JP6500705B2 - Electrode plate for plasma processing apparatus and method of manufacturing the same - Google Patents

Description

  The present invention relates to an electrode plate for a plasma processing apparatus which discharges a plasma generation gas while passing a plasma generation gas in a thickness direction in a plasma processing apparatus and a method of manufacturing the same.

  In a plasma processing apparatus such as a plasma etching apparatus or a plasma CVD apparatus used in a semiconductor device manufacturing process, a pair of electrodes connected to a high frequency power source are arranged opposite to each other in the vertical direction, for example, In a state where the substrate to be treated is disposed on the upper substrate, plasma is generated by applying a high frequency voltage while flowing the etching gas toward the substrate to be treated from a vent formed in the upper electrode, and etching of the substrate to be treated It is configured to perform processing. As the upper electrode used in this plasma processing apparatus, generally, a laminated electrode plate in which a silicon electrode plate is fixed to a cooling plate and superposed is used, and the heat of the electrode plate which rises during plasma processing is The heat is dissipated through the cooling plate.

In this type of electrode plate, an ingot made of single crystal silicon, polycrystalline silicon, or columnar crystal silicon having a directionally solidified structure is thinly cut into a substantially disc shape with a diamond band saw etc. After forming the air holes (pores of about 1 mm in diameter) and subjecting them to predetermined grinding, they are finished by etching and polishing.
As a method of forming a vent in the electrode plate, for example, Patent Document 1 and Patent Document 2 disclose a method by electric discharge machining. In electrical discharge machining, an electrode (an alloy based on copper) is brought close to a material to be processed (for example, Si) and a voltage is applied to generate an arc discharge between the electrode and the material to be processed, thereby scraping the material to be processed. In the hole processing by this electric discharge machining, the machining speed is faster than that of the drill machining etc., and the labor saving and the cost reduction are possible.

Unexamined-Japanese-Patent No. 11-92972 gazette Unexamined-Japanese-Patent No. 10-223613

  By the way, copper is often used for the processing electrode used by electric discharge machining. The copper of this processing electrode may be consumed gradually by electric discharge, and the finely cut copper component may adhere to the surface of the hole, thereby permeating and diffusing into the inside (around the hole) of the silicon electrode plate which is the work material 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 a vent is formed by electrical discharge machining using a copper processing electrode to save labor and reduce cost while preventing copper contamination in plasma processing. It is an object of the present invention to provide an electrode plate for a plasma processing apparatus that can be used and a method of manufacturing the same.

  The method of manufacturing an electrode plate for a plasma processing apparatus according to the present invention is a method of manufacturing an electrode plate having a plurality of vents for circulating a gas for plasma generation, wherein a copper processing electrode is used for a base plate to be an electrode plate. A drilling process for forming the lower hole having a diameter smaller than that of the vent hole by the electric discharge machining, and a heat treatment for 12 hours to 32 hours at a temperature of 900 ° C. to 1100 ° C. And an etching step of etching the perforated plate after the heat treatment to remove the damaged layer by the electric discharge machining on the inner peripheral portion of the lower hole.

Copper penetrates into the inner periphery of the lower hole of the perforated plate by the drilling process of electrical discharge machining using a copper electrode and diffuses into the inside, but the inner periphery of the lower hole forms a damaged layer by electric discharge machining In the heat treatment process after the drilling process, copper diffused in the electrode plate is moved to and collected in the damaged layer at the inner periphery of the lower hole. 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 of manufacturing an electrode plate for a plasma processing apparatus according to the present invention, in the etching step, an inner peripheral portion of the lower hole may be removed by 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 vent.

  In the method of manufacturing an electrode plate for a plasma processing apparatus according to the present invention, it is preferable to have a sizing step of sizing the lower hole by machining using a drill after the drilling step and before the etching step. .

It is possible to shorten the etching time by machining and then etching the lower holes. Since the machining in this case is a sizing process of the pre-formed lower hole, the processing time may be shorter than in the case of forming the lower hole by the mechanical process using a drill.
In addition, 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 more reliably captured 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 gas for plasma generation, wherein the copper concentration at a position 1 μm deep from the inner peripheral surface of the vent holes is 0.2 ppb The above is 5 ppb or less.

  If the copper concentration at a depth of 1 μm from the inner circumferential surface of the vent exceeds 5 ppb, copper may be released into the plasma during plasma treatment, which may cause 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 electrical discharge machining, to save labor and reduce costs, 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 drilling process in the manufacturing method of FIG. It is sectional drawing which compares and shows the lower 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 in which the electrode plate for plasma processing apparatuses is used.

Hereinafter, embodiments of an electrode plate for a plasma processing apparatus and a method of 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 in which the electrode plate 3 manufactured in the present embodiment is used. In the plasma etching apparatus 100, as shown in FIG. 4, an electrode plate (upper electrode) 3 is provided on the upper side in the vacuum chamber 2, and a gantry (lower electrode) 4 movable up and down on the lower side is the electrode plate 3. And they are provided parallel to each other at an interval. In this case, the upper electrode plate 3 is supported in an insulating state with respect to the wall of the vacuum chamber 2 by the insulator 5, and on the mount 4, the electrostatic chuck 6 and a silicon support surrounding it. A ring 7 is provided, and a wafer (substrate to be processed) 8 is placed on the electrostatic chuck 6 with its peripheral portion 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 connected to the electrode plate 3. The gas is flowed toward the wafer 8 through the pores 11 and discharged to the outside from the discharge port 12 at the side of the vacuum chamber 2. On the other hand, a high frequency voltage is applied between the electrode plate 3 and the mount 4 by the high frequency power supply 13.

  In addition, a cooling plate 14 made of aluminum or the like, which is excellent in thermal conductivity, is fixed to the back surface of the electrode plate 3. Through holes 15 are formed at the same pitch as the vent holes 11 so as to communicate with the vent holes 11 of the electrode plate 3 also in the cooling plate 14. The electrode plate 3 is fixed in the plasma etching apparatus 100 by screwing or the like in a state where the back surface is in contact with the cooling plate 14.

  The electrode plate 3 of this embodiment is formed of a single crystal silicon, a columnar crystal silicon, or a polycrystalline silicon, for example, in a disk having a thickness of about 5 to 12 mm and a diameter of about 300 to 400 mm. The vent holes 11 with an inner diameter of 0.2 mm to 0.8 mm are formed so as to penetrate in parallel in the thickness direction in a few mm to 10 mm pitch (several hundreds) to about several hundreds to 3,000 in vertical and horizontal alignment (matrix) .

  In the electrode plate 3 configured as described above, as shown in the flowchart of FIG. Step (S1), a heat treatment step (S2) of performing heat treatment on the perforated plate 33 having the lower holes 32 formed therein, and etching the perforated plate 33 after the heat treatment to discharge the inner periphery of the lower holes 32 An etching step (S3) for removing the damaged layer 35 due to the 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 manufactures through the washing process (S5) which wash | cleans 33.

  First, although not shown, an ingot consisting of single crystal silicon, polycrystalline silicon, or columnar crystal silicon having a directionally solidified structure is described with a diamond band saw etc. A blank 31 is prepared by cutting thinly into a substantially disc shape.

(Piercing process)
The lower holes 32 are formed in the blank 31 by electrical discharge machining. As shown in FIG. 2, the electrode 41 for electrical discharge machining has a plurality of pin-shaped protrusions 42 having a circular cross section for forming the lower holes 32, and is formed of copper (or a copper alloy). The pin-like projections 42 of the copper electrode 41 and the surface of the base plate 31 are opposed in the machining fluid, a voltage is applied between the processing electrode 41 and the base plate 31, and a pin is generated while generating a discharge therebetween. The projection 42 is moved in the thickness direction of the base plate 31. By penetrating the pin-like projections 41 to the base plate 31, the lower holes 32 are formed, and the perforated base plates 33 are formed.
In this drilling step, by forming a plurality of pin-shaped projections 42 of the electrode 41, each pilot hole 32 of the base plate 31 can be formed at one time or a plurality of times.

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

(Etching process)
The perforated base plate 33 is immersed in an etching solution to perform an etching process. By this etching process, the damaged layer 35 on 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. As an etching solution, an etching solution in which hydrofluoric acid (HF), nitric acid (HNO ₃ ), and acetic acid (CH ₃ COOH) are mixed at a ratio (volume ratio) of 5 to 8: 42 to 48: 16 to 24 ) Should be used. Although the surface of the perforated base plate 33 is removed by 20 μm or more by this etching process, it is preferable not to remove the surface more than necessary.

This etching process aims at 0.2 ppb-5 ppb copper concentration of the surface part (position 1 micrometer in depth from the surface) of the vent hole 11 of the last electrode plate 3 shown in FIG.3 (b). With this level of copper concentration, the problem of copper contamination due to plasma processing does not occur. 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 body is brought into close contact with the peripheral portion of one surface of the perforated base plate 33, and etching is performed in the box body. The etchant may be allowed to pass through the lower holes 32 of the perforated plate 33 while supplying the solution in a pressurized state.

(Polishing process, cleaning process)
The front and back surfaces of the perforated plate after the etching process are polished and smoothed.
Finally, in the cleaning step (S5), the perforated base plate is cleaned to finish the electrode plate 3. Specifically, the perforated base plate is immersed in a cleaning solution such as pure water for a certain period of time, and the perforated base plate is swung in the cleaning solution.

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

In the above embodiment, the electrode plate 3 was manufactured by performing the drilling process by electric discharge machining, the heat treatment process, and the etching process in this order, but after the drilling process and before the etching process, A sizing process may be performed in which only the surface portion of the hole 32 is slightly cut using a drill.
When this sizing process is performed, the lower holes 32 formed in the drilling process are formed smaller, and the surface portion of the lower holes 32 is cut in the sizing process. The cutting allowance may be small, and therefore, the working time may be reduced compared to the case where the drilling is performed from the beginning.
If this sizing step is performed before the heat treatment step, mechanical strain can be imparted to the damaged layer 35 of the lower hole 32 by electric discharge machining by drilling, and copper is trapped in the damaged layer 35 in the next heat treatment step. Can be done more reliably.

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

The electrode plate is manufactured using a disc of single crystal silicon having an outer diameter of 390 mm (12 inches) and a thickness of 12 mm, and the diameter of the disc (base plate) of single crystal silicon by electric discharge machining using a copper electrode. One thousand 0.5 mm lower holes were formed. Then, heat treatment was performed at a temperature and a time shown in Table 1 under a nitrogen atmosphere, and then an etching step was performed, and a predetermined polishing step and a cleaning step were performed to fabricate each electrode plate. 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.
For the sample after etching, the copper (Cu) concentration at a depth of 1 μm from the inner circumferential surface of the vent was measured using a secondary ion mass spectrometer.
The measurement results are shown in Table 1.

  As can be seen from Table 1, the copper concentration decreased to 0.2 ppb to 5 ppb by heat treatment at a temperature of 900 ° C. to 1100 ° C., and the copper concentration was the lowest at 1000 ° C. The copper concentration was as high as 10 ppb in both cases where the heat treatment temperature was lower or higher than the range of 900 ° C. or more and 1100 ° C. or less. Although the heat treatment time was 16 hours, it is assumed to be suitable if it is within the range of 12 hours to 32 hours.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

100 plasma processing apparatus 2 vacuum chamber 3 electrode plate (electrode plate for plasma processing apparatus)
4 stand 5 insulator 6 electrostatic chuck 7 support ring 8 wafer (substrate to be processed)
9 etching gas supply pipe 10 diffusion member 11 air vent 12 exhaust 13 high frequency power source 14 cooling plate 15 through hole 31 base plate 32 lower hole 33 hollow base plate 35 damaged layer

Claims (4)

  A method of manufacturing an electrode plate having a plurality of vent holes for circulating a gas for plasma generation, wherein a raw plate serving as the electrode plate is subjected to electrical discharge machining using a working electrode made of copper to prepare an underhole having a diameter smaller than the vent hole. And a heat treatment step of subjecting the perforated plate on which the lower hole is formed to a heat treatment at a temperature of 900 ° C. to 1100 ° C. for 12 hours to 32 hours, and a holed plate after heat treatment And an etching step of etching and removing a layer damaged by the electric discharge machining on an inner peripheral portion of the lower hole.   The method of manufacturing an electrode plate for a plasma processing apparatus according to claim 1, wherein the etching step removes the inner peripheral portion of the lower hole by 20 μm or more in thickness.   The plasma processing apparatus according to claim 1 or 2, further comprising a sizing step of sizing the lower hole by machining using a drill after the drilling step and before the etching step. Method of manufacturing electrode plate. An electrode plate having a plurality of vent holes for circulating a gas for plasma generation, wherein the copper concentration at a depth of 1 μm from the inner circumferential surface of the vent holes is 0.2 ppb to 5 ppb. Electrode plate for plasma processing equipment.

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