JP3116403B2 - Method 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 method for manufacturing a polycrystalline silicon thin film applicable to a semiconductor device such as a thin film transistor, and more particularly to a method for manufacturing a polycrystalline silicon thin film which can be formed on a substrate such as a low melting point glass at a low temperature.

[0002]

2. Description of the Related Art Attempts to fabricate a high-performance thin film transistor (TFT) using microcrystalline or polycrystalline Si (poly-Si) as an element material on a low-melting glass substrate have been activated. In particular, a low-melting glass substrate such as a Corning 7059 substrate is used as the substrate, and the maximum process temperature is 450
It is expected that a process for producing a TFT having a high mobility and a high ON / OFF ratio at a temperature of about ° C or less will be put to practical use.

Conventionally, a method for thermally decomposing monosilane gas at a substrate temperature of about 600 ° C. using a low pressure CVD method has been known for forming poly-Si on a glass substrate. A conventional method of producing a high-performance poly-Si TFT includes a method of forming a poly-Si in which amorphous Si (a-Si) is increased in particle size by a solid phase growth method to produce a TFT, and a method of producing a TFT. There has been a method of producing a TFT by melting and recrystallizing -Si or poly-Si by laser annealing.

[0004]

SUMMARY OF THE INVENTION In a low pressure CVD method, pol
In a method of forming a y-Si film, a low-melting glass cannot be used for a substrate due to a demand for a film forming temperature. In order to obtain poly-Si having a large particle size by the solid phase growth method, 6
Annealing must be performed at a temperature of about 00 ° C. for a long time of 4 to 70 hours, and a low melting point glass cannot be used for a substrate. Laser annealing has problems such as variations in device characteristics due to non-uniform characteristics of a laser beam and low throughput.

For this reason, JP-A-63-175417, JP-A-2-177368, JP-A-2-202018, and Mate
rials Research Society Simposia Proceedings, Volu
As shown in me95, p.225 (1987) and the like, a mixed gas of a silane gas and an etching gas such as fluorine or fluorosilane is decomposed by glow discharge decomposition by plasma enhanced chemical vapor deposition (PCVD), so that it can be produced at a low temperature. Attention has been focused on methods that can produce crystalline silicon.

The poly-S obtained by these film forming methods
Since the i-thin film contains a halogen gas such as fluorine gas and a halide such as fluorosilane and dichlorosilane as an etching gas, the obtained poly-Si contains halogen atoms such as fluorine and chlorine as impurities. pol
When manufacturing a y-Si TFT, these impurities cause crystal defects and cause an increase in the leak current of the TFT, which is a serious problem.

In the method of manufacturing a polycrystalline silicon thin film disclosed in Japanese Patent Application Laid-Open No. 2-248038, since hydrogen is used as an etching gas, the problem of impurity contamination described above does not occur. However, since the activation state of hydrogen is controlled by providing an activation chamber separate from the reaction gas, there is a problem that the apparatus becomes complicated. In addition to the above problems, the method of manufacturing a semiconductor thin film disclosed in Japanese Patent Publication No. 3-8102 states that the obtained thin film is a mixed state of amorphous silicon and polycrystalline silicon, and is not suitable for application to a TFT. There were also problems.

An object of the present invention is to provide a method capable of forming high-quality poly-Si containing no impurities such as halogen gas at a low temperature with a simple apparatus. It is in.

[0009]

According to the present invention, there is provided a method of manufacturing a thin film transistor having a polycrystalline silicon thin film on a substrate, wherein the polycrystalline silicon thin film has a hydrogen gas flow ratio to silane gas of 1.0 to 5.0%. The distance between electrodes for generating plasma is 45 mm using a gas of
Hereinafter, it is characterized by being formed by plasma enhanced chemical vapor deposition at a high frequency power of 0.01 to 5.0 W / cm ² and a reaction chamber pressure of 0.1 to 10.0 Torr.

[0010]

The production method of the present invention will be described below in detail.
The substrate to be used may be a low melting point glass, a ceramic substrate, or a quartz substrate as long as it is a substrate other than single crystal Si. When single-crystal Si is used for the substrate, an epitaxial Si film can be obtained instead of poly-Si. In this embodiment, a Corning 7059 substrate was used. As the PCVD apparatus, a PED-302 type manufactured by Anelva having parallel plate type electrodes was used. FIG. 1 shows a schematic diagram of a PCVD apparatus used in the present invention. 1 is a reaction chamber, 2 is an exhaust pipe, 3 is a counter electrode, 4 is a gas outlet, 5 is a gas inlet, 6 is a high frequency application electrode, 7
Is a substrate heater, 8 is a substrate, and 9 is a high frequency power supply.
W in FIG. 1 represents the distance between the electrodes. The deposition gas is Si
A mixed gas of H ₄ , Si ₂ H ₆ , Si ₃ H _8, etc. and H ₂ is used. In this embodiment, a mixed gas of silane (SiH ₄ ) and H ₂ was used.

The basic reaction mechanism complies with the following equation 1.
In the reaction of Formula 1, R1 is a film forming reaction and R2 is an etching reaction.

[0012]

Embedded image (N is a dimensionless number) In the formula 1, the reaction of R2 becomes dominant as the hydrogen concentration is increased, so that the Si—H bond having weak binding energy is selectively cut off by the etching reaction of R2. For this reason, only the Si-Si bond remains, and under such conditions, poly-S
i is deposited. On the other hand, when the silane gas concentration increases, Equation 1
, The film formation reaction of R1 becomes dominant, and amorphous silicon (a-Si) having a high hydrogen concentration is formed on the substrate. Such a competitive relationship between R1 and R2 can be easily adjusted by changing the ratio of the silane gas concentration to the hydrogen gas concentration.

Therefore, in order to form a poly-Si thin film, it is necessary to dilute the silane gas with a large flow rate of hydrogen gas so that the silane concentration / hydrogen concentration ratio is at least 0.1 or less. When actually forming a poly-Si film, the silane / hydrogen gas concentration ratio is SiH ₄ / H ₂ = 0.
5 to 5.0%, particularly preferably 1.0 to 3.0%. 0.5%
If the diameter is smaller, the etching reaction by the hydrogen gas becomes too dominant, the deposition rate becomes extremely small, and only poly-Si having a small particle diameter is formed. If it exceeds 5.0%, the film forming reaction becomes dominant, and only a-Si is formed.

The pressure in the reaction chamber is 0.1 to 10.0 Torr.
In particular, 0.3 to 1.5 Torr is preferable. The high frequency power for generating plasma has a power density of 0.01 to 5.0 W /
cm ² , preferably 0.03 to 0.06 W / cm ² .
If it is less than 0.01 W / cm ² , the etching reaction becomes too weak, and if it exceeds 5 W / cm ² , the thin film is damaged by plasma and a high quality film cannot be formed. Substrate temperature is 1
00-600 ° C. Preferably 200 ° C to 400 ° C
And When the substrate temperature is lower than 100 ° C., a-Si film is formed, and when the substrate temperature is higher than 600 ° C., the advantage of low temperature film forming PCVD cannot be utilized.

An important condition for forming a poly-Si film is a distance between opposed electrodes (hereinafter, distance between electrodes; W in FIG. 1) of a parallel plate type PCVD apparatus. In order for the etching reaction to proceed, the distance between the electrodes must be sufficiently short and hydrogen must reach the substrate in an active state. If the distance between the electrodes is long, the etching reaction occurs in the gas phase, and amorphous silicon is formed on the substrate. Therefore, the distance W between the electrodes is defined by the high-frequency power and the pressure. When the high frequency power is 0.03 W / cm ² and the pressure is 1.2 Torr,
The distance W between the electrodes must be less than 45 mm, preferably 27 mm or less, and more preferably 20 mm or less. Before the film formation, a mixed gas of SiH ₄ : H ₂ = 1.8: 98.2 was introduced into the reaction chamber evacuated to 1 × 10 ⁻⁶ Torr or less at a total flow rate of 20: 1.
It was supplied at 0 SCCM, and the internal pressure was adjusted to the pressure shown in Table 1. After setting the substrate temperature to the temperature shown in Table 1, a film forming gas was flowed for about 20 minutes until the substrate temperature was stabilized. Then, using a 13.56 MHz high frequency power supply, discharge power of 0.0
Discharging was performed at 3 W / cm ² for 120 minutes to grow a silicon thin film on a glass substrate. The growth rate was 9-22 ° / min. The average particle size of the obtained poly-Si was measured by X-ray diffraction.

Table 1 shows various characteristics of poly-Si produced by the production method of the present invention. As is clear from Table 1, poly-Si having a crystal grain size of about 1000 ° is formed even with a relatively thin film thickness of 1000 °. The crystal orientation was (111) for all films shown in Table 1,
The X-ray diffraction peak of the (220) direction is observed. In particular, in the films of No. 3 and No. 4, a poly-Si thin film in which the (220) direction is the preferred orientation is obtained. When a halogen-based gas is used as the etching gas, the film thickness is 2,500.
Å It is known that polycrystallization starts from the above, and it was difficult to make a thin film. However, according to the manufacturing method of the present invention, pol
Since the thickness of y-Si can be reduced, the effect is large when TFT is applied.

[0017]

[Table 1]

Table 2 shows a comparative example in which the distance between the electrodes was 45 m.
When m is set, various characteristics of the Si thin film formed in the same manner as in Table 1 are shown. As is clear from Table 2, poly-Si was not obtained under the conditions shown in the comparative example, and a-Si was formed.

[0019]

[Table 2]

In the present invention, a p-type or n-type poly-Si film can be formed by mixing a doping gas of Group III or Group V of the periodic table into the film forming gas. Examples of the doping gas include diborane, phosphine, arsine, and the like.

As described above, according to the present invention, high quality poly-Si can be formed at a low temperature of about 200 ° C. For this reason, a glass substrate having a low melting point can be used as the substrate glass, and a low-cost glass substrate can be used, which has a great effect on reducing the cost of devices such as a liquid crystal display, an adhesive image sensor, and a solar cell. . In addition, the required device may be a normal plasma CVD device, and no additional device for activating hydrogen gas is required.

Further, since the present invention does not use any halogen-based gas, there is a great advantage that impurity elements such as fluorine which adversely affect the characteristics of the TFT are not mixed into the poly-Si film.

Further, the poly-Si thin film obtained by the LPCVD method, the solid phase growth method, the laser annealing method, etc. has a problem that the electrical characteristics are deteriorated due to dangling bonds at the crystal grain boundaries. In order to solve the above problem, it is necessary to passivate dangling bonds by means of hydrogen plasma or the like after forming the poly-Si film. However, the method of the present invention has an advantage in that it is not necessary to perform hydrogen passivation later because the poly-Si film is exposed to hydrogen plasma during film formation.

Furthermore, the poly-Si thin film obtained by the LPCVD method, the solid phase growth method, the laser annealing method or the like has a preferred orientation of {111}, whereas the poly-Si thin film obtained by the method of the present invention is The preferred orientation is {110}. It is known that the electron mobility in the in-plane direction (horizontal direction) of the poly-Si thin film is larger in poly-Si of {110} coordination than in {111} coordination.
Therefore, the use of poly-Si obtained by the method of the present invention also has a great advantage that a high-performance TFT having high electron mobility can be easily produced. The present invention also provides a TFT for a load element of a highly integrated SRAM of 4 Mbits or more.
The present invention is also very effective for application to semiconductor devices such as ICs, LSIs, and three-dimensional SOI devices.

As described above, according to the present invention, a high-quality polycrystalline silicon film can be formed by setting the distance between the electrodes for glow discharge to less than 45 mm.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a PCVD apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction chamber 2 ... Exhaust pipe 3 ... Counter electrode 4 ... Gas blowing hole 5 ... Gas introduction part 6 ... High frequency application electrode 7 ... Substrate heater 8 ... Substrate 9 High frequency power supply

Continuation of the front page (56) References JP-A-3-250624 (JP, A) JP-A-63-223180 (JP, A) JP-A-63-197329 (JP, A) JP-A-60-204880 (JP, A) JP-A-64-10617 (JP, A) JP-A-3-219622 (JP, A) JP-A-4-211115 (JP, A) JP-A-4-318973 (JP, A) 4-318974 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205 H01L 21/31 C23C 16/00 H01L 21/336 H01L 29/786 H01L 31/04

Claims (1)

(57) [Claims] 1. A method for manufacturing a thin film transistor having a polycrystalline silicon thin film on a substrate, wherein the polycrystalline silicon thin film has a hydrogen gas flow ratio to silane gas of 1.
Using a gas of 0 to 5.0%, a distance between electrodes for generating plasma is set to 45 mm or less, and a high frequency power is set to 0 to 5.0%.
01-5.0 W / cm ² , the pressure in the reaction chamber is 0.1-1
A method for manufacturing a thin film transistor, wherein the thin film transistor is formed at 0.0 Torr by a plasma enhanced chemical vapor deposition method.