JP2006135192A - Method and apparatus for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polycrystalline semiconductor film having a larger crystal particle than that by a conventional laser annealing method by using two kinds of lasers for controlling substrate temperature, and to crystallize an entire desired region efficiently by reducing variations in crystal grain length in the semiconductor film. <P>SOLUTION: When the semiconductor film formed on a substrate is crystallized by applying laser beams, a method for manufacturing a semiconductor device comprises a process for applying first laser beams absorbed by the substrate, a process for applying second laser beams absorbed by the semiconductor film, and a process for expanding a region crystallized by relatively scanning the semiconductor film by the laser beams repeatedly. In this case, laser beam intensity is modulated so that desired temperature can be obtained in the substrate and the semiconductor film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for manufacturing a semiconductor device in which a semiconductor film is crystallized using a laser.

  A thin film transistor (TFT) formed as a semiconductor device on a semiconductor thin film is used in a display unit or a pixel controller in an active matrix liquid crystal display device, and an amorphous semiconductor thin film is mainly used as the semiconductor thin film. Yes. Further, in order to operate the TFT at high speed, channel characteristics have been improved by crystallizing a channel region in which an amorphous semiconductor film has been conventionally used. This is because the mobility of carriers in a crystal part with a uniform atomic arrangement is several hundred times greater than in an amorphous part. However, in the case of a polycrystal, carrier scattering occurs at the crystal grain boundary. Therefore, it is desired that the channel region becomes a single crystal by making the crystal grain larger. By creating a TFT using a crystal grain that is long in the channel direction, not only can the TFT have high performance, but also an integrated circuit such as a processor can be formed on a semiconductor thin film on a glass substrate.

  Several methods have been proposed for crystallization of amorphous semiconductor thin films, but if a pulsed laser is used, a large amount of energy can be input in a short time, so that crystallization can be performed at a relatively low temperature without damaging the substrate. The process becomes possible. Therefore, development of a crystallization technique using a pulsed laser is in progress. In such crystallization by laser annealing, generation of crystal nuclei and control of the crystal growth rate are important in order to produce a semiconductor polycrystalline thin film having a large grain size and small grain size variation.

  If the semiconductor film melted by laser annealing is rapidly cooled, many crystal nuclei are generated and the crystal growth rate is increased. Then, since adjacent crystal grains inhibit their growth, the crystal grain length after growth is shortened. Therefore, a method of warming the substrate is being studied so that the molten semiconductor film is gradually cooled.

Japanese Patent Application Laid-Open No. 4-338631 of Patent Document 1 proposes a crystallization process using a plurality of laser oscillators having different oscillation wavelengths. In this case, by simultaneously irradiating the main laser beam (for example, Ar laser) having a wavelength absorbed by the semiconductor film and the assist laser beam (for example, carbon dioxide laser) having a wavelength absorbed by the substrate, the temperature of the molten semiconductor film is increased. The crystal is grown while being controlled. As described above, in Patent Document 1, the orientation of the crystalline silicon film can be made uniform by melting the semiconductor film with the main laser and heating the substrate with the assist laser having a wavelength different from that of the main laser. It is said that.
JP-A-4-3388631

  When laser annealing is repeatedly performed while scanning a laser beam relative to a semiconductor film on a substrate to crystallize a certain region or the entire surface of the semiconductor film, the same portion may be irradiated with laser light many times. is there. In particular, when using a plurality of laser beams, the substrate temperature rises as the number of shots of the assist laser increases, so the crystal grain length in the crystallized semiconductor film varies from shot to shot and varies within the substrate plane. There is a problem.

  In view of such a problem, an object of the present invention is to provide a polycrystalline semiconductor film having a large crystal grain size and a small variation in grain size.

  According to the present invention, a semiconductor device manufacturing method includes a step of irradiating a semiconductor film formed on a substrate with laser light irradiation and irradiating the first laser light absorbed by the substrate; A step of irradiating the second laser light absorbed by the semiconductor film, and a step of enlarging a crystallized region by scanning the laser light relative to the semiconductor film and repeating the laser irradiation, The laser light intensity is modulated so that a desired temperature is obtained in the semiconductor film.

  The first laser light preferably has a wavelength in the range from the visible light region to the infrared region, and the second laser light preferably has a wavelength in the range from the ultraviolet region to the visible light region. Further, in the crystallization process, it is preferable that the first laser beam is irradiated ahead of the second laser beam by a predetermined time.

  In the crystallization process, the semiconductor film can be moved at a constant speed or a constant step feed relative to the laser light. In that case, the first laser beam is irradiated to an area equal to or larger than the region irradiated with the second laser beam, and the first laser beam is irradiated in that region until the semiconductor film finishes crystallization. It can be irradiated at least twice. In addition, after gradually decreasing the intensity of at least one of the first and second laser beams so that the temperature of the semiconductor film at the time of the second laser beam irradiation is the same every time the laser irradiation is repeated, It is preferable to make it constant. It is preferable that the intensity modulation mode for gradually decreasing the intensity of at least one of the first and second laser beams is determined by how many times the first laser beam is irradiated to the same location. However, the settings regarding the first and second laser beams are preferably the same every time except for the intensity condition in the process of repeating the laser irradiation. Note that in the process of repeating laser irradiation, a part of the semiconductor film may be overlapped with laser irradiation and melted a plurality of times.

  The manufacturing apparatus used for the semiconductor device manufacturing method as described above includes a first laser oscillator that emits a first laser beam, a second laser oscillator that emits a second laser beam, and these two lasers. And a controller for controlling the oscillator. The controller preferably controls the first and second laser oscillators so that the first laser beam is irradiated in advance for a predetermined time compared to the second laser beam.

  The semiconductor device manufacturing apparatus preferably further includes a substrate transfer means so that the semiconductor film is moved at a constant speed or a constant step feed with respect to the laser light. In addition, the controller sets the emission timings of the first and second laser beams, and the first and second laser beams are irradiated at the same location repeatedly even when the first laser beam is repeatedly irradiated multiple times. It is preferable to modulate the intensity of the second laser beam.

  According to the present invention, by controlling the substrate temperature using two types of lasers, it is possible to obtain a polycrystalline semiconductor film having larger crystal grains as compared with the conventional laser annealing method. It is possible to efficiently crystallize the entire desired region by reducing the variation in length.

[Example 1]
FIG. 2 is a schematic cross-sectional view for explaining a method for manufacturing a semiconductor device according to the present invention. In this figure, a base insulating film 22 and an amorphous semiconductor film 23 are formed on a substrate 21. The substrate 21 is preferably insulative, and a glass substrate, a quartz substrate, or the like can be used. However, it is preferable to use a glass substrate because it is inexpensive and a large-area substrate can be easily manufactured.

  As the base insulating film 22, a silicon nitride film, a silicon oxynitride film, a silicon oxide film, or the like can be used. The film thickness is preferably about 50 to 200 nm, but is not limited thereto. Such a base insulating film 22 can be deposited by plasma enhanced chemical vapor deposition (PECVD), vapor deposition, sputtering, or the like.

  The semiconductor film 23 can be deposited by PECVD, catalytic chemical vapor deposition (Cat-CVD), vapor deposition, sputtering, or the like so that the film thickness becomes 10 nm to 100 nm. The material of the semiconductor film 23 is not particularly limited as long as it exhibits semiconductor characteristics, but it is preferable to use an amorphous silicon film in which various characteristics are remarkably improved by increasing the crystal growth length. However, the semiconductor film 23 before being crystallized by laser irradiation is not limited to amorphous, and may be a crystalline semiconductor film such as microcrystal or polycrystal. Further, the material of the semiconductor film 23 is not limited to a material made of only silicon, and may be a silicon alloy containing other elements such as germanium.

  Then, the semiconductor device 25 as shown in FIG. 2 is irradiated with the laser beam 24 as indicated by the arrow F, whereby the semiconductor film 23 is laser annealed and crystallized.

  In normal laser annealing, the crystal grain size becomes the largest when the semiconductor film is completely melted. The crystallization mechanism in this case is illustrated in FIG. As shown in FIG. 3A, which is a schematic sectional view of the semiconductor film, crystal nuclei represented by white circles are generated at the interface between the completely melted semiconductor film and the substrate, as indicated by arrows. Crystallization is performed in the vertical direction (thickness direction) from the lower surface side (substrate side) of the semiconductor film toward the upper surface side (surface side of the semiconductor film). In this case, as shown in FIG. 3B, adjacent crystals to be grown collide with each other to complete the growth. When the thus-crystallized polycrystalline film is observed from the upper surface, as shown in the schematic plan view of FIG. 3C, crystals having a grain size of about 10 nm to 1 μm are gathered together. appear. Crystallization of the entire desired region of the semiconductor film is repeated by repeating laser light irradiation and scanning, such that the crystallization by laser light irradiation is one cycle and the crystallization is performed in the second cycle by moving to the next region. It will become.

  Note that the term “scan” here refers to the movement of the relative position between the laser irradiation region and the semiconductor film. That is, in scanning, the stage on which the semiconductor film is placed can be moved with respect to the fixed laser beam irradiation region. Conversely, the laser beam, that is, the irradiation region may be moved with respect to the fixed semiconductor film. It is also possible to scan relatively by moving both the semiconductor film and the laser light irradiation region at the same time. Regarding movement, it is possible to move continuously at a constant speed. Alternatively, the movement may be step-by-step so that the laser beam is irradiated after stopping at a predetermined position after moving at a certain speed, and the next laser beam is irradiated after stopping after moving again. . The scanning speed is directly related to the time required to crystallize a desired region of the semiconductor film, that is, the throughput. Therefore, in this embodiment, an optimum constant scanning speed determined in consideration of the oscillation frequencies of the first and second lasers and other factors is employed. Thus, a semiconductor device can be manufactured with high productivity by using a stage drive system that satisfies the positional accuracy by movement.

  FIG. 4 is a schematic block diagram showing a laser irradiation apparatus that can be used as a semiconductor device manufacturing apparatus in the present embodiment. The laser irradiation apparatus can crystallize a semiconductor film included in the semiconductor device 25, and includes a first laser oscillator 48, a second laser oscillator 42, and a controller 41 that controls these oscillators. In addition, variable attenuators 43a and 43b, field lens 44, mask 45, imaging lens 46, movable sample stage 47, and several mirrors are included.

  The first laser 48 is an assist laser that has the effect of being absorbed by the insulator substrate and heating it, and preferably has a wavelength in the range from the visible light range to the infrared range. The first laser may be either one that emits 48 pulses or one that continuously irradiates, but in this embodiment, the glass substrate has a wavelength of 9 to 11 μm that is absorbed by the glass substrate, and is pulsed at a constant oscillation frequency. A carbon dioxide laser was used. Although the pulse width depends on the oscillation frequency of the laser, it is in the range of 10 μs to 100 ms, and the temperature of the insulator substrate and thus the semiconductor film is sufficiently raised and the semiconductor film is not melted or damaged. It is desirable to be able to impart the energy of The pulse width, like the scanning speed, was always set constant during the crystallization process.

  The second laser 42 preferably has a wavelength in the ultraviolet region to the visible light region where the absorption coefficient is large in the solid semiconductor film so as not to damage the substrate. Further, since the second laser 42 serves as a main laser for melting the semiconductor film, it is necessary to repeat pulse irradiation at a constant oscillation frequency. In this example, an excimer laser with a wavelength of 308 nm was used.

The total energy amount of the first and second laser beams used in the method for manufacturing a semiconductor thin film according to the present invention has an energy amount enough to melt the solid state semiconductor film by one irradiation. It is preferably set so as not to cause aggregation or damage to the substrate. These energy amounts vary depending on the material of the semiconductor film, the film thickness, the area of the crystallization region, and the like, and cannot be uniquely determined. Therefore, the amount of energy is appropriately determined according to the embodiment of the method for manufacturing a polycrystalline semiconductor film. It is desirable to use a laser beam having an energy amount. In this embodiment, the energy amount of the second laser 42 is set to 0.1 to 0.4 J / cm ² per one pulse irradiation, and the first laser beam is irradiated with one pulse at a pulse width of 130 μs (full width at half maximum). 0.7 to 1.0 J / cm ² per unit.

  In the schematic graph of FIG. 5, the irradiation timing of the first and second laser beams and the waveform of the laser energy are shown. In this graph, the first laser 51 is irradiated at time t = 0, its pulse width is t2, and the second laser 52 is set to be irradiated at time t1. The irradiation timings of the first and second lasers 51 and 52 are synchronously controlled and oscillated at a constant repetition frequency. Thus, the first laser beam 51 is started to be irradiated at an earlier timing than the second laser beam 52 and the substrate is heated to an appropriate temperature, so that the crystal grain size is remarkably reduced to about 0.1 to 3 μm. Can be increased. This is because the temperature of the substrate and the semiconductor film is kept high, so that the solidification time when the semiconductor film is recrystallized becomes long and the total number of crystal nuclei decreases.

  In the graph of FIG. 6, an example of the crystal grain size range of the longitudinal growth obtained by the temperature of the semiconductor film and the recrystallization at that time is shown. From this graph, it can be seen that the crystal length increases as the temperature of the semiconductor film increases. The temperature of the semiconductor film can be controlled by appropriately changing the energy and pulse width t2 of the first laser 51 and the irradiation timing t1 of the second laser 52 in FIG. Among these, the irradiance of laser light is the easiest to modulate. In order to crystallize efficiently, it is more advantageous to modulate the laser energy while continuously scanning and irradiating at an optimum speed, rather than controlling the scanning speed of the substrate and the irradiation timing of the laser light. Therefore, in this embodiment, a control method is adopted that gives an optimum semiconductor film temperature by modulating only the laser energy for each irradiation.

  Here, as shown in the schematic plan view of FIG. 7A, the area of the region 71 irradiated with the first laser is wide, and the region 72 irradiated with the second laser is narrow. Think about the case. For example, when only the channel region of the TFT is crystallized, the irradiation region of the second laser is limited using a mask or the like. At this time, if the first and second laser energies are always set to be constant, the number of times of irradiation with the first laser varies depending on the position of the semiconductor film, and the substrate temperature varies depending on the position. That is, the region 72 in the first cycle immediately after the start of the laser beam irradiation receives “one first laser beam irradiation 71 and one second laser beam irradiation 72”, but has moved to the next region. As shown in FIG. 7B, the region 74 in the second cycle receives “two first laser light irradiations 71 and 73 and one second laser light irradiation 74”. . FIG. 7C shows that the region 76 in the third cycle receives “three first laser beam irradiations 71, 73, 75 and one second laser beam irradiation 76”. If such a cycle is continued, the first laser beam irradiation is always received three times thereafter.

  In this way, if the region irradiated with the second laser after n cycles of laser irradiation receives “n times of assist laser irradiation and one main laser irradiation”, the substrate is kept at substantially the same temperature. However, the crystal length is shorter in the process up to n cycles than in the subsequent processes. That is, in order to obtain uniform crystal grains, a run area for laser light irradiation is required, resulting in a problem of low productivity. On the other hand, if the first and second laser energies are set large so that a desired crystal length can be obtained in the first cycle and the irradiation is continued, damage to the substrate and aggregation of the semiconductor film may occur.

  The same problem occurs even when the region irradiated with the second laser beam is overlapped and irradiated many times. The multiple irradiation of the second laser beam is known as a method for suppressing the variation in crystal length, and in some cases, the irradiation may be performed several tens of times at the same location. However, when scanning is performed by moving the stage together with irradiation, the crystal lengths in the first several cycles of irradiation and the subsequent cycles of irradiation differ.

  This is a problem inherent to the use of a plurality of lasers having different wavelengths. Even if only the second laser absorbed in the semiconductor film is repeatedly irradiated alone, it does not cause a big problem. This is because the second laser used to absorb the semiconductor film and melt it is injected in a short time with sufficient irradiation energy, so that the cooling and solidification of the semiconductor film is completed in a short time. This is because the influence of heat storage on the substrate by the laser of can be ignored. On the other hand, the first laser absorbed by the insulator substrate needs to raise the temperature of the insulator substrate having a thickness one to three digits larger than that of the semiconductor film, and its pulse width is also set large. The graph of FIG. 8 shows the temperature change at the same location when the same location of the semiconductor film is irradiated with the laser multiple times. From this graph, it can be seen that the effect of heat storage on the substrate by the first laser is large.

  Therefore, the first laser energy is adjusted as shown in the graph of FIG. 9A so that the substrate is kept at the same temperature in all irradiation cycles. That is, the laser energy is gradually decreased from the first shot to several shots, and thereafter irradiation is continued with the same energy amount. In this case, in order to prevent the substrate temperature from continuing to rise due to heat storage on the substrate, the first increase in the substrate temperature due to the first laser light irradiation is the same for any number of cycles. One laser energy may be set. In FIG. 9 (a), scanning is performed at a constant speed and laser irradiation is repeated, so that it is only necessary to make the substrate arrival temperature constant for each irradiation. As a result, it is possible to obtain crystal grains with little variation without reducing the throughput or providing a running region. As shown in FIG. 9A, the second laser energy, the irradiation timing of each laser, the pulse width of the first laser light, etc. are constant, and no special setting or control is required. . The number of shots to which the first laser energy needs to be changed is determined depending on the positions and areas of the first and second laser irradiation regions.

  The same effect as in FIG. 9A can also be obtained by adjusting the second laser energy instead of the first laser energy, as shown in the graph of FIG. 9B. it can. That is, the substrate temperature during the first few shots is low, but since the energy of the first laser for melting the semiconductor film is large, crystal grains having a uniform crystal length can be obtained. However, since the second laser light is directly absorbed by the semiconductor film, it should be noted that if the laser energy is too large, the semiconductor film is damaged or aggregated.

  As described above, the first and second laser energies are optimized by the material of the semiconductor film, the film thickness, the area of the crystallized region, the scanning speed, the cycle of repeated irradiation, and the like. A range exists. It is also possible to set better energy conditions by modulating both the first and second laser energies. For example, as shown in the graph of FIG. 1, it is possible to stably and appropriately crystallize the first and second laser energy by modulating each irradiation.

[Example 2]
In the second embodiment, similarly to the first embodiment, crystallization is performed on the semiconductor device as shown in FIG. By the way, in the crystallization method using laser, as described with reference to FIG. 3, in the crystal growth in the thickness direction from the lower surface to the upper surface of the semiconductor film, adjacent crystals collide with each other during the growth, so Growth is inhibited. On the other hand, there is a method called a lateral growth method for crystal growth of a semiconductor film.

  In the lateral growth method, crystal growth is performed in the lateral direction from the boundary (broken line in FIG. 10A) between the region completely melted by laser irradiation of the semiconductor film and the solid region, and crystal grains in the lateral direction are grown. This is a technique to increase the length. This is because, as shown in the schematic cross-sectional view of FIG. 10A, in the molten region, the temperature is the lowest at the interface with the solid region and crystal nuclei are likely to be generated there. It utilizes the phenomenon that crystal growth proceeds to the center. The schematic plan view of FIG. 10B shows an enlarged view seen from the upper surface of the film crystallized by the lateral growth method. According to such lateral growth, large crystal grains having a crystal length of 0.1 to 2 μm can be obtained, and if the growth direction is made parallel to the channel direction of the TFT, a grain boundary intersecting with the carrier flow can be formed. Since it can be avoided, a larger carrier mobility can be obtained. Further, in the second embodiment, the crystal length grown in one laser shot can be increased to 1 to 10 μm by warming the substrate using the first laser as in the first embodiment.

  As a laser irradiation apparatus for crystallization by lateral growth, the apparatus of FIG. 4 can be used as in the case of the first embodiment, and the first and second laser conditions are the same as in the case of the first embodiment. Can be set to As the first and second laser energies are increased, the laterally grown crystal grains become longer. The schematic plan view of FIG. 11 shows an enlarged view seen from the upper surface of crystal grains grown in the lateral direction. By suitably narrowing the mask width used for the second laser and appropriately selecting the first and second laser energies, lateral growth is performed up to half the mask width as shown in FIG. And the entire inside of the mask can be laterally crystallized. However, if the mask width is too wide, the crystal growth in the lateral direction is slow, so that cooling near the center of the mask proceeds during the lateral growth. Then, a crystal nucleus is generated at the interface between the semiconductor film and the substrate at the center, and crystallization occurs in the vertical direction (thickness direction) from the lower surface side (substrate side) to the upper surface side (front surface side) of the semiconductor film. Begins. The crystal growth in the vertical direction is the same as the crystal growth described in the first embodiment with reference to FIG. As a result, as shown in FIG. 11A, a crystal growth structure in which lateral growth and vertical growth are mixed is obtained.

  The reason why the crystal length due to the lateral growth is remarkably increased by the first laser energy is due to the effect of heating the substrate as in the case of the first embodiment. The graph of FIG. 12 shows the relationship between the substrate temperature and the lateral crystal length. From this graph, it can be seen that when the substrate temperature is about 900 ° C., the crystal length increases abruptly. However, when a glass substrate is used, it is necessary to set the laser energy so that it is heated appropriately in a short time because of heat resistance. Also, it is necessary to appropriately set the number of irradiations and the region so as to prevent the substrate temperature from increasing due to heat storage. Even if the laser energy determined in such a manner is used, there is a problem that the crystal lengths are different for the first few shots after irradiation as follows.

  Here, as shown in FIG. 7A, a case is considered where the region 71 irradiated with the first laser is wide and the region 72 irradiated with the second laser is narrow. Thus, when the crystallization region is limited, if the first and second laser energies are always set to be constant, the number of times the first laser is irradiated differs depending on the position of the semiconductor film, and the substrate temperature depends on the position. Will be different. That is, the region 72 in the first cycle immediately after the start of laser beam irradiation receives “one first laser beam irradiation and one second laser beam irradiation” as shown in FIG. 7B. Thus, the region 74 in the second cycle receives “two times of the first laser light irradiation and one time of the second laser light irradiation”. Further, FIG. 7C shows that the region 76 in the third cycle receives “three times of first laser light irradiation and one time of second laser light irradiation”. If such a cycle is continued, the first laser beam irradiation is always received three times after the third cycle. In this way, depending on the areas and positions of the first and second laser light irradiations, if the substrate receives “n assist laser irradiations and one main laser irradiation” after n cycles, It is kept at about the same temperature. However, in the process up to n cycles, the crystal length is shorter than in the subsequent processes. On the other hand, if the first and second laser energies are set so that the entire mask region is crystallized in the first cycle and irradiation is continued with the energy amount, damage to the substrate and aggregation of the semiconductor film may occur. is there.

  Therefore, as in the case of Example 1, also in Example 2, the first laser energy is shown in FIGS. 9A and 9B so that the substrate is maintained at the same temperature in all irradiation cycles. ), Or modulated as shown in FIG. As a result, crystal growth can be reliably connected without lowering the throughput, and a desired region of the semiconductor film can be single-crystallized without damaging the semiconductor film or the substrate.

[Example 3]
In the third embodiment, similarly to the first embodiment, crystallization is performed on the semiconductor device as shown in FIG. However, in Example 3, a sequential lateral crystallization method (SLS: Sequential Lateral Solidification) that can obtain a longer crystal length than the lateral growth method is used. That is, as shown in the schematic plan view of FIG. 13A, in the semiconductor film grown in the lateral direction by one laser beam irradiation, the laser beam irradiation region is a distance 131 shorter than the crystal length 132. Move and re-irradiate. Then, the crystal grows again in the lateral direction from the interface between the molten region and the solid region of the semiconductor film. At this time, since the crystal growth is inherited with the crystal grain grown by the previous laser irradiation as the nucleus, the crystal length 132 is extended as shown in the schematic plan view of FIG. It becomes possible. In this case, as in the case of the second embodiment, also in the third embodiment, the lateral crystal length grown by one laser irradiation can be increased by using the first laser.

  As a semiconductor device manufacturing apparatus in the third embodiment, a manufacturing apparatus similar to those in the first and second embodiments can be used, but a laser irradiation apparatus as shown in the schematic block diagram of FIG. 14 is used. You can also The laser irradiation apparatus can crystallize a semiconductor film included in the semiconductor device 25, and includes a first laser oscillator 48, a second laser oscillator 42, and a controller 41 that controls these oscillators. Further, it includes variable attenuators 43a and 43b, beam shaping optical systems 81a and 81b, uniform irradiation optical systems 82a and 82b, a field lens 44, an imaging lens 46, a movable sample stage 47, and several mirrors.

  The optical path from the laser beam emitted from the second laser oscillator 42 to the semiconductor device and the apparatus configuration therebetween will be described. First, the laser beam emitted from the second laser oscillator 42 is transmitted by the variable attenuator 43a. The amount of energy is adjusted. The beam shaping optical system 81a and the uniform illumination optical system 82a have a function of shaping the laser light emitted from the second laser oscillator into an appropriate size and illuminating with uniform intensity light. Further, the field lens 44 was installed to form an image side telecentric optical system, and the imaging lens 46 was set so that the laser light was projected at a predetermined magnification.

  The second laser 42 desirably has a wavelength within a range from the ultraviolet region to the visible light region where the absorption coefficient of the solid semiconductor film is large so as not to damage the substrate of the semiconductor device 25. The second laser 42 serves as a main laser for melting the semiconductor film of the semiconductor device 25, and repeats irradiation at a constant oscillation frequency. In the third embodiment, a laser beam obtained by converting the fundamental wave of a YAG laser having a wavelength of 10.6 μm to a wavelength of 532 nm, which is the second harmonic, is used as the second laser 42. The repetition frequency was 1 KHz and the pulse width was 200 ns.

  Compared to excimer lasers, solid lasers do not require gas exchange or laser resonator maintenance, and can improve production efficiency. In this case, it is desirable to perform direct beam shaping using a lens or the like, rather than an imaging method on a semiconductor film using a mask. For example, as a beam shape suitable for the SLS method, as shown in the schematic plan view of FIG. 15A, the beam has a short side H parallel to the relative scanning direction G of the laser. A shape having a long side I in a direction perpendicular to the direction G is conceivable. As the dimensions of this rectangle, it is desirable to set the short side H to 10 to 100 μm and the long side I to be longer than the short side H. This is because, by using the laser irradiation apparatus of the present invention, the lateral growth distance can be obtained from several μm to about several tens of μm, and when the growth is performed by the SLS method, the short side H is set to the lateral growth distance. This is because it is optimal to make it about 2 to 4 times. Also, by making the long side I longer than the short side H, the processing area can be increased and the throughput can be increased. As the light intensity distribution, in order to make the lateral growth distance uniform, it is desirable to obtain a uniform intensity distribution in the cross section in the long side direction. Even if the cross section in the short side direction is not as strict as the cross section in the long side direction, it is desirable that the light intensity distribution be uniform, and a Gaussian distribution or a rectangular distribution be desirable.

  The optical path until the laser light emitted from the first laser oscillator 48 reaches the semiconductor device and the apparatus configuration therebetween will be described. First, the laser light emitted from the first laser oscillator 48 is changed by the variable attenuator 43b. The amount of energy is adjusted, and the energy is adjusted to an appropriate size by the beam shaping optical system 81b and the uniform illumination optical system 82b so as to have a uniform intensity distribution. As a result, the laser beam shape on the semiconductor device 25 becomes, for example, a rectangular shape.

  The first laser 48 is an assist laser that has the effect of being absorbed by the insulator substrate and heating it, and preferably has a wavelength in the range from the visible light range to the infrared range. In the first laser 48, either pulse irradiation or continuous irradiation may be performed, but in Example 3, the glass substrate has a wavelength of 9 to 11 μm that causes absorption, and pulse irradiation is performed at a constant oscillation frequency. A carbon dioxide laser was used. The laser light emitted from the first laser 48 needs to have a uniform intensity distribution over an area larger than the second laser beam region.

The total energy of the first and second lasers 48 and 42 used in the method for crystallizing a semiconductor thin film in Example 3 has an energy amount enough to melt the semiconductor film in a solid state by one irradiation. is doing. However, it is preferable to set the energy amounts of the first and second lasers 48 and 42 so as not to aggregate the semiconductor film or damage the substrate. These energy amounts vary depending on the material of the semiconductor film, the film thickness, the area of the crystallization region, etc., and cannot be uniquely determined. Therefore, the energy amount appropriate for the specific conditions in the crystallization method of the semiconductor film is appropriate. It is desirable to use a laser beam having In the third embodiment, the energy amount of the first laser 48 is 0.4 to 0.7 J / cm ² per one pulse irradiation, and the second laser 42 has a pulse width of 30 to 200 μs (full width at half maximum). In this case, the amount of energy was 0.75 to 1.0 J / cm ² . The irradiation timings and waveforms of the first and second laser beams are the same as those in the case of the first embodiment shown in FIG.

  As an example, the second laser beam 152 is irradiated with a rectangular laser beam cross-sectional shape as shown in FIG. 15A, and the SLS method is used as shown in the schematic plan view of FIG. Consider the case of connecting crystal growth. In FIG. 15B, only the longitudinal length of the rectangular laser beam cross section is shown enlarged for each number of irradiations for easy understanding, and the stage holding the semiconductor device is in relation to the laser light. The relative movement in the direction of arrow G is shown. The first laser beam 151 in FIG. 15 (a) may be irradiated in a wider area including at least the region irradiated with the second laser beam 152. In FIG. The laser beam is not shown. A region 153 is a region where the second laser beam is first irradiated, and the first laser beam is irradiated once. Thereafter, the stage moves, and the next laser light irradiation is performed at a position separated by a distance J shorter than the crystal length, and the first laser is irradiated twice in the region 154. Since the stage scanning speed and the timings of the first and second laser light irradiations are constant, the irradiation region is sent at the same distance J every time. However, since the number of times the first laser beam is irradiated in the regions 153, 154, 155, and 156 is different, the substrate temperature is different, and the length of crystal growth in each shot up to the first few shots is shortened. If the movement distance J is longer than the length of crystal growth in each shot up to the first few shots, there is a possibility that the crystal growth cannot be continued continuously. The area becomes unavailable. In order to prevent this, it is conceivable to shorten the distance J. However, since the stage is continuously scanned and crystallization progresses, the shortening of the distance J leads to a decrease in throughput, resulting in a problem that productivity is deteriorated. . Therefore, it is desirable to solve this problem while keeping the scanning speed constant.

  Therefore, as in the case of Examples 1 and 2, the laser energy that can be easily modulated in this Example 3 so that the substrate can be kept at the same temperature in all irradiation cycles is shown in FIGS. Change as shown in FIG. By doing so, crystal growth can be reliably connected between shots without a reduction in throughput, and a desired region of the semiconductor film can be crystallized without damaging the semiconductor film or the substrate.

  When a solid-state laser is used as the second laser, the influence of heat storage cannot be ignored. A solid-state laser has a longer wavelength than an excimer laser and a longer absorption length in a semiconductor film. For example, the absorption length in a silicon film is 5.5 nm for light with a wavelength of 248 nm, whereas it is 940 nm for light with a wavelength of 532 nm, and heat is transferred to a deeper depth. In addition, since the solid-state laser can increase the repetition frequency, it can be processed at a high speed in order to increase productivity, but it is necessary to consider heat storage of both the solid-state laser and the assist laser. In other words, the temperature of the substrate and the semiconductor film is kept the same in all irradiation cycles by taking into account not only the effect of heat storage due to overlapping laser irradiation but also the effect of heat storage due to the irradiation history so far. The laser energy is gradually reduced to a constant value thereafter. The number of shots at which the first or second laser energy needs to be changed is determined by the position and area of the first and second laser irradiation regions, the respective laser energy, and the structure of the semiconductor device used.

  According to the present invention, by controlling the substrate temperature using two types of lasers, it is possible to obtain a polycrystalline semiconductor film having larger crystal grains as compared with the conventional laser annealing method. It is possible to efficiently crystallize the entire desired region by reducing the variation in length. The crystallized semiconductor film can be preferably used for manufacturing a TFT having a high carrier mobility, for example.

6 is a schematic graph showing adjustment of laser energy during repeated irradiation of first and second laser beams at a predetermined relative scanning speed of a semiconductor film. It is a schematic sectional drawing of the semiconductor device used as the object of this invention. It is a schematic diagram for demonstrating the crystal growth of the vertical direction (film thickness direction) in a semiconductor film. It is a typical block diagram which shows an example of the laser irradiation apparatus which can be used for the manufacturing method of the semiconductor device of this invention. It is a typical graph which shows the irradiation timing of the 1st and 2nd laser beam in this invention. It is a graph which shows the relationship between semiconductor film temperature and longitudinal direction crystal length. It is a typical top view which shows the laser irradiation area | region of the semiconductor film surface in this invention, and the scanning in a repetition irradiation process. It is a typical graph which shows the relationship between the irradiation timing of the 1st laser absorbed by an insulator board | substrate, and semiconductor film temperature. It is a typical graph which shows adjustment of the laser energy in the repetition irradiation process of the 1st and 2nd laser beam. It is a schematic diagram for demonstrating the horizontal direction crystal growth in a semiconductor film. FIG. 4 is a schematic plan view showing a crystal structure grown in the lateral direction. It is a graph which shows the relationship between substrate temperature and lateral direction crystal length. It is a schematic plan view which shows a mode that a horizontal direction crystal growth is carried out in SLS method. It is a typical block diagram which shows the other example of the laser irradiation apparatus which can be used for the manufacturing method of the semiconductor device of this invention. FIG. 4 is a schematic plan view showing a laser irradiation region on a semiconductor film surface and scanning in an irradiation repetition process in the present invention.

Explanation of symbols

  F laser beam irradiation direction, G direction in which the stage holding the semiconductor device moves relative to the laser beam, H short side of the second laser beam cross section, I long side of the second laser beam cross section , J Distance by which the irradiation edge of the second laser moves relatively, 21 Substrate, 22 Underlying insulating film, 23 Amorphous semiconductor film, 24 Laser light, 25 Semiconductor device, 41 Controller, 42 Second laser oscillator 43a, 43b Variable attenuator, 44 field lens, 45 mask, 46 imaging lens, 47 sample stage, 48 first laser oscillator, 51 intensity waveform of the first laser light, 52 intensity waveform of the second laser light 71, first laser irradiation region of the first shot, 72 second laser irradiation region of the first shot, 73, first laser irradiation region of the second shot, 74 Second shot of second laser irradiation region, first third laser irradiation region of third shot 75, second second laser irradiation region of third shot 76, 81a, 81b beam shaping optical system, 82a, 82b uniform illumination optics 131, distance that the second laser irradiation edge moves relatively, 132 crystal length, 151 first laser irradiation area, 152 second laser irradiation area, 153 second laser irradiation area of the first shot, 154 Second laser irradiation region of the second shot, 155 Second laser irradiation region of the third shot, 156 Second laser irradiation region of the fourth shot.

Claims (13)

In the process of crystallizing the semiconductor film formed on the substrate by laser light irradiation,
Irradiating a first laser beam absorbed by the substrate;
Irradiating a second laser beam absorbed by the semiconductor film;
Expanding the crystallized region by scanning the laser beam relative to the semiconductor film and repeating laser irradiation,
A method of manufacturing a semiconductor device, characterized in that laser light intensity is modulated so that a desired temperature is obtained in the substrate and the semiconductor film.   The first laser light has a wavelength within a range from a visible light region to an infrared region, and the second laser light has a wavelength within a range from an ultraviolet region to a visible light region. The manufacturing method of the semiconductor device of description.   3. The semiconductor device manufacturing method according to claim 1, wherein, in the crystallization process, the first laser beam is irradiated ahead of the second laser beam by a predetermined time. Method.   4. The semiconductor device manufacturing according to claim 1, wherein the semiconductor film is moved at a constant speed or a constant step feed relative to the laser beam in the crystallization process. Method.   In the crystallization process, the first laser light is irradiated to an area equal to or larger than a region irradiated with the second laser light, and the semiconductor film is crystallized in the first laser light in the region. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is irradiated at least twice before the process is completed.   The intensity of at least one of the first and second laser beams is gradually increased so that the temperature of the semiconductor film at the time of irradiation with the second laser beam is the same every time the laser irradiation is repeated. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is made constant after being weakened.   The intensity modulation mode for gradually decreasing the intensity of at least one of the first and second laser beams is determined by how many times the first laser beam is irradiated to the same location. Item 7. A method for manufacturing a semiconductor device according to Item 6.   8. The method of manufacturing a semiconductor device according to claim 1, wherein the settings relating to the first and second laser beams are the same every time except for the intensity condition in the process of repeating the laser irradiation. .   9. The method of manufacturing a semiconductor device according to claim 1, wherein in the process of repeating the laser irradiation, a part of the semiconductor film is overlapped with the laser and melted a plurality of times.   A semiconductor device manufacturing apparatus used in the semiconductor device manufacturing method according to claim 1, wherein the first laser oscillator that emits the first laser light and the second laser light are used. A semiconductor device manufacturing apparatus comprising: a second laser oscillator that emits light; and a controller that controls the two laser oscillators.     The controller controls the first and second laser oscillators so that the first laser beam is irradiated in advance for a predetermined time compared to the second laser beam. An apparatus for manufacturing a semiconductor device according to claim 10.   12. The semiconductor device manufacturing apparatus according to claim 10, further comprising a substrate transfer unit so that the semiconductor film is moved at a constant speed or a constant step feed with respect to the laser beam.   The controller sets the emission timings of the first and second laser beams so that the temperature of the semiconductor film is the same each time even when the first laser beam is repeatedly irradiated to the same location multiple times. 13. The semiconductor device manufacturing apparatus according to claim 10, wherein the intensity of the first and second laser beams is modulated.

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