination layer selected from a silicon oxide film, a silicon nitride film, a silicon oxynitride (SiO.sub.X N.sub.Y) film and the like which are obtained by plasma CVD can be used.

As for a typical example of the base insulating film 11, it is preferable that a silicon oxynitride film is formed with a thickness of 50 to 100 nm by using SiH.sub.4, NH.sub.3 and N.sub.2 O as reaction gases and a silicon oxynitride film is formed with a thickness of 100 to 150 nm and with a film deposition temperature of 100 to 450.degree. C. by using SiH.sub.4 and N.sub.2 O as reaction gases, thereby forming a lamination structure.

Next, a semiconductor film 12 having an amorphous structure is formed on the base insulating film 11 at the same film deposition temperature of that of the base insulating film. (FIG. 1B) The film deposition temperature is made the same, preferably at 300 to 400.degree. C. between the base insulating film and the semiconductor film having an amorphous structure, whereby a flat surface of the semiconductor film which has no minute convex portion can be obtained at the stage before laser light irradiation. The minute convex portion is not seen in observation with SEM at this stage.

A semiconductor material containing silicon as its main constituent is used for the semiconductor film 12 having an amorphous structure. Typically, an amorphous silicon film, an amorphous silicon germanium film or the like is applied, and the film is formed to have a thickness of 10 to 100 nm by plasma CVD.

Subsequently, laser light irradiation is conducted as a technique of crystallizing the semiconductor film 12 having an amorphous structure. (FIG. 1C) A surface state of a semiconductor film 13 having a crystalline structure obtained by the laser light irradiation is good, that is, no minute hole is observed with SEM. Therefore, a size of surface unevenness due to the minute hole, which is regarded as the cause of the unevenness, and variation of characteristics of a TFT are reduced. Note that excimer laser light having a wavelength of 400 nm or less, second harmonic wave or third harmonic wave of a YAG laser, or laser light emitted from a YAG laser, YVO.sub.4 laser, YLF laser, YAlO.sub.3 laser, glass laser, ruby laser, alexandrite laser, or Ti:sapphire laser of continuous oscillation type or pulse oscillation type is used for laser light. Further, in the case where laser irradiation is conducted in an atmosphere containing oxygen, a thin oxide film (not shown here) is formed on the surface of the semiconductor film. Note that although not shown in the figure, unevenness called ridge is also formed.

Next, a semiconductor layer 14 having a desired shape is formed by patterning the semiconductor film 13 with a known technique. (FIG. 1D) Further, it is desirable that a thin oxide film is formed from ozone water on the surface of the semiconductor layer 14 before formation of a mask made of resist.

Next, after the surface of the semiconductor layer is cleaned with an etchant containing hydrofluoric acid, an insulating film containing silicon as its main constituent is formed as a gate insulating film 15. The surface cleaning and the formation of the gate insulating film are desirably performed in succession without exposure to an atmosphere.

Subsequently, after the surface of the gate insulating film 15 is cleaned, a gate electrode 16 is formed. Then, an impurity element imparting n-type conductivity (P, As or the like), in this case phosphorous, is appropriately added to the semiconductor, thereby forming a source region 17 and a drain region 18. After the addition, heat treatment, irradiation of a strong light or irradiation of a laser light is conducted for activating the impurity element. Further, simultaneously with the activation, plasma damage to the gate insulating film or plasma damage to an interface of the gate insulating film and the semiconductor layer can be recovered. Particularly, it is very effective that the second harmonic wave of the YAG laser is irradiated to a front surface or a back surface to thereby activate the impurity element in an atmosphere at room temperature to 300.degree. C. The YAG laser requires a little amount of maintenance, and thus, is a preferable activation means.

In the subsequent steps, an interlayer insulating film 20 is formed, hydrogenation is conducted, contact holes that reach the source region and the drain region are formed, and a source electrode 21 and a drain electrode 22 are formed, thereby completing a TFT (n-channel TFT). (FIG. 1E) Note that reference numeral 19 indicates a channel forming region and that a semiconductor layer containing at least the channel forming region 19, the drain region 18 and the source region 17 is called an active layer in this specification.

Further, the flatness of the semiconductor surface of the TFT thus obtained is rapidly improved since the occurrence of the minute hole can be suppressed in accordance with the process in this embodiment mode. Thus, an off-current value is reduced, and variation of the off-current value is also reduced. In addition, reliability of the TFT is increased in accordance with the process in this embodiment mode.

Further, the present invention is not limited to the TFT structure in FIG. 1E, and a lightly doped drain (LDD) structure, in which an LDD region is provided between a channel forming region and a drain region (or source region), may be adopted if necessary. In this structure, a region where an impurity element is added at a low concentration is provided between the channel forming region and the source region or the drain region formed by adding an impurity element at a high concentration, and is called an LDD region. Further, a so-called GOLD (gate-drain overlapped LDD) structure may be adopted in which an LDD region is arranged overlapping a gate electrode through a gate insulating film. Since the GOLD structure is a TFT structure with high reliability, higher reliability can be obtained in the case where the present invention is applied to the GOLD structure.

Further, the description is made here with the n-channel TFT. However, of course, a p-channel TFT can be formed by using a p-type impurity element instead of an n-type impurity element.

Further, the description is made here with an example of a top gate type TFT. However, the present invention can be applied irrespective of a TFT structure. For example, the present invention can be applied to a bottom gate type (inverted stagger type) TFT or a stagger type TFT. Also, the present invention can be applied to a TFT with a dual gate structure in which gate electrodes are respectively provided above and below a channel forming region through insulating films.

Moreover, the following may be adopted in which: the semiconductor layer having a desired shape is formed without conducting laser light irradiation before patterning; the surface of the semiconductor layer is cleaned to remove the oxide film or the like; and laser light irradiation is conducted.

Furthermore, the description is made here with an example of crystallization of laser light. However, the present invention is effective irrespective of a crystallization method and the like as long as the method includes a step of using laser light processing. The present invention can be applied to a crystallization method, for example, in which nickel is selectively added to a film and then a laser light irradiation is performed thereon.

Note that, in this specification, the "electrode" is a part of the "wiring" and indicates a point where electrical connection is made with another wiring or a point where the wiring intersects with the semiconductor layer. Therefore, for the sake of convenience of the description, the "wiring" and the "electrode" are separately used. However, the "wiring" is always included in the term "electrode".

Embodiment Mode 2

In this case, an example in which the present invention is applied to a technique of leveling a semiconductor film by laser light irradiation is shown in FIGS. 2A to 2G.

First, in this embodiment mode, the manufacturing steps until the formation of the amorphous semiconductor film are the same as those in Embodiment Mode 1, and thus, detailed description thereof is omitted.

In FIG. 2A, reference numeral 30 indicates a substrate having an insulating surface, reference numeral 31 indicates a base insulating film that becomes a blocking layer. Further, in FIG. 2B, reference numeral 32 indicates a semiconductor film having an amorphous structure. The base insulating film and the semiconductor film are formed at the same film deposition temperature, whereby a flat surface of the semiconductor film with no minute convex portion can be obtained at the stage immediately after the film deposition.

The state of FIG. 2B is obtained in accordance with Embodiment Mode 1. Then, first laser light irradiation (a repetition frequency of 10 to 100 Hz, energy density of 400 to 500 mJ/cm.sup.2) is conducted to crystallize the semiconductor film in an atmosphere containing oxygen. (FIG. 2C) Under the irradiation conditions: energy density of 476 mJ/cm.sup.2 ; a repetition frequency of 30 Hz; and an overlap ratio of 91%, the laser light irradiation is conducted in an atmosphere. After the laser light irradiation, a semiconductor film 33a having a crystalline structure is obtained, and an oxide film 34 is formed thereon. Note that, although not shown in the figure here, unevenness called ridge is formed.

Here, an example in which a pulse oscillation laser is used is shown, but a continuous oscillation laser may also be used. In order to obtain crystals with a large particle size in crystallization of the amorphous semiconductor film, it is preferable that a solid laser that enables continuous oscillation is used to apply second harmonic to fourth harmonic waves that have a fundamental wavelength. Typically, the second harmonic wave (532 nm) or the third harmonic wave (355 nm) of a Nd:YVO.sub.4 laser (fundamental wavelength, 1064 nm) may be applied. In the case where the continuous oscillation laser is used, laser light emitted from a continuous oscillation YVO.sub.4 laser with an output of 10 W is converted into harmonic wave by a non-linear optical element. Further, there is a method of emitting harmonic wave by putting YVO.sub.4 crystals and the nonlinear optical element into a resonator. Then, laser light is preferably formed to have a rectangular shape or an elliptical shape on an irradiation surface by an optical system, and the light is irradiated to a member to be processed. Note that the laser light (laser spot) on the irradiation surface is formed to have an elliptical shape having a short diameter of 3 to 100 .mu.m and a long diameter of 100 .mu.m or more with a beam forming means comprised of an optical system. Instead of the elliptical shape, a rectangular shape with a short side of 3 to 100 .mu.m and a long side of 100 .mu.m or more may be adopted. The rectangular shape or the elliptical shape is adopted for conducting laser annealing over the surface of the substrate with efficiency. Here, the reason the length of the long diameter (or long side) is set to 100 .mu.m or more is that it is sufficient that an operator may appropriately determine the length of the long diameter (or long side) as long as the laser light has energy density suitable for laser annealing. The energy density at this time needs to be appropriately 0.01 to 100 MW/cm.sup.2 (preferably 0.1 to 10 MW/cm.sup.2). The irradiation may be conducted while moving the semiconductor film relative to the laser light at a speed of approximately 10 to 2000 cm/s.

Next, the oxide film 34 is removed. (FIG. 2D)

Then, laser light (second laser light) is irradiated to the semiconductor film 33a having a crystalline structure in a nitrogen atmosphere or in a vacuum. The energy density of the second laser light is made larger than that of the first laser light, preferably larger by 30 to 60 mJ/cm.sup.2. Incidentally, if the energy density of the second laser light is larger by 90 mJ/cm.sup.2 or more than the energy density of the first laser light, the crystallinity of the semiconductor film is reduced, or the semiconductor film is micro-crystallized, which leads to deterioration of the characteristics. Here, with the irradiation conditions: energy density of 537 mJ/cm.sup.2 and a repetition frequency of 30 Hz, laser light irradiation is performed in a nitrogen atmosphere. In the case where the laser light irradiation is performed in a nitrogen atmosphere or in a vacuum, a minute hole is easily formed in the semiconductor film. However, the base insulating film and the semiconductor film are formed at the same film deposition temperature, whereby occurrence of the minute hole can be suppressed. Therefore, a size of surface unevenness due to the minute hole, which is regarded as the cause of the unevenness, and variation of characteristics of a TFT can be reduced. Further, the size of the ridge formed by the first laser light irradiation is reduced by the second laser light to level its surface.

Moreover, the continuous oscillation laser may be used for the second laser light. Typically, the second harmonic wave (532 nm) or the third harmonic wave (355 nm) of the Nd:YVO.sub.4 laser (fundamental wavelength, 1064 nm) may be applied.

A surface of a semiconductor film 33b having a crystalline structure thus obtained is very flat. Further, since the flatness is improved, a gate insulating film formed later can be made thin, and thus, an on-current value of a TFT can be increased. Further, the flatness is improved, whereby an off-current value can be reduced in case of manufacturing the TFT. The reliability of the TFT is also improved.

Next, a semiconductor layer 35 having a desired shape is formed from the semiconductor film by using a known patterning technique. (FIG. 2F)

The subsequent steps are conducted by using the same steps as in Embodiment Mode 1, thereby completing a TFT. (FIG. 2G)

In FIG. 2G, reference numeral 36 indicates a gate insulating film, 37 indicates a gate electrode, 38 indicates a source region, 39 indicates a drain region, 40 indicates a channel forming region, 41 indicates an interlayer insulating film, 42 indicates a source electrode, and 43 indicates a drain electrode.

Further, the following may be adopted in which: the second laser light irradiation is not performed before patterning; a semiconductor layer having a desired shape is formed; the surface of the semiconductor layer is cleaned; the oxide film and the like are removed; and the second laser light irradiation is conducted in an inert gas atmosphere or in a vacuum, thereby leveling the semiconductor layer.

In addition, in the second laser light irradiation, a nitrogen gas may be sprayed to the vicinity of a region to be irradiated.

Embodiment Mode 3

An example is shown in FIGS. 3A to 4E in which the present invention is applied to a technique in which: after a metal element that promotes crystallization of silicon is added, heat treatment is conducted for crystallization; after laser light irradiation is conducted, an oxide film is removed, and laser light irradiation is conducted again to flatten a semiconductor film; and gettering is conducted for removing the metal element.

First, in this embodiment mode, the manufacturing steps until the formation of the amorphous semiconductor film are the same as those in Embodiment Mode 1. Thus, detailed description thereof is omitted.

In FIG. 3A, reference numeral 50 indicates a substrate having an insulating surface, and reference numeral 51 indicates a base insulating film that becomes a blocking layer. Further, in FIG. 3B, reference numeral 52 indicates a semiconductor film having an amorphous structure. The base insulating film and the semiconductor film are formed at the same film deposition temperature, whereby a flat surface of the semiconductor film with no minute convex portion can be obtained at the stage immediately after the film deposition.

The state of FIG. 3B is obtained in accordance with Embodiment Mode 1. Then, the first semiconductor film 52 having an amorphous structure is crystallized by using a technique disclosed in Japanese Patent Application Laid-open No. Hei 8-78329 for crystallization of the first semiconductor film 52. With the technique disclosed in the above, a metal element that promotes crystallization is selectively added to an amorphous silicon film, and heat treatment is conducted thereto, thereby forming a semiconductor film having a crystalline structure which spreads with the added region as the starting point. First, a nickel acetate salt solution containing a metal element (in this case, nickel) of 1 to 100 ppm in weight which has catalysis that promotes crystallization, is applied to the surface of the first semiconductor film 52 having an amorphous structure by using a spinner, thereby forming a nickel containing layer 53. (FIG. 3C) Besides the formation method of the nickel containing layer 53 by application, a method of forming an extremely thin film by sputtering, evaporation or plasma processing may be used. Further, an example of application to the entire surface is shown here. However, the nickel containing layer may be selectively formed with the formation of a mask.

Next, heat treatment is conducted to perform crystallization. In this case, silicide is formed at the portion of the semiconductor film, which contacts the metal element that promotes crystallization of the semiconductor film, and the crystallization progresses with the silicide as the nucleus. Thus, a first semiconductor film 54a having the crystalline structure shown in FIG. 3D is formed. Note that a concentration of oxygen contained in the first semiconductor film 54a after crystallization is desirably set to 5.times.10.sup.18 /cm.sup.3 or less. Here, after heat treatment (450.degree. C. for 1 hour) for hydrogenation is conducted, heat treatment (550.degree. C. to 650.degree. C. for 4 to 24 hours) for crystallization is conducted. Further, in the case where crystallization is conducted by strong light irradiation, one of infrared light, visible light, and ultraviolet light or a combination thereof can be used. Typically, light emitted from a halogen lamp, a metal halide lamp, a xenon-arc lamp, a carbon-arc lamp, a high-pressure sodium lamp or a high-pressure mercury lamp is used. A lamp light source is turned on for 1 to 60 seconds, preferably 30 to 60 seconds, and this is repeated 1 to 10 times, whereby the semiconductor film is sufficiently heated to be instantaneously at about 600 to 1000.degree. C. Note that, before the strong light irradiation, heat treatment for releasing hydrogen contained in the first semiconductor film 52 having an amorphous structure may be conducted if necessary. Further, crystallization may be conducted by simultaneously performing the heat treatment and the strong light irradiation. Taking the productivity into consideration, it is desirable that crystallization is conducted with the strong light irradiation.

The metal element (in this case, nickel) remains in the first semiconductor film 54a thus obtained. The metal element remains at a concentration of more than 1.times.10.sup.19 /cm.sup.3 as an average concentration even if the metal element is not uniformly distributed in the film. Of course, even in the above-described state, various semiconductor elements, including a TFT, can be formed. However, the element is removed by the method shown below.

Next, in order to raise a crystallization rate (ratio of a crystal component to the total volume of the film) and to repair a defect remaining in a crystal grain, laser light (first laser light) is irradiated to the first semiconductor film 54a having a crystalline structure in an atmosphere or an oxygen atmosphere. In the case where the laser light (first laser light) is irradiated, a thin oxide film 55 is formed together with unevenness on the surface of the semiconductor film. (FIG. 3E) Excimer laser light with a wavelength of 400 nm or less, the second harmonic wave or third harmonic wave of a YAG laser, or the second harmonic wave (532 nm) or third harmonic wave (355 nm) of a continuous oscillation Nd:YVO.sub.4 laser (fundamental wavelength, 1064 nm) may be applied to the laser light (first laser light).

Then, the oxide film 55 formed by the first laser light irradiation is removed. (FIG. 3F)

Next, laser light (second laser light) is irradiated to the first semiconductor film having a crystalline structure in a nitrogen atmosphere or in a vacuum. In the case where the laser light is irradiated in the nitrogen atmosphere or in the vacuum, a minute hole is easily be formed in the semiconductor film. However, the base insulating film and the semiconductor film are formed at the same film deposition temperature, whereby the occurrence of the minute hole can be suppressed. Therefore, a size of surface unevenness due to the minute hole, which is regarded as the cause of the unevenness, and variation of characteristics of a TFT can be reduced. Further, in the case where the laser light (second laser light) is irradiated, the ridge formed by the first laser light irradiation is reduced, namely, flattened. (FIG. 3G)

Next, an oxide film (called chemical oxide) is formed with an ozone-containing aqueous solution (typically, ozone water) to form a barrier layer 56 comprised of an oxide film of 1 to 10 nm. A second semiconductor film 57 containing a noble gas element is formed on the barrier layer 56. (FIG. 4A)

Further, as another method of forming the barrier layer 56, ozone may be made to generate by irradiation of ultraviolet light in an oxygen atmosphere to thereby oxidize the surface of the semiconductor film having a crystalline structure. Further, as still another method of forming the barrier layer 56, an oxide film with a thickness of about 1 to 10 nm may be deposited by plasma CVD, sputtering or evaporation. Also as still another method of forming the barrier layer 56, a thin oxide film may be formed by heating to approximately 200 to 350.degree. C. with a clean oven. Note that the barrier layer 56 is not particularly limited as long as it is formed by one of the above methods or a combination thereof. However, it is required that the barrier layer has a film quality or a film thickness that enables the nickel in the first semiconductor film to move to the second semiconductor film by gettering which is performed later.

Here, a second semiconductor film 57 containing a noble gas element is formed by sputtering to form a gettering site. One or a plurality of elements selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) are used as the noble gas element. Above all, argon (Ar) is preferable since it is an inexpensive gas. The second semiconductor film is formed by using a target comprised of silicon in an atmosphere containing the noble gas element. There are two intentions to make noble gas element ions be contained in an inert gas in the film. One intention is to form dangling bonds to impart distortion to the semiconductor film. The other intention is to impart distortion between lattices of the semiconductor film. The distortion is remarkably imparted between lattices of the semiconductor film when an element having an atomic radius larger than that of silicon, such as argon (Ar), krypton (Kr) or xenon (Xe) is used. Further, the noble gas element is contained in the film, whereby not only the distortion between lattices but also the dangling bonds are formed, which contributes to a gettering action.

Next, heat treatment is performed to perform gettering for reducing the concentration of a metal element (nickel) or removing the metal element in the first semiconductor film. (FIG. 4B) Process of irradiating strong light or a heating process may be conducted as the heat treatment for performing gettering. By the gettering, the metal element moves in a direction indicated by an arrow in FIG. 4B (namely, a direction toward the surface of the second semiconductor film from the substrate side), and the removal of the metal element or the reduction of the concentration of the metal element, which is contained in a first semiconductor film 54d covered by the barrier layer 56 is conducted. It is sufficient that the distance in which the metal element moves in gettering is a distance substantially equal to at least a thickness of the first semiconductor film, and gettering can be completed for a relatively short time. Here, nickel is made to move to the second semiconductor film 57 such that it does not segregate in the first semiconductor film 54d, and gettering is sufficiently conducted such that nickel contained in the first semiconductor film 54d hardly exists, that is, the nickel concentration in the film is set to 1.times.10.sup.18 /cm.sup.3 or less, desirably 1.times.10.sup.17 /cm.sup.3 or less.

Further, in the above gettering, repairs of damage due to the laser light irradiation (first laser light and second laser light) are simultaneously performed.

Next, after only the second semiconductor film indicated by reference numeral 57 is selectively removed with the barrier layer 56 as an etching stopper, the barrier layer 56 is removed, and the first semiconductor film 54d is patterned with a known technique to form a semiconductor layer 58 having a desired shape.

A TFT is completed by conducting the subsequent steps that are the same as those in Embodiment Mode 1. (FIG. 4E)

In FIG. 4E, reference numeral 59 indicates a gate insulating film, 60 indicates a gate electrode, 61 indicates a source region, 62 indicates a drain region, 63 indicates a channel forming region, 64 indicates an interlayer insulating film, 65 indicates a source electrode, and 66 indicates a drain electrode.

Further, this embodiment mode can be combined with Embodiment Mode 1. In addition, this embodiment mode can be combined with another known gettering technique.

Further, in this embodiment mode, an example in which the second laser light irradiation is conducted before gettering is shown. However, the following process may be adopted in which: after the first laser light irradiation, a barrier layer and a semiconductor film containing a noble gas are formed; gettering is performed by heat treatment; the semiconductor film containing a noble gas element and the barrier layer are removed; and then, the second laser light irradiation is conducted in an inert gas atmosphere or in a vacuum.

Moreover, the second laser light irradiation may not be conducted before gettering. An oxide film and the like are removed by cleaning after the formation of a semiconductor layer having a desired shape, and then, the second laser light irradiation may be conducted in an inert gas atmosphere or in a vacuum for leveling the surface.

Furthermore, in the second laser light irradiation, a nitrogen gas may be sprayed to the vicinity of a region to be irradiated.

Embodiment Mode 4

Here, an example is shown in which a throughput is improved upon hereby to surface with laser light in Embodiment Mode 2 or Embodiment Mode 3.

Laser light irradiation is conducted twice in Embodiment Mode 2 or Embodiment Mode 3, and thus, the throughput is lowered. Therefore, in this embodiment mode, in case of a pulse oscillation type laser, the number of shots of the second laser, namely, the overlap ratio is made smaller than that of the first laser light.

Specifically, the overlap ratio of the first laser light is set to 90% or more, preferably 95 to 98%, and the overlap ratio of the second laser light is preferably set to 60 to 90%, preferably 70 to 85%. The overlap ratio of the second laser light can attain sufficiently leveling of the surface even if it is smaller than the overlap ratio of the first laser light.

Therefore, the overlap ratio of the second laser light can be made smaller, and thus, the throughput is remarkably improved. Further, since the second laser light irradiation is performed, the overlap ratio of the first laser light can also be lowered.

Note that this embodiment mode can be applied to Embodiment Mode 1 or Embodiment Mode 2.

The present invention structured as described above will further be described in detail with embodiments shown below.

Embodiments

Embodiment 1

An embodiment of the present invention is described with reference to FIGS. 5A to 7. Here, a method of simultaneously manufacturing a pixel portion and TFTs (n-channel TFTs and a p-channel TFT) of a driver circuit provided in the periphery of the pixel portion on the same substrate is described in detail.

First, a base insulating film 101 is formed on a substrate 100, and a first semiconductor film having a crystalline structure is obtained. Then, the semiconductor film is etched to have a desired sh