JP2020107716A - Laser annealing method and laser annealing apparatus - Google Patents

Abstract

To provide a laser annealing method capable of stably forming a high mobility polycrystalline silicon film or pseudo single crystal silicon film in a required area, having good controllability of laser irradiation conditions to a substrate to be processed, achieving a significant cost reduction.SOLUTION: As laser light, using continuous wave laser light emitted from a continuous wave laser, energy density of a downstream side portion in a moving direction (direction opposite to a substrate moving direction T) for relatively moving a beam spot LBS at the beam spot LBS is set higher than energy density of an upstream side portion of the beam spot LBS in the moving direction. After projecting the beam spot LBS at an edge of an area to be modified to form a seed crystal region, by moving the beam spot LBS in the moving direction, an entire surface of the area to be modified is modified into a crystallized silicon film with the seed crystal region as a starting point.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laser annealing method and a laser annealing apparatus.

A thin film transistor (TFT) is used as a switching element for actively driving a flat panel display (FPD). As a material of a semiconductor layer of a thin film transistor (hereinafter referred to as a TFT), amorphous silicon (a-Si:amorphous Silicon), polycrystalline silicon (p-Si:polycrystalline Silicon), or the like is used.

Amorphous silicon has a low mobility (μ), which is an index of electron mobility. For this reason, amorphous silicon cannot support the high mobility required for FPDs, which are becoming higher in density and definition. Therefore, as the switching element in the FPD, it is preferable to form the channel semiconductor layer from polycrystalline silicon, which has significantly higher mobility than amorphous silicon. As a method of forming a polycrystalline silicon film, an excimer laser annealing (ELA: Excimer Laser Annealing) device using an excimer laser is used to irradiate the amorphous silicon film with laser light to recrystallize the amorphous silicon. There is a method of forming polycrystalline silicon.

As a conventional laser annealing method, there is known a technique using a pulsed laser beam of excimer laser light generated by an excimer laser annealing (hereinafter referred to as ELA) device in an irradiation region (see Patent Document 1).

In this laser annealing method, the region to be processed is irradiated with a high-energy portion that generates a pulsed laser beam, and after passing through this high-energy portion, a low-energy portion that is a laser beam with a smaller energy than that is successively obtained. Irradiation. In this laser annealing method, the residual poorly crystallized region generated by the high energy portion by the irradiation of the low energy portion is crystallized.

As another laser annealing method, a method has been proposed in which a laser beam of pulsed laser light by an ELA device is provided with an energy distribution along the scanning direction.

JP 2002-313724A

However, the ELA device is a gas laser using a special gas, and there is a problem that the equipment cost and the maintenance cost are high. Further, the ELA device has a problem that the generated output is strong and it is difficult to keep the phase (coherence) of the laser light in phase and the output constant.

The laser annealing method disclosed in the above-mentioned Patent Document 1 requires a large number of light sources, and thus has a problem of higher cost. Further, the crystal grain size of the polycrystalline silicon formed by the pulsed light irradiation of the excimer laser is about several tens to 350 nm. With such a crystal grain size, higher mobility cannot be satisfied. Even today, a TFT of a driver circuit for turning on/off a pixel transistor in an FPD is required to have high mobility in a channel semiconductor layer region. Furthermore, in FPDs, with the increase in size, resolution, and speed of moving image characteristics, there is a demand for higher mobility in TFTs as pixel switching elements.

The present invention has been made in view of the above problems, and can stably form a high-mobility polycrystalline silicon film, a pseudo single crystal silicon film, or the like in a necessary region and perform laser irradiation on a substrate to be processed. It is an object of the present invention to provide a laser annealing method and a laser annealing apparatus which have good controllability of conditions and can achieve significant cost reduction.

In order to solve the above-mentioned problems and to achieve the object, an aspect of the present invention is to move a beam spot of laser light relative to a region to be modified in an amorphous silicon film, A laser annealing method for modifying a crystallized silicon by laser annealing a silicon film, wherein the laser beam is a continuous wave laser beam emitted from a continuous wave laser, and the beam spot in the beam spot is a relative beam. Energy density of the downstream side portion of the moving direction to be moved in a higher direction than the energy density of the upstream side portion of the beam spot in the moving direction,
After forming the seed crystal region by projecting the beam spot on the edge portion of the reforming scheduled region, the beam spot is moved in the moving direction, and the reforming scheduled from the seed crystal region as a starting point. It is characterized in that the entire surface of the region is modified into a crystallized silicon film.

In the above aspect, after the seed crystal region is formed, the emission of the continuous wave laser beam is stopped, and then the emission of the continuous wave laser beam is started within a predetermined time to move the beam spot. Is preferred.

In the above aspect, it is preferable that after the seed crystal region is formed, the beam spot is continuously moved while the continuous oscillation laser light is emitted.

In the above aspect, it is preferable that the energy density of the upstream side portion of the beam spot gradually decreases toward the upstream side in the moving direction.

In the above aspect, the continuous wave laser is preferably a semiconductor laser.

As the above aspect, the energy density of the downstream side portion of the beam spot is set higher than a threshold value for melting the amorphous silicon film, and the energy density of the upstream side portion of the beam spot in the moving direction is set. It is preferable that the threshold value is set so as to gradually decrease by passing through the threshold value toward the upstream side.

In the above aspect, the beam spot is formed in an elongated rectangular shape, and the beam spot is projected on the amorphous silicon film so that the major axis of the beam spot is in a direction orthogonal to the moving direction. It is preferable.

According to another aspect of the present invention, the beam spot is relatively moved with respect to the amorphous silicon film formed on the substrate to be processed, and the amorphous silicon film is laser-annealed to crystallize silicon. A laser annealing apparatus for reforming into a base, on which the substrate to be processed is arranged, and a continuous wave laser beam that is moved relative to the substrate to be processed arranged on the base and emits continuous wave laser light. An energy density of a downstream portion of the beam spot of the continuous wave laser beam emitted from the continuous wave laser in the moving direction in which the beam spot is relatively moved. Is set to be higher than the energy density of the upstream side portion of the beam spot in the moving direction.

In the above aspect, it is preferable that the energy density of the upstream side portion of the beam spot is set to gradually decrease toward the upstream side in the moving direction.

In the above aspect, the continuous wave laser is preferably a semiconductor laser.

In the above aspect, the energy density in the downstream portion of the beam spot is set higher than a threshold value for melting the amorphous silicon film, and the energy density in the upstream portion of the beam spot is in the moving direction. It is preferable that the threshold value is set so as to pass through the threshold value and gradually decrease toward the upstream side.

In the above aspect, it is preferable that the beam spot is formed in an elongated rectangular shape and is arranged such that a major axis of the beam spot is in a direction orthogonal to the moving direction.

In the above aspect, the laser beam irradiation unit includes an asymmetric cylindrical lens set such that the energy density of the downstream portion is higher than the energy density of the upstream portion of the beam spot. Is preferred.

According to the present invention, a high-mobility polycrystalline silicon film, a pseudo single crystal silicon film, or the like can be stably formed in a necessary region, controllability of laser irradiation conditions on a substrate to be processed is good, and significantly low cost is achieved. It is possible to realize a laser annealing method and a laser annealing apparatus that can achieve high efficiency.

FIG. 1 is a schematic configuration diagram of a laser annealing apparatus used in a laser annealing method according to an embodiment of the present invention. FIG. 2 is a perspective view showing an asymmetric cylindrical lens used in the laser annealing apparatus according to the embodiment of the present invention. 3A is an explanatory view showing the energy density distribution of the laser beam at the position A in FIG. 1, and FIG. 3B is an explanatory view showing the energy density distribution of the laser beam at the position B in FIG. (C) is an explanatory view showing the energy density distribution of the laser beam at position C in FIG. 1. FIG. 4 is an explanatory plan view showing a state in which the substrate to be processed is moved and laser annealing is started using the laser annealing apparatus according to the embodiment of the present invention. FIG. 5A is an explanatory plan view showing a substrate to be processed which is subjected to laser annealing by the laser annealing method according to the embodiment of the present invention. FIG. 5-2 is a plan view showing a state in which a beam spot is projected on the edge of the modification target region by the laser annealing method according to the embodiment of the present invention. FIG. 5C is an explanatory plan view showing a state in which the beam spot is moved to the intermediate portion of the modification target region by the laser annealing method according to the embodiment of the present invention. FIG. 6A is a plan explanatory view showing a state in which the beam spot is moved to the other end edge of the modification target region by the laser annealing method according to the embodiment of the present invention. FIG. 6-2 is an explanatory diagram showing a relationship between time and energy intensity when laser annealing is performed on a region to be modified by the laser annealing method according to the embodiment of the present invention. FIG. 6C is an explanatory diagram showing a relationship between time and energy intensity when laser annealing is performed on a region to be modified by another example of the laser annealing method according to the embodiment of the present invention. FIG. 7 is a perspective view showing a modified example of the asymmetric cylindrical lens used in the laser annealing apparatus according to the present embodiment of the present invention.

The details of the laser annealing method and the laser annealing apparatus according to the embodiment of the present invention will be described below with reference to the drawings. However, it should be noted that the drawings are schematic and the number of each member, the size of each member, the ratio of the sizes, the shape, and the like are different from the actual ones. In addition, the drawings include portions having different dimensional relationships, ratios, and shapes.

[Embodiment]
Prior to the description of the laser annealing method, an example of the substrate to be annealed by the laser annealing method and the laser annealing apparatus 10 used in the laser annealing method will be described.

(Substrate to be processed)
As shown in FIG. 1, a substrate 1 to be processed includes a glass substrate 2, a gate wiring 3 arranged on the surface of the glass substrate 2, a glass substrate 2 and a gate insulating film 4 formed on the gate wiring 3. And an amorphous silicon film 5 deposited on the entire surface of the gate insulating film 4. The substrate 1 to be processed finally becomes a TFT substrate in which a thin film transistor (TFT) or the like is formed. In the present embodiment, the entire surface of the amorphous silicon film 5 is used as the region to be modified, but it is not limited to this and the size and shape can be changed as appropriate.

(Schematic configuration of laser annealing device)
Hereinafter, the schematic configuration of the laser annealing apparatus 10 according to the present embodiment will be described with reference to FIGS. 1 to 4. As shown in FIG. 1, the laser annealing apparatus 10 includes a base 11 and a laser beam irradiation unit 12.

The base 11 is provided with a substrate transfer means (not shown). In this laser annealing apparatus 10, with the substrate 1 to be processed placed on the base 11, the substrate moving means T (not shown) moves the substrate moving direction T opposite to the relative moving direction Tr of the beam spot LBS described later. Transport to. As shown in FIG. 6A, the relative movement direction Tr of the beam spot LBS is a direction indicated by an arrow Tr in FIG. 6A and is a direction opposite to the substrate movement direction T of the substrate 1 to be processed. Is.

As shown in FIG. 1, the laser beam irradiation unit 12 includes a semiconductor laser 13 as a light source that oscillates continuous wave laser light (CW laser light), a first lens 14, a second lens 15, and a first fly's eye. The lens 16, the second fly-eye lens 17, the first cylindrical lens 18, the second cylindrical lens 19, and the asymmetric cylindrical lens 20 are provided. In the laser beam irradiation unit 12, as shown in FIG. 4, the beam spot LBS projected on the amorphous silicon film 5 is set to have an elongated rectangular shape.

In the present embodiment, the continuous wave laser light emitted from the semiconductor laser 13 becomes a laser beam which is diffused and expanded by the first lens 14 and the second lens 15. The laser beam emitted from the semiconductor laser 13 (the laser beam at the position A in FIG. 1) has an energy density distribution as shown in FIG. 3A and has a bilaterally symmetrical Gaussian distribution. The laser beam that has passed through the second cylindrical lens 19 has a rectangular wave-like energy density distribution as shown in FIG.

As shown in FIGS. 1 and 2, the asymmetric cylindrical lens 20 is formed such that a convex lens portion 21 and a concave lens portion 22 extend in the longitudinal direction. As shown in FIG. 1, the convex lens portion 21 has a function of converging light rays forming the laser beam LB. Further, the concave lens portion 22 has a function of dispersing the light rays forming the laser beam LB.

Therefore, as shown in FIG. 3C, the minor axis direction (direction parallel to the substrate moving direction T) of the laser beam LB (the laser beam at the position C in FIG. 1) that has passed through the asymmetric cylindrical lens 20. The energy density distribution of has a high area AH and a low area AL. When the high region AH is projected as a part of the beam spot LBS, the temperature at which the amorphous silicon film 5 is heated due to this high energy density is higher than the threshold value of the temperature at which the amorphous silicon film 5 is melted. Is also set high.

On the other hand, in the region AL having a low energy density shown in FIG. 3C, the energy density is set to gradually decrease toward the upstream side in the moving direction of the beam spot LBS (direction opposite to the substrate moving direction T). Has been done.

The slope portion SP in the energy density distribution of the low region AL in FIG. 3C has a slope that gradually decreases after passing the temperature at which the amorphous silicon film 5 is melted. The degree of inclination of the inclined portion SP is set based on experimental values.

(Laser annealing method)
The laser annealing apparatus 10 according to the present embodiment has been described above. Next, a laser annealing method for performing a laser annealing process on the amorphous silicon film 5 on the surface of the substrate 1 to be processed using the laser annealing apparatus 10 Will be described.

In the present embodiment, an example in which a plurality of substrates 1 to be processed are arranged on a base 11 as shown in FIG. 4 will be described, but the present invention is not limited to such a processing mode. Hereinafter, a case where the laser annealing process is performed on the entire surface of the amorphous silicon film 5 on the surface of one substrate 1 to be processed shown in FIG. 5A will be described.

First, the substrate 1 to be processed is placed at the standby position with respect to the position of the beam spot LBS created by the laser beam irradiation unit 12. At this point, the laser beam irradiation unit 12 is turned off.

Next, with the position of the beam spot LBS fixed, the substrate 1 to be processed is transported in the substrate moving direction T at a predetermined speed. As shown in FIG. 5-2, when the edge portion of the amorphous silicon film 5 serving as the modification target region moves to the position where the beam spot LBS is projected, the laser beam irradiation unit 12 is set to a predetermined short length. After turning on for a time, switch it off.

In the present embodiment, the seed crystal region 5A is formed at the edge of the amorphous silicon film 5 by the irradiation of the laser beam with the beam spot LBS for a short time (FIGS. 5-3 and 6). -1). The width dimension W of the seed crystal region 5A shown in FIG. 6A in the short axis direction is the same as the width of the beam spot LBS in the short axis direction, and as shown in FIG. It corresponds to the time width t in the energy density distribution in the axial direction (substrate length direction).

During the annealing with the beam spot LBS for the predetermined short time, the amorphous silicon film 5 in the region corresponding to the high region AH shown in FIG. 3C is instantly melted. At this time, the temperature gradient (gradient of energy density) in which the amorphous silicon film 5 (molten silicon) obtained by melting the amorphous silicon film 5 in the region corresponding to the low region AL gradually decreases in the substrate moving direction T Thus, the seed crystal region 5A made of microcrystalline silicon is formed in the substrate moving direction T.

Next, immediately after the seed crystal region 5A is formed as described above, as shown in FIG. 6B, the laser beam irradiation unit 12 is turned on again and the irradiation of the laser beam LB is restarted. At this time, the substrate 1 to be processed is moved along the substrate moving direction T at a constant speed. Then, when it reaches the position where the beam spot LBS is projected on the other edge of the reforming target area of the substrate to be processed 1, the laser beam irradiation unit 12 is turned off.

By performing such a laser annealing method, as shown in FIG. 6A, substantially the entire reformed region is crystallized from one edge of the amorphous silicon film 5 to the other edge. The pseudo single crystal silicon film 5B as silicon can be modified. Here, when the pseudo single crystal silicon film 5B is grown, the seed crystal region 5A serves as a starting point to promote the crystal growth of the high quality pseudo single crystal silicon film 5B. In the above embodiment, the beam spot LBS having the distribution of the region AH having high energy intensity and the region AL having low energy intensity is used when forming the seed crystal region 5A, but a beam spot having uniform energy intensity is used. You may use. The seed crystal region 5A may be formed while the substrate 1 to be processed is stationary with respect to the beam spot LBS. The laser used to form the seed crystal region 5A may be a pulse laser.

As described above, in the laser annealing method according to the present embodiment, the CW laser light emitted from the continuous wave laser is used as the laser light. Further, in this laser annealing method, the energy density of the beam spot LBS in the downstream side portion (higher area AH) in the moving direction (direction opposite to the substrate moving direction T) in the beam spot LBS is changed to the upstream side portion (lower area). It is set higher than the energy density of (AL).

Then, in the present embodiment, as shown in FIG. 6B, after the seed crystal region 5A is formed, the laser beam irradiation unit 12 is turned off to stop the emission of continuous wave laser light. After that, the emission of the continuous wave laser beam is started within a predetermined short time, and the beam spot LBS is moved relative to the substrate 1 to be processed.

In the present embodiment, as in the laser annealing method described above, the energy density of the low region AH (upstream side portion) in the beam spot LBS is directed toward the upstream side in the moving direction (direction opposite to the substrate moving direction T) Tr. By setting the beam spot LBS so as to be gradually reduced, the good quality seed crystal region 5A can be formed only by projecting the beam spot LBS on the amorphous silicon film 5. Therefore, the seed crystal region 5A can be used as a starting point for the subsequent growth of the high-quality pseudo single crystal silicon film 5B.

Since the laser annealing apparatus 10 according to the present embodiment uses the semiconductor laser as the continuous wave laser, the apparatus can be downsized.

In the above laser annealing method and laser annealing apparatus 10, the beam spot LBS is formed in an elongated rectangular shape, and the long axis of the beam spot LBS is perpendicular to the moving direction (direction opposite to the substrate moving direction T) Tr. By setting so that it is possible to cope with a wide area to be modified.

(Effects of laser annealing method and laser annealing apparatus)
According to the laser annealing method and the laser annealing apparatus 10 according to the present embodiment, crystallized silicon such as a high-mobility polycrystalline silicon film or pseudo single crystal silicon film can be stably formed in a necessary region.

Further, according to the laser annealing apparatus 10 according to the present embodiment, since continuous wave laser light can be used, especially the semiconductor laser 13, the controllability of the laser irradiation conditions on the substrate 1 to be processed is good, and the laser irradiation condition can be greatly improved. It is possible to achieve an extremely low cost.

In the laser annealing apparatus 10 according to the present embodiment, since the seed crystal region 5A and the pseudo single crystal silicon film 5B can be produced by using a single light source, it is possible to significantly reduce the number of laser annealing steps. is there. Therefore, by applying the laser annealing apparatus 10 according to the present embodiment to the manufacture of the TFT, the manufacturing process of the TFT can be simplified.

[Other Embodiments]
Although the embodiments have been described above, it should not be understood that the description and drawings forming part of the disclosure of the embodiments limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

For example, in the laser annealing method and the laser annealing apparatus 10 according to the above embodiment, the semiconductor laser 13 as a light source that oscillates continuous wave laser light (CW laser light) is applied, but the invention is not limited to this. It is also possible to use various lasers that oscillate a continuous wave laser beam such as a solid laser, a gas laser, and a metal laser. Further, as the continuous wave laser, it is also possible to use a pseudo continuous wave laser including a laser having a pulse width longer than the cooling time of the molten silicon, for example, a laser having a pulse width of several hundreds ns to 1 ms or more. It is a range.

In the laser annealing method according to the above-described embodiment, as shown in FIG. 6B, after forming the seed crystal region 5A, the laser beam irradiation unit 12 is turned off to stop the emission of continuous wave laser light. However, as shown in another embodiment of FIG. 6C, the beam spot LBS may be continuously moved relatively after forming the seed crystal region 5A.

In the laser annealing apparatus 10 according to the above-described embodiment, the structure having the concave lens portion 22 as the asymmetric cylindrical lens 20 is applied. However, as in the asymmetric cylindrical lens 20A shown in FIG. You may apply the thing of the structure which has and the plane part 23. The beam to be created depends on whether the concave lens portion 22 such as the asymmetric cylindrical lens 20 shown in FIG. 2 is selected or the plane portion 23 such as the asymmetric cylindrical lens 20 shown in FIG. 7 is selected. It can be determined according to the energy density distribution applied to the spot LBS.

Although the pseudo single crystal silicon film 5B is formed as the crystallized silicon film in the above-described embodiment, the polycrystalline silicon film may of course be grown from the seed crystal region. Also in this case, it becomes possible to form a high-quality polycrystalline silicon film starting from the seed crystal region 5A.

LB laser beam LBS beam spot T substrate moving direction (direction opposite to relative moving direction Tr of beam spot)
Tr Relative movement direction W Width dimension 1 Substrate 2 Glass substrate 3 Gate wiring 4 Gate insulating film 5 Amorphous silicon film 5A Seed crystal region 5B Pseudo-single crystal silicon (crystallized silicon) film 10 Laser annealing device 11 bases Table 12 Laser beam irradiation unit 13 Semiconductor laser 14 First lens 15 Second lens 16 First fly-eye lens 17 Second fly-eye lens 18 First cylindrical lens 19 Second cylindrical lens 20 Asymmetric cylindrical lens

Claims (13)

A laser annealing method in which a beam spot of laser light is moved relative to a region to be modified in an amorphous silicon film, and the amorphous silicon film is laser-annealed to be modified into crystallized silicon. ,
The laser light is continuous wave laser light emitted from a continuous wave laser,
In the beam spot, the energy density of the downstream side portion in the moving direction for relatively moving the beam spot is set higher than the energy density of the upstream side portion in the moving direction of the beam spot,
After forming the seed crystal region by projecting the beam spot on the edge portion of the modification target region,
A laser annealing method in which the beam spot is moved in the movement direction, and the entire surface of the modification target area is modified into a crystallized silicon film starting from the seed crystal area. After forming the seed crystal region, the emission of the continuous wave laser light is stopped,
After that, the laser annealing method according to claim 1, wherein the continuous wave laser light is started to be emitted within a predetermined time to move the beam spot. The laser annealing method according to claim 1, wherein after the seed crystal region is formed, the beam spot is continuously moved while the continuous wave laser light is emitted. The laser annealing method according to any one of claims 1 to 3, wherein the energy density of the upstream side portion of the beam spot gradually decreases toward the upstream side in the moving direction. The laser annealing method according to claim 1, wherein the continuous wave laser is a semiconductor laser. The energy density of the downstream side portion of the beam spot is set higher than a threshold value for melting the amorphous silicon film,
The energy density in the upstream portion of the beam spot is set so as to pass through the threshold value and gradually decrease toward the upstream side in the moving direction. Laser annealing method. The beam spot is formed in an elongated rectangular shape,
The laser annealing according to any one of claims 1 to 6, wherein the beam spot is projected onto the amorphous silicon film so that a major axis of the beam spot is a direction orthogonal to the moving direction. Method. It is a laser annealing apparatus that moves a beam spot relative to an amorphous silicon film formed on a substrate to be processed and performs laser annealing on the amorphous silicon film to modify it into crystallized silicon. hand,
A base on which the substrate to be processed is placed,
A laser beam irradiator provided with a continuous wave laser that is moved relative to the substrate to be processed arranged on the base and emits continuous wave laser light;
Equipped with
In the beam spot of the continuous wave laser beam emitted from the continuous wave laser, the energy density of the downstream side portion in the moving direction for relatively moving the beam spot is equal to that of the upstream side portion in the moving direction of the beam spot. Laser annealing equipment set higher than the energy density. The laser annealing apparatus according to claim 8, wherein the energy density of the upstream portion of the beam spot is set to gradually decrease toward the upstream side in the moving direction. The laser annealing apparatus according to claim 8 or 9, wherein the continuous wave laser is a semiconductor laser. The energy density in the downstream portion of the beam spot is set higher than a threshold value for melting the amorphous silicon film,
The energy density in the upstream portion of the beam spot is set so as to gradually decrease by passing the threshold value toward the upstream side in the moving direction. The laser annealing apparatus described. The beam spot is formed in an elongated rectangular shape,
The laser annealing apparatus according to any one of claims 8 to 11, wherein the major axis of the beam spot is arranged so as to be a direction orthogonal to the moving direction. The laser beam irradiation unit includes an asymmetric cylindrical lens set such that the energy density of the downstream side portion is higher than the energy density of the upstream side portion of the beam spot. 13. The laser annealing device according to any one of 12.

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