JP2017050118A - Electrode plate for plasma processing apparatus and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve labor saving and low cost and prevent copper contamination in plasma processing by forming a vent hole by electrical discharge machining using a machining electrode of copper.SOLUTION: A method of manufacturing an electrode plate for a plasma processing apparatus includes: a hole boring step for forming a lower hole having a smaller diameter than a vent hole by applying electrical discharge machining using a processing electrode made of copper to a blank plate serving as an electrode plate; a heat treatment step for applying heat treatment to a hole bored blank plate forming the lower hole at a temperature of 900°C or more and 1100°C or less for 12 hours or more and 32 hours or less; and an etching step for removing a damage layer due to the electrical discharge machining of an inner peripheral part of the lower hole by applying etching to the hole bored blank plate after heat treatment.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode plate for a plasma processing apparatus that discharges a plasma generating gas while passing it in the thickness direction in a plasma processing apparatus, and a method for manufacturing the same.

  A plasma processing apparatus such as a plasma etching apparatus or a plasma CVD apparatus used in a semiconductor device manufacturing process has a pair of electrodes connected to a high-frequency power source in a chamber, for example, vertically arranged, and the lower electrode With the substrate to be processed disposed thereon, plasma is generated by applying a high-frequency voltage while flowing an etching gas from the air hole formed in the upper electrode toward the substrate to be processed, and etching is performed on the substrate to be processed. It is set as the structure which processes. As the upper electrode used in this plasma processing apparatus, a laminated electrode plate in which a silicon electrode plate is fixed to a cooling plate is generally used, and the heat of the electrode plate rising during the plasma processing is The heat is dissipated through the cooling plate.

This type of electrode plate is obtained by cutting an ingot made of single crystal silicon, polycrystalline silicon, or columnar crystal silicon having a unidirectionally solidified structure into a thin plate with a diamond band saw or the like, and then in parallel in the thickness direction. The air holes (pores having a diameter of about 1 mm) are formed and subjected to a predetermined grinding process, followed by an etching process and a polishing process.
As a method for forming a vent hole in this electrode plate, for example, Patent Document 1 and Patent Document 2 disclose a method by electric discharge machining. In electric discharge machining, an electrode (alloy containing copper as a main component) is brought close to a workpiece (for example, Si) and a voltage is applied to generate an arc discharge between the electrode and the workpiece to cut the workpiece. In this hole machining by electric discharge machining, the machining speed is faster than in drilling and the like, and labor saving and cost reduction are possible.

Japanese Patent Laid-Open No. 11-92972 Japanese Patent Laid-Open No. 10-223613

  By the way, copper is often used for a machining electrode used in electric discharge machining. The copper in this processed electrode is gradually consumed by electric discharge, and the finely cut copper component adheres to the surface of the hole, so that it may permeate and diffuse inside the silicon electrode plate that is the workpiece (around the hole). There is. For this reason, when plasma processing is performed using the electrode plate, there is a problem that the copper component causes contamination.

  The present invention has been made in view of such circumstances, and forms air holes by electrical discharge machining using a copper machining electrode to prevent copper contamination in plasma processing while saving labor and reducing costs. An object of the present invention is to provide an electrode plate for a plasma processing apparatus and a method for manufacturing the same.

  The method for producing an electrode plate for a plasma processing apparatus of the present invention is a method for producing an electrode plate having a plurality of air holes through which a plasma generating gas is circulated, and a copper processed electrode is used as a base plate to be an electrode plate. A drilling step of forming a prepared hole having a smaller diameter than the vent hole by performing electric discharge machining, and a heat treatment of not less than 12 hours and not more than 32 hours at a temperature of 900 ° C. to 1100 ° C. And a step of etching the perforated base plate after the heat treatment to remove the damaged layer caused by the electric discharge machining on the inner peripheral portion of the lower hole.

Through the drilling process of electrical discharge machining using copper electrodes, copper penetrates into the inner peripheral part of the lower hole of the perforated base plate and diffuses inside, but a damaged layer is formed by electric discharge machining on the inner peripheral part of the lower hole In the heat treatment step after the drilling step, the copper diffused in the electrode plate moves to the damage layer on the inner periphery of the lower hole and is collected. Therefore, an electrode plate with a low copper concentration can be obtained by removing the damaged layer in the next etching step.
The copper electrode includes both a pure copper electrode and a copper alloy electrode.

In the method for manufacturing an electrode plate for a plasma processing apparatus according to the present invention, the etching step may remove an inner peripheral portion of the prepared hole with a thickness of 20 μm or more.
By removing the thickness of 20 μm or more, it is possible to obtain an electrode plate having almost no copper contamination on the inner peripheral portion of the air hole.

  The method for manufacturing an electrode plate for a plasma processing apparatus according to the present invention may include a sizing step of sizing the pilot hole by machining using a drill after the drilling step and before the etching step. .

Etching time can be shortened by etching the pilot hole after machining. Since the machining in this case is a sizing process for a prepared pilot hole, the machining time can be shorter than when the pilot hole is formed by machining with a drill.
Further, if this sizing step is performed before the heat treatment step, an appropriate strain can be introduced into the damaged layer, and copper can be captured more reliably in the damaged layer.

  The electrode plate for a plasma processing apparatus of the present invention is an electrode plate having a plurality of vent holes for circulating a plasma generating gas, and the copper concentration at a depth of 1 μm from the inner peripheral surface of the vent hole is 0.2 ppb. The above is 5 ppb or less.

  If the copper concentration at a depth of 1 μm from the inner peripheral surface of the vent hole exceeds 5 ppb, copper may be released into the plasma during the plasma treatment, which may cause a problem of copper contamination of the object to be treated.

  According to the present invention, it is possible to quickly process a large number of holes by electric discharge machining to save labor and cost, and to prevent copper contamination in plasma processing.

It is a flowchart explaining embodiment of the manufacturing method of the electrode plate for plasma processing apparatuses of this invention. It is a figure explaining the punching process in the manufacturing method of FIG. It is sectional drawing which compares and shows the pilot hole (a) after the drilling process in the manufacturing method of FIG. 1, and the vent hole (b) after an etching process. It is a schematic block diagram which shows an example of the plasma etching apparatus with which the electrode plate for plasma processing apparatuses is used.

Hereinafter, embodiments of an electrode plate for a plasma processing apparatus and a method for manufacturing the same according to the present invention will be described with reference to the drawings.
First, a plasma etching apparatus will be described as a plasma processing apparatus using the electrode plate 3 manufactured in the present embodiment. As shown in FIG. 4, the plasma etching apparatus 100 is provided with an electrode plate (upper electrode) 3 on the upper side in the vacuum chamber 2 and a gantry (lower electrode) 4 that can move up and down on the lower side. And in parallel with each other. In this case, the upper electrode plate 3 is supported in an insulated state with respect to the wall of the vacuum chamber 2 by the insulator 5, and the electrostatic chuck 6 and the silicon support surrounding the periphery are provided on the gantry 4. A ring (7) is provided, and a wafer (substrate to be processed) 8 is placed on the electrostatic chuck 6 with the peripheral edge supported by the support ring (7). Further, an etching gas supply pipe 9 is provided on the upper side of the vacuum chamber 2, and the etching gas sent from the etching gas supply pipe 9 passes through the diffusion member 10 and is then passed through the electrode plate 3. It is made to flow toward the wafer 8 through the pores 11 and is discharged to the outside from the discharge port 12 on the side of the vacuum chamber 2. On the other hand, a high frequency voltage is applied between the electrode plate 3 and the gantry 4 by a high frequency power source 13.

  A cooling plate 14 made of aluminum or the like having excellent heat conductivity is fixed to the back surface of the electrode plate 3. The cooling plate 14 is also formed with through holes 15 at the same pitch as the air holes 11 so as to communicate with the air holes 11 of the electrode plate 3. The electrode plate 3 is fixed in the plasma etching apparatus 100 by screwing or the like with the back surface in contact with the cooling plate 14.

  The electrode plate 3 of the present embodiment is formed of a single crystal silicon, columnar crystal silicon, or polycrystalline silicon, for example, into a disk having a thickness of about 5 to 12 mm and a diameter of about 300 to 400 mm. Ventilation holes 11 having an inner diameter of 0.2 mm to 0.8 mm are formed to penetrate several hundred to 3,000 in a pitch of several mm to 10 mm in parallel in the thickness direction in a state (matrix shape) aligned vertically and horizontally. .

  As shown in the flow chart of FIG. 1, the electrode plate 3 configured in this way is a hole in which a base plate 31 to be the electrode plate 3 is subjected to electric discharge machining to form a plurality of lower holes 32 having a smaller diameter than the air holes 11. Step (S1), a heat treatment step (S2) for performing heat treatment on the perforated base plate 33 in which the lower holes 32 are formed, and etching the perforated base plate 33 after the heat treatment to discharge the inner peripheral portion of the lower holes 32 An etching step (S3) for removing the damaged layer 35 due to processing, a polishing step (S4) for polishing the front and back surfaces of the perforated base plate 33 after the etching step (S3), and a perforated base plate after the polishing step (S4) It is manufactured through a cleaning step (S5) for cleaning 33.

  The steps of the above electrode plate manufacturing method will be described in detail. First, although not shown in the drawing, an ingot made of single crystal silicon, polycrystalline silicon, or columnar crystal silicon having a unidirectionally solidified structure is formed with a diamond band saw or the like. A base plate 31 formed by thinly cutting into a substantially disc shape is prepared.

(Drilling process)
A pilot hole 32 is formed in the base plate 31 by electric discharge machining. As shown in FIG. 2, the electrode 41 for electric discharge machining has a plurality of pin-shaped protrusions 42 having a circular cross section for forming the pilot holes 32, and is formed of copper (or a copper alloy). The pin-like protrusions 42 of the copper electrode 41 and the surface of the base plate 31 are made to face each other in the processing liquid, a voltage is applied between the processing electrode 41 and the base plate 31, and a discharge occurs between them. The protrusion 42 is moved in the thickness direction of the base plate 31. By passing this pin-shaped protrusion 41 through the base plate 31, a lower hole 32 is formed, and a perforated base plate 33 is formed.
In this drilling step, by forming a plurality of pin-like protrusions 42 of the electrode 41, the respective lower holes 32 of the base plate 31 can be formed at a time or in a plurality of times.

(Heat treatment process)
Next, the perforated base plate 33 is heat treated. The heat treatment is performed in a nitrogen or inert gas atmosphere at a temperature of 900 ° C. to 1100 ° C. for 12 hours to 32 hours. By performing the electrical discharge machining using the copper electrode 41 in the previous drilling step, the copper component of the copper electrode 41 diffuses from the inner peripheral surface of the lower hole 32 of the perforated base plate 33 to the inside, and this heat treatment is performed. By applying, the copper diffused in the perforated base plate 33 moves (diffuses) toward the surface. In this case, as shown in FIG. 3A, a damage layer 35 in which strain is accumulated by electric discharge machining is formed on the inner peripheral portion of the lower hole 32, so that copper is captured by the damage layer 35, It concentrates on the damaged layer 35 and precipitates.
If the heat treatment temperature is less than 900 ° C., the movement of copper is small and the concentration on the damaged layer 35 is not sufficient, and if it exceeds 1100 ° C., the movement of copper becomes too large and it is difficult to capture the damage layer 35. . If the heat treatment time is less than 12 hours, the effect is not sufficient. If the heat treatment time is longer than 32 hours, the oxide film layer formed on the electrode plate surface becomes thick due to exposure to high temperature for a long time, and cannot be completely removed in the subsequent etching process.

(Etching process)
Etching is performed by immersing the perforated base plate 33 in an etching solution. By this etching process, the damaged layer 35 in the inner peripheral portion of the lower hole 32 is removed, and the copper trapped in the damaged layer 35 is also removed together with the damaged layer 35. Etching solution (hydrofluoric acid acetic acid) in which hydrofluoric acid (HF), nitric acid (HNO ₃ ), and acetic acid (CH ₃ COOH) are mixed at a ratio (capacity ratio) of 5-8: 42-48: 16-24. ) Is recommended. By this etching process, the surface of the perforated base plate 33 is removed by 20 μm or more, but it is better not to remove more than necessary.

The target of this etching process is to set the copper concentration in the surface portion (position of 1 μm depth from the surface) of the air hole 11 of the final electrode plate 3 shown in FIG. 3B to 0.2 ppb to 5 ppb. With such a copper concentration, there is no problem of copper contamination due to plasma treatment. The immersion time in the etching solution may be about 2 minutes depending on the mixing ratio of each acid.
The copper concentration on the surface of the electrode plate 3 can be measured by secondary ion mass spectrometry (SIMS).
In this etching step, instead of immersing the perforated base plate 33 in the etching solution, the opening end of the box is brought into close contact with the peripheral portion of one surface of the perforated base plate 33, and the inside of the box is etched. The etching solution may be passed through each of the lower holes 32 of the perforated base plate 33 while supplying the solution in a pressurized state.

(Polishing process, cleaning process)
The front and back surfaces of the perforated base plate after the etching treatment are polished and smoothed.
Finally, in the cleaning step (S5), the perforated base plate is cleaned to finish the electrode plate 3. Specifically, it is performed by immersing the perforated base plate in a cleaning liquid such as pure water for a certain time and swinging the perforated base plate in the cleaning liquid.

  As described above, in this manufacturing method, after a plurality of prepared holes 32 are formed in the base plate 31 by electric discharge machining, copper diffused in the perforated base plate 33 by this electric discharge machining is prepared by the next heat treatment step. The electrode plate 3 with a small amount of copper component can be obtained by moving the damage layer 35 to the inner peripheral portion 32 and removing the damaged layer 35 by etching. Further, since the damaged layer 35 is removed, the generation of particles can be prevented during the plasma processing.

In the above embodiment, the electrode plate 3 is manufactured in the order of the drilling process by electric discharge machining, the heat treatment process, and the etching process. However, after the drilling process and before the etching process, the electrode plate 3 is formed in the drilling process. You may implement the sizing process which cuts only the surface part of the hole 32 slightly using a drill.
When this sizing process is performed, the pilot hole 32 formed in the drilling process is formed smaller, and the surface portion of the pilot hole 32 is cut in the sizing process. The cutting allowance is small, and therefore the working time is shorter than when drilling from the beginning.
If this sizing step is performed before the heat treatment step, mechanical damage due to drilling can be imparted to the damaged layer 35 caused by the electric discharge machining of the prepared hole 32, and copper is captured in the damaged layer 35 in the next heat treatment step. Can be performed more reliably.

  Next, in order to confirm the effect of the present invention, a plurality of electrode plates were produced by changing the heat treatment conditions, and the copper concentration in the inner peripheral portion of the vent hole of each electrode plate was measured.

The electrode plate is manufactured using a single crystal silicon disk having an outer diameter of 390 mm (12 inches) and a thickness of 12 mm, and the diameter is obtained by electric discharge machining using a copper electrode for the single crystal silicon disk (element plate). 1000 pilot holes of 0.5 mm were formed. And after performing heat processing by the temperature and time which are shown in Table 1 under nitrogen atmosphere, the etching process was performed and each electrode plate was produced through the predetermined polishing process and the washing | cleaning process. In the etching step, the sample was immersed for 2 minutes using an etching solution in which hydrofluoric acid (HF), nitric acid (HNO ₃ ), and acetic acid (CH ₃ COOH) were mixed at a ratio (volume ratio) of 7:45:20. The etching amount was 20 μm.
About the sample after an etching, the copper (Cu) density | concentration of the location of a 1 micrometer depth from the inner peripheral surface of a vent hole was measured using the secondary ion mass spectrometer.
The measurement results are shown in Table 1.

  As can be seen from Table 1, the heat treatment at a temperature of 900 ° C. or higher and 1100 ° C. or lower reduced the copper concentration to 0.2 ppb to 5 ppb, and the copper concentration was the lowest at 1000 ° C. In both cases where the heat treatment temperature was lower than the range of 900 ° C. or higher and 1100 ° C. or lower, the copper concentration was as high as 10 ppb. The heat treatment time is 16 hours, but it is assumed that the heat treatment time is preferably in the range of 12 hours to 32 hours.

  In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

100 Plasma processing apparatus 2 Vacuum chamber 3 Electrode plate (electrode plate for plasma processing apparatus)
4 Base 5 Insulator 6 Electrostatic Chuck 7 Support Ring 8 Wafer (Substrate to be Processed)
9 Etching gas supply pipe 10 Diffusion member 11 Vent hole 12 Discharge port 13 High frequency power supply 14 Cooling plate 15 Through hole 31 Base plate 32 Lower hole 33 Perforated base plate 35 Damaged layer

Claims (4)

  A method of manufacturing an electrode plate having a plurality of air holes through which a plasma generating gas is circulated, wherein a base plate serving as an electrode plate is subjected to electric discharge machining using a copper processing electrode, and a pilot hole having a smaller diameter than the air holes. A heat treatment step of subjecting the perforated base plate on which the lower hole is formed to a heat treatment of 900 ° C. to 1100 ° C. for 12 hours to 32 hours, and a post-heat treatment perforated base plate. A method for manufacturing an electrode plate for a plasma processing apparatus, comprising: an etching step of etching to remove a damaged layer caused by the electric discharge machining at an inner peripheral portion of the lower hole.   2. The method of manufacturing an electrode plate for a plasma processing apparatus according to claim 1, wherein the etching step removes an inner peripheral portion of the lower hole with a thickness of 20 μm or more.   The plasma processing apparatus according to claim 1, further comprising a sizing step of sizing the pilot hole by machining using a drill after the drilling step and before the etching step. Manufacturing method of electrode plate. An electrode plate having a plurality of air holes for circulating a plasma generating gas, wherein the copper concentration at a depth of 1 μm from the inner peripheral surface of the air holes is 0.2 ppb or more and 2 ppb or less. Electrode plate for processing equipment.

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