JPH0963984A - Laser annealing method and laser annealing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain uniform threshold value in the board surface of a plurality of crystalline silicon TFT to be formed on a glass board by a method wherein a uniform laser is made to irradiate on the glass board on which warpage is generated by the heat crystallization of an amorphous silicon film. SOLUTION: The title laser annealing method contains a process with which the amorphous silicon film, to be formed on a glass board 101, is formed into a crystalline silicon film 103 by heat-crystallization, a process with which the glass board 101 is flattened and placed on a stage 201, and a process with which a crystalline silicon film 103 is annealed by scanningly pojecting a linear laser beam on the crystalline silicon film 103.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser annealing method and apparatus for a crystalline silicon film on a glass substrate. The present invention relates to a laser annealing method and apparatus for a crystalline silicon film obtained by thermally crystallizing an amorphous silicon film formed on a glass substrate.

[0002]

2. Description of the Related Art In recent years, studies have been made on an insulating gate type semiconductor device having a thin-film active layer (also called an active region) on an insulating substrate. In particular, thin-film insulating gate type transistors, so-called thin film transistors (TFTs), have been earnestly studied. These are distinguished as amorphous silicon (amorphous silicon) TFTs or crystalline silicon (crystalline silicon) TFTs depending on the material and crystalline state of the semiconductor used. Crystalline silicon is non-single-crystal, not single-crystal. Therefore, these are collectively referred to as non-single crystal silicon TFTs.

Generally, the electric field mobility of a semiconductor in an amorphous state is small, and therefore TF which requires high speed operation.
Not available for T. Further, since amorphous silicon has a remarkably small P-type electric field mobility, a P-channel TFT (PMOS TFT) cannot be manufactured. Therefore, an N-channel TFT (NMOS TF) is not formed.
T) and complementary MOS circuit (CMOS)
Cannot be formed. On the other hand, a crystalline semiconductor has a larger electric field mobility than an amorphous semiconductor, and therefore can operate at high speed. For crystalline silicon, NM
Since not only the OS TFT but also the PMOS TFT can be obtained in the same manner, it is possible to form a CMOS circuit.

For a non-single crystal crystalline silicon film, an amorphous silicon film obtained by a vapor phase growth method is thermally annealed at an appropriate temperature (usually 600 ° C. or higher) for a long time, or
It was obtained by irradiating strong light such as a laser (light annealing). However, when an inexpensive and highly workable glass substrate is used as the insulating substrate, a crystalline silicon film having a sufficiently high electric field mobility (high enough to form a CMOS circuit) can be obtained only by thermal annealing. It was extremely difficult. This is because the glass substrate as described above generally has a low strain point temperature (about 600 ° C.), and the substrate temperature cannot be raised to a temperature required to obtain a crystalline silicon film having sufficiently high mobility. Is.

On the other hand, when optical annealing is used to crystallize a silicon film based on a glass substrate, it is possible to give high energy only to the silicon film without raising the temperature of the substrate so much. Therefore, it is considered that the optical annealing technique is very effective for crystallizing the silicon film based on the glass substrate. At present, a high-power pulsed laser such as an excimer laser is considered to be the optimum light source for optical annealing. The maximum energy of this laser is much larger than that of a continuous wave laser such as an argon ion laser. Therefore, it was possible to improve the mass productivity by using a large spot of several cm ² or more. However, in the case of a square or rectangular beam that is usually used, it is necessary to move the beam vertically and horizontally to process one large area substrate, and there is still room for improvement in terms of mass productivity. .

In this regard, the beam is deformed linearly,
By making the width of the beam longer than the substrate to be processed, and scanning this beam relative to the substrate, it was possible to greatly improve (scanning here means that linear lasers are slightly shifted while overlapping each other). Say to irradiate).
Details are described in JP-A-5-112355.

By performing thermal annealing before the optical annealing, a silicon film having higher crystallinity can be formed. Regarding the method by thermal annealing, as described in JP-A-6-244104, elements such as nickel, iron, cobalt, platinum, and palladium (hereinafter referred to as crystallization catalyst element or simply catalyst element) are used. By utilizing the effect of promoting crystallization of amorphous silicon, a crystalline silicon film can be obtained by thermal annealing at a lower temperature and shorter time than usual.

[0008]

By using a crystalline silicon film formed by performing optical annealing after thermal annealing,
TFTs arranged in a matrix were formed, and the distribution of their threshold voltages in the substrate surface was investigated. FIG. 2 shows a T using a crystalline silicon film formed by a conventional method.
The distribution of the threshold of FT in the substrate surface is shown. This distribution is a U-shaped distribution as shown in FIG. FIG.
The layout of the TFTs on the glass substrate is shown in FIG. As shown in FIG. 4, the data in FIG. 2 is 100 mm square Corning 70.
In the area of 40 × 50 mm on the 59 substrate, 4 TFTs are provided.
00 × 300 TFTs arranged in a matrix, 400 TFTs in a horizontal row from end to end in the central part of the substrate
The horizontal axis corresponds to each location (the portion surrounded by the dotted line in FIG. 4). For example, if the pixel matrix forming the pixel portion of the liquid crystal display has a threshold voltage distribution as shown in FIG. 2, the display state becomes non-uniform, which causes a defective image.

As a result of the investigation by the applicant of the cause that the threshold voltage shows such a U-shaped distribution in the plane of the substrate, the tendency of the U-shaped distribution is very similar to the warp of the substrate immediately before laser irradiation. I found out that In addition, the warpage of the substrate is not found in the glass substrate immediately after the amorphous silicon film is formed, and in the subsequent heat treatment step (which causes the film to undergo solid phase growth and crystallize), the substrate after the heat treatment is finished. It was revealed that when the film was cooled, the silicon film was warped because it contracted more than the glass substrate. This warpage occurs in a recess when viewed from the substrate film formation surface.

FIG. 3 shows how laser annealing is performed on the silicon film on the glass substrate in which warpage has occurred. As shown in FIG. 3, when laser annealing is performed in such a warped state, the focus of the laser shifts differently depending on the location of the substrate. It is considered that this deviation causes the degree of crystallinity of the silicon film to be different in the substrate surface, and as a result, the threshold voltage exhibits a specific distribution in the substrate surface. The warp of the 100 mm square substrate immediately before laser irradiation had a difference of about 50 μm between the central portion and the end portion of the substrate. The degree of this warpage depends on the temperature of the heat treatment step, the time required for the treatment, the material of the substrate, and the like, but it is about 20 to 200 μm.
It was within the range of m. When the size of the substrate is about 500 mm square, the warpage may be about 1 to 2 mm.

It is an object of the present invention to perform uniform laser irradiation on a surface to be irradiated on a glass substrate having a warp.

An object of the present invention is to provide a plurality of crystalline silicon TFTs formed on a glass substrate with a uniform threshold value in the plane of the substrate.

According to the present invention, when laser annealing using a linear laser beam is performed on a crystalline silicon film formed by thermally crystallizing an amorphous silicon film on a glass substrate, the crystalline silicon film is An object of the present invention is to provide a method and an apparatus for producing a plurality of crystalline silicon TFTs which have a uniform crystallinity in the plane of the substrate and which have a uniform threshold voltage in the plane of the substrate using the film. .

[0014]

In order to solve the above-mentioned problems, one of the constitutions of the present invention is a step of flattening and placing a glass substrate on a stage, and an irradiation surface on the glass substrate. On the other hand, the laser annealing method comprises the step of irradiating a linear laser beam while scanning and performing laser annealing.

Another aspect of the present invention is a step of heating and crystallizing an amorphous silicon film formed on a glass substrate to form a crystalline silicon film, and flattening the glass substrate on a stage. A laser annealing method comprising: a step of placing the crystalline silicon film; and a step of performing laser annealing on the crystalline silicon film while scanning with a linear laser beam.

Another aspect of the present invention is that the amorphous silicon film formed on the glass substrate is heated and crystallized to form a crystalline silicon film, and the lower surface of the glass substrate is formed into a flat surface. A step of closely contacting and mounting the glass substrate on the flat surface of the stage, and a step of performing laser annealing by irradiating the crystalline silicon film with a linear laser beam while scanning the same. The laser annealing method is characterized by having.

Another aspect of the present invention is that the amorphous silicon film formed on the glass substrate is heated and crystallized to form a crystalline silicon film, and the lower surface of the glass substrate is formed into a flat surface. The step of placing the glass substrate in close contact with the flat surface of the stage by vacuum suction and the step of performing laser annealing by irradiating the crystalline silicon film with a linear laser beam while scanning. And a laser annealing method.

Another aspect of the present invention is a step of heating and crystallizing an amorphous silicon film formed on a glass substrate to form a crystalline silicon film, and pressing a peripheral portion of the upper surface of the glass substrate. Then, the lower surface of the glass substrate is brought into close contact with the flat surface of the stage forming a flat surface, and the glass substrate is placed, while scanning the crystalline silicon film with a linear laser beam. And a step of performing laser annealing by irradiation, which is a laser annealing method.

One of other configurations of the present invention is a stage having means for flattening and mounting a glass substrate, and means for irradiating a surface to be irradiated of the glass substrate with a linear laser beam while scanning it. And a laser annealing apparatus.

One of other configurations of the present invention is a stage having a flat surface on which a glass substrate is placed and a means for bringing the lower surface of the glass substrate into close contact with the flat surface, and the glass substrate to be irradiated. And a means for irradiating the surface with a linear laser beam while scanning the laser annealing apparatus.

Another aspect of the present invention is a stage having means for flattening and mounting a glass substrate having a crystalline silicon film crystallized by heating, and crystalline silicon on the glass substrate. And a means for irradiating the film with a linear laser beam while scanning the film.

Another aspect of the present invention is a means for bringing a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is placed and a lower surface of the glass substrate into close contact with the flat surface. And a means for irradiating the crystalline silicon film with a linear laser beam while scanning the crystalline silicon film.

According to another aspect of the present invention, a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is placed and a lower surface of the glass substrate is vacuum-adsorbed on the flat surface. A laser annealing apparatus comprising: a stage having means; and means for irradiating the crystalline silicon film with a linear laser beam while scanning the same.

Another aspect of the present invention has a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is placed, and means for pressing the peripheral portion of the upper surface of the glass substrate. A laser annealing apparatus comprising: a stage; and means for irradiating the crystalline silicon film with a linear laser beam while scanning the same.

In the present invention, the crystalline silicon film may have impurities added to at least a portion thereof by ion doping or the like.

Further, the present invention uses a pulse laser, preferably an excimer laser, as the light source of the linear laser beam in the above structure.

The present invention is a crystalline silicon film obtained by thermally crystallizing an amorphous silicon film formed on a glass substrate, or a crystalline silicon film obtained by patterning, processing or shaping the crystalline silicon film, or these. When laser annealing is performed by scanning a linear laser beam on a material to which impurities have been added, the warpage of the glass substrate caused by the thermal crystallization process is forced on the stage on which the glass substrate is placed. Laser annealing is performed in the flattened state.

In the present invention, flattening the glass substrate means that the glass substrate is placed on the stage and some external force is applied to the glass substrate to reduce the warp of the glass substrate. It is to be. The flattening of the glass substrate is performed to such an extent that the crystalline silicon film on the glass substrate can be uniformly annealed using a linear laser beam. That is, after laser annealing, the in-plane height difference of the crystalline silicon film on the glass substrate is reduced so that the crystallinity of the crystalline silicon film is within a range where it is homogenized to a required level. It should be done.

In order to flatten the warp of the glass substrate, a stage having a flat surface is made to adsorb the glass substrate to the flat surface, and the peripheral portion on the glass substrate is pressed (pressurized).
And so on. Further, such flattening and correction means are added to the stage of the laser annealing apparatus.

Since the glass substrate is placed flat as described above, the linear laser beam is emitted onto the crystalline silicon film, which is the surface to be irradiated, even though the glass substrate itself has a warp. On the other hand, the irradiation is performed uniformly without defocusing. As a result, it is possible to obtain a crystalline silicon film having uniform and uniform crystallinity and mobility within the surface of the substrate.

According to the present invention, the crystalline silicon film on the glass substrate on which warpage has occurred after thermal crystallization can be irradiated with a linear laser beam after correcting the warpage of the glass substrate to a negligible extent. it can. Therefore, the focal point of the linear laser beam is prevented from deviating on the irradiated surface, and as a result, even if the linear laser beam is scanned and laser annealing is performed, uniform crystallization is performed and the film is formed using the film. The threshold voltage of the TFT can be made uniform in the plane of the substrate. As the glass substrate becomes larger, the degree of warpage becomes more severe, so the effect of the present invention becomes more remarkable as the glass substrate becomes larger. Examples will be described below.

[0032]

【Example】

 [Example 1]

FIG. 9 shows a manufacturing process of the embodiment. This embodiment will be described with reference to FIG. First, a glass substrate (100 mm square Corning 7059 is used in this embodiment. Other glass, for example, Corning 1737, OA2, NA4).
5 or the like may be used. ) 101, a base silicon oxide film 102 having a thickness of 2000 Å and an amorphous silicon film 103 having a thickness of 500 Å are continuously formed thereon by a plasma CVD method. Then, a 10 ppm nickel acetate aqueous solution was applied to the silicon surface, and a nickel acetate layer was formed by spin coating. It was better to add a surfactant to the nickel acetate aqueous solution. Since the nickel acetate layer is extremely thin, it is not always in the form of a film,
There is no problem in the subsequent process. (FIG. 9A)

Then, the silicon film is crystallized by thermal annealing at 550 ° C. for 4 hours. At this time, nickel plays a role of a crystal nucleus and promotes crystallization of the silicon film. It is a function of nickel that it can be processed at a low temperature of 550 ° C. for 4 hours (below the strain point temperature of Corning 7059) and in a short time. For details, see JP-A-6-2.
It is described in Japanese Patent No. 44104. The concentration of the catalytic element is
1 × 10 ¹⁵ to 1 × 10 ¹⁹ atoms / cm ³ was preferred. At a high concentration of 1 × 10 ¹⁹ atoms / cm ³ or more, metallic properties appeared in silicon and the semiconductor properties disappeared. The concentration of the catalytic element in the silicon film described in this example was 1 × 10 ^{17 to} 5 × 10 ¹⁸ atoms / cm ^{3 as the} minimum value in the film. In addition, these values are the minimum values of the concentration of the catalytic element in the silicon film analyzed and measured by the secondary ion mass spectrometry (SIMS). In this way,
A crystalline silicon film is obtained.

At this time, the glass substrate has a concave shape along the surface on which the crystalline silicon film is provided. Here, about 50 μm in the central portion and the peripheral portion of the substrate.
It has a level difference. The degree of warpage depends on the size, thickness, and type of the glass substrate.

In order to further enhance the crystallinity of the crystalline silicon film thus obtained, the film is irradiated with an excimer laser which is a high-power pulse laser. The laser annealing apparatus used in this example will be described below.
FIG. 6 shows a conceptual diagram of the laser annealing apparatus used in this embodiment. The laser annealing apparatus of FIG. 6 is a multi-chamber type, and a substrate transfer robot provided in a transfer chamber through which a substrate loaded from a loader / unloader chamber and positioned in an alignment chamber is placed. In this way, it is carried to each chamber and processed successively for each substrate. The substrate is first loaded into the heat treatment chamber, subjected to heat treatment such as preheating, laser annealed in the laser annealing chamber, then transported to the slow cooling chamber and slowly cooled, and then moved to the loader / unloader chamber. Move and get out.

This laser annealing apparatus has a hermeticity with respect to the surroundings and prevents contamination by impurities.
It also has an atmosphere control function during laser irradiation.
Further, it also has a function of heating the substrate, so that the object to be irradiated can be kept at a desired temperature during laser irradiation. Also,
Here, laser irradiation is performed at atmospheric pressure. Of course, it is also possible to use vacuum or another pressure.

As the oscillator, here, 3000-308 manufactured by Lambda Physics was used. The oscillated laser light is a XeCl excimer laser (wavelength 308 nm, pulse width 26 ns). Of course, other excimer lasers or lasers of other types can be used. However, it is necessary to use pulsed laser light.

The oscillated laser light is introduced into an optical system as shown in FIG. 7 because of its beam shape deformation. FIG. 7 shows an example of the optical system. The beam of laser light immediately before entering the optical system has a rectangular shape of about 3 × 2 cm ² , and depending on the optical system, the length is 10 to 30 cm and the width is 0.01 to 0.
It is processed into a slender beam (linear beam) of about 3 cm.
The maximum energy of laser light that has passed through this optical system is 10
It is 00 mJ / shot.

The reason why the laser beam is processed into such an elongated beam is to improve the processability. That is, when the sample is irradiated with a linear beam, if the beam length is longer than the sample width, the sample is moved in one direction to irradiate the sample with laser light. You can On the other hand, even when the length of the beam is shorter than the width of the sample, it does not take much time for processing as compared with the rectangular beam. However, in this case, it is necessary to move the beam vertically and horizontally relative to the sample.

The stage of the substrate (sample) on which the laser light is irradiated is controlled by a computer, and is designed to move in the direction perpendicular to the line direction of the linear laser beam (FIG. 7, h direction). There is. Furthermore, if the stage is provided with a function of moving in the line direction of the beam, laser processing can be performed on the entire sample even if the beam length is shorter than the sample.

The optical path (FIG. 7) inside the optical system for processing the laser beam into a linear laser will be described. The laser light oscillated from the laser light source a and incident on the optical system first passes through the fly-eye lenses b and c. Furthermore, the first
As the cylindrical lens of, the cylindrical convex lens d, and the second cylindrical lens provided to improve the homogeneity of the beam to be linearized in the line direction,
The light passes through the cylindrical convex lens e, is focused by the cylindrical lens g through the mirror f, and is irradiated onto the sample. Regarding the optical path length, the distance from the laser light source to the mirror g is 2000 mm, and the distance from the mirror f to the irradiated surface is 440 mm. Cylindrical lens g
Is used with a focal length of 100 mm. The optical system is
Any beam may be used as long as it can be transformed into the beam required for the present invention.

The optical system is not limited to the one shown in FIG. 7, but an optical system having lenses B and C (beam expander) as shown in FIG. 8 may be used.

The laser beam is shaped into a line, and the beam area in the irradiated portion is 150 mm × 0.4 mm (the line width of the beam is the half-value width with respect to the maximum value of energy). In addition, a generally used rectangle is used for the energy distribution in the line width direction of the laser beam. In order to make the shape of the energy distribution of the laser beam in the line width direction sharp at the peripheral portion (peripheral portion of the line width), a slit may be inserted in the laser optical path. For example, in FIG. 7, after the cylindrical lens e is preferable, and for example,
A slit is provided between the cylindrical lens e and the mirror f, or between the cylindrical lens g and the surface to be illuminated.

The glass substrate in which the warpage is caused by the thermal crystallization process is forcibly flattened and fixed on the stage (stand) of the laser annealing apparatus. In order to correct the warp of the glass substrate, means for flattening and mounting the glass substrate is provided on a stage having a flat surface on which the glass substrate is mounted during irradiation of the linear laser beam.

FIG. 10 shows an example of the structure of the stage. As an example of means for flattening and mounting and fixing the glass substrate on the stage, for example, in FIG. 10A, a plurality of suction ports 202 are provided on the upper surface of the stage 201.
Although the suction port 202 is a hole, a portion without the suction port 202 forms a flat surface. In FIG. 10B, a groove 212 is provided on the upper surface of the stage 211. This groove 2
12 communicates with the suction port 213 at the center of the stage,
A flat surface is formed in a place where the groove 212 is not provided.
FIG. 10C shows a plurality of protrusions 2 on the upper surface of the stage 221.
22 are provided, and the upper surfaces of the protrusions 222 and the peripheral portion of the stage form a flat surface. Further, a vacuum is drawn from the suction port 223. In each of FIGS. 10A to 10C, the glass substrate is vacuumed from the suction port, and the glass substrate is vacuum-sucked on the flat surface. Thus, the lower surface of the glass substrate is brought into close contact with the flat surface of the stage. Then, laser annealing is performed in this state.

Since the flat surface of the upper surface of the stage is flat except for the part related to the adsorption, the glass substrate adhered to such a flat upper surface is flattened according to the flat surface of the stage. According to this vacuum suction method, installation and removal of the glass substrate are extremely easy and can be completed in a short time. Also,
Since there are no obstacles or the like that hinder the irradiation of the laser beam on the surface of the glass substrate, the entire surface of the glass substrate can be uniformly irradiated with laser light.

The flatness on the flat surface of the stage is more preferable as it is flat, but it is required for the crystalline silicon film on the glass substrate mounted on the flat surface by using a linear laser beam. It is only necessary to be able to anneal so as to have a level of homogeneity. For example, the flat surface is such that the in-plane height difference of the irradiated surface on the glass substrate is at least less than or equal to the focal depth of the laser beam.

The method of bringing the glass substrate into close contact with the stage is not limited to the above-mentioned method by suction, and any method may be used as long as the glass substrate can be flattened and laser annealing can be performed. Besides, for example,
As shown in FIG. 10D, the peripheral portion or the end portion of the upper surface of the glass substrate 101 is mechanically pressed against the flat surface of the stage 231 by the presser 232 and pressed (pressurized).
However, laser annealing may be performed in that state. In this case, since the glass substrate can be flattened with a force stronger than that of the vacuum suction, it is possible to easily flatten even a strongly warped substrate that cannot be sufficiently flattened by the vacuum suction. Of course, the method shown in FIG. 10 (d) and the above-mentioned adsorption method may be used together.
Further, the material of the stage is preferably quartz, metal, ceramics or the like because it has high heat resistance and can maintain high flatness.

Here, a stage having the structure shown in FIG. 10A is used. Suction port 202 shown in FIG.
Have a diameter of about 1 mm and are provided at intervals of 10 mm. The glass substrate 101 is placed on the flat surface of the stage 201 with the surface on which the crystalline silicon film 103 is formed facing upward, and a vacuum is drawn from the suction port 202 to bring the glass substrate into close contact with the stage. Stage 2
According to the flat surface 01, the glass substrate is also flattened to the same extent as the in-plane height difference of the flat surface of the stage.

In addition to the structure shown in FIG. 10A, the glass substrate is not simply placed on the stage, but after the glass substrate is placed, the upper surface of the substrate, particularly the upper surface of the peripheral portion, is evacuated,
You may stick it to the stage. For example, by providing a presser 232 shown in FIG. 10D, the glass substrate 1
01 The upper surface of the peripheral portion may be pressed, a vacuum may be drawn to bring the glass substrate into close contact, and then the retainer may be removed, followed by laser annealing.

FIG. 1 shows a laser irradiation process. After the amorphous silicon film formed on the glass substrate 101 is thermally crystallized to obtain the crystalline silicon film 103 and gradually cooled, the glass substrate 101 is warped. FIG.
As shown in (a), the glass substrate 101 is placed on the stage 201. As shown in FIG. 1B, the glass substrate 101 having the warp is forcibly corrected by the means for flattening and placing the glass substrate provided on the stage 2011, here, the suction port 202. , Flattened and placed. The mounted glass substrate is flattened to have an in-plane height difference of about 5 μm.

Then, as shown in FIG. 1C, the flattened crystalline silicon film 103 on the glass substrate is formed.
On the other hand, irradiation is performed while scanning the linear laser beam. In this way, by placing the glass substrate flat, the linear laser beam is focused on the crystalline silicon film, which is the surface to be irradiated, even though the glass substrate itself has a warp. Irradiate uniformly without shifting.

The energy density of the laser is 100 mJ /
In the range of cm ^{2 to} 500 mJ / cm ² , for example, 370 m
Irradiation is performed at J / cm ² . Before this irradiation, 220
The crystallinity is further increased by the two-stage irradiation in which irradiation is performed with energy of about mJ / cm ² . Laser irradiation is performed by shifting a linear laser beam relative to an object to be irradiated, that is, a crystalline silicon film. The direction in which the linear laser is shifted is substantially perpendicular to the linear laser (direction h in FIG. 7). At this time, focusing on one point of the object to be irradiated, the laser beam is irradiated from 2 to 40 shots, for example, 32 shots. The substrate temperature during laser irradiation is 200 ° C. (Fig. 9 (B))

In this way, a crystalline silicon film is produced. The produced crystalline silicon film has a mobility variation within ± 10% in the plane of the substrate, and is a sufficiently homogeneous crystalline silicon film. On the other hand, in the crystalline silicon film which was laser-annealed without going through the planarization process shown in this example, the variation in the mobility within the substrate surface was ± 1.
If it is about 5 to 40%, sufficient homogeneity cannot be obtained.

A semiconductor device was produced based on the crystalline silicon film produced as described above. The semiconductor device is arranged in a matrix on the crystalline silicon film. Specifically, 400 × 300 thin film transistors are manufactured in a manufacturing area of 40 × 50 mm ² . First, the silicon film was etched to form the island-shaped silicon region 105. Next, the silicon oxide film 10 having a thickness of 1200 Å is formed by the plasma CVD method.
6 was deposited as a gate insulating film. TEOS and oxygen were used as source gases for plasma CVD. The substrate temperature during film formation was 250 to 380 ° C., for example, 300 ° C.

Subsequently, a thickness of 3 is obtained by the sputtering method.
An aluminum film (containing 0.1 to 2% of silicon) of 000 to 8000 Å, for example, 6000 Å was deposited. Then, the aluminum film is etched to form the gate electrode 10
7 was formed. (FIG. 9 (C))

Next, an impurity (boron) is formed in the silicon region using the gate electrode as a mask by an ion doping method.
Was injected. Hydrogen as a doping gas 1-10%
Diborane (B ₂ H ₆ ) diluted to 5%, for example, 5% was used. The acceleration voltage is 60 to 90 kV, for example 65 k
V, the dose amount is 2 × 10 ^{15 to} 5 × 10 ¹⁵ atoms / cm ² ,
For example, it is set to 3 × 10 ¹⁵ atoms / cm ² . The substrate temperature during ion doping was room temperature. As a result, P-type impurity regions 108 (source) and 109 (drain) were formed. (Fig. 9 (D))

Then, in order to activate the doped boron, laser annealing was performed again using the same laser annealing apparatus. At this time, similarly, the glass substrate is brought into close contact with the stage to be flattened. The energy density of the laser is 100 to 350 mJ / cm ² , for example,
It was set to 250 mJ / cm ² . 170m before this irradiation
Irradiation with an energy of about J / cm ² further increased the crystallinity. The laser irradiation method is as follows. That is, irradiation is performed while the linear laser beam is shifted relative to the object to be irradiated. The direction in which the linear laser was shifted was approximately at a right angle to the linear laser. At this time, focusing on one point of the object to be irradiated, laser light of 2 to 20 shots was irradiated. The substrate temperature during laser irradiation was 200 ° C. Then, thermal annealing was performed at 350 ° C. for 2 hours in a nitrogen atmosphere. (Fig. 9
(E))

Then, a silicon oxide film 11 having a thickness of 6000Å is formed.
0 was used as an interlayer insulator by a plasma CVD method, and a contact hole was opened therein. Then, the source / drain electrodes 111 and 112 of the TFT are made of a metal material, for example, a multilayer film of titanium and aluminum.
Was formed. Finally, 200 to 3 in 1 atmosphere of hydrogen atmosphere
Thermal annealing at 50 ° C. was performed. (Fig. 9 (F))

FIG. 5 shows the distribution of the threshold value of the TFT using the crystalline silicon film formed according to the embodiment in the plane of the substrate. In FIG. 5, the horizontal axis of FIG. 5 corresponds to the location of the TFT shown in FIG. 4 (the portion surrounded by the dotted line in FIG. 4), as in FIG. As shown in FIG. 5, the TFT manufactured in this example has a uniform threshold value in the surface of the substrate, and the conventional example, that is, the substrate adsorption is performed in any laser irradiation (annealing) step. Compared with FIG. 2, which is the distribution of the threshold voltages of the TFTs arranged in a matrix form without the
It can be seen that the substrate has a uniform threshold voltage in the plane.

[Embodiment 2] Embodiment 2 shows an example in which the laser annealing apparatus uses an array of optical systems and a stage configuration different from those in Embodiment 1. Similar to the first embodiment, FIG.
In accordance with the above, a glass substrate (300 × 300 mm in this embodiment)
Corning 1737 having a corner and a thickness of 0.7 mm is used. Of course, other glass substrates may be used. For example, Corning 7059, OA2, NA45, etc. ) 101 and thickness 20
A 00Å base silicon oxide film 102 and an amorphous silicon film 103 having a thickness of 500Å are continuously formed thereon by a plasma CVD method. And 10 ppm
The nickel acetate aqueous solution is applied to the silicon surface to form a nickel acetate layer by spin coating. It was better to add a surfactant to the nickel acetate aqueous solution. Since the nickel acetate layer is extremely thin, it is not always in the form of a film, but there is no problem in the subsequent steps. (Fig. 9
(A))

Then, the glass substrate is thermally annealed at 550 ° C. for 4 hours to crystallize the silicon film. At this time, nickel plays a role of a crystal nucleus and promotes crystallization of the silicon film. In addition, Corning 17
The strain point temperature of the 37 substrate is 667 ° C, which is 550 ° C above.
The annealing temperature is less than the strain point temperature. When the glass substrate is gradually cooled after the thermal crystallization, the silicon film shrinks,
A concave warpage occurs on the substrate.

It is due to the function of nickel that it can be processed at a low temperature of 550 ° C. for 4 hours (below the strain point temperature of Corning 1737) and in a short time. For details, see JP-A-6-24.
4104 publication. In this publication, it is specified that the temperature at the time of thermal annealing does not exceed the strain point temperature of the glass substrate, for example, thermal annealing is performed for 4 hours at 550 ° C. (below the strain point temperature). It is defined in order to prevent the glass substrate from being significantly deformed during crystallization.

The concentration of the catalytic element was preferably 1 × 10 ¹⁵ to 10 ¹⁹ atoms / cm ³ . 1 × 10 ¹⁹ atoms / c
At high concentration of m ³ or more, metallic properties appear in silicon,
The semiconductor characteristics have disappeared. The concentration of the catalytic element in the silicon film described in this example is 1 × as the minimum value in the film.
It was 10 ^{19 to} 5 × 10 ¹⁸ atoms / cm ³ . In addition, these values are the minimum values of the concentration of the catalytic element in the silicon film analyzed and measured by the secondary ion mass spectrometry (SIMS). In this way, a crystalline silicon film is obtained.

At this time, the glass substrate is concave along the surface on which the crystalline silicon film is provided. Here, in the central portion and the peripheral portion of the glass substrate, about 2
It has a height difference of about 00 μm. The degree of warpage depends on the size, thickness, and type of the glass substrate.

In order to further enhance the crystallinity of the crystalline silicon film thus obtained, the film is irradiated with an excimer laser which is a high-power pulse laser. The laser annealing apparatus has the configuration shown in FIG. 6 as in the first embodiment.

EX74 manufactured by LUMNICS as an oscillator
8 was used. The oscillated laser light is a KrF excimer laser (wavelength 248 nm, pulse width 25 ns). Of course, other excimer lasers or lasers of other types can be used. However, it is necessary to use pulsed laser light.

The oscillated laser light is introduced into the optical system as shown in FIG. 8 because of the deformation of the beam shape. FIG. 8 shows an example of the optical system. The beam of laser light immediately before entering the optical system has a rectangular shape of about 3 × 2 cm ² , and depending on the optical system, the length is 10 to 30 cm and the width is 0.01 to 0.
It is processed into a slender beam (linear beam) of about 3 cm.
The maximum energy of laser light that has passed through this optical system is 80
It is 0 mJ / shot.

The reason why the laser beam is processed into such an elongated beam is to improve the processability. That is, when the sample is irradiated with a linear beam, if the beam length is longer than the sample width, the sample is moved in one direction to irradiate the sample with laser light. You can On the other hand, even when the length of the beam is shorter than the width of the sample, it does not take much time for processing as compared with the rectangular beam. However, in this case, it is necessary to move the beam back and forth and left and right relative to the sample.

The stage (stand) of the substrate (sample) irradiated with the laser light is controlled by a computer and is perpendicular to the line direction of the linear laser beam (direction I in FIG. 8).
Designed to move to. Furthermore, by providing the stage with a function of moving in the line direction of the beam, laser processing can be performed on the entire sample even if the beam has a shorter length than the sample.

The optical path (FIG. 8) inside the optical system for processing the laser beam into a linear laser will be described. The laser light incident on the optical system passes through a cylindrical concave lens B, a cylindrical convex lens C (lenses B, C are collectively called a beam expander), and fly-eye lenses D, D2. Further, as a first cylindrical lens, a cylindrical convex lens E, and as a second cylindrical lens provided to improve the homogeneity of the beam to be linearized in the direction of the line, the cylindrical convex lens F is passed through and a mirror G is passed through. , Is focused by the cylindrical lens H, and the surface to be irradiated is irradiated. The distance between the laser light source and the cylindrical lens B is 230 mm, the distance between the fly-eye lenses D and D2 is 230 mm, the distance between the fly-eye lens D and the cylindrical lens E is 650 mm, and the distance between the cylindrical lens F and the illuminated surface is 650 mm (each lens The sum of the focal lengths). Of course, these can be changed depending on the situation. As the cylindrical lens H, an object having a focal length of 120 mm is used.

To make the shape of the energy distribution of the laser beam in the line width direction sharp at the peripheral portion (peripheral portion of the line width), it is advisable to insert a slit in the middle of the laser optical path. For example, in FIG. 8, the cylindrical lens E
Is preferable, for example, a cylindrical lens F and
The slit is provided between the mirror G or between the cylindrical lens H and the illuminated surface. The optical system is
Any beam may be used as long as it can be transformed into the beam required for the present invention.

The laser beam is shaped into a linear shape, and the beam area at the irradiated portion is 300 mm × 1 mm. The line width of the beam is the half width of the maximum energy of the laser beam.

The glass substrate having the concave warpage due to the thermal crystallization process is the stage (stand) of the laser annealing apparatus.
, Forcibly flattened and fixed. Here, FIG.
A stage having the configuration shown in 0 (d) is used. FIG.
In (d), the retainer 232 is made of ceramic here. Alternatively, metal, quartz or the like may be used.
A material that has high heat resistance and is resistant to thermal expansion is desirable. When the glass substrate 101 is conveyed, the presser 232 receives the stage 2
When the glass substrate 101 is placed on the substrate 31, the peripheral portion of the upper surface of the glass substrate 101 is automatically pressed and pressed, and the glass substrate 101 is closely attached to the stage and fixed. The glass substrate 101 is flattened and fixed according to the flat surface of the stage 231. The flattened glass substrate has an in-plane height difference of about 10 μm.

In this way, laser irradiation is performed on the glass substrate placed on the stage (stand). Laser irradiation is performed by shifting a linear laser beam relative to an object to be irradiated, that is, a crystalline silicon film.
The direction in which the linear laser is shifted is approximately perpendicular to the linear laser (I direction in FIG. 8). At this time, 1
Focusing on the point, the laser beam is irradiated from 2 to 20 shots, for example, 15 shots. Laser energy density is 100 mJ / cm ^{2 to} 500 mJ / cm
Irradiation is performed in the range of ² , for example, 370 mJ / cm ² . The crystallinity is further increased by performing a two-step irradiation in which irradiation is performed with an energy of about 220 mJ / cm ² before this irradiation. The substrate temperature during laser irradiation is 200
℃. (Fig. 9 (B))

Atmosphere control is not performed here, and irradiation is performed in the atmosphere. It may be performed in a vacuum, an inert gas such as argon or helium, or an atmosphere such as hydrogen or nitrogen. (Fig. 9 (B))

In this way, a crystalline silicon film having a uniform crystallinity in the plane of the substrate can be obtained. Thereafter, using the crystalline silicon film, in the same manner as in Example 1,
A thin film transistor is produced. In this way, the threshold voltage of the obtained TFT was extremely uniform in the distribution of the threshold voltage in the plane of the substrate as compared with the TFT manufactured without flattening the glass substrate. .

[0079]

According to the present invention, it is possible to perform uniform laser irradiation on a surface to be irradiated on a glass substrate having a warp. According to the present invention, even if a laser annealing process is introduced in the TFT manufacturing process, it is possible to manufacture a plurality of TFTs having a uniform threshold voltage in the substrate surface. In particular, the present invention is effective when a large number of TFTs are formed on a large-area glass substrate. As described above, the present invention is considered to be industrially useful.

[Brief description of drawings]

FIG. 1 is a diagram showing a laser irradiation process.

FIG. 2 is a diagram showing a distribution of threshold values of a TFT using a crystalline silicon film formed by a conventional method in a substrate surface.

FIG. 3 is a diagram showing a state where laser annealing is performed on a silicon film on a glass substrate in which warpage has occurred.

FIG. 4 is a diagram showing an arrangement of TFTs on a glass substrate.

FIG. 5 is a diagram showing a distribution of a threshold value of a TFT using a crystalline silicon film formed in an example in a substrate surface.

FIG. 6 is a diagram showing a conceptual diagram of a laser annealing apparatus used in this example.

FIG. 7 is a diagram showing an example of an optical system.

FIG. 8 is a diagram showing an example of an optical system.

FIG. 9 is a diagram showing a manufacturing process of an example.

FIG. 10 shows an example of a stage configuration.

[Description of Reference Signs] 101 glass substrate 102 silicon oxide film 103 amorphous silicon film 105 island-shaped silicon region 106 gate insulating film 107 gate electrode 108 source region 109 drain region 110 interlayer insulating film 111 source electrode, wiring 112 drain electrode, wiring 201 stage 202 suction port 211 stage 212 groove 213 suction port 221 stage 222 protrusion 223 suction port 231 stage 232

Claims (17)

[Claims] 1. A step of flattening and mounting a glass substrate having a surface to be irradiated on a stage, and laser annealing is performed by irradiating the surface to be irradiated on the glass substrate with a linear laser beam while scanning. A laser annealing method comprising the steps of: 2. A step of heating and crystallizing an amorphous silicon film formed on a glass substrate to form a crystalline silicon film; a step of flattening and mounting the glass substrate on a stage; A laser annealing method comprising: a step of irradiating a silicon film while scanning with a linear laser beam to perform laser annealing. 3. A step of crystallizing an amorphous silicon film formed on a glass substrate by heating to form a crystalline silicon film, the lower surface of the glass substrate being on the flat surface of a stage forming a flat surface, A laser annealing method comprising: a step of closely contacting and mounting the glass substrate; and a step of irradiating the crystalline silicon film while scanning with a linear laser beam to perform laser annealing. . 4. A step of heating and crystallizing an amorphous silicon film formed on a glass substrate to form a crystalline silicon film, the lower surface of the glass substrate being on the flat surface of a stage forming a flat surface, A step of placing the glass substrate in close contact by vacuum adsorption, and a step of irradiating the crystalline silicon film with a linear laser beam while scanning to perform laser annealing. Laser annealing method. 5. A step of heating and crystallizing an amorphous silicon film formed on a glass substrate to form a crystalline silicon film, and pressing a peripheral portion of the upper surface of the glass substrate to flatten the lower surface of the glass substrate. A step of bringing the glass substrate into close contact with the flat surface of a stage constituting a surface, and a step of performing laser annealing by irradiating the crystalline silicon film with a linear laser beam while scanning the same. A laser annealing method comprising: 6. The laser annealing method according to claim 1, wherein the crystalline silicon film has impurities added to at least a part thereof. 7. The laser annealing method according to claim 1, wherein the linear laser beam uses a pulse laser as a light source. 8. The laser annealing method according to claim 7, wherein the pulse laser is an excimer laser. 9. A stage having means for flattening and mounting a glass substrate, and means for irradiating a surface to be irradiated of the glass substrate with a linear laser beam while scanning the surface. Laser annealing equipment. 10. A stage having a flat surface on which a glass substrate is placed and a means for bringing the lower surface of the glass substrate into close contact with the flat surface, and a linear laser beam to a surface to be irradiated of the glass substrate. A laser annealing device comprising: a means for irradiating while scanning. 11. A stage having means for flattening and mounting a glass substrate having a crystalline silicon film crystallized by heating, and a linear laser beam to the crystalline silicon film on the glass substrate. A laser annealing device comprising: a means for irradiating while scanning. 12. A stage having a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is mounted, and means for bringing the lower surface of the glass substrate into close contact with the flat surface, and the crystallinity A laser annealing apparatus comprising: a means for irradiating a silicon film while scanning a linear laser beam. 13. A stage having a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is mounted, and means for vacuum-sucking the lower surface of the glass substrate to the flat surface, the crystal. And a means for irradiating the conductive silicon film with a linear laser beam while scanning the laser annealing film. 14. A stage having a flat surface on which a glass substrate having a crystalline silicon film crystallized by heating is mounted, and a means for pressing a peripheral portion of the upper surface of the glass substrate; On the other hand, a laser annealing apparatus comprising: a means for irradiating a linear laser beam while scanning. 15. A laser annealing apparatus according to claim 11, wherein the crystalline silicon film has impurities added to at least a portion thereof. 16. A laser annealing apparatus according to claim 9, wherein the linear laser beam uses a pulse laser as a light source. 17. The laser annealing method according to claim 16, wherein the pulse laser is an excimer laser.