JP2003007683A - Plasma treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma treatment apparatus that can prevent abnormal discharge for uniform etching in the plasma treatment of a silicon-based substrate. SOLUTION: As the material of an electrode member 17 for a plasma treatment apparatus, fitted onto the front of a gas supply port of an electrode for plasma generation in the plasma treatment apparatus, a ceramic porous body having three-dimensional mesh structure where a skeleton section 18a of ceramic containing alumina is allowed to continue in a three-dimensional mesh shape is used, and gas for plasma generation is made to pass through via a void section 18b being formed in the three-dimensional mesh structure irregularly, thus making uniform the distribution of the gas to be supplied for preventing abnormal discharge, and achieving uniform etching without variation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for etching a silicon substrate such as a silicon wafer with plasma.

[0002]

2. Description of the Related Art In the process of manufacturing a silicon wafer used for a semiconductor device, as the thickness of the semiconductor device is reduced, the back surface of the circuit forming surface is mechanically polished to reduce the thickness of the substrate. In the mechanical polishing process, a stress layer containing microcracks is generated on the surface of the silicon wafer, and in order to prevent the strength of the silicon wafer from being reduced by this stress layer, an etching treatment for removing the stress layer on the silicon surface is performed after the mechanical polishing. Done. In place of the conventional wet etching process using a chemical solution, plasma etching has been studied, which is free from the danger of using the chemical solution at the manufacturing site and does not generate industrial waste.

In this plasma etching process for silicon, in order to realize a higher etching rate, it is necessary to generate a high-density plasma. Abbreviated as "gas") is supplied to the surface of the silicon wafer by spraying. As such a method, there is conventionally known a method in which an upper electrode arranged so as to face a lower electrode holding a silicon wafer is used as a gas supply port to serve as a discharge electrode plate and a gas introduction plate. In this case, a gas is uniformly supplied to the surface of the silicon wafer by mounting a discharge electrode plate having a large number of fine gas supply holes formed on the upper electrode.

[0004]

However, when the above-mentioned discharge electrode plate is used, there are the following problems. In the method of supplying gas by injecting gas from the gas supply hole, there is a limit to making the distribution of the supplied gas uniform, and the amount of gas sprayed on the surface of the silicon wafer is directly below the supply hole and other parts. So it's not uniform.

For this reason, an abnormal discharge, which is generated by the concentration of plasma in the vicinity of the supply hole, is easily induced, and this abnormal discharge causes various problems. That is, since the etching is concentrated at the portion where the abnormal discharge occurs, the silicon wafer is damaged and the etching result is varied, and the discharge electrode plate having the gas supply hole is formed. Depending on the material, there was a problem that the discharge electrode plate was damaged by the plasma.

Therefore, an object of the present invention is to provide a plasma processing apparatus capable of preventing abnormal discharge and performing uniform etching in plasma processing of a silicon substrate.

[0007]

According to another aspect of the present invention, there is provided a plasma processing apparatus, wherein a processing chamber, a first electrode having a holding portion for holding a work in the processing chamber, and a position facing the first electrode. A second electrode having a gas supply port for supplying the plasma generating gas to the processing chamber, a pressure control unit for decompressing the processing chamber, and supplying the plasma generating gas to the processing chamber via the gas supply port And a high frequency generator for applying a high frequency electrode between the first electrode and the second electrode, and an electrode member mounted on the front surface of the gas supply port, wherein the electrode member is three-dimensional. It has a mesh structure, and the gaps of this three-dimensional mesh structure are a plurality of irregular paths for passing the plasma generating gas.

A plasma processing apparatus according to a second aspect is the plasma processing apparatus according to the first aspect, wherein the material forming the three-dimensional mesh structure includes alumina.

A plasma processing apparatus according to a third aspect is the plasma processing apparatus according to the first aspect, wherein the work is a silicon substrate.

A plasma processing apparatus according to a fourth aspect is the plasma processing apparatus according to the first aspect, wherein the work is a silicon substrate on which a damage layer is formed by mechanical polishing, and the damage layer is formed by plasma etching. Remove.

A plasma processing apparatus according to a fifth aspect is the plasma processing apparatus according to the first aspect, wherein the work is a silicon wafer having a circuit pattern formed on the front surface side, and the back surface side of the silicon wafer is damaged. The layer is removed by plasma etching.

A plasma processing apparatus according to a sixth aspect is the plasma processing apparatus according to the first aspect, wherein the plasma generating gas is a mixed gas containing a fluorine gas and a carrier gas.

A plasma processing apparatus according to a seventh aspect is the plasma processing apparatus according to the sixth aspect, wherein the carrier gas is helium.

According to the present invention, the electrode member mounted on the front surface of the gas supply port for supplying the plasma generating gas to the silicon substrate has a three-dimensional mesh structure, and the gap of the three-dimensional mesh structure is the above-mentioned. By using electrode members that have multiple irregular paths for passing plasma generation gas, the distribution of the supplied gas is made uniform to prevent abnormal discharge, and perform uniform etching without variations. You can

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1 is a sectional view of a plasma processing apparatus according to an embodiment of the present invention, FIG. 2 (a) is a sectional view of an electrode member according to an embodiment of the present invention, and FIG. 2 (b) is an embodiment of the present invention. 3 is an enlarged cross-sectional view of an electrode member of the present invention, FIG. 3 is a manufacturing flow chart of the electrode member of one embodiment of the present invention, FIG. 4 is an explanatory view of a manufacturing method of the electrode member of one embodiment of the present invention, and FIG. It is a figure which shows the gas flow rate distribution of the plasma processing apparatus of one embodiment of this invention.

First, the plasma processing apparatus will be described with reference to FIG. In FIG. 1, the inside of the vacuum chamber 1 is a processing chamber 2 for performing plasma processing. Inside the processing chamber 2, a lower electrode 3 (first electrode) and an upper electrode 4 (second electrode) are vertically opposed to each other. Are arranged. Lower electrode 3
Is provided with an electrode body 5, and the electrode body 5 is attached to the vacuum chamber 1 via an insulator 9 by a supporting portion 5a extending downward. A holding portion 6 made of a high thermal conductive material is mounted on the upper surface of the electrode body 5, and a silicon wafer 7 (silicon substrate) having a circuit pattern formed thereon is placed on the upper surface of the holding portion 6.

The silicon wafer 7 is in a state immediately after the back side of the circuit pattern forming surface is thinned by mechanical polishing, and a damaged layer containing microcracks is formed on the polished surface. The protective tape 7a (see FIG. 5) adhered to the circuit pattern forming surface of the silicon wafer 7 is brought into contact with the holding portion 6, that is, the polishing surface (the back side of the circuit forming surface) that is the processing target surface faces upward. It is placed in the state where it was turned off. Then, the damaged layer on the polished surface is removed (etched) by plasma treatment.

The holding portion 6 is provided with a large number of suction holes 6a which are open on the upper surface, and the suction holes 6a communicate with a suction passage 5d which penetrates through the inside of the support portion 5a of the electrode body 5. . The suction path 5d is connected to the vacuum suction unit 11, and the silicon wafer 7 is vacuumed in the holding unit 6 by vacuum suction from the vacuum suction unit 11 with the silicon wafer 7 placed on the upper surface of the holding unit 6. It is retained by adsorption.

Inside the holding portion 6, there is a coolant flow path 6 for cooling.
b, 6c are provided, and the refrigerant flow paths 6b, 6c are in communication with the pipe paths 5b, 5c provided so as to penetrate through the inside of the support portion 5a. The pipelines 5b and 5c are connected to the coolant circulation unit 10. By driving the coolant circulation unit 10, a coolant such as cooling water circulates in the coolant flow paths 6b and 6c, which is generated during plasma processing. The holder 6 heated by heat is cooled.

The electrode body 5 is electrically connected to the high frequency generator 12, and the high frequency generator 12 applies a high frequency voltage between the lower electrode 3 and the upper electrode 4. The processing chamber 2 in the vacuum chamber 1 is connected to the pressure control unit 13.
The pressure control unit 13 depressurizes the processing chamber 2 and releases the atmosphere in the processing chamber 2 when the vacuum in the processing chamber 2 is broken.

The upper electrode 4 is provided with an electrode body 15 which is arranged at a position facing the lower electrode 3 and is grounded to a grounding portion 20, and the electrode body 15 is interposed by an insulator 16 by a supporting portion 15a extending upward. Mounted in the vacuum chamber 1.
The electrode body 15 serves as a plasma generation electrode for supplying a gas for plasma generation to the processing chamber 2, and has a lower surface provided with a gas supply passage 15c that penetrates through the inside of the support portion 15a. A mouth 15b is provided. The gas supply path 15c is connected to the gas supply unit 19, which supplies carbon tetrafluoride (CF ₄ ) or sulfur hexafluoride (S).
A mixed gas containing a fluorine-based gas such as F ₆ ) and a carrier gas (for example, helium gas (He)) is supplied as a plasma generating gas.

An electrode member 17 is provided on the front surface of the gas supply port 15b.
Is installed. The electrode member 17 is a disk-shaped member made of a ceramic porous body. As shown in FIG. 2, the ceramic porous body has a ceramic skeleton portion 18a continuously formed in a three-dimensional mesh shape, A large number of holes 1
It has a three-dimensional mesh structure having 8b (gap). The holes 18b of the three-dimensional mesh structure are a plurality of irregular paths for passing gas from the gas supply port 15b through the electrode member 17.

A method of manufacturing the electrode member 17 will be described with reference to FIGS. The electrode member 17 is manufactured by adhering a ceramic to a polyurethane foam as a base material. First, a plate-shaped urethane foam 22 is prepared (ST1), and the urethane foam 22 is cut into a predetermined disk-shaped shape as shown in FIG.
3 is produced (ST2). The urethane foam 22 has a structure in which a core material 22a is continuous in a three-dimensional mesh shape, and a void portion 22b is formed inside with a high porosity.

In parallel with this, alumina powder as a ceramic raw material is prepared (ST3), and water and a surfactant for imparting fluidity to the alumina powder are added to prepare a slurry liquid (ST4).

After that, as shown in FIG. 4B, the base material 23 is immersed in the slurry 24 (ST5), and after pulling up, the excess slurry is removed from the base material 23 (ST6). Then, the base material 23 is dried to remove water (ST
7). Then, the ceramic is fired by heating to complete the electrode member composed of the ceramic porous body having the three-dimensional mesh structure (ST8). Since the base material 23 disappears due to the burning of urethane in the firing step, an electrode member containing nothing but the ceramic raw material can be obtained. In addition, (ST
The steps 5) to (ST7) may be repeated a plurality of times as necessary.

The electrode member thus manufactured has the following characteristics as compared with the conventional electrode member manufactured by sintering ceramic particles. First, since the skeleton portion 18a forming the pores 22b is formed by adhering ceramic around the core material 22a of the urethane foam 22, a porous body having a uniform pore size and distribution in the pores 22b. Can be obtained. The average pore size is preferably 800 μm or less in order to prevent plasma concentration (abnormal discharge).

Further, in the conventional electrode member made of porous ceramic, crystal grains of ceramic having a size corresponding to the required size of the pores 22b are prepared, and the crystal grain boundaries where these crystal grains come into contact with each other. Are joined together by sintering to form a porous body. The larger the pores 22b are, the larger the crystal grains are, the smaller the grain boundary area is, and the lower the bonding strength between the crystal grains is.

On the other hand, in the electrode member 17 made of the ceramic porous body shown in the present embodiment, the porosity is mainly determined by the arrangement density of the core material 22a in the urethane foam 22 used as the base material 23. Therefore, the core material 22
By attaching fine crystal grain ceramics to the periphery of a and sintering at a high temperature, it is possible to form the skeleton portion 18a composed of a dense ceramic fired body having high strength, heat resistance, and thermal shock resistance. .

The electrode member 17 made of the ceramic porous body produced in this manner is formed by connecting the skeleton portion 18a having a structure in which fine alumina crystals are bonded at a high density in a three-dimensional mesh. Therefore, it has excellent heat resistance and thermal shock resistance. That is, even when used in a severe place where plasma is directly exposed to plasma in a plasma processing apparatus, the skeleton portion 18a in which crystal grains are firmly bonded to each other is continuous in a three-dimensionally anisotropic structure. , No crack or damage due to thermal shock. Therefore, it has sufficient durability even when used in a place where it is directly exposed to plasma.

Generally, high-strength ceramics are difficult to process and difficult to form into arbitrary shaped parts, but the above-mentioned electrode member 17 is extremely easily desired by cutting the urethane foam 22 into a desired shape in advance. Can be formed into a shape.

This plasma processing apparatus is configured as described above, and the plasma processing (etching) performed on the silicon wafer 7 will be described below with reference to FIG. First, the silicon wafer 7 is placed on the holding portion 6 with the protective tape 7a facing downward. Then, the pressure control unit 13 (FIG. 1) depressurizes the inside of the processing chamber 2 and then drives the gas supply unit 19, whereby gas is ejected downward from the electrode member 17 mounted on the upper electrode 4.

The gas flow rate distribution at this time will be described. Since the gas supplied from the gas supply unit 19 is prevented from freely flowing out by the electrode member 17 in the gas supply port 15b, the gas is temporarily retained in the gas supply port 15b, so that the pressure distribution of the gas is almost equalized therein. Be uniform.

Due to this pressure, gas is generated in the electrode member 17
18b of the porous ceramic body that constitutes the (FIG. 2)
Through, reaches the lower surface of the electrode member 17 from the gas supply port 15b, and is sprayed toward the lower surface of the silicon wafer 7 from there. At this time, since a large number of holes 18b are formed irregularly inside the electrode member 17, the flow rate distribution of the gas blown downward from the lower surface of the electrode member 17 is almost the same as that of the gas supply port 15b. A uniform distribution with no bias over the entire range.

In this state, the high frequency generator 12 is driven to apply a high frequency voltage to the electrode body 5 of the lower electrode 3 to generate plasma discharge in the space between the upper electrode 4 and the lower electrode 3. . Then, the plasma generated by the plasma discharge performs the plasma etching process on the upper surface of the silicon wafer 7 placed on the holding unit 6.

In this plasma etching, the fluorine radical SF _* (active species) in the plasma reacts with silicon Si to form a compound of fluorine and sulfur (SFn),
Although it tends to adhere to the upper surface (etching surface) of the etched silicon wafer 7 as a reaction product, this reaction product is removed from the etching surface by the carrier gas.

When reaction products adhere to the etching surface,
As the plasma etching progresses, irregularities are formed on the etching surface, and the appearance of the etching surface becomes cloudy. However, by mixing with a carrier gas, clouding of the etching surface can be prevented and the surface can be mirror-finished. Helium (He) is most suitable as the carrier gas, and also has the function of stabilizing the discharge and preventing abnormal discharge.

In this plasma etching process, the silicon wafer 7 is removed by the electrode member 17 having a rectifying function.
Since the flow rate distribution of the gas blown to the surface of the wafer is uniform over the entire range, abnormal discharge does not occur due to the concentration of plasma discharge in the range where the gas has a high density, and the silicon wafer 7 is damaged. And problems such as variations in etching results do not occur.

Further, in the electrode member 17 shown in this embodiment, the skeleton portion 18a in which crystal grains are firmly bonded to each other is continuous in a three-dimensional structure having no anisotropy (three-dimensional mesh structure). Even when used in a harsh place where it is directly exposed to plasma,
No cracks or breaks due to thermal shock. Therefore, conventionally, if the gas supply port was to be equipped with a rectifying plate for equalizing the distribution of the gas flow rate, it was necessary to provide it separately from the discharge electrode plate exposed to the plasma. In the electrode member of the embodiment, the same electrode member can be made to have the functions of both the discharge electrode plate and the rectifying plate.

Although the embodiment of the present invention is as described above, various modifications can be made. For example, the electrode member 17
Although alumina has been described as an example of the material of the above, alumina-based ceramics other than alumina, aluminum-based ceramics, or the like may be used. In this case, it is important to select a material that does not easily react with the plasma generating gas used, that is, a ceramic having excellent corrosion resistance. With respect to the fluorine gas used in the present embodiment, in addition to the alumina type, the boiling point of the metal fluoride is high and the vapor pressure is high under a reduced pressure represented by oxides, nitrides, and carbides containing an alkaline earth metal. The one with low is good.

Further, an example in which the urethane foam structure is used as the three-dimensional network structure has been described, but a three-dimensional network structure of a woven cloth, a fiber such as a wire or a metal (three-dimensional network structure) is used instead of the urethane foam. Good.

The electrode member 1 having a three-dimensional mesh structure
The manufacturing method of 7 may be a method of mixing ceramic fine particles and bead-shaped resin particles and sintering them. In this case, the resin particles are burned down by the heat during sintering, but the space created by the burning becomes an irregular path, and the remaining structure becomes the skeleton portion 18a forming the three-dimensional mesh structure.

In the above embodiment, an example in which a silicon wafer 7 for a semiconductor device as a silicon substrate is targeted for plasma processing is shown, but the present invention is not limited to the silicon wafer 7. The present invention can be applied to, for example, a quartz plate used for a quartz oscillator as long as it is intended for a material containing silicon.

[0043]

According to the present invention, the electrode member mounted on the front surface of the gas supply port of the plasma generating electrode has a three-dimensional mesh structure, and the gap of the three-dimensional mesh structure passes the plasma generating gas. By using the electrode member having a plurality of irregular paths for making the distribution of the supplied gas uniform, abnormal discharge can be prevented, and uniform etching without variation can be performed. Further, by having a three-dimensional mesh structure, sufficient durability can be exhibited even in a place where it is directly exposed to plasma.

[Brief description of drawings]

FIG. 1 is a sectional view of a plasma processing apparatus according to an embodiment of the present invention.

FIG. 2A is a sectional view of an electrode member according to an embodiment of the present invention. FIG. 2B is an enlarged sectional view of an electrode member according to an embodiment of the present invention.

FIG. 3 is a manufacturing flow chart of the electrode member according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a method for manufacturing an electrode member according to an embodiment of the present invention.

FIG. 5 is a diagram showing a gas flow rate distribution of the plasma processing apparatus according to the embodiment of the present invention.

[Explanation of symbols]

1 vacuum chamber 2 processing room 3 Lower electrode 4 Upper electrode 7 Silicon wafer 17 Electrode member 18a skeleton 18b hole 19 Gas supply section

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Haji             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shoji Sakami             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 4G075 AA24 AA30 BC06 CA47 CA51                       DA01 DA02 EB42 EC21 EE07                       EE13 FA14 FA16 FB02 FB04                       FB12 FC06 FC20                 5F004 AA01 BA09 BB18 BB21 BB25                       BB28

Claims (7)

[Claims] 1. A processing chamber, a first electrode having a holding portion for holding a workpiece in the processing chamber, and a gas supply which is arranged at a position facing the first electrode and supplies a plasma generating gas to the processing chamber. A second electrode having a port, a pressure control unit for decompressing the processing chamber, a gas supply unit for supplying a plasma generating gas to the processing chamber via the gas supply port, the first electrode and the second electrode And a high-frequency generator for applying a high-frequency electrode, and an electrode member mounted on the front surface of the gas supply port. The electrode member has a three-dimensional mesh structure, and the gap of the three-dimensional mesh structure is A plasma processing apparatus having a plurality of irregular paths for passing the plasma generating gas. 2. The plasma processing apparatus according to claim 1, wherein the material forming the three-dimensional network structure includes alumina. 3. The plasma processing apparatus according to claim 1, wherein the work is a silicon substrate. 4. The plasma processing apparatus according to claim 1, wherein the work is a silicon substrate on which a damage layer is formed by mechanical polishing, and the damage layer is removed by plasma etching. 5. The plasma processing apparatus according to claim 1, wherein the work is a silicon wafer having a circuit pattern formed on the front surface side, and the damaged layer on the back surface side of the silicon wafer is removed by plasma etching. . 6. The plasma processing apparatus according to claim 1, wherein the plasma generating gas is a mixed gas containing a fluorine gas and a carrier gas. 7. The plasma processing apparatus according to claim 6, wherein the carrier gas is helium.