JP2001156006A - Plasma generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma generating method by which the occurrence of clusters can be suppressed. SOLUTION: Clustering of reaction molecules is suppressed in a device which generates a plasma, through introduction of the reaction molecules by using a frequency obtained by modulating the amplitude of high frequency (10-100 MHz) with a low frequency (1 kHz to 1 MHz) and pulse-oscillating the modulated frequency with the repetition frequency of an extremely low frequency (1-200 Hz).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a film forming method by a plasma CVD method. In particular, the present invention relates to a method for forming a film containing silicon (eg, silicon, silicon oxide, or silicon nitride) using a parallel plate type plasma CVD apparatus.

[0002]

2. Description of the Related Art In recent years, a vapor phase growth method (plasma CVD method) utilizing decomposition of gas by plasma has been used for manufacturing semiconductor devices such as semiconductor integrated circuits and thin film transistors. Generally, plasma CVD can form a film at a low temperature. In particular, in the manufacture of a thin film transistor, the thermal oxidation method or the vapor deposition method by thermal decomposition (thermal CVD method) used in the conventional single crystal silicon semiconductor process cannot be used due to the limitations of the substrate and the like, so that the film quality is excellent. It is strongly required to manufacture a silicon film, a silicon oxide film, a silicon nitride film, and the like by a plasma CVD method. In this case, the silicon oxide film as the gate insulating film includes
It is required that the film quality be dense and free of pinholes, and that the silicon film forming the semiconductor layer be free of impurities such as deposition dust in order to prevent deterioration of electrical characteristics.

Further, if film dust is mixed in the interlayer insulating film, wiring formed thereon may be disconnected, and reduction of the film dust is required. In a plasma CVD apparatus, in order to maintain in-plane uniformity of a film quality and a film formation rate of a film to be formed, it is necessary to make a plasma density uniform on a film formation surface such as a substrate. In order to generate such uniform plasma, a parallel plate type plasma CVD apparatus which usually uses parallel plate type electrodes is used. In this method, a pair of plate-like electrodes arranged in parallel in a chamber is provided, and by applying DC or AC power between the electrodes, capacitive coupling (capacitive resonance) is generated, and uniform plasma is generated between the electrodes. To be generated.

[0004]

In the conventional thermal CVD method, the decomposition of gas occurs at or near the substrate surface. Therefore, relatively large particles (clusters) only occupy a space, and it is rare that the particles become larger and larger and become film-forming dust, and a feature is that an extremely uniform film can be obtained. On the other hand, in a plasma CVD apparatus such as a parallel plate type plasma CVD apparatus, continuous discharge is performed by an AC power supply. Therefore, a reaction by plasma has already occurred in the deposition space before the reaction gas is adsorbed on the substrate, and cluster-like particles have begun to grow one after another. Then, the reaction proceeds further and the clusters are combined, and most of them become particles (film-forming dust).

The film-forming dust generated as described above is mixed in the film, or a semiconductor integrated circuit, a thin film transistor, and the like are formed by using a silicon film, a silicon oxide film, a silicon nitride film, and the like existing on the film surface. If made, as above,
This is a major cause of defects such as pinholes in the gate insulating film, deterioration of electrical characteristics of the semiconductor layer, and disconnection. Therefore, there has been a demand for a film forming method in which film forming dust is not generated as much as possible during film formation.

[0006]

According to the present invention, high frequency power is basically used as an alternating current to be applied to an electrode for generating plasma, the amplitude of which is modulated at a low frequency, and this is further reduced to an extremely low level. By supplying a pulse-modulated signal to the electrode at a repetition frequency of the frequency, generation of film-forming dust is suppressed. The extremely low frequency used here is a frequency of 1 to 200 Hz, preferably 20 to 10 Hz.
0Hz, low frequency, 1k-1MH
z, preferably 100 kHz to 500 kHz, high frequency 10 to 100 MHz, preferably 10 to 100 MHz
A 50 MHz one is used.

[0007] Of these frequencies, the lower frequencies contribute to disrupting the association of the reactive molecules (weak bonds between the molecules),
This is effective in improving the uniformity of the concentration difference between gas molecules in the chamber. High frequencies also contribute to breaking intermolecular bonds. Further, when pulse modulation is performed at an extremely low frequency, the uniformity of film formation is improved. When the pulse is on, it is dominant in the space where the plasma is generated, as in a normal plasma CVD film forming reaction. However, when the pulse is off, the film forming reaction is heated to the substrate. The portion is dominant, and therefore, abnormal growth of particles in the space of the chamber is suppressed, and as a result, deposition dust can be reduced.

The cycle of the pulse discharge is represented by d
Uty ratio is used. The duty ratio indicates (discharge time / (discharge time + pause time)). For example, in the case of a pulse discharge at a pulse frequency of 100 Hz and a duty ratio of 10%, a discharge of 1 msec and a discharge of 9 msec
And the repetition of the pause is repeated.

[0009] Since plasma is not generated by the pulse frequency when the discharge is stopped, the state of film formation is controlled by the duty ratio at this time.
That is, by optimizing the duty ratio, it is possible to control the reaction in the film formation space before the reaction gas is adsorbed on the substrate. This duty ratio is 10 to 70
% Is preferred. The optimal duty ratio depends on the type of reaction gas,
It may be determined according to the flow rate of the reaction gas or the distance between the electrodes.

FIG. 4 shows a high-frequency generator and high-frequency intensity used in the present invention. The present invention relates to a high-frequency power generator suitable for use in the present invention shown in FIG. 4, but it goes without saying that a similar high frequency can be generated by a device other than the configuration shown in FIG. FIG.
FIG. 4A shows a high frequency generator, and FIG. 4B shows the state of the high frequency in each stage. Sine high frequency generated by the high frequency oscillator 1 (for example, frequency 13.56 MHz)
Is a waveform like a in FIG. Such a high frequency is sent to an amplitude modulator (AM modulator) 4 at the next stage. As the amplitude modulator 4, a high-frequency amplifier whose amplification factor can be changed by an external signal may be used.

On the other hand, a low frequency oscillator 2 generates a sine low frequency (for example, 200 kHz), which is sent to an amplitude modulator 4. Then, the amplitude modulator 4 intensity-modulates a high frequency according to the low-frequency signal. The output waveform from the amplitude modulator 4 is as shown in FIG. The modulation rate in the above-mentioned modulation process was preferably 50% or more. However, it is necessary to suppress the generation of harmonics.
It is better to avoid overmodulation with a modulation rate of 00% or more. Further, a pulse of an extremely low frequency (for example, 50 Hz) is generated from the pulse oscillator 3, and the high frequency power is turned on / off in the pulse modulator 5. The high-frequency power generated in this manner has a mesh shape as shown in FIG. FIG. C 'shows an enlarged view of the on / off boundary portion of the pulse.

[0012]

[Embodiment 1] FIG. 1 schematically shows the present embodiment.
This embodiment is an example in which a silicon oxide film is formed by a parallel plate type plasma CVD apparatus according to the present invention. In FIG. 1, a vacuum vessel 101 (chamber) has a pair of electrodes facing each other. The pair of electrodes is an AC electrode 102
And the substrate electrode 103, and the gas introduction system 10
The reactive gas introduced from 4 is subjected to a plasma gas-phase reaction by an AC discharge between the pair of electrodes to form a film.

A substrate 105 on which a film is to be formed is held on a substrate holder 103 on a substrate electrode 103. In addition, gas is introduced from a gas introduction system 104 provided at the center of the substrate electrode 103. Then, the substrate electrode 103 is rotated by a rotation mechanism 106 provided on the substrate electrode 103 in order to measure the uniformity of the film. Also,
The substrate 105 includes a heater 1 provided below the substrate electrode.
07 can be heated. An exhaust system 108 is provided at the lower part of the outer periphery of the chamber so that the gas flows uniformly in the radial direction from the gas introduction system 104. The exhaust system 108 is provided with a vacuum pump.

The AC electrode used here is applied with pulse power of a very low frequency of a high frequency which is amplitude-modulated by a low frequency. A high-frequency power supply 109, a low-frequency power supply 110, and a very-low-frequency pulse power supply 111 are provided to generate alternating currents of these frequencies, and high-frequency power is modulated by amplitude modulators 112 and 113.

In this embodiment, the extremely low frequency is 50 Hz, the low frequency is 200 kHz, and the high frequency is 13.56 MHz. Here, the pulse of the extremely low frequency was performed so that the duty ratio became 50%.
Parallel plate type plasma CVD having the above configuration
Was used to form a silicon oxide film on the glass substrate 105. As a source gas, a SiH ₄ / O ₂ gas was used.

When a silicon oxide film is formed under the above conditions, the film forming speed is 200 ° / min. At the time when the silicon oxide film is deposited at 3000 °, 100 dust particles are formed on a 100 mm square substrate. Occurred to a degree. On the other hand, using the same film forming apparatus, for comparison, a pulse discharge of 50 Hz (duty ratio: 50%), a discharge of 200 kHz, and 13.
Only 56 MHz discharge was performed.

In this case, the film forming dust has a silicon oxide film of 3
At the time of deposition of 000 °, the number of substrates was 1,300, 1,000, and 1500 on a 100 mm square substrate, respectively. Further, in order to investigate the effect of the pulse discharge at a frequency of 50 Hz, a high frequency of 13.56 MHz was set to 200 k.
A high frequency power amplitude-modulated at a low frequency of Hz was applied to form a film.

Although the film forming speed was almost the same as 200 ° / min, the film forming dust generated was 3,000 °
At the time of deposition, on a 100 mm square substrate, 12
It was about 00 pieces. As described above, the film formation dust is effectively reduced by performing the film formation using the high-frequency power pulse-oscillated at the repetition frequency of the extremely low frequency, as in the present invention. It became clear what we could do. At that time, in order to prevent abnormal growth of dust in the plasma space, performing pulse discharge at a repetition frequency of 50 Hz was effective in reducing film deposition dust.

[Embodiment 2] FIG. 2 schematically shows the present embodiment. This embodiment is directed to a parallel plate type plasma CV according to the present invention.
This is an example in which a silicon nitride film is formed by a D apparatus. In FIG. 2, a pair of electrodes facing each other is provided in a chamber 201. The pair of electrodes is composed of an AC electrode 202 and a substrate electrode 203, and a reactive gas introduced from a gas introduction system 204 is subjected to plasma gas phase reaction by an AC discharge performed between the pair of electrodes to form a film. Is performed.

A substrate 205 on which a film is formed is held by a substrate holder on a substrate electrode 203. Further, the substrate electrode 203 is configured to be rotated by a rotation mechanism 206 provided on the substrate electrode 203 in order to make the film uniform. The substrate 205 can be heated by a heater 207 provided below the substrate electrode.

The gas is introduced from a gas introduction system 204 provided at the center of the AC electrode 202. In addition, a configuration is adopted in which gas is introduced from a gas introduction system 204 through a shower mesh 208 configured to cover the AC electrode 202 so that the gas is uniformly distributed to the substrate 205. The shower mesh 208 is made of an insulating material such as quartz. Further, an exhaust system 209 is provided at a lower part of the outer periphery of the chamber. The exhaust system 209 is provided with a vacuum pump.

The AC electrode used here is applied with pulse power of a very low frequency of a high frequency which is amplitude-modulated by a low frequency. A high-frequency power supply 210, a low-frequency power supply 211, and a very-low-frequency pulse power supply 212 are provided to generate alternating currents of these frequencies, and high-frequency power is modulated by amplitude modulators 213 and 214. In this embodiment, 100 Hz is used as the extremely low frequency, 300 kHz is used as the low frequency, and 13.56 MHz is used as the high frequency. The pulse discharge of the very long wave has a duty ratio of 20.
%.

A silicon nitride film was formed on the glass substrate 205 by using the parallel plate type plasma CVD having the above configuration. As a source gas, a SiH ₄ / NH ₃ gas was used. The silicon nitride film thus formed has a tendency substantially similar to the result of the amount of film forming dust in Example 1, and is compared with a silicon nitride film formed by a conventional parallel plate type plasma CVD apparatus. As a result, a silicon nitride film having little film formation dust by about one digit was obtained.

Embodiment 3 FIG. 3 shows a manufacturing process of this embodiment. In this embodiment, a thin film transistor (TFT) is manufactured by forming a silicon oxide film using the plasma CVD apparatus in the first embodiment. First, the substrate 301
(Corning 7059, 100 mm × 100 mm), an underlying silicon oxide film 302 was formed at 3000 ° by a plasma CVD method.

Then, an amorphous silicon film was formed at 500 ° by a plasma CVD method. As the film forming material gas,
A film was formed using silane (SH ₄ ) and hydrogen by the apparatus shown in FIG. At this time, the repetition frequency of the extremely low frequency pulse was 50 Hz, the low frequency was 200 kHz, and the high frequency was 13.56 MHz. In addition, film formation was performed with an extremely low frequency pulse so that the duty ratio was 50%. Thereafter, thermal annealing was performed to crystallize the amorphous silicon film. At this time, a small amount of nickel element or the like may be added to promote crystallization of the amorphous silicon film. Further, laser annealing may be performed to improve the crystallinity. (FIG. 3 (A))

Next, the crystallized silicon film 303 was patterned to form an island region 304. This island area 3
04 constitutes an active layer of the TFT. Then, as a gate insulating film 305, a silicon oxide film of 1000
It was formed by the VD method. The apparatus used is that shown in FIG. At this time, the repetition frequency of the extremely low frequency pulse was 50 Hz, the low frequency was 200 kHz, the high frequency was 13.56 MHz, and the film was formed so that the duty ratio was 50%. (FIG. 3 (B))

Thereafter, an aluminum (containing 1 wt% of Si or 0.1 to 0.3 wt% of Sc) film having a thickness of 1000 to 3 μm, for example, 5000 ° is formed by a sputtering method, and is patterned. A gate electrode 306 was formed. Next, the substrate was pH 7,
It was immersed in a 3% tartaric acid solution in ethylene glycol, and anodized using platinum as a cathode and the aluminum gate electrode as an anode. Anodization is initially performed at a constant current of 220
The voltage was increased to V, and the state was maintained for one hour to complete the operation. Thus, anodic oxide having a thickness of 1500 to 3500 °, for example, 2000 ° was formed.

Thereafter, the island is formed by ion doping.
The gate electrode 306 is used as a mask on the silicon
Impurities (phosphorus) were implanted in a self-aligned manner. Doping gas and
And phosphine (PH₃ ) Was used. In this case
Dose amount is 1 × 10¹⁴~ 5 × 10¹⁷cm^-2,acceleration
The voltage is 10 to 90 kV, for example, the dose amount is 2 × 10
^Fifteencm^-2And the accelerating voltage was 80 kV. As a result,
An N-type impurity region 307 was formed. (FIG. 3 (C))

Further, a KrF excimer laser (wavelength 2
Irradiation of 48 nm and a pulse width of 20 nsec) was performed to activate the doped impurity region 307. The energy density of the laser is 200-400 mJ / cm ²
And preferably 250 to 300 mJ / cm ² . This step may be performed by thermal annealing.

Next, as the interlayer insulating film 308, a silicon oxide film was formed to a thickness of 3000 ° by a plasma CVD method. Film formation was performed in the same manner as in Example 1. (FIG. 3
(D)) The interlayer insulating film 308 and the gate insulating film 30
5 was etched to form contact holes in the source / drain. Thereafter, an aluminum film was formed by a sputtering method, and was patterned to form a source / drain electrode 309, thereby manufacturing a TFT.
(FIG. 3 (E))

When a gate insulating film and an amorphous silicon film are formed by using the conventional plasma CVD, defects such as pinholes in the gate insulating film and deterioration of electrical characteristics of the semiconductor layer occur due to the influence of film forming dust. This has been a factor in lowering product yield. However, by forming a silicon oxide film using the plasma CVD apparatus according to the present invention,
Since the number of deposition dusts was reduced by about one digit as compared with the conventional plasma CVD apparatus, the yield was accordingly improved.

Embodiment 4 FIG. 5 shows an outline of this embodiment. In this embodiment, the distance between the electrodes is made wider than that of a normal parallel plate type plasma CVD apparatus, and the plasma space is made three-dimensional.
A set of CVD devices arranged at right angles to each other. FIG.
(A) is a cross-sectional view of the apparatus of the present embodiment as viewed from the lateral direction, and (B) is a cross-sectional view of the apparatus as viewed from above.

In FIG. 5, a chamber 401 has two pairs of electrodes facing each other, that is, a first pair of electrodes 402 and 403 and a second pair of electrodes 404 and 405. The first electrode pair and the second electrode pair are arranged so as to be substantially orthogonal. (FIG. 5B) High-frequency power is supplied to these electrodes, and the gas inlet 408 is provided.
The reactive gas to be introduced is subjected to plasma gas phase reaction in a space surrounded by the electrodes, and a film is formed on the substrate 407 on the substrate holder 406 disposed in the space. The unreacted gas is exhausted from the exhaust port 409.

In this embodiment, as in the first and second embodiments,
The pulse power of the very low frequency of the high frequency which was amplitude-modulated by the low frequency was used. The power supplies 410 and 411 for generating such high-frequency power are the same as those in the first and second embodiments. In this embodiment, both the power supplies 410 and 411 have the above-mentioned very low frequency of 50 Hz, the low frequency of 200 kHz,
13.56 MHz was used as the high frequency. The pulse discharge of the very long wave was performed so that the duty ratio became 20%.

However, the phases of the high frequencies were changed between the power supplies 410 and 411. The phase difference is, for example, 90 °, 1
80 ° and 270 °. Other values of the phase difference may be adopted. The phase difference changes the plasma state between the electrodes, and optimal film formation conditions can be obtained. A phase controller 415 is used to stabilize the phase difference between the electrode pairs. The phase controller supplies a signal to the high-frequency oscillator of each of the high-frequency power supplies 410 and 411 to control the oscillation. The phase difference set in the oscillator stage in this way is hardly affected even in the subsequent amplitude modulation stage, and is maintained at the same value as the initial stage. (FIG. 5 (A))

Conventionally, in a plasma CVD apparatus having such a large plasma space, film deposition dust is easily generated and its reduction has been a major problem. , Typically 1-2 orders of magnitude.

[0037]

According to the present invention, the generation of plasma using high-frequency power subjected to pulse modulation and low-frequency amplitude modulation is effective in reducing film formation dust. The amount of film forming dust in the plasma CVD apparatus according to the present invention could be reduced by about one digit as compared with the amount of film forming dust in the conventional plasma CVD apparatus.

As described above, the plasma CVD according to the present invention
It is effective to use a silicon film, a silicon oxide film, and a silicon nitride film in which film deposition dust is reduced by a device for manufacturing a semiconductor integrated circuit, a thin film transistor, and the like with a fine process. In particular, by using the silicon oxide film according to the present invention as an amorphous silicon film, a gate insulating film, and an interlayer insulating film which are semiconductor layers in a thin film transistor, electric characteristics and yield are improved, and It is effective for preventing disconnection of wiring. Thus, the present invention is an industrially useful invention.

[Brief description of the drawings]

FIG. 1 shows an apparatus configuration of a first embodiment.

FIG. 2 shows an apparatus configuration of a second embodiment.

FIG. 3 shows a process of Example 3.

FIG. 4 shows an example of a high-frequency generator of the present invention and a generated high-frequency waveform.

FIG. 5 shows an apparatus configuration of a fourth embodiment.

[Explanation of symbols]

 101: chamber 102: AC electrode 103: substrate electrode 104: gas introduction system 105: substrate 106: substrate electrode rotation mechanism 107: heater 108: exhaust system 109 ..High-frequency AC power supply 110 ... Low-frequency AC power supply 111 ... Ultra low frequency pulse power supply 112 ... Amplitude modulator 113 ... Pulse modulator

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasuhiko Takemura 398 Hase, Atsugi-shi, Kanagawa Inside Semiconductor Energy Laboratory Co., Ltd.

Claims (4)

[Claims] 1. A method for generating plasma using a high frequency, wherein the high frequency voltage is amplitude-modulated by a modulator using a low frequency at a modulation rate of less than 100%, and a modulator using an extremely low frequency pulse. A plasma generation method characterized by being turned on / off. 2. The extremely low frequency has a frequency of 1 to 200 Hz,
2. The method according to claim 1, wherein the low frequency signal has a frequency of 1 kHz to 1 MHz and the high frequency signal has a frequency of 10 MHz to 100 MHz. 3. The method according to claim 1, wherein the plasma is generated in a chamber. 4. A plasma having a duty ratio of 10 to 70.
%, And the plasma generation method according to claim 1. 5. The plasma generation method according to claim 1, wherein the method is used for manufacturing a semiconductor integrated circuit and a thin film transistor.