JP2005175211A - Process and equipment for producing semiconductor film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To elongate the crystal growth distance by single irradiation with a laser beam, and to improve the characteristics of a semiconductor element while enhancing production efficiency and lowering production cost. <P>SOLUTION: The process for producing a semiconductor film utilizing a laser beam comprises a step for forming a semiconductor film on a substrate, a step for forming a thermal diffusion layer having thermal conductivity higher than that of the substrate on the semiconductor film, a patterning step for separating a region where the thermal diffusion layer is formed from a region where the thermal diffusion layer is not formed by removing a part of the thermal diffusion layer, a first laser irradiation step for irradiating the region where the thermal diffusion layer is formed with a first laser beam to fuse the semiconductor film, and a step for crystallizing the fused semiconductor. <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 laser irradiation.

  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 obstacle to reducing the cost of the display device. For this reason, 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 is inexpensive. It can be provided.

  The laser crystallization technique is to heat a glass substrate on which an amorphous silicon thin film has been formed to about 400 ° C., and scan the glass substrate to apply a linear laser beam having a length of about 200 to 400 mm and a width of about 0.2 to 1.0 mm to the glass substrate. The method of continuously irradiating the top is common. 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 light is not melted over the entire thickness direction, but is melted over the entire surface of the laser light irradiated region by melting while leaving a part of the amorphous region. Crystal nuclei are generated, and the crystal grows toward the outermost surface layer of the silicon thin film, forming crystal grains with random orientation.

  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). A technique called super lateral growth irradiates a silicon thin film with a pulsed laser beam of a slit beam, and melts the silicon thin film in the slit-shaped portion over the entire thickness direction of the laser light irradiation region. The growth of crystal grains is controlled in the lateral direction from the boundary of the melted portion, that is, in the direction horizontal to the glass substrate, and needle-like crystals are obtained. Super lateral growth is completed by irradiating the laser pulse once, but when overlapping with a part of the needle-like crystal formed by the previous laser light irradiation, and sequentially irradiating the laser pulse, By taking over the already 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, an antireflection film is formed on a part of the semiconductor film, and the laser beam is not irradiated in a slit shape, but only on an area where the antireflection film such as silicon dioxide is formed. There is a method of melting and crystallizing only the region where the antireflection film is formed (see Patent Document 2). In addition, as an example of a method for producing polycrystalline silicon, an amorphous silicon film is provided on a substrate and crystallized by a laser. A film having different thermal conductivity is laminated on a substrate, and a silicon film is formed thereon. There is a method of improving the characteristics of the film obtained by forming (see Patent Document 3 and Patent Document 4).
Special Table 2000-505241 JP-A-57-210624 JP 2000-68520 A Japanese Patent Laid-Open No. 6-296023

  However, the growth distance of crystal grains by super lateral growth is only 1 to 2 μm. In order to obtain large crystal grains, it is necessary to repeat laser light irradiation many times. In addition, since the crystal growth distance is about 1 μm, it is necessary to irradiate a beam to be irradiated again by overlapping the previous crystal by about 0.5 μm in order to succeed and grow the crystal. However, in order to always obtain a shift amount of 0.5 μm, in terms of feed accuracy, a feed mechanism with a resolution of about 0.1 μm, that is, an extremely high accuracy is required, and the cost of the apparatus increases. Further, since only a small amount of feed can be obtained at a time, there is a drawback that the processing speed is slow.

  On the other hand, the above-described method of forming an antireflection film and crystallizing only the region where the antireflection film is formed is different from the super lateral growth, and irradiation to each region is completed at one time, so the processing speed is high. However, the growth distance of one time is limited to about 1 μm. However, since the channel of a normal transistor is about 1 μm or more in channel length, for example, about several μm to several tens of μm, it is difficult to manufacture such a channel.

  In addition, the method of improving the crystal characteristics by forming a film with high thermal conductivity under the semiconductor film forms a film with high thermal conductivity under the semiconductor film, resulting in high thermal conductivity to the substrate. In addition, there is a drawback that heat is easily diffused and the energy of the laser beam necessary for melting the semiconductor film is increased.

  An object of the present invention is to extend a crystal growth distance by one-time laser light irradiation, improve characteristics of a semiconductor element, increase manufacturing efficiency, and reduce manufacturing cost.

  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 a substrate, and a thermal diffusion layer having a higher thermal conductivity than the substrate on the semiconductor film. A thermal diffusion layer forming step to be formed, a patterning step in which a part of the thermal diffusion layer is removed to divide into a region where the thermal diffusion layer is formed and a region where the thermal diffusion layer is not formed, and thermal diffusion A first laser beam irradiation step of melting the semiconductor film by irradiating the region where the layer is formed with a first laser beam; and a crystallization step of crystallizing the melted semiconductor. To do.

  The semiconductor film manufacturing apparatus of the present invention includes a semiconductor film forming unit that forms a semiconductor film on a substrate, a thermal diffusion layer forming unit that forms a thermal diffusion layer having a higher thermal conductivity than the substrate, and a thermal diffusion unit. By removing a part of the layer, patterning means for dividing the region in which the thermal diffusion layer is formed and the region in which the thermal diffusion layer is not formed, and the region in which the thermal diffusion layer is formed in the first region A manufacturing apparatus comprising a first laser light irradiation means for melting a semiconductor film by irradiating laser light, and a crystallization means for crystallizing the molten semiconductor, wherein the first laser light irradiation means: An opening of the photomask through which the first laser beam passes is imaged on the substrate surface by the objective lens.

  According to the present invention, the length of the crystal can be made longer than before, the characteristics of the device to be manufactured can be improved, the manufacturing efficiency can be increased, and a low-cost device can be manufactured.

(Semiconductor film manufacturing method)
The manufacturing method of the present invention is a method of manufacturing a semiconductor film using laser light, and includes a step of forming a semiconductor film on a substrate, a step of forming a thermal diffusion layer on the semiconductor film, and a thermal diffusion layer. A patterning step of removing the portion, a step of melting the semiconductor film by irradiating the first laser beam, and a step of crystallizing the molten semiconductor. The thermal diffusion layer formed on the semiconductor film has a higher thermal conductivity than the substrate, and the patterning process removes a part of the thermal diffusion layer, so that the region where the thermal diffusion layer is formed and the thermal diffusion layer This is done by dividing it into regions that are not formed. In the subsequent first laser light irradiation step, the semiconductor film in the irradiated region is melted by irradiating the region where the thermal diffusion layer is formed with the first laser light. By this manufacturing method, the length of the semiconductor crystal can be made longer than before, and the characteristics of the device to be manufactured can be improved. Moreover, manufacturing efficiency can be improved and manufacturing cost can be reduced.

  FIG. 1 shows a typical example of a semiconductor element obtained by the manufacturing method of the present invention. In this semiconductor element, a diffusion prevention layer 3 is formed on a glass substrate 4 as shown in FIG. The diffusion prevention layer 3 is formed to prevent diffusion of impurities from the glass substrate 4. Specifically, for example, a silicon dioxide film can be used as the diffusion preventing layer 3. However, the present invention is not limited to this, and a film made of another material can be used as long as the diffusion of impurities from the glass substrate 4 can be prevented. There may be. The silicon dioxide film can be formed by a method such as vapor deposition, sputter deposition, or CVD.

  A semiconductor film 2 is provided on the diffusion prevention layer 3. The semiconductor film 2 is usually formed using amorphous silicon by a CVD method, but a sputtering method, a vapor deposition method, or the like can also be used as a film forming method. The thickness of the semiconductor film 2 can be arbitrarily designed depending on the required transistor characteristics, process conditions, etc., but a thickness of several tens of nm to several hundreds of nm is preferable, for example, a film thickness of 30 nm to 100 nm. be able to.

  The semiconductor film 2 immediately after film formation is usually amorphous and not crystallized. In addition, 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 directly manufactured using the semiconductor film 2 immediately after film formation, the electron mobility of the transistor is lowered.

  In the present invention, the thermal diffusion layer 1 is further provided on the semiconductor film 2. The thermal diffusion layer 1 is higher than the glass substrate 4 or the diffusion prevention layer 3 in order to enhance the thermal conductivity in the direction perpendicular to the semiconductor film, uniform the temperature distribution in the direction perpendicular to the semiconductor film, and promote crystal growth. Thus, a material having a high thermal conductivity is used. From such a viewpoint, a material having a thermal conductivity of 10 W / mK or higher is preferable for the thermal diffusion layer, and a material having a thermal conductivity of 20 W / mK or higher is more preferable. Further, for the thermal diffusion layer 1, it is possible to increase the crystallization efficiency by using a material whose light absorptance with respect to the first laser light irradiated in the laser annealing treatment described later is smaller than the light absorptivity such as a semiconductor film material. In terms, it is preferable. Specifically, suitable materials for the thermal diffusion layer 1 are nitrides such as silicon nitride and aluminum nitride, and oxides such as aluminum oxide. The thermal diffusion layer can be formed by sputtering, vapor deposition, CVD, or the like.

  FIG. 3 shows a plan view of the thermal diffusion layer. As shown in FIG. 3, the thermal diffusion layer is patterned into regions 301a and 301b where the thermal diffusion layer is formed and other regions where the thermal diffusion layer is not formed. As a patterning method, desired patterning can be performed on the thermal diffusion layer by combining lithography using a photoresist and an etching method using wet etching or dry etching.

  The thickness of the thermal diffusion layer can be set to 5 nm to 200 nm, but the reflectance is the lowest depending on the wavelength of the laser beam used for laser beam irradiation described later. In other words, the semiconductor film has the largest light absorption. It is preferable to select a film thickness. Specifically, the thickness of the thermal diffusion layer is set to be near the condition where the phase difference between the reflected light from the surface of the thermal diffusion layer and the surface of the semiconductor film is approximately 1/2 wavelength and the reflected light is weakened. It is preferable to do this. As a result, the reflected light can be lowered, the absorption of light into the semiconductor film can be increased, and the energy of the laser light necessary for melting and crystallization of the semiconductor film can be reduced. Further, there is an advantage that the laser device used for melting can be downsized.

  Next, the substrate is annealed by the first laser beam. An example of an apparatus used for the laser annealing process is shown in FIG. This apparatus has a first laser light source 205, a reflection mirror 207, a photomask 208 having an opening, an objective lens 209, and a stage 211, and optical elements such as a homogenizer and an expander as necessary. Group 206 can be attached. On the stage 211, a glass substrate 210 on which thin films made of multiple layers as shown in FIG. 1 are stacked can be installed, and the glass substrate 210 can be driven. The apparatus used for the laser annealing process is not limited to the configuration shown in FIG. 2 as long as it can irradiate a predetermined position on the substrate with light having a predetermined irradiance in a predetermined pattern.

  As the laser light source, a laser light source that performs pulse irradiation, such as an excimer laser, can be used. In the case of an excimer laser, the wavelength is in the ultraviolet region, and it is very easily absorbed by the semiconductor film. The pulse width is 10 ns to several tens ns, and the semiconductor film is melted almost instantaneously. Thereafter, the semiconductor film is rapidly cooled, and the melted semiconductor is crystallized in the process.

  A solid-state laser can also be used 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 oscillation efficiency of the semiconductor laser is good and the oscillation wavelength of the semiconductor laser is matched with 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 an excimer laser or a flash lamp-pumped solid-state laser.

The solid-state laser can excite a laser beam having a wavelength around 1.06 μm by exciting an optical crystal such as Nd-YAG with the above-described excitation light source. However, as it is, the absorption coefficient for amorphous silicon to be melted by irradiation 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 wavelength of the first laser light by two or four times with a nonlinear optical crystal and convert it into visible light. By using visible light with a wavelength of 550 nm or less, absorption in the thermal diffusion layer can be reduced, while absorption in the semiconductor film can be increased, crystallization efficiency is increased, and manufacturing time is shortened. Manufacturing cost can be reduced. As these nonlinear optical crystals, KDP (KH ₂ PO ₄ ), LBO (lithium borate), BBO, CLBO (CsLiB ₆ O ₁₀ ) and the like can be used. Visible light around 532 nm is obtained by the second harmonic wavelength of these. If the wavelength is 550 nm or less, the absorption coefficient of amorphous silicon becomes large and can be melted by laser light irradiation.

  As shown in FIG. 2, the beam emitted from the first laser light source 205 is converted into an appropriate beam size by an expander included in the optical element group 206, and the beam is also converted by the homogenizer included in the optical element group 206. The irradiance in the cross section is made uniform, and the photomask 208 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 208. 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.

  FIG. 4 shows a plan view of the photomask. The photomask includes a light-blocking portion 412 and an opening 413 on the mask substrate, and the opening 413 has a function of allowing irradiation light to pass through. A material such as quartz or glass is used as the mask substrate. As the light shielding portion 412, a metal thin film such as chromium, nickel, or aluminum, or a reflection or absorption film made of a dielectric multilayer laminated film can be used. When the opening 413 formed on the photomask has a slit shape, a rectangle, or a shape conforming to it, the average output of the laser is 300 W, the oscillation repetition frequency is 300 Hz, and the opening is rectangular, the dimensions are, for example, If 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 from the same magnification to 1/10 times (that is, the size of the opening on the mask is reduced from the same magnification image to 1/10 times the size). However, it is not necessarily limited to this shape and size, and can be arbitrarily designed depending on the output of the laser used for annealing and the size of one pulse output.

  Further, here, as shown in FIG. 2, the opening of the photomask 208 is irradiated with light that has passed through a homogenizer, and an image of the opening illuminated by the irradiation is reflected on the glass substrate of the substrate 210 by the objective lens 209. A mode in which the image is set on the surface is preferable. That is, as a result of forming an image of the opening on the glass substrate, a part of the semiconductor film on the substrate is irradiated and the other part is not irradiated. At this time, the heat diffusion layer 210 is set so as to irradiate a region where a plurality of patterns are provided.

  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 increases with the width of the resolving power at the edge of the image of the opening. A transition region that changes to In this region, the semiconductor film is in a semi-molten state, and the characteristics of the transistor formed there are deteriorated. Therefore, a transistor cannot be formed in that portion, which becomes an invalid region. For this reason, it is necessary to reduce the ineffective area and increase the area in which the transistor can be formed as much as possible. For this purpose, it is important to reduce the transition area. At this time, if the image of the opening of the photomask is set to be imaged on the substrate surface by the objective lens, the width of the transition region can be kept to the above-mentioned resolution, so that the beam is directly irradiated onto the substrate. As compared with the above, the area of the ineffective region can be remarkably reduced, and by reducing the ineffective region, there is an advantage that the density of transistors integrated on the substrate can be increased. In addition, with such a setting, it is possible to use the same process as the conventional one, and it is possible to suppress the capital investment and reduce the manufacturing cost.

  For example, if the NA is 0.1 and the wavelength is 308 nm, the width of the ineffective region is approximately 3 μm. In general, a beam from a laser is a Gaussian beam, and when the substrate is irradiated as it is, an ineffective region equivalent to the beam diameter is generated. Therefore, an objective lens is used and a photomask through which the first laser beam passes is used. By adopting a mode in which the opening forms an image on the substrate surface, the ineffective area can be greatly minimized.

  A crystal obtained by the present invention is shown in FIG. When the image of the opening is formed on the substrate by the objective lens, as shown in FIG. 5, the portions 501a and 501b where the pattern of the thermal diffusion layer is formed are selectively melted, and then pulse irradiation is performed. When finished, the melted portion cools rapidly and crystallizes. At this time, crystals 514 grow in the width direction in the thermal diffusion layer patterns 501a and 501b on the substrate, and as shown in FIG. 5, columnar crystals grown in the lateral direction are obtained. Further, in the region 515 other than the image of the opening, lateral crystal growth does not occur.

  Here, the structure of the thin film to be processed is a conventional structure, that is, an impurity diffusion prevention layer is provided on a glass substrate, a semiconductor film is provided thereon, and then an antireflection film pattern such as silicon dioxide is provided. In this structure, when the crystal growth distance L is limited to about 1 to 1.5 μm and the width D of the antireflection film pattern is set to 5 μm, for example, the crystal grows from both sides of the pattern through the melting and crystallization process. However, the remaining 2 to 3 μm in the central portion becomes microcrystalline or amorphous, and the entire pattern cannot be crystallized.

  However, when the pattern of the impurity diffusion prevention layer 3, the semiconductor film 2, and the thermal diffusion layer 1 is provided on the glass substrate 4 as shown in FIG. However, it expands to 2 to 3 times than before. That is, the length of the crystal grown by one melting and crystallization becomes 2 to 4 μm or more. For this reason, even if the width D of the pattern of the thermal diffusion layer 1 is set to 2 to 3 times or more of the conventional, the center part will not become microcrystalline or amorphous, or the center part microcrystalline or amorphous width Becomes narrower than the conventional structure.

  Therefore, in the case of the present invention, when a transistor having a structure in which carriers flow in the direction of a crystal grown in one direction (in the width direction of the pattern), the carriers are less likely to be scattered at the grain boundaries and the mobility is high. An extremely high transistor can be obtained. In the present invention, the direction of crystal growth can be freely controlled by patterning the thermal diffusion layer. In other words, by changing the position and orientation of the pattern, it is possible to freely determine at which position and in which direction the crystal should be grown. Accordingly, the arrangement and orientation of the transistors can be freely determined, the degree of freedom in arrangement of the transistors is increased, and circuit design with a high arrangement density can be easily performed.

  As described in the above embodiment, the reason why the crystal growth distance is increased by using the antireflection film as the thermal diffusion layer is considered to be due to the following phenomenon. 6 and 7 show the temperature distribution of the thin film according to the prior art. FIG. 6 shows an amorphous silicon film in an initial state in which a thin film having a diffusion prevention layer 603, an amorphous silicon film 602, and an antireflection film 619 is irradiated on the glass substrate 604, and the amorphous silicon film 602 is melted. Shows the temperature distribution. In the center, there is a melting region 620 in which the amorphous silicon film 602 is melted, and there is a region 621 that does not melt around it. At this time, it is considered that the temperature in the vicinity of the boundary between the melting region 620 and the non-melting region 621, that is, the temperature of the region 625 that is currently crystallized is higher than the surroundings. This is because once the molten silicon crystallizes, it releases latent heat.

  FIG. 7 shows changes in temperature distribution in the process of cooling the amorphous silicon film. The temperature level 622 in FIG. 6 and the temperature level 722 in FIG. 7 are the freezing points of silicon. It is considered that silicon crystallizes when the temperature of the molten silicon falls below this temperature level. As shown in FIG. 7, after irradiating a thin film having a diffusion prevention layer 703, an amorphous silicon film 702, and an antireflection film 719 onto a glass substrate 704, the silicon film 702 cools and the temperature decreases. Accordingly, the crystal 723 grows in order from the outer edge toward the central portion, and crystallization proceeds. At the same time, the temperature of silicon also decreases in the central portion, and crystallizes in order from the outer edge toward the central portion. Earlier, the crystal grains 724 begin to crystallize below the temperature level 722 and in this part pass through the temperature level 722 uniformly, so that no lateral crystal growth occurs and the crystal grains 724 are uniform microcrystals or amorphous. Occurs. The growth of the crystal 723 is inhibited by the crystal grains 724 generated in the central portion. For this reason, in the conventional film structure, it is thought that a crystal does not grow to the center part.

  On the other hand, the temperature distribution in the case of the present invention is shown in FIGS. FIG. 8 shows an amorphous silicon film in an initial state in which a thin film having a diffusion prevention layer 803, an amorphous silicon film 802, and a thermal diffusion layer 801 is irradiated with laser light on a glass substrate 804 and the amorphous silicon film 802 is melted. It is a schematic diagram which shows temperature distribution. In the center, there is a melting region 830 in which the amorphous silicon film 802 is melted, and there is a region 831 that does not melt around it. In the case of the present invention, as shown in FIG. 8, the temperature of the boundary region 825 between the non-melting region 831 and the melting region 830 is not particularly high, and is a temperature that gradually decreases from the central portion toward the outer edge portion. It is considered to be a distribution. This is because the heat diffusion layer 801 provided on the surface makes it easy for heat to flow laterally through the heat diffusion layer 801, and the temperature below the heat diffusion layer 801 is made uniform. That is, by providing the thermal diffusion layer 801 on the surface, the thermal conduction in the lateral direction can be promoted, and the temperature distribution with protrusions accompanying the release of latent heat can be leveled. Therefore, as shown in FIG. 9, after irradiating a thin film having a diffusion prevention layer 903, an amorphous silicon film 902, and a thermal diffusion layer 901 on a glass substrate 904, the silicon film 902 is cooled, As the film descends, the crystal grows smoothly from the outer edge to the center without causing a phenomenon that crystallization occurs in the center as well as the outer edge.

  As described above, the surface thermal diffusion layer can be made of a nitride such as aluminum nitride or silicon nitride. This is because many nitrides have a high thermal conductivity and heat resistance, and are generally transparent at the wavelength of light used for melting. For the same reason, many materials such as aluminum oxide that have high thermal conductivity and heat resistance, and that are generally transparent at the wavelength of light used for melting, can be used as the material for the thermal diffusion layer. It is. The thermal conductivity of aluminum nitride, silicon nitride, and aluminum oxide is 5 to 10 times the thermal conductivity of the glass substrate, and the crystal growth distance can be increased by using aluminum nitride, silicon nitride, and aluminum oxide as the thermal diffusion layer. It is confirmed in the following examples that the length becomes longer. From this, it is considered preferable to set the thermal conductivity of the thermal diffusion layer on the surface to 5 times or more of the thermal conductivity of the glass substrate because the effect of promoting crystal growth is enhanced.

  Depending on the combination of the material of the thermal diffusion layer and the laser light source, the thermal diffusion layer may absorb the first laser beam to a degree that cannot be ignored in the operation of the present invention. For example, the thermal diffusion layer may absorb ultraviolet rays emitted from an excimer laser, which is a laser light source, to some extent. In this case, there is a possibility that ultraviolet rays are absorbed by the thermal diffusion layer on the surface and sufficient heat is not given to the semiconductor film below the ultraviolet ray. Further, when a large amount of light is absorbed by the thermal diffusion layer and becomes heat, the temperature of the thermal diffusion layer rises, and in a severe case, the thermal diffusion layer may be damaged. Accordingly, it is preferable that the light absorption rate of the thermal diffusion layer with respect to the first laser light is at least smaller than the light absorption rate of the semiconductor film therebelow with respect to the first laser light.

  For this purpose, a mode in which the wavelength of the first laser light to be irradiated is changed, such as using visible light instead of the first laser light, increases the crystallization efficiency, increases the manufacturing efficiency, and increases the manufacturing cost. It is preferable in reducing the amount. If laser light that emits light having a high light transmittance with respect to the heat diffusion layer and a high absorption rate with respect to the semiconductor film is used, most of the light passes through the heat diffusion film and is absorbed by the semiconductor film to become heat. The semiconductor film can be sufficiently heated. For example, when amorphous silicon or silicon is used as the semiconductor film, light having a wavelength shorter than 550 nm is desirable. 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, and an oscillation wavelength of 532 nm can be obtained by using a second harmonic of a solid-state laser such as Nd-YAG. Is preferable. In particular, when a solid-state laser is used, the processing apparatus can be reduced in size and weight, and no gas is required for maintenance of the apparatus, and the apparatus cost and maintenance cost are low. It is possible.

  In the present invention, in addition to the first laser beam, the second laser beam may be irradiated. A typical example of irradiating the second laser beam together with the first laser beam is shown in FIG. This apparatus includes a first laser light source 1005, a reflecting mirror 1007, a photomask 1008 having an opening, an objective lens 1009, and a stage 1011 on which a glass substrate 1010 is mounted for driving. Further, an optical element group 1006 such as a homogenizer or an expander can be provided as necessary. As the second laser light source 1012, a carbon dioxide laser, a solid-state laser, or a gas laser can be used, and a similar effect can be obtained. Most preferably, a carbon dioxide laser is used.

  As shown in FIG. 10, it is preferable that the second laser light is irradiated on the substrate obliquely from the side of the first laser light. When a carbon dioxide laser is used as the second laser, the oscillation wavelength is between 9 μm and 11 μm, and ordinary optical glass, quartz glass, etc. are opaque in this wavelength range. Therefore, an optical system made of these materials cannot be used. In the case of a carbon dioxide laser, a ZnSe or Ge crystal or polycrystal is used to make an optical system with little absorption.

  When an excimer laser is used for the first laser, the optical system is mainly quartz, and since this optical system has a large absorption with respect to the carbon dioxide gas laser, it cannot be used. The substrate cannot be irradiated. 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 second laser light can be irradiated onto the substrate without passing through the optical system using quartz. It is convenient to construct an optical system with low absorption.

  The oscillation wavelength of the carbon dioxide laser is between 9 μm and 11 μm, but the semiconductor film hardly absorbs light in this wavelength region. For example, a silicon or amorphous silicon film has almost no absorption in this wavelength region, and it is difficult to efficiently cause melting of silicon only by irradiation with a carbon dioxide laser beam. However, silicon dioxide or glass containing silicon dioxide absorbs light of this wavelength well and can cause an increase in temperature upon irradiation. Therefore, by irradiating in synchronization with the first laser, the substrate can be heated after the semiconductor film is melted by the first laser light, while being melted, or before being melted. As a result, the semiconductor film on the substrate 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 can heat the semiconductor film formed thereon by heat conduction from the substrate.

  When the semiconductor film is melted and solidified by irradiation with the second laser light, an effect of slowing the solidification rate and promoting crystal growth can be obtained. That is, when an excimer laser is used as the first laser, the pulse width (irradiation time) is at most 10 ns to several tens ns, and the semiconductor film melts in a very short time and solidifies in a short time. In this case, the solidification time is several tens ns to several hundreds ns at the longest. As a result of solidification occurring in a short time, crystal growth does not continue for a long time, and the growth distance is about 1 μm to 2 μm.

However, a carbon dioxide gas laser is used in combination as the second laser, and at least a region including the irradiation region of the first laser beam is irradiated with the second laser beam, so that an SiO ₂ film or a glass substrate directly below the semiconductor film is mainly formed. By heating, crystal growth can be greatly promoted as compared with the case where only excimer laser is irradiated, and the degree of freedom for forming a large device can be increased. However, in this case, the crystal does not simply become large, but the crystal growth distance in the lateral direction is promoted by the combined use of the carbon dioxide laser. In the case of the present invention, it has been confirmed that the crystal growth distance can be promoted several times to 10 times as compared with the conventional case. In this way, by using the second laser together, it is possible to crystallize a large region at a time, and the crystallization region can be widened to greatly improve the degree of freedom of element arrangement.

  In this case, the region heated by the carbon dioxide laser is at most 1 μm to several tens of μm deep in the substrate direction, and the entire substrate is not heated. Therefore, the entire substrate is crystallized at a low temperature. It is not necessary to heat the entire substrate, and the apparatus can be simplified. In addition, since the entire substrate does not expand, it is advantageous in that expansion and contraction and expansion of the glass substrate can be prevented.

  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 pulse width can be freely changed to optimize the conditions. Is difficult. However, since the pulse width of the carbon dioxide laser can be freely changed, for example, from 1 μs to several tens of milliseconds as described above, it is melted by being heated for a relatively long time after being melted by the first laser. It is possible to solidify slowly by maintaining the state or lengthening the cooling time and selecting the optimum condition. In addition, since the CO2 laser has high oscillation efficiency, the cost per watt of output is low, and a high-power laser can be easily obtained, which helps to reduce the cost of the device. Is more advantageous. As described above, the carbon dioxide laser has various advantages, and since the oscillation wavelength is 9 to 11 μm, it is preferable to use the second laser beam having 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 pulsed manner 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 it is possible to avoid heating the substrate surface for a long time by irradiating in a pulsed manner, and to keep the average temperature of the substrate surface at a lower temperature, in order to cope with the cooling mechanism and thermal expansion of the substrate. This eliminates the need for the correction device and helps reduce the cost of the device. This is because, when the carbon dioxide laser is irradiated in a pulsed manner, the temperature of the substrate surface is kept high while the laser light is 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 value is lower than that of continuous irradiation.

  Further, even when irradiating in a pulsed manner, the amount of heat (energy amount) input as a result can be reduced by reducing the pulse width and increasing the pulse irradiance (instantaneous value). This is because the more heat is instantaneously applied, the smaller the amount of heat that escapes due to thermal diffusion, and the smaller the amount of heat input (= pulse width × pulse instantaneous value).

  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. It is preferable that the irradiation with the carbon dioxide gas laser is started in advance, the irradiation with the excimer laser is finished, and the semiconductor film is solidified. In this case, it is preferable that the time DL1 before the pulse (CLP) of the carbon dioxide gas laser is preceded by the pulse (ELP) of the excimer laser is set in the range of 1 μs to 50 ms.

  As described above, the shorter the pulse width, the smaller the amount of heat input. However, the instantaneous value of the laser must be increased, and the laser becomes larger, so the pulse width is set to an appropriate value. It is preferable to set. The pulse width W2 of the excimer laser is in the range of approximately 10 ns to 100 ns as described above, and the time for the completion of melting and solidification varies depending on the conditions. A range of 200 ns is preferred.

  As another irradiation method, as shown in FIG. 11B, 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 ms to 5 ms. This is because if DL2 becomes too large, the substrate cools down and the effect of irradiation diminishes. However, in any of these cases, the irradiation of the second laser light is started in advance of the first laser light in that the temperature of the substrate and the semiconductor film can be raised in advance. Is preferred.

  According to the present invention, when a thermal diffusion layer is provided on the surface and crystallization is performed by light irradiation, the thermal diffusion layer can be removed after crystallization, and the next step can be performed. Although the thermal diffusion layer may be left as it is, the removal of the thermal diffusion layer facilitates the subsequent process of forming a gate portion, forming an electrode wiring, doping, and other semiconductors. After the surface thermal diffusion layer is removed, the semiconductor film, the impurity diffusion preventing layer, and the glass substrate are formed, so that the conventional film structure is the same and there is an advantage that the conventional processing steps can be used as they are. .

  Moreover, since the conventional silicon dioxide can be used for the impurity diffusion preventing layer, this can also be performed by a conventional process. In particular, the diffusion preventing layer 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, there is no need to review the process, which is very convenient. It becomes. That is, in one form of the device manufacturing method of the present invention, a step of providing a thermal diffusion layer is inserted between the step of providing a semiconductor thin film and the step of laser annealing in the conventional device manufacturing method, and the step of laser annealing and after This is a mode in which a step of removing the thermal diffusion layer is inserted between the steps, and this mode has the advantage that there are few places to be changed from the conventional method and that the transition from the conventional method is easy.

(Semiconductor film manufacturing equipment)
The semiconductor film manufacturing apparatus of the present invention removes a part of the thermal diffusion layer, means for forming a semiconductor film on the substrate, means for forming a thermal diffusion layer having a higher thermal conductivity than the substrate, and the semiconductor film. By irradiating the first laser beam to the region where the thermal diffusion layer is formed and the patterning means for dividing the region where the thermal diffusion layer is not formed and the region where the thermal diffusion layer is formed A manufacturing apparatus comprising a first laser light irradiation means for melting a semiconductor film and a crystallization means for crystallizing the molten semiconductor, wherein the first laser light passes through the first laser light irradiation means. The opening of the photomask is imaged on the substrate surface by the objective lens. The apparatus of the present invention can increase the length of the crystal and improve the characteristics of the resulting device, shorten the manufacturing time, and reduce the manufacturing cost compared to the conventional apparatus. it can.

Example 1
In this embodiment, as shown in FIG. 1, a silicon dioxide film 3 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, a thermal diffusion layer 1 was further provided on the semiconductor film 2. The thermal diffusion layer 1 was formed using aluminum nitride as a material, and was formed to a thickness of 30 nm by vapor deposition. The thermal diffusion layer is a combination of lithography using a photoresist and a wet etching method, as shown in FIG. 3, regions 301a and 301b where the thermal diffusion layer is formed, and other regions where the thermal diffusion layer is not formed. Patterned into areas.

  Next, laser annealing treatment was performed on the substrate. The apparatus used for the laser annealing treatment is shown in FIG. This apparatus includes a first laser light source 205, a reflection mirror 207, a photomask 208 having an opening, an objective lens 209, a stage 211, and an optical element group 206 such as a homogenizer and an expander. . On the stage 211, a substrate 210 on which thin films composed of multiple layers as shown in FIG. As a laser light source, an excimer laser having a wavelength of 308 nm (using XeCl), a pulse width of 30 ns, and an average output of 300 W was used. Further, the opening of the photomask 208 is irradiated with light that has passed through a homogenizer so that an image of the opening is formed on the surface of the glass substrate of the substrate 210 by the objective lens 209, and a plurality of heat diffusion layers are formed. The laser beam was set so as to irradiate the area where the pattern-provided area was accommodated.

  The portions 501a and 501b in which the pattern of the thermal diffusion layer is formed in the semiconductor film in FIG. 5 are selectively melted by the laser light irradiation, and when the pulse irradiation is completed, the melted portions are rapidly cooled and crystallized. Turned into. As shown in FIG. 5, in the crystal obtained in this example, a crystal 514 grew in the width direction of the thermal diffusion layer patterns 501a and 501b, and a columnar crystal was obtained. The length of the crystal grown by one melting and crystallization was about 4 μm, and no microcrystal or amorphous silicon was observed in the center. Further, the region 515 remained without crystal growth.

Comparative Example 1
A semiconductor film was produced in the same manner as in Example 1 except that a silicon dioxide film having the same thickness was formed instead of the thermal diffusion layer made of aluminum nitride in Example 1, and was irradiated with laser light. The growth distance L of the obtained crystal was only about 1 μm, and amorphous silicon was observed in the central portion of 2 to 3 μm.

  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 the length of the crystal can be increased, a transistor with high mobility can be manufactured. Moreover, manufacturing efficiency can be improved and manufacturing cost can be reduced.

It is sectional drawing of the semiconductor element which concerns on the manufacturing method of this invention. It is a schematic diagram which shows the apparatus used by the laser annealing process in the manufacturing method of this invention. It is a top view of the thermal diffusion layer in the present invention. It is a top view of the photomask used in the manufacturing method of this invention. It is a top view of the crystal obtained by the manufacturing method of the present invention. It is a conceptual diagram which shows the temperature distribution of the semiconductor film manufactured by the conventional method. It is a conceptual diagram which shows the temperature distribution of the semiconductor film manufactured by the conventional method. It is a conceptual diagram which shows the temperature distribution of the semiconductor film manufactured by the method of this invention. It is a conceptual diagram which shows the temperature distribution of the semiconductor film manufactured by the method of this invention. It is a schematic diagram which shows the apparatus used by the laser annealing process in the manufacturing method of this invention. 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.

Explanation of symbols

  1 thermal diffusion layer, 2 semiconductor film, 3 diffusion prevention layer, 4 glass substrate.

Claims (11)

A method of manufacturing a semiconductor film using laser light,
A semiconductor film forming step of forming a semiconductor film on the substrate;
A thermal diffusion layer forming step of forming on the semiconductor film a thermal diffusion layer having a higher thermal conductivity than the substrate;
A patterning step of separating a region where the heat diffusion layer is formed and a region where the heat diffusion layer is not formed by removing a part of the heat diffusion layer;
A first laser light irradiation step of melting the semiconductor film by irradiating the region where the thermal diffusion layer is formed with the first laser light;
A method for producing a semiconductor film, comprising: a crystallization step of crystallizing a molten semiconductor.   2. The method of manufacturing a semiconductor film according to claim 1, wherein in the first laser light irradiation step, an opening of a photomask through which the first laser light passes is imaged on the substrate surface by an objective lens.   2. The method of manufacturing a semiconductor film according to claim 1, wherein the light absorption rate of the heat diffusion layer with respect to the first laser beam is smaller than the light absorption rate of the semiconductor film with respect to the first laser beam.   The method of manufacturing a semiconductor film according to claim 1, wherein the first laser light is visible light having a wavelength of 550 nm or less.   2. The method of manufacturing a semiconductor film according to claim 1, wherein a region including at least a region irradiated with the first laser beam is irradiated with the second laser beam. 3.   6. The method of manufacturing a semiconductor film according to claim 5, wherein the second laser beam has a wavelength of 9 to 11 [mu] m.   6. The semiconductor film manufacturing method according to claim 5, wherein the second laser light is irradiated in a pulsed manner, and irradiation of the second laser light is started at least prior to the irradiation of the first laser light. Method. A semiconductor film forming means for forming a semiconductor film on the substrate;
A thermal diffusion layer forming means for forming a thermal diffusion layer having higher thermal conductivity on the semiconductor film than the substrate;
Patterning means for removing a part of the thermal diffusion layer into a region where the thermal diffusion layer is formed and a region where the thermal diffusion layer is not formed;
A first laser beam irradiation means for melting the semiconductor film by irradiating the region where the thermal diffusion layer is formed with the first laser beam;
A manufacturing apparatus comprising a crystallization means for crystallizing a molten semiconductor,
An apparatus for manufacturing a semiconductor film, characterized in that, in the first laser light irradiation means, an opening of a photomask through which the first laser light passes is imaged on a substrate surface by an objective lens.   9. The semiconductor film manufacturing apparatus according to claim 8, wherein the light absorption rate of the thermal diffusion layer with respect to the first laser beam is smaller than the light absorption rate of the semiconductor film with respect to the first laser beam.   The semiconductor film manufacturing apparatus according to claim 8, wherein the first laser light is visible light having a wavelength of 550 nm or less.   9. The semiconductor film manufacturing apparatus according to claim 8, wherein the second laser beam is irradiated to a region including at least the first laser beam irradiation region.

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