JPH0214520A - Treatment by plasma - Google Patents

Abstract

PURPOSE:To transform an etching gas introduced into a reaction tube in a plasma and to quickly remove a reaction product which has adhered to an inner wall face of the reaction tube without detaching the reaction tube by a method wherein electric power is applied between a plurality of electrodes which have been installed at an outer periphery of the reaction tube and have been made of a specific material. CONSTITUTION:A lid body 15 is brought into contact with the lower end part of a reaction tube 1; the inside of the reaction tube 1 is kept in a desired low-pressure state. During this process, electrodes 8 which have already been connected to an RF power supply 11 and have been made of a material not permeated by a heavy metal in order to restrain a drop in a yield of a substrate to be treated are slid and shifted so as to be closely contacted to an outer periphery of the reaction tube 1. In such a state, an etching gas is supplied into the reaction tube 1 for a prescribed time. During this process, the inside of the reaction tube 1 is evacuated and controlled. High-frequency electric power is applied to the individual electrodes 8 from the RF power supply 11. Then, an electric charge is generated inside the reaction tube 1; the etching gas supplied into the reaction tube 1 is excited; a plasma is generated; a reaction product which has adhered to at least an inner wall face of the reaction tube 1 is removed by the plasma.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a plasma processing method.

(Prior art) Reactor, for example, CVD for heat-treating semiconductor wafers;
In diffusion furnaces, etc., reaction products adhere to reaction vessels other than wafers during the process, and if left as is, it will cause contamination and reduce the yield of semiconductor products, so the reaction products should be periodically removed. It was necessary to clean the pipes, etc.

Here, the conventional method for cleaning the reaction tube is to remove the reaction tube from the apparatus, perform wet etching with fluoronitric acid, etc. using a special cleaning machine, wash it with pure water, dry it in a dryer, and then perform the reaction. The tube was attached to the device, and the installation required subsequent adjustment.

According to the above-mentioned cleaning method, a lot of time and labor is required especially for attaching and detaching the reaction tube, and the operation rate of the apparatus is extremely low since the operation of the apparatus has to be stopped during this time.

This type of cleaning varies depending on the type of process, gas flow rate, etc., but the minimum cleaning time is one day, and the frequency of cleaning is usually once per week, and in particularly severe cases. As silicon nitride, Thio-X (TE
TRAET)IOXY 5ILANE; 5i(QC
2t(s)4) In the case of oxide film formation, 1 time/2~
The cleaning frequency was 3 days. It was extremely burdensome for the operator to remove and attach the reaction tubes with such frequency.

Therefore, a proposal to solve the above problems was made in JP-A No. 6
According to the proposal disclosed in Publication No. 1-476113, an inlet and an outlet for a cleaning chemical are connected to a reaction tube, and fluoronitric acid is introduced into the reaction tube through the inlet and left for a predetermined period of time. By doing this, wet etching of the reaction tube is performed. Thereafter, the fluoronitric acid is discharged, pure water is introduced from the injection port for cleaning, and then drying is performed, thereby cleaning the reaction tube without removing it from the apparatus.

Further, electric power is applied to a metal cylindrical electrode provided on the outer periphery of the reaction tube and a metal electrode inserted into the reaction tube, and the etching gas introduced into the reaction tube is turned into plasma by the electric power. A technique has also been disclosed in which reaction products adhering to the reaction tube are removed using the etching gas. Furthermore, Japanese Patent Laid-Open No. 196820/1983 discloses a technique in which a plurality of metal electrodes are provided around the outer periphery of a reaction tube and removed by etching in the same manner as described above.

(Problems to be Solved by the Invention) The cleaning method disclosed in Japanese Unexamined Patent Publication No. 61-1761.13 mentioned above was extremely difficult to put into practical use.

In other words, in order to perform wet etching while attached to the device, a supply system and a discharge system for the powerful cleaning liquid are required in addition to the conventional configuration, which increases the size of the equipment and requires less installation space. Expansion and cost increases are unavoidable. Moreover, it is virtually impossible to carry out such modifications to existing reactors.

Furthermore, since wet etching is used, it takes a long time to dry, and if vacuum drying is to be used to shorten the drying time, equipment for this purpose is also required.

In addition, in the technique of removing etching gas using an etching gas that is turned into plasma by applying electric power to a metal cylindrical electrode provided on the outer periphery of the reaction tube and a metal electrode inserted into the reaction tube, the electrode is inserted into the reaction tube. Since this electrode is used as a cylindrical electrode, it is sputtered by the plasma and contaminates the inside of the reaction tube.Therefore, it is necessary to cover the surface of the electrode inserted into the reaction tube with a material that will not be sputtered, such as quartz. There is.

There was a problem that the structure was complicated and the cost was high.

In addition, each of the above electrodes is heated by the heat of the reaction tube and the heat of the heater that heats the reaction tube, and since these electrodes are made of metal, each of the above 1! Heavy metals contained in the electrode, such as Na, Ke Mg*Fe, Cu, and Ni, are precipitated, and these heavy metals pass through the quartz reaction tube and enter the reaction tube. If any heavy metal is present in this reaction tube, it will adhere to the wafer being processed in the reaction tube and will be diffused into the wafer during heat treatment.

There is a problem in that the heavy metals have an adverse effect such as deterioration of the MO8 characteristics of semiconductor devices, and reduce the yield of the wafers.

The present invention has been made to address the above-mentioned problems, and allows reaction products to be removed without removing the reaction tube or the like.

Furthermore, the present invention aims to provide a plasma processing method that can remove reaction products in a short time.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a plasma processing method for removing reaction products adhering to at least the inner wall surface of a reaction tube during a treatment step, in which a plasma treatment method is provided that is formed of a material that does not permeate heavy metals and is provided on the outer periphery of the reaction tube. The method is characterized in that electric power is applied between the plurality of electrodes, the etching gas introduced into the reaction tube is turned into plasma by this electric power, and the reaction products adhering to the inner wall surface of the reaction tube are removed by the etching gas turned into plasma. The present invention provides a plasma processing method.

(Operation) Electric power is applied between a plurality of electrodes made of a material that does not permeate heavy metals provided around the outer periphery of the reaction tube, and the etching gas introduced into the reaction tube is turned into plasma by this electric power, and the etching gas turned into plasma is By removing reaction products adhering to the inner wall surface of the reaction tube with gas, plasma can be generated between the plurality of electrodes provided on the outer periphery of the reaction tube, so there is no need to insert electrodes into the reaction tube. Therefore, no sputtering contamination occurs due to the insertion of this electrode. In addition, by reusing the plurality of electrodes provided on the outer periphery of the reaction tube, for example, by dividing the conventionally used soaking tube provided around the reaction tube into multiple parts, there is no need to newly install other electrodes, and the cost is reduced. This can be achieved at low cost. Furthermore, by making the plurality of electrodes made of a material that does not permeate heavy metals, or by using a soaking tube made of a material that does not permeate heavy metals, heavy metals generated from the electrodes or existing around the electrodes can be reduced. The heavy metals do not pass through, making it possible to prevent a decrease in the yield of substrates to be processed due to the heavy metals.

Further, since the reaction product can be removed without removing the reaction tube, there is no need to provide any other device for removing the reaction product, and space can be used effectively.

(Example) Hereinafter, an example in which the method of the present invention is applied to a CVD apparatus that batch-processes a plurality of semiconductor wafers at the same time will be described with reference to the drawings.

First, the configuration of the CVD apparatus will be explained.

This equipment is a vertical reactor as shown in Figure 1.

There is a processing section (2) consisting of a reaction tube (2) whose axial direction is a vertical axis, and a plurality of substrates to be processed, such as semiconductor wafers (3), which can be set in this processing section (2), at predetermined intervals in the thickness direction. The boat (a) is placed in a predetermined boat (a) below the reaction tube.
(to) The receiver is composed of a transport mechanism (2) that loads and unloads the reaction tube from the transfer position (1) into the reaction tube.

The processing section (■) is equipped with a cylindrical reaction tube (■) made of a material that is heat-resistant and does not easily react with the processing gas, such as quartz, and whose upper surface is sealed, and the boat (■) described above can be installed inside this reaction tube (ω). It has a larger diameter and is elongated (like a boat). Around such reaction tube (2), a heating mechanism (2), such as a coil-shaped heater (2) capable of heating the inside of this reaction tube (2) to a desired temperature of, for example, 700 to 000°C, is provided at a predetermined distance from the reaction tube (ω). It is wrapped. Between the reaction tube (G) and the heater (2), a cylindrical conductor adapted to the outer circumferential shape of the reaction tube (2) is divided into a plurality of pieces in the vertical direction at predetermined angular intervals, for example, facing each other. An electrode (8) divided into two parts as shown in FIG. This electrode is electrically conductive and has a heat-uniforming effect inside the reaction tube, and also contains heavy metals such as Na, K, M
g+ Material that does not transmit Fe, Cu, Ni, etc. For example, silicon carbide, conductive ceramic.

It is made of graphite, etc. The above pole (8) is supplied with power by an RFfi source (11) having a balance transformer (9) and a matching box (10) as shown in Fig. 2 (A) and (B). It is considered possible. By supplying this power, a discharge occurs between the opposed electrodes (8), which excites the processing gas inside the reaction tube (1), making it possible to generate plasma. In order to improve the efficiency of this plasma generation, on the outer periphery of the reaction tube
Each of the electrodes (8) can be slid laterally so that the electrodes (8) are brought close to each other or in close contact with each other, and when replacing the reaction tube (2), insert the reaction tube into a predetermined position. A moving mechanism (12) is provided so that each electrode (2) can be slid to release the reaction tube (2) and each electrode (8) from close contact. Here, the coupling portion where the moving mechanism (12) and the electrode (2) are coupled also serves as a connection terminal for connecting the RF' to the source (11),
For example, the connection terminal and electrode (c) provided on the moving mechanism (12) are fastened with SUS screws via spring washers or the like. At this time, when the joint is heated by the heat of the heater (2), loosening occurs due to the difference in thermal expansion coefficient between the electrode (2) and the screw, so the joint is held at a temperature that does not cause the loosening, etc. 200℃
It is preferable to set the following.

Furthermore, a gas supply pipe (13) for supplying a predetermined processing gas into the reaction tube (2) is connected to the upper part of the reaction tube (2), and this gas supply pipe (13) is connected to a mass flow controller (not shown). connected to a gas supply source via etc. At the bottom of the reaction tube (1), an exhaust pipe (1
4) is connected to this exhaust pipe (14), and one reaction tube (υ
It is connected to a vacuum pump (not shown) that can reduce the internal pressure to a desired pressure and discharge processing gas and the like.

A lid (15) is detachably provided so as to make the interior of the reaction tube (ω) of the processing section (2) airtight as described above. Above the lid (15), a boat loaded with the above-mentioned Ueno 1) is provided. This boat (to) is
A heat-insulating cylinder (16) made of a material that is heat-resistant and does not easily react with the processing gas, such as quartz, and which can set the boat H,) at a predetermined height position within the reaction tube pile is attached to the boat. ) and the lid (15).

The lid body (15) is supported by a transport machine i, which includes, for example, a ball screw and a motor, and is movable in the vertical axis direction (toward the boat).

The operation of the CVD apparatus having the above-described configuration is controlled by a control section (not shown).

Next, a method for forming a film on the semiconductor wafer (1) after the above-mentioned CVD process and a method for removing reaction products adhering to the inner wall of the reaction tube, ie, a cleaning method, will be described.

First, a boat (A) loaded with wafers (I) by a wafer transfer device (not shown) is gripped, conveyed, and placed by a handler (17) on a heat-insulating tube (16) set at the transfer position rIl■. Then, transfer the transport mechanism 0) to the above boat.
is raised by a predetermined amount and set at a predetermined position within the reaction tube pile. At this time, the lower end of the reaction tube 1 is brought into contact with the lid (15) to make the inside of the reaction tube airtight. At the same time, a vacuum pump (not shown) is used to perform exhaust control to maintain the inside of the reaction tube ω at a desired low pressure, for example, 0.1 to 3 Torr, and a desired temperature, for example, about 500 to 1000° C. is set by the heater .

After this revision, processing gases such as SiH* and 02 are supplied from the gas supply pipe (13) into the reaction tube ω for a predetermined period of time while adjusting the flow rate using a mass flow controller (not shown) from the gas supply source while controlling the exhaust gas as described above. . Then, a 5in2 film shown in the following formula is deposited on the surface of the wafer (3) placed in one reaction tube (G).

SiH, + O, → Sin, l+ 2) +2 ↑
(2) After this CVD treatment, the supply of the processing gas is stopped, and the inside of the reaction tube 5 is replaced with an inert gas, such as N2 gas, to restore normal pressure. Then, the boat (A) loaded with the processed wafers (2) is transported to the transfer position (2) by the transport mechanism (2), and the processing is completed.

If such a CVD process is repeatedly performed, a reaction product such as Sin in the case of the above process will adhere to the inside of the reaction tube ω. If the above CVD treatment is performed with such reaction products still attached, the deposits will peel off from the reaction tube (2) during the treatment. I will become attached to the wafer and cause contamination. Therefore, it is necessary to periodically remove the attached reaction products.

Next, a method will be described in which the reaction products adhering to the inside of the reaction tube ω due to the treatment process, for example, the CVD process described above, are removed by plasma etching.

First, the lid body (15) is raised by the transport mechanism (Q) and brought into contact with the lower end of the reaction tube (2). This makes the inside of the reaction tube airtight. In this state, the inside of the reaction tube (ω) is adjusted to the desired Exhaust is controlled by a vacuum pump (not shown) to maintain a low pressure state, for example, I
The electrode ■ connected to the power source (11) is the moving mechanism (12)
It slides so that it comes into close contact with the outer periphery of the reaction tube (2). In this state, the flow rate is adjusted to 110005C from the gas supply source using a mass flow controller (not shown).
An etching gas such as NF3 is supplied from the gas supply pipe (13) into the reaction tube pile for a predetermined period of time while adjusting the etching temperature to approximately C.

At this time, the inside of the reaction tube ω is controlled to have a pressure of 0.2 to 1 Torr.

Then, from the RF power source (11), the frequency is, for example, 400kHz.
z, a power, for example IKw, is applied to each type tili+ (8). Then, a discharge occurs between each electrode (8), that is, a discharge occurs in the reaction tube (1), and the etching gas supplied into the reaction tube 9 is excited to generate plasma, and this plasma causes at least the reaction tube (1) Plasma etching, that is, removal of reaction tube products adhering to the inner wall surface.

This plasma etching is performed by chemical etching using radicals generated by plasma and sputter etching using ions accelerated by an ion sheath generated by plasma.

As mentioned above, plasma is generated inside the reaction tube.
At this time, by applying electric power with each of the electrodes (2) in close contact with the outer periphery of the reaction tube (1), it is confirmed that the reaction tube (2) is present between the electrodes (8), that is, quartz, which is the material of the reaction tube (2), is present. Since the dielectric constant of this quartz is several times higher than that of air, the capacitance between the electrodes (5) can be made sufficiently large, the plasma can be easily generated, and even stronger plasma intensity can be obtained. Therefore, low RF power (11)
It is now possible to generate plasma at a frequency of, for example, 10 MHz or less, and the conventional high frequency, for example, 13.56 MHz, is now possible.
The above plasma can be generated without using MHz.

This frequency of 13.56 MHz frequently causes troubles where it becomes a radio wave and causes other equipment in the vicinity to malfunction, and the radio wave shield for the above frequency has become Tanabe. However, by bringing each of the electrodes (1) into contact with the outer periphery of the reaction tube (2), plasma can be generated at a frequency of 10 MHz or less, so the problem of malfunctioning other devices as described above can be solved. Furthermore, each of the electrodes (1) can be set in contact or non-contact with the outer periphery of the reaction tube (G) by the moving mechanism (12), so at least when generating the plasma, the electrodes (2) are brought into contact with the outer periphery of the reaction tube (3). In the case of replacement, etc., the reaction tube can be easily removed by setting it in the non-contact state. Also, when removing the reaction tube (■), the above-mentioned electrodes (■) and the heater (■) provided around them should always be kept in a non-contact state, so that the above-mentioned heaters (■) may be damaged due to contact, and the above-mentioned electrodes (
) to prevent damage.

The reaction products removed by the etching gas are exhausted from the exhaust pipe (14), and no reaction products remain in the reaction tube. After etching for a predetermined period of time, the etching gas is stopped, and the inside of the reaction tube (1) is replaced with an inert gas, such as N2 gas, to return to normal pressure. After this, cover (1
5) is placed at the transfer position (2) by the moving mechanism (12), and the etching process is completed.

In the above embodiment, an example in which the electrode is divided into two parts is explained as a structure in which the electrode is divided into a plurality of parts, but the structure is not limited to this. For example, the same effect can be obtained even if the electrode is divided into eight parts as shown in FIG. . Electric power of different polarity may be applied to the plurality of divided electrodes (■) and the adjacent electrodes (■). In this case, a strong electric power may be applied between the adjacent electrodes (to), that is, near the surface of the inner wall of the reaction tube (■). Since an electric field (18) is generated, the reaction products adhering to the inner wall of the reaction tube can be etched efficiently and at high speed. At this time, the RF power source (II) that applies power to each of the electrodes (2) may be used in multiple systems, or may be distributed from one system of the RF power source (11) to each of the electrodes (C). .

Furthermore, the present invention is not limited to the above-mentioned embodiments, and for example, the reaction tube made of quartz may not be a single tube, but may be a double tube made of quartz, such as a cylindrical outer tube whose top surface is sealed, and The reaction tube may be composed of an outer tube and a cylindrical inner tube in a non-contact state. In this case, when the etching gas is supplied to the inner tube of the reaction tube having a double tube structure and the exhaust is controlled so that the etching gas flows between the inner tube and the outer tube, the etching gas flows along the outer electrode. Then, the electric field is strong near the electrode and a strong plasma is generated, which improves the conversion efficiency of the supplied etching gas into plasma.
3 gas flow rate 1100OSCC, RF frequency 400kt (
z, the conversion efficiency to plasma is 95% at 1k11 hours of electric power.
and high efficiency was obtained. Further, in the above embodiment, the RF power supply (1
The connecting terminal from 1) and the electrode ■ were connected using screws, etc., and the temperature of the joint was set at 200°C or lower to prevent the screws from loosening. However, when connecting at a location north of 200°C, Since the RF multiplied signal is transmitted from the power supply, it is sufficient if AC continuity can be obtained even if there is no DC continuity at the coupling part. That is, the bonding surface area between the electrode (8) made of SiC or the like and the metal terminal of the RF power source (11) is increased, and screws are secured at multiple locations. When SiC placed in the atmosphere becomes hot, an oxide film forms on its surface, making it impossible to conduct direct current, but since the bonding surface area is large, a large capacitance can be achieved, so a sufficient RFffi current can flow through the SiC. I can do it.

At this time, it is desirable to connect the metal connection terminal and the lead lead at a location where the temperature of the connection terminal is 200° C. or lower.

Furthermore, in the above embodiment, the electrodes were provided also as heat soaking tubes, but they may be provided in separate systems, and the electrodes can be divided into two.
Any number of divisions may be used as long as the plasma is effectively generated, and the electrode material may be a heat-resistant metal whose surface is coated with a material that does not transmit heavy metals, such as ceramic, and the frequency applied to the electrode may vary depending on the peripheral device. Any frequency may be used as long as it does not cause any adverse effects, for example, 10 MHz or less.

Furthermore, in the above example, the reaction products adhering to the inside of the quartz reaction tube were plasma etched, but the plasma etching was carried out with the quartz boat or heat insulating tube without any wafer placed inside the reaction tube. You may also perform etching.
In this way, it becomes possible to remove the reaction products adhering to the boat or the heat insulating tube, resulting in high versatility.

Furthermore, although the above embodiment has been described as a CVD apparatus consisting of a vertical reactor for batch processing wafers, it is not necessary to use a CVD apparatus, but any apparatus consisting of a reaction furnace such as a vapor phase epitaxial growth apparatus or a diffusion apparatus may be used. It goes without saying that the reactor can also be adapted to a horizontal type.Also, plasma CVD for batch processing wafers can be applied by applying the above embodiment.
It may also be used as a device.

As described above, according to this embodiment, electric power is applied between a plurality of electrodes made of a material that does not permeate heavy metals provided around the outer periphery of the reaction tube, and this electric power is used to control the etching gas introduced into the reaction tube. By converting the etching gas into plasma and removing the reaction products adhering to the inner wall surface of the reaction tube with this plasma-turned etching gas, plasma can be generated between the plurality of electrodes provided on the outer periphery of the reaction tube. There is no need to insert an electrode into the tube, and no sputtering contamination occurs due to the insertion of the electrode. In addition, by reusing the plurality of electrodes provided on the outer periphery of the reaction tube, for example by dividing the conventionally used soaking tube provided around the reaction tube into multiple parts, there is no need to newly install other electrodes, and the cost is reduced. It can be realized with. Furthermore, by making the plurality of electrodes made of a material that does not permeate heavy metals, or by using a soaking tube made of a material that does not permeate heavy metals, heavy metals generated from the electrodes or existing around the electrodes can be reduced. The heavy metals do not pass through, making it possible to prevent a decrease in the yield of substrates to be processed due to the heavy metals.

Furthermore, since the reaction product can be removed without removing the reaction tube, there is no need to provide any other device for removing the reaction product, and space can be utilized in a historic manner.

〔Effect of the invention〕

As explained above, according to the present invention, electric power is applied between a plurality of electrodes formed of a material that does not permeate heavy metals provided around the outer periphery of the reaction tube, and this electric power converts the etching gas introduced into the reaction tube into plasma. By removing the reaction products adhering to the inner wall surface of the reaction tube with the etching residue turned into plasma, plasma can be generated between the plurality of fflli provided on the outer periphery of the reaction tube. There is no need to insert an electrode into the device, and no sputtering contamination occurs due to the insertion of the electrode. Furthermore, since the reaction products can be removed without removing the reaction tube, the work of removing the reaction products can be carried out in a short time, and the operating efficiency of the apparatus can be improved. Furthermore, since it is possible to prevent heavy metals from entering the reaction tube, there is no adhesion of heavy metals during processing of the substrate to be processed, and a decrease in yield can be suppressed.

[Brief explanation of the drawing]

FIG. 1 shows a CVD process for explaining one embodiment of the method of the present invention.
FIG. 2 is an explanatory diagram of the electrode in FIG. 1, and FIG. 3 is an explanatory diagram of another embodiment of the electrode in FIG. 1. 1... Reaction tube 7... Heater 8... Electrode 11... RF power source 12... Moving mechanism 18... Electric field patent applicant Chill Sagami Co., Ltd. Figure (A)

Claims (1)

[Claims] In a plasma processing method for removing reaction products attached to at least the inner wall surface of a reaction tube during a treatment process, electric power is applied between a plurality of electrodes formed of a material that does not permeate heavy metals and is provided around the outer periphery of the reaction tube. The etching gas introduced into the reaction tube is turned into plasma by
A plasma processing method characterized in that reaction products adhering to the inner wall surface of the reaction tube are removed by the etching gas turned into plasma.