JP2005123475A - Semiconductor thin film, its manufacturing method, and thin film transistor using thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor thin film by which a region crystallized generally toward one direction and having no grain boundary in the direction of a crystal growth can be homogeneously formed at an arbitrary location in the semiconductor thin film. <P>SOLUTION: The method for manufacturing a semiconductor thin film comprises steps of forming at least a semiconductor thin film on a substrate, forming an anti-reflection film pattern and a reflection film pattern on the semiconductor thin film to be adjacent to each other, and forming direction-aligned semiconductor grains in the lower part of the anti-reflection film pattern by applying a first laser beam from the above side of the substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor thin film, a manufacturing method thereof, and a thin film transistor (TFT) using the thin film, and more particularly to a polycrystalline semiconductor thin film suitably used for a channel region of a TFT and a manufacturing method thereof.

  For a display device using liquid crystal or electroluminescence (EL), a polycrystalline silicon TFT using a polycrystalline silicon thin film as an active layer is preferably used.

  As a method for producing a polycrystalline silicon thin film, a method is known in which an amorphous silicon thin film formed on a glass substrate is crystallized at a low temperature of 600 ° C. or lower using a short pulse excimer laser.

In general, the crystallization by laser is performed by heating a glass substrate on which an amorphous silicon thin film is formed to about 400 ° C. and scanning the glass substrate while having a length of about 200 to 400 mm and a width of about 0.2 to 1.0 mm. The linear laser is continuously irradiated onto the glass substrate.
By this method, crystal grains having a grain size of about 0.2 to 0.5 μm are formed. At this time, the portion of the amorphous silicon irradiated with the laser does not melt over the entire thickness direction but melts leaving a part of the amorphous region.
For this reason, innumerable crystal nuclei are generated on the entire surface of the laser irradiation region, the crystal grows toward the outermost layer of the silicon thin film, and crystal grains with random orientation are formed.
A polycrystalline silicon TFT using a polycrystalline film obtained by this method has a small crystal grain size and a large number of grain boundaries in the channel length direction. Therefore, the electron mobility is small and the characteristics tend to vary.

In addition, a method of performing laser irradiation with a SiO ₂ cap formed on the surface is also known. In this method, the SiO ₂ cap functions as a heat insulating film for the molten silicon thin film, and the crystallinity is improved as a whole, but the improvement in uniformity is not sufficient.

Also known is a method of increasing the crystal grain size with good reproducibility by patterning an insulating film and forming it at an arbitrary position and then performing laser irradiation (see, for example, Patent Document 1).
In this method, as shown in FIG. 18, after forming a semiconductor thin film 303 made of amorphous silicon on an insulating substrate 301, an insulating film pattern 304 is selectively formed, and then a laser 305 is irradiated. Then, since the insulating film pattern 304 functions as a heat insulating layer, the cooling rate is lowered in the region below the insulating film pattern 304, and as a result, the insulating film pattern 304 is crystallized from both edges toward the center.
By this method, crystallized regions 306 and 307 having a large crystal grain size are uniformly formed at arbitrary positions. Then, both or one of these crystallized regions 306 and 307 is used as a channel region of the TFT.
JP 2000-260709 A

In the above method of forming a patterned insulating film at an arbitrary position, as shown in FIG. 18, lateral crystallization occurs simultaneously from both edges of the insulating film pattern 304, and the lateral crystal is formed at the center of the pattern. Since the growth is completed, a crystal grain boundary is formed at the center.
For this reason, as shown in FIG. 19, when the TFT 308 is formed using two crystallized regions 306 and 307, at least one grain boundary exists in the channel length direction, and the electron mobility is lowered.
As shown in FIG. 20, when the TFT 308 is formed in each of the crystallized regions 306 and 307 so that the channel does not cross the grain boundary, there are regions that cannot be used for the crystallized regions 306 and 307 due to design restrictions. As a result, the degree of freedom and efficiency of TFT design are reduced.

The present invention has been made in consideration of the above problems, and a crystallized region that is generally crystallized in one direction and does not have a grain boundary in the crystal growth direction can be provided at an arbitrary location on the semiconductor thin film. A method of manufacturing a semiconductor thin film that can be uniformly formed is provided.

  In the present invention, at least a semiconductor thin film is formed on a substrate, an antireflection film pattern and a reflection film pattern are formed adjacent to each other on a part of the semiconductor thin film, and the first laser is irradiated from above the substrate to prevent reflection. The present invention provides a first method for producing a semiconductor thin film comprising a step of forming semiconductor grains with uniform orientation under a film pattern.

  According to the present invention, at least a semiconductor thin film is formed on a substrate, an antireflection film pattern is formed on a part of the semiconductor thin film, a reflection film pattern is formed on a part of the antireflection film pattern, and from above the substrate. The present invention also provides a second method for manufacturing a semiconductor thin film, which includes a step of irradiating a first laser to form semiconductor grains having a uniform direction below the antireflection film pattern.

  Also, the present invention forms at least a semiconductor thin film on a substrate, forms a reflection film pattern on a part of the semiconductor thin film, and forms an antireflection film pattern so as to cover the reflection film pattern and a part of the semiconductor thin film. Also, the present invention provides a third method for manufacturing a semiconductor thin film comprising a step of irradiating a first laser from above the substrate to form semiconductor grains having a uniform direction below the antireflection film pattern.

  In the first method of manufacturing a semiconductor thin film according to the present invention, in the step of forming the antireflection film pattern and the reflection film pattern, a part of the edge of the antireflection film pattern is in contact with a part of the edge of the reflection film pattern. Thus, the process of forming an antireflection film pattern and a reflection film pattern may be used.

  In the second method of manufacturing a semiconductor thin film according to the present invention, the step of forming the reflective film pattern may be performed so that a part of the edge of the reflective film pattern coincides with a part of the edge of the antireflection film pattern. It may be a step of forming a film pattern.

  In the third method of manufacturing a semiconductor thin film according to the present invention, the step of forming the antireflection film pattern may be performed so that a part of the edge of the antireflection film pattern coincides with a part of the edge of the reflection film. It may be a step of forming a prevention film pattern.

  The first to third methods of manufacturing a semiconductor thin film according to the present invention further include a step of irradiating a region including the irradiation region of the first laser with the second laser with an irradiance and an irradiation time that do not melt the semiconductor thin film. May be.

  In the step of irradiating the second laser, the irradiation time of the second laser may be longer than the irradiation time of the first laser.

  The second laser is an infrared laser, and the absorption rate of the antireflection film pattern with respect to the infrared laser may be higher than the absorption rate of the reflection film pattern and the semiconductor thin film with respect to the infrared laser.

  In the first to third methods of manufacturing a semiconductor thin film according to the present invention, the antireflection film pattern may be composed of any one of a silicon oxide film and a silicon nitride film.

  In the first to third methods of manufacturing a semiconductor thin film according to the present invention, the reflective film pattern is composed of any one of an Al film, a Mo film, a W film, an Al—Mo alloy film, and an Al—W alloy film. May be.

  From another point of view, the present invention also provides a semiconductor thin film manufactured by the above-described first to third methods of manufacturing a semiconductor thin film according to the present invention.

  From another viewpoint, the present invention is a thin film transistor using the semiconductor thin film manufactured by the first to third methods of manufacturing a semiconductor thin film according to the present invention described above, and is provided below the antireflection film pattern. The present invention also provides a thin film transistor that includes formed semiconductor grains with uniform orientation in a channel region.

Here, the principle of the present invention will be described with reference to FIGS. 1 to 3 correspond to first to third methods of manufacturing a semiconductor thin film according to the present invention, respectively.
As shown in FIGS. 1 to 3, in the first to third methods for manufacturing a semiconductor thin film according to the present invention, in the step of irradiating the first laser 6, both of the antireflection film pattern 4 and the reflection from above the substrate 1. The first laser 6 is irradiated to the film pattern 5 and the direct irradiation regions (exposed regions of the semiconductor thin film 3) 3c and 3d.

At this time, since the antireflection film pattern 4 prevents reflection of the first laser 6, the first laser 6 is efficiently absorbed in the lower region 3 a of the antireflection film pattern 4, and the lower region 3 a of the antireflection film pattern 4 is absorbed. The semiconductor thin film 3 melts.
On the other hand, since the reflective film pattern 5 reflects the first laser 6, the first laser is not absorbed in the lower region 3b of the reflective film pattern 5, and the semiconductor thin film 3 in the lower region 3b of the reflective film pattern 5 is almost melted. do not do.

In the direct irradiation regions 3 c and 3 d to which the first laser 6 is directly irradiated, the first laser 6 is partially reflected, so that the amount of absorption of the first laser 6 is higher than that of the lower region 3 a of the antireflection film pattern 4. The direct irradiation areas 3c and 3d are in a molten or semi-molten state.
For this reason, the temperature of each region increases in the order of the lower region 3 b of the reflective film pattern 5, the direct irradiation regions 3 c and 3 d, and the lower region 3 a of the antireflection film pattern 4.

Here, of the direct irradiation regions 3c and 3d, the direct irradiation region 3d adjacent to the antireflection film pattern 4 is involved in crystallization in the lower part of the antireflection film pattern 4 which is the main point of the present invention. Accordingly, the irradiation of the first laser 6 directly on the irradiation region 3c is not necessarily essential for the operation of the principle of the present invention.

Since the lower region 3 b and the direct irradiation region 3 d of the reflection film pattern 5 have a lower temperature than the lower region 3 a of the antireflection film pattern 4, crystallization proceeds from both edges of the antireflection film pattern 4.
However, since the temperature of the lower region 3b of the reflective film pattern 5 is lower than that of the direct irradiation region 3d, crystallization from the reflective film pattern 5 side is started earlier, and the cooling rate is further increased by the heat retention effect of the antireflective film pattern 4. Slow down and crystals grow larger. For this reason, the crystallization regions 7 and 8 grown from both edges of the antireflection film pattern 4 collide at positions close to the direct irradiation region 3d.

Therefore, the lower region 3a of the antireflection film pattern 4 is largely crystallized substantially in one direction, and a crystallized region (semiconductor particles having uniform orientation) 7 having no grain boundary in the crystal growth direction is formed. .

According to the method for manufacturing a semiconductor thin film of the present invention, a temperature difference is generated in the semiconductor thin film irradiated with the first laser by the action of the antireflection film and the reflection film, and the lower part of the reflection film pattern having the lowest temperature and the highest temperature are produced. Crystallization starts from the boundary with the lower part of the antireflection film pattern, and the crystal growth continues in one direction due to the heat-retaining action of the antireflection film. Crystallized regions (semiconductor grains having uniform orientation) that are crystallized and have no grain boundary in the crystal growth direction can be formed.
As a result, a crystallized region having no grain boundary in the crystal growth direction can be formed uniformly at an arbitrary location on the semiconductor thin film.

  By using this crystallized region for the channel region of the TFT, it is possible to manufacture a TFT with high electron mobility and small variation in element characteristics. This crystallized region can be used not only for TFTs but also for active regions of various thin film semiconductor devices that require high-speed electron mobility.

  Furthermore, since this crystallized region has substantially no grain boundary in the crystal growth direction, the crystallized region in the direction of electron movement in the active region can be obtained without impairing the design freedom and design efficiency of thin film semiconductor devices such as TFTs. It facilitates the design of thin film semiconductor devices that do not have grain boundaries.

  (First Embodiment) In a method of manufacturing a semiconductor thin film according to a first embodiment of the present invention, as shown in FIG. 4A, a semiconductor thin film 3 is formed on a substrate 1, and FIG. As shown in FIG. 4, an antireflection film pattern 4 and a reflection film pattern 5 are formed on a part of the semiconductor thin film 3 so as to be adjacent to each other, and reflected from above the substrate 1 as shown in FIG. By irradiating the first laser 6 on the anti-reflection film pattern 4, the reflection film pattern 5, and the exposed region of the semiconductor thin film 3, the semiconductor thin film 3 below the anti-reflection film pattern 4 is crystallized, so that the film is generally directed in one direction. And a step of forming a crystallized region (semiconductor grain with uniform orientation) 7 that is largely crystallized and does not have a grain boundary in the crystal growth direction.

  The substrate 1 may be any substrate having a strength and heat resistance that can withstand the formation of the semiconductor thin film 3 and laser annealing. A glass substrate, a quartz substrate, a polymer substrate, or the like can be used, but an inexpensive glass substrate is preferable. Used.

The semiconductor thin film 3 includes an amorphous, microcrystalline, polycrystalline silicon film, or a thin film of a compound of silicon and germanium, and an amorphous silicon film is preferably used for this.
These are formed by a known method such as CVD, sputtering, or vapor deposition. The thickness varies depending on the required transistor characteristics, process conditions, and the like, but a film thickness in the range of about several tens to several hundreds of nm, particularly typically about 30 to 100 nm is employed. Dehydrogenation annealing may be performed by a known method after the formation. Thereby, damage to the semiconductor thin film at the time of laser irradiation can be prevented.

The step of forming the semiconductor thin film 3 on the substrate 1 includes forming the semiconductor thin film 3 directly on the substrate 1 or forming it through an insulating film or the like (not shown).
In order to prevent impurity diffusion from the substrate 1, it is preferable to form the semiconductor thin film 3 through an insulating film. As the insulating film, an inorganic insulating film such as a silicon oxide film or a silicon nitride film is preferably used.
The inorganic insulating film can be formed by a known method such as CVD, sputtering, or vapor deposition. Further, after the semiconductor thin film 3 is formed, the semiconductor thin film 3 may be patterned into an island shape. Thereby, in the irradiation process of the 1st laser 6 mentioned later, since the escape of a heat | fever becomes small, crystallization with lower energy is attained.

Further, the step of forming the antireflection film pattern 4 and the reflection film pattern 5 on a part of the semiconductor thin film 3 so as to be adjacent to each other is a part of the edge of the antireflection film pattern 4 and the edge of the reflection film pattern 5. And a step of forming the antireflection film pattern 4 and the reflection film pattern 5 so as to be close to each other with a slight gap therebetween.
That is, the antireflection film pattern 4 and the reflection film pattern 5 may be non-contact as long as crystal growth can be performed substantially in one direction. For example, when the antireflection film pattern 4 and the reflection film pattern 5 are formed in a substantially rectangular shape, one of the long sides of the reflection film pattern 5 is adjacent to one of the long sides of the antireflection film pattern 4 in parallel. It may be formed in the form.

Further, in the above-described process of forming the antireflection film pattern 4 and the reflection film pattern 5, either the antireflection film pattern 4 or the reflection film pattern 5 may be formed first or simultaneously.
The antireflection film pattern 4 is formed, for example, by forming an antireflection film on the semiconductor thin film 3 and patterning it.
The reflective film pattern 5 is formed, for example, by forming a reflective film on the semiconductor thin film 3 and patterning it.

The antireflection film pattern 4 may be a film having a low absorption rate with respect to the first laser 6, and an inorganic insulating film such as a silicon oxide film or a silicon nitride film is preferably used.
In order to exhibit the function as the antireflection film pattern 4, the thickness d (see FIG. 4B) is d when the wavelength of the first laser 6 is λ and the refractive index of the antireflection film is n. It is preferable that λ / 4n is satisfied.
The antireflection film pattern 4 may be a single layer or a multilayer. The antireflection film pattern 4 is formed by a known method such as CVD, sputtering, or vapor deposition.

The reflective film pattern 5 may be a film that reflects the first laser 6, and an Al film, a Mo film, a W film, an Al—Mo alloy film, an Al—W alloy film, or the like can be used.
When the first laser 6 is an ultraviolet laser, it is preferable to use an Al—Mo alloy film in consideration of both the reflectance in the ultraviolet region and the heat resistance against laser irradiation.
The thickness of the reflective film pattern 5 may be sufficient as long as it reflects the first laser 6. The reflective film pattern 5 can be formed by a known method such as CVD, sputtering, or vapor deposition. The thicknesses of the antireflection film pattern 4 and the reflection film pattern 5 may be different or the same.

  Also, a process of crystallizing the semiconductor thin film 3 under the antireflection film pattern 4 by irradiating the first laser 6 to the antireflection film pattern 4, the reflection film pattern 5 and the exposed region of the semiconductor thin film 3 from above the substrate 1. In “from above the substrate 1”, the first laser 6 is irradiated perpendicularly from above to the surface of the substrate 1, and the first laser 6 is obliquely inclined from above to the surface of the substrate 1. In order to form the crystallization region 7 accurately at the position where the antireflection film pattern 4 and the reflection film pattern 5 are formed, the first laser is perpendicular to the surface of the substrate 1 from above. 6 is preferably irradiated.

  In the above process, the first laser 6 may be irradiated to at least the antireflection film pattern 4, the reflection film pattern 5, and the exposed region of the semiconductor thin film 3. Therefore, the first laser 6 may irradiate a partial region of the semiconductor thin film 3 including the antireflection film pattern 4, the reflective film pattern 5, and the exposed region of the semiconductor thin film 3, or the entire region of the semiconductor thin film 3. May be irradiated.

The first laser 6 may be any laser that can melt the semiconductor thin film 3, and an XeCl laser, a KrF laser, an ArF laser, an XeF laser, a YAG laser, an Ar laser, or the like can be used, and an XeCl laser is preferably used. Although either continuous oscillation or pulse oscillation may be used, pulse oscillation is suitable for supplying high energy to the semiconductor thin film 3 without damaging the substrate 1.
In the XeCl laser, the pulse width can be, for example, 10 ns to several tens ns.
As a result, the film is melted almost instantaneously and then rapidly cooled, and crystallization occurs in the process. The irradiance of the laser may be any irradiance that can melt the semiconductor thin film 3.

  In the above step of crystallizing the semiconductor thin film 3 below the antireflection film pattern 4 by irradiating the first laser 6, “crystallizing” includes crystallizing the amorphous semiconductor thin film, and It includes growing semiconductor thin films such as microcrystals and polycrystals into larger crystals after melting.

  (Second Embodiment) In a method of manufacturing a semiconductor thin film according to a second embodiment of the present invention, as shown in FIG. 5A, a semiconductor thin film 3 is formed on a substrate 1, and FIG. As shown in FIG. 5, the antireflection film pattern 4 is formed on a part of the semiconductor thin film 3, and the reflection film pattern 5 is formed on a part of the antireflection film pattern 4 as shown in FIG. Then, as shown in FIG. 5D, the antireflection film pattern 4, the reflection film pattern 5, and the exposed region of the semiconductor thin film 3 are irradiated from above the substrate 1 to irradiate the first laser 6. By crystallizing the lower semiconductor thin film 3, a crystallized region (semiconductor grains with uniform orientation) 7 that is largely crystallized in one direction and has no grain boundary in the crystal growth direction is formed. The process of carrying out is provided.

The difference from the first embodiment is that the reflective film pattern 5 is formed on a part of the antireflection film pattern 4 without forming the reflective film pattern 5 on the semiconductor thin film 3.
When the reflection film pattern 5 is formed on a part of the antireflection film pattern 4, impurity diffusion from the reflection film pattern 5 to the semiconductor thin film 3 can be prevented.
Also in the second embodiment, as in the first embodiment described above, the crystal grows largely in one direction at the lower part of the antireflection film pattern 4, so that there is no grain boundary in the crystal growth direction. A crystallization region 7 is formed.

The reflective film pattern 5 may be formed at any location on the antireflective film pattern 4, but a part of the edge of the reflective film pattern 5 is reflected from the gist of the present invention that the crystal is grown in one direction. It is preferable to form the reflective film pattern 5 so as to coincide with (overlap with) part of the edge of the prevention film pattern 4.
For example, when the antireflection film pattern 4 and the reflection film pattern 5 are formed in a substantially rectangular shape, one of the long sides of the reflection film pattern 5 is the length of the antireflection film pattern 4 on the antireflection film pattern 4. It may be formed with a width W2 (see FIG. 5C) shorter than the width W1 (see FIG. 5B) of the antireflection film pattern 4 in a shape that coincides with (overlaps) one of the sides.

  (Third Embodiment) In a method of manufacturing a semiconductor thin film according to a third embodiment of the present invention, as shown in FIG. 6A, a semiconductor thin film 3 is formed on a substrate 1, and FIG. As shown in FIG. 6, a reflection film pattern 5 is formed on a part of the semiconductor thin film 3, and the reflection film pattern 5 and a part of the semiconductor thin film 3 are covered as shown in FIG. 6C. A film pattern 4 is formed, and the first laser 6 is irradiated from above the substrate 1 to the exposed areas of the antireflection film pattern 4, the reflection film pattern 5, and the semiconductor thin film 3 as shown in FIG. 6 (d). By crystallizing the semiconductor thin film 3 below the antireflection film pattern 4, a crystallized region (a semiconductor with uniform orientation) that is largely crystallized substantially in one direction and has no grain boundary in the crystal growth direction. Grain) 7 is provided.

The difference from the first embodiment is that the antireflection film pattern 4 is formed so as to cover the reflection film pattern 5 formed on the substrate 1 instead of making the antireflection film pattern 4 and the reflection film pattern 5 adjacent to each other. Is a point.
That is, a part of the antireflection film pattern 4 is overlapped on the reflection film pattern 5. As in the first and second embodiments, the crystal grows largely in one direction in the lower part of the antireflection film pattern 4, so that the crystallization region 7 having no grain boundary in the crystal growth direction is formed. It is formed.

The reflection film pattern 5 is only required to be covered with the antireflection film pattern 4, but a part of the edge of the antireflection film pattern 4 is formed in the reflection film pattern 5 from the gist of the present invention that the crystal is grown in one direction. It is preferable to form the antireflection film pattern 4 so as to coincide with a part of the edge of the film.
For example, when the reflection film pattern 5 and the antireflection film pattern 4 are formed in a substantially rectangular shape, one of the long sides of the antireflection film pattern 4 is the long side of the reflection film pattern 5 on the reflection film pattern 5. The reflective film pattern 5 may have a width W1 (see FIG. 6C) longer than the width W2 (see FIG. 6B) of the reflective film pattern 5.

  The method for manufacturing a semiconductor thin film according to the present invention is the second embodiment with the irradiance and irradiation time that do not melt the semiconductor thin film in the region including the irradiation region of the first laser 6 in the first, second, and third embodiments. You may further provide the process of irradiating a laser (not shown).

By separately irradiating the second laser, the antireflection film pattern 4 and the substrate 1 are heated to such an extent that the semiconductor thin film 3 is not melted. Therefore, the crystallization speed of the molten semiconductor thin film 3 under the antireflection film pattern 4 is increased. Further, the crystal grain size of the crystal grown under the antireflection film pattern 4 is further increased.
By using this crystallized region 7 for the TFT channel region, it is possible to manufacture a TFT having a higher electron mobility.
In addition, since the lateral crystal growth distance is increased, the width of the antireflection film pattern 4 can be increased, and the degree of design freedom and efficiency of semiconductor elements such as TFTs are further improved. Further, the irradiation energy of the first laser 6 can be reduced, and the apparatus can be miniaturized.

The irradiance and irradiation time of the second laser may be those that do not melt the semiconductor thin film 3. The irradiation time of the second laser may be the same as the irradiation time of the first laser 6, or may be longer or shorter than that. During the irradiation of the second laser, immediately before the irradiation of the second laser, The first laser 6 may be irradiated at any timing immediately after irradiation.
By irradiating the second laser before the irradiation of the first laser 6, the antireflection film pattern 4 and the substrate 1 are heated, and the semiconductor thin film 3 is kept warm by the heated antireflection film pattern 4 and the substrate 1. Therefore, the irradiation energy of the first laser 6 can be reduced.
Further, by irradiating the second laser after the irradiation of the first laser 6, the antireflection film pattern 4 and the substrate 1 are heated, and the molten semiconductor thin film 3 is kept warm by the heated antireflection film pattern 4 and the substrate 1. As a result, the crystallization rate can be made slower and the crystal grain size can be made larger.
In order to obtain these two effects, it is preferable that the irradiation time of the second laser is made longer than the irradiation time of the first laser 6 and the first laser 6 is irradiated during the irradiation of the second laser.

  The second laser may be either continuous wave or pulsed. In the case of pulse oscillation, the pulse width of the second laser may be the same as, longer or shorter than the pulse width of the first laser 6, but is sufficiently larger than the pulse width of the first laser 6. For example, those of several tens of μm to several ms are preferably used.

  The region irradiated with the second laser may include at least the region irradiated with the first laser 6, and is preferably the same as or wider than the region irradiated with the first laser 6. By irradiating at least the region including the irradiation region of the first laser 6 with the second laser, uniform crystal growth can be promoted in the entire region where crystallization occurs.

  The second laser may be irradiated from any direction above or below the substrate 1, but in order to effectively heat the antireflection film pattern 4 and the portion of the substrate 1 close to the semiconductor thin film 3, It is preferable to irradiate from above.

The second laser may be any laser that can heat the semiconductor thin film 3, the antireflection film pattern 4 and the substrate 1 to such an extent that the semiconductor thin film 3 does not melt, and an infrared laser such as an Er: YAG, CO, CO ₂ laser or the like is used. A CO ₂ laser is preferably used.
Further, when an infrared laser is used as the second laser, the absorption rate of the antireflection film pattern 4 with respect to the infrared laser is preferably higher than the absorption rate of the reflection film pattern 5 and the semiconductor thin film 3 with respect to the infrared laser. In this case, the output of the infrared laser can be increased without melting the semiconductor thin film 3, and the heat retention effect of the antireflection film pattern 4 can be more effectively exhibited.

  Instead of the step of heating the semiconductor thin film 3, the antireflection film pattern 4 and the substrate 1 with the second laser, or together with this step, the step of heating the substrate 1 with a heater or the like so that the semiconductor thin film 3 does not melt. May be provided. In this case, due to the heat from the substrate 1, the crystallization speed of the semiconductor thin film 3 in the lower region of the antireflection film pattern 4 becomes slower, and the crystal grain size of the crystal grown under the antireflection film pattern 4 becomes larger. .

  From another viewpoint, the present invention also provides a semiconductor thin film manufactured by the semiconductor thin film manufacturing method of the first, second, and third embodiments described above.

  From another point of view, the present invention is a TFT using a semiconductor thin film manufactured by the method for manufacturing a semiconductor thin film according to the first, second and third embodiments described above. A TFT including a crystallized region 7 crystallized in the lower part of the channel region in a channel region is provided.

  As described above, the crystallized region 7 crystallized under the antireflection film pattern 4 has no grain boundary in the crystal growth direction. A TFT with high mobility and small variation in element characteristics is manufactured.

  The TFT is manufactured by patterning the obtained semiconductor thin film so that the region crystallized under the antireflection film pattern 4 is included in the channel region of the TFT, and performing ion implantation, electrode formation, and the like by known methods. it can.

  Note that the crystallization region 7 is not limited to the TFT, and is preferably used for an active region of various thin film semiconductor devices that require high electron mobility.

  Each element demonstrated so far can also be combined arbitrarily.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. This does not limit the invention.

A manufacturing method of a polycrystalline semiconductor thin film according to Example 1 of the present invention and a TFT using the thin film will be described with reference to FIGS.
7 to 12 are process diagrams showing a method of manufacturing a polycrystalline semiconductor thin film according to Example 1, FIG. 13 is an explanatory diagram showing a schematic configuration of a laser irradiation apparatus used in the process shown in FIG. 11, and FIG. 12 is a plan view of a TFT manufactured using the polycrystalline semiconductor thin film obtained by the process shown in FIG. 12, FIG. 15 is a cross-sectional view taken along the line AA in FIG. 14, and FIG.
8 and 10, FIGS. 8A and 10A are cross-sectional views, and FIGS. 8B and 10B are plan views.

First, as shown in FIG. 7, a base film 12 made of silicon oxide, an amorphous silicon film 13 as a semiconductor thin film, and an antireflection film 14 made of silicon oxide are sequentially formed on a glass substrate 11 serving as a TFT substrate. Laminate.
The base film 12 functions as an impurity diffusion preventing film and is formed by a CVD method.
Further, the amorphous silicon film 13 and the antireflection film 14 are also formed by the CVD method, and their film thickness is 50 nm, respectively.

Next, as shown in FIGS. 8A and 8B, the antireflection film 14 (see FIG. 7) is patterned into a rectangular shape to form an antireflection film pattern 15.
Next, as shown in FIG. 9, a reflective film 16 made of an Al—Mo alloy is formed on the amorphous silicon film 13 and the antireflection film pattern 15.
Next, as shown in FIGS. 10A and 10B, the reflective film 16 is patterned to form a reflective film pattern 17. Here, as particularly shown in FIG. 10B, the reflective film pattern 17 is formed so that one of its long sides is in contact with one of the long sides of the antireflection film pattern 15.

Next, as shown in FIG. 11, the Xe-Cl excimer laser 18 as the first laser is irradiated with the antireflection film pattern 15, the reflection film pattern 17, and the direct irradiation region (exposed region of the amorphous silicon film 13) 13c, Irradiate 13d.
Here, FIG. 13 shows a laser irradiation apparatus 100 used for irradiation with the Xe-Cl excimer laser 18 (see FIG. 11). The laser irradiation apparatus 100 includes a first laser oscillator 31, an imaging lens 35, and a stage 37 that is driven by mounting a substrate that performs laser irradiation, and an optical element group such as a homogenizer or a beam expander as necessary. 32, a mirror 33, and a field lens 34. On the stage 37, the glass substrate 11 obtained through the steps shown in FIGS.

A Xe-Cl excimer laser beam is emitted from the laser oscillator 31. The beam emitted from the laser oscillator 31 is converted into an appropriate beam size by an expander, and the irradiance in the beam cross section is made uniform by a homogenizer. Incident.

Here, the beam expander is an optical system having a telephoto system or a reduction system, and determines the size of an incident region on the imaging lens 35. The homogenizer is composed of a lens array or a cylindrical lens array, and divides the beam and recombines it to make the irradiance uniform in the irradiation area on the mask. The field lens 34 has a function of causing the principal ray emitted from the first laser oscillator 31 to enter the imaging lens 35 perpendicularly.

The light that has passed through the homogenizer and the field lens 34 is imaged on the surface of the glass substrate 11 by the imaging lens 35. When the principal ray emitted from the first laser oscillator 31 is imaged on the glass substrate 11 by the imaging lens 35, the amorphous silicon film 13 (see FIG. 11) on the glass substrate 11 is melted by the laser power. When the pulse irradiation is completed, the crystal is rapidly cooled to cause crystallization.

In Example 1, as shown in FIG. 11, a Xe-Cl excimer laser 18 having a wavelength of 308 nm is used as the first laser, and the antireflection film pattern 15, the reflection film pattern 17, and the direct irradiation regions 13c and 13d are directly above the substrate 11. The amorphous silicon film 13 is once melted and then crystallized during cooling.
The film thickness of the antireflection film pattern 15 is 50 nm as described above, and this satisfies the relationship described in “Best Mode for Carrying Out the Invention”, that is, the relationship of 50 nm≈308 nm / 4n. .
For this reason, the antireflection film pattern 15 acts as an antireflection film, and in the lower region 13a of the antireflection film pattern 15, the incident energy is increased and the temperature is efficiently increased. Furthermore, since the antireflection film pattern 15 also has a heat retaining effect, the cooling rate is lowered in the lower region 13 a of the antireflection film pattern 15.

On the other hand, in the lower region 13b of the reflective film pattern 17, since the first laser 18 is reflected by the reflective film pattern 17 and does not reach, the incident energy is slight and hardly melts.
Therefore, large crystallization occurs in the lateral direction from one edge of the antireflection film pattern 15 in contact with the reflection film pattern 17 toward the other edge, and the first crystallization region 19 is formed.

Further, the temperature of the amorphous silicon film 13 in the direct irradiation regions 13 c and 13 d where the amorphous silicon film 13 is exposed and the Xe-Cl excimer laser 18 is directly irradiated is set in the lower region 13 a of the antireflection film pattern 15. Compared to the temperature of the amorphous silicon film 13, the antireflection film pattern 15 has a lower temperature because it does not have an antireflection effect and a heat retention effect.
As a result, lateral crystallization occurs also from the other edge of the antireflection film pattern 15 not in contact with the reflection film pattern, and the second crystallization region 20 is formed.

However, since the crystallization from one edge of the antireflection film pattern 15 in contact with the reflection film pattern 17 starts earlier than the other edge, the lateral crystallization that starts from both edges is the antireflection film pattern 15. It hits in the vicinity of the other edge of the antireflection film pattern 15 without hitting in the vicinity of the center.
As a result, in the lower region 13 a of the silicon oxide film pattern 15, the first crystallized region 19 is obtained in which the crystal grain growth directions are substantially aligned in one direction and have no grain boundaries in the crystal growth direction.
Further, the direct irradiation regions 13 c and 13 d that are not covered with the antireflection film pattern 15 and the reflection film pattern 17 are melted or semi-molten by the irradiation of the Xe—Cl excimer laser 18 and become the polycrystalline region 21.
Thereafter, as shown in FIG. 12, by removing the antireflection film pattern 15 and the reflection film pattern 17 (see FIG. 11), the first crystallization region 19, the second crystallization region 20, and the polycrystalline region 21 are removed. The polycrystalline semiconductor thin film manufacturing process is completed.

FIGS. 14 to 16 show TFTs manufactured using the polycrystalline semiconductor thin film manufactured by the above-described manufacturing process shown in FIGS.
The TFT 50 shown in FIGS. 14 to 16 is obtained in such a manner that the channel region 51 of the TFT 50 includes the first crystallized region 19 crystallized in the lower region 13 a (see FIG. 11) of the antireflection film pattern 15. It is produced by patterning a crystalline semiconductor thin film and performing ion implantation, electrode formation, etc. by a known method.
As shown in FIG. 16, since the TFT 50 includes the first crystallized region 19 in which the crystal growth direction is substantially aligned in one direction and has no grain boundary in the crystal growth direction, the channel length 51 No crystal grain boundary is formed near the center of the direction.
For this reason, the TFT 50 has high electron mobility and high performance, and variation in element characteristics during mass production is small.

Next, a method for manufacturing a polycrystalline semiconductor thin film according to Embodiment 2 of the present invention will be described. The processes up to forming the reflective film pattern 17 are the same as those in the first embodiment. In the manufacturing method according to the second embodiment, at least the Xe-Cl excimer laser 18 is irradiated using the laser irradiation apparatus 200 shown in FIG. 17 in the step of irradiating the Xe-Cl excimer laser 18 shown in FIG. The region to be irradiated or the region including the region irradiated with the Xe-Cl excimer laser 18 is irradiated with a CO ₂ laser 43 as a second laser with an irradiance and irradiation time at which the amorphous silicon film 13 does not melt. The only difference is that it further comprises a step of performing.

The laser irradiation apparatus 200 shown in FIG. 17 has an optical element group 39 such as a second laser oscillator 38 that emits a CO ₂ laser 43, an imaging lens 42, a homogenizer, and an expander in the configuration of the laser irradiation apparatus 100 in FIG. A mirror 40, a field lens 41, and an imaging lens 42 are added. The function of each element is the same as that of the laser irradiation apparatus 100 shown in FIG.

Here, the irradiation region of the CO ₂ laser 43 includes an irradiation region of the Xe—Cl excimer laser 18 and is wider than the region. A CO ₂ laser 43 having a wavelength of 10.6 μm is used, and pulse oscillation is performed with a pulse width of several tens μs to several ms. This pulse width is sufficiently larger than the pulse width of the Xe-Cl excimer laser 18.
Irradiation of xe-Cl excimer laser 18 during irradiation of the CO ₂ laser 43, just before the irradiation of the CO ₂ laser 43, or CO ₂ be performed immediately after the irradiation of the laser 43 is desired.

The CO ₂ laser 43 is irradiated from above the substrate 11 similarly to the Xe-Cl excimer laser 18. In FIG. 17, the CO ₂ laser 43 is irradiated obliquely from above, but this is merely for the sake of convenience in drawing the drawing.
The CO ₂ laser 43 is absorbed by the antireflection film pattern 15 (see FIG. 11) and exhibits a heat retaining effect, while being reflected by the reflection film pattern 17 (see FIG. 11).
Therefore, as in Example 1, the crystallization from one edge of the antireflection film pattern 15 in contact with the reflection film pattern 17 starts earlier than the crystallization from the other edge of the antireflection film pattern 15, and the reflection Crystallization continues to the vicinity of the other edge of the antireflection film pattern 15 without colliding near the center of the antireflection film pattern 15.
As a result, in the lower region 13a (see FIG. 11) of the silicon oxide film pattern 15, the first crystallized region 19 in which the growth direction of crystal grains is substantially aligned in one direction and has no grain boundary in the growth direction is formed. .

In addition, due to the heat retention effect by the CO ₂ laser 43 selectively absorbed in the antireflection film pattern 15, the cooling rate of the amorphous silicon film in the lower region 13 a of the antireflection film pattern 15 is further reduced, and the first crystallization region 19 Further increase in the crystal grain size.
Accordingly, the characteristics of the TFT 50 (see FIGS. 14 to 16) having the first crystallized region 19 as the channel region 51 are further improved, and the lateral growth distance of the crystal is also increased, so that the width of the silicon oxide film pattern 15 is increased. The degree of freedom in designing the TFT element is further improved.

It is explanatory drawing explaining the principal point of the 1st manufacturing method of the semiconductor thin film by this invention. It is explanatory drawing explaining the principal point of the 2nd manufacturing method of the semiconductor thin film by this invention. It is explanatory drawing explaining the principal point of the 3rd manufacturing method of the semiconductor thin film by this invention. It is process drawing which shows the manufacturing method of the semiconductor thin film by Embodiment 1 of this invention. It is process drawing which shows the manufacturing method of the semiconductor thin film by Embodiment 2 of this invention. It is process drawing which shows the manufacturing method of the semiconductor thin film by Embodiment 3 of this invention. It is a figure which shows the manufacturing method of the polycrystalline-semiconductor thin film by Example 1 of this invention. It is process drawing which shows the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is process drawing which shows the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is process drawing which shows the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is process drawing which shows the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is process drawing which shows the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is process drawing which shows schematic structure of the laser irradiation apparatus used with the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is a top view of TFT produced using the polycrystalline semiconductor thin film manufactured with the manufacturing method of the polycrystalline semiconductor thin film by Example 1 of this invention. It is AA schematic sectional drawing of TFT shown by FIG. It is the B section enlarged view of TFT shown by FIG. It is process drawing which shows schematic structure of the laser irradiation apparatus used with the manufacturing method by Example 2 of this invention. It is explanatory drawing which shows the manufacturing method of the conventional polycrystalline semiconductor thin film. It is a top view of TFT produced using the polycrystalline semiconductor thin film manufactured with the conventional manufacturing method. It is a top view of TFT produced using the polycrystalline semiconductor thin film manufactured with the conventional manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 3,303 Semiconductor thin film 3a, 13a Lower region 3b, 13b of antireflection film pattern Lower region 3c, 3d, 13c, 13d of reflection film pattern Direct irradiation region 4 Antireflection film pattern 5 Reflection film pattern 6 First laser 7 , 8, 306, 307 Crystallized region 11 Glass substrate 12 Base film 13 Amorphous silicon film 14 Antireflection film 15 Antireflection film pattern 16 Reflective film 17 Reflective film pattern 18 Xe-Cl excimer laser 19 First crystallization region 20 Second crystallized region 21 Polycrystalline region 31 First laser oscillator 32, 39 Optical element group 33, 40 Mirror 34, 41 Field lens 35, 42 Imaging lens 37 Stage 38 Second laser oscillator 43 CO ₂ laser 100, 200 Laser Irradiation device 50, 308 TFT
51 Channel region 301 Insulating substrate 304 Insulating film pattern 305 Laser

Claims (13)

  At least a semiconductor thin film is formed on a substrate, an antireflection film pattern and a reflection film pattern are formed on a part of the semiconductor thin film so as to be adjacent to each other, and a first laser is irradiated from above the substrate to lower the antireflection film pattern A method for producing a semiconductor thin film comprising a step of forming semiconductor grains having uniform orientation.   At least a semiconductor thin film is formed on the substrate, an antireflection film pattern is formed on a part of the semiconductor thin film, a reflection film pattern is formed on a part of the antireflection film pattern, and the first laser is irradiated from above the substrate. A method for producing a polycrystalline semiconductor thin film, comprising a step of forming semiconductor grains having uniform orientation under the antireflection film pattern.   At least a semiconductor thin film is formed on the substrate, a reflection film pattern is formed on a part of the semiconductor thin film, an antireflection film pattern is formed so as to cover the reflection film pattern and a part of the semiconductor thin film, and the first from above the substrate. A method for producing a semiconductor thin film, comprising a step of irradiating a laser to form semiconductor grains having a uniform direction below an antireflection film pattern.   The step of forming the antireflection film pattern and the reflection film pattern is a process of forming the antireflection film pattern and the reflection film pattern such that a part of the edge of the antireflection film pattern is in contact with a part of the edge of the reflection film pattern. The method for producing a semiconductor thin film according to claim 1.   3. The semiconductor according to claim 2, wherein the step of forming the reflective film pattern is a step of forming the reflective film pattern so that a part of the edge of the reflective film pattern coincides with a part of the edge of the antireflection film pattern. Thin film manufacturing method.   The step of forming the antireflection film pattern is a step of forming the antireflection film pattern so that a part of the edge of the antireflection film pattern coincides with a part of the edge of the reflection film. A method for manufacturing a semiconductor thin film.   The method for producing a semiconductor thin film according to any one of claims 1 to 6, further comprising a step of irradiating a region including the irradiation region of the first laser with the second laser at an irradiance and an irradiation time that do not melt the semiconductor thin film. .   The method for producing a semiconductor thin film according to claim 7, wherein the irradiation time of the second laser is longer than the irradiation time of the first laser.   The method of manufacturing a semiconductor thin film according to claim 1, wherein the antireflection film pattern is formed of any one of a silicon oxide film and a silicon nitride film.   The method for producing a semiconductor thin film according to any one of claims 1 to 9, wherein the reflective film pattern comprises any one of an Al film, a Mo film, a W film, an Al-Mo alloy film, and an Al-W alloy film. .   9. The method of manufacturing a semiconductor thin film according to claim 7, wherein the second laser is an infrared laser, and the absorption rate of the antireflection film pattern with respect to the infrared laser is higher than the absorption rate of the reflection film pattern and the semiconductor thin film with respect to the infrared laser.   The semiconductor thin film manufactured by the manufacturing method of the semiconductor thin film as described in any one of Claims 1-11.   13. A thin film transistor using the semiconductor thin film according to claim 12, wherein the channel region includes crystal grains having a uniform direction formed under the antireflection film pattern.

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