JPH05291150A - Plasma cvd device - Google Patents

Abstract

PURPOSE:To enable the films of various qualities to be stably deposited at variable rates by a method wherein the oscillation frequency of variable frequency power supply fed to a cathode electrode as well as the frequency of a DC or AC bias current to be impressed are specified. CONSTITUTION:A film formed substrate 3 held by a rotary mechanism 4 driven by a motor M is internally heated by an inner heater 5. A shield member 6 is arranged around a cathode electrode 2 so that a current may not be discharged into the space between the cathode electrode 2 and a reaction chamber 1. Besides, the cathode electrode 2 is connected to a bias voltage impressing means 13 of DC or AC in frequency not exceeding 2MHz through the intermediary of a low pass filter 12. Furthermore, the cathode electrode 2 is connected to a high-frequency power supply with oscillation frequency exceeding 13.56 MHz through the intermediary of a matching circuit 8. Through these procedures, the film quality as well as the reproducibility of and alpha-Si film can be notably enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystalline or non-single crystalline functionality useful for electrophotographic photoreceptor devices as semiconductor devices, image input line sensors, image pickup devices, photovoltaic devices and the like. The present invention relates to a plasma CVD apparatus that can preferably form a deposited film.

[0002]

2. Description of the Related Art Conventionally, amorphous silicon has been used as an element member used in electrophotographic photoreceptor devices as semiconductor devices, image input line sensors, image pickup devices, photovoltaic devices, and various other electronic elements and optical elements. A non-single crystalline deposited film such as that described above or a crystalline deposited film such as a diamond thin film has been proposed, and some of them have been put to practical use.

Then, such a deposited film is a plasma CV.
It is known that it is formed by the D method, that is, a method of decomposing a raw material gas with plasma by direct current discharge or high frequency discharge to form a deposited film on a substrate such as glass, quartz, heat resistant synthetic resin film, stainless steel, or aluminum. Various devices have been proposed for this purpose. As an example thereof, FIG. 22 shows a film forming apparatus for forming an amorphous silicon film (hereinafter referred to as a-Si film) for an electrophotographic photoreceptor on a cylindrical film forming substrate.

A cylindrical cathode electrode 2 electrically insulated from the reaction container 1 by an insulating material 11 and a cylindrical film-forming substrate 3 functioning as a counter electrode are arranged in a reaction container 1 capable of depressurizing. There is. The film formation substrate 3 is held by a rotating mechanism 4 driven by a motor M, and is heated from inside by a heater 5 inside. A shield member (earth shield) is provided around the cathode electrode 2 to prevent discharge from occurring between the cathode electrode 2 and the reaction vessel 1.
6 are arranged. By the way, the distance between the cathode electrode 2 and the shield member (earth shield) needs to be smaller than the thickness of the dark space (dark space) of the plasma in order to prevent discharge between them. Although the thickness of the dark portion changes depending on the discharge conditions, the distance between the cathode electrode 2 and the earth shield 6 is generally about 1 mm to 3 mm. The high frequency power supply 7 is connected to the cathode electrode 2 via a matching circuit 8. The oscillation frequency of the high frequency power supply 7 is 13.56M
Hz is commonly used. 9 is an evacuation means, 10
Is a gas supply means. Formation of an a-Si film using this apparatus is performed as follows.

After the inside of the reaction vessel 1 is evacuated to a high vacuum by the vacuum evacuation means 9, a raw material gas such as silane gas and disilane gas is introduced into the reaction vessel 1 by the gas supply means 10 and maintained at a pressure of several millitorr to several torr. To do. High frequency power of 13.56 MHz is supplied from the high frequency power supply 7 to the cathode electrode 2 to generate plasma between the cathode electrode 2 and the film formation substrate 3. By decomposing the raw material gas in this manner, the heating heater 4 causes the temperature to rise to 200 ° C to 300 ° C.
An a-Si film is deposited on the film-forming substrate 3 heated to about ° C. The maximum deposition rate of the a-Si film in this film forming method is about 6 (μm / hour).

In the above-mentioned conventional example, the oscillating frequency of the high frequency power source is 13.56 MHz, but in recent years, a plasma CVD method using a high frequency power source of 13.56 MHz or more using a parallel plate type plasma CVD apparatus (Plasma) has been reported.
Chemistry and Plasma Pro
cessing, Vol 7, No 3, (19
87) p267-273), and the possibility of improving the deposition rate has been shown, and is attracting attention.

[0007]

However, the above-mentioned conventional device configuration has the following problems.

The deposition rate of the a-Si film in the plasma CVD method using a high frequency power source of 13.56 MHz is 6 at maximum.
Since it is about (μm / hour), when the a-Si film is used as an electrophotographic photoreceptor, a general thickness required is 30 μm.
In order to obtain about m, a deposition time of about 5 hours is required and the productivity is not necessarily good.

When the surface potential of the film-forming substrate is a constant potential, the plasma space potential has various causes (fluctuations of discharge parameters such as pressure, gas flow rate, electric power, etc., temperature variations of reaction vessel wall, matching circuit, etc.). And the like), the difference between the plasma space potential and the surface potential of the film-forming substrate also changes, so the energy of ions in the plasma that accelerates and impacts the substrate surface may also change. That is, the quality of the thin film deposited on the surface of the substrate cannot always be stably controlled.

Further, as described above, the distance between the cathode electrode and the ground shield is very small, about 3 mm or less, because it is necessary to prevent the occurrence of discharge between them. Therefore, the electrostatic capacitance between the cathode electrode and the earth shield becomes large. Since the impedance is inversely proportional to the electrostatic capacitance, these impedances become small, and a large high frequency current may flow between the cathode electrode and the ground shield, resulting in loss of high frequency power.

Further, the present inventors conducted an experiment for forming an a-Si film by changing the oscillation frequency of the high frequency power source of the conventional apparatus shown in FIG. 22 to 13.56 MHz or higher in order to improve the deposition rate of the a-Si film. As a result, 13.5
When high-frequency discharge of 6 MHz or more was performed, it became clear that the following problems exist.

As the discharge frequency is increased, the film quality tends to deteriorate. As a result of conducting various experiments to investigate the cause of the deterioration of the film quality, as the discharge frequency was increased, the energy of ions in the plasma incident on the counter electrode tended to decrease. Ion bombardment to That is, it was found that the so-called plasma damage is reduced, but the assist energy for promoting the migration of deposited particles is also insufficient and the film quality is likely to deteriorate.

Further, as the discharge frequency is increased, the thickness of the plasma dark part becomes smaller, so that discharge is more likely to occur between the cathode electrode and the earth shield, and the distance between the cathode electrode and the earth shield is made smaller than in the conventional case. The need arises. Moreover, since the impedance is inversely proportional to the discharge frequency, the impedance between the cathode electrode and the ground shield is further reduced. As a result, the loss of high frequency power tends to increase.

[0014]

The preferred embodiments of the plasma CVD apparatus of the present invention are as follows.

That is, in a plasma CVD apparatus in which plasma is generated by high frequency discharge in a depressurizable reaction vessel to deposit a thin film on a substrate to be processed, the oscillation frequency of the high frequency power supply for supplying high frequency power to the cathode electrode is 13.56M.
And a means for applying a direct current or / and an alternating bias voltage having a frequency of 2 MHz or less to the cathode electrode.

In the present invention, the bias potential (V ₁ ) of the cathode electrode when the bias voltage is applied during the high frequency discharge and the self bias potential (V ₁ ) of the cathode electrode when the bias voltage is not applied during the high frequency discharge ( The bias voltage can be applied to the cathode electrode so that V ₂ ) becomes 0V <V ₁ −V ₂ ≦ 200V. Further, a means for detecting a floating potential of the plasma space and a means for controlling a bias voltage applied to the cathode electrode based on the floating potential of the plasma space can be provided.

Further, the cathode electrode has a cylindrical shape,
The cathode electrode may constitute a part of the reaction vessel, the counter electrode may be arranged inside the cathode electrode, and the shield member may be arranged outside the cathode electrode with a distance of 3 mm or more from the cathode electrode. it can.

According to the present invention, the means for applying the bias voltage to the cathode electrode is provided, so that the plasma space potential can be changed.

When the means for detecting the floating potential of the plasma space and the means for controlling the bias voltage applied to the cathode electrode based on the floating potential of the plasma space are provided, the plasma space potential causes various causes. Even if it fluctuates, the floating potential of the plasma space also fluctuates substantially, so that the difference between the plasma space potential and the surface potential of the film-forming substrate can be kept constant.

Further, the cathode electrode has a cylindrical shape,
When the cathode electrode constitutes a part of a depressurizable reaction vessel, the counter electrode is arranged inside the cathode electrode, and the shield member is arranged outside the cathode electrode with a distance of 3 mm or more from the cathode electrode. In addition, the capacitance between the cathode electrode and the earth shield can be reduced.

As a result, the discharge frequency is 13.56M.
Even if the frequency is higher than Hz, sufficient assist energy can be applied to the deposited particles with good controllability, and loss of high frequency power can be prevented.

In the present invention, as the raw material gas, any known material can be selectively used depending on the kind of the film to be formed. For example, in the case of forming an a-Si-based functional deposited film, silane, disilane and the like are listed as preferable source gases, and in the case of forming another functional deposited film, for example, germane, A raw material gas such as methane or a mixed gas thereof may be used. Examples of the carrier gas include hydrogen, argon and helium. Examples of the characteristic improving gas for changing the band gap width of the deposited film include nitrogen, a gas containing a nitrogen atom such as ammonia, a gas containing an oxygen atom such as oxygen, nitric oxide, and dinitrogen oxide, and methane. , Hydrocarbons such as ethane, ethylene, acetylene and propane, fluorine compounds such as silicon tetrafluoride, disilicon hexafluoride and germanium tetrafluoride, and mixed gases thereof. Examples of the dopant gas for doping include diborane, boron fluoride, phosphine and the like.

The pressure of the discharge space in the present invention may be any pressure as long as film formation can be performed.
When forming an a-Si film, preferably 1 mTorr
r to 5 Torr, more preferably 10 mTorr to 3T
orr.

The high frequency power in the present invention may be any power as long as it is a power for film formation. For example, a-
When forming a Si film, preferably 0.001 W /
cm ^{2 to} 10 W / cm ² , more preferably 0.01 W / c
a m ² ~5W / cm ^2.

The substrate temperature at the time of forming the deposited film in the present invention may be any temperature as long as the film is formed.
For example, when forming an a-Si film, preferably 2
The temperature is 0 ° C to 500 ° C, more preferably 50 ° C to 450 ° C.

[0026]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

(Embodiment 1) FIG. 1 shows a plasma CV of the present invention.
It is a schematic diagram which shows one example of a D apparatus.

In the apparatus shown in FIG. 1, a cylindrical cathode electrode 2 which is electrically insulated from the reaction container 1 by an insulating material 11 in the depressurizable reaction container 1 and a cylindrical electrode which functions as a counter electrode. A film formation substrate 3 is arranged.
The film formation substrate 3 includes a rotation mechanism 4 driven by a motor M.
And is heated from the inside by the heater 5 inside. A shield member (earth shield) 6 is arranged around the cathode electrode 2 so that no discharge occurs between the cathode electrode 2 and the reaction vessel 1. Further, unlike the conventional device, a bias voltage applying means 13 of direct current or / and alternating current having a frequency of 2 MHz or less is connected to the cathode electrode 2 via a low-pass filter 12. Further, the cathode electrode 2 has a matching circuit 8
A high frequency power source having an oscillation frequency of higher than 13.56 MHz is connected via the. Film formation using the apparatus of FIG. 1 is performed as follows.

First, the inside of the reaction vessel 1 is evacuated to a high vacuum by the vacuum evacuation means 9, and then a desired raw material gas such as silane gas and disilane gas is introduced by the gas supply means 10 to maintain the pressure of several millitorr to several torr. .. A desired high frequency power having a frequency higher than 13.56 MHz is supplied from the high frequency power supply 7 to the cathode electrode 2 through the matching circuit 8. At this time, the direct current and / or the frequency is 2 MH.
A desired bias voltage from an alternating bias voltage applying means 13 of z or less is applied to the cathode electrode 2 through the low pass filter 12, and plasma is generated between the cathode electrode 2 and the film formation substrate 3. By doing so, the source gas is decomposed, and a functional deposition film is formed on the film formation target substrate 3 heated to a desired temperature by the heater 4.

FIG. 5 to FIG. 8 use the apparatus of FIG.
6 is a graph showing the photoconductivity and the dark conductivity of a film obtained by forming a -Si film. When forming a film, the cathode electrode should have a voltage of -100 V to +
A DC bias voltage was applied in the range of 250 V, and the film forming conditions were as shown in Table-1. 5, FIG. 6, FIG. 7, and FIG.
Oscillation frequency of high frequency power supply is 40MHz, 10 respectively
The measurement results of the a-Si film formed under the film forming conditions of 0 MHz, 200 MHz, and 300 MHz are shown. Figure 9
For comparison with the conventional method, the oscillation frequency of the high frequency power source of the device of FIG. 1 is 13.56 MHz, except for the discharge frequency,
It is the figure which showed the result of having formed the a-Si film on the to-be-deposited substrate on the same film-forming conditions as Table-1, and measuring the electrical conductivity of the a-Si film.

(1) When the discharge frequency is 13.56 MHz, the self-bias potential generated at the cathode electrode is -3.
It was 5V. When a DC bias was applied to the cathode electrode and the potential of the cathode electrode was changed from −135 V to +215 V, as shown in FIG. 9, the photoconductivity of the a-Si film when the potential of the cathode electrode was −50 V /
The dark conductivity ratio showed the maximum value and was about 9000.
Also, when the potential of the cathode electrode is −35 V, it is 7000
It was about.

(2) When the discharge frequency was 40 MHz, the self-bias potential generated at the cathode electrode was -10V. When a DC bias was applied to the cathode electrode to change the potential of the cathode electrode from −110V to + 240V, the potential of the cathode electrode was + as shown in FIG.
The ratio of photoconductivity / dark conductivity of the a-Si film at 80 V showed the maximum value and was about 12,000. Also,
It was about 6000 when the potential of the cathode electrode was −10V.

(3) When the discharge frequency is 100 MHz,
The self-bias potential generated at the cathode electrode was -5V. When a DC bias was applied to the cathode electrode to change the potential of the cathode electrode from −105 V to +245 V, the potential of the cathode electrode was + as shown in FIG.
The ratio of photoconductivity / dark conductivity of the a-Si film at 140 V showed the maximum value and was about 70,000. Further, it was about 4000 when the potential of the cathode electrode was −5V.

(4) When the discharge frequency is 200 MHz,
The self-bias potential generated at the cathode electrode was -2V. When a DC bias was applied to the cathode electrode to change the potential of the cathode electrode from −102 V to +248 V, the potential of the cathode electrode was + as shown in FIG.
The ratio of photoconductivity / dark conductivity of the a-Si film at 170 V showed the maximum value and was about 100,000. Moreover, it was about 2000 when the potential of the cathode electrode was −5V.

(5) When the discharge frequency is 300 MHz,
The self-bias potential generated on the cathode electrode was 0V. When a DC bias was applied to the cathode electrode to change the potential of the cathode electrode from −100V to + 250V, the potential of the cathode electrode was +1 as shown in FIG.
The ratio of the photoconductivity / dark conductivity of the a-Si film at 80 V showed the maximum value and was about 100,000. Further, it was about 1000 when the potential of the cathode electrode was 0V.

As is clear from the results of the above examples,
When a bias voltage was not applied to the cathode electrode, that is, when the cathode electrode had a self-bias potential, the discharge frequency increased, the conductivity ratio of the a-Si film decreased, and the film quality tended to deteriorate. On the other hand, when a bias voltage was applied, there was no tendency for the film quality to deteriorate. When the discharge frequency is higher than 13.56 MHz, the conductivity ratio is
When the potential of the cathode electrode was within the range of the self-bias potential to the self-bias potential + 200V, the maximum value of 4 digits or more was exhibited, and the film quality was good.

FIGS. 10, 11 and 12 are graphs showing photoconductivity and dark conductivity of an a-Si film formed by using the apparatus of FIG. During film formation, the cathode electrode should be +50 with reference to the self-bias potential.
A DC bias voltage of V to +200 V was applied, and the discharge frequency was changed from 13.56 MHz to 300 MHz. The film forming conditions are as shown in Table-1. 10 and 1
1 and FIG. 12 show the measurement results of the conductivity when the bias voltage applied to the cathode electrode was + 50V, + 100V, and + 200V, respectively.

As shown in FIGS. 10 to 12, as the discharge frequency is increased from 13.56 MHz, the photoconductivity / dark conductivity ratio remarkably increases up to about 40 MHz.
Above 0 MHz, it gradually increased or decreased.

Although not shown, the deposition rate decreased with an increase in the discharge frequency, and drastically decreased at 250 MHz or more.

That is, the discharge frequency is 40 MHz to 250 M
In the range of Hz, the quality of the a-Si film was very good, and there was no rapid decrease in the deposition rate.

Although the bias voltage in the above embodiments was a DC voltage, in the sheath region of the plasma formed on the surface of the film-forming substrate, the ions in the plasma can follow the electric field fluctuation of the sheath. 2MHz which is the upper limit frequency
When the following AC bias voltage was applied to the cathode electrode, even if the discharge frequency was set higher than 13.56 MHz, the deterioration of the film quality could be prevented as in the case of applying the DC bias. In addition, a DC bias voltage and an AC bias voltage with a frequency of 2 MHz or less are applied simultaneously, and the discharge frequency is 13.56M.
Even when the frequency was higher than Hz, the deterioration of the film quality could be prevented as in the case of applying the DC high bias. At this time, the waveform of the AC voltage is
It was a sine wave, a half-wave rectified sine wave, a square wave, a triangular wave, and their combined wave. In particular, when the AC bias voltage or the AC bias voltage and the DC bias voltage are applied so that the potential of the cathode electrode is in the range of self-bias potential to self-bias voltage +200 V, the discharge frequency is set to 1
Even when the frequency was higher than 3.56 MHz, the conductivity ratio of the a-Si film was 4 digits or more at the maximum, and the film quality was good.

(Embodiment 2) FIG. 2 shows the plasma CV of the present invention.
It is a schematic diagram which shows another example of a D apparatus. In the figure, the same reference numerals as those in FIG. 1 are the same as those in the apparatus shown in FIG. 1, and detailed description thereof will be omitted. In the apparatus shown in FIG. 2, unlike the apparatus shown in FIG. 1, the floating potential measuring electrode 15 in the plasma space is provided inside the reaction vessel 1 via the insulating material 14, and the floating potential measuring electrode 15 is floating. It is connected to the bias voltage control means 17 via the potential measuring means 16. The bias voltage control means 17 is connected to the bias voltage application means 13. The bias voltage control unit 17 is configured to control the bias voltage application unit 13 based on the signal from the floating potential measuring unit 16. Film formation using the apparatus of FIG. 2 is performed as follows.

First, the inside of the reaction vessel 1 is evacuated to a high vacuum by the vacuum evacuation means 9, and then a desired raw material gas such as silane gas or disilane gas is introduced by the gas supply means 10 to maintain a pressure of several millitorr to several torr. .. The high frequency power supply 7 supplies the desired high frequency power having a frequency higher than 13.56 MHz to the cathode electrode 2 through a matching circuit 8. At this time, the bias voltage control means 17 is set so that the floating potential of the plasma space becomes a desired constant value, and the direct current and / or the frequency is 2 MHz.
A bias voltage is applied to the cathode electrode 2 via the low-pass filter 12 from the following AC bias voltage applying means 13. Thus, the cathode electrode 2 and the film-forming substrate 3
A plasma is generated between them and the source gas is decomposed to form a functional deposition film on the film formation substrate 3.

Using the apparatus of FIG. 1, discharge was performed under the conditions shown in Table 2 and the plasma space potential and the floating potential of the plasma space were measured. FIG. 13 is a graph showing the change with time. The measurement of the plasma potential was performed by using a general single-probe probe method. The floating potential also fluctuated following the fluctuation of plasma space potential, and the difference was kept almost constant.

FIG. 14 is a graph showing the change over time in the potential when discharge is generated using the apparatus of FIG.
The bias voltage control means 17 was set so that the floating potential of the plasma space was 15 V, and the discharge was performed under the conditions shown in Table-2. From FIG. 14, the plasma space potential was kept almost constant.

From the results of FIGS. 13 and 14, it is understood that the plasma space potential can be kept substantially constant by controlling the bias voltage applied to the cathode electrode so that the floating potential of the plasma space becomes constant. As a result, it can be presumed that the fluctuation of the energy of the ions in the plasma that accelerates and impacts the surface of the substrate kept at a constant potential can be reduced. Although it is more direct to detect the plasma space potential and control the bias voltage applied to the cathode electrode so that the plasma space potential becomes constant, the single probe electrostatic capacitance, which is a general plasma space potential detection means, is used. In the probe method, a metal needle is inserted into the plasma, a voltage (V) between the plasma and a vacuum container in contact with the plasma is applied to measure a current (I) flowing through the metal needle, and the current is calculated from the VI characteristic. It is difficult to detect the plasma space potential instantaneously because the plasma space potential is obtained, and it is not always practical because the measurement system is expensive.

FIG. 15 is a graph showing the electric conductivity of the film obtained by forming a film using the apparatus of FIG. Here, the floating potential of the plasma space is 20
The bias voltage control means 17 is set to V, and the
The a-Si film was formed under the film forming conditions shown in FIG. a-
The formation of the Si film was performed 10 times, and the samples obtained by the respective film formations were designated as Sample 1 to Sample 10.

FIG. 16 is a graph showing the electric conductivity of the film obtained by forming a film using the apparatus of FIG. Here, a constant bias voltage is applied to the cathode electrode by the bias voltage applying means so that the floating potential of the plasma space at the initial stage of discharge becomes 20V.
Film formation was performed under the film formation conditions shown in 3. The a-Si film was formed 10 times, and the samples obtained by the respective film formations were designated as Sample 11 to Sample 20.

From FIGS. 15 and 16, by controlling the bias voltage applied to the cathode electrode so that the floating potential of the plasma space becomes constant, the quality of the a-Si film can be improved and reproducibility can be remarkably improved. Is understood.

(Embodiment 3) FIG. 3 shows plasma CV of the present invention.
It is a schematic diagram which shows another example of D apparatus. 22, the same reference numerals as those in FIG. 22 showing the conventional device are the same as those in FIG. 22, and a detailed description thereof will be omitted. However, the device shown in FIG.
It differs from the device of FIG. 22 in the following points. That is, FIG.
In the above apparatus, the cathode electrode 2 is electrically insulated from the reaction container 1 by the insulating material 11 and constitutes a part of the reaction container capable of depressurizing. Oscillation frequency is 13.56MH
A high frequency power supply 7 larger than z is connected via a matching circuit 8. The earth shield 6 is arranged outside (atmosphere side) with a distance larger than 3 mm from the cathode electrode 2. In addition, the cathode electrode 2 has a direct current or / and a frequency of 2 MHz through the low pass filter 12.
The following AC bias voltage applying means 13 is connected, and the cathode electrode 2 is connected via a matching circuit 8 to a high frequency power source having an oscillation frequency of higher than 13.56 MHz. Film formation using the apparatus of FIG. 3 is performed as follows. That is, after the inside of the reaction vessel 1 is evacuated to a high vacuum by the vacuum evacuation means 9, a desired raw material gas such as silane gas or disilane gas is introduced into the reaction vessel 1 by the gas supply means 10 to change the pressure from several millitorr to several torr. maintain. A desired high frequency power having a frequency higher than 13.56 MHz is supplied from the high frequency power supply 7 to the cathode electrode 2 through the matching circuit 8. At this time, a desired bias voltage is applied to the cathode electrode 2 through the low-pass filter 12 from the direct-current or / and alternating-current bias voltage applying means 13 having a frequency of 2 MHz or less. Thus the cathode electrode 2
A functional deposition film is formed on the film formation base 3 by generating plasma between the film formation base 3 and the source gas to decompose the source gas.

For comparison with the conventional device, the discharge frequency was changed from 13.56 MHz to 300 MHz using the device of FIG.
While changing the distance between the cathode electrode 2 and the earth shield 6 from 1 mm to 150 mm.
-Si film was formed. Here, a bias voltage of +100 V was applied to the cathode electrode with reference to the self-bias potential, and film formation was performed under the film formation conditions shown in Table-4.

FIG. 17 is a graph showing the result of measuring the deposition rate. In FIG. 17, a, b, c, d, e, f,
g and h are the cathode electrode 2 and the earth shield 6 respectively.
Is 1mm, 3mm, 5mm, 10mm, 50
The deposition rate characteristic curves for mm, 100 mm, 110 mm, and 150 mm are shown. When the distance between the cathode electrode 2 and the earth shield 6 is 3 mm or less as in the conventional case, when the discharge frequency is increased from 13.56 MHz, the deposition rate does not change much up to about 40 MHz. The deposition rate tends to decrease together with the increase of the frequency, and particularly, it sharply decreases above 250 MHz. However, when the distance between the cathode electrode 2 and the earth shield 6 was set to be larger than 3 mm, the deposition rate was higher overall and the loss of high frequency power was reduced as compared with the case where the distance was 3 mm or less. Further, when the interval was made larger than 3 mm, the deposition rate increased up to about 250 MHz and decreased at 250 MHz or more even if the discharge frequency was increased. It is presumed that the reason for this decrease is that the high frequency power loss in the matching circuit 8 and the like increased as the discharge frequency increased. Also, if the distance is increased from 3 mm, it will be 10 m.
The deposition rate remarkably increased up to about m, and gradually increased or decreased from about 10 mm to about 100 mm.
Furthermore, when the thickness was 100 mm or more, the deposition rate decreased. The cause of this decrease is that the distance between the cathode electrode 2 and the matching circuit 8 becomes as large as 100 mm or more, so that the inductive impedance of the connecting line between the cathode electrode 2 and the matching circuit 8 increases and the capacitance in the matching circuit 8 accompanying it increases. It is presumed that the high frequency loss increased due to the increase in sexual impedance. From the result of FIG. 17, even if the discharge frequency is higher than 13.56 MHz, it is possible to prevent the decrease of the deposition rate by increasing the distance between the cathode electrode and the ground shield to be larger than 3 mm, and especially when the discharge frequency is 40 MHz to 250 Mz. It can be seen that the high frequency power loss prevention effect is remarkable. The distance between the cathode electrode and the earth shield is 1
In the case of 0 mm to 100 mm, the high frequency power loss prevention effect was remarkable.

FIG. 18 shows a-Si using the apparatus of FIG.
It is the graph which showed the photoconductivity and the dark conductivity of the obtained film after forming a film. Here, the distance between the cathode electrode and the earth shield was 50 mm, and a DC bias voltage was applied to the cathode electrode in the range of 0 V to +200 V with reference to the self-bias potential. The film forming conditions were as shown in Table-5. At this time, the self-bias potential generated at the cathode electrode was -3V. D on the cathode electrode
When the potential of the cathode electrode was changed from −3 V to +197 V by applying a C bias, the potential of the cathode electrode was formed to be +120 V as shown in FIG.
-The ratio of photoconductivity / dark conductivity of the Si film shows the maximum value,
It was about 70,000.

The deposition rate was about 19 (μm / hour) regardless of the bias potential of the cathode electrode.

Using the apparatus shown in FIG. 3, an a-Si film was formed with the distance between the cathode electrode and the earth shield set to 20 mm. At this time, an AC bias voltage having a frequency of 2 MHz or less or an AC bias and a DC bias voltage was applied so that the potential of the cathode electrode was in the range of self-bias potential to self-bias potential + 200V. Other film forming conditions are as shown in Table-6. When the photoconductivity and dark conductivity of the obtained a-Si film were measured, the ratio of photoconductivity / dark conductivity of the a-Si film was about 100,000 at maximum.

The deposition rate was about 15 (μm / hour) regardless of the bias potential of the cathode electrode.

In FIG. 19, the distance between the cathode electrode and the earth shield is 90 mm, and the discharge frequency is 13.56 MHz.
It is a graph which shows the change of photoconductivity and dark conductivity at the time of changing from to 30 MHz. Here, a DC bias voltage of +100 V was applied to the cathode electrode with reference to the self-bias potential, and film formation was performed under the film formation conditions shown in Table-7. As shown in FIG. 19, the discharge frequency is 13.56 MH
As it increases from z, the photoconductivity / up to about 40MHz
The dark conductivity ratio increased remarkably and gradually increased or decreased above 40 MHz.

The deposition rate was 16 (μm / hour) or more.

(Embodiment 4) FIG. 4 shows plasma CV of the present invention.
It is a schematic diagram which shows another example of D apparatus. In the figure, the same reference numerals as those in FIG. 3 are the same as those in FIG. The device shown in FIG. 4 differs from that of FIG.
A floating potential measuring electrode 15 in the plasma space is provided in the reaction vessel 1 via an insulating material 14, and the floating potential measuring electrode 15 is connected to a bias voltage control means 17 via a floating potential measuring means 16. Further, the bias voltage control means 17 is connected to the bias voltage applying means 13. The bias voltage control unit 17 is configured to control the bias voltage application unit 13 based on the signal from the floating potential measuring unit 16. Film formation using the apparatus of FIG. 4 is performed as follows.

After the inside of the reaction vessel 1 is evacuated to a high vacuum by the vacuum evacuation means 9, a desired source gas such as silane gas and disilane gas is supplied by the gas supply means 10 to the reaction vessel 1.
It is introduced into and maintained at a pressure of several millitorr to several torr. A desired high frequency power having a frequency higher than 13.56 MHz is supplied from the high frequency power supply 7 to the cathode electrode 2 through the matching circuit 8. At this time, the bias voltage control means 17 is set so that the floating potential of the plasma space becomes a desired constant value, and the direct current and / or the frequency is 2 MH.
A bias voltage from an alternating bias voltage applying means 13 of z or less is applied to the cathode electrode 2 via the low-pass filter 12.
Apply to. By doing so, plasma is generated between the cathode electrode 2 and the film-forming base 3, and the source gas is decomposed to form a functional deposition film on the film-forming base 3.

FIG. 20 shows a-Si using the apparatus of FIG.
It is the graph which showed the electric conductivity of the film which formed the film and was obtained. Here, the distance between the cathode electrode and the earth shield was set to 30 mm, the bias voltage control means 17 was set so that the floating potential of the plasma space was 50 V, and the film forming conditions shown in Table 8 were applied. The a-Si film was formed 10 times, and the obtained samples were designated as Sample 31 to Sample 40. At this time, the deposition rate is 15 (μ
m / hour).

FIG. 21 shows a-Si using the apparatus of FIG.
It is the graph which showed the electric conductivity of the film which formed the film and was obtained. Here, the distance between the cathode electrode and the earth shield was 30 mm, and a constant bias voltage was applied to the cathode electrode by the bias voltage applying means so that the floating potential at the initial stage of discharge was 50V. The a-Si film was formed 10 times under the film forming conditions shown in Table-8, and the obtained samples were designated as Sample 41 to Sample 50.
At this time, the deposition rate was 15 (μm / hour).

As is clear from the results shown in FIGS. 20 and 21, the quality of the a-Si film can be improved by controlling the bias voltage applied to the cathode electrode so that the floating potential of the plasma space becomes constant. The reproducibility was also significantly improved.

As is clear from the above description of Examples 1 to 4, the plasma CVD apparatus of the present invention makes it possible to perform high-speed, high-quality film deposition stably with good reproducibility. It was

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

[Table 4]

[0069]

[Table 5]

[0070]

[Table 6]

[0071]

[Table 7]

[0072]

[Table 8]

[0073]

According to the present invention, the discharge frequency is set to 13.5.
Even if the frequency is higher than 6 MHz, sufficient assist energy can be applied to the deposited particles with good controllability, and high frequency power loss can be prevented, so that a high quality deposited film can be formed stably at high speed. be able to.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a plasma CVD apparatus of the present invention.

FIG. 2 is a schematic diagram showing an example of a plasma CVD apparatus of the present invention.

FIG. 3 is a schematic diagram showing an example of a plasma CVD apparatus of the present invention.

FIG. 4 is a schematic diagram showing an example of a plasma CVD apparatus of the present invention.

FIG. 5 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 6 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 7 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 8 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 9 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 10 is a graph showing the discharge frequency dependence of conductivity.

FIG. 11 is a graph showing the discharge frequency dependence of conductivity.

FIG. 12 is a graph showing the discharge frequency dependence of conductivity.

FIG. 13 is a graph showing changes with time in plasma space potential and floating potential.

FIG. 14 is a graph showing changes with time in plasma space potential and floating potential.

FIG. 15 is a graph showing reproducibility of conductivity.

FIG. 16 is a graph showing reproducibility of conductivity.

FIG. 17 is a graph showing a deposition rate.

FIG. 18 is a graph showing the dependence of conductivity on the cathode electrode potential.

FIG. 19 is a graph showing the discharge frequency dependence of conductivity.

FIG. 20 is a graph showing reproducibility of conductivity.

FIG. 21 is a graph showing reproducibility of conductivity.

FIG. 22 is a schematic view showing an example of a conventional plasma CVD apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 2 Cathode electrode 3 Deposition substrate 4 Rotation mechanism 5 Heating heater 6 Earth shield 7 High frequency power supply 8 Matching circuit 9 Vacuum exhaust means 10 Gas supply means 11 Insulation material 12 Low pass filter 13 Bias voltage application means 14 Insulation material 15 Floating material Potential measuring electrode 16 Floating potential measuring means 17 Bias voltage control means

Claims (6)

[Claims] 1. In a plasma CVD apparatus for generating a plasma by a high frequency discharge in a depressurizable reaction vessel to deposit a thin film on a substrate to be processed, an oscillation frequency of a high frequency power source for supplying high frequency power to a cathode electrode is 13.56 MHz. A plasma CVD apparatus comprising a larger means for applying a DC or / and an AC bias voltage having a frequency of 2 MHz or less to the cathode electrode. 2. A bias potential (V ₁ ) of the cathode electrode when a bias voltage is applied during high-frequency discharge, and a self-bias potential (V ₂ ) of the cathode electrode when a bias voltage is not applied during high-frequency discharge. The plasma CVD apparatus according to claim 1, wherein the bias voltage is applied to the cathode electrode so that the voltage is 0V <V ₁ −V ₂ ≦ 200V. 3. A means for detecting a floating potential of a plasma space in which the plasma is formed, and a means for controlling the bias voltage applied to the cathode electrode based on the floating potential of the plasma space. Alternatively, the plasma CVD apparatus described in 2. 4. The cathode electrode has a cylindrical shape,
The cathode electrode constitutes a part of the reaction vessel, a counter electrode is arranged inside the cathode electrode, and a shield member is arranged outside the cathode electrode with a distance from the cathode electrode of 3 mm or more. The plasma CVD apparatus according to 1 or 2. 5. The plasma CVD apparatus according to claim 4, wherein the distance between the cathode electrode and the shield member is in the range of 1 cm to 10 cm. 6. The oscillation frequency of the high frequency power source is 40 MH.
The plasma CVD apparatus according to claim 1 or 2, which is in the range of z to 250 MHz.