JP2014060184A - Method of forming low temperature polysilicon film and method of manufacturing thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a low temperature polysilicon film which allows for elongation of the grain growth direction in a desired direction depending on the direction of movement of carriers, even if the planar shape of a channel region is complicated, and allows for formation of a channel region of high speed operation at an arbitrary position, and to provide a method of manufacturing a thin film transistor.SOLUTION: On an insulator film formed on a substrate 1, amorphous silicon films 3a, 3b are patterned in a predetermined channel shape. Subsequently, in a region 4 including the amorphous silicon films 3a, 3b, the amorphous silicon films 3a, 3b are irradiated with laser light and fused temporarily, before being solidified. Solidification of a fusion part is started from the edge of a channel region, and a polysilicon film having a grain boundary extending from the edge toward the central part is formed. When forming a source-drain electrode, and the like, by using the polysilicon film as a channel region, a transistor of high speed operation having a high carrier mobility can be obtained.

Description

  The present invention relates to a low-temperature polysilicon film that crystallizes a-Si into polycrystalline silicon (hereinafter referred to as polysilicon) by irradiating an amorphous silicon film (hereinafter referred to as a-Si film) with laser light and annealing. And a method for manufacturing a thin film transistor.

  The low-temperature polysilicon thin film transistor once forms an a-Si: H film in the channel region, and then irradiates the a-Si: H film with a laser beam such as a YAG laser or an excimer laser to perform laser annealing. It is manufactured by a low-temperature polysilicon process in which an a-Si: H film is crystallized into a polysilicon film by a phase transition of melt solidification in an extremely short time. As a crystal growth method in which the a-Si film is annealed by laser light irradiation and crystallized into a polysilicon film, there are an ELA (excimer laser annealing) method and an SLS (sequential lateral solidification) method. In the ELA method, a-Si film is irradiated a plurality of times (about 20 times) with a low energy laser beam to uniformly grow crystals. On the other hand, in the SLS method, a high-energy laser beam is irradiated once to form a crystal that is long in one direction. As described above, in the SLS method, a crystal structure in which crystal grains extend in one direction can be obtained. Therefore, by passing a channel current in this direction, a path with few crystal grain boundaries that become an obstacle for electron movement can be obtained. Channel current can flow, electron mobility can be increased, and the speed and performance of the transistor can be increased. For this purpose, it is necessary to control the growth direction of the crystal grains.

  Therefore, the applicant of the present application has already proposed a method for obtaining a low-temperature polysilicon film in which the growth direction of crystal grains is aligned in a certain direction (Patent Document 1). In this method, first, an amorphous silicon film is irradiated with laser light through a mask by a microlens, so that the amorphous silicon film is irradiated with laser light that has passed through the transmission region of the mask to Then, the amorphous silicon film is irradiated with laser light by a microlens without using the mask, so that the remaining amorphous silicon film is polycrystallized using the polysilicon region as a crystal nucleus. As a result, crystallization proceeds using the first polysilicon region as a crystal nucleus, and a low-temperature polysilicon film in which the main growth direction of crystal grains is aligned is obtained. In another method described in Patent Document 1, the irradiation condition of the laser light is sufficient to melt and crystallize the portion of the amorphous silicon film corresponding to the light shielding region of the mask. At this time, a temperature difference exists between the portion corresponding to the light shielding region and the portion corresponding to the transmission region in the amorphous silicon film. This method also provides a low-temperature polysilicon film in which the main growth direction of crystal grains is aligned.

JP 2012-4250 A

  However, in the conventional low-temperature polysilicon film forming method described above, when the channel region has a complicated planar shape, for example, because the channel region is curved, the carrier moving direction between the electrodes and the crystal grains There is a problem that it is complicated to control the growth of the crystal so that the growth direction coincides.

  The present invention has been made in view of such problems, and even if the planar shape of the channel region is complicated, the growth direction of crystal grains can be extended in a desired direction according to the moving direction of carriers, It is an object of the present invention to provide a method for forming a low-temperature polysilicon film and a method for manufacturing a thin film transistor capable of forming a channel region for high-speed operation at an arbitrary position.

  The method for forming a low-temperature polysilicon film according to the present invention includes a step of forming an amorphous silicon film on a substrate, a step of patterning the amorphous silicon film into a plurality of patterns having a predetermined island shape, And a step of crystallizing the amorphous silicon film into a polysilicon film by irradiating a region enveloping the pattern with laser light, and a step of forming an electrode on the polysilicon film.

  A method of manufacturing a thin film transistor according to the present invention includes a step of forming an insulating film on a substrate, a step of patterning a gate electrode on the insulating film, a step of forming a gate insulating film on the gate electrode, Forming an amorphous silicon film, and patterning the amorphous silicon film to form a plurality of island patterns having a predetermined channel region shape in a region facing the gate electrode with the gate insulating film interposed therebetween, Irradiating a region including the one or a plurality of patterns with laser light to crystallize the amorphous silicon film into a polysilicon film; and forming a source / drain electrode on the polysilicon film; It is characterized by having.

  According to the present invention, an amorphous silicon film is formed in a predetermined shape such as a channel region, and then the amorphous silicon film is once melted by irradiating the channel region with laser light by the SLS method. Thereafter, the molten region in the shape of the channel region is cooled by heat transfer to the lower layer film. At this time, first, cooling is started from the edge of the channel region toward the center of the channel region. Cooling proceeds. For this reason, after the amorphous silicon film in the shape of the channel region is melted and solidified, the formed polysilicon film has a shape in which crystal grains extend from the center of the channel region toward the edge. For this reason, a channel region of a crystal structure in which crystal grains extend in the direction in which carriers flow is formed, and there are few crystal grain boundaries in the carrier movement path, and the carrier mobility is high. Therefore, according to the present invention, it is possible to increase the driving speed and reduce the power consumption of the transistor. Further, since the growth direction of the crystal grains can be controlled only by forming an amorphous silicon film having a desired shape such as a channel region, the transistor design is facilitated.

It is a schematic diagram which shows the formation method of the low-temperature polysilicon film which concerns on 1st Embodiment of this invention, and shows the process of patterning an amorphous silicon film. It is a figure which shows the process of laser-annealing the patterned amorphous silicon film. It is a figure which shows the polysilicon film | membrane crystallized by laser annealing. It is a figure which shows the process of forming each electrode of a transistor by using a polysilicon film as a channel region. It is a figure which shows the temperature distribution of the fusion | melting part by laser irradiation. It is a figure which shows the laser annealing apparatus using a micro lens array. It is sectional drawing which shows the manufacturing method of the thin-film transistor to which the formation method of the low-temperature polysilicon film of this embodiment was applied.

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a plan view showing a method for forming a low-temperature polysilicon film according to an embodiment of the present invention. This low-temperature polysilicon film is applied to formation of a channel region of a thin film transistor. The right view of FIG. 1 shows the region 2 on the substrate 1 in an enlarged manner. An insulating film such as a SiO ₂ film is formed on the entire surface of the substrate 1 such as a glass substrate, and an amorphous silicon film is formed on the entire surface of the insulating film (not shown). Then, after coating the resist film on the entire surface, a pattern corresponding to the channel region is formed on the resist film by exposure and development, and then the amorphous silicon film is etched away using the resist pattern as a mask. Then, the amorphous silicon film is patterned into the shape of the channel region. Thereby, a plurality of amorphous silicon films 3a and 3b are formed at predetermined positions on the substrate 1 as island patterns having the shape of the channel region so as to be scattered at positions where the channel region is to be disposed. The

  The amorphous silicon films 3a and 3b have, for example, a U shape as shown in FIG. As will be described later with reference to FIG. 4, the source electrode 15 is formed in a straight line in a later process, and the drain electrode 14 is scheduled to be formed so as to surround the source electrode 15 from both sides. This is because the channel region is formed in a U shape as a region where the source electrode 15 and the drain electrode 14 face each other.

  After the amorphous silicon films 3a and 3b are formed in a channel shape, the region 4 including one or a plurality of amorphous silicon films 3a and 3b is irradiated with laser light as shown in FIG. This laser light is of high energy according to the SLS method, for example, excimer laser light. The entire rectangular region 4 including the amorphous silicon films 3a and 3b is irradiated with laser light. As a result, the amorphous silicon films 3a and 3b are irradiated with high-energy laser light and absorb the energy of the laser light to rise in temperature and melt, but the underlying insulating film is irradiated with laser light. However, since the laser beam energy is not absorbed, the temperature does not increase.

  As described above, the insulating film absorbs the energy of the laser beam not only in the lower layer portions of the amorphous silicon films 3a and 3b but also in the exposed portion, so that the temperature hardly increases. Mainly, only the amorphous silicon films 3a and 3b are irradiated with laser light, and the temperature rises and is once melted. Thereafter, for example, in about 20 ns, the molten silicon is cooled and solidified, but at this time, cooling starts from the edge of the U-shaped channel region and solidification starts, and solidification of the U-shaped center portion is performed. Remains until the end. That is, the central portion of the U-shaped channel region is a portion that remains undissolved until the end of solidification when the melted portion solidifies. As a result, as shown in FIG. 3, polysilicon films 13a and 13b are formed in which the crystal grains extend so as to extend from the center to the edge.

  Thereafter, as shown in FIG. 4, the source electrode 15 extending linearly with the polysilicon films 13 a and 13 b as channel regions, and the drain electrode 14 surrounding both sides of the source electrode 15, the source electrode 15 and A region facing the drain electrode 14 is formed so as to be aligned with a region where the polysilicon films 13a and 13b are formed. Then, a gate insulating film (not shown) is formed on the source electrode 15, the drain electrode 14, and the channel region (polysilicon films 13a and 13b), and the gate electrode 16 is formed on the gate insulating film. Form.

  Next, an example of an annealing apparatus using laser light irradiation will be described. FIG. 6 is a view showing an apparatus for irradiating an amorphous silicon film by irradiating the substrate 1 with laser light using a microlens array. In the laser annealing apparatus using the microlens, the laser light emitted from the light source 21 is shaped into a parallel beam by the lens group 22 and irradiated onto the substrate 1 through the microlens array 25 including a large number of microlenses 27. . The laser light source 21 is, for example, an excimer laser that emits laser light having a wavelength of 308 nm or 353 nm at a repetition period of 50 Hz, for example. The microlens array 25 has a large number of microlenses 27 arranged on a transparent substrate, and a light shielding film 26 for blocking stray light is formed on the upper surface of the transparent substrate corresponding to the microlenses 27. The laser light that has passed through the light-shielding film 26 is condensed by the microlens 27 onto a region to be formed of the channel region of the thin film transistor set on the substrate 1. A mask 23 is disposed above the microlens array 25, and the region 4 on the substrate 1 is irradiated with laser light through an opening of a light shielding film 24 provided on the mask 23. Accordingly, the opening of the light shielding film 24 of the mask 23 is formed in a size and position corresponding to the region 4 including the channel regions (amorphous silicon films 3a and 3b) on the substrate 1.

  Next, the operation of the method for forming a low-temperature polysilicon film and the method for manufacturing a thin film transistor configured as described above will be described. First, as shown in FIG. 1, an insulating film (not shown) is formed on the substrate 1, and an amorphous silicon film is formed thereon. Then, a resist pattern is formed in the shape of a predetermined channel region on the amorphous silicon film, and the amorphous silicon film is etched using the resist pattern as a mask to have the shape of the channel region as shown in FIG. Amorphous silicon films 3a and 3b are formed.

  Specifically, the present invention is applied to the manufacture of a thin film transistor as shown in FIG. FIG. 7 is a cross-sectional view showing a transistor in a general panel structure of an AMOLED (Active-Matrix Organic Light-Emitting Diode) as an example. FIG. 7 is a cross-sectional view in the direction perpendicular to the longitudinal direction of the source electrode 15 and the drain electrode 14 of the transistor shown in FIG. A buffer layer 31 as an insulating film is formed on a glass substrate as the substrate 1, an amorphous silicon film is formed on the buffer layer 31, and this amorphous silicon film is patterned as described later, Get the shape of the channel region. Then, as will be described later, this patterned amorphous silicon film is irradiated with laser light and annealed, and the amorphous silicon film is crystallized to form a polysilicon film 13a (13b). Thereafter, the lower layer portion of the insulating film 33 is formed on the entire surface, and the gate electrode 16 is patterned on the lower layer portion of the insulating film. The lower layer portion of the insulating film 33 is a portion that becomes a gate insulating film. Thereafter, the upper layer portion (interlayer insulating film) of the insulating film 33 is formed on the entire surface, contact holes are formed in the insulating film 33, and the source electrode 15 and the drain electrode 14 connected to the polysilicon film 13a (13b) are formed. Thereafter, an insulating film 38 as a passivation film is formed on the entire surface, and wiring layers 39 a and 39 b are formed on the insulating film 38. The wiring layers 39 a and 39 b are connected to the drain electrode 14 through a contact hole formed in the insulating film 38. Reference numeral 40 denotes a spacer for separating an organic EL color element formed on the insulating film 38. In FIG. 7, the source electrode 15 is disposed in the center, the source electrode 14 is disposed on both sides thereof, and the polysilicon film 13a (13b) is disposed between the source electrode 15 and the drain electrode 14 on both sides thereof. Has been. As shown in FIG. 4, the U-shaped polysilicon films 13a and 13b, the U-shaped drain electrode 14, and the linear source electrode 15 at the center thereof are arranged. This is because the two polysilicon films 13a (13b) and the two drain regions 14 are common to each other at the back or in front of the paper surface in FIG. It is connected to the.

  Next, laser annealing for the amorphous silicon film will be described in detail. Using the laser annealing apparatus using the microlens array shown in FIG. 6, the region 4 including these amorphous silicon films 3a and 3b is irradiated with laser light for each of one or a plurality of amorphous silicon films 3a and 3b. To do. The intensity of the energy of the laser beam is such that the amorphous silicon films 3a and 3b can be melted by one laser beam irradiation, and so-called SLS annealing is performed. In this annealing process, only the amorphous silicon films 3a and 3b substantially absorb the energy of the laser beam, and the underlying insulating film and the glass substrate 1 do not absorb the laser beam. Therefore, as shown in FIG. 5A, for example, when the temperature distribution is observed in the direction perpendicular to the longitudinal direction of the amorphous silicon film 3b, only the amorphous silicon film 3b rises as shown in FIG. 5B. The temperature of the substrate 1 and the insulating film is not raised, and the temperature of the substrate 1 and the insulating film is about 30 ° C., which is the same as before the laser light irradiation, and only the amorphous silicon film 3b is about 2000 ° C. A temperature pattern is obtained. Accordingly, the amorphous silicon film 3b is melted. However, as shown in FIG. 5B, when this temperature pattern is compared between the center portion in the width direction of the amorphous silicon film 3b and the edge portion, the laser beam is input at the center portion of the amorphous silicon film 3b. Although the temperature is as high as 2000 ° C. corresponding to the energy, the temperature is relatively low at the edge of the amorphous silicon film 3b. From the temperature of the substrate 1 and the insulating film (about 30 ° C.), the amorphous silicon film 3b A temperature gradient is formed up to 2000 ° C. at the center of the substrate. For this reason, when the irradiation of the laser beam is stopped and the melted part is cooled, the heat of the melted part flows and cools to the lower insulating film and the substrate 1, but during this cooling period of 20 ns, Cooling starts from the edge of the channel region and progresses, and solidification starts from the edge of the channel region. This solidification starts from the edge of the channel region to the center of the channel region (in the amorphous silicon films 3a and 3b). Go to the center of the area). Therefore, as shown in FIG. 3, the solidification of the molten portion proceeds from the edge of the channel region toward the center thereof, so that the crystal grains grow so as to extend from the edge of the channel region toward the center. . Eventually, the central portion of the channel region is solidified, and the solidification process is completed. Thereby, polysilicon films 13a and 13b in which crystal grains extend in the width direction of the channel region (direction perpendicular to the longitudinal direction) are formed.

  Thereafter, as shown in FIG. 4, the linear source electrode 15 and the drain electrode 14 having a shape surrounding the source electrode 15 are formed, and the region between the source electrode 15 and the drain electrode 14 is a polysilicon film. It is formed so as to match with 13a and 13b. Further, a gate insulating film is formed on the source electrode 15, the drain electrode 14, and the polysilicon films 13a and 13b, and then a gate electrode 16 is formed. Thus, a thin film transistor having a channel region in which a crystal grain boundary extends in a direction in which carriers flow can be obtained.

  A transistor having the polysilicon films 13a and 13b having such a crystal structure as a channel region has few crystal grain boundaries to be passed in the carrier movement region of the channel region, and has high carrier mobility. Therefore, a transistor operating at high speed can be obtained. In addition, since there are few crystal grain boundaries through which carriers pass, current conductivity is high and resistance is low, so that power consumption can be reduced.

  A conventional method for forming a low-temperature polysilicon film is to first form an amorphous silicon film, and then melt the amorphous silicon film once by excimer laser light irradiation, and then solidify to form a polysilicon film. Thereafter, the polysilicon film is etched to form a channel region having a predetermined shape. For this reason, control of the crystal growth direction at the time of laser annealing was complicated. However, in the present invention, after an amorphous silicon film is formed, the amorphous silicon film is patterned to form a channel region, and then the region including the patterned amorphous silicon film is irradiated with laser light. Then, it is crystallized into a polysilicon film.

  In the present invention, by patterning the amorphous silicon film so that the width is sufficiently shorter than the length, for annealing, simply irradiating the region including the pattern of the amorphous silicon film with laser light, A polysilicon film having a crystal grain boundary extending from the edge of the pattern toward the center can be formed. Therefore, by simply patterning the amorphous silicon film into a predetermined shape, the direction in which the crystal grain boundary extends after annealing can be controlled in a self-aligned manner according to the shape, and the channel region for high-speed operation can be placed at an arbitrary position. In addition, it is possible to control the flow direction of the high-speed operation carrier in an arbitrary direction. This facilitates transistor design.

  Needless to say, the shapes of the source electrode, the drain electrode, and the gate electrode are not limited to those shown in the above embodiment. Further, the structure of the transistor is not limited to the above embodiment.

  INDUSTRIAL APPLICABILITY The present invention is useful for manufacturing a thin film transistor that has transistor characteristics with high speed operation and low power consumption and is easy to design.

1: substrate 2: regions 3a, 3b: amorphous silicon film 4: regions 13a, 13b: polysilicon film 14: drain electrode 15: source electrode 16: gate electrode

Claims (2)

A step of forming an amorphous silicon film on the substrate; a step of patterning the amorphous silicon film into a plurality of patterns of a predetermined island shape; and irradiating a region enclosing the one or more patterns with laser light. A method for forming a low-temperature polysilicon film, comprising: a step of crystallizing the amorphous silicon film into a polysilicon film; and a step of forming an electrode on the polysilicon film. Forming an insulating film on the substrate; patterning a gate electrode on the insulating film; forming a gate insulating film on the gate electrode; forming an amorphous silicon film on the entire surface; Including a step of patterning the amorphous silicon film to form a plurality of island patterns having a predetermined channel region shape in a region facing the gate electrode with the gate insulating film interposed therebetween, and the one or more patterns included A thin film transistor comprising: a step of crystallizing the amorphous silicon film into a polysilicon film by irradiating a region to be irradiated with laser light; and a step of forming a source / drain electrode on the polysilicon film. Method.

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