JP2650046B2 - Thin film forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field The present invention relates to an amorphous silicon (a-Si: amorphous silic) formed by a plasma CVD method under a pressure near the atmospheric pressure.
on) and a device for forming a thin film containing Si such as silicon nitride (SiN).

Normally, amorphous silicon a-Si films containing several at% to several tens at% of H in the film are regarded as promising materials for low-cost solar cells. In addition, it is also used as a photosensitive material for copiers, image sensors, optical sensors, and thin film transistors. It has the advantage that it is cheaper and has a larger area than single crystal Si.

SiN is important as a passivation film for semiconductor devices.

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

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

Excitation energy is provided not in heat but in the form of kinetic energy of electrons and ions in the plasma and chemical energy of neutral radicals. Therefore, the temperature of the substrate can be lower than that of the thermal CVD.

For this reason, the plasma CVD method can form a thin film on a low-cost glass substrate or a polymer film having poor heat resistance.

As for amorphous silicon a-Si, a film formation method by glow discharge was invented by Spear, so that a stable one can be manufactured. WESpear, PGLecomber: Sol
id Commun., 17, p1193 (1975) This applies a light current of 100 kHz to 13.56 MHz to a parallel plate type electrode, and applies SiH ₄ / H ₂ , SiH ₄ -S at a low pressure of 0.1 to ₂ Torr.
Glow discharge is caused in a mixed gas such as iF ₄ / H ₂ .

Of course, a dopant may be added. This is PH
It is performed by mixing gas such as ₃ / H ₂ and B ₂ H ₆ / H ₂ .

(B) Prior art Since the invention of Spear, a-Si manufacturing equipment has been continuously improved, but basically, glow discharge is performed at low pressure, and H ₂ is used as a carrier gas. Have been.

Glow discharge does not occur unless the pressure is as low as about 0.1 to 10 Torr. Thus, such a pressure was chosen. Therefore, the container had to be a vacuum chamber and a vacuum pump was installed.

If the semiconductor wafer is a substrate, the dimensions are small,
The vacuum vessel need not be too large.

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

However, the plasma CVD method needs to maintain the plasma by maintaining the glow discharge, but the three glow discharge can be maintained stably only in a vacuum (about 0.1 to 10 Torr). Since a film can be formed only in a vacuum, if a large-area product is to be manufactured, the entire vacuum container must be enlarged.

 A high-power evacuation device is required.

Then, the equipment becomes extremely expensive.

(C) Atmospheric pressure plasma CVD method One of the features of an a-Si film is that it is inexpensive.

However, recently, under atmospheric pressure, plasma CVD
An invention was made that enabled the law.

 JP-A-63-50478 (S63.3.3 published).

This is to make a thin film of carbon C. For example, CH ₄ , C
The F ₄ as a raw material gas, but to which is added 90% He gas.

Because of the large amount of He gas, glow discharge can be maintained even at atmospheric pressure. Since it is under atmospheric pressure, a vacuum chamber and a vacuum exhaust device are unnecessary. The cost of forming a thin film can be significantly reduced.

 I think this is a great invention.

An important point of this method is that glow discharge occurs even at atmospheric pressure and is stable because He gas is used.

The inventor explains why He is as follows.

(A) He is easily excited by discharge.

(B) He has many metastable states and can produce many active particles in an excited state.

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

(D) In He, ions are easily diffused. Therefore, the discharge is likely to spread.

Naturally, the mixing ratio of He and CH ₄ becomes extremely important.

According to the description of the specification, at 92: 8, the spread of the glow discharge becomes narrower, and at 90:10, the corona discharge becomes
When 9.5: 10.5, spark discharge occurs.

FIG. 2 shows an apparatus disclosed in JP-A-63-50478.

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

Below the cylinder 12 is the electrode 14. RF oscillator 16, cylindrical
An RF voltage is applied to electrode 14 via a metal rod that passes through 12.

A support substrate (conductor) 17, an insulator 18, and a sample substrate 19 are provided below the container. There is also an annular external electrode 20.

A mixed gas of He and CH ₄ (the case of He, CH _4, CF ₄ also)
Is supplied from the gas inlet 21 at the upper end of the cylinder 12. This gas flows down the inner cylinder, passes by the side of the electrode 14, hits the data substrate 19, partially reacts to form a thin film, and the rest is discharged from the side gas outlet 22.

Glow discharge occurs between the electrode 14 and the supporting substrate (data electrode) 17.

According to this specification, the present invention also states that "the present invention can be similarly applied to the formation of other thin films such as a silicon nitride film, an amorphous silicon film, and a silicon carbide film."

(D) Problems to be Solved by the Invention According to the invention of Japanese Patent Application Laid-Open No. 63-50478, "at a pressure in the range of about 200 Torr to 2 atmospheres, about 90% or more of rare gas and film component A thin film formed on a substrate by forming a gaseous mixture with a gas containing nitrogen into a plasma state by glow discharge and forming a thin film on the substrate.

The present inventors have attempted to make a-Si according to this disclosure.

In order to produce a-Si, a mixed gas of Sih ₄ gas and He gas was used. The pressure is atmospheric pressure.

(I) Since it is sufficient that the He gas is 90%, Si
H ₄ : He = 10: 90 (volume ratio). When this was attempted, an arc discharge occurred and no glow discharge occurred.

(Ii) When the ratio of SiH ₄ / He was further reduced, a stable glow discharge could be generated between the electrodes.

(Iii) However, SiH ₄ gas is extremely easily decomposed. For this reason, the SiH ₄ does not enter the plasma region and is decomposed at the outer peripheral portion. Particle size of 0.05 ~
Dust consisting of fine powder of about 0.5 μm was only deposited.

An a-Si thin film could not be formed on the sample substrate. That is, from these facts, the invention of JP-A-63-50478 can be used for CH ₄ / He, but the a-S by SiH ₄ / He
It can be seen that i-film cannot be used as it is.

Further, the present inventor tried to form a large-area carbon film with a CH ₄ / He mixed gas, as disclosed in Japanese Patent Application Laid-Open No. 63-50478.

(I) When the RF electrode 14 was a flat plate, the discharge was concentrated on the periphery of the electrode 14, and a uniform film could not be obtained.

(Ii) It was necessary to make the RF electrode 14 brush-like in order to avoid the above-mentioned concentration of discharge, but in this case as well, if the diameter of the outer edge of the RF electrode exceeds 40 mm, the discharge also concentrates on the peripheral portion of the electrode 14. A uniform film could not be obtained.

(E) Objective It is an object of the present invention to provide an apparatus for forming a thin film of a-Si, SiN, or the like at atmospheric pressure by a plasma CVD method. It is another object of the present invention to provide an apparatus for forming a large area thin film. It is another object of the present invention to provide a thin film forming apparatus that effectively utilizes a mixed gas and has a small gas loss.

(F) Apparatus of the present invention When the gas is SiH ₄ / He, glow discharge does not occur if He is 90%. According to the experiments conducted by the present inventors, the ratio of SiH ₄ is even smaller than 10% (0.1), it was found that must be SiH ₄ / the He speaking ^10-4 to a ratio of ^2.

Further, since the raw material gas does not easily enter into the glow discharge, the flow does not flow from the top to the bottom as in JP-A-63-50478. Thus, the raw material gas was allowed to flow to the vicinity of the center between the electrodes.

The flow rate of the mixed gas sent between the electrodes within a unit time is Q
And the volume of the discharge space is S I am trying to be.

Furthermore, in order for the discharge to occur evenly between the parallel plate electrodes, a high resistance body is located on both electrodes. The resistivity r of this resistor is 10 ¹¹ Ωcm or more. The high resistance body is used as the upper wall and the lower wall facing each other in the film forming chamber. That is, a box-shaped film forming chamber including an upper wall and a lower wall made of a high-resistance body is used, and electrodes are attached to the outside thereof.

 As described above, the present invention has three features.

(1) Gas mixture ratio (2) The gas is parallel to the electrode plate, and the flow rate Q is (3) An electrode plate is mounted outside a box-shaped film forming chamber having an upper wall and a lower wall made of a high-resistance body.

 FIG. 1 illustrates a thin film forming apparatus according to the present invention.

At least the upper and lower walls of the box-shaped film forming chamber 1 are 10 ¹¹ Ω.
It is made of a high resistance body of cm or more. Outside the film forming chamber 1,
Parallel plate electrodes 2, 3 facing each other are provided. One is grounded. This is called a ground electrode 3.

 The other is referred to as the non-ground electrode 2.

The film forming chamber 1 has an upper wall 4 and a lower wall 5 facing each other.
This is, of course, a high resistance body. The ungrounded electrode 2 is attached to the outside of the upper wall 4. The ground electrode 3 is attached to the outside of the lower wall 5. A heater 9 is provided near the ground electrode 3.

The reason why the upper and lower opposing upper and lower walls 4 and 5 are inserted between the electrodes 2 and 3 is not to cause glow discharge locally but to cause the glow discharge to occur widely in the entire electrode plate.

The sample substrate 6 is placed in the film forming chamber 1 at a position just above the ground electrode 3.

A high frequency power supply 8 is connected to the non-ground electrode 2. this is,
For example, a 13.56 MHz RF oscillator and an amplifier can be used.

A nozzle 7 and a gas outlet are provided on the sides of the film forming chamber 1 so that the gas flows as a parallel flow in the space between the parallel plate electrodes.
10 is provided.

The mixed gas of the source gas and He is blown from the nozzle 7 into the inside of the film forming chamber 1.

The flow rate Q of the mixed gas is 1 / Q with respect to the volume S of the discharge space.
sec ^-1 to 10 ² sec ¹ .

The discharge space volume S is determined by the distance g between the sample substrate 6 and the upper wall 4,
It is given by the product of the area A of the electrodes. S = gA.

(G) Function The mixed gas of the source gas and He is drawn in from the nozzle 7.
A high frequency voltage is applied to the electrode 2.

 The pressure is at or near atmospheric pressure.

Glow discharge occurs between the electrodes. Since the proportion of He is large, glow discharge occurs even at atmospheric pressure, and is maintained stably.

The mixed gas is excited by the glow discharge to become plasma.

The sample substrate 6 is heated in advance by the heater 9. A thin film is formed on the substrate 6.

When the source gas is SiH ₄ , an a-Si thin film is formed in addition to SiH ₄ .
When ammonia NH ₃ is added, a thin film of SiN can be formed. For the formation of other thin films, a known reduced pressure plasma CV
The source gas used in the method D may be used.

The reason why the high-resistance element is interposed between the electrodes is to expand the range in which the glow discharge occurs and to make the discharge intensity uniform.

Unreacted gas and reaction products are removed from the gas outlet 10 together with He.

Gas is provided as parallel flow to the parallel plate electrodes, the Q / S is in 1 to 10 ² / sec, the raw material gas can reach the center of the electrode, i.e., the even uniform thin film is generated wide sample substrate.

If the gas flow rate Q is insufficient, the raw material gas undergoes a polymerization reaction at the outer edge on the gas inlet side of the glow discharge region, and becomes fine dust. Thus, the gas flow rate Q must be such that it replaces the volume S of the discharge space in at least one second.

If the gas flow rate Q is too large for the reaction, not only is the gas wasted unnecessarily, but also the film forming speed is reduced.

For this reason, Q / S is 1 to 10 ² / sec.

Next, the ratio of SiH ₄ / He when the source gas is SiH ₄ will be described.

Since SiH ₄ is diluted with He, the discharge sustaining voltage is low. If He is 100%, glow discharge can be maintained at atmospheric pressure. Since the amount of SiH ₄ mixed is small, glow discharge is possible even under atmospheric pressure.

By the action of He, transition to arc discharge can be prevented.

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

If the ratio of SiH ₄ / He exceeds 10 ^-2 , glow discharge cannot be maintained. Transition to arc discharge. Conversely, Si
If the H ₄ / He ratio is less than 10 ⁻⁴ , the film forming rate is undesirably reduced.

When using another source gas,
A preferred range of the ratio to He can be defined.

Since there are an upper wall and lower walls 4 and 5 which are high resistance bodies,
No DC current flows between the three. It becomes only exchange. Further, since the current density per area is limited, the plasma is easily 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 pair of improved walls 4 of the non-grounded electrode 2.

As g is smaller, glow discharge occurs more uniformly in the electrode surface.

 The value of g is desirably 10 mm or less.

However, if the distance is too close, it is difficult to uniformly set the distance between the pair enhancement wall 4 and the sample substrate 6. This is because a slight inclination or unevenness becomes a problem.

Practically, the value of g is preferably 0.1 mm or more. In the case of the present invention, g is fixed. Therefore, g cannot be treated as a variable. However, since g is determined in a stable manner as a film forming chamber, it is easy to set g to a value just before 0.01 mm.

Further, in order to prevent thermal damage to the improvement wall and the lower walls 4 and 5 due to local plasma heating, it is desirable that the material of the high-resistance film forming chamber 1 has a small thermal expansion coefficient.

In the present invention, the electrodes are outside the film forming chamber. For this reason,
The discharge space S can widely occupy the inside of the film forming chamber.
The film forming chamber can be used effectively. All of the introduced mixed gas passes through the discharge space S. A mixed gas is also used efficiently. This is important.

One of the features of plasma CVD is that it can be processed at low temperatures. However, heating is still required.

When the source gas is SiH ₄ , if the temperature of the sample substrate is too low, the film becomes rough and rough. It is inferior in electrical, physical and chemical terms and cannot be used.

If the temperature is too high, H is not taken into Si and the defect density increases. The characteristics of amorphous Si are stabilized because an appropriate amount of H is contained.

For this reason, the substrate temperature T _S when using SiH ₄ is preferably 150 ° C. ≦ T _S ≦ 400 ° C. The sample substrate may be an insulator such as glass or a metal such as a stainless plate.

The pressure P may be atmospheric pressure P ₀ or the vicinity thereof.

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

The pressure P, the slightly higher than the atmospheric pressure P ₀ can prevent contamination of impurity gases into the deposition chamber 1 from the outside.

The frequency of the high frequency power supply may be between 100kHz and 13.56MHz. The optimum values of the frequency and the power can be determined by the thickness of the high resistance elements 4 and 5 and the gap g between the electrodes.

However, in terms of discharge stability, glow discharge becomes unstable below 1 kHz. Therefore, it should not be lower than 1kHz.

The power of the high frequency power supply is 10 ^-2 W / cm ² to 10 ² W / cm ²
And If it exceeds 10 ² W / cm ² , the high resistance members 4 and 5 are sputtered by ions. Therefore, impurities are mixed into the thin film.

If the power is lower than 10 ^-2 W / cm ² , a substantial deposition rate cannot be obtained.

(H) Example (SiH ₄ / He ratio and Q / S) An a-Si thin film was formed by using the apparatus shown in FIG. 1 while changing the mixed gas ratio and the gas flow rate.

Substrate temperature T _S 250 ° C Pressure P Atmospheric pressure RF power 100W RF frequency 13.56MHz Electrode area 200mm × 200mm Distance between high-resistance elements 5mm High-resistance substance Quartz glass Resistivity r> 10 ¹⁷ Ωcm The above conditions are common.

The SiH ₄ / He ratio was set to five types of 10 ^-5 , 10 ^-4 , 10 ^-3 , 10 ^-2 , and 10 ^-1 .

The value Q / S obtained by dividing the supply gas flow rate Q by the discharge space volume S is 10
^-1 , 10 ⁰ , 10 ¹ , 10 ² , and 10 ³ / sec.

Thus, the film forming speed v at the center of the sample substrate was measured. Table 1 shows the results. The unit is Å / sec.

In this table, the shaded portion (SiH ₄ / He ratio is 1
0 ^-1 ) means that no discharge occurred at RF100W. Furthermore, increasing the RF power resulted in arm discharge.

When Q / S is 10 ⁻¹ , v = 0.
This is because the iH ₄ does not enter the plasma but creates dust around.

From this result, it is understood that the ratio of SiH ₄ / He is preferably in the range of 10 ⁻⁴ to 10 ⁻² .

For the Q / S, it is possible to say that 10 ⁰ ~10 ² / sec is satisfactory.

Further, under the same dynamic conditions as in Example I, an attempt was made to form a TiN film on a quartz glass substrate using the apparatus shown in FIG. 1 using TiCl ₄ and NH ₃ as source gases. Both TiCl ₄ / He ratio and NH ₃ / He ratio are 10
By setting it to ^-1 or less, a stable glow discharge could be maintained. Therefore, Ti production was performed using TiCl ₄ / H = 10 ^-2 , NH ₃ / He
= 10 ^-2 , Q / S = 10 ¹ sec ^-1 . Substrate temperature is 700
C. and the film formation time was 30 minutes. The thickness distribution of the obtained TiN film on the diagonal line of the substrate is shown by a solid line in FIG. It can be seen that the film thickness is uniform at the central part of the discharge and the central part of the electrode.

(G) Comparative Example For comparison, an attempt was made to form an a-Si thin film using the apparatus shown in FIG.

In addition to those shown in FIG. 2, a high-resistance body (quartz glass r> 10
¹⁷ Ωcm) is attached to the electrode.

 The gas flow goes from top to bottom.

 The conditions were as follows.

Substrate temperature T _S 250 ° C Pressure P Atmospheric pressure RF power 100W RF frequency 13.56MHz Electrode area 200mm × 200mm Sample substrate Glass Transparent conductive film These conditions are common, the distance between sample and high resistance body g, SiH ₄ / An attempt was made to form an a-Si thin film by changing the He ratio and the flow rate Q variously.

There were cases where glow discharge occurred and cases where glow discharge did not occur. Even if a glow discharge occurs, only a-Si dust is formed around the plasma. No thin film formation occurred on the sample substrate.

Further, an attempt was made to form a TiN thin film using the apparatus shown in FIG. 2 under the same conditions as in Example II. The film formation time was 30 minutes. In addition to those shown in FIG. 2, a high-resistance body (quartz glass r>
10 ¹⁷ Ωcm) is attached to the electrode. The thickness distribution of the obtained TiN film is shown by a broken line in FIG. At the central portion of the discharge and the central portion of the electrode, the source gas was not supplied, the film thickness was reduced, and it was found that a uniform film was not obtained and the film forming rate was low.

In contrast, in the present invention, it can be seen that a uniform film can be obtained with a large area.

According to the present invention, plasma CVD is performed at a pressure near atmospheric pressure.
By the method, a Si-based thin film such as an a-Si or SiN thin film can be formed. In addition, a uniform thin film having a large area can be formed.

Since it is near the atmospheric pressure, no vacuum chamber or vacuum exhaust device is required.

Since the electrodes are provided outside the upper and lower walls of the deposition chamber,
A wide discharge from the upper wall to the lower wall occurs inside the film forming chamber. All of the mixed gas passes through the discharge space. Therefore, the effect of using the mixed gas is enhanced. Since it is an expensive gas containing He, it is extremely desirable that the utilization effect is high. Further, since the film forming chamber can be made small, the equipment can be made compact.

In the production of a thin film such as a-Si of a solar cell which requires film formation over a large area, the cost required for equipment can be significantly reduced.

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

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an apparatus used for 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 film thickness distribution diagram of a TiN film formed by the method of the present invention and the conventional method measured in a diagonal direction. DESCRIPTION OF SYMBOLS 1 ... High-resistance film formation chamber 2 ... Ungrounded electrode 3 ... Ground electrode 4 ... Enhancement wall 5 ... Opposite lower wall 6 ... Sample substrate 7 ... Gas inlet 8 ... High frequency power supply 9 ... ... heater 10 ... gas outlet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuuji Tomikawa 1-1-1, Koyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Norihiko Fujita 1 Kunyokita, Itami-shi, Hyogo Chome 1-1 Sumitomo Electric Industries, Ltd. Itami Works

Claims (1)

(57) [Claims] 1. A box-shaped film-forming chamber 1 including an upper wall 4 and a lower wall 5 made of a high-resistance material having a parallel resistivity of 10 ¹¹ Ωcm or more and provided on the side of the film-forming chamber 1. The said improvement wall 4,
A gas inlet 7 for introducing a mixed gas containing a source gas and He between the opposed lower walls 5 so as to flow parallel to these walls;
A gas discharge port 10 provided on the side opposite to the gas inlet port 7 for discharging gas, a plate-shaped non-ground electrode 2 provided outside the pair of improvement walls 4 of the film formation chamber 1, And a heater 9 provided in the vicinity of the ground electrode 3. The ground electrode 3 has a plate shape provided on the outside of the opposing lower wall 5 and has substantially the same size as the non-ground electrode 2. Then, the sample substrate 6 is placed at a position directly above the ground electrode 3 and a gas mixture is introduced such that the value Q / S obtained by dividing the gas flow rate Q by the volume S of the discharge space is 1 to 10 ² sec ^−1. A thin film forming apparatus, wherein the thin film is formed on a sample substrate 6 by introducing from a port 7 and causing glow discharge between the non-ground electrode 2 and the ground electrode 3 under a pressure near the atmospheric pressure.