Semiconductor device and semiconductor device producing system Number:7,115,903 from the United States Patent and Trademark Office (PTO) owispatent An insulating film having depressions and projections are formed on a substrate. A semiconductor film is formed on the insulating film. Thus, for crystallization by using laser light, a part where stress concentrates is selectively formed in the semiconductor film. More specifically, stripe or rectangular depressions and projections are provided in the semiconductor film. Then, continuous-wave laser light is irradiated along the stripe depressions and projections formed in the semiconductor film or in a direction of a major axis or minor axis of the rectangle.<H semiconductor, Semiconductor, Semiconductor, d, 7115903.html, Patent, pto, 7115903

Title: Semiconductor device and semiconductor device producing system

Abstract: An insulating film having depressions and projections are formed on a substrate. A semiconductor film is formed on the insulating film. Thus, for crystallization by using laser light, a part where stress concentrates is selectively formed in the semiconductor film. More specifically, stripe or rectangular depressions and projections are provided in the semiconductor film. Then, continuous-wave laser light is irradiated along the stripe depressions and projections formed in the semiconductor film or in a direction of a major axis or minor axis of the rectangle.

Patent Number: 7,115,903 Issued on 10/03/2006 to Isobe, et al.

Inventors: Isobe; Atsuo (Atsugi, JP), Dairiki; Koji (Tochigi, JP), Shibata; Hiroshi (Higashine, JP), Kokubo; Chiho (Tochigi, JP), Arao; Tatsuya (Atsugi, JP), Hayakawa; Masahiko (Atsugi, JP), Miyairi; Hidekazu (Atsugi, JP), Shimomura; Akihisa (Atsugi, JP), Tanaka; Koichiro (Atsugi, JP), Yamazaki; Shunpei (Setagaya, JP), Akiba; Mai (Isehara, JP)
Assignee: Semiconductor Energy Laboratory Co., Ltd. (Kanagawa-ken, JP)

Appl. No.: 10/330,024

Filed: December 27, 2002

Foreign Application Priority Data


Dec 28, 2001 [JP]			2001-399038
Dec 28, 2001 [JP]			2001-401518

Current U.S. Class: 257/59 ; 257/60; 257/61; 257/64; 257/70; 257/71; 257/72; 257/75

Current International Class: H01L 31/036 (20060101); H01L 21/84 (20060101)

Field of Search: 257/59,57,79,72,54,55,56,58

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Primary Examiner: Flynn; Nathan J.
Assistant Examiner: Erdem; Fazli
Attorney, Agent or Firm: Robinson; Eric J. Robinson Intellectual Property Law Office, P.C.

Claims

What is claimed is:

1. A semiconductor device comprising: a primary insulating film having a rectangle shape depression formed over a substrate; and a crystalline semiconductor film having source and drain regions and a channel forming region between the source and drain regions, wherein the channel forming region is formed on a bottom of the depression of the primary insulating film, and wherein the channel forming region extends in a longitudinal direction of the rectangle shape depression.

2. A semiconductor device comprising: an insulating film comprising at least one of silicon nitride, silicon nitride oxide, silicon oxide and silicon oxide nitride and having a rectangle shape depression; and a crystalline semiconductor film having source and drain regions and a channel forming region between the source and drain regions, wherein the channel forming region is formed on a bottom of the depression of the insulating film, and wherein the channel forming region extends in a longitudinal direction of the rectangle shape depression.

3. A semiconductor device comprising: a thin film transistor in which a plurality of channel forming regions are provided in parallel in a crystalline semiconductor film, wherein the plurality of channel forming regions are formed on a bottom of each of a plurality of rectangle shape depressions of a primary insulating film, respectively, wherein each of the channel forming regions extends in a longitudinal direction of the rectangle shape depressions and connects to the plurality of channel forming regions, and wherein a source or drain region is formed in a crystalline semiconductor film formed continuously with the crystalline semiconductor film.

4. A semiconductor device comprising: a thin film transistor in which a plurality of channel forming regions are provided in parallel in a crystalline semiconductor film, wherein the plurality of channel forming regions are formed on a bottom of each of a plurality of rectangle shape depressions of a primary insulating film, respectively, wherein each of the channel forming regions extends in a longitudinal direction of the rectangle shape depressions and connects to the plurality of channel forming regions, and wherein a source or drain region is formed in a crystalline semiconductor film formed continuously with the crystalline semiconductor film and extending from the bottom of the rectangle shape depression to a top of a rectangle shape projection.

5. A semiconductor device comprising: a thin film transistor in which a plurality of channel forming regions are provided in parallel in a crystalline semiconductor film, wherein the plurality of channel forming regions are formed on a bottom of each of a plurality of noncyclic rectangle shape depressions of a primary insulating film, respectively, wherein each of the channel forming regions extends in a longitudinal direction of the rectangle shape depression and connects to the plurality of channel forming regions, and wherein a source or drain region is formed in a crystalline semiconductor film formed continuously with the crystalline semiconductor film and extending from the bottom of the rectangle shape depression to a top of a rectangle shape projection.

6. A semiconductor device according to any one of claims 3 to 5, wherein the primary insulating film has a grade change having a first insulating film of silicon oxide or silicon oxide nitride and a second insulating film of silicon nitride or silicon nitride oxide formed on the first insulating film in a rectangular or stripe pattern.

7. A semiconductor device according to any one of claims 3 to 5, wherein the primary insulating film has a grade change having a first insulating film of silicon oxide or silicon oxide nitride in a rectangular or stripe pattern and a second insulating film of silicon nitride or silicon nitride oxide formed on the first insulating film.

8. A semiconductor device comprising: a plurality of first gate electrodes each having rectangular or stripe; a first gate insulating film covering the plurality of first gate electrodes and having depressions and projections on the surface; a crystalline semiconductor film having a channel forming region of each of the depressions of the first gate insulating film; a second gate insulating film formed on the crystalline semiconductor film and being in contact with the projections of the first gate insulating film; and a second gate electrode formed on the second gate insulating film and being in contact with the plurality of first gate electrodes through contact holes in the first and second gate insulating films, wherein the channel forming region overlaps with any two of the plurality of first gate electrodes through the first gate insulating film and overlaps with the second gate electrode through the second gate insulating film.

9. A semiconductor device comprising: a primary insulating film having a rectangle shape depression formed over a substrate; and a thin film transistor having a crystalline semiconductor film formed over the primary insulating film, wherein a channel forming region in the crystalline semiconductor film is formed on a bottom of the depression of the primary insulating film, and wherein the channel forming region extends in a longitudinal direction of the rectangle shape depression.

10. A semiconductor device according to any one of claims 1, 5 and 8, wherein the semiconductor device is incorporated into an electronic apparatus selected from the group consisting of a mobile information terminal, a video camera, a digital camera, a personal computer, a television receiver, a mobile telephone and a projecting type display apparatus.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device including a semiconductor film having a crystal structure and particularly to a semiconductor device including a crystalline semiconductor film raised on an insulating surface and a field-effect transistor such as a thin film transistor and/or a bipolar transistor especially. In addition, the present invention relates to a semiconductor device producing system for crystallizing a semiconductor film by using laser light and for activating a semiconductor film after ion implantation.

2. Description of the Related Art

A technology has been known for crystallizing an amorphous semiconductor film over a substrate of, for example, glass through laser processing. The laser processing may be a technology for re-crystallizing a damaged layer or an amorphous layer on a semiconductor substrate or a semiconductor film, a technology for crystallizing an amorphous semiconductor film on an insulating surface, or a technology for improving the crystallinity of a semiconductor film having a crystal structure (crystalline semiconductor film). A laser oscillating device used for the laser processing generally uses gaseous laser such as excimer laser or solid laser such as YAG laser.

Laser beam is used because an area absorbing energy from irradiated laser beam can be heated selectively in comparison with heat processing using radiant heating or conductive heating. For example, laser processing using excimer laser oscillating device for oscillating ultra violet light having a wave length equal to or less than 400 nm heats a semiconductor film selectively and locally. Then, crystallization and/or activation processing can be performed on the semiconductor film by hardly damaging the glass substrate thermally.

JP Laid-Open 62-104117 (page 92) discloses laser processing in which an amorphous semiconductor film is crystallized without melting the semiconductor film completely by adopting rapid scanning using laser of (beam spot diameter.times.5000)/second or more. U.S. Pat. No. 4,330,363 (FIG. 4) discloses laser processing in which an extended laser beam is irradiated to an island-shaped semiconductor area to form a single crystalline area essentially. Alternatively, JP Laid-Open 8-195357 (Pages 3 to 4 and FIGS. 1 to 5) discloses a method in which a beam to be irradiated is processed linearly by an optical system such as a laser processing apparatus.

Furthermore, for example, JP Laid-Open 2001-144027 (Page 4) discloses a crystallization technology using a solid laser oscillating device with, for example, Nd:YVO.sub.4 laser. According to the technology, a second harmonic of a laser beam projected from the solid laser oscillating device is used such that a crystalline film having a larger crystal grain size than the conventional size can be obtained to be applied for a thin film transistor (called "TFT" hereinafter).

The application to a thin film transistor (called "TFT" hereinafter) in the crystallization technology using the solid laser oscillating device is reported in A. Hara, F. Takeuchi, M. Takei, K. Yoshino, K. Suga and N. Sasaki, "Ultra-high Performance Poly-Si TFT on a Glass by a Stable Scanning CW Laser Lateral Crystallization", AMLCD '01 Tech. Dig., 2001, pp. 227 230. According to the result described in the document, a second harmonic wave of a diode-excited solid continuous wave laser (YVO.sub.4) is used to crystallize an amorphous silicon film to be used for producing a TFT.

Conventionally, improvement in TFT characteristics may have required improvement in crystallinity of the active layer (which is a semiconductor film including regions and/or a semiconductor film having source or drain regions, here).

Forming a single crystalline semiconductor on an insulating surface has been attempted for a long time. A technology called Graphoepitaxy was designed as a more active attempt. According to Graphoepitaxy, grade changes are formed on a surface of a quartz substrate. Then, an amorphous film or a polycrystalline semiconductor film is formed thereon. By heating it by using a laser beam or a heater, an epitaxial growing layer is formed by having the grade change on the quartz substrate as a core. The technology is disclosed in J. Vac. Sci. Technol., "Grapho-epitaxy of silicon on fused silica using surface micropatterns and laser crystallization", 16(6), 1979, pp. 1640 1643, for example.

In addition, M. W. Geis, et al., "CRYSTALLINE SILICON ON INSULATORS BY GRAPHOEPITAXY" Technical Digest of International Electron Devices Meeting, 1979, pp. 210 discloses a semiconductor film crystallization technology called graphoepitaxy. The technology attempts epi-raising of a semiconductor film by inducing grade changes on a surface of an artificial amorphous substrate. In the graphoepitaxy disclosed in the document, grade changes are provided on a surface of an insulating film, and processing including heating or irradiating laser light is performed on a semiconductor film on the insulating film. Thus, crystal of the semiconductor film is epitaxially raised.

However, in order to form a semiconductor film having good crystallinity with fewer defects and/or crystal grain boundaries and with uniform alignment, a semiconductor is conventionally and mainly heated to a higher temperature to be melted and then is crystallized. This is known as a band melting method.

According to the publicly-known graphoepitaxy technology, grade changes in a primary layer is used. Thus, crystal grows along the grade changes. As a result, the grade changes remain on the surface of the formed single crystalline semiconductor film disadvantageously. Furthermore, a single crystalline semiconductor film cannot be formed by using the graphoepitaxy on a large glass substrate having smaller distortion points.

In all of the cases, a crystalline semiconductor film having fewer defects cannot be formed due to the volume shrinkage of the semiconductor, thermal stresses against the base, grating mismatch and so on caused by crystallization. Furthermore, distortions are accumulated. Thus, an area causing defects cannot be positionally controlled so as to position in the other area than element forming areas. Accordingly, without bonded SOI (silicon on insulator), a crystalline semiconductor film on an insulating surface cannot obtain the same quality as that of a MOS transistor provided on a single crystalline semiconductor.

SUMMARY OF THE INVENTION

The present invention was made in view of these problems. It is an object of the present invention to provide a semiconductor device including a fast semiconductor element having a higher current driving ability for forming a uniform crystalline semiconductor film, and, preferably, a single crystalline semiconductor film on a glass substrate having fewer distortion points.

Recently, technologies each for forming a TFT over a substrate have been evolved significantly. The technologies have been applied to the active matrix type semiconductor display device. Especially, a TFT using a polycrystalline semiconductor film has higher field effect mobility than that of a TFT having a conventional amorphous semiconductor film. Therefore, rapid operations are possible. Thus, pixel control, which has been performed by a drive circuit provided outside of a conventional substrate, can be performed by a drive circuit over a substrate on which pixels are also provided.

By the way, a glass substrate is preferred for a semiconductor device to a single crystalline silicon because of the costs. A glass substrate has low heat resistance and may be deformed by heat easily. Therefore, when a polysilicon TFT is formed on a glass substrate, laser-annealing may be used for crystallizing the semiconductor film. Thus, heat-deformation of the glass substrate can be avoided very effectively.

In comparison with an annealing method used for radiant-heating or conductive heating, laser annealing can reduce a processing time significantly. In addition, a semiconductor or a semiconductor film is heated selectively and locally, which can hardly damage the substrate thermally.

The "laser-annealing" herein refers to a technology for re-crystallizing a damaged layer on a semiconductor substrate or on a semiconductor film or a technology for crystallizing a semiconductor film over a substrate. In addition, the "laser-annealing" herein includes a technology to be applied for planarizing or improving the quality of the surface of a semiconductor substrate or a semiconductor film. A laser oscillating device to be applied may be a gaseous laser oscillating device such as excimer laser, a solid laser oscillating device such as YAG laser. These apparatus can heat a surface layer of a semiconductor for a very short period of time as much as several tens nano to several tens micro by irradiating laser light thereon such that the surface layer can be crystallized.

Lasers may be divided into two including those of a pulse type and of a continuous wave type. The pulse type of laser outputs higher energy. Therefore, the mass production characteristic can be improved by using a laser beam of several cm.sup.2 in size or more. Especially, the form of the laser beam may be processed by using an optical system so as to obtain a linear shape of 10 cm long or more. Then, the laser light can be irradiated to a substrate efficiently. As a result, the mass production characteristic can be further improved. Accordingly, using the pulse type of laser for the semiconductor film crystallization is becoming a main stream.

However, recently, when the continuous wave type of laser is used for crystallizing a semiconductor film, crystal formed within a semiconductor film is found larger in grain size than those obtained by using the pulse type of laser. The larger the crystal grain size is within a semiconductor film, the higher the mobility of a TFT formed by using the semiconductor film is. Therefore, the serial oscillating type of laser starts to gather attentions gradually.

A crystalline semiconductor film produced by using laser annealing, including those of the pulse type and the continuous wave type, are formed by gathering multiple crystal grains in general. The positions and sizes of the crystal grains are random. Therefore, a crystalline semiconductor film is difficult to form by specifying the positions and sizes of the crystal grains. As a result, an active layer formed by patterning the crystalline semiconductor into an island shape may have interfaces (grain boundaries) between crystal grains.

Unlike the inside of the crystal grain, the grain boundary has numberless centers of recombination and/or capture due to an amorphous structure or defective crystal. When a carrier is trapped by the center of capture, the potential at the grain boundary increases, which is a barrier against the carrier. Therefore, the current transportation characteristic of the carrier is reduced. Accordingly, when a grain boundary exists in a channel-forming region especially, the characteristics of the TFT may be affected significantly. The mobility of the TFT is significantly decreased. ON-current is reduced, and OFF current is increased because current flows at the grain boundary. The characteristics of multiple TFT produced for obtaining the same characteristics may vary depending on the presence of the grain boundary in the active layer.

When laser light is irradiated to a semiconductor film, the obtained crystal grains have random positions and sizes. The reasons are as follows: A certain period of time is required until a solid phase core is created in a liquid semiconductor film, which has been melted completely by the irradiation of the laser light. With a lapse of time, numberless crystal cores are caused in the completely-melted area. Then, crystal grows from the crystal cores. The crystal cores are caused at random positions. Therefore, the crystal cores range nonuniformly. The crystal finishes growing when the crystal grains touch each other. Therefore, the crystal grains in random size are caused at random positions.

Ideally, the channel-forming region affecting the characteristics of the TFT significantly is removed such that a single crystal grain can be formed. Forming an amorphous silicon film having no grain boundaries has been almost impossible by using laser annealing. Even today, a TFT cannot be obtained which has, as an active layer, a crystalline silicon film crystallized by using laser annealing and has the same characteristics as those of a MOS transistor produced on a single crystalline silicon substrate.

The present invention was made in view of these problems. It is another object of the present invention to provide a system of producing a semiconductor device by using a laser crystallizing method, which can prevent grain boundaries from forming in a channel-forming region of a TFT and which can prevent a significant increase in mobility, a decrease in ON-current, and/or an increase in OFF-current of a TFT due to the grain boundaries.

In order to solve these problems, according to the present invention, multiple insulating films are stacked. Alternatively, on a primary insulating film having rectangular or strip grade changes formed by chemically engraving a pattern on an insulating film, an amorphous semiconductor film or a crystalline semiconductor film is formed. Then, a laser beam is irradiated thereto for crystallization. Then, at least the crystalline semiconductor film in depression bottom portions of the primary insulating film is left. Then, a TFT is formed such that a channel forming region can be provided in the crystalline semiconductor film. The channel forming region extends longitudinally in the depression bottom portion of the rectangular or a strip grade change.

The primary insulating film having the grade changes is formed by using silicon nitride, silicon oxide, silicon nitride oxide or silicon oxide nitride. The grade change may be formed by etching the film or may be formed by stacking multiple films. In the present invention, the silicon nitride oxide contains oxygen of not less than 20 atomic % to not more than 30 atomic % in density, nitrogen of not less than 20 atomic % to not more than 30 atomic % in density and hydrogen of not less than 10 atomic % to not more than 20 atomic % in density. The silicon oxide nitride contains oxygen of not less than 55 atomic % to not more than 65 atomic % in density, nitrogen of not less than 1 atomic % to not more than 20 atomic % in density and hydrogen of not less than 0.1 atomic % to not more than 10 atomic % in density.

The rectangular or strip grade change is formed by forming a first insulating film containing silicon oxide or silicon oxide nitride all over a substrate and forming a second insulating film containing silicon nitride or silicon nitride oxide in a rectangular or strip pattern. Alternatively, a second insulating film, which is silicon oxide nitride film, is formed all over a first insulating film formed by using a rectangular or strip pattern of silicon nitride, silicon oxide, silicon nitride oxide or silicon oxide nitride.

Originally, a silicon nitride film has large stress. Therefore, when a crystalline semiconductor film is formed thereon, distortion is undesirably formed due to the stress effect. A silicon oxide film has smaller internal stress. Therefore, the crystalline semiconductor film and an interface can be kept in better contact. As a result, the interface level density can be reduced. Silicon oxide nitride has a characteristic combining an impurity blocking characteristic of silicon nitride with characteristics of silicon oxide. Thus, the internal stress can be controlled to be smaller. Therefore, silicon oxide nitride film is suitable for the primary insulating film.

The grade changes are formed in accordance with an alignment of TFTs over a substrate surface and does not have to be in a regular and cyclical pattern. According to the present invention, each of the grade changes in a primary