JPH09106948A - Manufacture of semiconductor and manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form a silicon thin film, which has a uniform crystalproperty, within the surface of a substrate by a method wherein an amorphous silicon film formed on a glass substrate is crystallized by heating and after the glass substrate is installed on a base having a convex curved surface, the glass substrate is heated at about the temperature of the distortion point of the glass substrate and thereafter, the substrate is slowly cooled. SOLUTION: A base silicon oxide film 102 is formed on a glass substrate (Corning 1737) 101 and moreover, an amorphous silicon film 103 is continuously formed thereon. The substrate 101 is subjected to thermal annealing for four hours at 550 deg.C, whereby the film 103 is crystallized. The temperature of the distortion point of the Corning 1737 substrate is 667 deg.C. After this crystallization, when the substrate is slowly cooled, the film 103 is shrinked and a recessed warpage is generated in the substrate. Accordingly, the substrate 101 is put on a base having a convex curved surface and is heated for several hours at 350 to 600 deg.C. Then, the substrate 101 is deformed into a form to extend along the base by its own weight and heat and by slowly cooling the substrate, a glass substrate, which is very flat, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating gate type semiconductor device such as a thin film transistor (TFT) formed by using a non-single crystalline crystalline silicon film provided on a glass substrate and other semiconductor devices. The present invention relates to a method for manufacturing a semiconductor, characterized in that a crystalline silicon film having higher homogeneity is obtained by improving the flatness of a substrate in the related steps. The present invention is particularly useful for manufacturing a semiconductor device formed on a glass substrate.

[0002]

2. Description of the Related Art Recently, an insulating gate type field effect transistor having a thin film active layer (also referred to as an active region) on an insulating substrate, that is, a so-called thin film transistor (TFT) has been earnestly studied.

These are distinguished as amorphous silicon TFTs or crystalline silicon TFTs depending on the material and crystal 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.

In general, a semiconductor in an amorphous state has a low electric field mobility, so that high speed operation is required.
Not available for FT. Further, in amorphous silicon, the P-type electric field mobility is extremely small, so that a P-channel type TFT (PMOS TFT) cannot be manufactured. Therefore, a P-channel type TFT and an N-channel type TFT (NMOS type) cannot be formed. It is impossible to form a complementary MOS circuit (CMOS) in combination with a TFT).

On the other hand, a crystalline semiconductor has a larger electric field mobility than an amorphous semiconductor, and therefore can operate at high speed. With crystalline silicon, not only NMOS TFTs but also PMOS TFTs can be obtained, so CM
It is possible to form an OS circuit.

For the non-single-crystal crystalline silicon film, an amorphous silicon film obtained by the 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 an insulating substrate, a crystalline silicon film having a sufficiently high electric field mobility (high enough to form a CMOS circuit) by only thermal annealing is used. It was extremely difficult to get.

The glass substrate as described above generally has a low strain point temperature (about 600 ° C.), and when the substrate temperature is raised to a temperature necessary to obtain a crystalline silicon film having sufficiently high mobility. , Because the substrate will be distorted.

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, the optical annealing technique is very effective for crystallizing the silicon film based on the glass substrate.

At present, a high-power pulse laser such as an excimer laser is optimally regarded as a 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 which is usually used, it is necessary to move the beam up and down and to the left and right in order to process one large area substrate, and there is still room for improvement in terms of mass productivity. was there.

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

[0014]

The crystalline silicon film formed by using both thermal annealing and optical annealing is used to form TFTs arranged in a matrix, and the threshold voltages of those TFTs are formed in the plane of the substrate. I examined the distribution.

FIG. 2 shows the distribution of the threshold value of the TFT using the crystalline silicon film formed by the conventional method in the plane of the substrate. This distribution is a U-shaped distribution as shown in FIG. Further, in FIG. 4, the TFT on the glass substrate
The following shows the arrangement.

As shown in FIG. 4, the data of FIG.
40 × 50m on 0mm □ Corning 1737 substrate
In the area of m, 400 × 300 TFTs are arranged in a matrix form, and in the central portion of the substrate, each row of 400 TFTs (the portion surrounded by a dotted line in FIG. 4) in a horizontal row from end to end. The horizontal axis corresponds to.

For example, when 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

The warpage of this substrate is not observed in the glass substrate immediately after the amorphous silicon film is formed, and the subsequent heat treatment step (this causes the film to undergo solid phase growth and crystallize).
It was revealed that the silicon film (or the silicon oxide film) is a warp caused by a higher shrinkage than that of the glass substrate when the substrate is cooled after the heat treatment.

This warp is formed in a concave shape when viewed from the substrate film formation surface. FIG. 3 shows a state in which 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 from place to place on the substrate. This deviation makes the degree of crystallinity of the silicon film different within the substrate plane,
As a result, it is considered that the threshold voltage causes the specific distribution in the substrate surface.

The warp of the 100 mm square substrate immediately before laser irradiation is 50 μm at the central portion and the end portion of the substrate.
The difference was about m. 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 is generally within the range of 20 to 200 μm. When the size of the substrate is about 500 mm square, the warpage may be about 1 to 2 mm.

An object of the present invention is to improve the flatness of a substrate on which a film is formed after heating and gradually cooling the substrate.

An object of the present invention is to provide a method for producing a crystalline silicon film formed on a glass substrate and having a uniform crystallinity in the plane of the substrate.

The present invention also provides a method of manufacturing a plurality of crystalline silicon TFTs formed on a glass substrate, the crystalline silicon TFTs having a uniform threshold voltage in the plane of the substrate. To aim.

In particular, in the step of crystallizing the silicon film on the glass substrate, which comprises the thermal annealing and the subsequent laser annealing step, uniform crystallinity is given within the plane of the substrate,
Further, it is an object of the present invention to provide a manufacturing method for obtaining a crystalline silicon TFT having a uniform threshold voltage in the substrate surface by using the film.

[0027]

In order to solve the above problems, the present invention is characterized in that an amorphous silicon film formed on a flat glass substrate is crystallized by heating, and the glass substrate is It is a semiconductor manufacturing method characterized in that the glass substrate is placed on a table having a convex curved surface, the glass substrate is heated at a temperature near the strain point of the glass substrate for a predetermined time, and then gradually cooled.

Another structure of the present invention is that an amorphous silicon film formed on a flat glass substrate is crystallized by heating, and the glass substrate is placed on a table having a convex curved surface. The glass substrate is placed, heated at a temperature near the strain point of the glass substrate for a predetermined time, and then gradually cooled, and then
Laser irradiation is performed on the silicon film, which is a semiconductor manufacturing method.

As described above, in the manufacturing process of a thin film transistor or the like formed on a glass substrate, the glass substrate is warped after the step of thermally annealing the amorphous silicon film on the glass substrate.

When a laser beam is applied to such a warped substrate, the focal point of the laser beam varies from place to place on the substrate, resulting in non-uniform crystallinity in the plane of the substrate.

Therefore, in one aspect of the present invention, the glass substrate is made flat after the thermal annealing process. After that, by performing laser irradiation, uniform crystallization can be performed in the plane of the substrate.

FIG. 6 shows an example of the method of the present invention. The first aspect of the present invention is, as shown in FIG. 6, roughly symmetrical with the curved surface of the glass substrate (deformed into a concave shape) after the thermal annealing process (heat crystallization and slow cooling) after the silicon film is formed. The glass substrate deformed into a concave shape is placed on a stage (stage) having a convex curved surface that is a curved surface. Heating is performed at a temperature near the strain point temperature of the glass substrate to deform the glass substrate and bring them into close contact with each other according to the convex curved surface of the table.

After that, it is gradually cooled. During this slow cooling, the silicon film shows a higher shrinkage than the glass substrate, and as a result, the glass substrate changes from the convex curved surface type to the flat state.

Further, according to another structure of the present invention, a flat glass substrate on which an amorphous silicon film is formed is placed on a table having a convex curved surface, and the glass substrate is attached to the glass substrate. It is a semiconductor manufacturing method characterized by comprising heating at a temperature near a strain point for a predetermined time and then gradually cooling.

Further, according to another structure of the present invention, a flat glass substrate on which an amorphous silicon film is formed is placed on a table having a convex curved surface, and the glass substrate is attached to the glass substrate. Heat at a temperature near the strain point for a specified time, then slowly cool,
Then, laser irradiation is performed on the silicon film,
Is a method for manufacturing a semiconductor.

FIG. 7 shows an example of the method of the present invention. According to another aspect of the present invention, when crystallizing an amorphous silicon film by thermal annealing, a glass substrate is placed on a convex curved surface type stage (stage) as shown in FIG. 7, and the substrate is deformed into a convex curved surface type. The heat treatment is performed.

Then, during the heat treatment, the glass substrate is
It follows the convex surface of the table due to the decrease in viscosity due to heat and the weight of the substrate. Heat treatment is performed while maintaining this state,
After completion of the heat treatment, the substrate is gradually cooled.

At this time, the silicon film shows a higher shrinkage than the glass substrate, and the glass substrate returns from the convex curved surface type to the flat state. In this way, the flattening of the glass substrate and the crystallization of the semiconductor film can be performed simultaneously.

When the temperature required for the flattening treatment of the glass substrate is within the range of 70% to 115% of the strain point temperature of the substrate, the flattening effect of the substrate was obtained.

When the heating temperature is lower than 70% of the strain point temperature of the substrate, the substrate is not deformed at all or requires a long time for the deformation. On the other hand, the heating temperature is 1 of the strain point temperature of the substrate.
When it is higher than 15%, the deformation of the substrate is so severe that the shape of the substrate becomes uncertain after cooling.

When the amorphous silicon film is crystallized simultaneously with the flattening of the glass substrate, the higher the temperature is, the better the crystallinity is. However, the crystallinity is sufficiently within the above temperature range. The improvement was confirmed. Note that these temperature ranges are values based on absolute zero.

FIG. 8 shows an example of the method of the present invention. As shown in FIG. 8, another configuration of the present invention is to install a glass substrate on which a silicon film has been formed along a table (stage) having a convex curved surface by pressing an edge of the substrate or the like, In the state before heating, the glass substrate is deformed according to the convex curved surface.

The stage is preferably made of quartz in order to prevent contamination of the substrate. While maintaining this state, the glass substrate is heated, and in this state, laser annealing is performed on the silicon film formed on the glass substrate. The heating temperature at this time is in the range from room temperature to 70% of the strain point temperature of the glass substrate.

The heating temperature is 70 which is the strain point temperature of the glass substrate.
When it exceeds%, the glass substrate is likely to be thermally deformed,
After gradual cooling, it becomes difficult for the substrate to return to a flat surface. When the temperature is unnecessarily lowered to room temperature or lower, heat is taken and crystallization becomes insufficient.

After that, it is gradually cooled. During this slow cooling, the silicon film shows a higher shrinkage than the glass substrate, and as a result, the glass substrate changes from the convex curved surface type to the flat state.

FIG. 9 shows an example of the substrate heating device. When the substrate is heated by the method shown in FIG. 9, a substrate having a curved surface can be efficiently heated. That is, it is possible to maintain the substrate at a desired temperature by installing a table having a heater under the substrate, warming the helium gas by the heater, and circulating the heated helium gas under the substrate. Helium gas is used here because it has a high thermal conductivity.

Further, according to another structure of the present invention, as shown in FIG. 10, the glass substrate after the silicon film is formed is pressed onto a table (stage) having a convex U-shaped curved surface, so that the glass The substrate is curved into a convex U-shaped curved surface.

While maintaining this state, the glass substrate is heated, and in this state, laser annealing is performed on the silicon film formed on the glass substrate.

The heating temperature at this time is from room temperature to 70% of the strain point temperature of the glass substrate.
The heating method is preferably the method shown in FIG.

The heating temperature is 70 which is the strain point temperature of the glass substrate.
When it exceeds%, the glass substrate is likely to be thermally deformed,
After gradual cooling, it becomes difficult for the substrate to return to a flat surface. When the temperature is unnecessarily lowered to room temperature or lower, heat is taken and crystallization becomes insufficient.

The laser beam used for laser annealing is processed into a linear shape. The linear processing is performed to improve the efficiency of laser processing.

FIG. 11 shows an example of the laser irradiation method. In FIG. 11, the height of the stage (stage) changes according to the degree of curvature of the substrate so that the focus of the laser beam is always constant.

The degree of curvature of the substrate can be known in advance from the shape of the table, the thickness of the substrate, etc. Therefore, based on the data,
By changing the height of the table, the focus of the linear laser beam can be kept constant regardless of the degree of curvature of the substrate, and the optical system can be left unchanged, which is substantially the same as when a flat substrate is used. Laser annealing can be performed under equivalent conditions.

That is, in order to irradiate a linear laser beam on a curved surface curved in a U shape as shown in FIG. 10, the substrate is curved as shown in FIG. Nevertheless, uniform laser irradiation can be performed, and high processing efficiency and homogeneity of laser annealing can be obtained similarly to a flat substrate.

This is a case of irradiating a U-shaped curved surface with a linear laser beam, but the same procedure is performed when a laser beam having a rectangular shape instead of a linear shape is used to irradiate a convex curved surface. can do.

Of course, the focus of the laser beam may be changed by adjusting the lens instead of the height of the substrate. However, to change the focus of the laser beam,
The energy distribution of the laser beam on the irradiated surface,
There may be a case where an optical device that does not change the depth of focus is required.

After that, it is gradually cooled. During this slow cooling, the silicon film shows a higher shrinkage than the glass substrate, and as a result, the glass substrate changes from the curved state of the convex U-shaped curved surface to the flat state, and a flat substrate having a crystalline silicon film is obtained. be able to.

The Applicant examined the influence of all steps for forming a thin film transistor on the substrate shape on the substrate, and found that the substrate deformation before and after the heat treatment for crystallizing the silicon film was the most prominent, and the subsequent deformation. No noticeable deformation was observed in the process. Therefore, if the substrate is processed into an extremely flat state immediately before laser irradiation, the substrate after all the steps can be kept in a considerably flat state.

Therefore, according to the method of the present invention, it is possible to obtain a crystalline silicon film whose crystallinity is extremely uniform in the plane of the substrate and a flat substrate.

In the case of the present invention, the roughness and waviness of the surface of the glass substrate have a thickness of 1.1 mm and a size of 100 mm × 1.
In a 00 mm substrate, it can be accommodated in about 10 μm or less.

The size of the substrate is about 500 mm square (for example, 370 × 400 mm ² , 400 × 500 mm).
² , 550 x 650 mm ² , the thickness is 0.5-
When the thickness is about 0.7 mm, the degree of height difference between the thermal crystallization of the amorphous silicon film and the warpage of the substrate after cooling is 1 to
Although it may be 2 mm, a substantially flat substrate can be obtained by the method of the present invention.

The convex curved surface and the U-shaped curved surface of the table on which the glass substrate is mounted have various sizes such as the size, thickness, material of the glass substrate to be mounted, the type and thickness of the coating, and various other factors. Determined by the conditions.

The larger the area of the substrate, the greater the degree of curvature of the substrate. In addition, it will be two-dimensionally curved. Therefore, in the case of a glass substrate having a size of about 100 mm × 100 mm, the table on which the substrate is placed may have a U-shaped convex curved surface that is curved in only one direction. In this case, the inverted U-shaped convex curved surface of the pedestal has a central portion of the convex curved surface in the region where the glass substrate is placed and a lowest portion of the end of the region. It is desirable that the difference in height is 20 to 200 μm, preferably about 50 μm.

When the size of the substrate is increased to about 500 mm square, the glass substrate may be curved in two directions, so that the cross section in the two directions is an inverted U-shaped convex curved surface. It is preferable to use a table having When a large-area glass substrate is used, in the region where the glass substrate is placed on the convex curved surface of the table, there is a difference in height between the central portion of the region and the lowest portion of the end of the region. 1-2
It is preferably about mm.

When a plurality of TFTs were formed using the crystalline silicon film formed according to the manufacturing method of the present invention, T
The distribution of the threshold voltage of the FT can be made extremely uniform in the plane of the substrate. This effect becomes larger as the area of the substrate becomes larger.

Further, when a crystalline silicon thin film transistor for pixels or driving is provided on a glass substrate by using the method of the present invention and a liquid crystal display is formed by using this substrate, the glass substrate can be made extremely excellent by the method of the present invention. Since the cells can be flattened, there is also an advantage that cell assembly can be performed easily and surely. In this case, even if there is no crystallization process by laser irradiation after thermal crystallization, the effect of the present invention of flattening the substrate is effective.

[0065]

【Example】

[Embodiment 1] FIG. 1 shows the manufacturing process of the embodiment. First, a glass substrate (in this embodiment, a Corning 1737 of 400 × 500 mm square and a thickness of 0.7 mm is used. Of course, another glass substrate may be used. For example, Corning 7
059, OA2, NA45, etc. ) 101 on the base silicon oxide film 102 having a thickness of 2000 Å, and 500 Å further on it
The amorphous silicon film 103 was continuously formed by the plasma CVD method.

Then, a 10 ppm nickel acetate aqueous solution was 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. 1 (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 above thermal crystallization, the silicon film shrinks and 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 × 10 6 as the minimum value in the film.
^{It was 19 to} 5 × 10 ¹⁸ atoms / cm ³ . These values are analyzed by secondary ion mass spectrometry (SIMS),
It is the minimum value of the concentration of the catalytic element in the measured silicon film.

In order to correct the warp of the glass substrate after the thermal crystallization step, the glass substrate is placed on a table having a convex curved surface as shown in FIG.
To 600 ° C. for several hours). The convex curved surface has a curved surface that is substantially symmetrical to the warp of the glass substrate.

Then, the glass substrate is deformed by its own weight and heat along the table. When the glass substrate is gradually cooled in this state, the silicon film formed on the substrate contracts higher than that of the glass substrate, and as a result, an extremely flat glass substrate can be obtained.

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 outline of the laser annealing apparatus is shown below. FIG. 12 shows a conceptual diagram of the laser annealing apparatus used in this example. The laser annealing apparatus shown in FIG.
It is a multi-chamber system, and the substrate loaded from the loader / unloader chamber and positioned in the alignment chamber is transferred to each chamber through the transfer chamber by the substrate transfer robot provided in the transfer chamber.
It is processed continuously for each substrate.

The substrate is first carried 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 the loader / unloader. You can move to the room and hit outside.

The variation in energy for each pulse of the laser annealing apparatus is within ± 3% at 3σ.

A pulse laser having a larger variation than this may be used, but the depth of focus is limited. In addition,
Those having 3σ of ± 10% or more are not suitable for the present invention.

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 and lasers of other systems can be used. However, it is necessary to use pulsed laser light.

This laser annealing apparatus has a hermetic sealing property 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.

The oscillated laser light is introduced into an optical system as shown in FIG. 13 due to the deformation of its beam shape. FIG. 13 shows an example of the optical system.

The beam of the laser light immediately before entering the optical system is a rectangle of about 3 × 2 cm ² , and depending on the optical system, an elongated beam (length of 10 to 30 cm, width of 0.01 to 0.3 cm) (linear shape) is used. Beam).

The energy density distribution in the width direction of the linear laser beam after passing through this optical system is shown in FIG.
It has a trapezoidal shape as shown in FIG. The maximum energy of the laser light that has passed through this optical system is 800 mJ /
It is a 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 takes less time and labor than 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) irradiated with the laser light is controlled by a computer and is designed to move at a right angle to the line direction of the linear laser beam. Also, the height of the substrate can be changed.

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 width is shorter than that of the sample.

The optical path inside the optical system for processing the laser beam into a linear laser (FIG. 13) 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 line direction, it passes through a cylindrical convex lens F and a mirror G. It is focused by the cylindrical lens H via the, and the surface to be irradiated is irradiated.

230 m between the cylindrical lenses A and B
230 mm between the fly-eye lens D and D2, and 650 between the fly-eye lens D and the cylindrical lens E.
mm, 65 between the cylindrical lens F and the illuminated surface
It was set to 0 mm (the sum of the focal lengths of the respective lenses). 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.

The shape of the energy distribution of the laser beam at the focus is made trapezoidal by changing the lens H up and down (J direction).

By moving the surface to be irradiated up and down relative to the lens H (direction J), the shape of the energy distribution of the laser beam on the surface to be irradiated (focus) is changed from a shape close to a rectangle to a shape close to a trapezoid. It can be deformed (see the lower diagram of Fig. 13. To make these shapes sharper, it is better to make a slit in the laser optical path). The optical system may be of any type 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 125 mm × 1 mm. The line width of the beam is the half width of the maximum energy of the laser beam.

The energy profile (energy distribution) of the linear laser beam in the line width direction is shown in FIG.
In (b), L1 = 0.4 mm, L2, L3 = 0.
It has a pseudo trapezoidal distribution of 25 mm and satisfies the inequalities 0.5L1 ≦ L2 ≦ L1 and 0.5L1 ≦ L3 ≦ L1. At this time, the depth of focus can be about ± 400 μm.

The extent of the tail of this trapezoidal distribution is
It changes depending on the distance between the final lens of the laser optical system and the irradiation surface. During the laser processing, the distance between the final lens of the optical system of the laser and the irradiation surface changes due to the unevenness of the irradiation target.

Along with this, the extent of the spread of the trapezoidal distribution of the laser beam changes, but if the range of the change falls within the range of the above inequality, the depth of focus is about ± 400 μm, and therefore, Irregularity of the irradiated surface is ± 40
If it is 0 μm or less, a homogeneous laser treatment becomes possible.

On the other hand, a general laser beam having a rectangular energy distribution has a depth of focus of about ± 200 μm or less, which is affected by the unevenness of the surface to be irradiated and the height difference, resulting in poor crystallinity in the substrate surface. It tends to be uniform.

The sample is placed on a stage (table), and irradiation is performed by moving the stage at a speed of 2 mm / s. The irradiation conditions of the laser light are such that the energy density of the laser light is 100 to 500 mJ / cm ² ,
Here, it is set to 300 mJ / cm ² , and the number of pulses is 30 pulses /
s. The energy density here means the density of the upper bottom portion (portion having the maximum value) of the trapezoidal beam. The substrate temperature during laser irradiation is 200
° C.

When laser irradiation is performed under the above-mentioned conditions, if one point on the sample is focused, the laser irradiation is 1
It will be a 5-step irradiation. This is 0.5 per beam pass
This is because it takes a second, and irradiation of 15 pulses is performed at one location by one irradiation while scanning the beam. In this case, in the above 15 irradiations, the irradiation of the first several times is the irradiation whose irradiation energy density is gradually increased, and the irradiation of the last several times is the irradiation whose energy density is gradually decreased. .

This state is schematically shown in FIG. The laser energy gradually increases in the first half of the fifteen stages (note A in FIG. 16), and gradually decreases in the latter half (note B in FIG. 16).

When such laser light irradiation is performed, a single pulsed laser light is conventionally used, and a weak pulsed laser light for preheating and a strong pulsed laser light for crystallization are conventionally used. The same effect as stepwise irradiation can be provided.

That is, since the energy supplied to the irradiated region does not change abruptly, the surface of the silicon film is not abruptly changed, surface roughness and internal stress accumulation are prevented, and a uniform crystal is formed. Can give sex.

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. 1 (B))

Next, a thin film transistor was produced as a semiconductor device based on the produced crystalline silicon film. The thin film transistors were arranged in a matrix on the substrate. Specifically, 400 × 300 thin film transistors were produced in a production area of 40 × 50 mm ² . The manufacturing process is shown below.

First, the silicon film was etched to form the island-shaped silicon region 105. Next, plasma CVD
A 1200 Å-thick silicon oxide film 106 was deposited as a gate insulating film by the method. TEOS and oxygen were used as source gases for plasma CVD. Substrate temperature during film formation is 2
50-380 degreeC, for example, it was 300 degreeC. (Figure 1
(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 8000Å, for example, 6000Å was deposited. Then, the aluminum film is etched to form the gate electrode 10
7 was formed. (Fig. 1 (C))

Next, impurities (boron) are formed in the silicon region by ion doping using the gate electrode as a mask.
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. 1 (D))

Then, in order to activate the doped boron, optical annealing was performed using the KrF excimer laser used in Example 1. The energy density of the laser is 100 to 350 mJ / cm ² , for example, 250.
mJ / cm ² . Before this irradiation, 170mJ / c
Irradiation with energy of about m ² further increased the crystallinity.

The laser irradiation method is as follows.
That is, irradiation is performed while shifting the linear laser beam relative to the non-irradiated object. 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, in a nitrogen atmosphere, 2
Thermal annealing was performed at 450 ° C. for an hour. (FIG. 1 (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. 1 (F))

FIG. 5 shows the distribution of the threshold value of the TFT using the crystalline silicon film formed in the example 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 the case of FIG.

As shown in FIG. 5, the TFT manufactured in this example has a uniform threshold value in the substrate surface, which is clearly shown in FIG. However, it is found that the substrate has a uniform threshold voltage in the plane of the substrate.

[Embodiment 2] In Embodiment 1, 400 × 50
A 0 mm square glass substrate 101 was used, but in this embodiment, a 100 mm square Corning 705 is used as the glass substrate.
9 is used. Therefore, when flattening the glass substrate after the crystallization step, the shape of the table on which the glass substrate shown in FIG. 6 is mounted may be an inverted U-shaped convex curved surface that is curved in one direction.

When the glass substrate is placed on a table having an inverted U-shaped convex curved surface and appropriate heat is applied (at 350 to 600 degrees for several hours), the glass substrate is placed on the stage by its own weight and heat. Deforms along the shape. When the glass substrate is gradually cooled in this state, the silicon film formed on the substrate contracts higher than that of the glass substrate, and as a result, an extremely flat glass substrate can be obtained.

After that, a TFT was manufactured in the same manner as in Example 1. In this way, the threshold voltage of the TFT thus obtained is similar to that of the TFT manufactured without flattening the glass substrate, as in Example 1, and the distribution of the threshold voltage is It was extremely uniform.

[Embodiment 3] This embodiment will be described with reference to FIG. First, a glass substrate (400 × 5 in this embodiment)
Corning 1737 of 00 mm square and 0.7 mm thickness is used. Of course, other glass substrates may be used. For example, Corning 7059, OA2, NA45, etc. ) 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, but there is no problem in the subsequent steps. (Fig. 1 (A))

Then, the glass substrate is placed on a convex table (the swelling of the central portion of the region on which the substrate is mounted is higher than the end portion of the region) and heat-annealed at 550 ° C. for 4 hours. , Crystallize the amorphous silicon film.

At this time, the glass substrate is deformed by its own weight and heat along the table. Further, at this time, nickel plays a role of a crystal nucleus and promotes crystallization of the silicon film. The strain point temperature of the Corning 1737 substrate is 667 ° C., and the annealing temperature of 550 ° C. is below the strain point temperature.

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 the above-mentioned 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 ^{17 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).

When the glass substrate is annealed after the thermal crystallization, the glass substrate is flattened because the shrinkage rate of the silicon film is larger than that 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.

In this example, a KrF excimer laser (wavelength 248 nm, pulse width 30 nsec) was linearly processed and used. The beam size was 1 × 125 mm ² . The energy density of the laser is 100 mJ / cm ² ~
In the range of 500 mJ / cm ² , for example, 370 mJ / cm
Irradiation was performed at ² . Before this irradiation, 220 mJ /
Irradiation with energy of about 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. (Fig. 1 (B))

After that, a TFT was manufactured in the same manner as in Example 1. In this way, the threshold voltage of the obtained TFT has a threshold voltage distribution similar to that of the TFT manufactured without flattening the glass substrate as in Example 1.
It was extremely uniformized in the plane of the substrate.

In this embodiment, 400 mm × 500.
Although the square mm glass substrate 101 was used, as in the case of Example 2, when the 100 mm square Corning 7059 was used as the glass substrate 101, when the glass substrate after the crystallization step was flattened, as shown in FIG. The shape of the table on which the glass substrate is placed may be an inverted U-shaped convex curved surface that is curved in one direction.

[Embodiment 4] This embodiment will be described with reference to FIG. First, a glass substrate (400 × in this embodiment)
Corning 1737 having a side of 500 mm 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, 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, but there is no problem in the subsequent steps. (Fig. 1 (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, and 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 the above-mentioned 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 ^{17 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 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 while heating the film. At this time, the flattening of the glass substrate warped in the concave shape is also performed at the same time.

In this example, a KrF excimer laser (wavelength 248 nm, pulse width 30 nsec) was used. The beam size was 30 × 20 mm ² . The energy density of the laser is 100 mJ / cm ^{2 to} 500 mJ / cm ^2.
Irradiation was performed in the range of, for example, 370 mJ / cm ² . Before this irradiation, irradiation with an energy of about 220 mJ / cm ² further increased the crystallinity.

The laser irradiation method is as follows.
First, as shown in FIG. 8, the glass substrate is placed on a convex table, and the end portion of the glass substrate is fixed by being pressed by an appropriate “holding” made of metal or the like. Then, the substrate is deformed into a convex shape.

As shown in FIG. 9, the pedestal has a mechanism for flowing out and circulating the heated helium gas under the substrate, whereby the substrate is kept at a desired temperature. Laser processing is performed in this state. The laser beam is moved back and forth and left and right, and irradiation is performed while the beams are superimposed on the substrate. Focusing on one point on the substrate, the number of laser irradiations is set to 2 to 5 times.

Since the substrate to be irradiated is warped convexly,
The glass substrate is moved up and down with respect to the laser so that the laser focus is always on the substrate. Since the thickness of the substrate and the shape of the convex surface are known in advance, the height of the substrate is controlled based on these data, and uniform annealing is performed on the convex substrate surface while keeping the focus constant. can do.

Of course, the height of the substrate may be fixed, the lens may be adjusted to move the focus, and the focus of the laser beam may always be set on the substrate. Alternatively, a laser displacement meter or the like may be used to measure the distance to the irradiation surface, and the height or focus of the substrate may be automatically changed based on the distance.

The substrate temperature during laser irradiation is 200.
° C. After that, when the "holding down" is removed and the material is gradually cooled, the substrate is flattened due to the contraction of the silicon film. (Figure 1
(B))

In this way, it was possible to obtain a silicon film having uniform crystallinity in the plane of the substrate and a flat substrate having the film.

After that, a TFT is manufactured in the same manner as in Example 1. In this way, the threshold voltage of the obtained TFT has a threshold voltage distribution similar to that of the TFT manufactured without flattening the glass substrate as in Example 1.
It was extremely uniformized in the plane of the substrate.

[Embodiment 5] This embodiment will be described with reference to FIG. First, a glass substrate (400 × 5 in this embodiment)
Corning 1737 of 00 mm square and 0.7 mm thickness is used. Of course, other glass substrates may be used. For example, Corning 7059, OA2, NA45, etc. ) 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, but there is no problem in the subsequent steps. (Fig. 1 (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 and 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 the above-mentioned 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 ^{17 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 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 while heating the film. At this time, the flattening of the glass substrate warped in the concave shape is also performed at the same time.

The laser irradiation method is as follows.
As in Example 1, the laser annealing apparatus shown in FIG. 12 was used. As the oscillator, here, 3000-308 manufactured by Lambda Physics was used. The laser light emitted is
It 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 the optical system as shown in FIG. 14 because of the deformation of its beam shape. FIG. 14 shows an example of the optical system.

The beam of the laser light immediately before entering the optical system is a rectangle of about 3 × 2 cm ² , and depending on the optical system, an elongated beam (length of 10 to 30 cm and width of 0.01 to 0.3 cm) (linear shape) is used. Beam).

The energy density distribution in the width direction of the linear laser beam after passing through this optical system is shown in FIG.
It has a trapezoidal shape as shown in FIG. The energy of the laser beam that has passed through this optical system is 1000 mJ at maximum.
/ It is a shot.

The reason why the laser beam is processed into such an elongated beam is to improve the workability. That is, when the sample is irradiated with a linear beam, if the beam width is longer than the sample width, the sample can be moved in one direction to irradiate the sample with laser light. it can.

On the other hand, even if the width of the beam is shorter than the width of the sample, it takes less labor than 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) irradiated with the laser light is controlled by a computer and is designed to move in a direction perpendicular to the line direction of the linear laser beam. Also, the height of the substrate can be changed.

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 width is short with respect to the sample.

The optical path (FIG. 14) inside the optical system for processing the laser beam into the linear laser will be described. The laser light emitted from the laser light source a and incident on the optical system is
First, it passes through the fly-eye lenses b and c.

Further, as the first cylindrical lens, a cylindrical convex lens d, and as a second cylindrical lens provided to improve the homogeneity of the beam to be linearized in the line direction, it passes through the cylindrical convex lens e and the mirror f. Then, the light is focused by the cylindrical lens g 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 illuminated surface is 440 mm. Cylindrical lens g
Is used with a focal length of 100 mm.

The shape of the energy distribution of the laser beam at the focus is made trapezoidal by changing the lens g up and down (direction j). Deforming the shape of the energy distribution of the laser beam on the irradiation surface (focus) from a shape close to a rectangle to a shape close to a trapezoid by moving the irradiation surface up and down relative to the lens g (j direction). You can The optical system may be of any type 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. 14, but an optical system having lenses B and C as shown in FIG. 13 may be used.

The laser beam is shaped into a linear shape, and the beam area at 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 energy value).

The energy profile (energy distribution) of the linear laser beam in the line width direction is shown in FIG.
In (b), L1 = 0.1 mm, L2, L3 = 0.
It has a pseudo trapezoidal distribution of 08 mm and satisfies the inequalities 0.5L1 ≦ L2 ≦ L1 and 0.5L1 ≦ L3 ≦ L1. At this time, the depth of focus can be about ± 400 μm.

The degree of spread of the trapezoidal distribution is
It changes depending on the distance between the final lens of the laser optical system and the irradiation surface. During the laser processing, the distance between the final lens of the optical system of the laser and the irradiation surface changes due to the unevenness of the irradiation target.

Along with this, the extent of the spread of the trapezoidal distribution of the laser beam changes, but if the range of the change falls within the range of the above inequality, the depth of focus is about ± 400 μm, and therefore, Irregularity of the irradiated surface is ± 40
If it is 0 μm or less, a homogeneous laser treatment becomes possible.

On the other hand, in the general laser beam having a rectangular energy distribution shown in FIG. 15A, the depth of focus is about ± 200 μm or less.

First, as shown in FIG. 10, the glass substrate is placed on a U-shaped convex table, and the end portion of the glass substrate is made of a suitable metal material such as metal. "
Press to fix and then bend the substrate into a U-shape.

As shown in FIG. 9, the pedestal has a mechanism for letting out and circulating the heated helium gas under the substrate, whereby the substrate is kept at a desired temperature.

The laser processing is performed while shifting the linear laser beam relative to the object to be irradiated. The direction in which the linear laser was shifted was substantially perpendicular to the linear laser, and the straight line contained in the U-shaped curved surface of the substrate to be irradiated was approximately parallel to the linear laser.

Since the substrate to be irradiated is curved in a convex U shape, as shown in FIG. 11, the glass substrate is placed above and below the laser so that the laser focus is always on the substrate during laser irradiation. move.

Since the thickness of the substrate, the shape of the curved surface, etc. are known in advance, the height of the substrate is controlled on the basis of these data, so that the U-shaped substrate surface is controlled while keeping the focus constant. The uniform annealing can be performed.

Of course, the height of the substrate may be fixed, the lens may be adjusted to move the focus, and the focus of the laser beam may always be set on the substrate.

Further, a laser displacement meter or the like may be used to measure the distance to the irradiation surface, and the height or focus of the substrate may be automatically changed based on the distance. The substrate temperature during laser irradiation was 200 ° C.

Since the energy distribution of the irradiated laser beam is trapezoidal and has a depth of focus of about ± 400 μm, the height difference between the center and the end of the U-shaped convex table is ± 400 μm. If it is not more than a certain degree, it is possible to perform uniform laser annealing in the plane of the substrate without changing the table or the focus at all.

Of course, by using a beam having such a depth of focus and varying the table and the focus in accordance with the height difference of the surface to be irradiated, extremely uniform laser annealing can be performed.

The glass substrate on the table is 2.5 mm / s.
It moves at a right angle in the width direction at the speed of. The laser light irradiation conditions are such that the energy density of the laser light is 100 to 50
The pulse number is set to 0 mJ / cm ² , here 400 mJ / cm ² , and the pulse number is set to 200 pulses / s. The energy density here means the density of the upper bottom portion (the portion having the maximum value) of the energy distribution of the trapezoidal laser beam.

When laser irradiation is performed under the above-mentioned conditions, if one point on the sample is focused, the laser irradiation is 3 times.
It will be a two-stage irradiation. This is 0.4 for each pass of the beam.
This is because it takes a second, so that irradiation of 32 pulses is performed at one location by one irradiation while scanning the beam. In this case, in the above 32 times of irradiation, the irradiation of the first several times is the irradiation of which the irradiation energy density is gradually increased, and the irradiation of the last several times is the irradiation of which the energy density is gradually decreased. .

This state is schematically shown in FIG. The laser energy gradually increases in the first half of the 32 stages (note A in FIG. 16), and gradually decreases in the latter half (note B in FIG. 16).

Further, the atmosphere control is not particularly performed here, and the 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.

After that, when the "holding down" is removed and the material is gradually cooled, the substrate is flattened due to the contraction of the silicon film. (Figure 1
(B))

In this way, it was possible to obtain a silicon film having uniform crystallinity in the surface of the substrate and a flat substrate having the film.

After that, a TFT was manufactured in the same manner as in Example 1. In this way, the threshold voltage of the obtained TFT has a threshold voltage distribution similar to that of the TFT manufactured without flattening the glass substrate as in Example 1.
It was extremely uniformized in the plane of the substrate.

[Embodiment 6] This embodiment will be described with reference to FIG. First, a glass substrate (400 × in this embodiment)
Corning 1737 having a side of 500 mm 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, 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.

In order to crystallize the amorphous silicon film thus obtained, the film is irradiated with an excimer laser which is a high-power pulse laser while heating the film. In this embodiment, a KrF excimer laser (wavelength 248n
m, pulse width 30 nsec) was used. The beam size was 30 × 20 mm ² . Range energy density of 100mJ / cm ² ~500mJ / cm ² laser,
Irradiation was performed at, for example, 370 mJ / cm ² . Before this irradiation, irradiation with an energy of about 220 mJ / cm ² further increased the crystallinity.

At this time, in order to prevent warpage of the substrate due to shrinkage of the silicon film after crystallization and gradual cooling, the laser irradiation method is as follows. First, the glass substrate is shown in FIG.
As shown in Figure 4, place the glass substrate on the convex table, press the edge of the glass substrate with a suitable “holding tool” made of metal or the like to fix it, and transform the substrate into a convex shape. . As shown in FIG. 9, the table has a mechanism for flowing and circulating heated helium gas under the substrate, thereby keeping the substrate at a desired temperature.

Laser processing is performed in this state. Here, irradiation is performed while moving the laser beam forward, backward, leftward and rightward so that the beams overlap each other on the substrate. Focusing on one point on the substrate, the number of laser irradiations is set to 2 to 5 times.

Since the irradiated substrate has a convex warp,
The glass substrate is moved up and down with respect to the laser so that the laser focus is always on the substrate. Since the thickness of the substrate and the shape of the convex surface are known in advance, the height of the substrate is controlled based on these data, and uniform annealing is performed on the convex substrate surface while keeping the focus constant. can do.

Of course, the height of the substrate may be fixed, the lens may be adjusted to move the focus, and the focus of the laser beam may always be set on the substrate. Alternatively, a laser displacement meter or the like may be used to measure the distance to the irradiation surface, and the height or focus of the substrate may be automatically changed based on the distance.

The substrate temperature during laser irradiation is 200.
° C.

After that, when the "holding" is removed and the substrate is gradually cooled, the substrate is flattened due to the contraction of the silicon film. (Figure 1
(B))

In this way, it was possible to obtain a silicon film having uniform crystallinity in the plane of the substrate and a flat substrate having the film.

Then, a TFT was prepared in the same manner as in Example 1. In this way, the threshold voltage of the obtained TFT has a threshold voltage distribution similar to that of the TFT manufactured without flattening the glass substrate as in Example 1.
It was extremely uniformized in the plane of the substrate.

[Embodiment 7] This embodiment will be described with reference to FIG. First, a glass substrate (400 × in this embodiment)
Corning 1737 having a side of 500 mm 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, 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.

In order to crystallize the amorphous silicon film thus obtained, the film is irradiated with an excimer laser which is a high-power pulse laser while heating the film. At this time, the flattening of the glass substrate warped in the concave shape is also performed at the same time. In this example, as in Example 4, crystallization was performed using a laser annealing apparatus having the optical system shown in FIG. Various conditions in the laser annealing are the same as in Example 4.

First, the glass substrate is placed on a U-shaped convex table as shown in FIG. 10, which is provided in the laser annealing chamber of the laser annealing apparatus shown in FIG. The end portion of the substrate is pressed and fixed by an appropriate “holding” made of metal or the like, and the substrate is curved into a U-shape.

As shown in FIG. 9, the pedestal has a mechanism for flowing out and circulating heated helium gas under the substrate, whereby the substrate is kept at a desired temperature.

The laser processing is performed while shifting the linear laser beam relative to the object to be irradiated. The direction in which the linear laser was shifted was substantially perpendicular to the linear laser, and the straight line contained in the U-shaped curved surface of the substrate to be irradiated was approximately parallel to the linear laser.

Since the substrate to be irradiated is curved in a convex U shape, the glass substrate is placed above and below the laser so that the laser focus is always on the substrate during laser irradiation, as shown in FIG. move.

Since the thickness of the substrate, the shape of the curved surface, etc. are known in advance, the height of the substrate is controlled on the basis of these data, so that the U-shaped substrate surface is controlled while keeping the focus constant. The uniform annealing can be performed.

Of course, the height of the substrate may be fixed, the lens may be adjusted to move the focus, and the focus of the laser beam may always be set on the substrate. Alternatively, a laser displacement meter or the like may be used to measure the distance to the irradiation surface, and the height or focus of the substrate may be automatically changed based on the distance.

Since the energy distribution of the irradiated laser beam is trapezoidal and has a depth of focus of about ± 400 μm, the height difference between the central portion and the end of the U-shaped convex base is ± 400 μm. If it is not more than a certain degree, it is possible to perform uniform laser annealing in the plane of the substrate without changing the table or the focus at all.

Of course, by using a beam having such a depth of focus and varying the table and the focus in accordance with the height difference of the irradiated surface, extremely uniform laser annealing can be performed.

The substrate temperature during laser irradiation was 200 ° C. After that, when the "holding down" is removed and the material is gradually cooled, the substrate is flattened due to the contraction of the silicon film. (Fig. 1 (B))

In this way, it was possible to obtain a silicon film having uniform crystallinity in the substrate surface and a flat substrate having the film.

After that, a TFT was manufactured in the same manner as in Example 1. In this way, the threshold voltage of the obtained TFT has a threshold voltage distribution similar to that of the TFT manufactured without flattening the glass substrate as in Example 1.
It was extremely uniformized in the plane of the substrate.

[0207]

According to the present invention, it is possible to reduce the occurrence of warpage of the substrate after heating and cooling the substrate on which the film is formed,
It was possible to flatten.

According to the present invention, a glass substrate on which a crystalline silicon film is formed can be flattened, and a crystalline silicon film having high crystallinity can be obtained even within the surface of the substrate even after the laser irradiation step.

Further, by using this crystalline silicon film, a crystalline silicon TFT having a uniform threshold voltage in the plane of the substrate is obtained.
Can be produced.

The present invention is particularly effective when a large number of TFTs are formed on a glass substrate and the area of the glass substrate is large.

Further, when a liquid crystal display is formed using the glass substrate, since the substrate is flat, cell assembly can be performed easily and surely. As described above, the present invention is considered to be industrially useful.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of an example.

FIG. 2 is a diagram showing a distribution of a threshold value 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 the example in a substrate surface.

FIG. 6 is a diagram showing an example of the method of the present invention.

FIG. 7 is a diagram showing an example of the method of the present invention.

FIG. 8 is a diagram showing an example of the method of the present invention.

FIG. 9 is a diagram showing an example of a substrate heating apparatus.

FIG. 10 is a diagram showing an example of the method of the present invention.

FIG. 11 is a diagram showing an example of a laser irradiation method.

FIG. 12 is a conceptual diagram of a laser annealing apparatus used in the examples.

FIG. 13 is a diagram showing an example of an optical system.

FIG. 14 is a diagram showing an example of an optical system.

FIG. 15 is a diagram showing an energy distribution of a laser beam.

FIG. 16 is a diagram showing an energy density distribution of a linearly processed laser beam in the line width direction.

[Explanation of symbols]

 101 Glass Substrate 102 Silicon Oxide Film 103 Amorphous Silicon Film 105 Island 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

Claims (25)

[Claims] 1. An amorphous silicon film formed on a flat glass substrate is crystallized by heating, the glass substrate is placed on a table having a convex curved surface, and the glass substrate is A method for manufacturing a semiconductor, comprising heating at a temperature near a strain point of the glass substrate for a predetermined time and then gradually cooling. 2. An amorphous silicon film formed on a flat glass substrate is crystallized by heating, the glass substrate is placed on a table having a convex curved surface, and the glass substrate is A method for manufacturing a semiconductor, comprising heating at a temperature near a strain point of the glass substrate for a predetermined time, then gradually cooling, and then irradiating the silicon film with a laser. 3. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having a convex curved surface, and the glass substrate is heated at a temperature near the strain point of the glass substrate. A method for manufacturing a semiconductor, which comprises heating for a predetermined time and then gradually cooling. 4. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having a convex curved surface, and the glass substrate is heated at a temperature near the strain point of the glass substrate. A method for manufacturing a semiconductor, comprising heating for a predetermined time, then gradually cooling, and then performing laser irradiation on the silicon film. 5. An amorphous silicon film formed on a flat glass substrate is crystallized by heating, and the glass substrate is placed on a table having an inverted U-shaped convex curved surface, A method of manufacturing a semiconductor, comprising heating the glass substrate at a temperature near a strain point of the glass substrate for a predetermined time and then gradually cooling the glass substrate. 6. An amorphous silicon film formed on a flat glass substrate is crystallized by heating, and the glass substrate is placed on a table having an inverted U-shaped convex curved surface, A method for manufacturing a semiconductor, comprising: heating the glass substrate at a temperature near a strain point of the glass substrate for a predetermined time, then gradually cooling, and then irradiating the silicon film with a laser. 7. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having an inverted U-shaped convex curved surface, and the glass substrate is near the strain point of the glass substrate. The method for producing a semiconductor, comprising: heating at the temperature for a predetermined time and then gradually cooling. 8. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having an inverted U-shaped convex curved surface, and the glass substrate is near the strain point of the glass substrate. The method for producing a semiconductor is characterized in that the semiconductor film is heated at the temperature for a predetermined time, then gradually cooled, and then the silicon film is irradiated with a laser. 9. The temperature in the vicinity of the strain point of the glass substrate according to claim 1, which is 70% or more and 115% or less (based on absolute zero) of the strain point temperature of the glass substrate. A method for manufacturing a semiconductor, comprising: 10. The method of manufacturing a semiconductor according to claim 1, wherein the table having the convex curved surface is made of quartz. 11. A semiconductor manufacturing method according to claim 1, wherein the silicon film is formed on a silicon oxide film formed on a glass substrate. 12. The inverse U according to any one of claims 4 to 8.
In the area where the glass substrate is placed on the convex curved surface, the character-shaped convex curved surface has a height difference of 20 to 200 μm between the central portion of the area and the lowest portion of the end of the area. A method for manufacturing a semiconductor, comprising: 13. The inverse U according to any one of claims 4 to 8.
In the convex curved surface of the V shape, in the region where the glass substrate is placed on the convex curved surface, the difference in height between the central portion of the region and the lowest portion of the end of the region is about 50 μm. A characteristic semiconductor manufacturing method. 14. An amorphous silicon film formed on a flat glass substrate is heated to crystallize, and the glass substrate is placed on a table having a convex curved surface along the convex curved surface. The laser beam is applied to the crystallized silicon film in a state of being kept at a temperature in the range of room temperature to 70% of the strain point temperature of the glass substrate for a predetermined time, and then gradually cooled. A method for manufacturing a semiconductor, comprising: 15. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having a convex curved surface along the convex curved surface, and the strain point temperature of the glass substrate from room temperature is set. In the state where the silicon film is held at a temperature in the range of 70% for a predetermined time, the silicon film is irradiated with laser, and then gradually cooled. 16. An amorphous silicon film formed on a flat glass substrate is crystallized by heating, and the glass substrate is placed on a table having a U-shaped convex curved surface, The glass substrate is warped to a convex U-shaped curved surface by pressing the end of the glass substrate against the table so that the glass substrate is along the table having the U-shaped convex curved surface. The temperature of the substrate is kept within a range of room temperature to 70% of the strain point temperature of the glass substrate for a predetermined time, and in this state, the silicon film is irradiated with laser and then gradually cooled. A characteristic semiconductor manufacturing method. 17. A flat glass substrate on which an amorphous silicon film is formed is placed on a table having a U-shaped convex curved surface, and the glass substrate is provided with the U-shaped convex curved surface. The glass substrate is warped to a convex U-shaped curved surface by pressing the end of the glass substrate against the table so as to follow the table, and in this state, the temperature of the glass substrate is changed from room temperature to a strain point of the glass substrate. A semiconductor manufacturing method, characterized in that the silicon film is kept in a temperature range of 70% of the temperature for a predetermined time, and in that state, the silicon film is irradiated with laser and then gradually cooled. 18. The method of manufacturing a semiconductor according to claim 14, wherein the glass substrate is installed with its end pressed against the base. 19. The method according to any one of claims 14 to 17,
The semiconductor manufacturing method, wherein the laser irradiation is performed by a linear beam. 20. In any one of claims 14 to 17,
A method for manufacturing a semiconductor, characterized in that the height of the pedestal is varied so that the silicon silicon film surface is located at a focal position of a laser beam. 21. In any one of claims 14 to 17,
A semiconductor manufacturing method, wherein the table having a convex curved surface is made of quartz. 22. In any one of claims 14 to 17,
A method for manufacturing a semiconductor, characterized in that heated helium gas is used as a means for keeping a glass substrate at a predetermined temperature. 23. In any one of claims 14 to 17,
A method of manufacturing a semiconductor, wherein the silicon film is formed on a silicon oxide film formed on a glass substrate. 24. A method of manufacturing a semiconductor device, comprising forming a thin film transistor by using a silicon film formed by the method according to any one of claims 1 to 23. 25. A semiconductor device according to claim 1, wherein the glass substrate constitutes a liquid crystal display, and a thin film transistor is formed on the glass substrate by using the silicon film. Method.