JPH04144128A - Microwave plasma processing equipment - Google Patents

Abstract

PURPOSE:To facilitate uniform and high speed treatment over a wide area and protect a microwave window from breakage and overheat by a method wherein a means which reduces the pressure in a microwave radiator to which the microwave window is attached under conditions which do not generate a discharge is provided to reduce a differential pressure applied to the microwave window through which a microwave is introduced into a vacuum container. CONSTITUTION:A microwave is introduced into an electromagnetic horn 4 of which a microwave radiator is composed from a microwave source 1 through a microwave guide system 2 and a vacuum sealing is provided with a quartz plate 3 in the middle of a waveguide 2a. A quartz partition plate 8 is provided at the opening part of the electromagnetic horn 4 as a microwave window to separate the electromagnetic horn 4 from the reaction chamber 6 of a vacuum container airtight. A pressure on the electromagnetic horn 4 side is reduced by a depressurizing means 16 to reduce a differential pressure between the vacuum chamber 6 and the horn 4 and hence a force applied to the microwave window 8 is reduced and its breakage is avoided. The pressure on the electromagnetic horn 4 side can be selected to be lower than 10<-4>Pa. On the other hand, if a high pressure of 5-50kPa is selected, a cooling means 20 is attached at least to the radiator 4 and the microwave window 8 is cooled by the convection of gas in the radiator 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a plasma processing apparatus used for manufacturing semiconductor devices, electronic parts using thin films such as liquid crystal display elements, line sensors, thin film magnetic heads, etc. In particular, the present invention relates to a plasma processing apparatus suitable for plasma processing such as thin film formation and etching.

[Conventional technology]

As a conventional microwave plasma processing apparatus of this type, one disclosed in, for example, Japanese Unexamined Patent Publication No. 122217/1983 is known. In this case, a discharge tube is installed in the vacuum chamber, a coil is attached to it, a magnetic field is applied to it, and microwaves with the same frequency as the electron cyclotron frequency are introduced through a waveguide to cause a discharge. This decomposes the reactant gas introduced into the vacuum chamber, thereby performing chemical vapor deposition on a substrate, which is a sample placed in the vacuum chamber, or etching a thin film on the substrate.

However, in order to process large-area substrates, a large discharge tube is required, and a large power microwave is also required, but a large discharge tube is subjected to the large force of atmospheric pressure, and There is a high possibility of damage due to heating by the internal plasma and high-power microwaves passing through the tube.In addition, in this type of discharge tube method, the distribution of plasma density reflects the shape of the discharge tube, with the center being higher and the periphery being higher. There is a strong tendency for the part to be lower.

In addition, a microwave emission window provided at the end of the microphone A-wave waveguide is configured as a part of the partition wall of the vacuum container, and a plasma processing apparatus is installed directly below this window to satisfy the electron cyclotron resonance condition. has also been proposed. In this device, the size of the window determines the area that can be plasma processed, so in the case of a device that processes large area substrates,
A large diameter window is required. Therefore, as the window becomes larger, it is necessary to increase the thickness to provide strength. but,
In general, the thickness of the window cannot be increased unnecessarily because it increases absorption of microwaves and causes power loss. In the end, the practical size and thickness of the window was determined from the relationship between the power loss due to the thickness of the window and the strength of the window material, and the reason why it was not possible to plasma-process large area substrates with this type of equipment until now is It is here.

On the other hand, as a different method, there is a method using a gitano coil described in Japanese Patent Application Laid-Open No. 62-254419. However, with this method, when introducing high-power microwaves necessary to generate high-density plasma over a large area, sparks tend to occur at the introduction section, making it difficult to put it into practical use.

[Problem to be solved by the invention]

As described above, the conventional technology does not take uniform processing of large-area substrates into account.1 For example, it is difficult to process liquid crystal display panels using large substrates, and there are also problems such as the inability to process large-diameter wafers. was there.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a microwave plasma processing apparatus that can stably perform uniform microwave plasma processing over a large area. This enables plasma CVD using low pressure, high density microwave plasma.
The goal is to create a device that can be used to process large-area substrates using thin film formation and plasma etching, and that also enables continuous processing and is compatible with mass production.
For example, the performance of thin film manufacturing and thin film etching processing for large liquid crystal display elements, facsimile line sensors, thermal heads, etc. has been significantly improved.

This contributes to cost reduction.

[Means to solve the problem]

In order to achieve the above object, the present inventors have made the following findings as a result of various experiments. That is, the structure of the radiator at the end of the microwave waveguide is, for example, an electromagnetic horn type, and the microwave is expanded to the processing area of the substrate to generate plasma over a large area.

At this time, in order to homogenize the plasma, the microwave introduction window that introduces the microwave into the plasma region is a large-area flat plate made of, for example, quartz, which forms part of the partition wall of the vacuum container and is parallel to the substrate holder. In addition, in order to uniformly decompose the reactant gas in the plasma, a perforated plate was installed close to the microwave window, and the holes in the perforated plate were used to pass the reactant gas between the perforated plate and the microwave window. The configuration was such that the reactive gas was ejected more toward the substrate. It goes without saying that in order to cause microwave discharge, there is a point between the microwave introduction window and the perforated plate that satisfies the electron cyclotron resonance condition. Additionally, when plasma is generated, if atmospheric pressure is applied to this large-area microwave window from the waveguide side, the microwave window is likely to be damaged due to the pressure difference because the inside of the vacuum chamber is vacuum. A pressure reducing means was installed on the electromagnetic horn side (waveguide side) to reduce the pressure difference. However, it is important to set the pressure reduction conditions so that no discharge occurs on the electromagnetic horn side, that is, on the waveguide side, and by doing so, even if the electromagnetic horn side satisfies the electron cyclotron resonance condition, Even if it were possible, no discharge would occur, and no microwave power would be lost due to unnecessary discharge. The pressure on the electromagnetic horn side (waveguide side) that does not cause this discharge is 5 to 50 kPa or 10-4P.
It was found that it is sufficient to set it to a or less. Even if the pressure on the electromagnetic horn side (waveguide side) is reduced, the conditions are set so that no discharge occurs, so there is no need to apply a magnetic field to the electromagnetic horn, and the coil can be made smaller. . Also, the pressure on the electromagnetic horn side (waveguide side) is 5
If ~5QkPa is selected, the microwave window heated by microwaves or plasma will have a cooling effect due to the heat conduction of the gas, and even if the device is used continuously, the window will not be damaged or the reaction gas will not heat up. It was found that it does not cause decomposition and is practical and preferable. In this device description, the structure of the radiator at the end of the microwave waveguide is described as an electromagnetic horn type, but the structure is not limited to this. The present invention is generally applicable to microwave plasma processing apparatuses configured such that there is a point immediately below the window that satisfies the electron cyclotron resonance conditions.

The present invention has been made based on the above findings, and specific means for achieving the object of the present invention will be explained below.

The object of the present invention is as follows: (1) A vacuum container including a gas supply means and an evacuation means, a waveguide for guiding microwaves into the vacuum container, and a waveguide connected to one end of the waveguide. a radiator; a microwave window that seals the opening of the radiator and forms part of the bulkhead of the vacuum container; and an electron cyclotron resonance at the frequency of the microwave immediately below the microwave window in the vacuum container. A microwave plasma processing apparatus comprising means for generating a magnetic field that causes a This is achieved by a microwave plasma processing apparatus configured to reduce the pressure difference applied to the microwave window into which microwaves are introduced. And, more preferably, (2), the pressure inside the radiator connected to the waveguide is set to lX
The microwave plasma processing apparatus according to (1) above, which is a means for reducing the pressure to 10-4 Pa or less or 5 to 50 kPa, also (3) reduces the pressure in the radiator connected to the waveguide. 5～
50 kPa, and at least a cooling means is added to the radiator connected to the waveguide, so that the microwave window is cooled by gas convection within the radiator. This is accomplished using a microwave plasma processing device.

The cooling means preferably includes a cooling pipe arranged around the outer periphery of the radiator, in which a refrigerant such as water or air is circulated, and is water-cooled or air-cooled to exchange heat with the gas inside the radiator. That is to say. Furthermore, more preferably, (4) a depressurized part of the waveguide to which the radiator is connected;
In addition to providing piping to connect to the vacuum container, a safety valve is connected in the middle of the piping to open when the pressure difference between the two exceeds the withstand pressure of the microwave window to prevent damage to the microwave window. By using the microwave plasma processing apparatus according to any one of (1) to (3) above configured, and (5), sealing the waveguide with a material that transmits microwaves in the middle, and opening a microwave window from this part. By the microwave plasma processing apparatus according to any one of (1) to (4) above, which is provided with means for evacuating and depressurizing the space between This is achieved by the microwave plasma processing apparatus according to (5) above, which is configured such that a cooling means is added to the sealed part to cool the sealed part. The cooling means includes water-cooling the periphery of a part of the waveguide sealed with a material such as a quartz plate through which microwaves pass, and the sealed material is cooled from the side of the waveguide maintained at atmospheric pressure with water. It is preferable to blow compressed air directly onto the area for air cooling.

Furthermore, the structure of the radiator connected to one end of the waveguide is preferably one that extends toward the vacuum vessel side, and is preferably an electromagnetic horn type radiator.

Furthermore, the microwave window that seals the opening of the radiator connected to one end of the waveguide and constitutes a part of the partition wall of the vacuum container is highly transparent to microwaves and has heat resistance; Any material may be used as long as it has excellent mechanical strength and is chemically stable, such as a quartz plate, which is practical and preferred.

[Effect]

The electromagnetic horn that constitutes the microwave radiator expands the microwave to the aperture diameter of the horn. Although the microwave intensity is not uniform, if the microwave input power is sufficiently large, the plasma density will be saturated and the plasma density will be uniform. By passing the reactive gas between a perforated plate and a microwave window arranged parallel to the substrate surface and blowing it out from the holes in the perforated plate toward the substrate, the degree of decomposition by the plasma of the reactive gas becomes constant. Acts uniformly on the substrate surface. Microwave windows are exposed to high power microwaves and plasma and are susceptible to heating and surface damage. If the electromagnetic horn side (waveguide side) is brought to atmospheric pressure as in the conventional case, a great force is applied to the microwave window and the window is likely to be damaged. Therefore,
In the present invention, the pressure on the electromagnetic horn side (waveguide side) is lowered to a state where no discharge occurs using a pressure reducing means, reducing the pressure difference with the vacuum container and reducing the force applied to the microwave window, thereby preventing damage to the microwave window. Avoiding. In this case, if the pressure on the electromagnetic horn side (waveguide side) is 10 to 3 Pa to 1 kPa, microwave discharge will occur within the electromagnetic horn and the loss of microwave power will be large, so this region must be avoided. 10
It is also possible to choose the one with a lower pressure of -4 Pa or less,
This is more reliable in order to prevent discharge, but it requires a high vacuum evacuation system and a large conductance in order to evacuation to a high vacuum. Many holes will be made in the waveguide system, resulting in a decrease in microwave transmission efficiency. On the other hand, if you choose one with a higher pressure of 5 to 50 kPa, an oil rotary pump may be sufficient as the exhaust system.
The exhaust hole also needs to be small. In addition, at pressures above 1 kPa, heat transfer by gas convection is almost the same as at atmospheric pressure, and therefore, heat transfer by gas convection cools microwave windows heated by microwaves or plasma. Therefore, it is extremely practical and preferable.

When performing plasma CVD, a gas with a relatively low thermal decomposition temperature, such as monosilane or disilane, is often used as one reaction gas, and in that case, if the microwave window is overheated, thermal decomposition will occur there, causing a reaction. This may cause loss of gas or deterioration of the characteristics of the film formed on the substrate. but,
If the microwave window is cooled as in the present invention, such problems due to overheating of the microwave window will not occur.

〔Example〕

Example 1゜ An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic vertical cross-sectional view of essential parts of a microwave plasma processing apparatus according to the present invention.

A configuration was adopted in which microwaves of 2.45 GHz were guided from a microwave generation source 1 through a microwave waveguide system 2 to an electromagnetic horn 4 constituting a radiator.

A quartz plate 3 is placed in the middle of the waveguide 2a of the microwave waveguide system 2 to provide a vacuum seal, and then the vacuum seal is applied to the valve 1 so that the pressure inside the electromagnetic horn is reduced to 10 kPa by the exhaust pump 16.
The evacuation was controlled using 5.

The opening of the electromagnetic horn 4 has a thickness of 5 m as a microwave window.
A partition plate 8 made of quartz having a diameter of m is placed to seal the space between the reaction chamber 6 and the electromagnetic horn 4 that constitute the vacuum container. A magnetic field is generated by passing an electric current through the electromagnetic coil 5, so that the electron cyclotron resonance point is present in the spatial region between the quartz porous plate 9 directly below the partition plate 8 and the substrate 10 placed on the substrate holder 11. It was set to

The reaction gas is fed into the reaction gas buffer 7 from the gas introduction lower a, passes through a 0.3 mm gap between the partition plate 8 and the perforated plate 9, and is ejected into the reaction chamber 6 from the holes in the perforated plate 9.

The quartz plate 3 sandwiched in the middle of the waveguide 2a is heated as high-density microwaves pass through it, so a cooling water plumber 9 is installed as a cooling means on the flange of the quartz plate 3 to cool the quartz plate 3. Air cooling is also performed by blowing compressed air toward the plate 3 from a nozzle 18 provided on the waveguide side maintained at atmospheric pressure.

Further, the partition plate 8 and the porous plate 9 are heated by microwaves and plasma in the reaction chamber 6.

The following configuration was adopted as a cooling means for this.

That is, a piping 20 for flowing cooling water as a heat exchanger is provided around the outer periphery of the electromagnetic horn 4, thereby indirectly cooling the electromagnetic horn 4 through heat conduction due to convection of air at a pressure of 10 kPa.

The opening diameter of the electromagnetic horn 4 is 400 mm, and the diameter of both the partition plate (microwave window) 8 and the perforated plate 9 is 420 mm, but due to this cooling effect, the center temperature is lower than that of nitrogen plasma with input microwave power of 4 kW. When generated continuously, the balance becomes constant at about 200°C.

If the quartz plate 3 is damaged or the reaction chamber 6 leaks, a pressure difference will occur between the circular electromagnetic horn 4 side and the reaction chamber 6 side.
A safety valve 17 is provided through the communication pipe 21 to prevent the partition plate 8 from being damaged.

This safety valve 17 opens at a pressure difference of 20 kPa, and is configured to prevent pressure above that from being applied to the partition plate 8.

In addition, 12 in the figure is a conductance adjustment valve.

13 is a turbo molecular pump, and 14 is an exhaust pump.

22 indicates a tuner provided in the waveguide.

The partition plate 8 of this example is made of quartz and has a diameter of 420 mm and a thickness of 5 mm. Since the inside of the electromagnetic horn 4 connected to the waveguide is in a reduced pressure state, the pressure applied to the partition plate 8 is reduced. Plasma treatment is possible with sufficient stability even with a certain thickness. However, unlike the conventional device, the electromagnetic horn 4
In the case where the inside of the window is maintained at atmospheric pressure, the minimum thickness of the microwave window 8 for plasma processing to be performed safely is 30 mm, which is about 6 times that of this example, and a safety factor of 3 times is required. 45mm is required. When the thickness of the window increases in this way, power loss due to absorption of microwaves increases significantly, making a practical device no longer possible.

Furthermore, what is important in the present invention is not to simply bring the inside of the radiator (electromagnetic horn) 4 connected to the waveguide into a reduced pressure state, but to make it under reduced pressure so that microwave discharge does not occur even if the pressure is reduced. .

The configuration of the apparatus has been described above. Next, three typical examples of actual plasma processing using this apparatus will be introduced.

Example 2 First, a first example will be described in which a silicon nitride film is formed using this apparatus.

As the substrate 10, a glass disk having a diameter of 300 mm was used, and this was placed on the substrate holder 11.

The reaction gases were monosilane at a rate of 40 cm 3 per minute and nitrogen gas at a rate of 400 cm 3 per minute through the reaction gas buffer 7 and through the holes in the porous plate 9, and then exhausted by the turbo molecular pump 13. The pressure in the reaction chamber 6 was adjusted to 0.4 Pa using a conductance adjustment valve 12. When a 4 kW microwave was applied for 5 minutes to generate plasma, a silicon nitride film was formed with a thickness of 0.60 μm at the center of the substrate and 0.55 μm at the edges.

Example 3 The second example describes a case where a silicon nitride film is etched using this apparatus.

The diameter of the silicon nitride film formed in Example 2 is 300 m.
m glass substrate 10 with a thickness of 0.5 μm as a mask.
An aluminum film patterned into lines and spaces of 3 μm was used as a substrate.

The reaction gas is carbon tetrafluoride containing 3% oxygen at a rate of 90% per minute.
cm' was poured through the holes in the perforated plate 9 and evacuated using the turbo molecular pump 13. The ECR point (electron cyclotron resonance point) is 2.5k, assuming that it is 20 mrn above the substrate 10.
I turned on the W microwave.

As a result, a fairly uniform plasma was generated, and silicon nitride was etched using the aluminum pattern as a resist. Etching rate is 0.08 to 0.0 per minute
The thickness was 85 μm and was substantially uniform over the entire surface.

Example 4 The third example shows an example in which this device was used as an oxygen asher.

Polyimide is applied to a thickness of 1.5 μm on a substrate 10 consisting of a glass disc with a diameter of 300 mm, and a layer of 0.2 μm
A silicon oxide film was formed, and a hole pattern of 2 μm in diameter was formed as a mask pattern in this silicon oxide film, and this was used as the substrate 10.

Oxygen gas was flowed from the introduction lower a through the gas bach 7 at a rate of 100 cm' per minute, the pressure in the reaction chamber 6 was IPa, and microwave power of 2 kW was applied to generate plasma.

As a result, the etching rate of polyimide is approximately 1μ per minute.
m was almost constant over the entire surface.

〔Effect of the invention〕

According to the present invention, a large area can be uniformly processed with microwave plasma, and high-speed processing using high-density microwave plasma can be performed in the manufacture of large-area devices. Furthermore, there is no problem of microwave window damage or overheating, and a large number of substrates can be processed continuously. The coil can also be made smaller in proportion to the processing area for this type of device, and power consumption can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a schematic main part of a microwave plasma processing apparatus according to an embodiment of the present invention. <Explanation of symbols> 1...Microwave generation source, 2...Microwave waveguide system. 3... Quartz plate, 4... Electromagnetic horn (radiation!), 5... Electromagnetic coil, 6... Reaction chamber (vacuum container chamber), 7... Reaction gas buffer. 8... Partition plate (microwave window), 9...perforated plate,
DESCRIPTION OF SYMBOLS 10... Substrate, 11... Substrate holder, 12... Conductance adjustment valve, 13... Turbo molecular pump. 14.16...Exhaust pump, 15...Valve, 1
7...Safety valve, 19.2o...Cooling water pipe, 21...Communication pipe.

Claims (1)

[Claims] 1. A vacuum container equipped with a gas supply means and an evacuation means, a waveguide that guides microwaves into the vacuum container, and a radiator connected to one end of the waveguide. , sealing the opening of the radiator so as to cause electron cyclotron resonance at the frequency of the microwave directly under the microwave window in the vacuum container with the microwave window forming a part of the partition wall of the vacuum container; A microwave plasma processing apparatus comprising a means for generating a magnetic field, further comprising means for reducing the pressure within the radiator provided with the microwave window under conditions where no discharge occurs, and a microwave plasma processing apparatus comprising: a means for generating a magnetic field; A microwave plasma processing apparatus configured to reduce a pressure difference applied to the microwave window through which waves are introduced. 2. Reduce the pressure inside the radiator connected to the waveguide to 1×10
2. The microwave plasma processing apparatus according to claim 1, which is a means for reducing the pressure to 4 Pa or less or 5 to 50 kPa. 3. Increase the pressure inside the radiator connected to the waveguide to 5-50
kPa, and a cooling means is added to at least a radiator connected to the waveguide, so that the microwave window is cooled by gas convection within the radiator. Wave plasma treatment equipment. 4. A pipe is provided to connect the reduced pressure part of the waveguide to which the radiator is connected and the vacuum container, and the pipe is opened when the pressure difference between the two becomes equal to or higher than the withstand pressure of the microwave window. 4. The microwave plasma processing apparatus according to claim 1, further comprising a safety valve connected thereto to prevent damage to the microwave window. 5. The microwave plasma according to any one of claims 1 to 4, wherein the waveguide is sealed with a material that allows microwaves to pass therethrough, and means is provided for evacuating and reducing the pressure between this part and the microwave window. Processing equipment. 6. The microwave plasma processing apparatus according to claim 5, wherein a cooling means is added to a portion of the waveguide that is sealed with a material that allows microwaves to pass therethrough, so as to cool the sealed portion. 7. The above-mentioned cooling means water-cools the area around the part of the waveguide that is sealed with a material that allows microwaves to pass therethrough, and also blows compressed air directly onto the sealed material from the waveguide side that is maintained at body pressure. 7. The microwave plasma processing apparatus according to claim 6, wherein the microwave plasma processing apparatus is air-cooled. 8. The microwave plasma processing apparatus according to claim 1, wherein the radiator connected to one end of the waveguide is an electromagnetic horn radiator. 9. Any one of claims 1 to 4, wherein the microwave window that seals the opening of the radiator connected to one end of the waveguide and forms part of the partition wall of the vacuum container is constructed of a quartz plate. The microwave plasma processing apparatus described above.