JPH0284772A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a non-doped silicon thin film having an even crystalline orientation and a large crystal particle diameter and to make it possible to form a thin film transistor having superior characteristics and the like on an amorphous insulating substrate by a method wherein a silicon thin film is laminated on recrystallization silicon islands and the silicon thin film is crystal grown using the recrystallization silicon islands as seeds. CONSTITUTION:Impurity-doped silicon islands are formed on an amorphous insulating substrate 1-1 and the islands are crystal grown to form recrystallization silicon islands 1-4 and 1-5. Then, a silicon thin film 1-6 is laminated thereon and the film 1-6 is crystal grown using the islands 1-4 and 1-5 as seeds. After that, in the above recrystallization silicon thin film 1-7, two adjacent are used as a source region and a drain region and a semiconductor device is formed using the above silicon thin film 107 held between two adjacent recrystallization silicon islands 1-4 and 1-5 as a channel region. For example, a gate electrode 1-10 is formed on the above film 1-7 through a gate oxide film 1-9 and a thin film transistor is formed.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention involves forming a semiconductor thin film with excellent crystallinity on an amorphous insulating substrate such as a quartz substrate or a glass substrate, and applying the semiconductor thin film to an active region. The present invention relates to a method of manufacturing a semiconductor device having excellent characteristics that can be used for.

[Prior Art] A method for forming a polycrystalline silicon thin film or a single crystal silicon thin film with a large crystal grain size and uniform crystal orientation on an amorphous insulating substrate or an amorphous insulating film is 5OI (S
ilicon On In5ul ator
) technology is known. (S○ Tank Structure Formation Technology Industrial Book). Broadly classified, there are recrystallization methods, epitaxial methods, insulating layer embedding methods, and bonding methods. Recrystallization methods are classified into two types: a method in which silicon is melted and recrystallized by laser annealing or electron beam annealing, and a solid phase growth method in which silicon is grown in a solid phase without raising the temperature to a melting temperature. The solid phase growth method is superior in that it can be recrystallized at a relatively low temperature.

It has also been reported that crystal grains in silicon thin films grew despite low-temperature heat treatment at 550°C. (I
EEE Electron Device
L et ter s, vo 1.
EDL-8, No.

8. p361. August 1987)
.

It is known that a silicon thin film doped with impurities has a lower activation energy for crystal growth and a larger crystal grain size than a silicon thin film without doping.

[Problems to be Solved by the Present Invention] The solid phase growth method requires a single crystal silicon sheet that serves as a starting point for crystal growth. In the absence of the single-crystal silicon sheet, many crystal grains grow due to nuclei randomly existing in the silicon film, and each of the crystal grains does not grow large. Furthermore, since the growth of crystal grains is random, it is not known at all where the crystal grain boundaries exist in the obtained recrystallized silicon thin film. Furthermore, the crystal orientation is not aligned. Therefore, when a thin film semiconductor device such as a thin film transistor is manufactured using such a recrystallized silicon thin film, the variation in characteristics within the same substrate is large, making it impractical.

The impurity-doped silicon thin film is the undoped silicon 'f
Although it is known that the activation energy for crystal growth is lower and the crystal grain size is larger than that of an fI film, the impurity-doped silicon thin film cannot be used in the active region of a thin film transistor. The large crystal grain size of such impurity-doped silicon thin films has not been effectively utilized by conventional techniques.

The present invention solves the above-mentioned problems in the SOX method, particularly in the solid-phase growth method, and uses the large crystal grain size of the impurity-doped silicon thin film as a sheet to solid-phase grow an undoped silicon thin film, thereby changing the crystal orientation. The purpose of this method is to form an additive-free silicon thin film with large crystal grains of uniform size. The present invention also provides a method for manufacturing a thin film semiconductor device such as a thin film transistor with excellent characteristics on an amorphous insulating substrate such as a quartz substrate or a glass substrate.

[Means for Solving the Problems] A method for manufacturing a semiconductor device of the present invention includes a first step of forming an impurity-doped silicon island on an amorphous insulating substrate, and a step of forming the impurity-doped silicon island. a second step of growing crystals to form recrystallized silicon islands, a third step of laminating a silicon thin film on the recrystallized silicon islands, and crystallizing the silicon thin film using the recrystallized silicon islands as a sheet. a fourth step of growing, two adjacent recrystallized silicon thin films are used as a source region and a drain region, and the silicon thin film sandwiched between the two adjacent recrystallized silicon islands is used as a channel region. The method is characterized in that it includes at least a fifth step of forming a semiconductor device.

[Example] An example will be described by taking as an example a case where the present invention is applied to a thin film transistor as a semiconductor device. In FIG. 1(a), 1-1 is an amorphous insulating substrate. A quartz substrate, a glass substrate, or the like is used. Si covered with SiO2
A substrate may also be used. A silicon thin film doped with impurities is deposited on the amorphous insulating substrate, and then a silicon island 1- doped with impurities is formed by photolithography.
2 and 1-3. Appropriate film thickness is approximately several thousand to several μm. The pattern edges may also be tapered. Patterning can be done using a wet etching method using a hydrofluoric acid/nitric acid mixture or a dry etching method using Freon gas plasma, but the dry etching method is preferable because taper etching can be easily performed by simply changing the mixing ratio of Freon gas and oxygen gas. Are suitable.

The impurity-doped silicon islands 1-2 and 1-3 become the source and drain regions of the thin film transistor. The method for forming the impurity-doped silicon thin film is as follows:
1) A method of adding impurities during film formation. 2) A method of ion-implanting impurities after depositing an undoped silicon thin film. and so on. As the method 1), the vapor phase growth method is simple. For example, in the case of the LPCVD method, a doping gas such as phosphine gas (PH3), diporane gas (B2Ha), or arsine gas (A s H3) is flowed together with silane gas (SiH4) into a reaction tube and thermally decomposed.
Form a film. If the film formation temperature is set to a low temperature of about 500° C. to 600° C., the probability of nucleation will be small, and the subsequent solid phase growth will grow to a larger crystal grain size. Other effective methods include plasma CVD and photoexcitation CVD.

Methods of 2) include LPCVD method, APCVD method, photoexcitation CVD method, plasma CVD method, vacuum evaporation method,
After depositing an impurity-free silicon thin film by a method such as a sputtering method, impurities are added by a method such as an ion implantation method, a laser doping method, a plasma doping method, or the like. When a quartz substrate is used as the amorphous insulating substrate 1-1, a thermal diffusion method can be used. The impurity concentration is approximately 1×10 29 cm −1 to 1×10 29 cm −1 .

Next, the impurity-doped silicon islands 1-2 and 1-3 are grown in the same phase to form recrystallized silicon islands 1-4 and 1-5. In-phase growth is performed by heat treatment in a nitrogen gas, hydrogen gas, argon gas, or helium gas atmosphere. The heat treatment is performed for several hours to several tens of hours at a low temperature of 500° C. to 600° C., and for about one hour at a high temperature of 6′OO° C. or higher. If the temperature is 600°C or higher, 1-1 needs to be a quartz substrate. Also, slow solid phase growth at low temperatures results in larger crystal grain sizes. When the impurity-doped silicon islands are formed by plasma CVD, 300%
It is necessary to desorb the hydrogen in the film by heat treatment at a temperature of ~'450°C.After solid phase growth, the value of the sheet resistance ρ of the recrystallized silicon islands 1-4 and 1-5 is as follows: The resistance will be as low as several ohms/ro to several tens of ohms/ro.

Next, as shown in FIG. 1(e), an undoped silicon thin film 1-6 is laminated. Recrystallized silicon islands 1-4 and 1
It is important to clean the surface of -5, and it is effective to remove the oxide film with hydrogen plasma, argon plasma, etc. after chemical cleaning using acid or alkali. After cleaning the surfaces of the recrystallized silicon thin films 1-4 and 1-5 in this manner, a non-impurity silicon thin film 1-6 is laminated thereon. The impurity-free silicon thin film [1
-6 uses a material with a low density of crystal growth nuclei. Also, the thickness of the film will be reduced from several hundred to several thousand. In the case of the LPCVD method, conditions are suitable where the devoting temperature is as low as possible and the devoting speed is fast. When using silane gas (SiHa), the temperature is about 500°C to 560°C.
When using s), decomposition deposition is possible at a deposition temperature of about 300°C to 500°C. Trisilane gas (SisH
s) has a lower decomposition temperature. If the deposition temperature is raised, the deposited film becomes polycrystalline, so there is also a method of temporarily making it amorphous by S1 ion implantation. In the case of the plasma CVD method, film formation is possible even when the substrate temperature is 500° C. or lower. Further, if hydrogen plasma or argon plasma treatment is performed immediately before the deposition, cleaning of the substrate surface and film formation can be performed continuously. The photo-excited CVD method is also effective in that low-temperature deposition at 500"C or less and cleaning of the substrate surface and film formation can be performed continuously. In the case of high-vacuum deposition methods such as the EB deposition method, etc. Since the film is porous, oxygen from the atmosphere is easily absorbed into the film, which hinders crystal growth.To prevent this, 30,0%
It is necessary to densify the film by performing low-temperature heat treatment at a temperature of about 500°C to 500°C. The sputtering method is similar to the high vacuum evaporation method.

Subsequently, the undoped silicon thin film 1-6 is grown in a solid phase to form a recrystallized undoped silicon thin film 1-7 (hereinafter abbreviated as i-silicon thin film) as shown in FIG. 1(d). As a solid phase growth method, furnace annealing using a quartz tube is convenient. As the annealing atmosphere, nitrogen gas, hydrogen gas, argon gas, helium gas, etc. are used. lXl0-'
The annealing may be performed in a high vacuum atmosphere of 1×10-”T or r.The solid phase growth annealing temperature is 500°
C to 700°C. In such low-temperature annealing, only crystal grains having a crystal orientation with a small activation energy for crystal growth grow selectively, and moreover, they grow slowly and to a large size. The solid phase growth of the i-silicon thin film 1-7 is performed by growing the recrystallized silicon thin films 1-4 and 1-5 and the i-silicon thin film 1-7.
It starts from the contact surface with the silicon thin film 1-7 and progresses radially around this part. Then, at the midpoint between the recrystallized silicon thin films 1-4 and 1-5, the crystal grains grown from both directions collide, forming a crystal grain boundary 1-8. Next, the i-silicon thin film 1-7 is patterned by photolithography as shown in FIG. 1(e). Etching is performed using a method such as plasma etching using Freon gas.

Next, as shown in FIG. 1(f), a gate oxide film 1-9 is formed. The gate oxide film can be formed by LPCVD, photo-excited CVD, plasma CVD, ECR plasma CVD, high vacuum evaporation, plasma oxidation, or high pressure oxidation at temperatures below 500°C. There is a low temperature method. The gate oxide film formed by the low-temperature method becomes an excellent film that is denser and has fewer interface states by heat treatment.

When using a quartz substrate as the amorphous insulating substrate 1-1,
A thermal oxidation method can be used. The thermal oxidation method includes a dry oxidation method and a wet oxidation method, and the oxidation temperature is 1000°C.
The dry oxidation method is more suitable because the film quality is excellent, although it is expensive.

Next, as shown in FIG. 1(g), the gate electrode 1-1
form 0. The gate electrode material may be polycrystalline silicon thin film, molybdenum silicide, metal film such as aluminum or chromium, or IT.
A transparent conductive film such as O or SnO2 can be used.

As a film forming method, there are methods such as CVD method, sputtering method, vacuum evaporation method, etc., but detailed description thereof will be omitted here.

The gate electrode must be formed to vertically overlap the recrystallized silicon islands 1-4 and 1-5.

Next, as shown in FIG. 1(h), the glabella insulating film 1-
11. Laminate. As the material for the glabellar insulating film, an oxide film, a nitride film, or the like is used. The film thickness may be any thickness as long as the insulation is good, but it is usually from several thousand to several micrometers. A simple method for forming the nitride film is the LPCVD method or the plasma CVD method. For the reaction, a mixed gas of ammonia gas (NH3), silane gas, and nitrogen gas, or a mixed gas of silane gas and nitrogen gas, etc. is used.

Here, hydrogen plasma method or hydrogen ion implantation method,
Alternatively, if hydrogen ions are introduced into the i-silicon thin film 1-7 by a method such as hydrogen diffusion from a plasma nitride film,
Defects such as dangling bonds existing at grain boundaries are inactivated. Such a hydrogenation process is performed for the glabella insulating film 1-
It may be performed before laminating 11.

Next, as shown in FIG. 1(i), contact holes are formed in the interlayer insulating film and the gate insulating film, and contact electrodes are formed to make contact with the recrystallized silicon islands 1-4 and 1-5. A source electrode 1-12 and a drain electrode 1-13 are formed. The source electrode and drain electrode are
Made of metal material such as aluminum. In this way, a thin film transistor is formed.

[Effects of the Invention] Conventionally, it was unknown how many crystal grain boundaries existed in the channel region of a thin film transistor. It was not possible to know where the grain boundaries were located or how large the grains were. However, according to the present invention,
A large grain size can be obtained, and furthermore, the location of grain boundaries in the channel region of a thin film transistor can be controlled.

The location of the grain boundary is also exactly at the midpoint of the channel region. Therefore, the ON current of the thin film transistor increases and the OFF current decreases compared to the conventional thin film transistor. In addition, the threshold voltage is also reduced, and transistor characteristics are greatly improved. Variations in transistor characteristics are extremely small.

Since it has become possible to produce a silicon thin film with excellent crystallinity in which the location of crystal grain boundaries is controlled on an amorphous insulating substrate, this will greatly contribute to the development of SOI technology. Since a silicon thin film doped with large crystal grains is used as a sheet and an undoped silicon thin film is grown in a solid phase, a non-impurity silicon thin film having a larger crystal grain size than before is formed. Since it can be manufactured using a low-temperature process of 600° C. or lower, it is possible to use a glass substrate that is inexpensive and has a low heat-resistant temperature. Since expensive and large-scale equipment is not required, the cost does not increase even though an excellent silicon thin film can be obtained.

Since it is possible to fabricate thin film transistors with excellent characteristics on an amorphous insulating substrate, sufficient high-speed operation can be achieved even when applied to an active matrix substrate in which a driver circuit is integrated on the same substrate. Furthermore, it has great effects on reducing power supply voltage, reducing current consumption, and improving reliability.

In addition, since it is possible to manufacture by a low-temperature process at 600° C. or less, this is highly effective in reducing the cost and increasing the area of the active matrix substrate.

When the present invention is applied to a contact image sensor in which a photoelectric conversion element and its scanning circuit are integrated on the same chip, it is possible to increase the reading speed, increase the resolution, and increase the gradation. produce an effect. Once high resolution is achieved, it will be easier to apply it to a contact type image sensor for color reading. Of course, this has great effects in reducing power supply voltage, reducing current consumption, and improving reliability.

Also, since it can be produced by a low-temperature process,
Close-contact image sensor chip can be made longer,
- A reading device for large-sized facsimiles such as A4 or A3 size can be realized using a book chip. Therefore, it is possible to avoid the troublesome and unreliable technique of joining two sensor chips, and the mounting yield is also improved.

In addition to quartz and glass substrates, sapphire substrates (
A1203) A6 't'&t M g O-A 1
Crystalline insulating substrates such as 203+13P and CaF2 can also be used.

Although the description has been given above using a thin film transistor as an example, the present invention can also be applied to elements using thin films such as bipolar transistors or heterojunction bipolar transistors. In addition, So
The present invention can also be applied to elements using engineering technology.

[Brief explanation of drawings]

FIGS. 1(a) to 1(i) are process diagrams showing a method for manufacturing a thin film semiconductor device according to the present invention. 1-1; Amorphous insulating substrate 1-4. 1-5 S Recrystallized silicon island (impurity-doped silicon island) 1-7 : Recrystallized non-doped silicon thin film (i-silicon thin film) 1-8 ; Grain boundary 1-9 ; Gate oxide film (a) ( b) Applicant: Seiko Epson Co., Ltd. Representative Patent Attorney Masayoshi Kamikushi (and 1 other person) Figure 1 (d) (e) (g) (h)

Claims (1)

[Claims] a first step of forming an impurity-doped silicon island on an amorphous insulating substrate; a second step of crystal-growing the impurity-doped silicon island to form a recrystallized silicon island; a third step of laminating a silicon thin film on the recrystallized silicon island; a fourth step of crystal-growing the silicon thin film using the recrystallized silicon island as a sheet; A semiconductor device comprising at least a fifth step of forming a semiconductor device by using the silicon thin film sandwiched between the two adjacent recrystallized silicon islands as a channel region, with the silicon thin film sandwiched between the two adjacent recrystallized silicon islands serving as a source region and a drain region. manufacturing method.