JP2006135232A - Method and apparatus for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein crystal length grown by the influence of substrate heat storage is different for each irradiation shot in a process for repeating crystallization in the irradiation of two kinds of laser beams by an SLS method. <P>SOLUTION: The manufacturing method of a semiconductor device including a process for crystallizing a semiconductor film formed on an insulator substrate with laser beams for crystallization comprises a process for applying first laser beams having a wavelength adsorbed by the insulator substrate or a fused semiconductor film, a process for fusing the semiconductor film by the irradiation of second laser beams having the wavelength adsorbed by the semiconductor film before crystal growth, and a process for expanding a crystallized region by relatively scanning the semiconductor film with laser beams repeatedly. In this case, the substrate scan speed is changed for each irradiation of second laser beams. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a method and apparatus for manufacturing a crystallized semiconductor device using laser light irradiation.

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

  Several methods have been proposed for crystallization of an amorphous semiconductor film, but if a pulse laser is used, a large amount of energy can be input in a short time, and a process at a low temperature can be performed without damaging the substrate. Therefore, the process is being developed. In the crystallization method by laser annealing, control of crystal nuclei and crystal growth rate is important in order to produce a polycrystal with a large grain size. Among such methods, there is a method called a lateral growth method of crystals and a sequential lateral crystallization method (SLS) using the method.

  In the lateral growth method, a semiconductor film formed on a substrate is irradiated with laser light, and when the semiconductor film is completely melted, it is crystallized laterally along the substrate surface from the boundary between the part and the solid part. This is a technique for increasing the crystal length in the direction. That is, the interface between the melted part and the solid part has the lowest temperature in the melted part, and crystal nuclei are likely to be generated there. Therefore, the phenomenon that crystal growth proceeds from the end of the melted area toward the center is utilized. ing.

  FIG. 2A is a schematic enlarged plan view seen from above (film surface normal direction) of the semiconductor film crystallized by the lateral growth method. When the lateral crystal growth starts from both ends of the region 21 melted by the laser light irradiation and the crystals collide with each other at the center portion, the growth is finished, and the entire region 21 is filled with the lateral crystal 22. However, when the energy density of the irradiated laser is small or the width of the irradiated region is too wide, as shown in FIG. The growth of the directional crystal 22 is inhibited. That is, these different-direction crystals 23 are produced as a result of the cooling of the central portion of the region 21 during the growth of the lateral crystal 22, and are generated at the interface between the semiconductor film melted at the central portion and the substrate. The crystal nuclei grown are longitudinal crystal grains grown in the surface direction of the semiconductor film. In this vertical growth, many crystal nuclei are formed and neighboring crystals collide with each other during the growth of these crystal nuclei, so that they cannot grow into large crystal grains. On the other hand, in the lateral growth, a large crystal grain can be obtained at a slow growth rate, and if the growth direction coincides with the channel direction of the TFT, there is no grain boundary perpendicular to the carrier flow and a large movement occurs. The degree is known to be obtained.

  The schematic plan view of FIG. 3 illustrates the SLS method, which is a method for obtaining larger crystal grains. For example, a stage (ie, a semiconductor film) holding a substrate by a distance B shorter than the crystal length A grown as shown in FIG. 3A with respect to the semiconductor film grown in the lateral direction by irradiating the region 31 with laser light. Is moved relative to the laser beam, and the region 33 (indicated by hatching) is again irradiated with the laser beam. Then, when the crystal grows laterally from the interface between the melted part and the solid part of the semiconductor film, the crystal growth proceeds by taking over the crystal grains grown by the previous laser light irradiation as the nucleus, As shown in 3 (b), it is possible to grow the crystal from the crystal width after the previous irradiation. As a result, the lateral crystal length A can be increased. As described above, in the SLS method, the crystal length is extended to a desired length by repeating scanning with laser light irradiation and stage movement (hereinafter referred to as one cycle). In this case, the longer the lateral crystal length by one laser light irradiation, the longer the scanning distance, and the higher the throughput.

From such a viewpoint, Japanese Patent Application Laid-Open No. 11-307450 of Patent Document 1 proposes a crystallization process using a plurality of laser oscillators having different wavelengths. In this process, an excimer laser having a wavelength absorbed by the semiconductor film and a carbon dioxide laser as an auxiliary beam having a wavelength absorbed by the substrate are used to grow the crystal while heating the substrate. By doing so, it is taught that large crystal grains can be obtained without damaging the substrate. In this case, however, a new problem arises. That is, in relation to the heating by the auxiliary beam, the annealing conditions that were appropriate at the start of annealing gradually become excessive.
JP-A-11-307450

  The inventors of the present application also appropriately heat the substrate by the lateral growth method using a plurality of lasers as described above, and can extend the crystal length by 5 to 10 times compared to the lateral growth by the conventional single laser. confirmed. Furthermore, the assist laser for heating the substrate is irradiated in advance for a certain time before the main laser for melting the semiconductor film, thereby reducing the total number of crystal nuclei when the semiconductor film is recrystallized. It was found that crystal grains were obtained. By using large crystal grains in the channel portion of the TFT, the electrical characteristics can be improved, for example, the carrier mobility can be increased several times, and the characteristic variation between elements can be reduced compared to the case of conventional vertical crystal growth. did it. In addition, by extending the crystal length, the throughput time can be shortened, and the merit of improving productivity can be obtained.

  Further, in Patent Document 1, an excimer laser is used as a main laser for melting a crystal. However, an excimer laser is a gas laser, which requires a great deal of cost for gas exchange and maintenance of a laser resonator. Have. Therefore, the inventors of the present application tried to perform crystallization by lateral growth using a solid laser as a main laser.

  The crystal length of lateral growth is sensitive to the temperature of the semiconductor film at the time of melting, and the temperature depends on the energy of the main laser and assist laser, the pulse width of the assist laser, and the irradiation start time (irradiation timing) of the main laser. Must be controlled. Here, in the SLS method, since the same portion is irradiated with the laser beam a plurality of times, there is a problem that the substrate temperature gradually rises due to heat accumulation in the substrate and the resulting crystal length changes. In addition, the semiconductor film may be altered or ablated, or the substrate may be damaged.

  In order to prevent such problems, even if the appropriate conditions are set in consideration of the effect of heat storage, the crystal length varies in the region near the start of laser light irradiation, and crystal growth may be continued sequentially. In some cases, this was not possible, and problems related to the nature of the crystallization method by the SLS method occurred.

  FIG. 4 shows the irradiation area of the main laser in a schematic plane in order to explain this problem. This figure shows a case where the width of the irradiation region of the main laser is A and the lateral crystal is grown to the center. That is, the crystal length when the main laser is irradiated once is A / 2. Then, in order to reliably connect the crystal growth, 1/4 of the width A is set as the substrate feed distance (B in FIG. 4), and scanning is performed at a constant speed while sequentially irradiating the laser beam, and four lasers are performed. An example in which a crystal having a length A is formed by light irradiation is shown. The assist laser is irradiated to a range that covers the irradiation region of the main laser. Here, it is assumed that the same region as the main laser is irradiated with pulses or continuously. The region 41 irradiated with the laser light in the first cycle receives only one laser beam irradiation, whereas the region 42 in the second cycle moved to the next region receives two laser beam irradiations. Become. It is shown that the region 43 in the third cycle is irradiated with the laser beam three times, and the region 44 in the fourth cycle is irradiated with the laser beam four times. The area after the fourth cycle is always subjected to four times of laser beam irradiation. As described above, if the laser light irradiation is performed n times after n cycles from the relationship between the irradiation region of the main laser and the assist laser and the position on the semiconductor film, the substrate is maintained at substantially the same temperature after the n cycles. However, since only 1 to (n-1) shots are irradiated with the laser beam in the previous cycle, the crystal length to grow at a low substrate temperature is shortened.

  Such heat storage on the substrate is a problem inherent to using a plurality of lasers having different absorption lengths relative to the substrate or the semiconductor film, and the main laser (eg, excimer laser) absorbed by the semiconductor film is irradiated alone. Repeating this will not be a big problem. This is because the excimer laser used for melting inputs sufficient irradiation energy in a short time, so that the cooling and solidification time can be shortened and the influence of heat storage on the substrate can be ignored. On the other hand, the assist laser absorbed by the insulator substrate needs to raise the temperature of the substrate having a thickness that differs by 1 to 3 digits compared to the semiconductor film, and the pulse width is also increased by 3 digits or more compared to the excimer laser. The schematic graph of FIG. 5 shows the temperature change of the semiconductor film when the same location is irradiated with the assist laser light a plurality of times. As can be seen from this graph, although depending on the repetition frequency of the assist laser light irradiation, the influence of the heat storage becomes a magnitude that cannot be ignored.

  Furthermore, when the main laser is changed from an excimer laser to a solid-state laser, the effect of this heat storage becomes large. 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 to the silicon film is 5.5 nm for light having a wavelength of 248 nm, whereas the absorption length is 940 nm for light having a wavelength of 532 nm, and heat is transferred to a deep depth. In addition, since the solid-state laser can increase the repetition frequency, the heat storage of both the solid-state laser and the assist laser cannot be ignored when high-speed processing is performed to increase productivity. In other words, it is no longer true that “if the laser beam irradiation is performed n times after n cycles, the substrate is maintained at substantially the same temperature after the n cycles” described with reference to FIG. The growth crystal length does not become constant until a constant temperature is reached by balancing the amount of input and diffusion.

  In such a case, the region until the substrate temperature becomes constant and the growth crystal length of the semiconductor film can be stably and reliably connected by the SLS method is considered as a laser beam irradiation run-up region, This run-up region is not used for device fabrication, but only the uniform crystal length portion of the semiconductor film after the substrate reaches a certain temperature must be used. That is, it is necessary to design so that no element is formed in the regions 41, 42, and 43 in FIG. Recently, however, demands for miniaturization of liquid crystal display panels have increased, and in many cases, a circuit such as a driver is incorporated into the end region of the substrate by reducing the area of the frame portion. In order to crystallize the entire semiconductor film on the substrate, it is necessary to reduce the running region as much as possible.

  In view of the above problems, an object of the present invention is to provide a method and apparatus for crystallizing the entire desired area of a semiconductor film without providing a run-up region.

  According to the present invention, in a semiconductor device manufacturing method including a process of crystallizing a semiconductor film formed on an insulator substrate by laser light irradiation, the semiconductor device has a wavelength that is absorbed by the insulator substrate or the molten semiconductor film. A step of irradiating the first laser light; a step of crystal growth after melting the semiconductor film by irradiation of a second laser light having a wavelength absorbed by the semiconductor film; and And a step of enlarging the crystallized region by repeating laser beam irradiation, and the substrate scanning speed is changed every time the second laser beam is irradiated.

  The first and second laser beams preferably have a wavelength in the range from the ultraviolet to the visible light region. In addition, the first laser beam is irradiated for a predetermined time before the second laser beam, and the first laser beam is irradiated for a predetermined time after the irradiation of the second laser beam is completed. It is preferable that the irradiation is completed.

  The second laser beam has an energy density per pulse that can melt the semiconductor film over the entire thickness direction, and the first laser beam has an energy density per pulse that cannot melt the semiconductor film over the entire thickness direction. It is preferable. The first laser beam is irradiated to the same area as or larger than the region irradiated with the second laser beam, and in the process where the semiconductor film is repeatedly irradiated with the laser beam, a part of the semiconductor film is overlapped with the laser beam. Irradiation is preferred. In the process in which the semiconductor film is repeatedly irradiated with the laser beam, the intensity of the first and second laser beams can be constant.

  The substrate is moved relative to the second laser light by a feeding distance shorter than the crystal length grown when the semiconductor film is irradiated with the second laser light. The moving distance can be increased. The semiconductor film may be made constant after the substrate scanning speed is gradually increased in accordance with the crystal length grown when the second laser light is irradiated to the semiconductor film. The semiconductor film may be made constant after the substrate scanning speed is gradually increased according to the crystal length grown when the second laser light is irradiated to the semiconductor film, and the pulse width of the first laser light may be made constant after being gradually narrowed. . The substrate scan speed is gradually increased in accordance with the crystal length grown when the semiconductor film is irradiated with the second laser beam, and then constant, and the second laser beam is irradiated after the first laser beam is irradiated. It may be made constant after changing the time until. The semiconductor film is made constant after the substrate scanning speed is gradually increased according to the crystal length grown when the second laser light is irradiated, and the pulse width of the first laser light is made constant after being gradually narrowed, Furthermore, it may be combined with changing the time from the irradiation of the first laser light to the irradiation of the second laser light and then making it constant.

  A semiconductor device manufacturing apparatus used in the semiconductor device manufacturing method as described above includes a first laser oscillator, a second laser oscillator, and a movable sample stage, and controls the driving of these two laser oscillators and the sample stage. May also include a controller. Note that the sample stage is made constant after the scanning speed is gradually increased from the start of driving, and at least one of the irradiation timing and pulse width of the first and second laser oscillators is controlled synchronously with the sample stage driving. The controller preferably controls to execute at least one of them.

  According to the present invention, in crystallization of a semiconductor film on a substrate, a crystal longer than a lateral crystal formed by laser light irradiation using a single laser oscillator can be obtained, and the effect of heat storage on the substrate can be obtained. In consideration of the above, it is possible to efficiently crystallize the entire desired area.

  The present invention provides a laser light irradiation control method for crystallizing the entire desired area of a semiconductor film without providing the above-described run-up region. There are two methods for this, one is a method in which the temperature of the semiconductor film is constantly controlled so that a certain crystal length is always obtained in each irradiation cycle, and the other is a method in which the crystal length is changed in each irradiation cycle. This is a method of controlling the irradiation position of the next cycle so as to follow even if different. For this purpose, parameters that can be controlled include the energy of the main laser and the assist laser, the pulse width of the assist laser, the irradiation start time (irradiation timing) of the main laser, and the scanning speed of the semiconductor film.

  In scanning here, the stage on which the semiconductor film is placed may move relative to the fixed laser beam irradiation region, and conversely, the laser beam (that is, the irradiation region) moves because the semiconductor film is fixed. It may be possible to move the two at the same time. In such relative movement, it may be possible to continue to move at a constant speed. After moving at a certain speed and stopping at a predetermined position, the laser beam is irradiated and further moved and then stopped before the next laser. It may be irradiated with light.

  The scanning speed is related to the time taken to crystallize the desired area, i.e. directly related to the throughput. Therefore, it is desirable that the scanning speed be constant at the fastest scanning speed determined by the oscillation frequency of the main laser and the assist laser and other factors. In consideration of positional accuracy in movement, it is preferable to use a stage drive system that continues scanning at a certain speed, rather than a method that repeats scanning and stopping.

  Based on the above considerations, as a method to solve the problem of the short laterally grown crystal length of the first run-up region, the feed distance is shortened immediately after laser light irradiation is started, and the distance is gradually lengthened. Then, it is proposed to control the scanning speed of the stage so as to make the scanning speed constant. By controlling in this way, the temperature difference of the semiconductor film between each laser beam irradiation can be reduced, and the feeding distance can be determined according to the crystal length formed. Either of the methods can be realized. By gradually increasing the scanning speed, it is possible to realize stable rising of laser oscillation and stage driving. Then, after a certain cycle, it is designed to be constant at an optimum scanning speed, and crystallization is repeated with high productivity. However, the irradiation region needs to be aligned with a desired region of the semiconductor film at the moment of irradiation with the main laser, and an optimum crystal cannot be obtained simply by increasing the scanning speed. The change in scanning speed must be determined by the crystal length of the lateral crystal, and it is necessary to set the irradiation start time (irradiation timing) of the main laser and the assist laser.

  FIG. 6 is a schematic cross-sectional view of a semiconductor device irradiated with laser light in the present invention. As shown in this figure, a base device insulating film 62 and an amorphous semiconductor film 63 are laminated on a substrate 61 to form a semiconductor device 65. The substrate 61 is preferably insulative, and a glass substrate, a quartz substrate, or the like can be used, but a glass substrate is preferably used from the viewpoint of being inexpensive and easily obtaining a large-area substrate.

  As the base insulating film 62, 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. The base insulating film 62 can be formed by depositing a raw material compound by plasma enhanced chemical vapor deposition (PECVD), vapor deposition, sputtering, or the like.

  The semiconductor film 63 can be deposited by plasma enhanced chemical vapor deposition (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 63 is not particularly limited as long as it is a conventionally known material that 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 63 is not limited to an amorphous material such as amorphous silicon, and the semiconductor film 63 before being crystallized by the laser light irradiation 64 may be a crystalline semiconductor film such as a microcrystal or a polycrystal. The material of the semiconductor film 63 is not limited to a material made only of silicon, and may be a material mainly composed of silicon containing other elements such as germanium.

  FIG. 7 shows a schematic block diagram of a semiconductor device manufacturing apparatus used in the present invention. The laser light irradiation apparatus can crystallize the semiconductor film 63 included in the semiconductor device 65, and includes a first laser oscillator 79, a second laser oscillator 72, and a controller 71 that controls these oscillators. Yes. The controller 71 also controls driving of the sample stage 83. The amount of energy of the laser light emitted from the second laser oscillator 72 is adjusted by the variable attenuator 73. The beam shaping optical system 74 and the uniform illumination optical system 75 function to shape the laser light emitted from the second laser oscillator to an appropriate size and illuminate it with light of uniform intensity. Further, a field lens 76 is installed to form an image side telecentric optical system, and the projection lens 78 is set so that the laser light is projected onto the semiconductor device 65 at a predetermined magnification. An example of the shape of the laser beam on the semiconductor device 65 may be a substantially rectangular shape.

  FIG. 8 shows an example of the cross-sectional shape of the laser beam and the light intensity distribution in a cross section parallel to each side direction. In the cross section of the laser beam used in the present invention, it is desirable to set the width M to 10 to 100 μm and the length L to be longer than the width M. This is because the lateral growth distance can be obtained from several μm to several tens of μm by using the laser beam irradiation apparatus of the present invention. When crystal growth is connected by the SLS method, the lateral growth distance is set as the width M. It is because it is appropriate to make it about 2 to 4 times. Further, by making the length L longer than the width M, the processing area can be increased and the throughput can be increased. Here, the rectangular width M is a length along the scanning direction of the laser beam, and the rectangular length L is a length in a direction perpendicular to the scanning direction. The intensity distribution is desirably uniform in the cross section parallel to the length L direction in order to make the lateral growth distance uniform. The cross-section parallel to the width direction M is desirably a uniform distribution, even if it is not as strict as the cross-section in the length direction, and is preferably a Gaussian distribution or a rectangular distribution.

  The amount of energy of the laser light emitted from the first laser oscillator 79 is adjusted by the variable attenuator 80, and is shaped into an appropriate size by the beam shaping optical system 81 and the uniform illumination optical system 82 to obtain a uniform intensity distribution. Adjusted to have. Thereby, the laser beam shape on the semiconductor device 65 becomes, for example, a rectangular shape. The first laser beam region needs to have an area larger than that of the second laser beam region and have a uniform light intensity distribution.

  Although the block diagram of FIG. 7 is depicted in a simplified manner, a mirror can be appropriately provided in the laser beam path, and the laser beam can be folded. There are no restrictions on the location and quantity of these mirrors, and they can be appropriately arranged according to the optical design and mechanism design of the laser irradiation apparatus. The method of shaping the beam cross section into a rectangular shape is not limited, and a diffractive optical element or an aspherical optical element can be used.

  The first laser is an assist laser that has the effect of being absorbed by an insulator substrate or a melted semiconductor film and heating them, and preferably has a wavelength from visible light to infrared. The first laser may be either pulsed irradiation or continuous irradiation, but in this embodiment, a carbon dioxide gas laser having a wavelength of 9 to 11 μm absorbed by the glass substrate and continuously irradiated is used.

  The second laser preferably has a wavelength in the ultraviolet to visible light range where the absorption coefficient of the solid semiconductor film is large so as not to damage the substrate. In addition, since the second laser serves as a main laser for melting the semiconductor film, it is necessary to repeat pulse irradiation at a constant oscillation frequency. In this embodiment, a laser beam obtained by converting a fundamental wave of a YAG laser having a wavelength of 10.6 μm into a second harmonic wave having a wavelength of 532 nm is used. The repetition frequency can be 1 KHz and the pulse width can be 200 ns.

With respect to one irradiation of the laser beam, it has an energy amount capable of melting the semiconductor film in the solid state by the sum of the energy of the first and second laser beams, and the semiconductor film is aggregated or the substrate is damaged. It is preferable to set the amount of energy so as not to give it. These amounts of energy vary depending on the type of material of the semiconductor film, the thickness of the semiconductor film, the area of the crystallization region, etc., and cannot be uniquely determined. Therefore, in the method of manufacturing a semiconductor film of the present invention, It is desirable to use a laser beam having an appropriate amount of energy appropriately according to the embodiment. In this embodiment, the second laser energy is 0.4 to 0.7 J / cm ² , the pulse width of the first laser beam is 30 to 200 μs (full width at half maximum), and the energy amount is 0.75 to 1.0 J. / Cm ² .

  The schematic graph of FIG. 1 shows the irradiation timing and scanning speed of the first and second laser beams. This graph shows an example in which the first and second laser light irradiations are performed four times after the fourth cycle with respect to the irradiation regions and positions of the first and second laser light. In the conventional method, laser light irradiation is repeated at a constant feed distance (a constant scanning speed). However, the present invention is characterized in that a feed distance is set according to the crystal length of lateral growth. That is, as shown in the schematic plan view of FIG. 9, at least the relationship of B1 <B2 <B3 <B4 is satisfied.

More specifically, when the first shot of the second laser is irradiated, the lateral crystal length is L1 (μm), and in order to reliably connect the crystal growth, the feed distance B1 should be shorter than L1. Good. When the second laser light is irradiated at a constant period of frequency f (Hz), the stage speed v1 (μm / s) is v1 = B1 / f
It becomes.

In the second cycle, the lateral crystal length L2 has a relationship of L2> L1, and the feed distance B2 is also set to satisfy B2> B1. Therefore, the stage speed v2 is v2 = B2 / f
Thus, since v2> v1, the speed is increased.

Similarly, in the third cycle, v3 = B3 / f
And in the fourth cycle, v4 = B4 / f
It is. After the fifth cycle, the speed change is not as great as before, but the speed change amount is gradually decreased to be constant. By increasing the feed distance for each cycle in this way, the area where the laser beam irradiation overlaps can be reduced as compared with the case where the feed distance is fixed, and the influence of heat storage is further reduced. Here, the first and second lasers are controlled synchronously, and the oscillation frequency, pulse width, and irradiation timing of the second laser (delay time from the first laser light irradiation to the second laser light irradiation) are constant. Was set. Although the scanning speed is initially slowed down, the steady state speed, which is constant, is faster than the conventional method, so that the throughput can be improved. An appropriate change in scanning speed (ie acceleration) can be used by back-calculating the change in crystal length from cycle to cycle.

  On the other hand, in the method of changing the irradiation timing of the second laser light in accordance with the scanning speed, the timing of the trigger pulse that promotes the oscillation of the laser light may be set appropriately. In the schematic graph of FIG. 10, the irradiation timing and scanning speed of the first and second laser beams are shown. In this case, since the second laser light irradiation is performed at a timing when the semiconductor film is appropriately heated, as shown in the schematic plan view of FIG. Grains can be obtained. Such control is desirable when it is desired to reflect the irradiation timing more appropriately, such as when the crystal length is controlled by monitoring the temperature of the semiconductor film and reflecting the result.

The first cycle is the first laser beam irradiation, and since it takes time until the semiconductor film is heated appropriately, the feed distance B is scanned over time P1. That is,
v1 = B / P1
It is.

In the second cycle, it is assumed that the stage speed v2 is v2 = B / P2 assuming that it is appropriately heated at time P2.
Since P1> P2, v2> v1, and the speed is increased.

  Thereafter, similarly, the second laser beam irradiation timing P is obtained by calculating backward from the desired crystal length, and an appropriate scanning speed may be determined from this.

  The change in the scanning speed shown here is an example and is not limited. That is, the above-described example explains the concept of changing the scanning speed in order to surely connect crystals in the SLS method.

  In the second embodiment, the first laser beam is irradiated with pulses at a constant oscillation frequency. Since the semiconductor device, the manufacturing method thereof, and the laser irradiation apparatus in this case are the same as those in the first embodiment, description thereof will not be repeated. However, as the first laser, a carbon dioxide gas laser having a wavelength of 9 to 11 μm absorbed by the glass substrate and irradiating with a pulse at a constant oscillation frequency is used. The pulse width depends on the oscillation frequency of the laser, but an optimum value for the semiconductor film can be adopted within a range of 10 μs to 100 ms.

  The schematic graphs of FIGS. 12 and 13 show the irradiation timings and waveforms of the first and second laser beams. As shown in FIG. 13, the first laser 121 was started to irradiate at time t = 0, its pulse width was t2, and the second laser 122 was set to irradiate at time t1. . In this way, irradiation of the first laser beam 121 is started at an earlier timing than the second laser beam 122. By continuing irradiation even after the semiconductor film is melted by the second laser beam irradiation, the semiconductor film is regenerated. The total number of crystal nuclei when crystallizing is reduced and the solidification time is lengthened, so that a polycrystal having a large grain size can be obtained. Thus, the irradiation timings of the first and second lasers are synchronously controlled and oscillated at a constant repetition frequency. With these laser light irradiations as one cycle, the laser scans the semiconductor film and moves by a predetermined feeding distance, and then performs the next laser light irradiation. By repeating this a desired number of times, crystal grains having a certain length can be obtained by the SLS method.

  This is the same effect as described in the first half of Example 1, and the crystal region to be formed is the same as that shown in FIG. On the other hand, excessive energy input can be prevented by using the first laser beam for pulse irradiation.

  The laser irradiation shown in the schematic graph of FIG. 14 can be proposed as a further improvement of the laser irradiation of FIG. In this case, the first and second laser beams are irradiated at a constant frequency, but by gradually reducing the pulse width of the first laser as the scanning speed increases, excessive substrate heating is prevented and the effect of heat storage is reduced. Can be small. Further, since the scanning speed can be made faster and constant, the throughput is also improved.

  Conversely, when it is difficult to change the scanning speed abruptly, as another improvement method, as shown in the schematic graph of FIG. There are ways to change. In this case, slowing the change in the scanning speed causes a decrease in throughput, and in order to prevent this, the second laser beam irradiation timing is advanced simultaneously with the speed change, that is, as shown in FIG. Time t1 is shortened for each cycle. And in the case of FIG. 15, there exists an advantage that the irradiation frequency of a 1st laser becomes fixed and it is easy to irradiate a 1st laser.

  The laser irradiation method shown in the schematic graph of FIG. 16 is also configured so that both the pulse width of the first laser beam and the irradiation timing of the second laser beam are modulated by combining the ideas of FIG. 14 and FIG. Though conceivable, it is desirable to use a control method that can operate most stably in consideration of the controllability of the constituent devices and each laser among the laser irradiation methods proposed in the present invention.

  According to the present invention, it is possible to provide a method and an apparatus for crystallizing the entire desired area of a semiconductor film, and the crystallized semiconductor crystallized region can be preferably used as a TFT formation region, for example.

It is a schematic graph which shows an example of the time change of the irradiation intensity | strength, irradiation timing, and scanning speed in the repetition irradiation process of the 1st and 2nd laser beam. It is a typical enlarged plan view for demonstrating lateral direction crystal growth. It is a typical top view for demonstrating the method of connecting a horizontal direction crystal growth by SLS method. It is a schematic plan view illustrating scanning of laser irradiation at a constant speed. It is a schematic graph which shows the relationship between the timing of irradiation of a 1st laser, and semiconductor film temperature. It is a typical sectional view of a semiconductor device irradiated with a laser in the present invention. It is a block diagram which shows the laser irradiation apparatus which can be used for the manufacturing method of a semiconductor device in this invention. It is a schematic diagram which shows the shape and intensity distribution of the irradiation area | region of the 2nd laser beam which can be used for the manufacturing method of a semiconductor device in this invention. FIG. 2 is a schematic plan view showing a semiconductor film region crystallized by the laser irradiation method of FIG. 1. It is a schematic top view which shows another example of the time change of the irradiation intensity | strength, irradiation timing, and scanning speed in the repetition irradiation process of the 1st and 2nd laser beam. FIG. 11 is a schematic plan view showing a semiconductor film region crystallized by the laser irradiation method of FIG. 10. It is a schematic graph which shows another example of the time change of the irradiation intensity | strength in the repetition irradiation process of a 1st and 2nd laser beam, irradiation timing, and a scanning speed. It is a schematic graph which shows an example of the irradiation timing of a 1st and 2nd laser beam, and a waveform. It is a schematic graph which shows another example of the time change of the irradiation intensity | strength in the repetition irradiation process of a 1st and 2nd laser beam, irradiation timing, and a scanning speed. It is a schematic graph which shows another example of the time change of the irradiation intensity | strength in the repetition irradiation process of a 1st and 2nd laser beam, irradiation timing, and a scanning speed. It is a schematic graph which shows another example of the time change of the irradiation intensity | strength in the repetition irradiation process of a 1st and 2nd laser beam, irradiation timing, and a scanning speed.

Explanation of symbols

  A Crystal length in the transverse direction, B feed distance, B1 1st cycle feed distance, B2 2nd cycle feed distance, B3 3rd cycle feed distance, B4 4th cycle feed distance, F laser light irradiation direction, L laser The length in the direction perpendicular to the scanning direction in the beam irradiation region, the length in the direction parallel to the scanning direction in the M laser beam irradiation region, the irradiation timing of the second laser in the first cycle of P1, the second in the second cycle of P2 Irradiation timing of the second laser, irradiation timing of the second laser in the third cycle of P3, irradiation timing of the second laser in the fourth cycle of P4, 21 laser light irradiation region, 22 region crystallized by lateral growth, 23 vertical Area crystallized by directional growth, 31 Main laser light irradiation area, 32 Assist laser light irradiation Area, 33 main laser light irradiation area after scanning, 34 assist laser light irradiation area after scanning, 41 1st cycle laser light irradiation area, 422 2nd cycle laser light irradiation area, 433 3rd cycle laser light irradiation Area, 44 4th cycle laser light irradiation area, 61 substrate, 62 base insulating film, 63 amorphous semiconductor film, 64 laser light, 65 semiconductor device, 71 controller, 72 second laser oscillator, 73 variable attenuator, 74 beam shaping optical system, 75 uniform illumination optical system, 76 field lens, 78 projection lens, 79 first laser oscillator, 80 variable attenuator, 81 beam shaping optical system, 82 beam intensity uniformizing optical system, 83 sample stage, 121 intensity waveform of the first laser, 122 intensity waveform of the second laser.

Claims (13)

In a semiconductor device manufacturing method including a process of crystallizing a semiconductor film formed on an insulator substrate by laser light irradiation,
Irradiating a first laser beam having a wavelength absorbed by the insulator substrate or the molten semiconductor film;
A step of crystal growth after melting the semiconductor film by irradiation with a second laser beam having a wavelength absorbed by the semiconductor film;
Expanding the crystallized region by scanning the semiconductor film relative to the laser beam and repeating the laser beam irradiation,
A method of manufacturing a semiconductor device, wherein the substrate scanning speed is changed for each irradiation of the second laser beam.   The first laser light has a wavelength in a range from ultraviolet to visible light, and the second laser light has a wavelength in a range from visible light to infrared. Semiconductor device manufacturing method.   The first laser beam is irradiated for a predetermined time before the second laser beam, and the first laser beam is irradiated for a predetermined time after the irradiation of the second laser beam is completed. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the irradiation is completed later.   The second laser beam has an energy density per pulse that can melt the semiconductor film over the entire thickness direction, and the first laser beam per pulse that cannot melt the semiconductor film over the entire thickness direction. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device has an energy density.   The first laser light is irradiated to an area equal to or larger than a region irradiated with the second laser light, and a part of the semiconductor film overlaps in the process of repeatedly irradiating the semiconductor film with the laser light. The method of manufacturing a semiconductor device according to claim 1, wherein the laser beam is irradiated a plurality of times.   6. The method of manufacturing a semiconductor device according to claim 1, wherein intensities of the first and second laser beams are constant in a process in which the semiconductor film is repeatedly irradiated with a laser beam. .   The substrate is moved relative to the second laser beam by a feeding distance shorter than a crystal length grown when the second laser beam is irradiated onto the semiconductor film, and the second laser beam 7. The method of manufacturing a semiconductor device according to claim 1, wherein the moving distance is gradually increased for each irradiation.   6. The semiconductor film according to claim 1, wherein the semiconductor film is made constant after the substrate scanning speed is gradually increased in accordance with a crystal length grown when the second laser light is irradiated onto the semiconductor film. Semiconductor device manufacturing method.   The semiconductor film is made constant after the substrate scanning speed is gradually increased in accordance with the crystal length grown when the second laser light is irradiated to the semiconductor film, and is made constant after the pulse width of the first laser light is gradually narrowed. 6. The method of manufacturing a semiconductor device according to claim 1, wherein:   The semiconductor film is made constant after the substrate scanning speed is gradually increased in accordance with the crystal length grown when the second laser light is applied to the semiconductor film, and the second laser light is applied after the first laser light is applied. 6. The method of manufacturing a semiconductor device according to claim 1, wherein the time until the laser beam is irradiated is made constant after being changed.   The semiconductor film is made constant after the substrate scanning speed is gradually increased in accordance with the crystal length grown when the second laser light is irradiated to the semiconductor film, and is made constant after the pulse width of the first laser light is gradually narrowed. And further, making the time constant after changing the time from the irradiation of the first laser beam to the irradiation of the second laser beam. 6. A method for producing a semiconductor device according to any one of 5 above.   12. A semiconductor device manufacturing apparatus for use in the method of manufacturing a semiconductor device according to claim 1, comprising a first laser oscillator, a second laser oscillator, and a movable sample stage. An apparatus for manufacturing a semiconductor device, comprising a controller for controlling two laser oscillators and driving of a sample stage.   The sample stage is made constant after the scanning speed is gradually increased from the start of driving, and at least one of the irradiation timing and pulse width of the first and second laser oscillators is controlled synchronously with the sample stage driving. 13. The semiconductor device manufacturing apparatus according to claim 12, wherein the controller controls to execute at least one of them.

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