JP6221088B2 - Laser annealing apparatus and laser annealing method - Google Patents

Description

  The present invention mainly relates to a laser annealing apparatus and a laser annealing method used for manufacturing a TFT (thin film transistor) substrate such as a liquid crystal panel or an organic EL panel, and more particularly, a laser is applied to an amorphous silicon film (hereinafter referred to as an a-Si film). The present invention relates to a laser annealing apparatus and a laser annealing method used for forming a low-temperature polysilicon film that crystallizes a-Si into polycrystalline silicon (hereinafter referred to as polysilicon) by annealing by irradiating light.

  As a thin film transistor having an inverted stagger structure, a gate electrode is formed of a metal layer such as Cr or Al on an insulating substrate, and then, for example, a SiN film is formed as a gate insulating film on the substrate including the gate electrode. A hydrogenated amorphous silicon (hereinafter referred to as a-Si: H) film is formed on the entire surface, and the a-Si: H film is patterned in an island shape in a predetermined region on the gate electrode. There is an amorphous silicon transistor in which a drain electrode is formed.

  However, since this amorphous silicon transistor uses an a-Si: H film for the channel region, there is a drawback that the mobility of charges in the channel region is small. Therefore, an amorphous silicon transistor can be used as a pixel transistor in a pixel portion of a liquid crystal display device, for example. However, as a drive transistor in a peripheral drive circuit that requires high-speed rewriting, the charge mobility in the channel region is high. It is too small and difficult to use.

  On the other hand, when a polycrystalline silicon film is formed directly on a substrate, it is formed by LPCVD (Low Pressure Chemical Vapor Deposition), which is a high temperature process of about 1500 ° C. A polycrystalline silicon film cannot be directly formed on a transparent glass substrate (softening point is 400 to 500 ° C.).

  Therefore, once an a-Si: H film is formed in the channel region, and then this a-Si: H film is irradiated with a laser beam such as a YAG excimer laser to perform laser annealing, thereby melting in an extremely short time. Due to the solidification phase transition, a low-temperature polysilicon process for crystallizing an a-Si: H film into a polysilicon film has been adopted. As a result, the channel region on the glass substrate can be formed of a polysilicon film that has high charge mobility and can speed up the transistor operation (Patent Document 1).

  However, the conventional low-temperature polysilicon film forming method described above condenses excimer laser light on the line, scans the entire amorphous silicon film formed on the glass substrate of the liquid crystal display device, and performs amorphous processing. By laser annealing the entire surface of the silicon film, the amorphous silicon film is melted and solidified to be polycrystallized. For this reason, since regions other than the channel region of the TFT involved in the operation of the TFT substrate are also polycrystallized by exposure, the exposure processing is useless except for the channel region. In addition, even in the TFT channel region, the region for forming a transistor that does not require high speed, such as a pixel transistor in a display portion, is also wasteful in processing because the channel region is polycrystallized. is there.

  Accordingly, the applicant of the present application has already proposed a low-temperature polysilicon film forming apparatus that uses a microlens array to expose only a region (channel region) that needs to be polycrystallized by laser light to polycrystallize ( Patent Document 2).

JP-A-5-63196 JP 2012-4250 A

  Although the invention described in Patent Document 2 achieves the intended purpose, it is desired to further increase the speed of a transistor having a low-temperature polysilicon film as a channel region.

  The present invention has been made in view of such problems, and by growing crystal grains in the direction of current flow in the channel region of the transistor, the grain boundaries in the current flow direction in the channel region are reduced, An object of the present invention is to provide a laser annealing apparatus and a laser annealing method that enable high-speed operation of a transistor.

The laser annealing apparatus according to the present invention is:
By irradiating the amorphous silicon film with laser light, the irradiated portion is melted and solidified to be transformed into a polysilicon film, and the channel region of the transistor arranged in a two-dimensional lattice pattern in the polysilicon film In the laser annealing apparatus for forming
A laser light source for emitting laser light;
A plurality of microlenses are two-dimensionally arranged corresponding to the channel region, and the laser light from the laser light source is condensed toward the amorphous silicon film by the microlens and is applied to each microlens. A microlens array that illuminates the corresponding area;
Wherein a respective said to optical path microlens and the open mouth you interposed in a one-to-one correspondence between the microlenses, and mask the opening, which defines an irradiation pattern of laser light by the microlens,
Have
The opening of the mask has a shape in a portion where the polysilicon film is to be formed such that a direction in which the channel current of the transistor flows and a part of an edge of the opening are substantially orthogonal to each other. Is defined,
Laser beam passing through each aperture, with respect to the irradiation unit, relatively near the edges is low temperature state, and are not confer temperature distribution center of the opening becomes high,
One of the source electrode and the drain electrode of the transistor has an edge facing the other side including the part of the edge, and the other of the source electrode and the drain electrode of the transistor corresponds to the center of the opening. The shape of the opening is defined so as to have a shape covering the portion .

The laser annealing method according to the present invention includes:
By irradiating the amorphous silicon film with laser light, the irradiated portion is melted and solidified to be transformed into a polysilicon film , and the channel region of the transistor arranged in a two-dimensional lattice pattern in the polysilicon film In the laser annealing method for forming
A microlens array in which a plurality of microlenses are two-dimensionally arranged corresponding to the channel region condenses laser light toward the amorphous silicon film and irradiates the region corresponding to each microlens. And
The mask is positioned such that a plurality of openings is interposed so as to correspond to each microlens in a one-to-one to the optical path of each said microlenses, a laser irradiated to the respective irradiation portions by the opening Define the light irradiation pattern,
The laser beam that passes through each opening gives a temperature distribution in which the vicinity of the edge of the opening is relatively low and the center of the opening is relatively high with respect to the irradiation part. ,
Shape such that the opening of the mask before Symbol moiety to form the polysilicon film, and a portion of edge of said opening and the direction in which the channel current flows in that portion the transistor is substantially orthogonal Is defined,
One of the source electrode and the drain electrode of the transistor has an edge opposite to the other side including the part of the edge, and the other of the source electrode and the drain electrode of the transistor corresponds to the center of the opening. The shape of the opening is defined so as to have a shape covering a portion to be formed .

In this laser annealing method,
The method of imparting the temperature distribution to the irradiating part by laser light passing through each opening is as follows.
For example, the first laser beam that is the focal point at a position closer to the microlens than the amorphous silicon film and the second laser beam that is the focal point on the amorphous silicon film are irradiated in this order, Alternatively, the mask is provided with a gradation in which the amount of transmitted light is the smallest at the edge of the opening and the amount of transmitted light increases toward the center of the opening in the opening. The amount of light irradiation is reduced at the edge of the opening and increased toward the center of the opening.

  According to the present invention, since the laser light is collected by the microlens, for example, only the channel region in the amorphous silicon film is irradiated with the laser light and annealed only in the region that becomes the channel region of the transistor of the TFT substrate, It can be modified to a polysilicon film. Thereby, the irradiation efficiency of a laser beam can be improved. Since the laser beam gives the temperature distribution such that the temperature is low at the edge of the opening and the temperature is high at the center of the opening, the silicon melted by the laser irradiation is crystallized. At the time of conversion, crystal grains grow from the edge of the opening toward the center. The shape of the opening of the mask is defined so that the current direction between the source electrode and the drain electrode in the channel region and a part of the edge of the opening are substantially orthogonal to each other. Since the crystal growth direction matches, the electron mobility in the current direction of the polysilicon film can be increased, and the operation speed of the transistor can be improved.

It is a figure which shows the laser annealing apparatus by the microlens array of embodiment of this invention. It is a conceptual diagram of a TFT substrate. (A) thru | or (d) are figures which show the shape of the opening part of a mask. (A) And (b) is a figure which shows the method of providing temperature distribution to the irradiation part of a laser beam. Similarly, it is a figure which shows the method of providing temperature distribution to the irradiation part of a laser beam. It is a figure which shows the modification of the method of providing temperature distribution to the irradiation part of a laser beam. It is a figure which shows temperature distribution and crystal growth when a uniform laser beam is irradiated.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a diagram showing a laser annealing apparatus using a microlens array of this embodiment, FIG. 2 is a conceptual diagram of a TFT substrate, and FIG. 3 is a diagram showing the shape of an opening of a mask. Laser light emitted from a laser light source such as an Nd: YAG excimer laser is introduced into the irradiation unit shown in FIG. 1 by appropriate optical means. In this irradiation unit, a microlens array 2 in which microlenses 3 are two-dimensionally arranged is installed, and laser light transmitted through each microlens 3 passes through each microlens 5 on each surface of the substrate 4. A position corresponding to the lens 3 is irradiated. The laser light from the laser light source passes through the opening 1a of the mask 1 and then enters the microlens 3 corresponding to each opening 1a. Therefore, the laser beam is condensed by the microlens 3 and the microlens 5 corresponding to each opening 1a in a pattern shaped by the opening 1a of the mask 1, and is then given to a predetermined area (a channel area described later) on the substrate 4. ).

  The substrate 4 is, for example, the TFT substrate 41 of the liquid crystal display panel shown in FIG. 2. A gate electrode is patterned on a glass substrate with a metal layer such as Cr or Al, and then the substrate including the gate electrode is formed. For example, an SiN film is formed as a gate insulating film, and then an amorphous silicon (hereinafter referred to as a-Si) film such as hydrogenated amorphous silicon is formed on the entire surface.

  As shown in FIG. 2, the TFT substrate 41 is provided with a pixel region 4a and a gate line region 4b and a drain line region 4c provided in the periphery thereof. The pixel region 4a includes a gate line and a drain. A pixel transistor 6 is formed at the intersection with the line. In addition, a drive transistor 6 is formed in each of the gate line region 4b and the drain line region 4c.

  In the present embodiment, as shown in FIG. 3A, after the gate electrode 10 of each transistor 6 is patterned, the substrate 4 having an a-Si film (not shown) formed on the entire surface is formed. It is installed in the laser beam irradiation part of the annealing device. The laser light from each microlens 3 and microlens 5 is irradiated to the portion of each a-Si film that becomes each channel region on the gate electrode 10, and after the a-Si film in this portion is once melted, it is solidified. Then, it is crystallized and modified into a polysilicon film.

  As shown in FIG. 3B, the opening 1a of the mask 1 has, for example, a hexagonal shape in which the edge 12 is formed by combining a right-side rectangle and a left-side trapezoid. As shown in the outline 20 of the microlens 3 in FIG. 3B, each channel region is irradiated with laser light collected from one microlens 3, and this laser light passes through the opening 1 a of the mask 1. Only the transmitted light is irradiated onto the a-Si film, and the remaining laser light is shielded by the mask 1. Further, as will be described later, the laser light gives a temperature distribution in which the vicinity of the edge 12 of the opening 1a is a low temperature and the center of the opening 1a is a high temperature relative to the irradiated portion. . That is, the laser light has an illuminance distribution in the irradiated portion of the a-Si film such that the input energy is low in the portion corresponding to the edge 12 of the opening 1a and high in the portion corresponding to the center of the opening 1a. is there. For this reason, as schematically shown by a thin line in FIG. 3C, the pulse laser beam that has passed through the opening 1a and applied to the a-Si film is used to form the a-Si film corresponding to the opening 1a. The part is heated, and the part is melted and then cooled to solidify. At this time, crystal grains grow from the vicinity of the relatively low temperature edge 12 toward the high temperature center and correspond to the edge 12. A polysilicon region 21 having a grain boundary extending long from the position toward the center is obtained.

  Therefore, the source electrode 13 and the drain electrode 14 are formed on the substrate 4 after the annealing treatment, as shown in FIG. The source electrode 13 has a shape in which the edge facing the drain electrode 14 is a part of the edge 12 of the opening 1 a and corresponds to the trapezoidal portion on the left side of the edge 12. The region 21 has a shape covering a portion corresponding to the center of the opening 1a. For this reason, in the region where the source electrode 13 and the drain electrode 14 are opposed, the polysilicon region 21 has a crystal grain extending long in a direction perpendicular to both edges of the source electrode 13 and the drain electrode 14 facing each other. . The opposing region between the source electrode 13 and the drain electrode 14 is a region in which current flows from the source electrode 13 toward the drain electrode 14 using the polysilicon region 21 as a channel region. It will flow in a small area and the electron mobility will be high. Therefore, the transistor of this embodiment can operate at high speed.

  In other words, when designing a transistor, the shape and position of the gate electrode 10 shown in FIG. 3A and the shapes and positions of the source electrode 13 and the drain electrode 14 shown in FIG. 3D are determined. Therefore, the direction of current flow in the polysilicon channel region is determined. After that, in the present embodiment, the shape of the opening 1a of the mask 1 is the shape of the edge 12 so that the direction in which this current flows and a part of the edge 12 of the opening 1a are substantially orthogonal to each other. The position of the opening 1a in the mask 1 is determined. In this way, the direction of the channel current and the growth direction of the crystal flow can be matched, and the electron mobility can be increased.

  FIG. 7 is a diagram showing the relationship between crystal growth and a mask. When the laser beam is irradiated, the region shielded by the mask is at a room temperature level. However, at the opening, the temperature of the a-Si film is changed to the shield region at the time of irradiation (when the pulse laser beam is irradiated). On the other hand, it rises stepwise. Then, after 200 ns, 300 ns, and 400 ns have elapsed, the temperature distribution in the opening is lowered. The decrease in temperature distribution occurs faster near the edge of the opening than in the opening. For this reason, in the opening, a temperature gradient is generated from the edge toward the inside, and crystal grains grow from the edge of the opening toward the inside. However, as shown in FIG. 7, the irradiation light amount distribution (energy distribution) of the laser light is uniform, and when the laser light is evenly irradiated in the opening, a certain temperature gradient occurs at the edge 12, The degree is small and not enough to grow the crystal grains in one direction.

  Therefore, in the present invention, a distribution that increases from the edge 12 of the opening 1a toward the center is given to the amount of laser light to be irradiated. That is, by irradiating the laser beam so that the amount of light (energy) increases from the edge 12 of the opening 1a toward the center, as shown in FIG. A temperature distribution is provided such that the vicinity of the edge 12 of 1a is relatively low temperature and the center is relatively high temperature.

  FIG. 4A shows a method for providing a distribution to the light amount (energy) of the laser light in this way. As shown in FIG. 4A, the laser light is condensed on the substrate 4 by the microlens 3 and the microlens 5. At this time, if the optical system of the microlens 3 and the microlens 5 is designed so that the laser beam having a wavelength of 1064 nm is focused on the surface of the substrate 4, the focal position of the laser beam having a wavelength of 355 nm is the substrate. 4 is above the surface of the substrate 4. Therefore, as shown in FIG. 5, first, the substrate 4 is irradiated with one shot of laser light having a wavelength of 355 nm, and thereafter, one shot of laser light having a wavelength of 1064 nm is irradiated with a time difference. Then, since the focal position of the laser beam having an initial wavelength of 355 nm is shifted from the substrate 4, the laser beam is irradiated over a wide area on the substrate 4, while its irradiation energy is small and the temperature rise is low. Next, when a laser beam having a wavelength of 1064 nm is irradiated, the laser beam is focused on the substrate 4, so that the central portion of the irradiation region is irradiated with relatively high energy. Thereby, in the irradiation part, as shown in FIG. 4B, a temperature distribution in which a low temperature part exists around the high temperature part is obtained.

  As a result, as shown in FIG. 3C, crystal grains grow from the edge 12 of the opening 1a toward the center of the opening 1a, and in the vicinity of the edge 12 of the opening 1a, from the edge 12 An elongated grain boundary extending in a substantially vertical direction is obtained. In the center of the opening 1a, the above-described flat crystal grains are not obtained, and an equiaxed crystal structure having no directionality in the crystal grain boundary is obtained. Therefore, if the source electrode 13 and the drain electrode 14 are formed so that the vicinity of a part of the edge 12 of the opening 1a serves as a channel current flow region, the channel current is obtained by converting the flat crystal grains into the crystal grains. The channel flows in a long direction, and the number of crystal grain boundaries in the current flow region is small, and a channel region with high electron mobility can be obtained.

  Next, the operation of the present embodiment configured as described above will be described. In the present embodiment, the position of the opening 1a of the mask 1 is set so that the irradiation position of the laser light that passes through the opening 1a and is focused on the substrate 4 by the microlens 3 becomes the channel region of the transistor. The shape of the opening 1a is set so that a part of the edge 12 is substantially perpendicular to the direction of current flow in the channel region. The temperature distribution formed in the irradiated portion by the laser light irradiation is set to be relatively low at a position corresponding to the edge 12 of the opening 1a and relatively high at the center of the opening 1a. . As a result, in the region including the irradiated portion of the a-Si film due to the laser light irradiation, the temperature of the a-Si film does not rise in the portion corresponding to the light shielding region by the mask outside the opening 1a and remains at room temperature. As the temperature increases from the edge 12 of the opening 1a toward the inside, a temperature distribution is obtained in which the temperature is low in the vicinity of the edge 12 and the temperature is high in the center of the opening 1a. For this reason, the portion of the a-Si film corresponding to the opening 1a is heated and melted by laser light irradiation, but the melt has a relatively low temperature in the vicinity of the edge 12 and is in the middle. The temperature becomes relatively high and the temperature rises to near the boiling point. When the melt is solidified, solidification starts from the vicinity of the edge 12 of the low-temperature opening 1a, and the crystal grains grow in a substantially vertical direction from the edge 12 according to the temperature gradient. Crystal grains extending in the vertical direction are obtained. In the opening 1a, a part of the edge 12 is substantially perpendicular to the direction in which the channel current flows. Therefore, the direction of the channel current coincides with the direction in which the crystal grains extend, and the portion in which the channel current flows is an electron movement. The region becomes a high degree, and the operation of the transistor becomes high speed.

  Therefore, according to the present embodiment, waste of the entire surface annealing process by the conventional entire surface laser irradiation can be omitted, and the operation speed of the transistor can be increased.

  FIG. 6 shows a modification of the method for giving the temperature distribution to the laser light irradiation region. In this modified example, in the opening of the mask 30, the mask 30 is provided with a gradation in which the vicinity of the edge 30a is a dark part with a small amount of transmitted light and the central part 30b of the opening is a bright part with a relatively large amount of transmitted light. Is used. The central portion 31 of the mask 30 is an area where the amount of transmitted light that transmits the laser light as it is is maximum. In this way, by providing a gradation that provides a difference in the amount of transmitted laser light to the opening of the mask 30, a temperature distribution can be imparted to the irradiated portion, as in FIG. 4B. it can.

  In the present invention, the direction in which the current flows and a part of the edge of the opening of the mask are substantially orthogonal, but this substantially orthogonal means orthogonal with a certain width. In other words, even if a part of the edge 12 of the opening 1a is slightly inclined from 90 ° rather than 90 ° with respect to the current direction, it is possible to reduce the grain boundaries in the current flow region by flattening the crystal grains. Thus, it can be said that a part of the edge 12 is substantially orthogonal to the current direction as long as the increase in electron mobility due to the flattening of the crystal grains is recognized as compared with the case where the crystal grains are messy.

1: Mask 1a: Opening 2: Micro lens array 3: Micro lens 4: Substrate 5: Micro lens 6: Transistor 10: Gate electrode 12: Edge 13: Source electrode 14: Drain electrode 20: Micro lens outline 21: Channel Region 41: TFT substrate

Claims (4)

By irradiating the amorphous silicon film with laser light, the irradiated portion is melted and solidified to be transformed into a polysilicon film, and the channel region of the transistor arranged in a two-dimensional lattice pattern in the polysilicon film In the laser annealing apparatus for forming
A laser light source for emitting laser light;
A plurality of microlenses are two-dimensionally arranged corresponding to the channel region, and the laser light from the laser light source is condensed toward the amorphous silicon film by the microlens and is applied to each microlens. A microlens array that illuminates the corresponding area;
Wherein a respective said to optical path microlens and the open mouth you interposed in a one-to-one correspondence between the microlenses, and mask the opening, which defines an irradiation pattern of laser light by the microlens,
Have
The opening of the mask has a shape in a portion where the polysilicon film is to be formed such that a direction in which the channel current of the transistor flows and a part of an edge of the opening are substantially orthogonal to each other. Is defined,
Laser beam passing through each aperture, with respect to the irradiation unit, relatively near the edges is low temperature state, and are not confer temperature distribution center of the opening becomes high,
One of the source electrode and the drain electrode of the transistor has an edge facing the other side including the part of the edge, and the other of the source electrode and the drain electrode of the transistor corresponds to the center of the opening. A laser annealing apparatus , wherein the shape of the opening is defined so as to have a shape covering the portion . By irradiating the amorphous silicon film with laser light, the irradiated portion is melted and solidified to be transformed into a polysilicon film , and the channel region of the transistor arranged in a two-dimensional lattice pattern in the polysilicon film In the laser annealing method for forming
A microlens array in which a plurality of microlenses are two-dimensionally arranged corresponding to the channel region condenses laser light toward the amorphous silicon film and irradiates the region corresponding to each microlens. And
The mask is positioned such that a plurality of openings is interposed so as to correspond to each microlens in a one-to-one to the optical path of each said microlenses, a laser irradiated to the respective irradiation portions by the opening Define the light irradiation pattern,
The laser beam that passes through each opening gives a temperature distribution in which the vicinity of the edge of the opening is relatively low and the center of the opening is relatively high with respect to the irradiation part. ,
Shape such that the opening of the mask before Symbol moiety to form the polysilicon film, and a portion of edge of said opening and the direction in which the channel current flows in that portion the transistor is substantially orthogonal Is defined,
One of the source electrode and the drain electrode of the transistor has an edge opposite to the other side including the part of the edge, and the other of the source electrode and the drain electrode of the transistor corresponds to the center of the opening. A laser annealing method , wherein the shape of the opening is defined so as to have a shape covering a portion to be formed . The laser light that passes through each of the openings includes a first laser light that is a focal point at a position closer to the microlens than the amorphous silicon film, and a second laser light that is a focal point on the amorphous silicon film. The laser annealing method according to claim 2, wherein the temperature distribution is imparted by irradiating in this order. The mask is provided with a gradation in which the amount of transmitted light is the smallest at the edge of the opening and the amount of transmitted light increases toward the center of the opening. 3. The laser annealing method according to claim 2, wherein the temperature distribution is imparted by decreasing the amount of irradiation light at the edge of the opening and increasing toward the center of the opening.

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