JP2581371B2 - Film forming method for thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film transistor (T
The present invention relates to a method of forming a silicon semiconductor film such as an amorphous silicon film or a polycrystalline silicon film in FT) and a gate insulating film (such as SiNx) laminated thereon by a plasma CVD method.

[0002]

2. Description of the Related Art A silicon semiconductor film in a thin film transistor and a gate insulating film laminated thereon are formed by plasma CV.
Often formed by the D method. In this case, the source gas for forming these films is turned into plasma by continuous discharge in which high-frequency power of a predetermined frequency is continuously applied.

[0003]

However, the surface roughness of a silicon semiconductor film or a gate insulating film obtained by plasma CVD using such a continuous discharge is 30 ° to 50 °.
The degree of flatness is extremely poor, so that the flatness of the interface between the silicon semiconductor film and the gate insulating film in contact with the silicon semiconductor film is deteriorated. As a result, the electron mobility between the source and the drain is reduced (0.3 cm ² / V). S or less), which causes a problem that the performance of the final product transistor is not satisfactory.

Therefore, the present invention provides a thin film transistor (TF)
A method for forming a film for a thin film transistor by a plasma CVD method capable of improving the flatness of an interface between a silicon semiconductor film for T) and a gate insulating film in contact therewith, thereby increasing electron mobility between a source and a drain in a TFT. The purpose is to provide.

[0005]

According to the present inventor, according to the present invention, when the raw material gas is converted into plasma by the continuous discharge, the gas phase reaction is promoted, and the reactive species pours from a position away from the substrate toward the substrate. Therefore, focusing on the fact that the surface roughness of the film becomes large, further research has been carried out, and when applying a high frequency subjected to pulse modulation, in other words, applying a high frequency that repeats intermittent, not only the conventional gas phase reaction but also the substrate The present inventors have found that a reaction at the surface and / or at a position close thereto (hereinafter, referred to as “surface reaction”) also occurs, thereby reducing the surface roughness of the film formed, and completed the present invention.

That is, according to the present invention, a silicon semiconductor film and a gate insulating film for a thin film transistor are formed on a substrate for a thin film transistor by a plasma CVD method, respectively .
In forming each of the films, the plasma of the raw material gas for forming the film is formed by dropping reactive species onto the substrate,
Supply of reactive species at and / or near the surface
A basic height of a predetermined frequency so that the films are formed
A method for forming a film for a thin film transistor (first method), characterized in that the method is performed by applying high frequency power in a state where pulsed modulation is applied to the high frequency power;
An amorphous silicon film is used as a recon semiconductor film.
A silicon nitride film as a gate insulating film and a plasma C
Formed on a substrate for a thin film transistor by the VD method,
In each film formation, a source gas for the film formation
From 100 mTorr to 600 mTorr
Under a vacuum degree of film formation within the range of
Pass high frequency power within the range of 400 Hz to 1000 Hz.
This is performed by applying high-frequency power with
A film forming method for a thin film transistor (second
Method) . The first method smell
It is, as a condition of the pulse modulation, from the viewpoint to improve the flatness of both film interface, also reduce the deposition rate
From the point of view, for example , 400 to 100 as in the second method.
A condition of 0 Hz is conceivable.

[0007]

According to the method of the present invention, a silicon semiconductor film for a thin film transistor and a gate insulating film laminated thereon are
It is formed by a plasma CVD method in which the source gas of each film is turned into plasma by applying a pulse-modulated high-frequency power. The application and application of pulsed high-frequency power, in other words, the intermittent application of high-frequency power repeatedly generates and stops the plasma, so that the reactive species is separated from the substrate or the film previously formed thereon. In addition to the generated gas phase reaction, when the plasma is stopped, the source gas reaches the substrate surface or the surface of the film previously formed thereon and / or close to the substrate surface, and then this is converted into plasma, whereby the reactive species are converted to the reactive species. A surface reaction generated on the surface and / or near the surface also proceeds, and as a result, a film with small surface roughness is formed, and the flatness of the interface between the silicon semiconductor film and the gate insulating film in contact with the silicon semiconductor film is good. Becomes

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a plasma CV used for carrying out the method of the present invention.
1 shows a schematic cross section of an example of a D device. The device shown is
A vacuum chamber 1, a vacuum pump 2 connected to the chamber via an electromagnetic valve 21, an electrode 3 installed in the chamber 1,
4. A film forming gas source 5 connected to the chamber 1 via an electromagnetic valve 61 is provided.

The electrode 3 is a ground electrode, which is provided with a heater 31 for adjusting the film forming temperature. The electrode 4 is a high-frequency electrode, to which a high-frequency voltage is applied from a high-frequency power source 7 via a matching box 8 which is already known. The high-frequency power supply 7 has a high-frequency signal generator 71 and a high-frequency amplifier (RF power amplifier) 72 that can perform arbitrary high-frequency pulse modulation.
(A) in FIG. 2) and a high-frequency power (see FIG. 2 (B) in FIG.

According to the apparatus described above, the method of the present invention is carried out as follows. It is conceivable that the former is formed first of the silicon semiconductor film and the gate insulating film, and the latter is formed first. In any case, these films are formed sequentially. In forming the first film, first, the substrate 9 to be formed is placed on the electrode 3. Thereafter, the opening of the solenoid valve 21 and the pump 2
In the operation described above, a vacuum is evacuated to a predetermined pressure, the first film forming material gas is introduced from the film forming gas source 5 into the chamber, and the inside of the chamber is maintained at a predetermined film forming vacuum. Further, the substrate 9 is controlled to a predetermined film forming temperature by the heater 31. Next, a high-frequency voltage pulse-modulated is applied to this gas by the power supply 7 to turn the gas into plasma, and form a film on the substrate 9. Similarly, the next source gas source is prepared, and the next film is formed using the gas. Thus, a stack of the silicon semiconductor film and the gate insulating film is formed.

During the first film formation, a pulse-modulated high-frequency power is applied to the source gas, so that not only a gas phase reaction at a position distant from the substrate but also a substrate surface and / or a position close thereto. Therefore, the film formation on the substrate is not only performed by pouring the reactive species from a position away from the substrate surface, but also by the gradual supply of the reactive species by the surface reaction. It becomes flat. Also, the next film formed on this film is formed by the supply of reactive species by gas phase reaction to the previous flat film surface and the supply of fine reactive species by surface reaction,
The flatness of the interface between the first film and the next film formed thereon is extremely good.

Therefore, regardless of which of the silicon semiconductor film and the gate insulating film is formed first and which is formed later, the interface flatness between the two is extremely good, and the two are in close contact with each other. Therefore, in the final TFT transistor using such a film, the electron mobility between the source and the drain becomes higher than that of the related art. According to the method described above, a 100 mm square glass substrate (Corning 70
59), a laminated film of an amorphous silicon (a-Si) semiconductor film and a SiNx gate insulating film was formed, and the following results were obtained.

Degree of vacuum for film formation: 100 to 600 mTorr (here, 500 mTorr) High frequency power supply: 13.56 MHz, 1000 W Pulse modulation: 500 Hz Area of electrodes 3 and 4: 700 mm × 700 mm Glass substrate temperature: when forming a-Si film When forming a SiNx film at 300 ° C. 350 ° C. Deposition gas: SiH ₄ 50 ccm H ₂ 150 ccm for a-Si film SiH ₄ 50 ccm NH ₃ 150 ccm N ₂ 50 ccm for SiNx film (Result) Note: In the following, pulse modulation A-Si SiNx film formation rate 200 300 (Å / min) (150) (250) Surface roughness 10 10 (Å) (30) (40) mobility ^{(0.3) (cm 2 / V} · s) as seen from the above results According to the present invention method, compared with the conventional method, the surface roughness of the film formation is greatly reduced, the electron mobility in the TFT is increased by about 3 times.

[0014]

As described above, according to the present invention, the flatness of the interface between the silicon semiconductor film for a thin film transistor (TFT) and the gate insulating film in contact with the silicon semiconductor film is improved. A film formation method for a thin film transistor by a plasma CVD method which can increase mobility can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a plasma CVD apparatus used for carrying out the method of the present invention.

FIG. 2A is a diagram schematically showing a conventional high frequency without pulse modulation, and FIG. 2B is a diagram schematically showing a high frequency according to the present invention with pulse modulation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Vacuum pump 21 Electromagnetic valve 3 Ground electrode 31 Heater 4 High frequency electrode 5 Source gas source for film formation 61 Electromagnetic valve 7 High frequency power supply 71 High frequency signal generator 72 RF power amplifier 8 Matching box

Claims (2)

(57) [Claims] 1. A thin by each plasma CVD silicon semiconductor film and the gate insulating film of the thin film transistor
Forming on a substrate for a film transistor, in forming each of the above-mentioned films, forming a plasma of a source gas for the film formation by pouring a reactive species onto the substrate,
The supply of reactive species at a position close to the
To form a pulse at
A method for forming a film for a thin film transistor, wherein the method is performed by applying high-frequency power in a state in which a modulation is applied . 2. A silicon semiconductor film for a thin film transistor.
Amorphous silicon film as gate insulating film
Each silicon nitride film is thinned by plasma CVD.
The respective films formed on a substrate for a film transistor
In the formation, plasma of source gas for the film formation
Within the range of 100 mTorr to 600 mTorr
Under a high vacuum power at a predetermined frequency
Pulse modulation within the range of 400 Hz to 1000 Hz
It is performed by applying high-frequency power in the
Film forming method for a thin film transistor.