JP2004289140A - Laser irradiation device, laser irradiation method, and manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making the whole surface of irradiation traces a more uniform crystalline state, by making a crystal inferior region formed in both ends of a large grain size region as small as possible, by suppressing the ununiformity in the crystalline state due to the diffraction fringe, and by increasing grain size in the whole surface of laser irradiation traces. <P>SOLUTION: This device comprises a first laser oscillator which outputs a wavelength below visible light, a means for processing a first laser beam emitted from the first laser oscillator into a long beam in an irradiation surface, and a means for cutting off the both ends in the major axis direction of the long beam at the front side of the irradiation surface. The device further comprises a second laser oscillator which outputs a fundamental wave, a means for irradiating a second laser beam emitted from the second laser oscillator simultaneously with the first laser beam in the range where the first laser beam is irradiated in the irradiation surface, and a means for relatively moving the irradiation surface to the first laser beam and the second laser beam. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for irradiating a laser beam, a laser irradiating apparatus for performing the method (an apparatus including a laser and an optical system for guiding a laser beam output from the laser to an object to be irradiated), and a method for manufacturing a semiconductor device. .

In recent years, techniques for crystallizing an amorphous semiconductor film formed on an insulating substrate such as glass to form a semiconductor film having a crystal structure (hereinafter, referred to as a crystalline semiconductor film) have been widely studied. As a crystallization method, a thermal annealing method using a furnace annealing furnace, an instantaneous thermal annealing method (RTA method), a laser annealing method, and the like have been studied. Crystallization can be performed by combining any one or a plurality of these methods.

A crystalline semiconductor film has much higher mobility than an amorphous semiconductor film. Therefore, a thin film transistor (TFT) is formed using this crystalline semiconductor film, and for example, an active matrix type in which a TFT for a pixel portion or a TFT for a pixel portion and a driver circuit is formed over one glass substrate. Used in liquid crystal display devices and the like.

Usually, in order to crystallize an amorphous semiconductor film in a furnace annealing furnace, a heat treatment at 600 ° C. or more for 10 hours or more was required. The substrate material applicable to this crystallization is quartz, but the quartz substrate is expensive, and it is very difficult to process a large area in particular. One of the means for increasing the production efficiency is to increase the area of a substrate. This is the reason why research on forming a semiconductor film on a glass substrate that is inexpensive and easily processed into a large-area substrate is performed. In recent years, the use of a glass substrate having a size exceeding 1 m on one side has been considered.

As one example of the above research, the thermal crystallization method using a metal element disclosed in Japanese Patent Application Laid-Open No. Hei 7-183540 makes it possible to lower the crystallization temperature, which has conventionally been considered a problem. According to this method, a trace amount of an element such as nickel, palladium, or lead is added to an amorphous semiconductor film, and then a crystalline semiconductor film can be formed by heat treatment at 550 ° C. for 4 hours. If the temperature is 550 ° C., the temperature is not higher than the strain point temperature of the glass substrate, so that there is no risk of deformation or the like.

On the other hand, in the laser annealing method, high energy can be selectively and locally applied to the semiconductor film without increasing the temperature of the substrate so much that the substrate is hardly thermally damaged. Therefore, this technology has attracted attention because it can be used not only for glass substrates having a low strain point temperature but also for plastic substrates and the like. Further, the laser annealing method can significantly reduce the processing time as compared with the annealing method using radiation heating or conduction heating.

Here, the laser annealing method refers to a technique for recrystallizing a damaged layer or an amorphous layer formed on a semiconductor substrate or a semiconductor film, or a technique for crystallizing an amorphous semiconductor film formed on a substrate. pointing. It also includes techniques applied to planarization and surface modification of semiconductor substrates or semiconductor films.

One example of the laser annealing method is that a pulsed laser beam represented by an excimer laser is processed by an optical system so that a square spot of several cm square or a linear shape having a length of 100 mm or more is formed on an irradiation surface. Is performed by moving the irradiation position relative to the irradiation target. Here, the term “linear” does not mean “line” in a strict sense, but means a rectangle (or a long ellipse) having a large aspect ratio. For example, an aspect ratio of 2 or more (preferably 10 to 10000) refers to a laser beam (rectangular beam) having a rectangular shape on the irradiation surface. Note that the linear shape is used to secure an energy density for performing sufficient annealing on the irradiation target, and sufficient annealing can be performed on the irradiation target even in a rectangular shape or a planar shape. If it is, it does not matter.

The crystalline semiconductor film thus manufactured is formed by assembling a plurality of crystal grains, and the positions and sizes of the crystal grains are random. The TFT manufactured on the glass substrate is formed by separating the crystalline semiconductor into island-shaped patterning for element isolation. In that case, it has not been possible to form the crystal grains by specifying the position and size of the crystal grains. Compared with the inside of the crystal grain, the interface (crystal grain boundary) of the crystal grain has a myriad of recombination centers and capture centers due to an amorphous structure, crystal defects, and the like. It is known that, when carriers are trapped in the trapping center, the potential of the crystal grain boundary increases and acts as a barrier to the carriers, so that the current transport characteristics of the carriers are reduced. Although the crystallinity of the semiconductor film in the channel formation region has a significant effect on the characteristics of the TFT, it is almost impossible to form the channel formation region with a single crystal semiconductor film by eliminating the influence of the crystal grain boundaries. there were.

Lasers used for laser annealing are roughly classified into two types, pulse oscillation and continuous oscillation (CW), depending on the oscillation method. In recent years, it has been found that the diameter of crystals formed in a semiconductor film is larger when a continuous wave laser is used than in a pulsed laser in crystallization of a semiconductor film. When the crystal grain size in the semiconductor film is increased, the number of grain boundaries entering the TFT channel region formed using the semiconductor film is reduced, so that the mobility is increased and the device can be used for developing a device with higher performance. For this reason, continuous wave lasers have begun to be spotlighted.

When performing laser annealing of a semiconductor or a semiconductor film, a laser beam emitted from a laser oscillator is processed by an optical system so as to have a rectangular shape having a large aspect ratio on a surface to be irradiated, and a beam spot is formed on the surface to be irradiated. There is known a scanning method. With the above method, a substrate can be efficiently irradiated with a laser beam, and mass productivity can be improved. Therefore, the substrate is industrially favorably used (for example, see Patent Document 1).

JP-A-8-195357

In order to efficiently perform laser annealing of a semiconductor film formed on a substrate, a laser beam emitted from a continuous wave laser oscillator is used by using an optical system such that a beam spot on an irradiation surface has a linear shape. A method of processing and irradiating a semiconductor film is used. A method of performing laser annealing of a semiconductor film by moving a scanning stage on which a substrate is placed in the short width direction of a linear beam spot is often used. The size of a beam spot that can be formed by a continuous wave laser is extremely small, and even among a laser oscillator having a wavelength range that can be absorbed by a semiconductor film, the size is 500 μm × 20 μm even when a 10 W green laser that is close to the maximum output is used. It is just a long ellipse. By moving the beam spot having such a size back and forth and right and left on the surface to be irradiated, laser annealing is performed on a necessary portion on the surface to be irradiated.

FIG. 1 shows an irradiation trace of the beam spot 101 on the semiconductor film. The irradiation trace of the beam spot on the semiconductor film is roughly classified into two crystal states. In regions A and C, crystal grains similar to crystals formed when laser crystallization is performed with a pulse oscillation excimer laser are formed, and in region B, the crystal grain size is determined by the pulse oscillation laser. A crystal state which is much larger than that in the case of crystallization (hereinafter, this state is called a large grain size) is formed.

  More specifically, the long crystal grains formed in the area B are crystal grains having a short side of several μm and a long side of several tens to several hundred μm long in the laser scanning direction. Crystals are formed in a state in which countless crystals are laid. On the other hand, the crystals formed in the regions A and C are crystal grains having a long side of several μm or less or crystal grains having a diameter of about 1 μm, which are extremely small as compared with large grain crystals. Regions A and C are formed as an aggregate of such small crystal grains. The small crystal grains formed in the regions A and C can be said to be crystal grains in a state similar to crystals formed when laser crystallization is performed with a pulsed excimer laser. Hereinafter, a region where crystal grains similar to a crystal formed when laser crystallization is performed with a pulse oscillation excimer laser is referred to as a poorly crystalline region.

When the crystal grain size in the semiconductor film increases, the mobility increases because the number of grain boundaries in the channel region of the TFT formed using the semiconductor film decreases. Further, the mobility of the TFT formed in the poorly crystalline region is much lower than the mobility of the TFT formed in the large grain size region. That is, there is a large difference between the electrical characteristics of the TFT formed in the large grain size region and the TFT formed in the poorly crystalline region. Therefore, it is required that the poorly crystalline region formed in the semiconductor film be as small as possible.

Therefore, in order to make the poorly crystalline region as small as possible, a slit is arranged above the substrate, which is the irradiation surface, and the energy density of the rectangular beam processed by the optical system in the poorly crystalline region is reduced. A portion contributing to the formation is removed so that only a beam having an energy density necessary for forming a large grain size reaches the irradiation surface.

When the laser annealing of the semiconductor film was performed by the above method, as expected, poorly crystalline regions formed at both ends of the large grain size region could be significantly reduced. However, since the laser beam passed through the slit, the laser beam caused a diffraction phenomenon, and the crystal state of the laser irradiation trace had a stripe distribution reflecting diffraction fringes.

The present invention cuts a portion corresponding to the formation of the poorly crystalline region where the energy density on the irradiation surface is cut in front of the irradiation surface, thereby making the poorly crystalline regions formed at both ends of the large grain size region as small as possible. It is another object of the present invention to provide a method for suppressing the non-uniformity of the crystal state due to the diffraction fringes and increasing the grain size of the entire laser irradiation trace to make the entire irradiation trace a more uniform crystal state.

In the step of crystallizing a semiconductor film using a continuous wave laser, a laser beam is processed into a long elliptical shape on an irradiation surface in order to improve productivity as much as possible, and the elliptical laser beam (hereinafter referred to as an elliptical beam) is shortened. Scanning in the radial direction to crystallize a semiconductor film is actively performed. The shape of the laser beam after processing becomes elliptical because the shape of the original laser beam is a circle or a shape close thereto. Alternatively, if the original shape of the laser beam is rectangular, it may be enlarged in one direction by a cylindrical lens or the like, processed into a long rectangular shape, and used similarly. In this specification, an elliptical beam and a rectangular beam are collectively called a long beam.

The present invention relates to a laser irradiation apparatus disclosed in this specification, which includes a continuous wave first laser oscillator that outputs a wavelength equal to or shorter than visible light, and a first laser beam emitted from the first laser oscillator. Means for processing into a long beam, means for cutting both ends in the major axis direction of the long beam in front of the irradiation surface, a continuous wave second laser oscillator for outputting a fundamental wave, and light emitted from the second laser oscillator. Means for simultaneously irradiating the second laser beam with the first laser beam in a range including a part or all of the area on the irradiation surface where the first laser beam is illuminated; and a first laser beam and a second laser beam. Means for moving the irradiation surface relative to the laser beam in the first direction, and moving the irradiation surface relative to the first laser beam and the second laser beam in the second direction; It is characterized by causing a laser irradiation apparatus and means. Further, the first direction and the second direction are orthogonal to each other.

In the present invention, the reason why the first laser oscillator and the second laser oscillator are used simultaneously is as follows. First, a part of the semiconductor film is melted in a wavelength region (usually, visible light or less) which is sufficiently absorbed by the semiconductor film. Next, the melted semiconductor film is irradiated with a continuous wave fundamental wave (for example, a fundamental wave of an Nd: YAG laser) having an output of, for example, 1000 W or more, which can obtain an output 10 times or more as compared with a continuous wave laser of visible light or less. While scanning, the semiconductor film is relatively scanned with respect to a laser beam having a wavelength of visible light or less and a fundamental wave laser.

The fundamental wave is generally hardly absorbed by the semiconductor film, but when the semiconductor film is in a molten state, the absorption coefficient is dramatically increased, and sufficient absorption is obtained. By simultaneously irradiating a fundamental beam having a width wider than that of a long beam, the heat supplied by the laser irradiation is increased in the melting region in the semiconductor film by increasing the melting time compared to the case of irradiating the long beam alone. It is possible to grow the laser irradiation trace to a uniform large particle size state.

In the above structure of the invention, the first laser beam or the second laser beam is emitted from a continuous wave gas laser, solid laser, or metal laser. As a gas laser, there are an Ar laser, Kr laser, CO ₂ laser, a solid laser, YAG laser, Y ₂ O ₃ laser, YVO ₄ laser, GdVO ₄ laser, YLF laser, YAlO ₃ laser, alexandrite laser, Ti : A sapphire laser or the like, and a helium-cadmium laser as a metal laser.

Further, in the above structure of the invention, the first laser beam is converted into a higher harmonic by a non-linear optical element in order to make visible light. The fundamental wave that is already visible light may be used as it is. The crystal used for the nonlinear optical element is excellent in conversion efficiency when, for example, a material called LBO, BBO, KDP, KTP, KB5, or CLBO is used. By placing these nonlinear optical elements in the laser cavity, the conversion efficiency can be greatly increased.

In the structure of the present invention, it is preferable that the first laser beam be oscillated by the TEM ₀₀ , because the energy uniformity of the obtained long beam can be improved. Furthermore, a longer beam can be obtained because the beam width can be narrower and focused. This enables more efficient laser annealing.

In the case where a semiconductor film formed on a substrate having a light-transmitting property with respect to a laser beam is annealed, in order to realize uniform laser beam irradiation, a plane perpendicular to an irradiation surface is required, and When one of the surface including the short side and the surface including the long side when defining the beam shape as a rectangle is defined as the incident surface, the incident angle φ of the laser beam is the short side or the long side included in the incident surface. When the length of the substrate is W, the substrate is disposed on the irradiation surface, and the thickness of the substrate having a property of transmitting laser light is d, it is preferable that φ ≧ arctan (W / 2d) be satisfied.

When the trajectory of the laser beam is not on the incident surface, the incident angle of the projection of the trajectory on the incident surface is φ. When the laser beam is incident at this incident angle φ, the reflected light from the front surface of the substrate and the reflected light from the back surface of the substrate do not interfere with each other, and uniform laser beam irradiation can be performed.

The above discussion has assumed that the refractive index of the substrate is 1. Actually, in many cases, the refractive index of the substrate is around 1.5, and if this value is taken into account, a calculated value larger than the angle calculated in the above discussion can be obtained. However, since the energy of the beam spot is attenuated as approaching the end of the beam spot, the influence of interference at this portion is small, and the above-described calculated value can sufficiently obtain the effect of interference attenuation. This argument holds true for both the first laser beam and the second laser beam, and it is preferable that both inequalities are satisfied. However, for an extremely short coherent laser such as an excimer laser, There is no problem even if the above inequality is not satisfied.

As a substrate, a glass substrate, a quartz substrate, a silicon substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a flexible substrate, or the like can be used. Examples of the glass substrate include a substrate made of glass such as barium borosilicate glass or aluminoborosilicate glass. The flexible substrate is a film-shaped substrate made of PET, PES, PEN, acrylic, or the like. If a semiconductor device is manufactured using the flexible substrate, weight reduction is expected. If a barrier layer such as an aluminum film (AlON, AlN, AlO, etc.), a carbon film (DLC (diamond-like carbon), etc.), SiN, etc. is formed as a single layer or multiple layers on the front surface or the front and back surfaces of a flexible substrate It is desirable because the durability is improved. The above inequality for φ is not applied to any substrate except that the substrate is transparent to the laser beam. This is because, in this case, the thickness d of the substrate becomes a meaningless numerical value.

Further, the configuration of the invention related to the laser irradiation method disclosed in this specification is to process a continuous wave first laser beam having a wavelength equal to or shorter than visible light into a long beam on an irradiation surface, and to apply both ends in the major axis direction of the long beam. A second laser beam of a fundamental wave, which is cut off in front of the irradiation surface and is a continuous wave, is simultaneously irradiated with the first laser beam in a range including a part or all of the region irradiated with the first laser beam on the irradiation surface. The laser irradiation method moves the irradiation surface relative to a long beam in the first direction.

In the above structure of the invention, the first laser beam or the second laser beam is emitted from a continuous wave gas laser, solid laser, or metal laser. As a gas laser, there are an Ar laser, Kr laser, CO ₂ laser, a solid laser, YAG laser, Y ₂ O ₃ laser, YVO ₄ laser, GdVO ₄ laser, YLF laser, YAlO ₃ laser, alexandrite laser, Ti : A sapphire laser or the like, and a helium-cadmium laser as a metal laser.

In the configuration of the invention described above, the first laser beam is converted into a harmonic by a nonlinear optical element. The crystal used for the nonlinear optical element is excellent in conversion efficiency when, for example, a material called LBO, BBO, KDP, KTP, KB5, or CLBO is used. By placing these nonlinear optical elements in the laser cavity, the conversion efficiency can be greatly increased.

In the above structure of the present invention, it is preferable that the first laser beam be oscillated by the TEM ₀₀ , because the energy uniformity of the obtained long beam can be increased and the long beam can be made longer.

When annealing a semiconductor film formed on a substrate having a light-transmitting property with respect to a laser beam, in order to realize uniform laser beam irradiation, a plane perpendicular to the irradiation surface and at the same time as beam irradiation is required. If one of the surface including the short side and the surface including the long side when defining the shape as a rectangle is defined as the incident surface, the incident angle φ of the laser beam becomes the length of the short side or the long side included in the incident surface. When W is set on the irradiation surface and the thickness of the substrate that transmits light to the laser beam is d, it is preferable that φ ≧ arctan (W / 2d) be satisfied. If multiple laser beams are used, this argument must hold for individual laser beams.

When the trajectory of the laser beam is not on the incident surface, the incident angle of the projection of the trajectory on the incident surface is φ. When the laser beam is incident at this incident angle φ, the reflected light from the front surface of the substrate and the reflected light from the back surface of the substrate do not interfere with each other, and uniform laser beam irradiation can be performed. The above discussion has assumed that the refractive index of the substrate is 1. Actually, in many cases, the refractive index of the substrate is around 1.5, and if this value is taken into account, a calculated value larger than the angle calculated in the above discussion can be obtained. However, since the energy at both ends in the long side direction of the beam spot is attenuated, the influence of interference at this portion is small, and the above-described calculated value can sufficiently obtain the effect of interference attenuation. This argument holds true for both the first laser beam and the second laser beam, and it is preferable that both inequalities are satisfied. However, for an extremely short coherent laser such as an excimer laser, There is no problem even if the above inequality is not satisfied.

As a substrate, a glass substrate, a quartz substrate, a silicon substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a flexible substrate, or the like can be used. The above inequality for φ is not applied to any substrate except that the substrate is transparent to the laser beam. This is because, in this case, the thickness d of the substrate becomes a meaningless numerical value.

In addition, the structure of the invention relating to a method for manufacturing a semiconductor device disclosed in this specification includes a step of forming an amorphous semiconductor film over a substrate and a step of generating a continuous wave first laser beam having a wavelength equal to or shorter than visible light. Making the first laser beam a long beam on the irradiation surface, processing the first laser beam into a long beam on the irradiation surface, making the surface of the amorphous semiconductor film correspond to the irradiation surface, Cutting a portion contributing to the formation of a poorly crystalline region in front of the irradiation surface, generating a second laser beam as a fundamental wave by continuous oscillation, and applying a second laser beam to the irradiation surface in the first direction. A step of moving the irradiation surface relative to the long beam in the first direction while simultaneously irradiating the first laser beam to a range including a part or all of the region irradiated with the laser beam; Characterized by a step of moving the irradiation surface relatively second direction with respect to the first laser beam and the second laser beam. Further, the first direction and the second direction are orthogonal to each other.

In the above structure of the invention, the first laser beam or the second laser beam is emitted from a continuous wave gas laser, solid laser, or metal laser. As gas lasers, there are Ar laser, Kr laser, CO ₂ laser, etc., and as solid lasers, YAG laser, Y ₂ O ₃ laser, YVO ₄ laser, YLF laser, YAlO ₃ laser, Alexandrite laser, Ti: sapphire laser, etc. There is a helium-cadmium laser as a metal laser.

In the configuration of the invention described above, the first laser beam is converted into a harmonic by a nonlinear optical element. The crystal used for the nonlinear optical element is excellent in conversion efficiency when, for example, a material called LBO, BBO, KDP, KTP, KB5, or CLBO is used. By placing these nonlinear optical elements in the laser cavity, the conversion efficiency can be greatly increased.

In the above structure of the present invention, it is preferable that the first laser beam be oscillated by the TEM ₀₀ , because the energy uniformity of the obtained long beam can be increased and the long beam can be made longer.

When annealing a semiconductor film formed on a substrate having a light-transmitting property with respect to a laser beam, in order to realize uniform laser beam irradiation, a plane perpendicular to the irradiation surface and at the same time as beam irradiation is required. If one of the surface including the short side and the surface including the long side when defining the shape as a rectangle is defined as the incident surface, the incident angle φ of the laser beam is the length of the short side or the long side included in the incident surface. When the thickness is W, the thickness of the substrate that is set on the irradiation surface and has a light-transmitting property with respect to the laser beam is d, it is preferable that φ ≧ arctan (W / 2d) is satisfied. If multiple laser beams are used, this argument must hold for individual laser beams.

When the trajectory of the laser beam is not on the incident surface, the incident angle of the projection of the trajectory on the incident surface is φ. When the laser beam is incident at this incident angle φ, the reflected light from the front surface of the substrate and the reflected light from the back surface of the substrate do not interfere with each other, and uniform laser beam irradiation can be performed. The above discussion has assumed that the refractive index of the substrate is 1. Actually, in many cases, the refractive index of the substrate is around 1.5, and if this value is taken into account, a calculated value larger than the angle calculated in the above discussion can be obtained. However, since the energy at both ends in the long side direction of the beam spot is attenuated, the influence of interference at this portion is small, and the above-described calculated value can sufficiently obtain the effect of interference attenuation. This argument holds true for both the first laser beam and the second laser beam, and it is preferable that both inequalities are satisfied. However, for an extremely short coherent laser such as an excimer laser, There is no problem even if the above inequality is not satisfied.

As a substrate, a glass substrate, a quartz substrate, a silicon substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a flexible substrate, or the like can be used. The above inequality for φ is not applied to any substrate except that the substrate is transparent to the laser beam. This is because, in this case, the thickness d of the substrate becomes a meaningless numerical value.

According to the present invention, in laser annealing of a semiconductor film using a continuous wave laser, it is possible to minimize the crystallinity defective region as much as possible and to uniformly increase the grain size over the entire laser irradiation trace. Further, according to the present invention, it is possible to uniformly increase the grain size over the entire surface of the semiconductor film. If the present invention is applied to a mass production line of low-temperature polysilicon TFTs, TFTs with high operation characteristics and reliability and reduced variations in characteristics can be efficiently produced.

(Embodiment 1)
An embodiment of a laser irradiation apparatus proposed by the present invention will be described with reference to FIG. Note that FIG. 2B is a cross-sectional view of a position orthogonal to the irradiation surface in FIG. 2A and including a laser beam incident position. First, the laser oscillator 201 of the maximum output 10W of continuous wave (LD pumped solid state Nd: YVO ₄ laser, a second harmonic wave, wavelength 532 nm) is prepared. The laser oscillator, an oscillation mode of TEM _00, is converted into the second harmonic by a nonlinear optical element. It is not particularly necessary to limit to the second harmonic, but the second harmonic is superior to higher harmonics in terms of energy efficiency. Although FIG. 2 illustrates an example in which one laser oscillator 201 is provided, the number of laser oscillators included in the laser irradiation device of the present invention is not limited to this number. The beam spots of the respective laser beams output from the laser oscillator may be superimposed on each other and used as one beam spot.

A laser beam 212 emitted from the laser oscillator 201 whose output is set to 6.5 W is made incident on a convex lens 203 placed horizontally by a mirror 202. Here, the angle of incidence of the laser beam on the convex lens was set to 20 ° so as not to interfere with the reflected light from the back surface of the substrate. In the present embodiment, the incident angle is set to 20 °, but may be changed as appropriate. The convex lens 203 has a curvature of 10.38 mm, a thickness of 5.2 mm, and is made of BK7 (registered trademark). The lens lower surface is flat and the distance between the lens lower surface and the semiconductor film 205 is about 15 mm. It was arranged to become.

The laser beam 212 that has passed through the convex lens 203 has a part of the beam spot cut off by a slit 204 arranged 0.5 mm above the semiconductor film 205. Here, the slits were arranged such that the slit interval was 560 μm and the center of the slit was the center of the optical axis. As a result, on the irradiation surface, a beam portion forming a poorly crystalline region formed at both ends of the large grain size region when there is no slit 204 is cut off, and a beam subjected to a diffraction effect is formed. .

Next, a continuous-wave fundamental laser oscillator 206 (Nd: YAG laser, wavelength 1.064 μm) having an output of 300 W is prepared. The laser beam 213 emitted from the φ300 μm optical fiber 207 connected to the laser oscillator 206 is irradiated by the 1 × projection lens 208 so as to overlap the region irradiated with the laser beam 212 on the irradiation surface 205. Here, the laser beam 213 is incident so as to have an incident angle of about 50 ° with respect to the irradiation surface, and has a beam spot of about 300 μm × 500 μm on the irradiation surface 205. The beam spot becomes elliptical because the incident angle of the laser beam with respect to the irradiation surface is not 0 °. As a result, the combined beam 211 is irradiated on the semiconductor film 205, and a uniform large particle size having a width of 220 μm is formed on the semiconductor film.

A fundamental wave having a wavelength of about 1 μm is hardly absorbed by a normal semiconductor thin film and has poor efficiency. However, when the second harmonic is used at the same time, the fundamental wave is well absorbed by the semiconductor thin film melted by the second harmonic. Thus, the annealing efficiency of the semiconductor film is improved. That is, the fundamental wave can be adopted in this step by utilizing the increase in the absorption coefficient due to the liquefaction of the semiconductor film. The effect is to suppress a rapid change in temperature of the semiconductor film, to assist the energy of the second harmonic laser beam having a small output, and the like.

The laser beam 212 of the second harmonic passes through the slit and irradiates the region irradiated with the diffracted beam with the laser beam 213 of the fundamental wave as shown in FIG. The melting time can be extended as compared with the case where the laser beam 212 is irradiated alone, and as a result, the heat supplied by the laser irradiation is made uniform in the melting region in the semiconductor film by heat conduction, and the laser irradiation is performed. The trace can be grown into a uniform large particle size state. Note that the hatched portion in FIG. 5A indicates a molten state. The reason why the width of the beam spot in the major axis direction is smaller than the slit width is that the laser beam is focused by the lens before reaching the irradiation surface 205 from the slit 204.

As shown in FIG. 5B, when only the second harmonic is irradiated, only the area irradiated with the laser beam, approximately 10 μm in the scanning direction, is melted, so that the melting time is short and the heat conduction is short. It is unlikely that the heat will be uniformized. On the other hand, as shown in FIG. 5A, when the fundamental wave and the second harmonic are simultaneously irradiated, the width of the melted region in the scanning direction is 10 times or more as compared with the case where only the second harmonic is irradiated. The time required for the heat to be uniform is prolonged, and a uniform large particle size state can be formed. Note that the fundamental laser beam 213 needs to appropriately determine the power at which the semiconductor film does not evaporate. The same reference numerals in FIG. 5 as those in FIG. 2 are used for easy identification.

Unlike the harmonic, the fundamental wave does not require the use of a non-linear optical element for wavelength conversion, and it is possible to obtain a very high-power laser beam, for example, a laser beam having an energy of 100 times or more of the harmonic. is there. Such an energy difference occurs because the resistance of the nonlinear optical element to the laser is very weak. In addition, the nonlinear optical element that generates harmonics is liable to be deteriorated, and has the disadvantage that the maintenance-free state, which is an advantage of the solid-state laser, cannot be maintained for a long time. Therefore, it can be said that assisting a harmonic with a fundamental wave according to the present invention is very significant.

Next, an example of a method for manufacturing a semiconductor film will be described. The semiconductor film is formed on a glass substrate. Specifically, a 200-nm-thick silicon oxynitride film is formed over one surface of a glass substrate having a thickness of 0.7 mm, and an a-Si film having a thickness of 70 nm is formed thereover by a plasma CVD method. Further, in order to increase the resistance of the semiconductor film to laser, thermal annealing at 500 ° C. for one hour is performed on the semiconductor film. In addition to the thermal annealing, the semiconductor film may be crystallized with the metal element described in the section of the related art. Regardless of which film is used, the optimum laser beam irradiation conditions are almost the same.

Next, an example of laser irradiation on the semiconductor film 205 will be described. Although the output of the laser oscillator 201 is about 10 W at the maximum, the energy density is sufficient because the size of the formed beam spot is relatively small, and irradiation is performed with the output reduced to about 6.5 W. The output of the laser oscillator 206 is set to 300 W, and a combined beam 211 is formed on the semiconductor film 205. By using the Y-axis robot 210 to scan the substrate on which the semiconductor film 205 is formed in the short diameter direction, a large particle size region can be formed. The scanning speed is suitably about several tens cm / s to several hundred cm / s, and is set to 50 cm / s here.

FIG. 3 shows an irradiation method in which the entire surface of the semiconductor film has a large grain size region. The same reference numerals as in FIG. 2 are used in the figure to facilitate identification. The substrate on which the semiconductor film is formed is fixed to a suction stage, and the laser oscillator 201 and the laser oscillator 206 are oscillated. First, one line scan of the semiconductor film surface is performed by the Y-axis robot 210 at a scanning speed of 50 cm / s. The one line corresponds to a portion A1 in FIG. In FIG. 3, after the Y-axis robot irradiates the laser beam on the forward path Am (m is a positive integer), the X-axis robot 209 is slid in the direction perpendicular to the scanning direction by the width of the large particle size region. Then, the portion of the return path Bm is irradiated with laser. By repeating such a series of operations, the entire surface of the semiconductor film can be made a large grain size region. The characteristics of a semiconductor film in a large grain size region are very high, and it is expected that a semiconductor device such as a TFT is manufactured. It is not necessary to form a large grain size region in the portion. Therefore, such a portion may not be irradiated with a laser beam or may be irradiated with a laser beam so as not to form a large grain size region. In order to efficiently anneal the semiconductor film without forming a large grain size region, for example, the scanning speed may be increased. For example, if scanning is performed at a speed of about 2 m / s, the a-Si film can be crystallized, but at this time, a large grain size region is not formed, and a so-called p-Si film is generally formed. .

(Embodiment 2)
In this embodiment, an example in which several long beams obtained by shaping the second harmonic are combined to form a longer beam, and energy is assisted by a fundamental wave is shown in FIG.

First, _four laser oscillators (not shown) with a continuous oscillation maximum output of 10 W (LD-pumped solid-state Nd: YVO ₄ laser, second harmonic, wavelength 532 nm) are prepared. The laser oscillator, an oscillation mode of TEM _00, has a built-in LBO crystal in the resonator, are converted into the second harmonic. By using several reflection mirrors, the traveling directions of the laser beams are respectively changed in directions shifted by an angle β from the vertical direction, and the laser beams are incident from four directions so that they are almost combined into one on the irradiation surface. Here, the laser oscillator output was set to 7 W. The four directions coincide with the optical axis A, the optical axis B, the optical axis C, and the optical axis D, respectively. A plane including the laser beam irradiation position and perpendicular to the irradiation surface is defined as a plane A, and the optical axis A and the optical axis B, and the optical axis C and the optical axis D are positioned plane-symmetrically with respect to the plane A. The angle between A and the optical axis B and the angle between the optical axis C and the optical axis D are each set to 20 °. The optical axis A and the optical axis C, and the optical axis B and the optical axis D are positioned in plane symmetry with respect to the plane A and the plane B perpendicular to the irradiation surface. An angle formed by a plane C including the axis B and a plane D including the optical axis C and the optical axis D is 50 °.

Next, the plano-convex cylindrical lenses 401a, 401b, 401c, and 401d having a focal length of 150 mm are set so that the optical axes A, B, C, and D are incident on the cylindrical lenses 401a to 401d at 0 °. Deploy. At this time, the light condensing direction of the plano-convex cylindrical lens is a direction included in the plane C or the plane D. The distance between the plano-convex cylindrical lenses 401a to 401d and the irradiation surface is adjusted within a range of 110 to 120 mm measured on each optical axis.

Furthermore, the planes of the plano-convex cylindrical lenses 402a and 402b having a focal length of 20 mm are arranged so as to be included in the planes C and D, respectively. The bus is a bus located at a position farthest from a plane portion of the cylindrical lens in a curved surface portion of the cylindrical lens. The plane portions of the plano-convex cylindrical lenses 402a and 402b and the plane C and the plane D are arranged so as to be orthogonal to each other. The distance between the plano-convex cylindrical lenses 402a, 402b and the irradiation surface is adjusted around about 18 mm measured on each optical axis.

With the above arrangement, four long beams having a size of about 400 μm in major axis and about 20 μm in minor axis are formed on the irradiation surface. In this state, the four beams are completely combined into one on the irradiation surface, so that a longer beam cannot be formed. However, by finely adjusting the position of each lens, it is described in FIG. It can be converted to such an arrangement. That is, by arranging the major axes of the four longer beams 407a, 407b, 407c, and 407d on a straight line and offsetting them in the direction of the straight line, the longer beam can be made a longer beam.

A slit 403 is arranged above the irradiation surface 405, and one end of the long beam 407a and one end of the long beam 407d are cut out. Thereby, the poorly crystalline regions formed at both ends of the large grain size region can be made as small as possible. By disposing the slits 403, a diffraction effect appears, and a crystalline state having a stripe distribution is formed. Note that by adjusting the distance between the long beams between the long beams 407a and 407b, between 407b and 407c, and between 407c and 407d, an energy density sufficient to increase the grain size of the semiconductor film can be obtained. Can be.

Next, two continuous wave LD pumped solid-state Nd: YAG lasers (fundamental wave, wavelength: 1.064 μm) with an output of 500 W are used, and the optical system 406 forms 300 μm × 400 μm elliptical beams 408 a and 408 b on the irradiation surface 405. At this time, the elliptical beams 408a and 408b are formed near the slit 403 where the diffraction effect of the slit 403 appears in the long beams 407a to 407d. Thus, the diffraction effect of the slit of the second harmonic can be suppressed by the fundamental wave.

As the optical system 406, a lens that projects a laser beam emitted from an optical fiber of φ300 μm connected to a laser oscillator onto the irradiation surface 405 at a magnification of 1 is used. Here, the laser beam is incident on the irradiation surface so that the incident angle becomes about 50 °, and a beam spot of about 300 μm × 500 μm is formed on the irradiation surface 405. The beam spot becomes elliptical because the incident angle of the laser beam with respect to the irradiation surface is not 0 °. What is important here is that the fundamental wave must never be returned to the laser oscillator. Since the surface of the semiconductor film has some degree of reflection, it is not sufficient to make the laser beam perpendicular to the irradiation surface.

The semiconductor film may be entirely crystallized using the long beam formed as described above and using, for example, the uniaxial robot 209 for the X axis and the uniaxial robot 210 for the Y axis described in the first embodiment. The semiconductor film may be manufactured by, for example, the method described in Embodiment Mode 1. The advantage of using this embodiment is that the processing time is short because a longer beam is formed, and the energy distribution is made uniform in the major axis direction by overlapping and adjoining long beams having a Gaussian-like energy distribution. It is preferable because unevenness in temperature can be relatively suppressed.

FIG. 6 illustrates irradiation traces of a laser beam. The figure explaining the means of the present invention. FIG. 2 illustrates an embodiment of the present invention. FIG. 2 illustrates an embodiment of the present invention. FIG. 2 illustrates an embodiment of the present invention.

Claims (14)

A first laser oscillator that outputs a wavelength equal to or less than visible light;
Means for processing a first laser beam emitted from the first laser oscillator into a long beam on an irradiation surface;
Means for cutting both ends in the major axis direction of the long beam in front of the irradiation surface,
A second laser oscillator that outputs a fundamental wave,
Irradiating a second laser beam emitted from a second laser oscillator simultaneously with the first laser beam to an area including a part or all of an area irradiated with the first laser beam on the irradiation surface. Means,
Means for moving the irradiation surface relative to the first laser beam and the second laser beam in a first direction;
Means for moving the irradiation surface relative to the first laser beam and the second laser beam in a second direction;
A laser irradiation device having: 2. The laser irradiation apparatus according to claim 1, wherein the first laser oscillator or the second laser oscillator is a continuous wave gas laser, a solid laser, or a metal laser. In Claim 1, the first laser oscillator or the second laser oscillator is an Ar laser, a Kr laser, a CO ₂ laser, a YAG laser, a Y ₂ O ₃ laser, a YVO ₄ laser, a YLF laser, a YAlO ₃ laser, A laser irradiation device, which is an Alexandrite laser, a Ti: sapphire laser, or a helium cadmium laser. 4. The laser irradiation device according to claim 1, wherein the first direction and the second direction are orthogonal to each other. 5. 5. The irradiation surface according to claim 1, wherein the irradiation surface is a film formed on a substrate having a thickness d having a light-transmitting property with respect to the first laser beam. When the length of the major axis or the minor axis is W, the incident angle φ of the first laser beam with respect to the irradiation surface is:
φ ≧ arctan (W / 2d)
A laser irradiation apparatus characterized by satisfying the following. A first laser beam having a wavelength equal to or less than visible light,
Processing into a long beam on the irradiation surface,
Cut both ends in the major axis direction of the long beam in front of the irradiation surface,
A second laser beam, which is a fundamental wave, is irradiated simultaneously with the first laser beam on a range including a part or all of a region irradiated with the first laser beam on the irradiation surface,
A laser irradiation method of irradiating the irradiation surface with the long beam while relatively moving the irradiation surface in a first direction. 7. The laser irradiation method according to claim 6, wherein the first laser beam or the second laser beam is emitted from a continuous wave gas laser, solid laser, or metal laser. In claim 6, the first laser beam or the second laser beam is an Ar laser, a Kr laser, a CO ₂ laser, a YAG laser, a Y ₂ O ₃ laser, a YVO ₄ laser, a YLF laser, a YAlO ₃ laser, A laser irradiation method characterized by being emitted from an Alexandrite laser, a Ti: sapphire laser or a helium cadmium laser. The irradiation surface according to any one of claims 6 to 8, wherein the irradiation surface is a film formed on a substrate having a thickness d having a light-transmitting property with respect to the first laser beam. When the length of the major axis or the minor axis is W, the incident angle φ of the first laser beam with respect to the irradiation surface is:
φ ≧ arctan (W / 2d)
A laser irradiation method characterized by satisfying the following. Forming an amorphous semiconductor film on the substrate;
Processing a continuous wave first laser beam having a wavelength equal to or shorter than visible light into a long beam on an irradiation surface;
Matching the surface of the amorphous semiconductor film to the irradiation surface;
Of the long beam, a step of cutting a portion of the amorphous semiconductor film where the energy density contributes to the formation of a poorly crystalline region in front of the irradiation surface;
Generating a second laser beam as a fundamental wave by continuous oscillation;
While irradiating the second laser beam simultaneously with the first laser beam to a range including a part or all of a region where the first laser beam is irradiated on the irradiation surface, the second laser beam A step of relatively moving the irradiation surface in a first direction;
Moving the irradiation surface relative to the first laser beam and the second laser beam in a second direction. 11. The method for manufacturing a semiconductor device according to claim 10, wherein the first laser beam or the second laser beam is emitted from a continuous wave gas laser, a solid-state laser, or a metal laser. In claim 10, wherein the first laser beam or the second laser beam is an Ar laser, a Kr laser, a CO ₂ laser, a YAG laser, a Y ₂ O ₃ laser, a YVO ₄ laser, a YLF laser, a YAlO ₃ laser, A method for manufacturing a semiconductor device, which is emitted from an alexandrite laser, a Ti: sapphire laser, or a helium cadmium laser. 13. The method for manufacturing a semiconductor device according to claim 10, wherein the first direction and the second direction are orthogonal to each other. 14. The irradiation surface according to claim 10, wherein the irradiation surface is a film formed on a substrate having a thickness d having a light-transmitting property with respect to the first laser beam. When the length of the major axis or the minor axis is W, the incident angle φ of the first laser beam with respect to the irradiation surface is:
φ ≧ arctan (W / 2d)
And a method for manufacturing a semiconductor device.

Images