JP2005228808A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device, wherein a crystal semiconductor film formed on a semiconductor substrate is superior in crystallinity and the surface of the crystal semiconductor film has superior planarity. <P>SOLUTION: The method for manufacturing a semiconductor device, wherein a crystal semiconductor film is formed on a semiconductor substrate, includes a non-crystal semiconductor film formation step (S101) of forming a non-crystalline semiconductor film on the semiconductor substrate, a first laser light irradiation step (S102) of melting the non-crystal semiconductor film by its thickness, by having a first laser light irradiated to the non-crystalline semiconductor film, a crystallization step (S103) of crystalizing the non-crystalline semiconductor film and transform it to a crystal semiconductor film, a cap film forming step (S104) of forming a cap film on the crystal semiconductor film, and a second laser light irradiation step (S105) of having a second laser light that does not have the amount of energy sufficient to melt the crystal semiconductor film by its thickness, irradiated to the crystal semiconductor film via the cap film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a semiconductor device in which an amorphous semiconductor film is crystallized using laser light.

  In general, there is a method using single crystal silicon as a method for manufacturing a semiconductor device, but there is a manufacturing method using a silicon thin film in which a silicon thin film is formed on a glass substrate. A semiconductor device manufactured by using a silicon thin film formed on a glass substrate is used as a part of an image sensor or an active matrix liquid crystal display device.

  In an active matrix liquid crystal display device, semiconductor devices are used as TFTs (Thin Film Transistors) arranged as a regular array on a transparent substrate. Each TFT in the active matrix liquid crystal display device functions as a pixel controller.

  Conventionally, a TFT in an active matrix liquid crystal display device has been manufactured by forming an amorphous silicon film on a glass substrate. However, in recent years, a TFT liquid crystal display that uses a polycrystalline silicon film with high electron mobility instead of an amorphous silicon film with low electron mobility to enhance the switching characteristics of the TFT and increase the display speed. Devices are being manufactured. Here, as a method of manufacturing a polycrystalline silicon film, for example, a method of forming a polycrystalline silicon film by irradiating an amorphous silicon film or a microcrystalline silicon film deposited on a glass substrate with excimer laser light ( ELC method).

  The ELC method uses a linear film having a length of about 200 to 400 mm and a width of about 0.2 to 1.0 mm while scanning an amorphous or microcrystalline silicon film deposited on a glass substrate at a constant speed. In this method, laser light is continuously irradiated. At this time, the portion irradiated with the laser light does not melt over the entire thickness direction of the film, but melts while leaving a partial region. For this reason, crystal nuclei are generated all over the interface between the unmelted region and the molten region of the silicon film, and the crystal grows toward the outermost layer of the silicon film, thereby forming crystal grains with random orientation. The crystal grain size of the polycrystalline silicon film is as very small as 100 to 200 nm.

  Since many unpaired electrons exist in the crystal grain boundary of the polycrystalline silicon film and a potential barrier is formed, electrons are often scattered in the crystal grain boundary of the polycrystalline silicon film. Therefore, in general, a TFT formed of a polycrystalline silicon film with fewer crystal grain boundaries, that is, a larger crystal grain size, has higher electron mobility due to the electric field effect.

  However, in the ELC method, it is difficult to obtain a polycrystalline silicon film having a large crystal grain size because it causes longitudinal crystal growth in which crystallization occurs at random positions at the interface between the unmelted region and the molten region. It was difficult to obtain a TFT with high electron mobility. In addition, due to the random crystallization, non-uniformity occurs in the structure of the polycrystalline silicon film between the TFTs, and non-uniformity in switching characteristics occurs in the TFT array. It was. In addition, when such a problem occurs, there is a problem in the TFT liquid crystal display device that pixels having a high display speed and pixels having a low display speed coexist in one display screen.

  In order to obtain a higher performance TFT liquid crystal display device, it is necessary to increase the crystal grain size of the polycrystalline silicon film and to control the crystal orientation. Therefore, many proposals have been made for the purpose of obtaining a polycrystalline silicon film having performance close to that of single crystal silicon. Among them, the laser crystallization technique classified as the lateral growth method is attracting attention because a long crystal having a uniform orientation in the crystal growth direction can be obtained.

  One of the lateral growth methods is to irradiate an amorphous silicon film with a pulsed laser beam having a small width and melt the irradiated portion of the amorphous silicon film over the entire thickness direction of the laser beam irradiation region. Then, there is a method (SLS method) in which crystallization is performed by repeating solidification thereafter (see, for example, Patent Document 1). This method irradiates an amorphous silicon film with a pulse laser beam having a fine width, melts the amorphous silicon film over the entire thickness direction of the irradiation region of the pulse laser beam, and then solidifies the crystal. It is what makes it.

  FIG. 12 shows a schematic cross-sectional view of a conventional object to be processed irradiated with pulsed laser light. The object to be processed 50 includes a transparent substrate 52 having a light transmission property, a base film 54, and an amorphous silicon film 53. Then, as shown in FIG. 12, in forming the crystal region along the extending direction of the amorphous silicon film 53 (the AB direction in FIG. 12), heat is induced in the region C of the amorphous silicon film 53. . The induction of heat is performed by irradiating the amorphous silicon film 53 with a laser beam 58 after masking a region other than the region C of the amorphous silicon film 53. As a result, the energy of the laser beam 58 applied to the region C is converted into thermal energy, heat can be induced in the region C, and the amorphous silicon film 53 can be melted over the thickness of the film. it can.

  Next, when the amorphous silicon film 53 melted in the region C is solidified by cooling, as shown in the schematic top view of FIG. From this point, the crystal grows toward the center of the region C. Further, as shown in FIG. 13B, a new region D adjacent to the region C is set so as to include a portion where no crystal is formed in the region C, and the region D is set in the same manner as the region C. Melt. Then, when the portion melted in the region D is solidified, a crystal grows in the region D as shown in FIG. When such a procedure is repeated and crystallized stepwise along the extending direction of the amorphous silicon film 53, the crystal growth region of the amorphous silicon film 53 is expanded as shown in FIG. can do. Thereby, a crystalline semiconductor film having a large crystal grain size can be formed.

  However, in the case of crystal growth by the conventional lateral growth method, if the laser light is irradiated with an energy amount per irradiation area that can obtain a crystal having a sufficiently long crystal growth length, the surface of the crystalline semiconductor film becomes crystalline. A ridge having a height of about 1 to 2 times the film thickness of the semiconductor film is generated. This ridge is formed when adjacent crystal grains collide with each other during crystal growth. Therefore, when forming a TFT using such a crystalline semiconductor film as an active layer, if a gate insulating film is formed on the crystalline semiconductor film, the gate insulating film on the ridge of the crystalline semiconductor film becomes thin. I guess that. As a result of such local thinning of the gate insulating film, the electric field concentrates on the gate insulating film on the ridge, so that the ridge of the crystalline semiconductor film is lower than the portion where the ridge is not formed. Leakage current flows with voltage. For this reason, in a TFT using such a crystalline semiconductor film as an active layer, it is necessary to increase the thickness of the gate insulating film to reduce the leakage current. However, as the thickness of the gate insulating film increases, the on-current of the TFT decreases. Therefore, the ridge on the surface of the crystalline semiconductor film has a problem that the performance of the TFT is lowered.

  As a method for reducing the ridge on the surface of such a crystalline semiconductor film, a method of forming a crystalline semiconductor film by irradiating a laser beam after forming a cap film on the amorphous semiconductor film has been proposed (for example, , See Patent Document 2).

  However, when the present inventors conducted experiments, this method reduces the ridge on the surface of the crystalline semiconductor film, but the crystal grown at this time contains a large number of subgrain boundaries, which is the cause of electron scattering. Therefore, a high mobility TFT could not be obtained. This is because the growth of crystals above the surface of the semiconductor substrate is suppressed due to the presence of the cap film, so that a large internal stress is generated inside the grown crystal and the internal stress is relaxed. It is estimated that a large number of subgrain boundaries were formed.

Thus, in the conventional semiconductor device manufacturing method, a crystalline semiconductor film excellent in surface flatness and crystallinity could not be obtained.
Japanese Patent No. 3204986 JP-A-6-97196

  The present invention has been made in view of the above circumstances, and an object of the present invention is a flatness in which the crystalline semiconductor film formed on a semiconductor substrate has excellent crystallinity and the surface of the crystalline semiconductor film is excellent. It is an object of the present invention to provide a method for manufacturing a semiconductor device having characteristics.

  The present invention relates to a method of manufacturing a semiconductor device in which a crystalline semiconductor film is formed on a semiconductor substrate, the amorphous semiconductor film forming step of forming an amorphous semiconductor film on the semiconductor substrate, and the amorphous semiconductor film Irradiating the first laser beam to the first laser beam irradiation step for melting the amorphous semiconductor film over the thickness of the film, and crystallizing the amorphous semiconductor film to convert it into a crystalline semiconductor film A crystallization step, a cap film formation step of forming a cap film on the crystalline semiconductor film, and a second laser beam having no energy amount for melting the crystalline semiconductor film over the thickness of the film. And a second laser light irradiation step of irradiating the crystalline semiconductor film via the semiconductor device.

  Here, in the method for manufacturing a semiconductor device of the present invention, the crystallization step is preferably performed by moving the irradiation region of the first laser light stepwise to enlarge the crystallization region.

  In the semiconductor device manufacturing method of the present invention, in the crystallization step, the amorphous semiconductor film is irradiated with a third laser beam having no energy amount for melting the amorphous semiconductor film over the thickness of the film. It is preferable to be performed in a state.

  In the method for manufacturing a semiconductor device of the present invention, the cap film forming step is a step of making the reflectance in a part of the second laser light irradiation region lower than the reflectance in the other region. Is preferred.

  According to the present invention, there is provided a method for manufacturing a semiconductor device in which a crystalline semiconductor film formed on a semiconductor substrate has excellent crystallinity and the surface of the crystalline semiconductor film has excellent flatness. Can do.

  Therefore, according to the present invention, a TFT having high electron mobility can be manufactured by using a crystalline semiconductor film having excellent crystallinity for the active layer.

  Further, according to the present invention, since a crystalline semiconductor film having excellent surface flatness is used for the active layer, it is not necessary to increase the thickness of the gate insulating film formed on the active layer. Performance degradation can be prevented.

  Embodiments of the present invention will be described below. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

  FIG. 1 shows a flowchart of a preferred example of a method for manufacturing a semiconductor device of the present invention. Here, in the semiconductor device manufacturing method of the present invention, the amorphous semiconductor film forming step S101 for forming the amorphous semiconductor film on the semiconductor substrate, and the first laser beam is irradiated to the amorphous semiconductor film. A first laser light irradiation step S102 for melting the amorphous semiconductor film over the thickness of the film, a crystallization step S103 for crystallizing the amorphous semiconductor film into a crystalline semiconductor film, and a crystalline semiconductor Cap film forming step S104 for forming a cap film on the film, and irradiation of the crystalline semiconductor film through the cap film with a second laser beam having no energy amount for melting the crystalline semiconductor film over the thickness of the film Second laser light irradiation step S105.

  In the semiconductor device manufacturing method of the present invention, the amorphous semiconductor film is crystallized by irradiating the first laser light without forming the cap film on the amorphous semiconductor film, so that the semiconductor by the cap film is formed. Since crystal growth above the surface of the substrate is not suppressed and internal stress is less likely to occur in the crystal grains constituting the crystalline semiconductor film, subgrain boundaries tend not to be formed in the crystal grains than in the prior art.

  In the method of manufacturing a semiconductor device according to the present invention, a cap film is formed on the crystalline semiconductor film after the crystalline semiconductor film is formed, and has an energy amount for melting the crystalline semiconductor film over the thickness of the film. By irradiating the crystalline semiconductor film with the second laser light that does not pass through the cap film, the ridge on the surface of the crystalline semiconductor film can be eliminated, and the surface of the crystalline semiconductor film can be planarized.

  Here, in the present invention, the “semiconductor device” is a device including a structure in which a crystalline semiconductor film is formed on a semiconductor substrate, and has a structure other than the semiconductor substrate and the crystalline semiconductor film. Alternatively, another semiconductor film may be provided between the semiconductor substrate and the crystalline semiconductor film. Further, the “amorphous semiconductor film” is a semiconductor film in which an amorphous part is more than a crystalline part, and the entire semiconductor film may not be amorphous. Further, the “crystalline semiconductor film” is a semiconductor film in which a crystalline part is more than an amorphous part, and the entire semiconductor film may not be crystalline.

  A schematic cross-sectional view of FIG. 2 shows a preferred example of the manufacturing process of the semiconductor device manufacturing method of the present invention. In FIG. 2A, an object to be processed 100 used in the method for manufacturing a semiconductor device of the present invention includes a buffer film 5 formed on a semiconductor substrate 2 and an amorphous semiconductor film formed on the buffer film 5. It consists of three. Here, the semiconductor substrate 2 is preferably insulative, and a glass substrate or a quartz substrate can be used. However, it is preferable to use a glass substrate because it is inexpensive and can easily manufacture a large area substrate. It is.

  The buffer film 5 is formed in order to prevent the semiconductor substrate 2 from being affected by the heat of the melted amorphous semiconductor film 3 mainly when the amorphous semiconductor film 3 is melted and crystallized by laser light. The Further, by forming the buffer film 5, it is possible to prevent diffusion of impurities from the semiconductor substrate 2 to the amorphous semiconductor film 3. As the buffer film 5, for example, a silicon oxide film, a silicon nitride film, or a silicon oxynitride film having a film thickness of 100 to 300 nm formed by vapor deposition, ion plating, sputtering, or the like can be used.

  The amorphous semiconductor film 3 is formed by, for example, plasma enhanced chemical vapor deposition (PECVD), vapor deposition, sputtering, or the like so that the film thickness becomes 10 nm to 100 nm. The amorphous semiconductor film 3 has various characteristics by increasing the crystal growth length in the crystalline semiconductor film (for example, values of electron mobility, threshold voltage, etc. due to the field effect, and variations in these values). It is preferable to use an amorphous silicon film in which the resistance is remarkably improved. The material of the amorphous semiconductor film 3 is not limited to a material made of silicon, and a material mainly containing silicon containing other elements such as germanium can also be used.

  Next, as shown in FIG. 2B, the amorphous semiconductor film 3 is irradiated with the first laser light 7 to melt the amorphous semiconductor film 3 to be in a liquid state.

  FIG. 3 shows a configuration diagram of a laser beam irradiation apparatus used in the present invention. This laser beam irradiation apparatus includes a first laser beam oscillator 11, a variable attenuator 12, a field lens 13, and a projection mask. 14, an imaging lens 15, a sample stage 16, and mirrors 10 a, 10 b, and 10 c. The first laser beam oscillator 11 and the sample stage 16 are controlled by a controller 17 and can adjust the irradiation timing of the first laser beam 7 and the position of the sample stage 16. Accordingly, the area irradiated with the first laser beam 7 can be moved by moving the sample stage 16 in the direction of the arrow in FIG.

  In this laser beam irradiation apparatus, the first laser beam 7 oscillated from the first laser beam oscillator 11 passes through the variable attenuator 12 and is then reflected by the mirrors 10a and 10b. Thereafter, the first laser beam 7 passes through the field lens 13 and the projection mask 14. Then, the first laser light 7 that has passed through the projection mask 14 is imaged as an image of the projection mask 14 by the imaging lens 15 and irradiated onto the amorphous semiconductor film 3.

  Then, the amorphous semiconductor film 3 irradiated with the first laser beam 7 is melted to be in a liquid state, and thereafter the amorphous semiconductor film 3 in the liquid state is cooled and solidified to be crystallized. It is converted into a crystalline semiconductor film 4 shown in FIG.

  Here, the first laser beam 7 has an energy amount for melting the amorphous semiconductor film 3 in a solid state per one irradiation and irradiation area. Specifically, it is recommended that the first laser beam 7 has an energy amount that can heat the amorphous semiconductor film 3 to a temperature equal to or higher than the melting point in the entire film thickness.

  The first laser light 7 is not particularly limited as long as the amorphous semiconductor film 3 can be melted. For example, the first laser light 7 is oscillated from various solid-state lasers typified by excimer laser light and YAG laser. It is preferable to have a wavelength in the ultraviolet region such as a third harmonic of laser light. When the first laser light 7 has a wavelength in the ultraviolet region, the amount of energy of the first laser light 7 is increased, so that the amorphous semiconductor film 3 can be easily converted into the crystalline semiconductor film 4. This is because it tends to be possible. Among these, the first laser beam 7 is particularly preferably an excimer laser beam having a wavelength of 308 nm capable of pulsed emission. When the first laser beam 7 is an excimer laser beam, a laser beam oscillator capable of stably oscillating a laser beam having an energy amount necessary for the present invention is obtained relatively easily and at a low cost. This is because it is possible.

  The crystallization process for converting the amorphous semiconductor film 3 into the crystalline semiconductor film 4 is performed by moving the irradiation region of the first laser light stepwise to enlarge the crystallization region (SLS method). It is preferable that When the amorphous semiconductor film 3 is solidified by cooling after melting by irradiation with the first laser beam 7, the first laser beam is generated from the boundary between the irradiation region of the first laser beam 7 and the other region. A crystal grows toward the center of the irradiation region 7. Next, a new region adjacent to this region is set so that the portion where the crystal is not formed in the irradiation region of the first laser beam 7 is included, and the first laser beam 7 is applied to this new region. When solidified after irradiation and melting, crystals grow in this new region. When such a procedure is repeated and crystallized stepwise along the extending direction of the amorphous semiconductor film 3, the crystal growth region can be expanded. Thereby, a crystalline semiconductor film having a large crystal grain size and a uniform crystal growth direction can be formed.

  FIG. 4 shows a configuration diagram of another preferred example of the laser beam irradiation apparatus used in the present invention. This laser beam irradiation apparatus is characterized by including a third laser beam oscillator 20 together with the first laser beam oscillator 11.

  That is, in the laser beam irradiation apparatus shown in FIG. 4, the first laser beam 7 oscillated from the first laser beam oscillator 11 is irradiated to the amorphous semiconductor film 3 to melt the amorphous semiconductor film 3. Energy that causes the amorphous semiconductor film 3 to melt over the thickness of the film from the third laser light oscillator 20 during crystallization by solidification of the amorphous semiconductor film 3 in the liquid state. A third laser beam 8 having no quantity is oscillated, and the third laser beam 8 passes through an optical element group 21 composed of an expander, a homogenizer, and the like, and is reflected by the mirror 10d, and then the amorphous semiconductor film 3 is irradiated. As a result, the temperature drop rate of the amorphous semiconductor film 3 in the liquid state can be reduced and the time until solidification can be lengthened. Therefore, the amorphous semiconductor film 3 in the liquid state is generated by solidification. The crystal growth length of the crystals constituting the crystalline semiconductor film 4 can be greatly increased.

  Here, it is preferable that the third laser light 8 has a wavelength in a range in which the absorption rate of the amorphous semiconductor film 3 in the solid state is lower than that of the first laser light 7. In this case, the third laser beam 8 does not contribute to melting the amorphous semiconductor film 3, but tends to contribute only to lowering the temperature drop rate of the amorphous semiconductor film 3. It is.

  Further, it is preferable that the third laser light 8 has a wavelength in a range where the absorption rate to the amorphous semiconductor film 3 in a liquid state is higher than that of the first laser light 7. In this case, it is because the tendency that the temperature lowering rate of the amorphous semiconductor film 3 in the liquid state can be more efficiently reduced is increased.

  In particular, the third laser light 8 preferably has a wavelength from the visible range to the infrared range. For example, the third laser beam 8 includes a YAG laser beam having a wavelength of 532 nm, a YAG laser beam having a wavelength of 1064 nm, or a carbon dioxide laser beam having a wavelength of 10.6 μm.

  Further, the amount of energy per irradiation and irradiation area of the third laser beam 8 is less than the amount of energy for melting the amorphous semiconductor film 3 in the solid state. In particular, it is recommended that the third laser beam 8 has an energy amount that cannot heat the amorphous semiconductor film 3 to a temperature higher than the melting point. In the present invention, for example, as shown in FIG. 4, the first laser beam 7 can be incident from the vertical direction, and the third laser beam 8 can be incident from the oblique direction.

  Further, the first laser beam 7 is, for example, reduced and projected as an irradiation region of the first laser beam 7 on the surface of the amorphous semiconductor film 3 on the surface of the amorphous semiconductor film 3 with a predetermined pattern formed thereon. Irradiated. At this time, it is preferable that the irradiation region of the third laser light 8 has a larger area than the irradiation region of the first laser light 7 including the irradiation region of the first laser light 7. In this case, it is possible to reduce the temperature lowering rate of all the melted regions of the amorphous semiconductor film 3 that is melted and in a liquid state, so that crystals of a uniform size can be easily obtained.

  Further, it is desirable that the relationship between the irradiation time of the first laser beam 7 and the third laser beam 8 and the output is similar to the relationship shown in FIG. Here, the pulse waveform 23 of the first laser beam 7 indicates that the irradiation of the first laser beam 7 is started at the time t = 0, and the pulse waveform 24 of the third laser beam 8 is It shows that the third laser beam 8 is irradiated with a low output in the time zone excluding time t = t1 to t2, and is irradiated with a high output in the time zone of time t = t1 to t2.

  At time t1, since the first laser beam 7 is irradiated, the amorphous semiconductor film 3 is melted and in a liquid state. By irradiating the amorphous semiconductor film 3 in the liquid state with the third laser light 8 in addition to the first laser light 7, the temperature drop rate of the amorphous semiconductor film 3 can be reduced. In addition, since the time until solidification can be increased, the crystal growth length of the crystals constituting the crystalline semiconductor film 4 can be greatly extended.

  Further, after moving the irradiation region of the first laser light 8, irradiating the irradiation region with the third laser light to crystallize the irradiation region before the movement is repeated a plurality of times, thereby aligning the crystal growth direction. A crystal having a large crystal grain size can be grown.

  When the crystalline semiconductor film 4 shown in FIG. 2C is formed as described above, the grown crystals collide with each other, so that the crystalline semiconductor film 4 is located near the center of the irradiation region of the first laser beam 7. A ridge 9 protruding upward from the surface of the substrate is formed.

  Then, a cap film 6 is formed on the crystalline semiconductor film 4 as shown in FIG. The cap film 6 is formed by plasma enhanced chemical vapor deposition (PECVD), vapor deposition, sputtering, or the like so as to have a predetermined film thickness. The cap film 6 is made of, for example, silicon dioxide.

  Subsequently, the second laser beam 18 is irradiated to the crystalline semiconductor film 4 through the cap film 6. At this time, the amount of energy of the second laser light 18 to be irradiated is the thickness of the crystalline semiconductor film 4 in the solid state per one irradiation and irradiation area in the region where the ridge 9 is not formed. Is less than the amount of energy that can be melted.

  Here, by forming the cap film 6 on the crystalline semiconductor film 4, the reflectance with respect to the second laser light 18 in the vicinity of the central portion of the first laser light irradiation region where the ridge 9 is generated has the ridge 9. It is preferable that the reflectance is lower than the reflectance with respect to the second laser light 18 in a region other than the vicinity of the central portion of the first laser light irradiation region where no occurrence occurs. In this case, since the second laser beam 18 is well absorbed near the center of the first laser beam irradiation region where the ridge 9 is generated, the ridge 9 can be melted more efficiently.

  For example, as shown in the schematic top view of FIG. 6, when the width 25 of the first laser light irradiation region is represented by W and the crystal growth length 29 is represented by L, the first laser light irradiation region central portion 27. A cap film having a low reflectivity with respect to the second laser beam is formed from point 19a to 19b at least (W / 2-9L / 10) away from the first laser beam irradiation region end 28 to It is preferable that a cap film having a high reflectivity with respect to the second laser beam is formed in a region other than the above, or that the reflectivity with respect to the second laser beam is increased by not forming the cap film. If the region where the cap film having a low reflectivity for the second laser beam is formed is narrower than this, the ridge cannot be completely covered with the cap film, and the surface of the crystalline semiconductor film 4 is planarized. It tends to be smaller. In addition, even when the region where the cap film having low reflectivity with respect to the second laser beam is formed is wider than this, the crystalline semiconductor film 4 is melted again, and the region to be crystallized becomes wide. Since a new ridge is formed on the surface of the film 4, the planarization effect on the surface of the crystalline semiconductor film 4 is reduced.

  In this case, the low reflectance region 26 where the cap film having a low reflectance with respect to the second laser light is formed can be selectively heated. For this reason, it becomes easy to adjust the energy amount of the second laser beam so as to melt the region where the ridge is formed without melting the region where the ridge is not formed. Here, the crystal growth length 29 refers to the length from the first laser light irradiation end portion 28 where crystal growth starts to the portion where crystal growth is completed.

  When the crystalline laser film is irradiated with the second laser light through the cap film in this way, the ridge is melted again and crystallized, and the surface flatness of the entire crystalline semiconductor film is improved.

  Thereafter, the cap film is removed to complete the semiconductor device 1 shown in FIG.

(Embodiment 1)
First, as shown in FIG. 2A, a buffer film 5 made of a silicon dioxide film is formed on a semiconductor substrate 2 made of glass, and an amorphous semiconductor film 3 made of an amorphous silicon film is formed on the buffer film 5. To be processed 100 is formed.

  The buffer film 5 is laminated with a film thickness of 300 nm on the semiconductor substrate 2 by vapor deposition, ion plating, sputtering, or the like. Then, the amorphous semiconductor film 3 is laminated with a film thickness of 50 nm on the buffer film 5 by plasma enhanced chemical vapor deposition (PECVD), vapor deposition, sputtering, or the like.

  Next, the target object 100 shown in FIG. 2A is placed on the sample stage 16 of the laser beam irradiation apparatus shown in FIG. Then, as shown in FIG. 2B, the amorphous semiconductor film 3 is irradiated with the first laser beam 7 to melt the amorphous semiconductor film 3 and then solidify, so that polycrystalline silicon is obtained. The film is converted into a crystalline semiconductor film 4 shown in FIG.

Here, an excimer laser beam having a wavelength of 308 nm is used as the first laser beam 7, and the amount of energy per irradiation area is 200 mJ / cm ² and the irradiation time is about 50 ns per one irradiation. In the present embodiment, the first laser beam is maintained in a state where the temperature of the semiconductor substrate 2 in the region other than the region irradiated with the first laser beam 7 is maintained at a temperature equivalent to room temperature (25 ° C.). 7 is irradiated.

  Then, as shown in FIG. 2C, a ridge 9 is generated near the center of the irradiation region of the first laser beam 7.

  Subsequently, after removing the natural oxide film on the surface of the crystalline semiconductor film 4 by HF cleaning, a cap film 6 made of a silicon dioxide film is formed as shown in FIG.

  The cap film 6 is formed on the crystalline semiconductor film 4 by vapor deposition, ion plating, sputtering, or the like. Further, here, the width 25 of the first laser light irradiation region shown in FIG. 6 is 20 μm, and the crystal growth length 29 by one first laser light irradiation is 2 μm. The low reflectance region 26 is a point 19a, 19b away from the irradiation region central portion 27 by a distance of 8.2 μm toward the first laser light irradiation region end portion 28. The low reflectance region 26 has a film thickness of 50 nm. The cap film 6 is formed in a region other than the low reflectance region 26 with a film thickness of 100 nm.

  When the crystalline semiconductor film 4 is irradiated with the second laser light 18 through the cap film 6, the type of the second laser light 18, the type and thickness of the cap film 6, the crystalline semiconductor The reflectivity changes depending on the film thickness of the film 4 and the like. FIG. 7 shows the relationship between the thickness of the cap film made of silicon dioxide and the excimer laser beam reflectance. When the thickness of the cap film is 100 nm, the reflectivity with respect to the excimer laser beam is maximized, and when the thickness of the cap film is 50 nm, the reflectivity with respect to the excimer laser beam is minimized. Therefore, as a result, the low reflectance region 26 can be selectively heated.

Then, as shown in FIG. 2D, the second laser beam 18 is irradiated. Here, an excimer laser beam having a wavelength of 308 nm is used as the second laser beam 18, the energy amount per irradiation area per irradiation is 150 mJ / cm ² , and the irradiation time is about 50 ns. In the present embodiment, the second laser beam 18 is maintained in a state where the temperature of the semiconductor substrate 2 in the region other than the region irradiated with the second laser beam 18 is maintained at a temperature equivalent to room temperature (25 ° C.). Irradiation.

  After the irradiation with the second laser beam 18, the cap film 6 is removed by HF, whereby the semiconductor device 1 shown in FIG.

  Here, FIG. 8 shows a crystalline semiconductor film (silicon film A) made of a polycrystalline silicon film before flattening that has not been irradiated with the second laser light, and after flattening by irradiation with the second laser light. 2 shows the results of measuring the surface roughness of the crystalline semiconductor film (silicon film B) and the crystalline semiconductor film (silicon film C) after planarization according to the prior art, using an atomic force microscope. Note that the unevenness on the surface of the crystalline semiconductor film shown in FIG. 8 is represented by the distance between the ridge portion and the non-ridge portion. As the silicon film C, an amorphous silicon film having a thickness of 50 nm is formed on a glass substrate, a cap film made of silicon dioxide having a thickness of 50 nm is formed on the amorphous silicon film, and then laser light is emitted. It is a polycrystalline silicon film crystallized by irradiation. Other manufacturing methods and manufacturing conditions are the same as in the present embodiment.

  As shown in FIG. 8, the ridge that was high in the silicon film A before planarization is reduced to about the silicon film C in the silicon film B. In this embodiment, since the second laser light is irradiated after the cap film is formed, the region where the ridge is formed is changed to minute unevenness by melting and crystallizing again. It is.

  Next, the surfaces of the silicon film A, the silicon film B, and the silicon film C were observed with a SEM (Scanning Electron Microscope). The result is shown in FIG. The crystal observation was performed on the surface of each silicon film (silicon film A, silicon film B, silicon film C) after performing SECCO etching. 9A is a film surface image obtained by photographing the film surface of the silicon film A by SEM, and FIG. 9B is a film surface image obtained by photographing the film surface of the silicon film B by SEM. (C) is a film surface image obtained by photographing the film surface of the silicon film C by SEM.

  As shown in FIG. 9, in the silicon film A and the silicon film B according to the present embodiment, the number of sub-boundaries 31 formed in the crystal grain 30 is extremely small as compared with the silicon film C according to the prior art. . This is because according to the crystallization according to the present embodiment, the cap film is not formed on the amorphous semiconductor film 3 at the time of crystallization, so that the crystal growth in the upward direction from the surface of the semiconductor substrate is not suppressed. It is considered that the internal stress generated in the grown crystal is very small, and the sub-grain boundary 31 is not formed in the crystal grain 30.

(Embodiment 2)
The present embodiment is characterized in that an SLS method is used as a method for growing a crystal. According to the SLS method, the crystal can be grown in the extending direction by one irradiation of the first laser beam. Therefore, each time the first laser light is irradiated, the crystal region can be enlarged stepwise by moving the irradiation region of the first laser light stepwise (step movement). This makes it possible to align the growth direction of each crystal in the semiconductor device obtained by the present invention with the extending direction.

  In the present embodiment, the step movement is performed 10 times with the width 25 of the first laser light irradiation region shown in FIG. 6 being 20 μm and the step movement amount being 1 μm.

  Then, a ridge is formed near the center of the first laser light irradiation region for the tenth time, and the surface of the crystalline semiconductor film is flattened in the same manner as in the first embodiment. As a result, also in this embodiment, as shown in FIG. 7, the crystalline semiconductor film (silicon film A) before planarization, the crystalline semiconductor film (silicon film B) after planarization, and the conventional silicon film C The silicon film B is flattened more than the silicon film A, and is equivalent to the silicon film C. As the silicon film C, an amorphous silicon film having a thickness of 50 nm is formed on a glass substrate, a cap film made of silicon dioxide having a thickness of 50 nm is formed on the amorphous silicon film, and then the SLS method is used. It is a polycrystalline silicon film formed by irradiating with laser light.

  Next, the surfaces of the silicon film A, the silicon film B, and the silicon film C were observed with a SEM (Scanning Electron Microscope). The result is shown in FIG. The crystal observation was performed on the surface of each silicon film (silicon film A, silicon film B, silicon film C) after performing SECCO etching. 10A is a film surface image obtained by photographing the film surface of the silicon film A by SEM, and FIG. 10B is a film surface image obtained by photographing the film surface of the silicon film B by SEM. (C) is a film surface image obtained by photographing the film surface of the silicon film C by SEM.

  As shown in FIG. 10, in the silicon film A and the silicon film B according to the present embodiment, the number of subgrain boundaries formed in the crystal grains 30 is extremely small as compared with the silicon film C according to the prior art. This is because, according to the crystallization according to the present embodiment, since the cap film is not formed on the amorphous semiconductor film at the time of crystallization, crystal growth in the upward direction from the surface of the semiconductor substrate is not suppressed, It is considered that the internal stress generated in the grown crystal is very small, and the subgrain boundary 31 is not formed in the crystal grain 30.

(Embodiment 3)
In the present embodiment, the first laser beam 7 and the third laser beam 8 are irradiated to the amorphous semiconductor film 3 made of an amorphous silicon film using the laser beam irradiation apparatus shown in FIG. The amorphous semiconductor film 3 is characterized by being converted to a crystalline semiconductor film made of a polycrystalline silicon film.

Here, in this embodiment, in the relationship between the irradiation time and the output of the first laser beam 7 and the third laser beam 8 shown in FIG. 5, the first laser beam 7 has a wavelength of 308 nm. Using excimer laser light, the amount of energy per irradiation area per irradiation is 200 mJ / cm ² and the irradiation time is about 50 ns. Further, as the third laser beam 8, a carbon dioxide laser beam having a wavelength of 10.6 μm is used. The energy amount per irradiation area per irradiation is about 5 mJ / cm ² and the irradiation time is about 3 ms.

  Further, in the present embodiment, the temperature of the semiconductor substrate 2 in a region other than the irradiation region of the first laser beam 7 and the third laser beam 8 is maintained at a temperature equivalent to room temperature (25 ° C.). Then, the first laser beam 7 and the third laser beam 8 are irradiated.

  In the present embodiment, the first laser light 7 is irradiated from a direction perpendicular to the surface of the semiconductor substrate 2, and the third laser light 8 is directed to a direction perpendicular to the surface of the semiconductor substrate 2. Irradiate at an angle of 30 °.

  Thus, in the present embodiment, the third laser beam 8 is irradiated while the amorphous semiconductor film 3 is melted. Then, the amorphous semiconductor film 3 in the liquid state is irradiated with the third laser light 8 in addition to the first laser light 7, thereby reducing the temperature drop rate of the amorphous semiconductor film 3. In addition, since the time until solidification can be extended, a crystalline semiconductor film having crystals with a larger grain size can be obtained efficiently. For example, when crystal growth is performed by irradiating a first laser beam having a slit width of 20 μm, the crystal growth length is about 2 μm, but according to the present embodiment, the crystal growth length is 10 μm. It can be.

  As described above, as a result of converting the amorphous semiconductor film into the crystalline semiconductor film, a ridge is formed in the vicinity of the central portion of the irradiation region of the first laser beam, and this ridge is made crystalline as in the first embodiment. The surface of the semiconductor film is planarized. As a result, also in this embodiment, as shown in FIG. 7, the crystalline semiconductor film (silicon film A) before planarization, the crystalline semiconductor film (silicon film B) after planarization, and the conventional silicon film C The silicon film B is flattened more than the silicon film A, and is equivalent to the silicon film C. As the silicon film C, an amorphous silicon film having a thickness of 50 nm is formed on a glass substrate, a cap film made of silicon dioxide having a thickness of 50 nm is formed on the amorphous silicon film, and then laser light is emitted. It is a polycrystalline silicon film formed by irradiation.

  Next, the surfaces of the silicon film A, the silicon film B, and the silicon film C were observed with a SEM (Scanning Electron Microscope). The result is shown in FIG. The crystal observation was performed on the surface of each silicon film (silicon film A, silicon film B, silicon film C) after performing SECCO etching. 11A is a film surface image obtained by photographing the film surface of the silicon film A by SEM, and FIG. 11B is a film surface image obtained by photographing the film surface of the silicon film B by SEM. (C) is a film surface image obtained by photographing the film surface of the silicon film C by SEM.

  As shown in FIG. 11, in the silicon film A and the silicon film B according to the present embodiment, the number of subgrain boundaries formed in the crystal grains 30 is extremely small as compared with the silicon film C according to the prior art. This is because, according to the crystallization according to the present embodiment, since the cap film is not formed on the amorphous semiconductor film at the time of crystallization, crystal growth in the upward direction from the surface of the semiconductor substrate is not suppressed, It is considered that the internal stress generated in the grown crystal is very small, and the subgrain boundary 31 is not formed in the crystal grain 30.

  As described above, according to the first to third embodiments, it is possible to obtain a polycrystalline silicon film composed of crystals with significantly large crystal grains and excellent crystallinity. Therefore, a TFT having a high electron mobility can be manufactured by using such a polycrystalline silicon film as an active layer.

  In addition, according to the first to third embodiments, a polycrystalline silicon film having excellent flatness on the surface can be obtained. Therefore, when manufacturing a TFT using such a polycrystalline silicon film as an active layer, it is not necessary to increase the thickness of the gate insulating film formed on the active layer. Therefore, it is possible to prevent the performance degradation of the TFT.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. 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 crystalline semiconductor film having excellent crystallinity and surface flatness can be obtained, a TFT as an example of a semiconductor device manufactured according to the present invention can be used as a pixel controller of a liquid crystal display device. It is suitably used as a display element.

It is a flowchart of a preferable example of the manufacturing method of the semiconductor device of this invention. It is typical sectional drawing which shows a preferable example of the manufacturing process of the manufacturing method of the semiconductor device of this invention, (A) is typical sectional drawing of an example of the to-be-processed object used for this invention, (B) FIG. 4A is a schematic cross-sectional view of the object to be processed shown in FIG. 4A irradiated with the first laser beam, and FIG. 4C is a schematic view of a semiconductor device in which a ridge is formed on the surface of the crystalline semiconductor film. (D) is a schematic cross-sectional view of a semiconductor device irradiated with the second laser light after the cap film is formed, and (E) is a schematic cross-sectional view of the semiconductor device manufactured according to the present invention. FIG. It is a typical block diagram of a preferable example of the laser beam irradiation apparatus used for this invention. It is a typical block diagram of another preferable example of the laser beam irradiation apparatus used for this invention. It is the figure which showed a preferable example of the relationship between the irradiation time of the 1st laser beam used for this invention, and a 3rd laser beam, and an output. It is a typical top view of a preferable example of the crystalline semiconductor film in the present invention. It is the figure which showed the relationship between the film thickness of the cap film used for this invention, and the reflectance with respect to an excimer laser beam. It is the figure which showed the uneven | corrugated relationship in the surface of the crystalline semiconductor film of the silicon film A before the planarization in this invention, the silicon film B after the planarization in this invention, and the silicon film C according to a prior art. (A) is the film | membrane surface image which image | photographed the film | membrane surface of the silicon film A before planarization in Embodiment 1 of this invention by SEM, (B) is the silicon | silicone after planarization in Embodiment 1 of this invention. FIG. 2C is a film surface image obtained by photographing the film surface of the film B by SEM, and FIG. 3C is a film surface image obtained by photographing the film surface of the silicon film C according to the conventional technique by SEM. (A) is the film | membrane surface image which image | photographed the film | membrane surface of the silicon film A before planarization in Embodiment 2 of this invention by SEM, (B) is the silicon | silicone after planarization in Embodiment 2 of this invention. FIG. 2C is a film surface image obtained by photographing the film surface of the film B by SEM, and FIG. 3C is a film surface image obtained by photographing the film surface of the silicon film C according to the conventional technique by SEM. (A) is the film | membrane surface image which image | photographed the film | membrane surface of the silicon film A before planarization in Embodiment 3 of this invention by SEM, (B) is the silicon | silicone after planarization in Embodiment 3 of this invention. FIG. 2C is a film surface image obtained by photographing the film surface of the film B by SEM, and FIG. 3C is a film surface image obtained by photographing the film surface of the silicon film C according to the conventional technique by SEM. It is typical sectional drawing of the conventional to-be-processed object irradiated with a pulse laser beam. It is a typical top view which shows an example of the conventional lateral growth method, (A) is a typical top view of a to-be-processed object shown in FIG. 12, (B) is before irradiating the laser beam to the area | region D (C) is a schematic top view of the target object shown in (A) after irradiating the region D with laser light. D) is a schematic top view of the object to be processed shown in (A) after the end of the lateral growth.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor device, 2 Semiconductor substrate, 3 Amorphous semiconductor film, 4 Crystalline semiconductor film, 5 Buffer film, 6 Cap film, 7 1st laser beam, 8 3rd laser beam, 9 Ridge, 10a, 10b, 10c, 10d mirror, 11 first laser beam oscillator, 12 variable attenuator, 13 field lens, 14 projection mask, 15 imaging lens, 16 sample stage, 17 controller, 18 second laser beam, points 19a and 19b, 20 Third laser light oscillator, 21 Optical element group, 23 Pulse waveform of the first laser light, 24 Pulse waveform of the third laser light, 25 Width of the first laser light irradiation region, 26 Low reflectance region, 27 1st laser light irradiation area center part, 28 1st laser light irradiation area edge part, 29 Crystal growth length, 30 Crystal grain, 31 Subgrain boundary, 50, 00 workpiece, 52 a transparent substrate, 53 an amorphous silicon film, 54 base film, 58 a laser beam.

Claims (4)

A method of manufacturing a semiconductor device in which a crystalline semiconductor film is formed on a semiconductor substrate,
An amorphous semiconductor film forming step of forming an amorphous semiconductor film on the semiconductor substrate;
Irradiating the amorphous semiconductor film with a first laser beam to melt the amorphous semiconductor film over the thickness of the film; and
A crystallization step of crystallizing the amorphous semiconductor film and converting it to the crystalline semiconductor film;
A cap film forming step of forming a cap film on the crystalline semiconductor film;
A second laser beam irradiation step of irradiating the crystalline semiconductor film through the cap film with a second laser beam having no energy amount for melting the crystalline semiconductor film over the thickness of the film;
A method for manufacturing a semiconductor device, comprising:   2. The method of manufacturing a semiconductor device according to claim 1, wherein the crystallization step is performed by moving the irradiation region of the first laser light stepwise to enlarge the crystallization region. 3.   The crystallization step is performed in a state where the amorphous semiconductor film is irradiated with a third laser beam having no energy amount for melting the amorphous semiconductor film over the thickness of the film. The manufacturing method of the semiconductor device of Claim 1 or 2.   The cap film forming step is a step of making a reflectance in a part of the irradiation region of the second laser light lower than a reflectance in another region. The manufacturing method of the semiconductor device in any one of.

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