JP7635606B2 - Electrode plate for plasma processing apparatus and method for manufacturing same - Google Patents

Description

The present invention relates to an electrode plate used in a plasma processing device and a method for manufacturing the same.

In plasma processing equipment such as plasma etching equipment and plasma CVD equipment used in semiconductor device manufacturing processes, a pair of electrodes connected to a high-frequency power source are arranged, for example, facing each other in the vertical direction within a chamber, with the substrate to be processed placed on the lower electrode, and a high-frequency voltage is applied while a processing gas is passed toward the substrate to be processed through an air hole formed in the upper electrode, generating plasma and performing processing such as etching on the substrate to be processed.

The electrode plates used in this plasma processing device are made by cutting ingots of single crystal silicon, columnar silicon, etc. into thin disks, then finishing them through machining such as forming ventilation holes, etching to polish the surface, polishing, etc. Furthermore, in order to perform uniform plasma processing on the substrate to be processed, the electrode plates are required to have little variation in resistivity within their surfaces.

Patent Document 1 discloses that when manufacturing an electrode plate made of P-type silicon, the method includes a first heat treatment process in which the silicon material is held at a temperature of 550°C to 700°C for 30 to 120 minutes, and then cooled at a rate of 100°C/min to 180°C/min, and a second heat treatment process in which the silicon material is held at a temperature of 300°C to 350°C for 20 to 30 hours, and then cooled, after the first heat treatment process. The electrode plate is then manufactured through a vent hole forming process and a finishing process. In this case, the thickness of the electrode plate is described as 5 mm to 20 mm.

Patent Document 2 discloses that after forming vent holes in a base plate obtained from a silicon ingot, the plate is etched to remove surface damage, and then a donor killing process is carried out at a temperature of 400 to 1000°C to stabilize the resistance. Patent Document 2 does not disclose the thickness of the resulting electrode plate or the diameter of the vent holes.

Patent Document 3 discloses that a porous silicon carbide sintered body (base plate) made mainly of α-SiC with an open porosity of 10-40% and a 6H-type crystal structure is drilled to form a large number of gas introduction holes (vent holes), and then the sintered body is heat-treated in an inert gas atmosphere at 1500-2300°C for 10-600 minutes to re-sinter the grain boundary parts of the inner walls of the holes that have been weakened by the drilling, thereby suppressing the generation of particles. It is stated that this electrode plate has a diameter of 100-300 mmφ and a thickness of 1-5 mmt, and that the specific resistance is preferably 10 Ω·cm or less.

JP 2018-133537 A Special Publication No. 2010-519763 JP 2001-7082 A

Conventional electrode plates, as described in Patent Document 1, have a thickness of 5 mm to 20 mm, but in recent years, there has been a demand to increase the thickness of electrode plates in order to extend their lifespan. In such cases, it is difficult to make the resistivity uniform using conventional methods.

The present invention was made in consideration of these circumstances, and aims to provide an electrode plate for a plasma processing device and a manufacturing method thereof that can suppress the variation in resistivity during plasma processing, even in a thick electrode plate, and can perform uniform plasma processing and achieve a long service life.

The method for manufacturing an electrode plate for a plasma processing device of the present invention includes a slicing process for forming a base plate having a thickness of 15 mm to 35 mm from a silicon ingot, a vent hole forming process for forming a large number of vent holes penetrating the base plate so that the ratio of the total volume of the vent holes to the volume of the base plate is 0.04% to less than 1.0%, and a heat treatment process for heating the base plate with the vent holes to a temperature of 550°C or higher, and then cooling it at a rate of 100°C/min to 180°C/min.

In order to suppress the variation in the resistivity, the oxygen donors can be reduced and the resistivity stabilized by rapidly cooling after heating. If the electrode plate is thick, the effects of heating and rapid cooling do not easily reach the inside.
In this manufacturing method, the base plate is heat-treated after forming vent holes at a predetermined volume ratio, and the presence of the vent holes at a predetermined volume ratio allows the base plate to be heated evenly to the inside during heat treatment and to be rapidly cooled to the inside during cooling. If the volume ratio of the vent holes is less than 0.04 % , the effects of heating and rapid cooling do not easily reach the inside, and the resistivity value is not stable. If the volume ratio is 1.0 % or more, the processing gas will wrap around the electrode plate, making it easy to generate particles. The volume ratio of the vent holes is preferably 0.05% or more and 0.8% or less.

In addition, if the cooling rate during the heat treatment is less than 100° C./min, the donor suppression effect is reduced and the resistivity value is not stable. If it exceeds 180° C./min, there is a risk of cracks occurring in the electrode plate. The cooling rate is preferably 110° C./min or more and 180° C./min or less.
The thickness of the electrode plate is preferably more than 20 mm, and is particularly effective for electrode plates having a thickness of 25 mm or more. If the thickness of the electrode plate exceeds 35 mm, it becomes difficult to stabilize the resistivity value.
Silicon ingots are also produced from single crystal silicon, columnar silicon or polycrystalline silicon.

In this method for manufacturing an electrode plate for a plasma processing device, it is preferable to have an etching process for etching the surface of the base plate after the heat treatment process. By etching, not only can the processing damage layer be removed, but also an oxide film that may form on the surface of the base plate during heat treatment can be removed, thereby further suppressing the generation of particles.

The electrode plate for a plasma processing apparatus of the present invention is made of silicon, has a thickness of 15 mm to 35 mm, has a ratio of the total volume of the vent holes to the volume of the electrode plate of 0.04 % to less than 1.0 % , and has an in-plane variation in resistivity of 0.1 Ω cm to 1.5 Ω cm. The variation in resistivity is preferably 3 Ω cm or less.
If the variation in resistivity is small, the plasma generated during plasma processing is stable, which reduces the defective rate of the processed plate and also leads to uniform wear of the electrode plate, which is advantageous for extending the life of the plate.

According to the present invention, even with thick electrode plates, it is possible to suppress the variation in resistivity during plasma processing, allowing uniform plasma processing to be performed and achieving a longer life.

1A and 1B are a plan view and a partial sectional view showing an electrode plate for a plasma processing apparatus according to an embodiment of the present invention; 4 is a flowchart illustrating a method for manufacturing an electrode plate for a plasma processing apparatus according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an electrode plate for a plasma processing apparatus and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
The electrode plate for plasma processing apparatus (hereinafter simply referred to as electrode plate) 11 of this embodiment is formed of single crystal silicon, columnar silicon, or polycrystalline silicon in a disk shape having a thickness of 15 mm to 35 mm and a diameter of 200 mm to 600 mm, as shown in Fig. 1. In addition, this electrode plate 11 has several hundred to several thousand vent holes 21 formed in a parallel manner penetrating the thickness direction at a pitch of several mm to 10 mm. Each vent hole 21 is formed by drilling or laser processing, and the ratio of the total volume of the vent holes 21 to the volume of the electrode plate 11 (hereinafter referred to as the volume ratio) is set to 0.04% or more and less than 1.0%. The ends of the vent holes 21 may be chamfered, and the volume is measured including the chamfered parts.
Moreover, the electrode plate 11 has an in-plane variation in resistivity of 1.5 Ω·cm or less.

As shown in the flowchart of FIG. 2, the electrode plate 11 thus configured is manufactured through an ingot formation process in which a silicon ingot such as single crystal silicon is formed, a slicing process in which the silicon ingot is thinly cut (sliced) into a disk shape to form a plate-shaped base plate, a contour processing process in which the outer periphery of the base plate is cut to form a base plate with a specified outer diameter, a vent hole forming process in which a large number of vent holes 21 are formed in the base plate after the contour processing, a heat treatment process in which a heat treatment is performed on the base plate with the vent holes 21 formed, an etching process in which an etching process is performed on the base plate after the heat treatment, and a finishing process such as polishing the surface after the etching process.

In the ingot formation process, silicon ingots in the shape of cylinders, blocks, etc. are formed using single crystal silicon, columnar crystal silicon, or polycrystalline silicon by methods such as the Czochralski method or casting.

In the slicing process, the material is cut into thin disk-shaped base plates using a diamond band saw, wire saw, etc. After cutting, both sides are ground to reduce the amount of damage caused by the process.
In the outer shape processing, the outer shape of the base plate is processed by cutting to form it into a disk shape that will be the outer shape of the intended electrode plate 11.

In the vent hole forming process, the vent holes 21 are machined one by one by lowering a drill parallel to the thickness direction from one surface side of the base plate, or by irradiating with a laser. In this vent hole forming process, hundreds to thousands of vent holes 21 are formed as described above, and the total volume of these vent holes 21 is formed so that the volume ratio of the volume of the base plate to the volume of the base plate is 0.04 or more and less than 1.0. For example, if 606 vent holes 21 with an inner diameter of 0.8 mm are formed in a base plate with a diameter of 380 mm, the volume ratio will be 0.27.

After multiple ventilation holes 21 are formed in the base plate in the ventilation hole forming process, in the heat treatment process, the base plate with the ventilation holes 21 formed therein is placed in a heating furnace and heated to a temperature of 550°C or higher in an inert atmosphere such as an argon atmosphere. For example, the plate is heated to a temperature of 550°C or higher and 1000°C or lower. After maintaining the plate at the peak temperature for 4 hours to 16 hours, the plate is removed from the heating furnace and rapidly cooled by blowing cold air. The cooling rate is 100°C/min to 180°C/min. In particular, when cooling in the temperature range of around 450°C, electrons are released from the oxygen in the base plate, which becomes a donor and causes the resistivity to vary. Therefore, by passing through the temperature range quickly, the release of electrons is suppressed, and as a result, the variation in the resistivity is suppressed.

In this heat treatment process, since a large number of ventilation holes 21 are formed in the base plate in the ventilation hole forming process prior to the heat treatment process, the base plate is heated evenly to the inside during heating, and the entire base plate is rapidly cooled during quenching, effectively suppressing the emission of electrons and suppressing the variation in resistivity. The cooling rate is preferably 110°C/min or more and 180°C/min or less.
This heat treatment also has the effect of removing distortions that occur in the preceding slicing and venting steps.

The etching process is performed by immersing the base plate in an acid etching solution. For example, hydrofluoric acid (HF), nitric acid (HNO ₃ ), and acetic acid (CH ₃ COOH) are mixed to form hydronitric acid-acetic acid. The immersion time in the etching solution is 10 to 95 minutes. An oxide film is formed on the surface by cooling in the air in the heat treatment process, and this is removed in the etching process. In addition, processing damage such as microcracks on the inner surface of the ventilation hole 21 formed in the ventilation hole forming process can also be removed.

In the finishing process, both sides of the base plate are polished while a slurry (polishing liquid) containing abrasives such as colloidal silica or diamond abrasive grains is supplied onto a rotating polishing pad. After polishing, the base plate is finished into an electrode plate 11 by washing with running water or the like. Ultrasonic cleaning may also be performed.

The electrode plate 11 manufactured in this manner is subjected to a heat treatment process after the vent hole forming process, and since the vent holes 21 are present at a volume ratio of 0.04 or more and less than 1.0, the electrode plate 11 is heated evenly to the inside during the heat treatment and can be rapidly cooled to the inside. Therefore, the electrode plate 11 can be manufactured with a small in-plane variation in resistivity of 1.5 Ω cm or less, and a uniform process can be performed by a stable plasma process.
If the volume ratio of the ventilation holes 21 is less than 0.04, the effects of heating and quenching do not easily reach the inside, and the resistivity value is not stable. If the volume ratio is 1.0 or more, the process gas will be drawn around the electrode plate 11, generating particles. The volume ratio of the ventilation holes 21 is preferably 0.05 or more and 0.8 or less. Also, the in-plane variation of the resistivity value is preferably 3 Ω cm or less.

The present invention is not limited to the configuration of the above embodiment, and various changes can be made to the details of the configuration without departing from the spirit of the present invention.
All the vent holes 21 may be formed to have the same inner diameter, or the inner diameter may be changed depending on the position on the electrode plate 11. Also, the vent holes 21 on the front and back sides of the electrode plate 11 may have different inner diameters.

A single crystal silicon ingot was sliced to form a base plate of various thicknesses with an outer diameter of 380 mm, and the electrode plate was fabricated through a vent hole forming process, a heat treatment process, an etching process, and a finishing process. The inner diameter of the vent hole and its volume ratio to the volume of the electrode plate were as shown in Table 1. The vent hole was formed in a straight shape with a uniform inner diameter. The inner diameter was measured by a three-dimensional measuring machine for the opening of the vent hole on the surface of the electrode plate, and the volume was calculated by measuring the thickness of the electrode plate. In addition, an electrode plate without a vent hole was also fabricated for comparison (Comparative Example 2).
The heat treatment was carried out by heating to 630° C. and cooling at the cooling rate shown in Table 1. A comparative example was also produced without heat treatment (Comparative Example 1).
For these electrode plates, the in-plane variation in resistivity and the number of particles generated during plasma processing were measured, and the service life was evaluated.
The resistivity was measured by a four-probe method with a probe placed on the surface of the electrode plate, and the difference between the maximum and minimum values measured at three points on the surface of the electrode plate was taken as the variation.
The number of particles generated was measured by attaching the electrode plate to the sputtering device.
Pressure in chamber: 10 ⁻¹ Torr
Etching gas composition: 90 sccm _CHF3 + 4 sccm _O2 + 150 sccm He
High frequency power: 2kW
Vacuum frequency: 20kCycle
Sputtering was carried out continuously for 100 hours under the above conditions, and the number of particles was counted using a particle counter. Those with 100 or more particles were rated as "no good" and those with less than 100 particles were rated as "good."
The service life was judged based on the time of use, with a service life of 500 hours being rated "good" and a service life of less than 500 hours being rated "poor."
The overall evaluation was given as "A" when the resistivity was 1.5 Ω cm or less and both the number of particles generated and the service life were "good", "B" when the resistivity was 1.5 Ω cm or more, the number of particles generated was "good" and the service life was "good", and "C" when the resistivity exceeded 1.5 Ω cm, the number of particles generated was "poor", or the service life was "poor". Comparative Example 2 was given a "-" because no vent holes were formed, and was given a "C" because it had no properties as an electrode.

The results are shown in Table 1. For Comparative Example 2, in which no ventilation holes were formed, only the resistivity value was measured. For Comparative Example 6, cracks occurred during the heat treatment, so measurements below the resistivity value were not performed.

In Table 1, for Examples 1 to 6, the variation in resistivity was small, at 1.3 Ω cm or less, when the thickness was 15 mm or more and 30 mm or less. In addition, there was little generation of particles, and the life was sufficient.

In contrast, in Comparative Example 1, since no heat treatment was performed, the variation in resistivity was as large as 1.8 Ω·cm, and therefore uniform plasma treatment could not be performed. Comparative Example 2 was an electrode plate without vent holes, and even after heat treatment, the variation in resistivity was as large as 1.6 Ω·cm. Comparative Example 3 had a large volume ratio of vent holes of 1.0, so the variation in resistivity was small, but many particles were generated, and the overall evaluation was C. Comparative Example 4 had a large thickness of 40 mm and a small cooling rate during heat treatment of 80° C./min, so the variation in resistivity was large as 1.7. Comparative Example 5 had a small cooling rate during heat treatment of 50° C./min, so the variation in resistivity was large as 1.8. Comparative Example 6 had a large cooling rate during heat treatment of 200° C./min, so cracks occurred during cooling.
All of the conventional examples were thin, at 13 mm, had small variations in resistivity, and no particle generation was observed, but had a short lifespan due to wear.

11 Electrode plate 21 Ventilation hole

Claims (3)

1. A method for manufacturing an electrode plate for a plasma processing apparatus, comprising: a slicing step for forming a silicon base plate having a thickness of 15 mm or more and 35 mm or less; a vent hole forming step for forming a large number of vent holes penetrating the base plate such that the ratio of the total volume of the vent holes to the volume of the base plate is 0.04 % or more and less than 1.0 % ; and a heat treatment step for heating the base plate with the vent holes formed therein to a temperature of 550° C. or more and then cooling at a rate of 100° C./min. or more and 180° C./min. or less. The method for manufacturing an electrode plate for a plasma processing apparatus according to claim 1, further comprising an etching step for etching the surface of the base plate after the heat treatment step. 1. An electrode plate for a plasma processing apparatus, comprising: a silicon electrode plate having a thickness of 15 mm or more and 35 mm or less; a ratio of the sum of the volumes of the air holes to the volume of the electrode plate of 0.04 % or more and less than 1.0 % ; and an in-plane variation in resistivity, which is the difference between the maximum and minimum resistivity values measured at three points within the plane of the electrode plate, of 0.1 Ω-cm or more and 1.5 Ω-cm or less.

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