JP3149450B2 - Method and apparatus for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, SO
I. a method of manufacturing an active matrix type thin film transistor.

[0002]

2. Description of the Related Art Conventionally, it has been known that a semiconductor thin film on a single crystal insulating substrate has the following advantages as compared with a bulk semiconductor as seen in SOS (silicon on sapphire).

When cutting or dielectric isolation is performed in an island shape, isolation between elements can be easily and reliably performed. The stray capacitance can be reduced by reducing the PN junction area.

Further, since a single-crystal insulating substrate such as sapphire is expensive, an alternative is to use a fused quartz plate or an amorphous SiO ₂ film formed by oxidizing a Si substrate at a temperature of 1000 ° C. or higher. Amorphous Si deposited on Si substrate
A method has been proposed in which an O ₂ film or an amorphous SiN film is used and a semiconductor thin body is formed thereon. However,
Since these SiO ₂ films and SiN films are not single crystals, if a silicon layer is formed thereon and crystallized by a process at a temperature of 1000 ° C. or more, polycrystals grow on the substrate. The grain size of this polycrystal is several tens of nanometers, and even if a MOS transistor is formed thereon, the carrier mobility is about one-seventh of that of a MOS transistor on bulk silicon.

Further, a MOS transistor on an inexpensive glass substrate having a strain point of 850 ° C. or less for an active matrix substrate of a liquid crystal display cannot use a process at 1000 ° C. or more. Even if a silicon layer is deposited by a growth method, since the grain size of the polycrystal is at most several nm, even if a MOS transistor is formed thereon,
The carrier mobility is about one-tenth of the MOS transistor on bulk silicon.

In recent years, a method of scanning a silicon thin film with a laser beam, an electron beam, or the like, and performing melting and re-singulation of the thin film to increase the crystal grain size to form a single crystal or polycrystal has been studied. ing. According to this method,
A high-quality silicon single-crystal phase or a high-quality polycrystal can be formed on an insulating substrate, and the characteristics of a device manufactured using the same can be improved to about the same level as the characteristics of a device formed on bulk silicon. Further, according to this method, the elements can be stacked, and a so-called three-dimensional IC can be realized. Then, a circuit having characteristics such as high density, high speed, and multiple functions can be obtained.

As an example of manufacturing a thin film transistor by forming a high quality silicon layer by a laser beam, Ext
ended Abstracts of the22n
d (1990 International) Conf
erence on Solid State Dev
ices and Materials, Senda
i, 1990, pp. 967-970 "XeCl Ex
cimer Laser-Induced Amorp
hization and Crystallizati
on of Silicon Films ".

[0008]

However, it is difficult to uniformly crystallize the silicon layer over the entire substrate by irradiating a laser beam. In order to obtain a high-quality silicon layer by a laser beam from a silicon layer formed by a PECVD method or a low pressure chemical vapor deposition method, a certain appropriate energy is required. In the case of an amorphous silicon layer containing hydrogen formed by decomposing monosilane by glow discharge as in the above-described conventional example, a polycrystalline silicon film having a large grain size can be obtained if a certain appropriate beam energy is applied. Can be formed, but if the energy is lower than the energy, the silicon layer becomes fine crystal grains.

In the excimer laser used in the above-mentioned conventional example, the energy distribution of the beam in a cross section perpendicular to the beam traveling direction has a pseudo Gaussian distribution as shown in FIG. It is not a beam having an energy distribution. Then, a silicon layer having a large grain size or a microcrystalline silicon layer is formed in accordance with the energy intensity of the beam, and a silicon layer of uniform quality cannot be obtained. Therefore, in a conventional example, in order to obtain a uniform polycrystalline silicon layer over a large area, a method is attempted in which a laser beam is annealed while shifting the position at a fine interval. However, this method has a drawback that the efficiency is very low because the silicon layer at the same point must be irradiated several tens of times. In addition, in this method, a laser beam having an intensity larger than the energy for obtaining a silicon layer having particles having a large particle diameter is originally irradiated, so that the surface of the silicon layer becomes rough or the silicon layer is adhered. There is a disadvantage that the thin film is damaged.

On the other hand, attempts have been made to provide a special optical system between the oscillation source of the laser beam and the silicon layer as a sample to make the energy distribution of the beam uniform.

However, as a result of the improvement of the beam intensity distribution by this special optical system, non-uniformity is still observed at the beam edge without being uniform over the entire beam. In the portion where the energy intensity is insufficient, in the case of a silicon layer formed by PECVD, the portion where the energy intensity of the beam is insufficient becomes a microcrystalline silicon layer. Irradiation with energy necessary for forming a silicon layer having particles does not change in a microcrystalline state. Therefore, in an energy beam having a non-uniform energy intensity distribution as in the related art,
Irradiation with a pulse laser has a disadvantage that a silicon layer having a larger area than a pulse laser beam cannot be uniformly improved in quality.

[0012]

According to the present invention, there is provided a method of manufacturing a thin film transistor having a silicon layer on a substrate, comprising the steps of: forming the silicon layer on the substrate; Passing through the concave lens, and a step of irradiating the silicon layer by blocking a part of the parallel light beam by the shielding means, so that the surface of the silicon layer irradiated by the laser beam overlaps It is characterized by being irradiated a plurality of times. Preferably, the laser beam is
It is a pulse beam having a rectangular energy distribution.
Preferably, the method includes a step of changing a beam size by changing a distance between the convex lens and the concave lens.
The thin film transistor manufacturing apparatus of the present invention includes a laser source, a convex lens that receives a short-wavelength light beam from the laser source, a concave lens that receives light emitted from the convex lens, and a part of the light emitted from the concave lens, Shielding means for irradiating the silicon layer.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments will be described below in detail with reference to the drawings.

An embodiment is shown in FIG.

First, as shown in FIG. 1A, a silicon dioxide film 102 having a thickness of 200 nm is formed on a transparent insulating substrate 101 by electron cyclotron resonance sputtering. Instead of the silicon dioxide film, SiNx, SiON,
An insulating film such as PSG may be used.

Next, an amorphous silicon layer 103 having a thickness of 50 nm is formed at a temperature of 550 ° C. by, for example, low pressure chemical vapor deposition. As described above, the silicon layer formed by the low pressure chemical vapor deposition method has a hydrogen content of 1% or less in atomic ratio.

Next, as shown in FIG. 1B, the surface of the silicon layer 103 is irradiated with a laser beam 104. Since the laser beam is a XeCl excimer laser and has a wavelength of 308 nm, the absorption coefficient of 308 nm is as large as 10 ⁶ cm ^{−1 in the} amorphous silicon layer. Absorbed by the layer. The condition of the laser beam is that the half width is 50n.
and the energy density is 200 to 400 mJcm ^-2
And the geometric size of the beam irradiation surface is 1 on each side.
It is a square of 0 mm. The geometric size of this beam can be changed as needed.

Next, improvement of the energy distribution of the laser beam 104 will be described with reference to the drawings. FIG.
The energy distribution of the laser beam 202 emitted from the laser source 201 shown in FIG. 2 has a pseudo Gaussian distribution as shown in FIG. The laser beam 202 passes through an attenuator 203 and a special optical lens 204 such as a fly-eye lens. The attenuator 2
At 03, the energy of the laser beam is attenuated as required. With the special optical lens 204, the energy distribution of the laser beam is changed from the pseudo Gaussian distribution in FIG.
The energy density is improved to a pseudo trapezoidal energy distribution having a constant peak _EMAX as shown in FIG. Next, the laser beam whose energy distribution has been improved into a pseudo trapezoidal shape is passed through the convex lens 205. Next, the convex lens 20
The laser beam that has passed through 5 passes through the concave lens 206. Next, the beam size can be changed by changing the distance between the convex lens 205 and the concave lens 206. The laser beam that has passed through the concave lens 206 becomes a parallel light beam. The laser beam that has passed through the concave lens 206 is passed through a mask 207. The material of the substrate of the mask 207 is high quality quartz, and as shown in FIG. 4, the drawing portion 401 of the mask that blocks laser light is a refractory metal such as tungsten. Alternatively, a metal thin film having a large reflection coefficient for light having a wavelength of 308 nm may be used. By passing through the mask 207, the laser beam 2 having a rectangular energy distribution in which the edge of the beam is extremely steep and the energy density of the portion other than the edge is uniform as shown in FIG.
08 is obtained.

The atmosphere around the silicon layer 103 when the silicon layer 103 is subjected to beam annealing is a vacuum, an inert gas atmosphere, a nitrogen atmosphere, or an air atmosphere.

The intensity of the laser beam 104 is
By changing the distance between the attenuator 203, the convex lens 205, and the concave lens 206, it can be adjusted as appropriate.

As shown in FIG. 2, a substrate 209 on which the silicon layer 103 is formed is placed on a stage 210, and a driving system 211 installed perpendicularly or obliquely to the beam traveling direction is connected. The irradiation position of the pulse beam can be changed while the stage 210 is controlled by the computer 212 which controls the laser oscillation frequency of the laser source 201, the laser transmission timing, and the operation of the drive system.

When annealing the silicon layer 103 having an area larger than the geometric size of the laser beam 104, it is necessary to irradiate the surface of the silicon layer with a plurality of pulse beams of different irradiation positions.

FIG. 6 shows how the silicon layer is crystallized when the irradiation position is changed.

FIG. 6A shows an example of the special optical lens 204.
An example is shown in which the irradiation position of a laser beam that passes through the convex lens 205 and the concave lens 206 but does not pass through the mask 207 is changed and the silicon layer is annealed.
This laser beam has a trapezoidal energy distribution as shown in FIG. 3a.

FIG. 3B shows a state of the silicon layer when a pulse beam having the trapezoidal energy distribution is irradiated. As shown in Figure 3a, in the range the energy density E is O ≦ E ≦ E ₁ pulse lasers, the silicon layer 103
Does not change. When the energy density E of the pulse laser is in the range of E ₂ ≦ E ≦ E ₃ , the silicon layer 10
3 is a high-quality polycrystalline silicon layer 30 having a crystal having a large grain size.
Changes to 1. When the energy density E of the pulse laser is in the range of E ₁ ≦ E ≦ E ₂ , the silicon layer 103 changes to a silicon layer 302 having microcrystalline particles. Further, the energy density E of the pulse laser is E
_{In the case of 3} ≦ E, the energy density is too large, and the silicon layer changes to an amorphous silicon layer. Therefore, FIG. 3B shows a case where the maximum energy density E _MAX of the pulse laser is smaller than E ₃ . As shown in FIG. 3B, a polycrystalline silicon layer is formed in a central portion 301 of the irradiated portion,
In the peripheral portion 302, a silicon layer having microcrystalline particles is formed.

Next, as shown in FIG. 6A, the irradiation position is changed, and a second pulse beam irradiation is performed so as to form a portion 603 overlapping the first irradiation portion. Maximum energy E of the first pulse beam and the second pulse beam
_{If the MAX} energies are equal, region 601 and region 602
Are in the same crystalline state. As described above, in the case of an amorphous silicon layer having a low hydrogen content by a low pressure chemical vapor deposition method or the like, the laser beam 10
Crystals in the same state can be obtained irrespective of the number of times of irradiation of the pulse beam of No. 4. Therefore, the silicon layers in the region 601, the region 602, and the region 603 are in the same crystalline state. However, even when the silicon layer having the microcrystalline particles in the peripheral portion 302 is irradiated with the laser beam having the energy E in the range of E ₂ ≦ E ≦ E ₃ , the silicon layer having the microcrystalline particles remains unchanged. . In addition, the above E ₁ ≦
Even if a pulse laser having an energy in the range of E ≦ E ₂ is applied to the polycrystalline silicon layer in the central portion 301, no change is recognized. In FIG. 6A, the irradiation area where the energy of the first and second pulse beams is E ₁ ≦ E ≦ E ₂ is set to 604.
It was shown.

Therefore, when the silicon layer is annealed by changing the irradiation position of the pulse beam having the energy distribution shown in FIG. 3A, a region 606 of the silicon layer having fine crystal grains is formed as shown in FIG. 6B for the above-described reason. You.

That is, E ₁ ≦ E ≦ as shown in FIG.
When a pulse beam of an energy distribution or similar thereto trapezoidal shape having an energy of E ₂ by changing the irradiation position is irradiated a plurality of times in the silicon layer 103, the crystal state is uneven silicon layer is formed, thus forming The characteristics of the thin film transistor using the obtained non-uniform crystalline silicon layer as a material have a non-uniform distribution over the entire substrate.

FIG. 6B is a schematic diagram showing the distribution of the crystalline state of the silicon layer when irradiated as shown in FIG. 6A. A high-quality silicon layer region 605 having large-sized particles and a silicon layer 606 having microcrystalline particles are formed.

FIG. 7 shows the state of the silicon layer when the energy distribution of the laser beam is improved by the above method. The first irradiation with the pulse beam changes the silicon layer 103 into a polycrystalline silicon layer 701. Next, the irradiation position is changed, and a portion 70 overlapping with the first irradiation portion is obtained.
A second pulse beam irradiation is performed to form No. 3. If the first pulse beam and the second pulse beam have the same energy, the silicon layers 701 and 702 have the same crystal state.

As described above, in the case of an amorphous silicon layer having a low hydrogen content by a low pressure chemical vapor deposition method or the like, the same state is maintained regardless of the number of pulses of the laser beam 104. Crystals are obtained. Therefore, the crystal state of the region 703 shown in FIG. 7A is the same as that of the region 701 and the region 702. Further, as described above, since the crystal beam is not formed at the boundary 704 due to the laser beam having a rectangular energy distribution, there is substantially no boundary state between the region 701, the region 702, and the region 703. A crystalline silicon layer is formed. FIG. 7B is a schematic diagram showing the distribution of the crystalline state of the silicon layer when irradiated as shown in FIG. 7A. Only a high-quality silicon layer region 705 having large-sized particles is formed, and a silicon layer having microcrystalline particles is not formed. Therefore, a pulse beam having a rectangular energy distribution as shown in FIG. 5 and having an appropriate energy is applied to the silicon layer 10 of the entire substrate so that the irradiation positions are changed and the individual pulse beams form overlapping portions.
3 is annealed, as shown in FIG. 1c, a good quality silicon layer 1 having uniform large crystal grains over the entire substrate.
05 can be obtained. Thus, by irradiating the silicon layer 103 with the laser beam 208, ie, the laser beam 104, a uniform polycrystalline silicon layer 105 is obtained over the entire substrate,
A high-performance thin film transistor having high mobility and uniform characteristics over the entire substrate can be manufactured.

Although the above embodiment describes the crystallization of the silicon layer formed by the low pressure chemical vapor deposition method,
Even a silicon layer formed by PECVD has a 450
Since annealing at 60 ° C. in a nitrogen atmosphere for 60 minutes reduces the hydrogen content to 1% or less, the present invention can be applied to a silicon layer formed by PECVD. Of course, the present invention can be applied to a silicon layer formed by a sputtering method.

In the above embodiment, the crystallization of the silicon layer was described. However, the present invention is not limited to the above embodiment, and the present invention can be applied to a case where a thin film or a substrate is uniformly modified over a large area by a pulsed laser beam. Is applicable.

[0034]

As described above, according to the present invention, a silicon layer having an area larger than the geometrical shape of a laser beam can be uniformly crystallized. By irradiation, a high-quality silicon layer having a large crystal grain size can be uniformly formed. Therefore, a high-performance thin film transistor with high mobility can be formed on the entire surface of the substrate by laser annealing at room temperature over the entire surface of the substrate, so that an active matrix type flat display body with a built-in drive circuit is manufactured on a glass substrate instead of quartz. can do. As a result, the cost of the flat display body can be reduced to an inexpensive glass substrate instead of a quartz substrate that is effective for the substrate, so that the cost of the flat display body is reduced.

Further, since the quality of the silicon layer can be improved by a pulse excimer laser having a wavelength having a large absorption coefficient of the silicon layer, a three-dimensional semiconductor integrated circuit can also be formed.

[Brief description of the drawings]

FIG. 1 is a process chart of an embodiment for forming a silicon semiconductor layer of the present invention.

FIG. 2 is a diagram of an optical system of a method for improving the energy distribution of a pulsed laser beam into a rectangular shape according to the present invention.

FIG. 3 is a diagram showing an energy intensity distribution of a laser beam before the energy distribution is improved, and a change of a silicon layer with respect to the energy intensity.

FIG. 4 is a view of a mask for improving the energy intensity distribution of the pulse laser beam into a rectangular shape according to the present invention.

FIG. 5 is a diagram showing an energy intensity distribution of a pulsed laser beam improved according to the present invention.

FIG. 6 is a diagram showing a change in a silicon layer when a conventional pulse laser beam having an energy intensity distribution is irradiated a plurality of times.

FIG. 7 is a diagram illustrating a change in a silicon layer when a pulse laser beam improved according to the present invention is irradiated a plurality of times.

[Explanation of symbols]

 REFERENCE SIGNS LIST 101 transparent insulating substrate 102 silicon dioxide film 103 silicon layer 104 laser beam 105 polycrystalline silicon layer 201 laser source 202 laser beam before improvement 203 attenuator 204 special optical lens 205 convex lens 206 concave lens 207 mask 208 rectangular laser beam with energy distribution

Claims (4)

(57) [Claims] 1. A method of manufacturing a thin film transistor having a silicon layer on a substrate, wherein the step of forming the silicon layer on the substrate, the step of passing short-wavelength light through a convex lens, and thereafter the concave lens, Irradiating the silicon layer by irradiating the silicon layer while blocking a part of the parallel light beam by means, and irradiating the silicon layer with the laser beam a plurality of times so as to overlap each other. Method. 2. The method according to claim 1, wherein the laser beam is a pulse beam having a rectangular energy distribution. 3. The method according to claim 1, further comprising a step of changing a beam size by changing a distance between the convex lens and the concave lens. 4. A laser source, a convex lens receiving a short-wavelength light beam from the laser source, a concave lens receiving light emitted from the convex lens, and irradiating a silicon layer on a substrate with a part of the light emitted from the concave lens blocked. An apparatus for manufacturing a thin film transistor, comprising: