JPH0744028B2 - Glow discharge device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glow discharge device, and more specifically, deposition of a thin film on the surface of a substrate or etching of the substrate surface causes plasma damage and pinholes. The present invention relates to a glow discharge device that operates at a sufficient speed.

[Conventional technology]

In recent years, a method of depositing or etching a thin film by glow discharge has been favorably used as a plasma CVD apparatus or a plasma etching apparatus in various industrial fields such as semiconductor element manufacturing, and will continue to be used in the future. It is expected that the fields of application will further expand as the application development of functional thin film elements progresses.

The equipment itself for depositing thin films by glow discharge is the Journal of Polym
er Science) 44, 551, 1960 years as reported by Goodman the long history, parallel plate capacitively coupled electrode electrode structure for generating the glow discharge is also currently used at that time had already been used. The initial application was for the deposition of organic thin films and surface modification.
Year, UK ITT STL Division of Sterling and Swann in Yotsute the Si ₃ N ₄ film deposition (Soritsudo State Electronics) (Solid State Electronics) 8, reference 653,1965)
In 1970, Texas Instruments (T
Since Alan Reinberg of I) developed a plasma reactor for the purpose of Si ₃ N ₄ deposition (see US Pat. No. 3,757,733), application to semiconductor device manufacturing process has been tried in earnest, and now IC It has been put to practical use as device passivation. However, until now, essentially no technical improvements have been made to the glow discharge generation part, and the glow discharge generation electrode structure, which is the heart of the device, is basically the same as the parallel plate capacitive coupling type electrode. It can be regarded as.
However, along with the demand for fine processability such as VLSI circuits, the demand for film quality has also increased, and the conventional parallel plate capacitively coupled electrode device is used for plasma damage and pinholes due to high energy ions during glow discharge. Due to the above problem, it will not be possible to use it in future device processes.

On the other hand, the plasma etching equipment was first used in the semiconductor element manufacturing process for resist stripping by the inductively coupled electrode device, and then the parallel plate capacitively coupled electrode device was used for the poly-etching because of the demand for microfabrication. -Si, Si ₃ N ₄ , S
It has been adopted for etching of iO ₂ and Al one by one, but currently, the reactive ion etching device is the mainstream among the parallel plate capacitively coupled electrode devices which are more excellent in microfabrication. Since reactive ion etching originally uses a physical reaction by ion irradiation, anisotropic etching is possible.
Damage (including resist damage) is unavoidable and will be difficult to use in high-speed etching and future VLSI circuit element manufacturing.

[Problems to be solved by the invention]

Recently, a thin film forming method using DC or AC glow discharge utilizing a weak electric field region has been developed (Japanese Patent Laid-Open No. 54-91048), and by using the weak electric field region, a thin film with less plasma damage and pinholes. Has been confirmed to be formed. In the future, the glow discharge using the weak electric field region may be adopted for forming various high quality thin films, but this method uses the plasma reaction in the weak electric field region instead of the strong electric field region. Therefore, the productivity is insufficient, that is, the film forming speed or the etching speed is insufficient.

On the other hand, the impedance between the electrodes of the glow discharge device using the conventional parallel plate capacitively coupled electrodes is about 1 KΩ at the highest, and thus the commercially available impedance / matching circuit for the glow discharge device is at most 2.5 KΩ or less. In general, it has been considered that a high impedance is not suitable for a plasma generation glow discharge device because a discharge current becomes difficult to flow when the impedance becomes high, resulting in an unstable glow discharge.

[Means for solving problems]

The inventors of the present invention have conducted intensive studies to develop a device having a high film formation (etching) rate for a glow discharge device using a weak electric field region, and as a result, in the glow discharge using a high frequency (several hundred Hz to several hundred KHz) power source. It was surprisingly found that the higher the impedance between the electrodes, the higher the film formation rate under the condition of constant power supply. It has been found that a glow discharge device capable of high-speed film formation (etching) can be obtained by setting the impedance between the electrodes within a certain range.

That is, the gist of the present invention is to form a weak electric field region by glow discharge using a high-frequency power source, and use the weak electric field region to deposit a thin film on the surface of a substrate arranged on one electrode of an electrode pair. Or in a glow discharge device for etching the surface of the substrate, the impedance between the electrodes is in the range of 2.5 kΩ to 40 kΩ when the power of the high frequency power source is 30 W and the frequency is 25 kHz. It exists in the glow discharge device.

In the present invention, when the reaction product of the plasma reaction due to glow discharge is volatile, it is etched, and when it is non-volatile, it is thin film deposition.

Further, the substrate includes not only a plate-shaped one but also a drum-shaped one and the like.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a cross-sectional view of a glow discharge device in the weak electric field region of the present invention. A cylindrical ceramic pillar 6 is arranged on a metal base (for example, aluminum or stainless steel) 5 vacuum-bonded to the housing 4, and an aluminum circle having a thickness of 15 mm and a diameter of 180 mm is mounted on the ceramic pillar 6. The plate electrode 2 is arranged. The substrate 1 supported by the electrodes 2 is a silicon wafer (e.g. 4 inch size). The counter electrode 3 is an aluminum disc plate having an inner diameter of 80 mm, an outer diameter of 150 mm and a wall thickness of 2 mm, and the electrode 2 is a desired gear (for example, 8 m).
m) is kept. FIG. 2 (a) shows a front view and a plan view of the electrodes 2 and 3. The vacuum pump 12 uses a valve V and a nipple to make the base 5 (for example, SUS3
04, metal such as Al). The gas is guided to the inside of the housing 4 by the connectors 7 and 8 through the base 5 and the insulator tubes 9 and 10. The measuring instrument VG is a capacitance manometer for measuring the pressure inside the housing 4. The signal from the instrument VG automatically adjusts the butterfly valve 11 by a servo mechanism to maintain the desired pressure in the housing 4. By keeping the pressure in the apparatus constant, glow discharge can be stably performed and uniform film formation (etching) can be performed. The high frequency power supply is designed to be impedance-matched by a matching transformer 13, and the power is supplied by a conductive wire (not shown) connected through an insulated electrical bushing 14 embedded in the base 5. A high frequency power source (not shown) is applied between the electrode 2 and the counter electrode 3. Resistance heaters 16 and 17 are incorporated inside the electrode 2 for heating the electrode 2 and are connected to a control power source (not shown) through conductors 18 and 19 and insulating bushings 20 and 21.

The operation is performed as follows.

After exhausting the inside of the housing 4 to a pressure of about 0.01 Torr or less by the pump 12, a desired gas is guided through the insulator tube 9 by a mass flow controller (not shown). For example, for Si ₃ N ₄ film formation, He-based 10% diluted SiH ₄ and NH ₃ , SiO ₂ films are formed using He.
Trimethylaluminum and N ₂ O are guided through 9 to form a 10% diluted SiH ₄ and N ₂ O, Al ₂ O ₃ film, and in the case of Si ₃ N ₄ film formation, NH ₃ gas, SiO ₂ film or N ₂ O for Al ₂ O ₃ film formation
The gas is guided through the insulator tube 10 into the housing 4 and the valve 11 is adjusted to maintain the desired pressure in the housing 4 (eg, 1.0 Torr). In the case of etching, only the insulator tube 9 is used to introduce CF ₄ and O ₂ gas to a silicon wafer, for example. The electrode 2 and the counter electrode 3 are a cathode and an anode, and a desired electric power (for example, 30 W) is supplied between the electrode 2 and the counter electrode 3 to start glow discharge.

2 (b) to (d) show another example of the electrode structure of the present invention.

Referring to FIG. 2 (b), this electrode has a thickness of 15 mm and a diameter of 180 mm.
mm aluminum disc-shaped electrode 22 and outer diameter 30 mm x wall thickness 1 mm x height 1
A 30 mm copper cylindrical counter electrode 23 has a structure in which it is kept at a desired gear (for example, 8 mm), and the electrode 22 and the counter electrode 23 are a cathode and an anode, and a desired electric power for initiating a glow discharge in the meantime. (For example, 30 W) may be supplied. Second
Referring to FIG. (C), the present electrode has an aluminum disc-shaped electrode 24 having a thickness of 15 mm × a diameter of 180 mm and a copper cylindrical counter electrode 25 having an outer diameter of 30 mm × a wall thickness of 1 mm × a height of 130 mm, which is a desired gear tap ( For example 8m
m) and the counter electrode 25 is further covered with a Teflon insulating cap 26, so that the outside of the counter electrode 25 is exposed only at a height of 2 cm. As described in the figure, the discharge can be contained only in a desired portion. Electrode 24 and counter electrode
Reference numeral 25 denotes a cathode and an anode, between which a desired electric power (for example, 30 W) is supplied to start glow discharge.

Referring to FIG. 2 (d), this electrode has a thickness of 20 mm and a diameter of 180 mm.
Aluminum disk-shaped electrode 27 and outer diameter 6 mm x wall thickness 1.5 mm x length 12
0mm stainless steel (SUS316) cylindrical counter electrode 2
The structure consists of 8 (sideways).

In the present invention, the power range of the high frequency power source is about 20 W to several hundred W, but when the power is increased to some extent, the impedance between the electrodes decreases. This is considered to be due to the transition from glow discharge due to γ action to arc discharge due to thermionic or strong electric field effect.

The frequency of the high frequency power supply is from several hundred Hz to several hundred KHz, preferably 5KH
Select from the range of z to 100 KHz. As is clear from FIG. 6, the impedance between the electrodes changes with frequency, but when the frequency is 25 KHz, it is 2.5 KΩ to 40 KΩ, preferably
It is 4KΩ to 25KΩ. If it is lower than 2.5 KΩ, the film forming (etching) speed is not sufficient, and at 40 KΩ, the withstand voltage of the impedance matching transformer is high because of impedance matching.
Since the supply power of 100W exceeds 2000V (effective value), there is a problem in terms of device safety and electrical insulation.

FIG. 3 shows an example of a glow discharge device of the present invention in which discharge is contained only in a desired portion. That is, under high power and high vacuum conditions, the metal base 5 shown in FIG.
Since plasma is likely to be generated at the exhaust port, and plasma is particularly concentrated at the exhaust port, the uniformity of the film thickness is deteriorated and the film formation rate is likely to decrease. However, in the apparatus shown in FIG. 3, plasma is generated at the base 5. This is to prevent this.

In FIG. 3, an electrode 30 supporting a substrate 29 and a counter electrode 31
Is held in a desired gear, and a counter electrode 31 is provided in a vacuum container composed of a pyrex glass housing 32, which is an insulator, a stainless steel base 33, and an electrically insulated aluminum lid 34.
A Teflon disk 35 is placed between the base 33 and the base. The exhaust has a gap of about 10 mm between the housing 32 and the disk 35, and the exhaust port
Exhausted to 36. Substrate temperature when He-based 10% diluted SiH ₄ and 100% NH ₃ were used at a pressure of 1.0 Torr and a power supply of 50 W.
No plasma discharge was observed on the base 33 at 300 ° C., the film thickness distribution was improved, and the uniformity was increased. Further, it is also an effective means to magnetically contain the plasma discharge only in a desired portion by an external magnetic field.

FIG. 4 is a plan view 1 of the electrode structure of the apparatus suitable for mass production.
Here is an example:

In FIG. 4, an aluminum disk-shaped electrode 37 having a wall thickness of 15 mm, an inner diameter of 30 mm and an outer diameter of 250 mm and a copper ring-shaped counter electrode 38 having a wall thickness of 1.5 mm, an inner diameter of 10 mm and an outer diameter of 20 mm have a desired gear tap (5 mm. Substrate 39, which is a 4-inch wafer, is set on the electrode 37. The electrode 37 and the counter electrode 38 are a cathode and an anode, and supply desired electric power for initiating glow discharge between them. This electrode structure can process four 4-inch wafers at the same time, but an electrode structure in which the wafer size and the number of processed wafers are changed according to the purpose is also included in the scope of the present invention.

FIG. 5 shows an example of a plan view in which a plurality of electrodes according to the present invention are arranged in the same large casing 40, and a disc-shaped electrode 41 made of aluminum and a counter electrode (not shown) made of copper are paired. A substrate 42, which is a silicon wafer, is set on each electrode 41. When electric power is supplied to each electrode 41 and the counter electrode (not shown) at the same time, the impedance of each electrode pair is 2.5 KΩ or more because it electrically forms a load in which a plurality of resistors are connected in parallel. However, the impedance of the entire device may be less than 2.5 KΩ, but such an embodiment is also included in the scope of the present invention.

In order to make it an industrial mass production apparatus, it is effective to provide the apparatus of the present invention with an automatic transfer mechanism such as belt transfer, walking beam transfer, robot arm transfer, etc., and especially the robot arm transfer mechanism is preferable. . Also, for those with load / lock system in the reaction chamber and for multi-layer film formation,
A device equipped with a mechanism such as a separate reaction chamber for separating three chambers to prevent auto-doping is also effective as a mass production device.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Example 1 The apparatus shown in FIG. 1 was used, and electrodes shown in FIG.
Each electrode structure of (d), the outer diameter of the counter electrode of electrode structure (b) 30mm
Impedance between electrodes when the frequency of the high frequency current was changed using the electrode structure (b ') with 20 mm and the electrode structure (c') with the outer diameter 30 mm of the counter electrode of electrode structure (c) of 20 mm and The film formation rate was measured. The pressure inside the housing is 1.0T
Orr, supply current is 30W, 4 inch silicone wafer is used as substrate, and 10% SiH ₄ and 100% NH ₃ are used as gas.
The substrate temperature was kept constant at 300 ° C. and the measurement was performed. The impedance between the electrodes was obtained from the tap position by performing impedance matching by switching the tap of a matching transformer in which the impedance was changed according to the tap position. The film thickness of the formed thin film was obtained by optical interference method assuming that the refractive index of Si ₃ N ₄ was 2.0.

The results are shown in Table 1 below.

From Table 1, it can be seen that the lower the frequency, the higher the impedance between the electrodes and the higher the film formation rate.

FIG. 6 shows the relationship between the frequency and the impedance between the electrodes, and FIG. 7 shows the relationship between the impedance and the film formation rate. In the figure, △ indicates the electrode structure (a),
○ indicates (b), ● indicates (b ′), □ indicates (c), ■ indicates (c ′), × indicates
Indicates the value for (d).

Comparative Example 1 In the apparatus shown in FIG. 1, the electrode having the structure of (b) was used, glow discharge was performed by DC power, and the inter-electrode impedance and the film formation rate were measured.

The pressure in the housing, the used gas, the type of the substrate, and the temperature were set in Example 1.
When the power supply voltage was set to 630 V (constant) (no matching transformer was used), the discharge current was initially 7 mA and the impedance was about 90 KΩ. The discharge was unstable, and the film formation rate was 50Å / min in the initial 30 minutes.

〔The invention's effect〕

According to the present invention, there is provided an apparatus suitable for mass production, which can perform deposition of a thin film that does not generate plasma damage or pinholes or etching that does not generate plasma damage at a sufficient film formation speed or etching speed. can do.

The device of the present invention is not limited to the semiconductor element manufacturing process, but an optical IC,
It is suitable for high-quality plasma processing in various fields such as a-Si (amorphous silicon) thin film for solar cells.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the glow discharge device of the present invention. 2 (a) to 2 (d) are electrode structures (a) used in the device of the present invention.
FIG. 4A is a front view and FIG. FIG. 3 is a cross-sectional view of the glow discharge device of the present invention. FIG. 4 shows a plan view of the electrode structure used in the present invention. FIG. 5 shows a plan view when a plurality of electrodes are used. FIG. 6 is a diagram showing the relationship between the frequency and the impedance between the electrodes in Example 1, and FIG. 7 is a diagram showing the relationship between the impedance and the film formation rate.

Claims (6)

[Claims] 1. A weak electric field region is formed by glow discharge using a high frequency power source, and the weak electric field region is used to form one of the electrode pairs.
In a glow discharge device in which a thin film is deposited on the surface of a substrate arranged on one electrode or the surface of the substrate is etched, the power of a high frequency power source is 30 W and the frequency is 25 kHz.
, The impedance between the electrodes is 2.5 kΩ to 40 kΩ
A glow discharge device characterized by being within the range. 2. The glow discharge device according to claim 1, wherein the frequency of the high frequency power source is selected from the range of 5 kHz to 100 kHz. 3. When the frequency of the high frequency power supply is 25 kHz,
The glow discharge device according to claim 1 or 2, wherein the impedance between the electrodes is in the range of 4 kΩ to 25 kΩ. 4. The glow discharge device according to claim 1, further comprising means for matching the impedance of the high frequency power source with the impedance between the electrodes. 5. The glow discharge device according to any one of claims 1 to 4, further comprising means for adjusting a pressure in the device to stabilize the glow discharge. 6. The glow discharge device according to any one of claims 1 to 5, wherein the glow discharge is contained by an electric field or a magnetic field so as to generate the glow discharge only in a desired portion. .