JP2005158942A - Method and device for manufacturing semiconductor film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing semiconductor film by which a semiconductor film having no step on its surface and formed in a flat film as a whole can be manufactured and, in addition, a high-quality element having no roughness in its surface and does not contain any impurity, such as oxygen etc., can be formed. <P>SOLUTION: The method of manufacturing the semiconductor film utilizes laser light and includes a semiconductor film forming step of forming the semiconductor film on a substrate, a first optical film forming step of forming a first optical film on the semiconductor film, and a patterning step of dividing the surface of the semiconductor film into an area where the first optical film is formed and another area where the first optical film is not formed by removing part of the first optical film. The method also includes a second optical film forming step of forming a second optical film in the area where the first optical film is formed and the area where the first optical film is not formed, a first laser beam projecting step of melting the semiconductor film by projecting a first laser beam upon the film through the second optical film and a crystallizing step of crystallizing the melted semiconductor. The laser beam reflectivity of the area where the first optical film is formed is set so that it may become equal to that of the area where no first optical film is formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor film manufacturing method and a manufacturing apparatus for crystallizing a semiconductor film on a substrate by irradiating it with laser light.

  A thin film transistor used in a display device using liquid crystal or electroluminescence (EL) uses amorphous or polycrystalline silicon as an active layer. Among them, a polycrystalline silicon thin film transistor has many advantages over an amorphous silicon thin film transistor because of its high electron mobility. For example, not only a switching element can be formed in the pixel portion, but also a driver circuit and a part of the peripheral circuits can be formed on a single substrate in the peripheral portion of the pixel. For this reason, it is not necessary to separately mount a driver IC or a drive circuit board on the display device, so that the display device can be provided at a low price. Further, as another advantage, since the size of the transistor can be miniaturized, a switching element formed in the pixel portion can be reduced and a high aperture ratio can be achieved. Therefore, it is possible to provide a display device with high brightness and high definition.

  As a method for producing a polycrystalline silicon thin film, an amorphous silicon thin film is formed on a glass substrate by a CVD method or the like, and then a separate step for polycrystallizing amorphous silicon is required. Usually, when the annealing step for crystallization is performed by a high-temperature annealing method at 600 ° C. or higher, it is necessary to use an expensive substrate that can withstand high temperatures, which is an impediment to cost reduction of display devices. In recent years, a technique for crystallizing amorphous silicon at a low temperature of 600 ° C. or lower using a laser has been generalized, and a display device in which a polycrystalline silicon transistor is formed on a low-cost glass substrate can be provided at a low price. It has become.

  The laser crystallization technique is a linear laser beam having a length of about 200 to 400 mm and a width of about 0.2 to 1.0 mm while heating a glass substrate on which an amorphous silicon thin film is formed to about 400 ° C. and scanning the glass substrate. Is generally a method of continuously irradiating a 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 throughout the entire thickness direction, but melts while leaving a part of the amorphous region, so that the entire surface of the laser irradiated region is crystallized. Nuclei are generated, crystals grow toward the outermost layer of the silicon thin film, and randomly oriented crystal grains are formed.

  In order to obtain a display device with higher performance, it is necessary to increase the crystal grain size of polycrystalline silicon and to control the crystal orientation. A lot of research and development has been done. Among them, there is a technique called super lateral growth (see Patent Document 1). The super lateral growth method irradiates a silicon thin film with a slit-shaped pulse laser, melts the silicon thin film in the slit-irradiated region over the entire thickness direction of the laser irradiation region, and forms a boundary between the molten portion and the unmelted portion. The crystal growth is controlled in the horizontal direction, that is, in the direction horizontal to the glass substrate, to obtain needle-like crystals. Super lateral growth is completed by irradiating the laser pulse once. However, if the laser pulse is sequentially irradiated with a part of the needle crystal formed by the previous laser irradiation, By taking over the grown crystal, a longer needle-like crystal grows, and a large crystal having a uniform orientation in the crystal growth direction is obtained.

Apart from this, as shown in FIG. 10, after forming the diffusion prevention layer and the semiconductor film 102 on the substrate, the antireflection film 109 is formed on a part of the semiconductor film 102 (FIG. 10A). The laser beam L is not irradiated in a slit shape, but the entire substrate (FIG. 10B), and only the semiconductor film 102a in the region where the antireflection film made of silicon dioxide or the like is formed is melted (FIG. 10). 10 (c)), there is a method of crystallizing only the region where the antireflection film is formed (FIG. 10 (d)). Thereafter, the antireflection film can be removed (see FIG. 10E) (see Patent Document 2).
Special Table 2000-505241 JP 57-210624 A

  However, the growth distance of crystal grains according to the super lateral method described in Patent Document 1 is only 1 to 2 μm, and it is necessary to repeat laser irradiation many times in order to obtain large crystal grains. In particular, since the crystal growth distance is about 1 μm, it is necessary to irradiate the irradiation beam with the previous crystal overlapping again in order to succeed the growth of the crystal, resulting in a shift of about 0.5 μm. Will be. However, in order to always obtain a shift amount of 0.5 μm, in terms of feed accuracy, a resolution of about 0.1 μm, that is, a feed mechanism with extremely high accuracy is required, and the apparatus cost increases. Moreover, since only a small amount can be given at a time, there is a disadvantage that the processing speed is slow.

  On the other hand, unlike the method described in Patent Document 1, the method described in Patent Document 2 is fast in processing speed because irradiation to each region is completed once. However, in particular, as shown in FIG. 10, a step 102c is generated between the portion 102a where the antireflection film 109 is present and the portion 102b where the antireflection film 109 is not present, and a thin film is formed during element formation or wiring pattern formation. There is a drawback that a defect tends to occur in the portion 102a. Further, even in the portion 102b without the antireflection film, depending on the laser irradiation conditions, melting occurs to some extent even if it does not lead to complete melting, and this causes roughness on the surface, which adversely affects the overall device formation. There is a case.

The manufacturing method of the present invention is a method of manufacturing a semiconductor film using laser light,
A semiconductor film forming step of forming a semiconductor film on the substrate;
A first optical film forming step of forming a first optical film on the semiconductor film;
A patterning step of separating a region where the first optical film is formed and a region where the first optical film is not formed by removing a part of the first optical film;
A second optical film forming step of forming a second optical film in a region where the first optical film is formed and a region where the first optical film is not formed;
A first laser light irradiation step of irradiating the semiconductor film with the first laser light through the second optical film and melting the semiconductor film;
A crystallization step of crystallizing a molten semiconductor,
The reflectance of the laser light in the region where the first optical film is formed is set to be equal to the reflectance of the laser light in the region where the first optical film is not formed.

Another embodiment of the manufacturing method of the present invention is a method of manufacturing a semiconductor film using laser light,
A semiconductor film forming step of forming a semiconductor film on the substrate;
An optical film forming step of forming an optical film on the semiconductor film;
A patterning step of separating a thin region of the optical film and a thick region of the optical film by removing a part of the optical film;
A first laser light irradiation step of irradiating the semiconductor film with the first laser light through the optical film and melting the semiconductor film;
A crystallization step of crystallizing a molten semiconductor,
The reflectance of the laser beam in the region where the optical film is thin is set to be equal to the reflectance of the laser beam in the region where the optical film is thick.

  A semiconductor film manufacturing apparatus according to the present invention is a manufacturing apparatus for performing the above-described method, wherein the wavelength of the second laser light is 9 μm to 11 μm. Another embodiment of the semiconductor film manufacturing apparatus of the present invention is a manufacturing apparatus for performing the above-described method, in which the second laser beam is irradiated in a pulsed manner and prior to the first laser beam irradiation. The second laser beam irradiation is started.

  According to the present invention, there is no step on the surface of the semiconductor film, and a flat semiconductor film can be manufactured as a whole. In addition, since the surface is not rough and impurities such as oxygen are not mixed, a high-quality element can be formed.

(Semiconductor film manufacturing method)
The method for producing a semiconductor film of the present invention includes a step of forming a semiconductor film on a substrate, a step of forming a first optical film on the semiconductor film, and a patterning step of removing a part of the first optical film. , A step of forming the second optical film, a step of irradiating the semiconductor film with the first laser beam and melting it, and a step of crystallizing the molten semiconductor. With this manufacturing method, there is no step in the semiconductor film at the edge of the first optical film, and a flat semiconductor film can be formed as a whole, and a high-quality device can be easily obtained. . Further, since the melting is performed by the laser light in a state where the whole is covered with the optical film, the surface can be prevented from being rough. Furthermore, since the entire film is melted and covered with an optical film and crystal growth is possible, the semiconductor film may be oxidized in contact with oxygen or other impurity elements may be mixed during melting. Therefore, it is possible to form a high-quality element.

  In the manufacturing method of the present invention, the reflectance of the region where the first optical film and the second optical film overlap is set to be equal to the reflectance of the other region. With this aspect, the region where the second optical film overlaps the first optical film and the other regions have the same amount of laser light absorbed by the semiconductor film, and are uniformly heated, melted and crystallized. Therefore, uniform crystal growth is possible. Here, the reflectance of the region in which the second optical film overlaps the first optical film and the reflectance of the other region are substantially equal in addition to the case where the reflectances of both are completely coincident with each other. Is also included. In addition, substantially equal means that there is a technical effect that almost the same crystal growth is obtained in the region where the second optical film overlaps the first optical film and the other region. Any embodiment in which the reflectivity is preferably different within 15%, more preferably within 10%, and particularly preferably within 5% is included in the present invention.

  FIG. 1 shows a first embodiment of the manufacturing method of the present invention. As shown in FIG. 1A, first, the diffusion prevention layer 3 is formed on the glass substrate 4. The diffusion prevention layer 3 is formed to prevent diffusion of impurities from the glass substrate 4. Specifically, a silicon dioxide film is used as the diffusion prevention layer 3, but the present invention is not limited to this, and a film made of another material may be used as long as the diffusion of impurities from the glass substrate 4 can be prevented. . The silicon dioxide film can be formed by a method such as vapor deposition, sputtering, or CVD.

  Next, as shown in FIG. 1A, the semiconductor film 2 is formed on the diffusion prevention layer 3. The semiconductor film 2 is usually formed by CVD using amorphous silicon as a material, but it is also possible to use sputtering or vapor deposition as the film forming method. The thickness of the semiconductor film 2 varies depending on the required transistor characteristics, process conditions, and the like, but can be several tens of nanometers to several hundreds of nanometers, and usually 30 to 100 nm.

  The semiconductor film 2 immediately after film formation is normally amorphous and is not crystallized. According to a certain film forming method, it is possible to obtain a very small collection of crystals (microcrystals), but in any case, it is difficult to obtain such a large crystal grain. Therefore, when a transistor is formed directly on the semiconductor film 2 immediately after film formation, the electron mobility of the transistor is lowered.

  Subsequently, in the present embodiment, the first optical film 1 is formed on the semiconductor film 2 as shown in FIG. In this specification, an optical film refers to a film that can change the reflectance, transmittance, absorptivity, polarization characteristics, and the like of light on the surface by forming the film. Suitable materials for the optical film 1 are nitrides such as silicon nitride and aluminum nitride, and oxides such as silicon oxide, silicon dioxide, and aluminum oxide. As a film formation method, a CVD method, a sputtering method, an evaporation method, or the like can be used.

  Next, a patterning process is performed. In the patterning step, by removing a part of the first optical film, as shown in FIG. 1B, regions 1a and 1b in which the first optical film 1 is formed, and the first optical film And patterning into areas where no is formed. The patterning can be performed by photolithography and etching. For example, the first optical film is patterned into a desired shape by combining lithography using a photoresist and an etching method using wet etching or dry etching. be able to.

  Subsequently, as shown in FIG. 1C, a second optical film 5 is formed. In the step of forming the second optical film, the second optical film 5 is formed in the region 6 where the first optical film is formed and the region 7 where the first optical film is not formed. Suitable materials for the second optical film 5 include nitrides such as silicon nitride and aluminum nitride, and oxides such as silicon oxide, silicon dioxide, and aluminum oxide. As a film forming method, a CVD method, a sputtering method, an evaporation method, or the like can be used. Here, since the second optical film is formed on the entire substrate, only the region 6 where the first optical film 1 and the second optical film 5 overlap and the second optical film are formed on the substrate. Region 7 is generated.

  Here, the thickness of each of the first optical film and the second optical film can be set to 5 nm to several hundreds nm. As a result, the reflectance of the laser beam is changed depending on the region. That is, in the present invention, the semiconductor film 2 is melted and crystallized by irradiating the laser beam. At this time, the absorption rate of the laser beam into the semiconductor film 2 is changed to change the semiconductor film on the substrate. 2 is set so that melted and non-melted portions are created and crystal growth is performed. The reflectance and absorptance of the semiconductor film 2 vary depending on the wavelength of the laser used for laser irradiation, the optical constants (refractive indices) of the first and second optical films, the optical constants of the semiconductor film 2 itself, and the like. The absorptance can be known by performing a known optical calculation or by measuring the fabricated product by a known technique.

  FIG. 8 shows an example of the reflectance of the laser beam when the first optical film made of silicon dioxide is formed on the semiconductor film made of amorphous silicon. As described above, the reflectivity varies depending on the wavelength of the laser used for laser irradiation, the optical constant (refractive index) of the optical film, and the optical constant of the semiconductor film itself, but the relationship between the film thickness of the optical film and the reflectivity. This is schematically shown in FIG. In the example of FIG. 8, the change is repeated so that the reflectance becomes maximum or minimum when the film thickness of the optical film is D1, D2, D3, D4, or the like.

  Here, the combination of the film thicknesses in the present embodiment is as follows. In FIG. 1C, the reflectance of the region 6 where the second optical film 5 overlaps the first optical film 1 and the other regions 7 are compared. A mode in which both the reflectances are small is preferable. According to such an embodiment, both the region 6 where the second optical film 5 overlaps the first optical film 1 and the other region 7 increase the amount of laser light absorbed by the semiconductor film 2 and are heated to a high temperature. Melting and crystallization can be performed.

  Further, as a specific method for setting both the reflectance of the region 6 where the second optical film 5 overlaps the first optical film 1 and the reflectance of the other region 7 to be small. The phase difference between the reflected light from the surface of the second optical film 5 and the reflected light from the surface of the semiconductor film 2 in the region 6 where the second optical film 5 overlaps the first optical film 1 is approximately. If the wavelength is set to 1/2 and the reflected light is weakened, the reflectance can be lowered and the absorption of light into the semiconductor film can be increased. At the same time, in this case, the reflected light from the surface of the second optical film 5 and the reflected light from the surface of the semiconductor film 2 also in the region 7 where only the second optical film 5 is laminated on the semiconductor film 2. By setting the phase difference to approximately ½ wavelength and setting it in the vicinity of the condition where the reflected light weakens, the reflectance can be lowered, the absorption of light into the semiconductor film 2 can be increased, and the semiconductor film It becomes possible to heat to high temperature. Here, as an example for reducing the reflectance, the case where the phase difference is approximately ½ wavelength has been selected and described. However, in the present invention, the reflected light is weakened by providing the reflected light with a phase difference. Therefore, the effect of increasing the absorption of light into the semiconductor film and enabling the semiconductor film to be heated to a high temperature is expected. In addition to the case of using two wavelengths, the present invention also includes a mode in which reflected light is weakened by (1/2 + 1) wavelength or (1/2 + 2) wavelength.

  In order to realize such a condition, as shown in FIG. 8, as the film thickness of the second optical film, for example, D1 is selected, and the film thickness of the first optical film laminated thereunder is as follows: What is necessary is just to select the film thickness of D3-D1. That is, as the second optical film, a film thickness (for example, D1) that minimizes the reflectance is selected, and as the first optical film, the film thicknesses of the first optical film and the second optical film are selected. The film thickness of the first optical film may be set to D3-D1 so that the sum of the film thickness becomes a film thickness (for example, D3) at which the reflectance is minimal.

  By setting in this way, in FIG. 1C, the reflectance in the region 6 where the second optical film 5 overlaps the first optical film 1 is lowered, and the absorption of light into the semiconductor film is increased. At the same time, also in the region 7 where only the second optical film 5 is stacked on the semiconductor film 2, the reflectance can be lowered and the absorption of light into the semiconductor film can be increased. As described above, in the present embodiment, desired optical characteristics can be obtained only by patterning the first optical film and optimally managing the thickness of the laminated optical film as described above. There is.

  Next, as shown in FIG. 1 (d), the substrate is irradiated with laser, and then the molten semiconductor is crystallized to produce a crystalline semiconductor film as shown in FIG. 1 (e). Can do. In the laser light irradiation step, as shown in FIG. 1D, the semiconductor film 2 is irradiated with the first laser light L through the second optical film 5 to melt the semiconductor film 2. The melting includes both the case where the entire semiconductor film on the substrate is melted and the case where only a partial region of the semiconductor film on the substrate is melted. An example of an apparatus used for laser irradiation is shown in FIG. The apparatus includes a first laser light source 308, a reflection mirror 309, a photomask 310 having an opening, an objective lens 311, and a stage 313 that is driven by mounting a glass substrate 312. As shown in FIG. 3, an optical element group 314 such as a homogenizer and an expander can be provided as necessary.

  In the laser processing, the beam emitted from the first laser light source 308 is converted into an appropriate beam size by an expander included in the optical element group 314, and the beam cross section is also converted by the homogenizer included in the optical element group 314. The irradiance is made uniform, and the photomask 310 is irradiated. Here, the beam expander is an optical system having a telephoto system or a reduction system, and determines the size of an irradiation region on the photomask 310. The homogenizer is composed of a lens array or a cylindrical lens array as an example of its configuration, and divides the beam and recombines it to make the irradiance uniform within the irradiation area on the mask. .

  Here, the aperture of the photomask 310 is irradiated with light that has passed through a homogenizer, and an image of the aperture illuminated by this irradiation is formed on the surface of the substrate 312 by the objective lens 311. That is, as a result of forming an image of the opening on the substrate 312, a part of the semiconductor film on the substrate is irradiated, and the other part is not irradiated. At this time, a setting is made so that the laser beam is irradiated to a region in which the region where the plurality of patterns 1a and 1b of the first optical film 1 in FIG.

  As the laser light source 308, a laser light source that performs pulse irradiation, such as an excimer laser, is used. In the case of an excimer laser, the oscillation wavelength is in the ultraviolet region, and it is very easily absorbed by the semiconductor film. Further, the pulse width is 10 to several tens of ns, and the film melts almost instantaneously, but then rapidly cooled and crystallizes in the process.

  As described above, an image of the opening of the photomask 310 is formed on the substrate 312 by the objective lens 311 and irradiated with laser light having a substantially uniform irradiance. FIG. 4 shows the distribution of light (energy) absorbed by the semiconductor film by the first laser at this time. FIG. 4C is a cross-sectional view of a substrate on which an optical film is laminated according to the present invention, and FIG. 4B is a plan view of the substrate. FIG. 4A shows the distribution of laser light absorbed by the semiconductor film in each region. FIG. 5 is a plan view of a semiconductor film obtained by irradiating the semiconductor film shown in FIG. In the present invention, the region 406 where the first and second optical films are stacked and the region 407 where only the second optical film is stacked in FIG. 4 are set to the same reflectance, The same amount of absorption occurs for the irradiated laser light, and the semiconductor film is similarly melted.

  However, in this case, in the vicinity of the boundary 416 between the region 406 and the region 407, the reflectance increases, the amount of laser light absorption locally decreases, and a phenomenon occurs in which only the temperature near the boundary 416 decreases. The reason is that the regions 406 and 407 have almost the same reflectivity as shown in FIG. However, in the vicinity of the boundary 416, as can be seen in FIG. 8, the film thickness continuously changes from D3 to D1, and during this time, the film thickness D2 having a high reflectance always passes. Therefore, in the vicinity where the light passes, the reflectance is always high, the amount of light absorption is reduced, and the temperature is lowered.

  FIG. 6 shows an example of a photomask. The photomask illustrated in FIG. 6 includes a light shielding portion 618 and an opening 619. When the image of the opening of the photomask is formed on the substrate by the objective lens, the region where the optical film pattern is formed melts, and when the pulse irradiation ends, the melted portion cools rapidly. Crystallize. At this time, since the temperature first decreases in the vicinity of the boundary 416 in FIG. 4, crystal growth starts from there. That is, on the substrate, starting from a boundary 416 between the region 406 and the region 407, a crystal grows in the width direction of the pattern and in the opposite direction to obtain a columnar crystal grown in the lateral direction. This phenomenon is schematically shown in FIG. The horizontal arrow in FIG. 1 (e) indicates the direction of crystal growth. Further, as shown in FIG. 5, the obtained semiconductor film has crystals 506 and 507 grown in one direction.

  In the present invention, by patterning the first optical film, the first optical film is formed, the reflectance of the laser beam in the region overlapping the second optical film, and the first optical film Since it is not formed, the reflectance of the laser beam in the region where only the second optical film is formed is set to be substantially equal. Preferably, the conditions are set such that the reflected light in each region weakens and the reflectance is set low. According to such an embodiment, as described above, a transistor having a structure in which a crystallization position and a crystallization direction (pattern width direction) can be specified, and carriers flow in the crystal growth direction in accordance with the specific position and direction. By configuring this, a high-performance transistor with extremely high mobility can be obtained with less carrier scattering at the grain boundaries. In addition, a crystal can be formed on the entire irradiation region by one laser irradiation, and high-efficiency crystallization can be performed.

  According to the present invention, unlike the conventional manufacturing method of forming an antireflection film as shown in FIG. 10, there is no phenomenon that a step is generated in the semiconductor film at the edge of the optical film, and the entire semiconductor is flat. A film can be formed, and it becomes easy to obtain high quality characteristics when a device is constructed. Further, since the melting is performed by the laser light in a state where the whole is covered with the optical film, the surface can be prevented from being rough. Furthermore, since the entire film is melted and covered with an optical film and crystal growth is possible, the semiconductor film may be oxidized in contact with oxygen or other impurity elements may be mixed during melting. Therefore, it is possible to form a high-quality element.

  In the present invention, the direction of crystal growth can be freely controlled by patterning such an optical film. That is, by changing the position and direction in which a plurality of patterns of the optical film are arranged, it is possible to freely determine at which position and in which direction the crystal is to be grown. Therefore, the arrangement and direction of the transistors can be freely designed, the degree of freedom of arrangement of the transistors is high, and the circuit design with a high arrangement density can be easily performed.

  Further, according to the present invention, as shown in FIG. 4, the temperature at the boundary 416 between the region 406 and the region 407 first decreases, and as a result, the molten semiconductor starts to crystallize from the boundary 416 and grows laterally. . For this reason, as shown in FIG. 5, in both the region 506 where the first optical film and the second optical film are laminated and the region 507 where only the second optical film is disposed, Crystals grown in the lateral direction grow by the laser irradiation. That is, crystallization of the entire surface of the substrate is completed by a single laser irradiation. Therefore, crystallization can be performed in an extremely fast time, and the crystal production cost can be reduced.

  In the case of the present invention, as shown in FIG. 3, it is preferable to have a second laser light source 315 in addition to the first laser light source 308. The second laser light source 315 is configured to irradiate the substrate 312 obliquely from the side of the beam of the first laser light source 308, and the irradiation region of the second laser is at least the irradiation of the first laser light. The aspect which makes it the range containing an area | region is preferable. By including at least part of the irradiation region of the first laser beam on the irradiation region of the second laser beam on the substrate, the crystal growth distance can be increased by connecting the crystals. As the second laser, a carbon dioxide laser, a solid state laser, a gas laser, or the like can be used, and a similar effect can be obtained. Most preferably, a gas laser is used.

  When a carbon dioxide laser is used as the second laser, the oscillation wavelength is between 9 and 11 μm, and ordinary optical glass, quartz glass, and the like are opaque in this wavelength region. Therefore, an optical system made of these materials cannot be used. In the case of a carbon dioxide gas laser, a ZnSe, Ge crystal or polycrystal is used to make an optical system with low absorption. However, when an excimer laser is used for the first laser, the optical system is mainly quartz. Since this optical system has a large absorption with respect to a carbon dioxide laser, it cannot pass through this optical system, and the substrate cannot be irradiated through the same optical system. That is, like many other types of optical systems, the two optical systems cannot coexist on the same axis. However, if the substrate is irradiated obliquely, the optical system can be configured separately and the substrate can be irradiated without passing through the optical system using quartz. It is convenient to configure.

  The oscillation wavelength of the carbon dioxide laser is between 9 and 11 μm, but the semiconductor film hardly absorbs light in this wavelength region. For example, a silicon or amorphous silicon film hardly absorbs in this wavelength region, and it is difficult to efficiently cause melting of silicon due to only irradiation with a carbon dioxide laser. However, silicon dioxide or glass containing silicon dioxide absorbs light of this wavelength well and can cause an increase in temperature upon irradiation. For this reason, by irradiating in synchronization with the first laser, the substrate can be heated after the semiconductor film is melted or melted by the first laser light, and as a result, the semiconductor on the substrate is heated. The film can be heated, and crystal growth can be promoted. That is, the carbon dioxide laser cannot directly heat the semiconductor film itself, but can heat the substrate immediately below it, and heat the semiconductor film formed thereon by heat conduction from the substrate. it can.

  In this case, the region heated by the carbon dioxide laser is at most up to a depth of 1 to several tens of μm in the substrate direction, and the entire substrate is not heated, so that the entire substrate can be crystallized at a low temperature. This is advantageous for simplification of the apparatus, expansion and contraction of the glass substrate, and prevention of expansion. Further, the carbon dioxide laser can be continuously oscillated and pulsed, the pulse width and intensity can be freely changed, and the degree of freedom of irradiation is high. When an excimer laser is used as the first laser, the excimer laser is pulse oscillation, the pulse width is determined by the laser, and is 10 ns to 100 ns. The conditions can be optimized by freely changing the pulse width. Have difficulty. However, since the pulse width of the carbon dioxide gas laser can be freely changed, for example, from 1 μs to several tens of milliseconds as described above, after being melted by the first laser, it is heated for a relatively long time to change the melted state. The time required for holding or cooling can be increased, and optimum conditions can be selected to allow solidification slowly. In addition, since the carbon dioxide laser has high oscillation efficiency, the cost per watt of output is low, which is more advantageous than melting and crystallization using only an excimer laser. Thus, the carbon dioxide laser has various advantages, and the oscillation wavelength is 9 to 11 μm. Therefore, the second laser beam preferably has a wavelength of 9 to 11 μm.

  When the carbon dioxide laser and the excimer laser are used in combination, the excimer laser can be irradiated in a pulse shape while continuously irradiating the carbon dioxide laser. However, it is more preferable to irradiate the excimer laser in synchronization with the carbon dioxide laser while irradiating it in a pulsed manner. This is because, by using pulse irradiation, it is possible to avoid heating the substrate surface for a long time and to keep the average temperature of the substrate surface at a lower temperature, thereby suppressing the thermal expansion of the substrate and making the process stable. be able to. That is, when the carbon dioxide laser is irradiated in pulses, the temperature of the substrate surface is kept high while the irradiation pulse is being emitted, but when the pulse irradiation of the carbon dioxide laser is completed, the substrate is quickly cooled and averaged over time. This is because the temperature is lower than that of continuous irradiation.

  When an excimer laser is used as the first laser and a carbon dioxide laser is used as the second laser, the irradiation timing of these two pulses is the excimer laser irradiation pulse (ELP) as shown in FIG. There is a method of irradiating a carbon dioxide gas laser until the carbon dioxide laser irradiation is started, the excimer laser irradiation is finished, and the solidification of the semiconductor film is finished. In this case, the time DL1 before the pulse of the carbon dioxide laser (CLP) precedes the pulse of the excimer laser (ELP) can be set in the range of 1 μs to 50 ms. Further, the pulse width W2 of the excimer laser is in the range of approximately 10 ns to 100 ns as described above. As a result, the time for the completion of melting and solidification varies depending on the conditions. The range is 200 ns.

  As another irradiation method, as shown in FIG. 9B, there is a method of irradiating an excimer laser after a certain time (DL2) after the pulse irradiation of the carbon dioxide laser is completed. In this case, DL2 is preferably set to about 0 to 5 ms. This is because if DL2 becomes too large, the substrate is cooled and the effect of irradiation is reduced. However, in any of these cases, the irradiation of the second laser beam is started prior to the irradiation of the first laser beam because the temperature of the substrate and the semiconductor film can be raised in advance. Embodiments are preferred.

  Here, when the carbon dioxide laser and the excimer laser are used in combination, crystal growth can be remarkably promoted, and large crystal grains can be obtained. That is, according to the experiment, the crystal growth several times or more is confirmed as compared with the case of irradiating only the excimer laser, and it is possible to obtain a large crystal growth that has not been conventionally achieved. FIG. 7 shows a plan view of a semiconductor film after crystal growth according to the present invention. FIG. 7A shows the state of the semiconductor film when only excimer laser light is irradiated, and FIG. 7B shows the state of the semiconductor film when the excimer laser and the carbon dioxide laser are used in combination. As shown in FIG. 7, when an excimer laser and a carbon dioxide laser are used in combination, a crystal several times larger can be grown and a large region can be crystallized at one time. The degree of freedom of arrangement can be greatly improved.

  In the case of the present invention, it is also possible to use a solid-state laser as the laser light source. Solid-state lasers excite laser crystals by irradiating optical crystals such as Nd-YAG with flash lamps or semiconductor lasers, and do not require the halogen gas required for excimer lasers. There is. In addition, when using a semiconductor laser as an excitation light source instead of using a flash lamp, the semiconductor laser has good oscillation efficiency and the oscillation wavelength of the semiconductor laser must match the absorption band of the optical crystal of the solid-state laser. Thus, highly efficient laser oscillation is possible. For this reason, the power consumption and the size of the apparatus can be greatly reduced as compared with the excimer laser or the flash lamp-pumped solid-state laser.

The solid-state laser can excite laser light having a wavelength around 1.06 μm by exciting an optical crystal such as Nd-YAG with the above-described excitation light source. However, in this state, the absorption coefficient for amorphous silicon to be irradiated and melted is small, and light is not easily absorbed by amorphous silicon, so that melting does not easily occur. For this reason, it is desirable to multiply the light of this wavelength by visible light by multiplying the wavelength by a nonlinear optical crystal. As the nonlinear optical crystal, KDP (KH ₂ PO ₄ ), LBO (lithium borate), BBO, CLBO (CsLiB ₆ O ₁₀ ), or the like can be used. Visible light in the vicinity of approximately 532 nm is obtained by these second harmonic wavelengths. If the wavelength is less than this vicinity, amorphous silicon has a large absorption coefficient and can be melted by laser light irradiation.

  Further, depending on the combination of the material of the optical film formed on the semiconductor film and the laser light source, the optical film may absorb the laser light to a degree that cannot be ignored in the operation of the present invention. For example, it may absorb to some extent ultraviolet rays emitted from an excimer laser that is a laser light source. In this case, ultraviolet light is absorbed by the optical film on the surface, and heat may not be sufficiently applied to the semiconductor film underneath. Further, when a large amount of light is absorbed and heated by the optical film, the temperature of the optical film rises, and in a severe case, damage may occur. Therefore, the light absorption rate of the optical film needs to be at least smaller than the absorption rate of the underlying semiconductor film.

  For this reason, a good result can be obtained by changing the wavelength of light to be irradiated, such as using visible light instead of ultraviolet rays. If a laser light source that emits light with a wavelength that has a high transmittance with respect to the optical film and a high absorption rate with respect to the semiconductor film is used, most of the light passes through the thermal diffusion film and is absorbed by the semiconductor film to become heat. Sufficient heat can be applied. For example, when amorphous silicon or silicon is used as the semiconductor film, the wavelength of light is preferably shorter than 550 nm. This is because silicon does not sufficiently absorb light having a wavelength longer than 550 nm. As a light source that emits light having a wavelength shorter than 550 nm, it is preferable to use visible light from a solid-state laser as described above. If a second harmonic of a solid-state laser such as Nd-YAG is used, an oscillation wavelength of 532 nm can be obtained. Therefore, it is convenient.

  As shown in FIG. 6, the photomask used in the present invention has a light shielding portion 618 and an opening 619 on the mask substrate, and the light shielding portion 618 has a function of shielding the irradiated light. As a substrate for the photomask, a material such as quartz or glass is used, and the light-shielding portion 618 is formed by using a metal thin film such as chromium, nickel, or aluminum, or a reflection or absorption film formed by a dielectric multilayer film on the substrate. be able to. The opening 619 formed on the photomask has a slit shape, a rectangular shape, or a shape conforming thereto, and when the average output of the laser is 300 W and the oscillation repetition frequency is 300 Hz, When the width is about 5 mm and the length is about 15 mm (on the substrate), the semiconductor film can be generally melted and crystallized. At this time, the optical magnification at the time of image formation is set to the same magnification to 1/10 (that is, the light transmitted through the opening 619 is set to the same magnification to 1/10 the size of the opening 619). However, it is not necessarily limited to this shape and size, and can be designed arbitrarily according to the laser output used for annealing and the size of the single pulse output. It is.

  At this time, since the resolving power of the objective lens is generally expressed by λ / NA (λ is the wavelength, NA is the numerical aperture of the objective lens), the light intensity gradually changes in the edge portion of the image of the opening 619. A transition region occurs. In this region, the semiconductor film is in a semi-molten state, and the characteristics of the transistor formed there are deteriorated. Therefore, this portion becomes an ineffective region where a transistor cannot be formed. Therefore, it is important to reduce the transition region in order to reduce the ineffective region and increase the region where the transistor can be formed as much as possible. At this time, if a method of forming an image of the opening 619 is used, the width of the transition region can be kept to the above-described resolution, so that the ineffective region can be reduced as compared with the case where the beam is directly irradiated onto the substrate. This has the advantage that the density of transistors integrated on the substrate can be increased.

  For example, if the numerical aperture NA of the objective lens is 0.1 and the wavelength of the excimer laser to be used is 308 nm, the ineffective area is approximately 3 μm. In general, the beam from the laser is a Gaussian beam, and if the beam is irradiated onto the substrate as it is, an invalid area comparable to the beam diameter is generated. If the beam diameter is, for example, 5 mm, the invalid area is at least Although about 10% of the diameter is generated, this ineffective region can be greatly minimized by using an objective lens.

  In FIG. 1, when the optical films 1 and 5 are formed on the surface of the semiconductor film 2 and crystallization is performed by laser light irradiation according to the present invention, the optical films 1 and 5 are removed after the crystallization, and then You may perform the process of. Further, although the optical film may be left as it is, the removal of the optical films 1 and 5 facilitates the subsequent process of forming a gate portion, forming a semiconductor such as an electrode wiring, and doping. In this case, after the optical films 1 and 5 on the surface are removed, the semiconductor film 2, the diffusion prevention layer 3, and the glass substrate 4 are configured, so that the conventional film structure is the same as that of the conventional film structure. There is an advantage that you can.

  In addition, since the conventional silicon dioxide can be used for the diffusion preventing layer 3, this can be conveniently performed by a conventional process. In particular, the diffusion preventing layer 3 is a film having an important function of preventing diffusion of impurities from the substrate, and if a conventionally used material can be used as it is, it is not necessary to review the process, which is very convenient. It becomes. That is, one form of the device manufacturing method of the present invention includes a step of providing an optical film between the step of providing a semiconductor thin film and the step of annealing by laser in the conventional device manufacturing method, and the step of annealing by laser A step of removing the optical film may be inserted between the subsequent steps, and there are few portions to be changed from the conventional method, and it can be said that the transition from the conventional method is easy.

  Next, FIG. 2 shows a second embodiment of the manufacturing method of the present invention. In this embodiment, first, as illustrated in FIG. 2A, a diffusion prevention layer 203 and a semiconductor film 202 are provided over a glass substrate 204. As a material for the semiconductor film 202, amorphous silicon is usually used and formed by a CVD method, but a sputtering method or a vapor deposition method can also be used as a film forming method. The thickness of the semiconductor film 202 varies depending on the required transistor characteristics, process conditions, and the like, but can be several tens to several hundreds of nanometers, usually 30 to 100 nm. An optical film 201 is formed on 202. Suitable materials for the optical film 201 include nitrides such as silicon nitride and aluminum nitride, and oxides such as silicon oxide, silicon dioxide, and aluminum oxide. The steps up to here are the same as those in the first embodiment, and can be performed using equivalent materials and methods.

  Subsequently, as shown in FIG. 2B, a part of the optical film 201 is removed, thereby patterning into a thin area 201a of the optical film and a thick area 201b of the optical film. . As a patterning method, lithography using a photoresist and an etching method using wet etching or dry etching can be combined. However, in the patterning, unlike the first embodiment, in the second embodiment, the optical film 201 is not completely removed, but the etching is terminated halfway so that a part remains. The planar shape at this time is such that the optical film remains thick and the film thickness of other regions is the same as the pattern of the first optical film (1a, 1b in FIG. 1) in the first embodiment. Pattern to make it thinner. That is, the optical film 201 is left thick only in the region where 1a and 1b in FIG. 1 are stacked, and the other regions are removed so as to be thin.

  Here, the film thickness of the optical film 201 after the etching is set so that the reflectivity of the region 201b where the optical film 201 is thick is equal to that of the thin region 201a. Further, it is preferable to set the reflectance of the region 201b and the reflectance of the region 201a to be low. In order to realize such conditions, as shown in FIG. 8, as the film thickness of the optical film to be formed, for example, the vicinity of D3 may be selected, and the etching amount for etching the optical film may be D3-D1. . That is, for the thin region 201a (etched region) of the optical film, the film thickness (that is, in the vicinity of D1) at which the reflectance is minimized is selected, and the thick region 201b (that is, not etched) is left as it is. The film thickness of the region is selected to be a film thickness that minimizes the reflectance (that is, in the vicinity of D3).

  Next, as shown in FIG. 2C, after the semiconductor film is irradiated with the first laser light L through the optical film to melt the semiconductor film, as shown in FIG. Crystallization occurs. The horizontal arrow shown in FIG. 2D indicates the crystal growth direction. In the second embodiment, both the semiconductor film below the thick region 201b of the optical film 201 and the semiconductor film below the thin region 201a reach a high temperature, and the semiconductor film melts and crystallizes in the lateral direction. The reason why such a phenomenon occurs is the same as in the first embodiment. As shown in FIG. 4, the thick region and the thin region of the optical film have the same or substantially the same reflectance. Therefore, the same amount of light is absorbed with respect to the irradiated laser light, and the semiconductor film is similarly melted. However, in the vicinity of the boundary between the thick region and the thin region, the reflectance is high, the amount of laser light absorbed locally decreases, and only the temperature near the boundary decreases. This is because the film thickness continuously changes from D3 to D1, and always passes through the highly reflective film thickness D2, and in the vicinity of the film thickness D2, the reflectivity always increases, and the amount of light absorption is increased. This is because the temperature decreases.

  In addition, the aspect in which the reflectance of the laser beam in the region where the optical film is thin and the reflectance of the laser beam in the region where the optical film is thick can be reduced can heat the semiconductor film to a high temperature. Is preferable. As described above, the crystallization process is the same as that of the first embodiment, and the subsequent steps are the same as those of the first embodiment. A crystal having a shape as shown in FIG. 5 can be obtained. It is possible to obtain the same effect as that of the first embodiment. On the other hand, in the case of the second embodiment, since the number of optical film formation can be reduced from two times to one as compared with the first embodiment, the manufacturing process can be simplified and the cost can be reduced. This is advantageous.

(Semiconductor film manufacturing equipment)
A semiconductor film manufacturing apparatus according to the present invention is a manufacturing apparatus for performing the above-described method, wherein the wavelength of the second laser light is 9 μm to 11 μm. According to such a manufacturing apparatus, it is possible to provide a high-quality semiconductor film that is flat as a whole, has no rough surface, and is not mixed with impurities such as oxygen. In addition, as a laser that oscillates a laser beam having a wavelength of 9 to 11 μm, there is a carbon dioxide gas laser, which can easily oscillate a high-power laser beam, thereby providing a low-cost manufacturing apparatus. Further, the second laser beam is irradiated in a pulse form in that the temperature rise of the substrate can be minimized, and the irradiation of the second laser beam is started prior to the irradiation of the first laser beam. Manufacturing equipment is preferred. Such a manufacturing apparatus is advantageous in that it can be a low-cost apparatus because it is not necessary to provide a substrate cooling mechanism and a thermal expansion correction device.

Example 1
In this example, as shown in FIG. 1A, a silicon dioxide film having a thickness of 150 nm was formed on the glass substrate 4 as a diffusion preventing layer 3 by vapor deposition. Next, the semiconductor film 2 was formed on the diffusion preventing layer 3. As the semiconductor film 2, amorphous silicon was used as a material, and a thickness of 50 nm was formed by a CVD method. Thereafter, the first optical film 1 was further provided on the semiconductor film 2. The first optical film 1 was formed using aluminum nitride as a material and having a thickness of 80 nm by vapor deposition. Next, the first optical film 1 is combined with lithography using a photoresist and a wet etching method, as shown in FIG. 1B, regions 1a and 1b where the first optical film is formed, Then, after patterning into other regions where the first optical film is not formed, a second optical film 5 is formed on the entire substrate as shown in FIG. The second optical film was made of aluminum nitride as a material and formed to a thickness of 30 nm by vapor deposition. As a result, an area 6 where the first optical film and the second optical film overlap each other and an area 7 where only the second optical film is formed are formed on the substrate.

  Next, laser annealing treatment was performed on the substrate. An apparatus used for the laser annealing treatment is shown in FIG. The apparatus includes a first laser light source 308, a reflection mirror 309, a photomask 310 having an opening, an objective lens 311, and a stage 313 that is driven by mounting a glass substrate 312. In addition, an optical element group 314 such as a homogenizer or an expander is provided so that light that has passed through the homogenizer is irradiated to the opening of the photomask 310, and an image of the opening is formed on the surface of the substrate 312 by the objective lens 311. Adjusted. In addition, the second laser light source 315 was provided in addition to the first laser light source 308 so as to irradiate the region where the first optical film pattern was provided with the laser beam. The beam from the second laser light source 315 is configured to irradiate the substrate 312 obliquely from the side of the beam from the first laser light source 308. The irradiation region of the second laser light on the substrate is the first region. It adjusted so that a part of irradiation area of 1 laser beam might be included. Then, the glass substrate 312 on which the thin film shown in FIG. 1 was laminated was placed on the stage 313 in FIG.

  As the laser light source, an excimer laser having a wavelength of 308 nm (using XeCl), a pulse width of 50 ns, and an average output of 300 W was used as the first laser. As the second laser, a carbon dioxide gas laser having a wavelength of 10.6 μm, a pulse width of 1 ms, and a peak output of 5 kW was used. The timing of the laser pulse irradiation is that the irradiation of the carbon dioxide gas laser as the second laser is started from 1 ms before the pulse irradiation of the excimer laser as the first laser, and the irradiation of the excimer laser is terminated. After 200 ns had elapsed, carbon dioxide laser irradiation was stopped.

  In FIG. 4, the reflectance of the first laser light in the region 406 where the first optical film and the second optical film are stacked is 30%, and in the region 407 where only the second optical film is stacked. The reflectivity of the first laser beam was 31%. Therefore, the reflectance in the region 406 and the reflectance in the region 407 are substantially equal, and both the reflectances are small. The semiconductor film in the region 406 and the region 407 was selectively melted by the laser light irradiation, and when the pulse irradiation was completed, the melted portion was crystallized. The obtained crystal grew from the boundary 416 between the region 406 and the region 407 in the width direction of the pattern and in the opposite direction, and was a columnar crystal. The state of the formed crystal is shown in FIG. The length of the crystal grown by one melting and crystallization was about 5 μm, and it was a semiconductor film with a flat surface as a whole, and there was no roughness on the surface.

Comparative Example 1
Instead of the first optical film made of aluminum nitride in the first embodiment, a silicon dioxide film having a thickness of 150 nm is formed and patterned in the same manner to form a region where no silicon dioxide film is formed and a silicon dioxide film. Patterned in the area. Further, the second optical film was not formed. As the laser light source, only the excimer laser which is the first laser in Example 1 was used. Except for these points, a semiconductor film was produced in the same manner as in Example 1 and irradiated with laser light. The length of the obtained crystal was about 1 μm. Further, in the semiconductor film, there was a step between a region with and without a silicon dioxide film, and innumerable roughness was observed on the surface.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, since a semiconductor film in which crystals are grown in one direction is obtained, by using a transistor having a structure in which carriers flow in the crystal growth direction, carriers are not scattered at grain boundaries. A transistor with high mobility can be provided. Further, since the position and direction of the crystal can be freely controlled, the arrangement and direction of the transistor can be freely determined.

It is process drawing which shows the manufacturing method of this invention. It is process drawing which shows the manufacturing method of this invention. It is a block diagram of the apparatus used in the laser annealing process of this invention. It is a schematic diagram which shows distribution of the light absorbed by the semiconductor film of this invention. It is a top view which shows the crystal structure of the semiconductor film obtained by this invention. It is a top view of the photomask used for this invention. It is a top view of the semiconductor film after the crystal growth by this invention. It is a schematic diagram which shows the relationship between the film thickness of the optical film in the semiconductor film manufactured by this invention, and a reflectance. It is a schematic diagram which shows the relationship between the pulse signal of the excimer laser in this invention, and the pulse signal of a carbon dioxide gas laser. It is process drawing which shows the conventional manufacturing method which forms an antireflection film.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st optical film, 2 Semiconductor film, 3 Diffusion prevention layer, 4 Glass substrate, 5 2nd optical film.

Claims (9)

A method of manufacturing a semiconductor film using laser light,
A semiconductor film forming step of forming a semiconductor film on the substrate;
A first optical film forming step of forming a first optical film on the semiconductor film;
A patterning step of separating a region where the first optical film is formed and a region where the first optical film is not formed by removing a part of the first optical film;
A second optical film forming step of forming a second optical film in the region where the first optical film is formed and in the region where the first optical film is not formed;
A first laser light irradiation step of irradiating the semiconductor film with the first laser light through the second optical film and melting the semiconductor film;
A crystallization step of crystallizing a molten semiconductor,
The reflectance of the laser beam in the region where the first optical film is formed is set to be equal to the reflectance of the laser beam in the region where the first optical film is not formed. A method for manufacturing a semiconductor film.   The reflectance of the laser beam in the region where the first optical film is formed and the reflectance of the laser beam in the region where the first optical film is not formed are set to be small. The method of manufacturing a semiconductor film according to claim 1. A method of manufacturing a semiconductor film using laser light,
A semiconductor film forming step of forming a semiconductor film on the substrate;
An optical film forming step of forming an optical film on the semiconductor film;
A patterning step of separating a thin region of the optical film and a thick region of the optical film by removing a part of the optical film;
A first laser light irradiation step of irradiating the semiconductor film with the first laser light through the optical film and melting the semiconductor film;
A crystallization step of crystallizing a molten semiconductor,
A method of manufacturing a semiconductor film, wherein the reflectance of the laser beam in the region where the optical film is thin is set to be equal to the reflectance of the laser beam in the region where the optical film is thick.   4. The laser beam reflectance in the region where the optical film is thin and the laser beam reflectance in the region where the optical film is thick are set to be small. Manufacturing method of the semiconductor film.   5. The method of manufacturing a semiconductor film according to claim 1, wherein a region including at least a part of a region irradiated with the first laser beam is irradiated with the second laser beam.   The method of manufacturing a semiconductor film according to claim 5, wherein the wavelength of the second laser light is 9 μm to 11 μm.   6. The method of manufacturing a semiconductor film according to claim 5, wherein the second laser light is irradiated in a pulse shape, and irradiation of the second laser light is started prior to the irradiation of the first laser light.   6. A manufacturing apparatus for carrying out the method according to claim 5, wherein the wavelength of the second laser beam is 9 [mu] m to 11 [mu] m.   6. The manufacturing apparatus for performing the method according to claim 5, wherein the second laser beam is irradiated in a pulsed manner, and irradiation of the second laser beam is started prior to the irradiation of the first laser beam. An apparatus for manufacturing a semiconductor film.

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