JPH0250967A - Thin film forming method and device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (a) Technical field The present invention relates to the production of amorphous silicon (a-Si) by a plasma CVI method under pressure near atmospheric pressure.
) and silicon nitride (SjN
) and the like.

Amorphous silicon aS1 films, which normally contain several at % to several at % (atomic percent) of H, are considered promising as materials for low-cost solar cells. Other uses include image sensors, optical sensors, thin film transistors, and photosensitive materials for copying machines. than single crystal S1,
It has the advantage of being inexpensive and easily available over a large area.

Further, SIN is important as a passivation film for semiconductor devices.

A thermal CVD method is often used as a thin film forming method. Since this requires heating the substrate, it can only be used with heat-resistant materials.

Therefore, a plasma CVD method has been developed and is in use. This method can form a thin film at a lower temperature than the thermal CVD method.

Excitation energy is provided not in the form of heat, but in the form of the kinetic energy of electrons and ions in the plasma, and the chemical energy of neutral radicals.

Therefore, the temperature of the substrate is lower than that of thermal CVD.

Therefore, the plasma CVD method can form a thin film on a low-cost glass substrate, polymer film, etc. with poor heat resistance.

Since 5pear invented a film forming method using glow discharge for amorphous silicon A-3L, it has become possible to produce stable amorphous silicon A-3L.

W, E, 5pear, P, G, Recomber; 5o
lld Common,, +7゜p1193 (+975
) This is a parallel plate type electrode with a frequency of 100kHz to 13.5kHz.
[Apply an AC voltage of iMHz, 0.1 to 2 Torr
SiH4/H2,5iH4-SiF4/H2 at low pressure of
It causes glow discharge in a mixed gas such as 9.

Of course, dopants may also be added. This is the pH
3/ H2, 82116/ This is done by mixing gases such as H2.

(B) Prior art Since the invention of 5pear, the manufacturing equipment for a-3i has been improved many times, but basically it performs glow discharge at low pressure, and N H2 is used as a carrier gas. Ta.

Glow discharge does not occur unless the pressure is as low as 0.1 to 10 Torr. That's why this kind of pressure is chosen.

Therefore, the container is a vacuum chamber, and if the substrate is a semiconductor wafer or the like, which requires a vacuum evacuation device, the dimensions are small and the vacuum container does not need to be very large.

However, in the case of a-5l, it is often used as a photoelectric conversion material for solar cells. In this case, it is strongly required from a cost standpoint that a large area thin film can be formed all at once.

However, the plasma CVD method maintains glow discharge to keep the plasma stable. Glow discharge occurs in vacuum (0,1-
It can only be maintained stably at a temperature of about 10 Torr). Although films can only be formed in a vacuum, if a large-area film is to be produced, the entire vacuum container must be enlarged.

A high-output vacuum pump is also required.

In this case, the equipment becomes extremely expensive.

(1) Atmospheric pressure plasma CVD method One of the characteristics of the a-5'r film is that it is inexpensive, so if the equipment cost increases, nothing will be achieved.

However, recently, plasma CV under atmospheric pressure
I) An invention was made that made the law possible.

JP-A-63-50478 (S[i3.3.3 published).

This creates a thin film of carbon C. For example, CH4,
CF4 is used as a raw material gas, and 90% or more He gas is added to it.

Because there is a large amount of He gas, glow discharge can be maintained even under atmospheric pressure. Since it is under atmospheric pressure, there is no need for a vacuum chamber or evacuation equipment. I think this is a great invention that can significantly reduce the cost of forming thin films.

The important point of this method is that since He gas is used, glow discharge occurs even under atmospheric pressure and continues stably.

The inventor explains the reason for He as follows.

(a) He is easily excited by discharge.

(b) He has many metastable states and can create many active particles in the excited state.

(c) He active particles dissociate hydrocarbons and hydrogen halides.

(d) Ions diffuse easily in He. Therefore, the discharge tends to spread.

Naturally, the blending ratio of He and CH4 is extremely important.

According to the description in the specification, at 92:8 the spread of glow discharge becomes narrower, at 90:10 it becomes corona discharge, and at 89.5:10.5 it becomes fireworks discharge.

FIG. 2 shows the device disclosed in Japanese Patent Application Laid-Open No. 63-50478.

A cylinder 12 is suspended from above into a vertically long reaction vessel 11.

Below the cylinder 12 is an electrode 14 . An RF lightning voltage is applied from the RF oscillator 16 to the electrode 14 via a metal rod penetrating the cylinder 12 .

Below the container, a support substrate (conductor) 17, an insulator 18,
A sample substrate 19 is provided. There is also a ring-shaped external electrode 20.

A mixed gas of HB (!: CH4 (sometimes He, CH4, and CF4) is supplied from the gas port 21 at the upper end of the cylinder 12. This gas flows down inside the inner cylinder and flows to the side of the electrode 14. The gas passes through and hits the material substrate 19, where it reacts and becomes a thin film, and the rest is discharged from the gas outlet 22 on the side.

Glow discharge occurs between the electrode 14 and the support substrate (material electrode) 17.

The specification also states that the invention "can be similarly applied to the formation of other thin films such as silicon nitride films, amorphous silicon, and silicon carbide films."

(1) Problems to be Solved by the Invention The invention of JP-A No. 63-50478, as per the claim, states that "at least about 90% of the rare gas and membrane components are "A thin film forming method characterized by forming a mixed gas with a gas containing a gas into a plasma state by glow discharge and forming it as a Nj film on a substrate."

The inventor attempted to make a-St based on this disclosure.

In order to make a-3l, a mixed gas of SiH4 gas and He scum was used. The pressure is atmospheric.

(i) Since it is sufficient that the He gas content is 90%, the ratio of 5IR4:He was set to 10:90 (volume ratio). When I tried this, an arc discharge occurred and no glow discharge occurred.

(ii) If the ratio of SiH4/He is further reduced,
We were able to generate a stable glow discharge between the electrodes.

(ii) However, SiH4 gas is extremely easy to decompose.

Therefore, SiH does not enter the plasma region and is
4 will disintegrate. Only dust consisting of fine powder with a particle size of about 0.05 to 0.5 μm was deposited on the outer periphery of the plasma region.

It was not possible to form a thin film of a-5l on the sample substrate. In other words, from these reasons, Japanese Patent Application Laid-Open No. 63-50478
Although the invention of No. 1 can be used for CH4/He, it is not suitable for SiH4.
It can be seen that /He cannot be used as is to form an a-Si film.

(e) Purpose Using SiH4 under atmospheric pressure,
It is an object of the present invention to provide a method for forming a film containing i by plasma CVD.

(Force) When the method gas of the present invention is SiH4/He, when He is 90%,
No glow discharge occurs. According to the inventor's experiments, S
The ratio of iH4 is even smaller than 10% (0,1), and S
It was found that the iH4/He ratio must be 10-' to 10-2.

Let Q be the gas flow rate sent between the electrodes within a unit time,
If the volume of the discharge space is S, then 1/sec≦≦
+02/sec (1).

Additionally, a high resistor is placed on top of both electrodes so that the discharge occurs uniformly between the opposing electrodes. Resistivity r of this resistor
shall be 1011 Ωcm or more.

r ≧ 1011Ωcm As described above, the present invention has three characteristics.

(1) Gas mixing ratio He ■The gas flow JiQ supplied between the opposing electrodes is 1/sec
≦≦102/sec (3) Attach a high resistance element to the electrode plate.

The thin film forming apparatus of the present invention will be explained with reference to FIG.

Inside the film forming chamber 1, electrodes 2.3 facing each other are provided. One side is grounded. This is called the ground electrode 3.

The other electrode will be referred to as the non-grounded electrode 2.

A high-resistance element 4.5 having at least the same size as the opposing electrode surface is pasted on each electrode.

The high resistance element 4.5 is inserted so that the glow discharge does not occur locally but widely over the entire electrode plate.

A sample substrate 6 is placed on the high resistance element 5 of the ground electrode 3.

A high frequency power source 8 is connected to the non-grounded electrode 2 . This can use, for example, a 13.56 MHz RF oscillator and an amplifier.

7 so that gas is supplied to the space between the opposing electrodes.
[A nozzle 7 and a gas exhaust port 10 are provided on the side of 0M2.3.

The SiH4/He scum is blown into the film forming chamber 1 from the nozzle 7.

For the volume S of the discharge space, M of the SiH4/He mixed gas
E ffl Q is Q/S is i 5ec-' ~1G2s
ec-'.

(g) Production A mixed gas of SiH4/He is drawn through the nozzle 7.

A high frequency voltage is applied to electrode 2.

The pressure is at or near atmospheric pressure.

A glow discharge occurs between the electrodes. Since the proportion of He is as high as 90% or more, glow discharge occurs even at atmospheric pressure.
Maintained stably.

The mixed gas is excited by the glow discharge and becomes plasma.

The sample substrate 6 is heated in advance by a heater 9.

An amorphous thin film of SX is gradually formed on the substrate 6.

If ammonia NH3 or nitrogen N2 is added in addition to SiH4, a thin SIN film can be formed.

In addition, if a gas containing carbon such as methane CI (4, ethylene C2H4, acetylene C2H2) is added, SI
When a thin film of C is added, a thin film of SIO is used when laughing gas N20 or oxygen 0□ is added, and when a germane GeH4 is added, a thin film of SIO is used.
A thin film of IG4 can be made. Further, hydrogen H2 may be added to change the amount of H contained in the film. In addition, to perform doping, the volume ratio of P 11 or B2H to the film-forming gas such as SiH4 or CH4 is several percent or less.
, just add.

Here, NH3, N2, CH4, B2, PH3, B2H
8 to SiH4, 90% of the total gas supply
If the above is He, stable glow discharge can be maintained without transitioning to arc discharge. However, C2H
4. When adding C2H2, N20.02, GeH4,
If the ratio to He exceeds 10-2, it will shift to arc discharge, so in order to form a thin film that maintains stable glow discharge, CJ4/He, C2)12/)le
, N20 / 'de10゜/ He, GeH4/
The ratio of He is preferably lo-2 or less.

The reason why the high resistance material is interposed between the electrodes is to expand the range in which glow discharge occurs and to make the intensity of the discharge uniform. The size of this high-resistance body may be at least the same size as the electrode material. It depends on the type of RF power gas used, etc.
It is preferable that the outer side is 5 mm or more larger than the electrode material.

Unreacted gas, reaction products, and the like are removed from the gas outlet 10 along with He.

The waste is supplied between the opposing electrodes, and the Q/S is 1 to +02/
sec, so 5l) I4 gas can reach the center of the electrode. In other words, even if the sample substrate is wide, an amorphous thin film of Si is formed uniformly.

If the gas flow rate Q is insufficient, the 5il14 gas undergoes a polymerization reaction outside the glow discharge region, resulting in fine dust. Therefore, the waste flow ff1Q must be generated for a period of time such that the volume S of the discharge space is replaced in at least 1 second.

On the other hand, if the gas flow rate Q is too large, not only will the gas be wasted, but the film formation rate will decrease.

This is why the Q/S is 1 to 10''/sec.

Next, the ratio of NSiH4/He will be described.

Since SiH4 is diluted with He, the discharge sustaining voltage is low. If He is OO% for a month, glow discharge can be maintained under atmospheric pressure. Since the amount of SiH4 mixed is small, glow discharge is possible even under atmospheric pressure.

The action of He can prevent transition to arc discharge.

Even at the same pressure, the mean free path of gas molecules in He is long. Therefore, plasma spreads easily.

If the ratio of Sin, . . . /He exceeds lo-2, glow discharge cannot be maintained. Transition to arc discharge.

On the other hand, if the SiH4/He ratio is smaller than lo-4, the film formation rate will decrease, which is undesirable.

Since the high resistance element 4.5 is attached to the electrode 2.3, no direct current flows. There will be only interaction. This limits the current density per area, making it easier for the plasma to spread uniformly.

In order to make the film thickness distribution uniform, it is better to narrow the gap g between the sample substrate 6 and the high resistance element 4 of the non-grounded electrode 2.

The narrower g, the more uniformly the glow discharge occurs within the electrode surface.

The value of g is preferably 10 mm or less.

However, if they are brought too close together, it becomes difficult to set a uniform distance between the high resistance element 4 and the sample substrate 6. This is because slight inclinations and irregularities become a problem.

Practically, it is preferable that the value of g is 0.1 mm or more.

Furthermore, in order to prevent thermal damage to the high-resistance element 4.5 due to local plasma heating, the high-resistance element 4.5 is 5IO9
It is preferable to use a material with a small coefficient of thermal expansion, such as

Dust due to decomposition of SiH4 gas may adhere to the vicinity of the non-grounded electrode 2. If such dust adheres to the sample substrate 6, it will cause pinholes to occur. This causes variations in device characteristics and thin film characteristics.

In order to prevent this, it is preferable to provide the non-grounded electrode 2 with heating means or cooling means (not shown).

By doing so, the decomposition reaction of SiH4 does not occur near the non-grounded electrode, and dust adhesion can be prevented.

Let's talk about substrate temperature.

One of the features of plasma CVD is that it can be processed at low temperatures. However, it still needs to be heated.

If the temperature of the sample substrate is too low, the film will have a rough and rough surface. It is electrically, physically, and chemically inferior and is of no use.

If the temperature is too high, H will not be incorporated into Si and the defect density will increase. The characteristics of amorphous S1 are stable because it contains an appropriate amount of H.

For this reason, the substrate temperature T6 is +50°C≦T8≦4θo’c is good.

The sample substrate may be an insulator such as glass, or
It may also be made of metal such as a stainless steel plate.

Pressure P is atmospheric pressure P. Or it may be in the vicinity.

The greatest advantage of the present invention is that there is no need to create a vacuum.

The pressure P is atmospheric pressure P. If it is made slightly higher, it is possible to prevent impurity gas from entering the film forming chamber 1 from the outside.

The frequency of the high frequency power supply is 100kH2 to 13.5 [iM
It may be Hz. The optimum values of frequency and power can be determined by the thickness of the high resistance element 4.5 and the gap g between the electrodes.

However, in terms of discharge stability, glow discharge becomes unstable below IKHz. Therefore, lKH2
Do not:

Also, the power of the high frequency power supply is N 10-”W/cm2
~102 W/cm2. When it becomes larger than 102 W/cm2, the high resistance element 4.5 is sputtered by ions. Therefore, impurities are mixed into the thin film.

If the power is lower than 1O-2W/Cm2, a substantial film formation rate cannot be obtained. Although the electrodes are described as parallel plates, their shape is not limited to parallel plates.
It can be of any shape, such as a circular plate or a mesh. Alternatively, cylindrical electrodes arranged concentrically may be used. Further, the installed electrode 3 is not necessarily required.

(ri) Example I (SIR4/He ratio and Q/S) An a-8t thin film was produced using the apparatus shown in FIG. 1 while changing the mixed gas ratio and gas flow rate.

Furthermore, since it is difficult for SiH4 to penetrate into the glow discharge, the flow is not from top to bottom as in JP-A No. 63-50478, but parallel flow is used, and a considerable m ffl is provided. In this way, the SiH4 gas was allowed to flow into the vicinity of the center between the electrodes.

Substrate temperature T 5250°C Pressure P Atmospheric pressure RF power 30W RF frequency 13.5Ei Hz Electrode area
40mmX 40mm high resistance distance 5
mm High resistance material Silica glass resistivity r >10" Ωcm or more" The second condition is common.

The ratio of SiH4/He is 10-510-' 1O-
There were five types: 310-2IO-1.

The value Q/S obtained by dividing the supply gas flow rate Q by the discharge space volume S is 1
There were five types: 0-'10010'10210''/sec.

In this way, the film formation rate V at the center of the sample substrate was measured.

The results are shown in Table 1. The unit is person/sec.

Table 1 SiH4/He ratio Q/S and substrate center deposition rate V (person/5ee) (Q is gas flow rate cc/sec + S is discharge volume cc) In this table, the shaded area (SiH4/lie A ratio of 10-') means that no discharge occurred at an RF power of 30 W. Although it was possible to generate a discharge by increasing the RF power, it was an arc discharge.

When Q/S is 10-1, v=0, but this is because the raw material gas SiH4 does not enter the plasma and forms dust around it.

From this result, the ratio of SiH4/He is 10-' ~ 10
It can be seen that the range of -2 is good.

Regarding Q/S, it can be said that 10° to IO27 sec is good.

(k) Example ■ (Discharge state and SiH4/He ratio) 1st
The values in the table are the deposition rates at the center of the substrate. Even if the film is formed quickly in the center, it will be of no use if the film is not uniformly formed all the way to the periphery.

In order to form a uniform film, the glow discharge must be uniform.
That is necessary.

Therefore, the glow discharge state was investigated by changing the SiH4/He ratio.

The conditions are the same as in Example (2).

Regarding Q/S, it is known from Table 1 that 10'/sec is the best.

Therefore, with Q/S = 10'/see, Si
The ratio of H4/He is 10-510-' 10-3.1
0-210-'.

The plasma state due to glow discharge is not shown in Fig. 10-1.
If so, it was arc discharge. This is He:S
This means that iH4=9f:9. In other words, H
90% e is not enough.

When the gas mixture ratio becomes 0-2, glow discharge occurs, but the plasma region becomes narrow in the middle of the electrodes.

At lo-3, the glow discharge becomes so strong that the edge of the electrode and the plasma region become almost identical in extent to 10-'
10-', the plasma region protrudes outward in the middle of the electrode.

(J) Example ■ (Resistivity and discharge state) In the present invention, materials with different resistivities are used on the sample substrate, except for the high-resistance material on the ground side electrode, which is exposed on the second side of the electrode. The state of glow discharge was investigated using

The sample substrate was quartz glass r >10"00m soda glass r-10"ΩCm crystalline silicon r<
In the case of 104 Ωcm crystalline silicon, the discharge is not uniform.

It is concentrated near the center. This is because crystalline silicon easily conducts electric current. The discharge is concentrated along the path with the lowest direct current resistance.

This result shows that placing a high-resistance material on top of the electrode is effective for expanding the discharge.

(S) Example ■ (Discharge state and other types of gas/He ratio) NH3 added when producing films such as SIN and SIC
, CH4, etc., the state of glow discharge was also investigated by changing the ratio to He. Other types of gas were used instead of SiH4 gas under the same conditions as in Example (2). Moreover, Q/S was set to 10'/see.

The results are shown in Table 2.

Table 2 Ratio to He and state of glow discharge (Q/S
=IO"/sec) When adding an external gas, stable discharge can be obtained by setting He to 80% or more, but C2H4, C2H2
It can be seen that when adding NGe)+4, it is desirable that the ratio of these gases to He be 10-2 or less.

Next, under the same conditions as the example work, S I H4/He
As a result of producing thin films containing various types of S1 at the gas flow rate ratios shown in Table 3 as "I O-'Q/S~l02sec-", it was possible to obtain Si-based thin films with excellent mechanical and electrical properties. Table 3: Waste flow rate ratio and thin film produced In this table, the X mark indicates that the transition to arc discharge occurs. C2H4, C2H2, N2o1o2, GeH4
(iv) Comparative Example For comparison, an attempt was made to produce an aS1 thin film using the apparatus shown in FIG.

In addition to those shown in Figure 2, high-resistance elements (quartz glass r >
10" Ωcm) on the electrode.

Gas flow is from top to bottom.

The conditions are the same as those in Example ~■, Substrate temperature T 5250'C Pressure P Atmospheric pressure RF power 30W RF frequency 13.5 [iMHz Electrode area
40mmX 40mm sample substrate
Glass transparent conductive film These conditions are common, and the distance g between the sample and the high resistance object is
1SIH4/HQ ratio and flow rate Q are varied to a-
I tried to make a 5l thin film.

There were cases where glow discharge occurred and cases where it did not occur.

Even if a glow discharge occurs, the a-
There is a lot of 5i dust.

No film formation occurred on the sample substrate.

(S) Thin film properties The properties of the a-3l thin film prepared in Example I were investigated.

Band gap Eg = 1.8! ] eV photoconductivity Δσph=1×10″5S/cm photoconductivity
σa = 5×10-”S/cm.

The bandgap is a value calculated by measuring the transmittance in the visible light region and plotting the measured values on a Tauck plot.

The photoconductivity is a value measured using a light source with an A M of 1.5100 mW/cm2.

The larger the ratio of 8011.1 to 04, the more desirable it is as a material for solar cells.

Almost the same photoconductivity Δσph as that of the a-3i film produced by the conventional low-pressure plasma CVD method was obtained.

An a-3i thin film was attached to a glass substrate with a transparent conductive film under the same conditions as in Example I. A-3J thin film was similarly attached to the transparent conductive film (SnO3).

a on the glass substrate described above and the glass substrate with a transparent conductive film.
ESCA analysis was performed on the film on which -8I was formed.

This is shown in FIGS. 5 and 6.

A peak appears near 99 eV. This is sl 2
This is a signal from p electrons.

This allows N to be applied both on the glass substrate and on the transparent conductive film.
It can be seen that it is possible to form a thin film of a-3l.

(S) Effect According to the present invention, plasma CVD is performed at a pressure near atmospheric pressure.
By using this method, Si-based films such as a-S+ and SiN thin films can be formed.

Since the pressure is close to atmospheric pressure, there is no need for a vacuum chamber or evacuation equipment.

In producing an a-3l film for a solar cell that requires film formation over a wide area, the cost required for equipment can be significantly reduced.

Also, since the pressure is high, compared to low pressure plasma CVD,
The film formation rate can be increased.

Note that the volume S of the discharge space is the area A of the electrode,
The distance g between the high resistance element 4 and the sample substrate 6 is increased. In other words, S 2 Ag.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus used in the thin film forming method of the present invention. FIG. 2 is a sectional view of a thin film forming apparatus disclosed in Japanese Patent Application Laid-Open No. 63-50478. FIG. 3 is a diagram showing the state of glow discharge when the ratio of SiH4/He is changed in the method of the present invention. FIG. 4 is a diagram showing differences in discharge states due to differences in resistivity on the sample substrate side (ground side) in the method of the present invention. Figure 5 shows the ESCA analysis results of an a-3i film formed on a glass substrate by the method of the present invention. Figure 6 shows an a-3t film formed on a transparent conductive film on a glass substrate by the method of the present invention. The head showing the results of ESCA analysis of the product formed in 1. Deposition chamber Ungrounded electrode Grounded electrode High resistance object High resistance object Sample substrate Nozzle High frequency power supply Heater Gas outlet Yuiji Tomikawa

Claims (2)

[Claims] (1) The resistivity is 1 on the opposing surfaces of electrodes 2 and 3 facing each other.
High resistance elements 4 and 5 with a resistance of 0^1^1 Ωcm or more are pasted, a sample substrate 6 is placed on either of the high resistance bodies, and 90% or more of the volume of He and at least SiH as a film forming gas are attached.
Including _4, the volume ratio of SiH_4/He is 10^-^4
For a mixed gas of ~10^-^2, the value Q/S obtained by dividing the gas flow rate Q by the volume S of the discharge space is 1~10^2 sec^-
A high frequency voltage is applied between electrodes 2 and 3, and a glow discharge is caused between high resistance elements 4 and 5 under pressure near atmospheric pressure. A thin film forming method characterized by forming a thin film containing Si on a substrate 6. (2) A high frequency wave is generated between the electrodes 2 and 3 facing each other, the high resistance elements 4 and 5 with a resistivity of 10^1^1 Ωcm or more attached to the opposing surfaces of the electrodes 2 and 3, and the electrodes 2 and 3. SiH_4 and He are contained between a high frequency power source 8 that applies voltage, a film forming chamber 1 that surrounds the electrodes 2 and 3 and high resistance elements 4 and 5 and is kept at a pressure near atmospheric pressure, and the counter electrodes 2 and 3. Consisting of a nozzle 7 and a gas outlet 10 provided on the wall of the film forming chamber 1 to supply a mixed gas, and a heater 9 to heat the sample substrate 6, more than 90% of the volume of He and film forming A gas containing at least SiH_4 and having a volume ratio of SiH_4/He of 10^-^2 to 10^-^4 is supplied between opposing electrodes to cause a glow discharge between the electrodes, thereby increasing the height of either electrode. A thin film forming apparatus characterized in that a thin film containing Si is formed on a sample substrate 6 placed on a resistor and heated by a heater 9.