JP2008311494A - Manufacturing method of crystalline semiconductor film, and laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a crystalline semiconductor film high in pressure resistance, and small in dispersion of characteristics among regions; and a laser device suitably used for the manufacturing method. <P>SOLUTION: This method is for manufacturing a crystalline semiconductor film formed by melting and crystallizing an amorphous semiconductor film by alternately repeating irradiation and movement of a laser beam. In the manufacturing method of the crystalline semiconductor film, the laser beam is emitted to a region including a bulge part of the crystalline semiconductor film formed by immediately preceding emission at an intensity leaving a part of the crystalline semiconductor film located under the bulge part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for manufacturing a crystalline semiconductor film and a laser device. More specifically, the present invention relates to a method for changing a semiconductor film included in a semiconductor element such as a thin film transistor from an amorphous semiconductor film to a crystalline semiconductor film using a sequential lateral growth method, and a laser device suitably used for the method. Is.

In an electronic device such as an active matrix liquid crystal display device, a semiconductor element such as a thin film transistor (TFT) is provided as a switching element or a control circuit. As a structure of the TFT, a structure in which a semiconductor film is stacked on a glass substrate is generally used, and silicon (Si) is often used as a material of the semiconductor film.

Silicon is classified into amorphous silicon (amorphous silicon) and crystalline silicon (polysilicon) due to the difference in crystallinity. Silicon used as a semiconductor film is preferably polysilicon from the viewpoint of carrier mobility. As a method for forming a polysilicon film, a method of forming a polysilicon film by first forming an amorphous silicon film and then irradiating a laser beam to melt and solidify the amorphous silicon film to be crystallized is known. Among them, it is known that the carrier mobility is particularly excellent for a polysilicon film formed by a sequential lateral solidification (SLS) method (see, for example, Patent Documents 1 to 5). .)

The SLS method is a method of forming a polysilicon film by sequentially irradiating an amorphous silicon film while moving laser light in one direction, repeatedly melting and solidifying, and growing crystals in the lateral direction (moving direction). FIG. 6 is a schematic diagram showing a state of crystallization from an amorphous silicon film to a polysilicon film by the SLS method. As shown in FIG. 6A, when the amorphous silicon film 113a is irradiated with the laser beam 114, the amorphous silicon film 113a is thermally melted. The amorphous silicon film 113a that has been melted by heat advances crystal growth while solidifying from the boundary of the irradiated region toward the inside (in the direction of the arrow). Then, as shown in FIG. 6B, the crystals grown from both sides collide with each other in the center of the irradiation region to form a raised portion called a ridge 116. When the melting and solidification of the amorphous silicon film 113a is repeated, crystal grains that are long in the moving direction of the laser beam 114 are formed, and a polysilicon film 113b is formed.

The SLS method is further classified into 2shot-SLS and Directional-SLS depending on how the irradiation areas are overlapped. 2shot-SLS is a method of irradiating the second shot so as not to overlap the ridge formed in the first shot (see, for example, Patent Documents 1 and 2). On the other hand, Directional-SLS is a method of irradiating the second shot so as to overlap the ridge formed in the first shot (see, for example, Patent Documents 3 to 5).

However, there is a strong demand for higher performance of semiconductor elements, and there is also a demand for more efficient manufacturing processes. There is room for improvement in the characteristics and manufacturing methods of silicon films formed by such methods. there were.
JP 2004-214614 A JP-A-2005-005722 JP 2003-347208 A JP 2003-31496 A JP 2006-190897 A

As a result of various studies on these two SLS methods, the present inventors have the following characteristics regarding the polysilicon film formed by the 2shot-SLS method and the polysilicon film formed by the Directional-SLS method. I found out.

First, with respect to the polysilicon film formed by the 2shot-SLS method, the second shot is irradiated so as not to overlap the ridge formed by the first shot. Crystal growth proceeds in the form of taking over. According to the 2shot-SLS method, the crystal planes vary uniformly. Therefore, TFTs formed from the polysilicon film crystallized in this way have characteristics variations such as carrier mobility and threshold (Vth) in each TFT. small. In addition, since the second shot is irradiated with the overlap width with the irradiation region of the first shot being reduced, the processing speed is faster than the Directional-SLS method described below. However, since the polysilicon film formed by the 2shot-SLS method has large unevenness due to the ridge on the surface, the formed polysilicon film has low pressure resistance. In addition, due to the presence of the ridge, crystal grains formed for each shot do not have continuity.

On the other hand, with respect to the polysilicon film formed by the Directional-SLS method, a silicon film is completely formed by using a laser beam having energy that completely dissolves to the bottom so as to overlap the ridge formed by the first shot. Since the film is melted, the first shot ridge does not remain even after irradiation. The ridge is also generated by the second shot, but disappears at the third shot. According to the Directional-SLS method, crystal growth occurs in the second shot by taking over the crystal on the side opposite to the irradiation progress direction with the ridge as a boundary. Therefore, the growth direction is more uniform than the polysilicon film formed by the 2shot-SLS method. As a result, a polycrystalline silicon film having excellent carrier mobility is obtained. However, since the irradiation is performed so as to overlap with the ridge formed by the first shot, the feed width of the laser beam is small, and the processing speed is slower than that of the 2shot-SLS method. In addition, since the number of times of irradiation increases, the number of times heating and cooling are repeated increases, so that thermal stress increases, and twinning may occur due to the thermal stress. A twin crystal is generated in a certain column, and the twin crystal portion has a different crystal orientation. Therefore, the characteristics of the manufactured TFT and the like vary depending on whether the twin crystal is included. In particular, a polysilicon film formed by the Directional-SLS method has a continuous crystal grain, and twins are generated in a lump, so that the influence on the TFT characteristics is great. Although twins are not generated at all by the 2shot-SLS method, twins are less likely to be generated because the number of times of irradiation is less than that of the Directional-SLS method, and the formed polysilicon film has crystal grains formed by ridges. Are separated, and twins are generated in a small region. For this reason, even if twins are included in the channel portion of the TFT, for example, they are uniformly included in each channel portion, so that variations in TFT characteristics are unlikely to occur.

The present invention has been made in view of the above-described present situation, and has a high pressure resistance and a crystalline semiconductor film manufacturing method with little variation in crystallinity between regions, and a laser suitably used for the manufacturing method. The object is to provide an apparatus.

The inventors of the present invention have studied various methods for producing a crystalline silicon film capable of suppressing the influence of ridges and twins, and have focused on the irradiation conditions of the laser beam to be irradiated. Then, the irradiation region includes the ridge formed by the first shot, and two shots with a strength that leaves a part of the crystalline semiconductor film located under the ridge of the crystalline semiconductor film formed by the first shot. By irradiating the laser light of the eyes, we found that it is possible to form a crystalline semiconductor film with less variation in crystallinity between regions while reducing the height of the ridge, and solve the above problems brilliantly Thus, the present invention has been achieved.

That is, the present invention is a method of manufacturing a crystalline semiconductor film formed by melting and crystallizing an amorphous semiconductor film by alternately repeating irradiation and movement of laser light, and the laser light is emitted immediately before This is a method for manufacturing a crystalline semiconductor film that is irradiated with an intensity that leaves a portion of the crystalline semiconductor film located under the raised portion in a region including the raised portion of the crystalline semiconductor film formed by irradiation.
Hereafter, the manufacturing method of this invention is explained in full detail.

According to the method for manufacturing a crystalline semiconductor film of the present invention, the amorphous semiconductor film (amorphous silicon film) is melted by repeating irradiation and movement of laser light, and crystallized to form a crystalline semiconductor film (polysilicon film). It is a manufacturing method. Therefore, it can be said that the manufacturing method of the present invention is an embodiment of a method for manufacturing a crystalline semiconductor film by the SLS method. According to the manufacturing method of the present invention, a crystalline semiconductor film can be formed by growing a crystal in a lateral direction (moving direction of laser light). Since the crystal structure thus formed has excellent carrier mobility, a TFT having excellent response characteristics can be obtained by using this crystalline semiconductor film, for example, as a semiconductor film included in the TFT. . Examples of the semiconductor material include silicon, germanium, selenium, and the like, but silicon is particularly preferable. The type of laser light is not particularly limited as long as it can melt a semiconductor material such as silicon, and examples of such laser light include a solid-state laser and an excimer laser. In the case of using silicon, a solid laser capable of obtaining second and third harmonics having a high silicon absorption coefficient is preferable. The shape of the laser beam is not particularly limited, but a long shape is preferable from the viewpoint of production efficiency. Examples of the laser beam shaping method include a method using a mask. When using an energy distribution having a Gaussian distribution, the base can be cut by using a mask. When a trapezoidal energy distribution is used, it is not necessary to use a mask. The adjustment of the laser beam may be appropriately performed according to the types of laser and optical system and the required profile. As a method of moving the laser light, a method of moving the laser light emission port may be used, or a method of moving the irradiated crystalline semiconductor film may be used.

The laser beam is applied to a region including a raised portion (ridge) of a crystalline semiconductor film (polysilicon film) formed by the last irradiation. In the manufacturing method of the present invention, since the irradiation is performed so as to overlap with the ridge formed in the irradiation region immediately before the laser beam, the ridge can be lost once. Although the ridge is formed again, the height of the ridge formed by the manufacturing method of the present invention is low, so that a crystalline semiconductor film having no large unevenness on the surface as a whole is formed. The Rukoto.

The laser light is irradiated with an intensity that leaves a part of the crystalline semiconductor film located under the raised portion. The depth of the crystalline semiconductor film to be melted is determined by the energy of the irradiated laser beam. In the manufacturing method of the present invention, the energy is sufficient for erasing the ridge formed in the first shot and the solid region of the crystalline semiconductor film partially remains under the region where the ridge is formed. Irradiation is performed by selecting a laser beam having

According to the manufacturing method of the present invention, the crystal growth after the second shot proceeds from the boundary of the irradiation region and the surface of the solid region located under the ridge. Crystal growth proceeds in the horizontal direction as viewed from the cross section of the film from the boundary of the irradiation region, and in the vertical direction from the surface of the solid region at the bottom of the ridge portion as viewed from the cross section of the film. The horizontal crystal growth and the vertical crystal growth collide with each other, and as a result, a ridge having a low height is formed. Since the height of the ridge depends on the distance over which the crystal has grown, the height of the ridge formed by the present invention is sufficiently lower than that of the ridge formed by the conventional 2shot-SLS method.

The structure of the method for producing a crystalline semiconductor film of the present invention may or may not include other steps as long as such steps are formed as essential, for example, laser irradiation. It is also possible to perform a treatment such as adding a catalyst element in advance.

According to the present invention, since the ridge having a low height is formed on the surface, the crystalline semiconductor film is flat as a whole, and as a result, the pressure resistance of the crystalline semiconductor film is improved. In addition, the twins are not formed as a lump, and even if the twins are formed, the microregions are dispersed and formed, so that the variation in crystallinity is small as a whole. For this reason, for example, even if this crystalline semiconductor film is provided in a TFT and the size of the TFT is reduced, characteristics such as carrier mobility and threshold value hardly vary between TFTs.

The present invention is also a laser device for producing a crystalline semiconductor film formed by melting and crystallizing an amorphous semiconductor film with a laser beam, the laser device alternately irradiating and moving the laser beam. A mechanism for repeating, and a mechanism for irradiating a laser beam with an intensity that leaves a part of the crystalline semiconductor film located under the raised portion in the region including the raised portion of the crystalline semiconductor film formed by the last irradiation. It is also a laser device.

The laser device of the present invention is suitably used in the production method of the present invention, and can adjust the movement of the laser beam and the irradiation intensity. The mechanism for repeating the irradiation and movement of the laser beam may be a mechanism in which the laser beam emitting section itself can move, for example, a substrate with a crystalline semiconductor film placed thereon by an XYZ stage or the like It may be a mechanism in which is moved. Then, using this mechanism, the movement of the laser beam is adjusted so as to overlap the ridge formed by the last irradiation. As a mechanism for adjusting the irradiation intensity of laser light, there is a mechanism for adjusting the energy of laser light by an attenuator (attenuator).

According to the method for manufacturing a crystalline semiconductor film of the present invention, the height of the ridge formed on the surface can be reduced, and a flat crystalline semiconductor film can be formed as a whole, and the pressure resistance is improved. . In addition, since the generation of twins is suppressed, even if the formed crystalline semiconductor film is provided in a TFT and the size of the TFT is reduced, variation in TFT characteristics such as carrier mobility and threshold value is suppressed to a low level. It is done. Thus, the production method of the present invention can be said to be a method in which the good points of the 2shot-SLS method and the Directional-SLS method are adopted and the respective defects are improved.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited only to these examples.

Example 1
FIGS. 1A to 1G and FIG. 2 are schematic views showing a method for forming a polysilicon film (crystalline semiconductor film) of this example. 1 (a) to 1 (g) are cross-sectional views at each manufacturing stage, and FIG. 2 is a perspective view showing the state of laser light irradiation shown in FIG. 1 (e) in more detail.

First, as shown in FIG. 1A, a base coat film 12 for preventing contamination and diffusion is formed on a substrate 11. As the substrate 11, a glass substrate or the like can be used. The base coat film 12 can be formed by a CVD (Chemical Vapor Deposition) method, a sputtering method, or the like. As a material of the base coat film 12, silicon oxide (SiO ₂ ), silicon nitride (SiNx), or the like can be used. In this embodiment, the base coat film 12 is formed with a film thickness of 150 nm.

Next, as shown in FIG. 1B, an amorphous silicon film (amorphous semiconductor film) 13 a is formed on the entire base coat film 12. The amorphous silicon film 13a can be formed by a CVD method, a sputtering method, or the like. In this embodiment, the amorphous silicon film 13a is formed with a film thickness of 50 nm. Then, it progresses to the laser beam irradiation process for polysilicon film formation.

As shown in FIG. 1C, the amorphous silicon film 13a is irradiated with a first shot of laser light 14 from a laser emission port 15. In this example, a solid laser (YAG; Yttrium Aluminum Garnet) having an average irradiation energy of 1000 mJ / cm ² and an irradiation region width of 5.7 μm was used. In this example, the second harmonic of a YAG laser was used. The YAG laser has a fundamental wavelength of 1060 nm, its second harmonic is 530 nm, and its third harmonic is 353 nm. As the shape of the laser beam 14, a long one was used, and the energy distribution was a Gaussian distribution, but the tail portion was sharply adjusted. In this embodiment, since the amorphous silicon film 13a is formed with a thickness of 50 nm, the irradiation of the laser light 14 under these conditions can sufficiently melt the amorphous silicon film 13a in the irradiated area to the bottom surface. . After melting, as shown in FIG. 1 (d), crystallization proceeds in the lateral direction (in the direction of the arrow in the figure) from the boundary of the irradiated region, and a polysilicon film 13b is formed. Then, the amorphous silicon film 13a settles at the boundary of the irradiation region, crystal growth proceeding from both sides near the center of the irradiation region collide with each other, and the polysilicon film 13b has a polysilicon film thickness of 1.5-2. A ridge 16 having a height of 0 times is formed. In this example, the ridge 16 having a height of 75 to 100 nm was formed.

Next, as shown in FIG. 1 (e) and FIG. 2, the laser emission port 15 is moved so that the irradiation region overlaps the ridge 16 formed by the first shot, and the average irradiation energy is 1000 mJ as in the first shot. / cm ^2, irradiating the amorphous silicon film 13a and the polysilicon film second shot of the laser beam 14 toward the 13b at the second harmonic of the YAG laser irradiation region width 5.7 .mu.m. Preferably, the laser shot 14 is moved to a position where the end opposite to the traveling direction of the irradiation region of the laser beam 14 is aligned with the ridge of the ridge, and the second shot of the laser beam 14 is irradiated. Thereby, the processing speed can be increased while the ridge 16 disappears.

By this step, in the region where the ridge 16 is not formed, the bottom surface (substrate side) of the amorphous silicon film 13a and the polysilicon film 13b is sufficiently melted. Then, as shown in FIG. 1F, a ridge 16 similar to the first shot is formed. On the other hand, in the region where the ridge 16 is formed by the first shot, energy does not reach the bottom surface, and the polysilicon solid region 17 remains on the bottom surface. Then, crystal growth progresses in a direction perpendicular to the boundary surface (in the direction of the arrow in the figure) from the irradiation region boundary and the solid region surface at the bottom of the ridge, and these collide with each other. Thus, a low ridge 18 is formed. Since the solid region 17 is formed under the ridge 16, the ridge 18 having a sufficiently low height is formed on the opposite side to the traveling direction of the laser beam from the position where the ridge 16 was formed. The crystal grains will not be continuous.

In this step, the average irradiation energy and the irradiation region width may be appropriately changed according to the silicon film thickness. Since the crystal grains need only be divided by collision of crystal growth starting from each boundary between the solid region 17 and the irradiation region, the ridge 16 portion does not have to be melted in all layers, and may remain at the atomic level. In the present invention, as a measure of energy for leaving the solid region 17 on the bottom surface while melting the ridge 16 at a minimum, when the laser wavelength is 500 to 550 nm, 1000 to 1500 J for an amorphous silicon film of about 50 nm. / cm ² about a while and the like to the beam profile, since different optimal energy by the silicon film surface treatment method is not particularly limited to this range.

Note that amorphous silicon and polysilicon are more likely to melt because amorphous silicon has a higher light absorption coefficient even when irradiated with the same energy, but the ridge 16 is formed under the conditions of this embodiment. In the region where the ridge 16 is not formed, it is possible to distribute energy to the bottom surface of both the amorphous silicon film 13a and the polysilicon film 13b, and in the region where the ridge 16 is formed, energy is not distributed to the bottom surface. It is possible.

After the third shot, as shown in FIG. 1 (g), the laser beam 14 irradiation method similar to that for the second shot is repeated. As a result, the crystal on the opposite side to the irradiation progress direction is taken over with the ridge 16 as a boundary, and crystal growth on and after the third shot proceeds to form a polysilicon film 13b.

After the formation process of the polysilicon film is completed, the polysilicon film is patterned into a desired shape such as an island shape by photolithography, for example, and a gate insulating film, a gate electrode, and a source electrode are formed on the polysilicon film. The TFT can be formed by patterning the drain electrode and other insulating films. Since the TFT manufactured according to this embodiment has a small variation in crystallinity between regions, a TFT that hardly causes variations in characteristics such as carrier mobility and threshold value is formed.

FIG. 3 is a schematic cross-sectional view of the silicon film 13 showing the laser light irradiation and movement profile of this example. 3A shows the first shot, and FIG. 3B shows the second and subsequent shots. Under the laser light irradiation conditions according to the present embodiment, as shown in FIG. 3A, the laser light irradiation region width L is 5.7 μm, so the lateral width R of the ridge is about 1.5 μm. . In this case, as shown in FIG. 3B, the laser beam feed width M is preferably about 2.1 μm calculated by M = (5.7−1.5) / 2. The lateral width R of the ridge refers to the width between the ridges located on both sides of the ridge and the boundary between the flat portion of the film surface. Since the optimal feed width varies depending on the laser beam profile, it is necessary to determine the feed width conditions suitable for the laser device and optical system.
Optimum feed width: M = (LR) / 2

FIG. 4 shows the threshold voltage variation (ΔVth) dependence on the TFT channel width W between the TFT having the polysilicon film formed according to this embodiment and the TFT having the polysilicon film formed by the conventional Directional-SLS method. It is a graph which shows sex. As shown in FIG. 4, according to this embodiment, the allowable range of the TFT channel width W with respect to threshold fluctuation is widened. Specifically, the threshold fluctuation does not increase even when the transistor size is smaller than in the conventional case.

According to the polysilicon film forming method of this embodiment, a flat polysilicon film having no ridges on the surface can be formed, and the pressure resistance is improved. In addition, since the generation of twins is suppressed, even if the TFT is provided with a polysilicon film manufactured in this way and the size of the TFT is reduced, variations in TFT characteristics such as carrier mobility and threshold value are not uniform. Hard to occur.

In this embodiment, crystallization from an amorphous silicon film to a polysilicon film was performed using a laser apparatus capable of adjusting movement of laser light and adjusting irradiation intensity with high accuracy. In this example, the laser beam was moved by moving an XYZ stage on which a substrate with a polysilicon film was placed. FIG. 5 is a schematic diagram showing the overall configuration of the laser apparatus used in this example. As shown in FIG. 5, the excited laser light is irradiated onto the substrate 21 on the XYZ stage 20 through a beam intensity attenuating means, a beam uniformizing means, and an imaging means. In this embodiment, an attenuator is used as the beam intensity attenuating means, a homogenizer is used as the beam uniformizing means, and a condenser lens is used as the imaging means.

It is a schematic diagram which shows the formation method of the polysilicon film (crystalline silicon film) of Example 1, (a)-(g) is sectional drawing of each manufacturing stage. It is a perspective view which shows the mode of the laser beam irradiation shown to FIG.1 (e) in detail. 2 is a schematic cross-sectional view of a silicon film showing a laser light irradiation and a movement profile of Example 1. FIG. (A) shows the first shot, and (b) shows the second and subsequent shots. The graph which shows the variation ((DELTA) Vth) dependence of the threshold voltage with respect to TFT channel width W of TFT provided with the polysilicon film formed by Example 1, and TFT provided with the polysilicon film formed by the conventional Directional-SLS method It is. 1 is a schematic diagram illustrating an overall configuration of a laser device used in Example 1. FIG. It is a schematic diagram which shows the mode of crystallization from amorphous silicon to polysilicon by SLS method. (A) shows a mode that an amorphous silicon film is irradiated with a laser beam. (B) shows how the ridge is formed.

Explanation of symbols

11, 21: substrate 12: base coat film 13: silicon film 13a, 113a: amorphous silicon film (amorphous semiconductor film)
13b, 113b: polysilicon film (crystalline semiconductor film)
14, 114: Laser beam 15: Laser emission port 16, 116: Ridge 17: Solid region 18: Ridge (the height is sufficiently low)
20: XYZ stage L: laser beam irradiation area width R: lateral width of ridge M: laser beam feed width

Claims (2)

A method for producing a crystalline semiconductor film formed by melting and crystallizing an amorphous semiconductor film by alternately repeating irradiation and movement of laser light,
The laser light is irradiated with an intensity that leaves a part of the crystalline semiconductor film located under the raised portion in a region including the raised portion of the crystalline semiconductor film formed by the last irradiation. A method for manufacturing a crystalline semiconductor film. A laser device for producing a crystalline semiconductor film formed by melting and crystallizing an amorphous semiconductor film with laser light,
The laser device includes a mechanism for repeating irradiation and movement of laser light alternately, and a crystalline semiconductor film positioned under the raised portion in a region including the raised portion of the crystalline semiconductor film formed by the immediately preceding irradiation. A laser device characterized by having a mechanism for irradiating a laser beam with an intensity that remains partially.

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