JPH05217908A - Forming method for film transistor - Google Patents

Abstract

PURPOSE:To form a film having small surface roughness and to improve flatness of a boundary between a silicon semiconductor film and a gate insulating film by generating a plasma of material gas for forming the film by applying high frequency power obtained by superposing a first pulse modulation and a second pulse modulation having a period shorter than that of the first pulse modulation. CONSTITUTION:A high frequency power source 7 has a high frequency signal generator 71 and a high frequency amplifier 72 for performing an arbitrary high frequency pulse modulation. It can apply high frequency power obtained by performing a high frequency of a predetermined frequency to be conducted by a desired first pulse modulation and a second pulse modulation having a period shorter than that of the first pulse modulation or high frequency power obtained by further performing it by a third pulse modulation having a period shorter than that of the second pulse modulation. Here, plasma is generated in gas by applying the high frequency power obtained by performing film forming gas by the first and second pulse modulations or further the third pulse modulation by the power source 7, and a film is formed on a substrate 9. Thus, flatness of a boundary of the film can be improved.

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 (SiNx or the like) 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 plasma CVs.
It is often formed by the D method. In this case, the raw material gas for forming the films is made 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 by such continuous discharge is 30Å to 50Å.
The degree and flatness are extremely poor, so that the flatness of the interface between the silicon semiconductor film and the gate insulating film in contact therewith becomes poor, and as a result, the electron mobility between the source and the drain becomes low (0.3 cm ² / V・ There was a problem that the performance of the final product transistor was not satisfactory.

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

[0005]

The inventor of the present invention, when the raw material gas is turned into plasma by the continuous discharge, facilitates the gas phase reaction, and the reactive species flow down from the position away from the substrate toward the substrate. Therefore, paying attention to the fact that the film formation surface roughness becomes large, further research is carried out, and if a pulse-modulated high frequency, in other words, a high frequency that repeats intermittent is applied, not only the conventional gas phase reaction but also the substrate It was found that a reaction (hereinafter referred to as "surface reaction") on the surface and / or at a position close to the surface also occurs, and this reduces the film surface roughness.

In this way, the second pulse modulation having a shorter period than the first pulse modulation is superimposed on the first pulse modulation, and the third pulse having a shorter period than the second pulse modulation. By superimposing the modulation, it becomes possible to control the electron temperature in the plasma that contributes to the necessary radical generation, while further advancing the surface reaction.
The present invention has been completed by finding that the film formation rate can be improved.

That is, according to the present invention, a silicon semiconductor film and a gate insulating film for a thin film transistor are formed by a plasma CVD method, and at the time of forming each film, plasma conversion of a raw material gas for forming the film is performed by first pulse modulation and The present invention provides a film forming method for a thin film transistor, which is characterized in that it is performed by applying a high frequency power on which a second pulse modulation having a shorter period than the first pulse modulation is applied.

Further, the present invention provides the method as described above, wherein the raw material gas is turned into plasma by the high frequency power further superposed with the third pulse modulation having a shorter period than the second pulse modulation. The condition of the first pulse modulation is not particularly limited, but from the viewpoint of improving the flatness of the interface between both films, for example, 1 KHz or less, and further 40
Conditions of 0 to 1000 Hz are conceivable.

The ON time t1 and the OFF time t2 of the high frequency input by the second pulse modulation are, for example, 0.5 μs.
ec ≦ t1 ≦ 100 μsec, 3 μsec ≦ t2 ≦ 10
0 μsec is conceivable. Furthermore, when superimposing the third pulse modulation, the high frequency input on-time t3 due to the modulation,
The off time t4 is, for example, 0.05 μsec ≦ t3 ≦
50 μsec, 0.05 μsec ≦ t4 ≦ 50 μsec
Can be considered.

[0010]

According to the method of the present invention, the silicon semiconductor film for the thin film transistor and the gate insulating film laminated thereon are
It is formed by the plasma CVD method sequentially and plasma-converting the source gas of each film by the application of the high-frequency power on which the first and second pulse modulations are superimposed or the third pulse modulation is further superimposed. ..

Since the generation and stop of plasma are repeated by the application of the pulse-modulated high-frequency power, in other words, the intermittent application of the high-frequency power as described above, the plasma is separated from the substrate or the film previously formed on the substrate. In addition to the gas-phase reaction in which reactive species are generated at different positions, when the plasma is stopped, the source gas reaches the surface of the substrate or the surface of the film previously formed on it and / or near it, and this is subsequently turned into plasma. As a result, the surface reaction in which the reactive species are generated on and / or near those surfaces also progresses, and as a result, a film having a low surface roughness is formed, and the silicon semiconductor film and the gate insulating film in contact therewith are formed. The flatness of the interface is good.

By superimposing the second pulse modulation or the third pulse modulation, it is possible to control the electron temperature in the plasma to a desirable state for radical generation required, thereby forming a film. Is improved.

[0013]

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.
The schematic structure of an example of D apparatus is shown. The device shown is
A vacuum chamber 1, a vacuum pump 2 connected to the chamber via a solenoid 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, and a heater 31 for adjusting the film forming temperature is attached to the ground electrode. The electrode 4 is a high frequency electrode, and a high frequency voltage is applied from a high frequency power supply 7 through a matching box 8 which is already known per se. The high-frequency power source 7 has a high-frequency signal generator 71 and a high-frequency amplifier (RF power amplifier) 72 capable of performing arbitrary high-frequency pulse modulation, and uses a desired first pulse modulation and first pulse modulation for a high frequency of a predetermined frequency. High frequency power with second pulse modulation with short period, or
It is configured so that the high frequency power subjected to the third pulse modulation having a shorter period than the second pulse modulation can be applied.

Turning on the high frequency input by the first pulse modulation,
The off state is as schematically shown in the upper part of FIG. 2, the high frequency input by the second pulse modulation is on and the off state is as schematically shown in the middle part of FIG. 2, the high frequency input is on by the third pulse modulation, The off state is as schematically shown in the lower part of FIG. According to the apparatus described above, the method of the present invention is carried out as follows.

It is conceivable that the former of the silicon semiconductor film and the gate insulating film is formed first or the latter is formed first. In any case, these films are sequentially formed. In forming the first film, first, the substrate 9 to be formed is placed on the electrode 3. Then, the chamber 1 is evacuated to a predetermined pressure by opening the electromagnetic valve 21 and operating the pump 2, and the first film-forming source gas is introduced from the film-forming gas source 5 into the chamber. The inside is maintained at a predetermined film forming vacuum degree. Further, the substrate 9 is controlled by the heater 31 to a predetermined film forming temperature. Then, the gas is first and second pulse-modulated by the power source 7, or the third pulse is further modulated.
A pulse-modulated high-frequency power is applied to turn the gas into plasma, and a film is formed 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.

Since pulse-modulated high-frequency power is applied to the source gas during the first film formation, not only the gas-phase reaction at a position away from the substrate but also at the substrate surface and / or a position close to it. Therefore, the film formation on the substrate is performed not only by pouring the reactive species from a position distant from the substrate surface but also by slowly supplying the reactive species by the surface reaction. It becomes flat. Further, since the next film formed on this film is also formed by supplying the reactive species by the gas phase reaction to the flat film surface and the fine reaction species by the surface reaction,
The flatness of the interface between the first film and the next film formed thereon becomes extremely good.

Therefore, no matter 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 becomes extremely good and the two adhere well. Therefore, in the final TFT transistor using such a film, the electron mobility between the source and the drain is higher than in the conventional case. Further, in the film formation, the second pulse modulation is superimposed or the third pulse modulation is further superimposed, whereby the electron temperature in the plasma is controlled to a desired state, and the film formation speed is improved.

By the method described above, an amorphous silicon (a-Si) semiconductor film and SiN were formed on a 100 mm square glass substrate (Corning 7059) under the following specific conditions.
When a laminated film of x gate insulating film was formed, the following results were obtained. Deposition degree of film formation: 100 to 600 mTorr (however, here 500 mTorr) High frequency power supply: 13.56 MHz, 1000 W Cycle of first pulse modulation: 400 Hz to 1000 Hz (here, 500 Hz) Second pulse modulation: ON time t10. 5 μsec OFF time t2 1.5 μsec Third pulse modulation: ON time t3 0.2 μsec OFF time t4 0.3 μsec Area of electrodes 3 and 700: 700 mm × 700 mm Glass substrate temperature: a-Si film formation 300 ° C. SiNx film formation 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: The values in parentheses below are for the conventional method without pulse modulation. result As can be seen from the above results, according to the method of the present invention, the surface roughness of film formation is reduced to about 1/4 or less as compared with the conventional method, and T
The electron mobility in FT has increased about 4 times.

It should be noted that the first and second pulse modulations are superimposed, the third pulse modulation is not superimposed, and other conditions are the same as those described above or appropriately changed to perform film formation. The roughness is much lower than before, and the a-Si film,
The flatness of the SiNx film interface is improved.

[0021]

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 therewith is improved, whereby electrons between the source and drain in the TFT are improved. It is possible to provide a film forming method for a thin film transistor by a plasma CVD method which can increase the mobility and also improve the film forming rate.

[Brief description of 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. 2 is a diagram schematically showing an ON / OFF state of a high frequency input by pulse modulation.

[Explanation of symbols]

 1 Vacuum Chamber 2 Vacuum Pump 21 Electromagnetic Valve 3 Grounding Electrode 31 Heater 4 High Frequency Electrode 5 Source Gas Source for Film Formation 61 Electromagnetic Valve 7 High Frequency Power Source 71 High Frequency Signal Generator 72 RF Power Amplifier 8 Matching Box

Claims (2)

[Claims] 1. A silicon semiconductor film and a gate insulating film for a thin film transistor are formed by a plasma CVD method, and in forming each of the films, plasma conversion of a raw material gas for forming the film is performed by first pulse modulation and the first pulse modulation. A method of forming a film for a thin film transistor, which is performed by applying a high frequency power on which a second pulse modulation having a shorter period than the pulse modulation is superimposed. 2. A silicon semiconductor film and a gate insulating film for a thin film transistor are formed by a plasma CVD method, and in forming each of the films, plasma conversion of a raw material gas for forming the film is performed by a first pulse modulation and a first pulse modulation. A method for forming a film for a thin film transistor, which comprises performing high frequency power application by superimposing a second pulse modulation having a short period by pulse modulation and a third pulse modulation having a shorter period than the second pulse modulation.