JP3286951B2 - Plasma CVD film forming method and apparatus - 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 plasma CVD film forming method and apparatus used for film formation of FT), solar cells, various sensors, and the like.

[0002]

2. Description of the Related Art Conventionally, as a plasma CVD apparatus of this type, for example, as shown in FIG.
Is provided with two or more electrodes d and e in a vacuum chamber c connected thereto, and one of the electrodes d is supplied with high-frequency power from a high-frequency power source f via a matching circuit i. A device that mounts a substrate g on the electrode e and heats the substrate g from the back thereof with a heater h is used, and SiH ₄ , NH ₃ , and the like are introduced into the vacuum chamber c via the gas introduction system a.
When a reaction gas such as N ₂ O is introduced and the pressure reaches a certain pressure, high-frequency power is supplied from a high-frequency power source f to the electrode d to generate a plasma between the electrodes d and e, and the reaction gas is generated by the plasma. And a film is formed on the substrate g heated by the heater h. The high-frequency power source f used for this purpose is usually a 13.56 MHz power source, and generates continuous discharge plasma. As shown in FIG. 1, another vacuum chamber j is connected to the vacuum chamber c via a valve k, and a substrate g is placed on an electrode d of a tray so that a space between the vacuum chambers c and j is provided. Conveyed. One electrode d is provided with a shower plate m having a hollow inside and a gas ejection port l formed on the surface, and a gas introduction system a is connected to the hollow portion to uniformly react gas toward the opposing substrate g. Squirts. n is an adhesion-preventing plate, and O is a reflector.

[0003]

When a film is formed on a large number of substrates g by the plasma CVD film forming apparatus as described above, the electrode e, the shower plate m, the reflector n, etc. of the tray other than the substrate g are formed. Film and powder accumulate,
These unnecessary films and the like may be mixed as impurities into the film of the substrate g, and thus need to be removed. Conventionally, the vacuum chamber c is opened to the atmosphere to replace parts and the like, and the film attached to the removed parts and the like is subjected to a GBB (glass blast method).
However, cleaning with plasma has recently been demanded due to poor workability and reduced operation efficiency of the apparatus. This cleaning method
This is a method in which an etching gas such as NF ₃ or CHF ₃ is introduced into a vacuum chamber instead of a reaction gas to generate plasma, and an unnecessary film or powder is removed by etching.

However, in the conventional plasma CVD film forming apparatus, in order to obtain a high quality a-Si: H film, the film is formed under a condition of the reaction law with a sufficiently high flow of SiH ₄ gas and a low high frequency power. Needed. When the input power is increased in order to increase the deposition rate, the amount of powder generated during the deposition increases sharply, resulting in a decrease in film quality and an increase in defects. The upper limit of the film forming speed was 100 angstroms / min. The phenomenon that the amount of generated powder increases with an increase in input power is caused by the poly-Si
Film, Ge film, carbon film, p-type or n-type a-Si film, S
This is also seen when forming an iCx film.

For example, during the formation of an a-Si: H film,
The H ₄ gas is decomposed to form SiH ₃ *, SiH ₃ ⁻ , SiH ₂ *, S
It is known that various radicals and ions are generated, such as iH ₂ ⁻ and SiH ₂ ^−, of which radicals of SiH ₃ * contribute to film formation. Although the amount of SiH ₂ ions generated at this time is small, according to a recent report, since the radius of the SiH ₂ ions is large and charged, a gas phase reaction occurs to generate Si ₂ Hxn −, and once, Since the generated Si ₂ Hxn− has a large radius, it causes a gas phase reaction at an accelerated rate, and
This means that large clusters of inHm are formed and eventually they are recognized as powder. Also,
It has been reported that the growth rate of the particle size of the generated powder takes one second or more until the particle size is saturated.

From the above known techniques, it can be inferred that the generation of powder can be reduced by stopping the discharge before the particle diameter grows. For that purpose, it is possible to modulate the high frequency power by pulse modulation. However, when the discharge is stopped during the pulse modulation, the film formation is also stopped, so that there is a disadvantage that the film formation speed is reduced. In addition, generation of a small amount of powder is observed even after pulse modulation, and it is desirable to remove the powder and continue film formation in order to improve productivity.

It is a first object of the present invention to provide a method capable of forming a film by plasma CVD while suppressing generation of powder without significantly reducing the film forming speed. An object of the present invention is to provide a plasma CVD film forming method which enables plasma cleaning at high speed while achieving the object of the present invention. The third object is to provide an apparatus suitable for achieving the first and second objects.

[0008]

According to the present invention, two or more electrodes are provided in a vacuum chamber to which a gas introduction system and an exhaust system are connected, and one of the electrodes is supplied with high-frequency power from a high-frequency power source and the other is supplied with high-frequency power. A substrate is mounted on the electrodes of the above, and a reaction gas introduced into the vacuum chamber is decomposed by plasma generated between the electrodes to form a film on the substrate. At a modulation cycle of 100 kHz, a duty ratio of 95% to 40% is supplied. When cleaning the inside of the vacuum chamber, high-frequency power is supplied at a duty ratio of 80% to 100% by changing the high frequency power during film formation. The first and second objects are achieved by performing plasma cleaning with an etching gas introduced into the chamber. The third object is to provide two or more electrodes in a vacuum chamber to which a gas introduction system and an exhaust system are connected, supply high-frequency power from a high-frequency power source to one of the electrodes, and mount a substrate on the other electrode. mounted, the reaction gas introduced into the vacuum chamber at the apparatus for forming the substrate is decomposed by the plasma generated between the electrodes, connect the cleaning etch gas source into the vacuum tank Connecting the high-frequency power supply to the electrode via control means for changing a modulation period and a duty ratio of the high-frequency power , and controlling the high-frequency power during film formation by the control means.
With a duty cycle of 95 at a modulation period of 50 Hz to 100 kHz.
% To 40% to clean the vacuum chamber
The high-frequency power was changed to that at the time of film formation, and the duty ratio was 8
This is achieved by configuring to supply between 0% and 100% .

[0009]

A substrate is prepared in a vacuum chamber, the pressure inside the substrate is adjusted to an appropriate vacuum pressure, the substrate is heated, and a reaction gas is flowed at an appropriate flow rate in the same manner as in the ordinary plasma CVD method. While applying a high-frequency power to the electrodes to form a film is the same as the conventional method, the method of the present invention not only modulates the high-frequency power with a pulse at a modulation cycle of 50 Hz to 100 kHz, but also reduces the duty ratio. By forming a film by a new method of inputting at 95 to 40%, generation of powder accompanying the film formation can be suppressed even when a large amount of electric power is applied, and a long-time film formation can be performed, and the electrode is formed as the film formation time elapses. Film and powder adhering to the shower plate, the reflector, etc. can be removed by etching by applying high frequency power with a duty ratio of 80 to 100%, and disassembly and replacement of the device become unnecessary. Efficiency is improved. In addition, the above method can be performed by a relatively simple change in which a normal plasma CVD film forming apparatus is provided with a modulator for modulating high-frequency power and a control unit for changing a duty ratio.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
In FIG. 2, reference numeral 1 denotes a vacuum chamber to which a gas introduction system 2 connected to a reaction gas source and an exhaust system 3 connected to a vacuum pump are connected. In the vacuum chamber 1, two flat electrodes are provided. 4 and 5 are provided facing each other, an external high-frequency power supply 6 is connected to one of the electrodes 4 via a matching circuit 7, and a substrate 8 on which a film is formed is mounted on the other electrode 5. The other electrode 5 is formed in a tray shape, and a chain, a robot arm, or the like (not shown) is provided between the vacuum chamber 1 and another vacuum chamber 10 for taking in and out a substrate 8 connected to the vacuum chamber 1 via a valve 9. And maintained at the ground potential during the film formation in the vacuum chamber 1. The one electrode 4 is constituted by a hollow electrode provided with a shower plate 11 on the front surface thereof, and the gas introduction system 2 is connected to the hollow portion to provide a large number of gas ejection ports provided on the shower plate 11. The gas was uniformly ejected from 12. Reference numeral 13 denotes a heater provided behind the electrode 5 for heating the substrate 8. The gas introduction system 2
As a reaction gas, SiH ₄ , NH ₃ , N ₂ O, etc. are introduced as a reaction gas. When an a-Si: H film is formed on the substrate 8, S
iH ₄ is introduced. Reference numeral 16 denotes a deposition-preventing plate, and reference numeral 17 denotes a reflector.

[0011] The above apparatus configuration is the same as that of the conventional plasma CVD.
The configuration is substantially the same as the configuration of the film forming apparatus. The same applies to the case where the reaction gas introduced into the vacuum chamber is decomposed by plasma generated between the electrodes 4 and 5 to form a film on the substrate 8. If the power supplied from the high-frequency power source 6 is increased to increase the power, there is a problem that the generation of powder increases, and it takes a long time to clean the powder. However, in the present invention, the high-frequency power supplied to the electrode 4 is pulse-modulated. The new method of setting the duty ratio to a specific range during film formation and during cleaning as well as reducing the generation of powder even with a large input power compared to the conventional method. The cleaning by etching at high speed was made possible so as not to lower the effective input power by continuous discharge of large high frequency power. In order to execute this method, high-frequency power to the electrode 4 is supplied via control means of a modulator 14 for pulse-modulating the high-frequency power supply 6 and a changer 15 for changing a duty ratio.

When a-Si: H is deposited, the glass substrate 8 attached to the electrode 5 is heated by a heater 13 and
_The high-frequency power is applied to the electrode 4 while flowing into the vacuum chamber 1 where the _four gases are evacuated, and the gas is ionized by the discharge generated between the electrodes 4 and 5, and the radicals generated by the ionization are heated. Although a thin film of a-Si: H is formed by reacting and adhering to the surface of the substrate 8 thus formed, the applied high frequency power is increased, and the modulator 14 and the modifier 15 are increased.
By adjusting the duty ratio to a specific range while performing pulse modulation, powder generation is reduced.
As a result, the film formation rate is reduced, but this can be compensated for by increasing the input power. Further, when cleaning powder generated to some extent, NF ₃ , C
An etching gas such as HF ₃ is introduced into the vacuum chamber 1 and high-frequency power having a high duty ratio is applied to the electrode 4 to remove plasma etching at a relatively high etching rate. As the high-frequency power supply 6, a high-frequency power supply of 1 MHz to 60 MHz is used, which is pulse-modulated by the modulator 14 at a modulation cycle of 50 Hz to 100 KHz, and the duty ratio is 4
It is changed by the changer 15 at 0 to 100%. If one high-frequency power supply cannot be changed at this duty ratio, two high-frequency power supplies capable of pulse modulation and a high-frequency power supply that outputs continuous high-frequency power may be provided.

The reason why the high frequency power of 1 MHz to 60 MHz is selected as the high frequency power supply 6 is that the upper limit of the frequency of the mobile ions in the plasma is 1 MHz and the stable discharge obtained by the concentrated L and C is 60 MHz or less. Further, in order to reduce the generation of powder, it is only necessary to stop the discharge for a time for eliminating all the radicals in the reaction space. However, if the discharge stop time is too long, the deposition rate (film forming rate) is reduced. In other words, the elimination time of the SiH ₃ * radical is long, and it is not practical to stop the discharge for the elimination time. Therefore, the modulation period was calculated from the diffusion rate of the radical, and the modulation period was set to 50 Hz to 100 KHz. That is, the electrode 4,
The distance between the discharge spaces 5 is usually about 20 mm. When the pressure is 1 Torr, which is the standard for plasma CVD, all the radicals reach one of the electrodes and disappear in about 1 msec. Is 1 millisecond as a guide. If the duty ratio is set to 50%, the modulation period becomes 50 Hz . The reason for setting the maximum of the modulation period to 100 kHz is that the OFF time is too short at 100 kHz or more,
This is because generation of powder is not suppressed.

The specific embodiments of the present invention are as follows.
In the apparatus having the configuration shown in FIG. 2, a reaction gas source of SiH ₄ and an etching gas source of NF ₃ are connected to the gas introduction system 2 so as to be alternately introduced, and the electrode 5 on which the glass substrate 8 is mounted is connected. After preparing the vacuum chamber 1 and evacuating the vacuum chamber 1 by the exhaust system 3, the pressure is adjusted to 0.65 Torr while uniformly flowing SiH ₄ gas to the substrate 8 at a rate of 500 sccm through the shower plate 11. I do. At the same time, the substrate 8 is heated to 250 ° C. 13.56 MHz for the high frequency power supply 6
z, use 500W, this is 1kHz
And duty ratio (ON / ON +
OFF) was changed from 30% to 100%. In order to measure the amount of powder generated, the shower plate 11
A 20 mm square cover glass was placed on the end face, and only the powder was taken after film formation and its weight was measured. The deposition rate of the thin film deposited on the substrate 8 under these conditions was measured by dividing the film attached to the substrate 8 by a stylus-type step meter and dividing the film by the deposition time. The relationship between the deposition rate (deposition rate), the amount of generated powder, and the duty ratio under these conditions is shown in FIG.
It can be seen that, when the duty ratio is 40%, the deposition rate is reduced to about 60% as compared with the case where the duty ratio is 100%, but the amount of generated powder sharply decreases as the duty ratio decreases. The deposition rate was proportional to the input power, but the duty ratio at which the loss of the deposition rate was within an allowable range was in the range of 40 to 95%. Even powder occurs somewhat during the film formation, electrodes and the shower plate over the deposition time, but the film or powder to the reflector or the like will adhere, NF ₃ into the vacuum chamber 1 when the appropriate time has elapsed The gas was flowed at a rate of 2000 sccm through the gas introduction system 2, the pressure in the vacuum chamber 1 was adjusted to 0.3 Torr, and 2 kW
High frequency power of 1KHz and a duty ratio of 30
When it was charged into the electrode 4 while being changed to １００100%, the etching rate changed as shown in FIG. In the case of cleaning the plasma CVD apparatus, an etching rate of 1 μm / min is a standard, and therefore, the duty ratio is 80 to
A range of 100% is selected. Duty ratio 100%
Is a continuous discharge without modulation, and if the existing high-frequency power supply cannot be controlled at 40 to 100%, a high-frequency power supply capable of pulse modulation may be separately provided.

In the above embodiment, the vertical type apparatus in which the substrate 8 is attached to the tray type electrode 5 and transported vertically is described. However, the present invention is not an apparatus which transports the substrate horizontally or a tray type. The present invention is also applicable to a single wafer type apparatus. Also, a-S
Although the present invention has been described in the embodiment of the formation of the i: H film, the film formation accompanied by the generation of powder in the gas phase polymerization, for example, poly-S
i film, Ge film, carbon film, p-type / n-type a-Si film, S
It can also be applied to the formation of an iCx film or the like.

[0016]

As described above, according to the present invention, when plasma CVD film formation is performed with high-frequency power, the high-frequency power is applied to a substrate when a reactive gas is introduced and when the etching gas is introduced. In this case, the duty ratio is changed between the time of the plasma cleaning and the time of the plasma cleaning, so that the amount of powder generated due to the film formation can be reduced, so that the film can be formed for a long time with a large high frequency power. This method has an effect that the method can be implemented by a device having a simple configuration in which only a modulator for high-frequency power and a control unit for a duty ratio changer are provided.

[Brief description of the drawings]

FIG. 1 is a cutaway plan view of a conventional example.

FIG. 2 is a cutaway plan view of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a duty ratio, a deposition rate, and an amount of generated powder.

FIG. 4 is a diagram showing a relationship between a duty ratio and an etching rate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vacuum tank 2 Gas introduction source 3 Exhaust system 4, 5 electrode 6 High frequency power supply 8
Substrate 13 Heater 14 Modulator 15 Duty ratio changer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanori Hashimoto 523 Yokota, Yamatake-cho, Yamatake-gun, Chiba Japan Vacuum Engineering Co., Ltd. Chiba Super Materials Laboratory Co., Ltd. (72) Noriaki Tani 523 Yamatake-cho Yokota, Yamatake-gun, Chiba Prefecture Japan Vacuum Engineering Co., Ltd.Chiba Super Materials Research Laboratories (72) Inventor U.S. Inside Vacuum Technology Co., Ltd. (72) Inventor Yasuo Shimizu 2500 Hagizono, Chigasaki City, Kanagawa Prefecture Inside Japan Vacuum Technology Co., Ltd. (72) Inventor Masahiro Ichiyama 2500 Hagizono, Chigasaki City, Kanagawa Prefecture Inside Japan Sky Technology Co., Ltd. 56) References JP-A-5-160045 (JP, A) JP-A-62-115037 (JP, A) JP-A-60-140726 (JP, A ) (58) investigated the field (Int.Cl. ^7, DB name) H01L 21/205 C23C 16/50

Claims (3)

(57) [Claims] 1. A high-frequency power source is supplied from a high-frequency power source to one of two electrodes provided in a vacuum chamber to which a gas introduction system and an exhaust system are connected, and a substrate is mounted on the other electrode. An apparatus for decomposing a reaction gas introduced into the vacuum chamber by plasma generated between these electrodes and forming a film on the substrate, and using a high frequency power of 50 Hz to 100 kHz during the film formation.
At a duty cycle of 95% to 40% with a modulation cycle of
A plasma CVD method characterized in that when cleaning the inside of the vacuum chamber, high-frequency power is supplied at a duty ratio of 80% to 100% while changing from the time of film formation, and plasma cleaning is performed using an etching gas introduced into the vacuum chamber. Film formation method. 2. The high-frequency power source is 1 MHz to 60 MHz.
2. The plasma CVD film forming method according to claim 1, wherein a power source is used. 3. A method according to claim 1, wherein two or more electrodes are provided in a vacuum chamber to which a gas introduction system and an exhaust system are connected, high-frequency power is supplied to one of the electrodes from a high-frequency power supply, and a substrate is mounted on the other electrode. the reaction gas introduced into the vacuum chamber at the apparatus for forming the substrate is decomposed by the plasma generated between the electrodes, connect the cleaning etch gas source into the vacuum vessel, the A high-frequency power supply is connected to the electrodes via control means for changing the modulation cycle and duty ratio of the high-frequency power, and the control means controls the high-frequency power during film formation.
Duty ratio 95% with modulation period of 50Hz to 100kHz
~ 40%, when cleaning the vacuum chamber
Changes the high frequency power to that at the time of film formation and changes the duty ratio to 80.
% . A plasma CVD apparatus characterized in that it is supplied at a rate of 100% to 100% .