Method of manufacturing semiconductor device Number:7,151,017 from the United States Patent and Trademark Office (PTO) owispatent In a step of doping a silicon-based semiconductor film as a TFT active layer such as channel doping or the like, a protective film is formed by a CVD method as a pretreatment so as to prevent the silicon-based semiconductor film from being contaminated and etched. However, in the case of using the protective film formed by the CVD method, the problems in terms of throughput and production cost (an expensive apparatus is required) have been pointed out. The present invention is intended to solve the above-mentioned problems. Instead of the CVD method, a step of forming a chemical oxide film on a silicon-based semiconductor film is introduced as the pretreatment in the step of doping the silicon-based semiconductor film. Alternatively, a step is introduced in which unsaturated bonds present at the surface of the silicon-based semiconductor film are made to terminate with an element (for instance, oxygen) to be bonded with bonding energy higher than that of Si--H bonds. The above-mentioned pretreatment step can prevent the silicon-based semiconductor film from being etched by hydrogen ions used in the doping step.<H semiconductor, manufacturing, Method, of, manuf, 7151017.html, Patent, pto, 7151017

Title: Method of manufacturing semiconductor device

Abstract: In a step of doping a silicon-based semiconductor film as a TFT active layer such as channel doping or the like, a protective film is formed by a CVD method as a pretreatment so as to prevent the silicon-based semiconductor film from being contaminated and etched. However, in the case of using the protective film formed by the CVD method, the problems in terms of throughput and production cost (an expensive apparatus is required) have been pointed out. The present invention is intended to solve the above-mentioned problems. Instead of the CVD method, a step of forming a chemical oxide film on a silicon-based semiconductor film is introduced as the pretreatment in the step of doping the silicon-based semiconductor film. Alternatively, a step is introduced in which unsaturated bonds present at the surface of the silicon-based semiconductor film are made to terminate with an element (for instance, oxygen) to be bonded with bonding energy higher than that of Si--H bonds. The above-mentioned pretreatment step can prevent the silicon-based semiconductor film from being etched by hydrogen ions used in the doping step.

Patent Number: 7,151,017 Issued on 12/19/2006 to Ohnuma

Inventors: Ohnuma; Hideto (Atsugi, JP)
Assignee: Semiconductor Energy Laboratory Co., Ltd. (Kanagawa-ken, JP)

Appl. No.: 10/053,572

Filed: January 24, 2002

Foreign Application Priority Data


Jan 26, 2001 [JP]			2001-019293

Current U.S. Class: 438/151

Current International Class: H01L 21/00 (20060101)

Field of Search: 438/149-166

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Primary Examiner: Geyer; Scott B.
Attorney, Agent or Firm: Robinson; Eric J. Robinson Intellectual Property Law Office, P.C.

Claims

What is claimed is:

1. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; forming a chemical oxide film on a surface of the crystallized semiconductor film comprising silicon by using a liquid chemical; doping the crystallized semiconductor film comprising silicon with impurity ions through the chemical oxide film; and forming at least one channel region comprising a portion of the doped semiconductor film.

2. A method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor film comprising silicon is an amorphous semiconductor film comprising silicon.

3. A method of manufacturing a semiconductor device according to claim 1, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, and a heat treatment is conducted to form a polycrystalline semiconductor film comprising silicon.

4. A method of manufacturing a semiconductor device according to claim 1, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, a catalytic element having an effect of accelerating crystallization is applied to the silicon-containing amorphous semiconductor film, and a heat treatment is conducted to form a silicon-containing crystalline semiconductor film.

5. A method of manufacturing a semiconductor device according to claim 4, wherein at least one element selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au is added as the catalytic element.

6. A method of manufacturing a semiconductor device according to claim 1, wherein a material including hydrogen is used as an ion source for the impurity ions used in the doping step.

7. A method of manufacturing a semiconductor device according to claim 1, wherein the doping step allows channel doping to be implemented.

8. A method of manufacturing a semiconductor device according to claim 1, wherein the chemical oxide film is formed by a treatment with ozone water.

9. A method of manufacturing a semiconductor device according to claim 1, wherein the chemical oxide film is formed by a treatment with a hydrogen peroxide solution.

10. A method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

11. A method of manufacturing a semiconductor device according to claim 1, wherein the chemical oxide film is 5 nm thick or less.

12. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; terminating dangling bonds on a surface of the crystallized semiconductor film comprising silicon with oxygen to prevent the semiconductor film from being etched by a subsequent doping step; doping the crystallized semiconductor film comprising silicon with impurity ions after terminating dangling bonds on a surface of the crystallized semiconductor film; and forming at least one channel region comprising a portion of the doped semiconductor film.

13. A method of manufacturing a semiconductor device according to claim 12, wherein the semiconductor film comprising silicon is an amorphous semiconductor film comprising silicon.

14. A method of manufacturing a semiconductor device according to claim 12, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, and a heat treatment is conducted to form a polycrystalline semiconductor film comprising silicon.

15. A method of manufacturing a semiconductor device according to claim 12, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, a catalytic element having an effect of accelerating crystallization is applied to the amorphous semiconductor film comprising silicon, and a heat treatment is conducted to form a crystalline semiconductor film comprising silicon.

16. A method of manufacturing a semiconductor device according to claim 12, wherein a material including hydrogen is used as an ion source for the impurity ions used in the doping step.

17. A method of manufacturing a semiconductor device according to claim 12, wherein the doping step allows channel doping to be implemented.

18. A method of manufacturing a semiconductor device according to claim 12, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

19. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; terminating dangling bonds on a surface of the crystallized semiconductor film comprising silicon with an element to be bonded with bonding energy higher than that of Si--H bonds to prevent the semiconductor film from being etched by a subsequent doping step; doping the crystallized semiconductor film comprising silicon with impurity ions after terminating dangling bonds on a surface of the crystallized semiconductor film; and forming at least one channel region comprising a portion of the doped semiconductor film.

20. A method of manufacturing a semiconductor device according to claim 19, wherein the semiconductor film comprising silicon is an amorphous semiconductor film comprising silicon.

21. A method of manufacturing a semiconductor device according to claim 19, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, and a heat treatment is conducted to form a polycrystalline semiconductor film comprising silicon.

22. A method of manufacturing a semiconductor device according to claim 19, wherein an amorphous semiconductor film comprising silicon is deposited as the semiconductor film comprising silicon, a catalytic element having an effect of accelerating crystallization is applied to the amorphous semiconductor film comprising silicon, and a heat treatment is conducted to form a crystalline semiconductor film comprising silicon.

23. A method of manufacturing a semiconductor device according to claim 19, wherein a material including hydrogen is used as an ion source for the impurity ions used in the doping step.

24. A method of manufacturing a semiconductor device according to claim 19, wherein the doping step allows channel doping to be implemented.

25. A method of manufacturing a semiconductor device according to claim 19, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

26. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; forming a chemical oxide film on a surface of the crystallized semiconductor film comprising silicon by using a liquid chemical; doping the crystallized semiconductor film comprising silicon with impurity ions through the chemical oxide film; patterning the semiconductor film to form at least one active layer after doping; forming a gate insulating film over the active layer after patterning the semiconductor film; and forming a gate electrode over the semiconductor film with the gate insulating film interposed therebetween, wherein the chemical oxide film is formed by a treatment with at least one material selected from the group of: ozone water and a hydrogen peroxide solution.

27. A method of manufacturing a semiconductor device according to claim 26, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

28. A method of manufacturing a semiconductor device according to claim 26, wherein the chemical oxide film is 5 nm thick or less.

29. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; forming a chemical oxide film on a surface of the crystallized semiconductor film comprising silicon by using a liquid chemical; doping the crystallized semiconductor film comprising silicon with impurity ions through the chemical oxide film; forming a gate insulating film over the semiconductor film after doping; and forming a gate electrode over the gate insulating film.

30. A method of manufacturing a semiconductor device according to claim 29, wherein, in the doping step, a material gas is at least one selected from the group consisting of diborane, phosphine, arsine and those obtained through dilution thereof with hydrogen.

31. A method of manufacturing a semiconductor device according to claim 29, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

32. A method of manufacturing a semiconductor device according to claim 29, wherein the chemical oxide film is 5 nm thick or less.

33. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; terminating dangling bonds on a surface of the crystallized semiconductor film comprising silicon with oxygen to prevent the semiconductor film from being etched by a subsequent doping step; doping the crystallized semiconductor film comprising silicon with impurity ions after terminating dangling bonds; forming a gate insulating film over the semiconductor film after doping; and forming a gate electrode over the gate insulating film.

34. A method of manufacturing a semiconductor device according to claim 33, wherein, in the doping step, a material gas is at least one selected from the group consisting of diborane, phosphine, arsine and those obtained through dilution thereof with hydrogen.

35. A method of manufacturing a semiconductor device according to claim 33, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

36. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor film comprising silicon over an insulating substrate; crystallizing the semiconductor film comprising silicon; terminating dangling bonds on a surface of the crystallized semiconductor film comprising silicon with an element to be bonded with bonding energy higher than that of Si--H bonds to prevent the semiconductor film from being etched by a subsequent doping step; doping the crystallized semiconductor film comprising silicon with impurity ions after terminating dangling bonds; forming a gate insulating film over the semiconductor film after doping; and forming a gate electrode over the gate insulating film.

37. A method of manufacturing a semiconductor device according to claim 36, wherein, in the doping step, a material gas is at least one selected from the group consisting of diborane, phosphine, arsine and those obtained through dilution thereof with hydrogen.

38. A method of manufacturing a semiconductor device according to claim 36, wherein the semiconductor device is at least one device selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display device, a DVD player, a CD player, a portable telephone, a front type projector and a rear type projector.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a semiconductor device using an ion doping method, and more specifically to a method of forming a protective film as a pretreatment in an ion doping step. In this specification, the "semiconductor device" denotes any of semiconductor devices in general which has a circuit structure with a thin film transistor (hereinafter abbreviated as a "TFT"), and semiconductor display device such as an active matrix type liquid crystal display device, an organic electro-luminescence (EL) display device, or the like are included in this category.

2. Description of the Related Art

Recently, demands for active matrix type liquid crystal display devices have increased rapidly and development of the technique for manufacturing TFTs with a semiconductor film formed on a glass substrate or a quartz substrate has been carried out actively. TFTs manufactured on an insulating substrate such as a glass substrate or the like in a unit of one million and several hundreds of thousands of pieces have to exhibit predetermined electric characteristics according to the function of an electric circuit to be formed therewith. There is a parameter called "Vth" as one of the electric characteristics of a TFT.

The "Vth" denotes a gate voltage measured at the moment when a drain current of a TFT starts flowing and is defined as a voltage at which an inversion layer is formed in a channel region. Hence, it can be said that the higher the Vth is, the higher the TFT operating voltage is.

Note that, the Vth has a problem in that it fluctuates easily by various external factors including, for instance, contamination impurities in an active layer, fixed and mobile charges in a gate insulating film, an interface level at an active layer/gate insulating film interface, and the difference in work function between a gate electrode and an active layer. In this case, the contamination impurities in an active layer, the mobile charge in a gate insulating film, and the like can be reduced through cleaning in processes. However, the fixed charge, the interface level, and the difference in work function depend on the device material and thus cannot be modified easily.

The above-mentioned external factors cause the Vth of a TFT to shift to the plus or minus side to vary. In TFT manufacturing steps, control of variable Vth is an important technique, and a channel doping technique has been known as a Vth control technique. The "channel doping" is a technique for controlling Vth by adding a predetermined concentration of impurity to an active layer located under a gate insulating film to shift the Vth of a TFT intentionally so that the Vth reaches a desired level. For example, a p-type impurity element is used as a dopant when the Vth shifts to the minus side, while an n-type impurity element is used as a dopant when the Vth shifts to the plus side. Thus, the Vth is controlled.

For such channel doping, an ion doping method for doping with an n-type or p-type impurity element is used. The ion doping method is a method of implanting an impurity element without implementing mass separation. Since the ion doping method employs no mass separation means, it is easy to achieve an increase in area subjected to processing. Hence, the ion doping method is generally applied to the manufacture of an active matrix type liquid crystal display device. In the ion doping method, B(boron), Ga(gallium), or In(indium) is used as a p-type impurity, and P(phosphorus), As(arsenic), Sb(antimony), or the like is used as an n-type impurity.

When a doping process such as channel doping or the like is carried out directly with respect to a silicon-based semiconductor film as an active layer of a TFT, there is a problem in that the silicon-based semiconductor film is etched. Conventionally, as measures for solving the problem, a protective film such as a silicon oxide film, a silicon oxynitride film, or the like is deposited by a chemical vapor deposition (CVD) method as a pretreatment in a doping step and then the process of doping with impurity ions is conducted from the top of the protective film. However, the measures have the following demerits and therefore are not preferable.

First, since the CVD method is applied to the mere pretreatment, the time required for the pretreatment is lengthened and the processing time required for the whole step of doping with impurity ions is also lengthened accordingly. Therefore, with respect to the whole step of doping with impurity ions, the above-mentioned measures are not preferable in terms of throughput since the number of substrates to be processed per unit time is reduced. In addition, the above-mentioned measures also are not preferable in view of the fact that the cost for the pretreatment increases since a CVD apparatus such as a plasma CVD apparatus, a low pressure CVD apparatus, or the like is used for the pretreatment and thus the whole production cost increases accordingly. Therefore, an easy low-cost measure for preventing etching has been requested as a measure for preventing a silicon-based semiconductor film from being etched.

SUMMARY OF THE INVENTION

The present invention is intended to solve the above-mentioned problems inherent in the conventional technique. More specifically, the present invention is intended to provide a step of doping a silicon-based semiconductor film with an easy low-cost pretreatment step as a measure for preventing the silicon-based semiconductor film from being etched. In other words, the present invention is intended to provide a method of manufacturing a semiconductor device including a measure for preventing a silicon-based semiconductor film from being etched by the above-mentioned pretreatment step.

Experiment on Pretreatment for Channel Doping

Since an active layer of a TFT is formed from a silicon-based semiconductor film such as an amorphous silicon film, a polycrystalline silicon film, a crystalline silicon film formed using a catalytic element, or the like, it is possible to form a chemical oxide film as an ultrathin silicon oxide film by an easy treatment step such as an ozone water treatment or the like. If the above-mentioned chemical oxide film can function as a protective film during the step of ion-doping the silicon-based semiconductor film, the above-mentioned problems of the conventional art can be solved. Accordingly, the following experiment was conducted under the experimental conditions indicated in Table 1.

In the specification, the chemical oxide film is a film formed by use of liquid chemicals having oxidation such as ozone water or a hydrogen peroxide solution. In general, the chemical oxide film is 5 nm thick or less.

First, an amorphous silicon film with a thickness of 53 nm was deposited on each of four glass substrates Nos. 1 to 4 at a deposition temperature of 300 C by a plasma CVD method. Since a natural oxide film was attached to each amorphous silicon film, it was removed with dilute hydrofluoric acid. Next, with respect to the two substrates Nos. 2 and 4, the whole surface of the amorphous silicon film was oxidized with ozone water and thus a chemical oxide film (an ultrathin silicon oxide film) with a thickness of 5 nm or less was formed. Afterward, using an ion doping apparatus, the four substrates Nos. 1 to 4 were subjected to a process of doping with a dose of boron having a range of 1.times.10.sup.13 to 1.times.10.sup.14 atoms/cm.sup.2. The experiment was conducted using a material gas obtained by diluting diborane (B.sub.2H.sub.6) gas with hydrogen as a material gas of the boron with respect to the cases of dilution ratios of 0.1% and 1.0%. After the ion doping, the thickness of the residue of each amorphous silicon film was measured. Thus, the state of etching caused during the doping process was examined.

The results of this experiment are shown in FIG. 1. As can be seen from FIG. 1, it was observed that the amorphous silicon film was etched during the doping process when the chemical oxide film had not been formed on the surface of the amorphous silicon film by the ozone water treatment, while the amorphous silicon film was hardly etched when the chemical oxide film had been formed on the surface of the amorphous silicon film. It was also observed that in the case of using diborane gas with a dilution ratio of 0.1%, the etching of the amorphous silicon film was progressed further as compared to the case of using diborane gas with a dilution ratio of 1.0%, in other words, a higher hydrogen ion ratio caused heavier etching of the amorphous silicon film. Accordingly, it is considered that the reaction with hydrogen ions participates in the etching of the amorphous silicon film (see FIG. 1).

The results of this experiment show that the chemical oxide film with a thickness of 5 nm or less formed using ozone water can prevent the amorphous silicon film from being etched due to the hydrogen ions during the doping process. The method of forming the chemical oxide film is not limited to the treatment with ozone water. The chemical oxide film can be formed by a treatment with a hydrogen peroxide solution. Alternatively, an ultrathin silicon oxide film can also be formed by ultraviolet (UV) irradiation in an atmosphere containing oxygen although it is not a chemical oxide film. It is considered that no matter which method is used for its formation, the amorphous silicon film can be prevented from being etched due to the hydrogen ions.

In this experiment, the discussion was directed to the chemical oxide film with a thickness of 5 nm or less. However, it is considered that etching also can be prevented to some degree by making unsaturated bonds present at the surface of the amorphous silicon film terminate with oxygen when the hydrogen ion ratio is low in the ion doping apparatus. When being terminated with oxygen, the unsaturated bonds become Si--O bonds and the bonding energy (193.5 kcal/mol) of the Si--O bonds is higher than that (71.5 kcal/mol) of Si--H bonds. Therefore, even when the hydrogen ions approach the Si--O bonds, the reaction with the hydrogen ions is depressed. Thus, it is suggested that the amorphous silicon film can be prevented from being etched when the unsaturated bonds present at the surface of the amorphous silicon film are made to terminate with an element to be bonded with bonding energy higher than that of the Si--H bonds.

The above-mentioned bonding energies of the Si--H bonds and the Si--O bonds are cited from the data as to the bond strength of diatomic molecules (Table 1 0.35) described on page 561 of Applied Physics Data Book (edited by The Japan Society of Applied Physics).

According to the above-mentioned experiment, the following inventions are led out which are effective in the case of doping with a material gas producing hydrogen ions. Note that examples of the material gas producing hydrogen ions include diborane(B.sub.2H.sub.6), phosphine(PH.sub.3), arsine(AsH.sub.3), and those obtained through dilution thereof with hydrogen. Furthermore, when ion implantation is conducted using an ion implantation apparatus having a mass separation means, it is considered that the silicon film is not etched since basically hydrogen ions can be removed by mass separation.

Invention 1

In the step of ion-doping a silicon-based semiconductor film, a step of forming a chemical oxide film on the surface of the silicon-based semiconductor film is introduced as a pretreatment in place of the formation of a protective film by the CVD method.

Invention 2

In the step of ion-doping a silicon-based semiconductor film, a step of terminating unsaturated bonds present at the surface of the silicon-based semiconductor film with an element to be bonded with bonding energy higher than that (71.5 kcal/mol) of Si--H bonds (hereinafter simply referred to as an "unsaturated bond termination step") is introduced as a pretreatment in place of the formation of a protective film by the CVD method.

Method of Manufacturing a Semiconductor Device

In order to solve the above-mentioned problems in the conventional art, the configurations of the present invention are described from the viewpoint of the method of manufacturing a semiconductor device.

According to one aspect of the present invention, a method of manufacturing a semiconductor device includes a first step of forming a silicon-based semiconductor film on an insulating substrate and a second step of doping the silicon-based semiconductor film with impurity ions, and is characterized in that the second step includes, as a pretreatment, the steps of: forming a chemical oxide film on the surface of the silicon-based semiconductor film; terminating unsaturated bonds present at the surface of the silicon-based semiconductor film with oxygen; or terminating the unsaturated bonds present at the surface of the silicon-based semiconductor film with an element to be bonded with bonding energy higher than that of Si--H bonds.

According to another aspect of the present invention, a method of manufacturing a semiconductor device includes: a first step of forming a silicon-containing amorphous semiconductor film on an insulating substrate; a second step of carrying out channel doping with respect to the silicon-containing amorphous semiconductor film; a third step of heat-treating the silicon-containing amorphous semiconductor film to form a silicon-containing polycrystalline semiconductor film; a fourth step of forming a semiconductor film to serve as an active layer of a TFT through pattern formation of the silicon-containing polycrystalline semiconductor film; a fifth step of depositing a gate insulating film on the semiconductor film; a sixth step of forming gate electrodes on the semiconductor film with the gate insulating film interposed therebetween; and a seventh step of doping the semiconductor film with impurity ions with the gate electrodes used as a mask, and is characterized in that the second step includes, as a pretreatment, the steps of: forming a chemical oxide film on the surface of the silicon-containing amorphous semiconductor film; terminating unsaturated bonds present at the surface of the silicon-containing amorphous semiconductor film with oxygen; or terminating the unsaturated bonds present at the surface of the silicon-containing amorphous semiconductor film with an element to be bonded with bonding energy higher than that of Si--H bonds.

According to still another aspect of the present invention, a method of manufacturing a semiconductor device includes: a first step of depositing a silicon-containing amorphous semiconductor film on an insulating substrate and heat-treating it to form a silicon-containing polycrystalline semiconductor film; a second step of carrying out channel doping with respect to the silicon-containing polycrystalline semiconductor film; a third step of forming a semiconductor film to serve as an active layer of a TFT through pattern formation of the silicon-containing polycrystalline semiconductor film; a fourth step of depositing a gate insulating film on the semiconductor film; a fifth step of forming gate electrodes on the semiconductor film with the gate insulating film interposed therebetween; and a sixth step of doping the semiconductor film with impurity ions with the gate electrodes used as a mask, and is characterized in that the second step includes, as a pretreatment, the steps of: forming a chemical oxide film on the surface of the silicon-containing polycrystalline semiconductor film; terminating unsaturated bonds present at the surface of the silicon-containing polycrystalline semiconductor film with oxygen; or terminating the unsaturated bonds present at the surface of the silicon-containing polycrystalline semiconductor film with an element to be bonded with bonding energy higher than that of Si--H bonds.

According to yet another aspect of the present invention, a method of manufacturing a semiconductor device includes: a first step of depositing a silicon-containing amorphous semiconductor film on an insulating substrate, adding a catalytic element having an effect of accelerating crystallization to the amorphous semiconductor film, and heat-treating it to form a silicon-containing crystalline semiconductor film; a second step of carrying out channel doping with respect to the silicon-containing crystalline semiconductor film; a third step of forming a semiconductor film to serve as an active layer of a TFT through pattern formation of the silicon-containing crystalline semiconductor film; a fourth step of depositing a gate insulating film on the semiconductor film; a fifth step of forming gate electrodes on the semiconductor film with the gate insulating film interposed therebetween; and a sixth step of doping the semiconductor film with impurity ions with the gate electrodes used as a mask, and is characterized in that the second step includes, as a pretreatment the steps of: forming a chemical oxide film on the surface of the silicon-containing crystalline semiconductor film; terminating unsaturated bonds present at the surface of the silicon-containing crystalline semiconductor film with oxygen; or terminating the unsaturated bonds present at the surface of the silicon-containing crystalline semiconductor film with an element to be bonded with bonding energy higher than that of Si--H bonds.

According to another aspect of the present invention, a method of manufacturing a semiconductor device includes: a first step of depositing a silicon-containing amorphous semiconductor film on an insulating substrate; a second step of carrying out channel doping with respect to the silicon-containing amorphous semiconductor film; a third step of adding a catalytic element having an effect of accelerating crystallization to the silicon-containing amorphous semiconductor film and heat-treating it to form a silicon-containing crystalline semiconductor film; a fourth step of forming a semiconductor film to serve as an active layer of a TFT through pattern formation of the silicon-containing crystalline semiconductor film; a fifth step of depositing a gate insulating film on the semiconductor film; a sixth step of forming gate electrodes on the semiconductor film with the gate insulating film interposed therebetween; and a seventh step of doping the semiconductor film with impurity ions with the gate electrodes used as a mask, and is characterized in that the second step includes, as a pretreatment, the steps of: forming a chemical oxide film on the surface of the silicon-containing amorphous semiconductor film; terminating unsaturated bonds present at the surface of the silicon-containing amorphous semiconductor film with oxygen; or terminating the unsaturated bonds present at the surface of the silicon-containing amorphous semiconductor film with an element to be bonded with bonding energy higher than that of Si--H bonds.

In the above-mentioned aspects of the present invention, the silicon-based semiconductor film is not limited as long as it is a semiconductor film containing silicon. The silicon-based semiconductor film may be, for example, a silicon-containing amorphous semiconductor film, a silicon-containing polycrystalline semiconductor film that is obtained by heat-treating a silicon-containing amorphous semiconductor film, or a silicon-containing crystalline semiconductor film that is obtained by adding a catalytic element having an effect of accelerating crystallization to a silicon-containing amorphous semiconductor film and heat-treating it. In this specification, the technical terms of a silicon-containing amorphous semiconductor film, a silicon-containing polycrystalline semiconductor film, and a silicon-containing crystalline semiconductor film are distinguished from one another in their use. Hence, their definitions are made clear as follows. The "silicon-containing amorphous semiconductor film" denotes a silicon-containing amorphous film that is provided with semiconductor properties by being crystallized. The term of the silicon-containing amorphous semiconductor film, of course, covers amorphous silicon films and further all the silicon-containing amorphous semiconductor films. For example, the term also covers amorphous films formed of a compound of silicon and germanium expressed by a formula of Si.sub.xGe.sub.1-x (0<X<1). The "silicon-containing crystalline semiconductor film" denotes a crystalline semiconductor film that is obtained using a catalytic element having an effect of accelerating crystallization. The silicon-containing crystalline semiconductor film is characterized by having crystal grains orientated in substantially the same direction, having higher field-effect mobility, and the like as compared to an ordinary polycrystalline semiconductor film. Hence, the silicon-containing crystalline semiconductor is described intentionally in distinction from the polycrystalline semiconductor film.

Here, the description is directed to the catalytic element having an effect of accelerating crystallization. The catalytic element is added to a silicon-containing amorphous semiconductor film in order to accelerate its crystallization. A metallic element such as Ni(nickel) or the like is used as the catalytic element. Besides the Ni element, typical metallic elements used as the catalytic element include Fe(iron), Co(cobalt), Ru(ruthenium), Rh(rhodium), Pd(palladium), Os(osmium), Ir(iridium), Pt(platinum), Cu(copper), Au(gold), and the like. As the catalytic element, usually one selected element is used, but a combination of two elements or more may be used. According to the experiments implemented by the present inventors et al., it has been proved that the Ni element is the most preferable catalytic element.

Furthermore, in the above-mentioned aspects of the present invention, examples of the impurity ions include n-type impurities represented by a P(phosphorus) element and an As(arsenic) element and p-type impurities represented by a B(boron) element. When using the phosphorous element, the As element, and the boron element, an ion source obtained by diluting phosphine (PH.sub.3) with hydrogen, an ion source obtained by diluting arsine (AsH.sub.3) with hydrogen, and an ion source obtained by diluting diborane (B.sub.2H.sub.6) with hydrogen are used, respectively. Since all the ion sources are obtained through dilution with hydrogen, hydrogen ions are produced in doping. It is considered that when a silicon-based semiconductor film is doped with such impurity ions, the hydrogen ions act as an etchant for the silicon-based semiconductor film.

In the above-mentioned aspects of the present invention, a typical example of the chemical oxide film formed on the surface of the silicon-based semiconductor film is a silicon oxide film with a thickness of 5 nm or less obtained by a treatment with ozone water, but the chemical oxide film may be formed by a treatment with a hydrogen peroxide solution. Alternatively, an ultrathin silicon oxide film having an effect similar to that of the chemical oxide film can also be formed by ultraviolet (UV) irradiation in an atmosphere containing oxygen although it is not an exact chemical oxide film. Furthermore, in place of the formation of the chemical oxide film, it is also considered to terminate unsaturated bonds present at the surface of the silicon-based semiconductor film with oxygen or with an element to be bonded with bonding energy higher than that of Si--H bonds.

According to the present invention with the configurations as described above, since a chemical oxide film formed by a simple method is used as a protective film for the silicon-based semiconductor film when the silicon-based semiconductor film is doped with impurity ions, the present invention is effective in improving throughput of the whole ion doping step. In addition, since an expensive plasma CVD apparatus or low pressure CVD apparatus is no longer necessary for the pretreatment in the ion doping step, the present invention is effective in reducing production cost. In the case where unsaturated bonds present at the surface of the silicon-based semiconductor film are made to terminate with an element to be bonded with bonding energy higher than that of Si--H bonds, for example, with oxygen in place of the formation of the chemical oxide film, this termination step is considered to have an effect similar to that of the chemical oxide film since it is easier than the CVD step.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows experimental data indicating dependence of the thickness of an amorphous silicon residual film on a dose;

FIGS. 2A to 2E are cross-sectional views showing TFT manufacturing steps;

FIGS. 3A to 3D are cross-sectional views showing TFT manufacturing steps;

FIGS. 4A to 4E are cross-sectional views showing TFT manufacturing steps;

FIGS. 5A and 5B show data as to I.sub.D-V.sub.G (current-voltage) characteristics of an n-channel type TFT;

FIGS. 6A and 6B are cross-sectional views showing steps of manufacturing an active matrix type liquid crystal display device;

FIGS. 7A and 7B are cross-sectional views showing steps of manufacturing the active matrix type liquid crystal display device;

FIGS. 8A and 8B are cross-sectional views showing steps of manufacturing the active matrix type liquid crystal display device;

FIGS. 9A and 9B are cross-sectional views showing steps of manufacturing the active matrix type liquid crystal display device;

FIGS. 10A and 10B are cross-sectional views showing steps of manufacturing the active matrix type liquid crystal display device;

FIGS. 11A to 11F are schematic drawings showing devices as examples of electronic equipment with a semiconductor display device installed therein;

FIGS. 12A to 12D are schematic drawings showing devices as examples of electronic equipment with a semiconductor display device installed therein; and

FIGS. 13A to 13C are schematic drawings showing devices as examples of electronic equipment with a semiconductor display device installed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment Mode 1

In the present embodiment mode, as an example of a method of manufacturing TFTs in which channel doping is conducted with respect to a silicon-based semiconductor film with a crystal structure, a method of manufacturing TFTs in which channel doping is conducted with respect to a crystalline silicon film crystallized using a catalytic element is described concretely with reference to FIGS. 2A to 3D. Note that the channel doping is conducted with respect to an n-channel type TFT alone.

First, a base film 102 made of a silicon oxynitride film with a thickness of 100 nm is deposited on a glass substrate 101 by the plasma CVD method. Subsequently, an amorphous silicon film 103 with a thickness of 15 to 70 nm, more preferably a thickness of 30 to 60 nm is deposited thereon. In the present embodiment mode, the amorphous silicon film 103 with a thickness of 50 nm was deposited by the plasma CVD method. In depositing the amorphous silicon film 103, a natural oxide film (not shown) is attached to the surface of the amorphous silicon film 103 due to the effect of oxygen in the air. Therefore, washing is implemented by a treatment with dilute hydrofluoric acid. Afterward, a chemical oxide film 104 made from an ult