JP2019147984A - Silicon carbide member - Google Patents

Abstract

To provide a silicon carbide member capable of being adopted to a focus ring having a corrosion resistance, a heat resistance, and an excellent mechanical property in a plasma treatment apparatus used in manufacturing a semiconductor.SOLUTION: A silicon carbide member 1 has a major component of silicon carbide including a dopant, a ring shape having an outer peripheral 2 and an inner peripheral 3. When a dopant concentration of the outer peripheral part 2a is D1atoms/cmand a dopant concentration of the inner peripheral part 3a is D2atoms/cm, D1 is larger than D2, and a conductivity σ1 of the outer peripheral part 2a is larger than a conductivity σ2 of the inner peripheral part 3a.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to silicon carbide members.

In a plasma processing apparatus used for semiconductor manufacturing, a focus ring is used so that plasma converges on the surface of a wafer. Since the focus ring is used close to the wafer, a material such as quartz or silicon carbide having the same element as that of the wafer as a main component and having high purity or a material that is not easily corroded by plasma is used. Especially chemical vapor deposition (Chemical Vapor)
Silicon carbide material (CVD-SiC material) formed by Deposition, CVD method)
Compared to a silicon carbide material produced by a sintering method, it is highly pure and dense, and has high corrosion resistance, heat resistance, and mechanical strength.

  In the plasma processing apparatus, various members such as a wafer, a focus ring, a peripheral member, and a casing are disposed in a plasma generation region. Plasma may be locally concentrated or plasma may become unstable due to the difference in electrical characteristics of each member. For example, Patent Document 1 discloses a method of reducing plasma concentration by adjusting the conductivity between members by combining a quartz focus ring, which is an insulating material, and a conductive member.

JP 2002-246370 A

The silicon carbide member of the present disclosure has a ring shape having silicon carbide containing a dopant as a main component and having an outer periphery and an inner periphery. The outer peripheral portion of the dopant concentration D1atoms / cm ^3, when the inner peripheral portion D2atoms / cm ³ a dopant concentration of, D1 is greater than D2.

It is a perspective view which shows typically the external appearance of a silicon carbide member. It is a top view which shows typically the arrangement | positioning of the base | substrate in a CVD apparatus, and a gas introduction nozzle.

  The silicon carbide member 1 of the present disclosure has an annular shape having an outer periphery 2 and an inner periphery 3 as shown in FIG.

Silicon carbide materials, especially CVD-SiC materials created by chemical vapor deposition (CVD), are used as various semiconductor manufacturing equipment members because of their high purity and high plasma resistance. Yes. Further, the conductivity of the CVD-SiC material can be adjusted by introducing a dopant, and a focus ring having an intermediate conductivity between the conductivity of the wafer and the conductivity of the peripheral casing can be realized. Hereinafter, silicon carbide may be referred to as SiC.

  Silicon carbide member 1 is mainly composed of silicon carbide containing a dopant. Here, the main component is a component that occupies 90% or more of the member. The silicon carbide member 1 includes silicon carbide not containing a dopant, silicon carbide not containing a dopant, and crystalline or amorphous carbon such as graphite, silicon crystals, and impurities not affecting the characteristics. Ingredients may be included.

The conductivity of silicon carbide varies depending on the dopant concentration, which is the number of dopant atoms per unit volume. Silicon carbide member 1 of the present disclosure, D1atoms / cm ³ a dopant concentration of the peripheral portion 2a, when the dopant concentration of the inner peripheral portion 3a was D2atoms / cm ^3, D1 is greater than D2. The outer peripheral portion 2 a is a portion in the vicinity including the outer periphery 2, and the inner peripheral portion 3 a is a portion in the vicinity including the inner periphery 3. The vicinity of the outer periphery 2 is a range where the distance to the outer periphery 2 is 10 mm or less, and the vicinity of the inner periphery 3 is a range where the distance to the inner periphery 3 is 10 mm or less. For example, the outer peripheral side from the middle point between the outer periphery 2 and the inner periphery 3 may be the outer peripheral part 2a, and the inner peripheral side from the middle point may be the inner peripheral part 3a.

  Silicon carbide has higher conductivity as the dopant concentration is higher. Therefore, when the conductivity of the outer peripheral portion 2a of the silicon carbide member 1 is σ1 and the conductivity of the inner peripheral portion 3a is σ2, since D1 is larger than D2, σ1 is larger than σ2.

Semiconductor manufacturing equipment, especially CVD (Chemical Vapor Deposition), PV
In a plasma processing apparatus such as D (Physical Vapor Deposition) and a plasma etching apparatus, a wafer such as Si is subjected to plasma processing. In these apparatuses, a focus ring is disposed on the outer periphery of the wafer to stabilize the plasma on the wafer. By using a material having a resistivity equivalent to or similar to that of the wafer and high corrosion resistance to the plasma for the focus ring, the plasma can be stabilized and the wafer can be processed more uniformly. Also, since the wafer is a semiconductor and other peripheral members such as the casing of the plasma processing apparatus are often conductors, the wafer and the peripheral members can be provided by providing the focus ring with an intermediate conductivity between the semiconductor and the conductor. And the rapid change in conductivity is relaxed, and the plasma is more stabilized. However, in this case as well, the conductivity of the focus ring is uniform between the semiconductor and the conductor, so that the conductivity changes abruptly at the boundary between the wafer and the focus ring and at the boundary between the peripheral member and the focus ring. As a result, plasma concentrates on these boundary portions, and the plasma density at these boundary portions tends to increase. As a result, there is a concern that abnormal discharge occurs at the boundary between these members, or the etching state of the wafer varies and the yield of the semiconductor is lowered.

  When the silicon carbide member 1 of the present disclosure is a focus ring, the outer peripheral portion 2a, that is, the portion D1 in the vicinity of the peripheral member that is a conductor is large and σ1 is large, and therefore the conductivity at the boundary between the focus ring and the peripheral member The abrupt change is relaxed, making it difficult for plasma to concentrate on the boundary. In addition, since D2 in the inner peripheral portion 3a, that is, a portion close to the wafer, which is a semiconductor, is small and σ2 is small, an abrupt change in conductivity is reduced at the boundary between the focus ring and the wafer, and plasma is generated at the boundary It becomes difficult to concentrate.

  In addition, the silicon carbide member 1 is different in the dopant concentration between the outer peripheral portion 2a and the inner peripheral portion 3a, but is a single material and is used for a long period of time compared to a combination of a plurality of members having different conductivity. However, the electrical conductivity and durability against plasma are hardly changed.

  The dopant concentrations D1 and D2 may be appropriately adjusted so as to obtain desired σ1 and σ2 depending on the type and conductivity of the wafer to be plasma-treated and the type and conductivity of the peripheral member. As for the ratio of D1 and D2, LogD1 / LogD2 may be 1.01 or more, for example. By setting LogD1 / LogD2 to 1.01 or more, the conductivity σ2 of the inner peripheral portion 3a close to the wafer can be made closer to the conductivity of the wafer, and the conductivity σ1 of the outer peripheral portion 2a close to the peripheral member can be set to The electrical conductivity of the peripheral member can be approached. In addition, since the dopant concentration changes by a digit, it is usually compared logarithmically.

The conductivity σ1 of the outer peripheral portion 2a may be 5 or more in the ratio σ1 / σ2 with respect to the conductivity σ2 of the inner peripheral portion 3a. By setting σ1 / σ2 to 5 or more, the conductivity σ2 of the inner peripheral portion 3a is close to the conductivity of the Si wafer, and the conductivity σ1 of the outer peripheral portion 2a adjacent to the peripheral member is close to the conductivity of the peripheral member. Become. By using such a silicon carbide member 1 as a focus ring, a sudden change in conductivity is mitigated at the boundary between the wafer and the focus ring and the boundary between the outer peripheral member and the focus ring, and plasma is generated at the boundary. It becomes difficult to concentrate.

  The conductivity of silicon carbide member 1 may continuously increase from inner peripheral portion 3a toward outer peripheral portion 2a. Here, the electrical conductivity continuously increases from the inner peripheral portion 3a toward the outer peripheral portion 2a means that the conductivity σ3 of the intermediate portion between the inner peripheral portion 3a and the outer peripheral portion 2a is larger than σ2 and larger than σ1. It is small.

Such a silicon carbide member 1 can be manufactured by a chemical vapor deposition method (Chemical Vapor Deposition, CVD method) as follows. The CVD apparatus used for producing SiC member 1 is not particularly limited. The CVD apparatus may include, for example, a vertical or horizontal batch type CVD chamber having gas inlets and outlets, and an electric heating means. In a CVD apparatus that heats using a high frequency, the substrate can be selectively heated. The frequency of the high frequency used for heating may be, for example, 3 kHz or more and 100 kHz or less.

  Any CVD method may be used as long as a substrate is set in the CVD chamber, a gas such as a source gas or a carrier gas is introduced into the CVD chamber, and a chemical vapor deposition (CVD) reaction is performed on the substrate.

  The source gas may be a gas containing carbon atoms and silicon atoms. As the gas containing a silicon atom, a gas having a structure in which one or more chlorine atoms are bonded to a silicon atom in the molecule may be used. Methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, a mixed raw material of silicon chloride and hydrocarbon gas, or the like may be used. By using these source gases, CVD-SiC can be deposited at high speed, and the SiC member 1 can be produced efficiently.

  These source gases are mixed with a carrier gas such as hydrogen or argon at a predetermined ratio and introduced into the CVD chamber as a mixed gas. As for the mixing ratio of the source gas and the carrier gas, for example, the volume of the carrier gas may be 3 to 10 times the volume of the source gas containing silicon atoms. The carrier gas may be hydrogen. When hydrogen is used as a carrier gas, the dechlorination reaction from silicon atoms can be promoted.

  A gas containing atoms as dopants is further introduced into the CVD chamber. Nitrogen, boron, or the like may be used as the dopant atom. Examples of the nitrogen-containing gas include nitrogen, ammonia, trimethylamine, and triethylamine. Examples of the boron-containing gas include boron trichloride and diborane. Hereinafter, a gas containing an atom serving as a dopant may be simply referred to as a dopant gas.

  The ratio between the source gas and the dopant gas may be appropriately adjusted according to the type of the dopant gas and the amount of the desired dopant introduced. For example, the volume of the dopant gas may be 0.01% or more and 5000% or less with respect to the volume of the source gas containing silicon atoms. Hereinafter, the mixed gas of the source gas, the carrier gas, and the dopant gas is generally referred to as a mixed source gas.

FIG. 2 shows one example of the arrangement of the substrate 4 and the gas introduction nozzle 5 in the CVD chamber. In FIG. 2, the gas introduction nozzle 5 is arranged on the outer periphery of the disk-shaped base 4. The substrate 4 may be, for example, 5 mm to 20 mm in thickness. The substrate 4 may be rotated about the center O of the disk. The white arrow indicates the direction of the mixed raw material gas introduced from the gas introduction nozzle. By introducing the mixed source gas from the outer periphery of the substrate 4 toward the center along the surface of the substrate, CVD-SiC having different dopant concentrations in the radial direction can be obtained.

  By adjusting the type, ratio, and flow rate of the source gas, dopant gas, and carrier gas, the distribution of the dopant concentration contained in CVD-SiC can be adjusted. When hydrogen is used as the carrier gas, decomposition of the source gas and the dopant gas can be promoted or suppressed depending on the ratio of the source gas and the dopant gas.

  The CVD reaction temperature may be, for example, 1200 ° C. or higher, and may be 1250 ° C. or higher. When the reaction temperature is less than 1200 ° C., the deposition rate of CVD-SiC is remarkably lowered, and the production efficiency is lowered. The reaction temperature may be particularly 1350 ° C. or higher, more preferably 1350 ° C. or higher and 1500 ° C. or lower.

  For example, graphite may be used as a substrate on which CVD-SiC is deposited. Since the thermal expansion coefficient of graphite is close to the thermal expansion coefficient of SiC, the use of graphite as the substrate can reduce deformation due to thermal stress of the substrate and the CVD-SiC formed on the surface of the substrate.

  The thermal expansion coefficient of graphite may be slightly larger than the thermal expansion coefficient of CVD-SiC. When the substrate and the CVD-SiC are cooled to room temperature after depositing the CVD-SiC, if the thermal expansion coefficient of graphite is slightly larger than the thermal expansion coefficient of the CVD-SiC, the thermal stress generated in the CVD-SiC is a compressive stress. It becomes. By applying compressive stress to CVD-SiC, cracks are less likely to occur in CVD-SiC.

  The SiC member 1 used for the focus ring uses CVD-SiC as a self-solid (also referred to as a self-supporting film). In the SiC member 1 used as a self-three-dimensional object, it is necessary to remove the substrate from the formed CVD-SiC. A graphite substrate is easily removed from CVD-SiC by oxidation or grinding.

By using a silicon tetrachloride (SiCl ₄ ) containing silicon as a raw material gas for SiC, methane containing carbon (CH ₄ ), hydrogen (H ₂ ) as a carrier gas, and ammonia (NH ₃ ) as a dopant gas, a CVD method is used. Then, CVD-SiC was formed on the graphite substrate.

  The CVD apparatus used was an apparatus that heated graphite by high-frequency induction heating. The frequency of the high frequency was 60 kHz. In the CVD chamber, a graphite disc having a diameter of 350 mm and a thickness of 15 mm was placed as a substrate. The two disks were overlapped with an interval of 15 mm, the center of each disk was held by a substrate support made of heat insulating material, and further connected to a rotating mechanism.

  On the outer periphery of the disc, four gas introduction nozzles having an inner diameter of 15 mm were respectively arranged at four locations as shown in FIG. The distance between the gas introduction nozzle and the outer periphery of the disc was 5 mm.

  While the CVD chamber was evacuated, the graphite disk was heated to a temperature of 1400 ° C. While rotating the two disks at a rotation speed of 5 rpm each, a mixed gas in which a source gas, a carrier gas and a dopant gas are mixed into the gap between the two disks is introduced by a gas insertion nozzle, and the surfaces of the two disks CVD-SiC was deposited on the substrate. Table 1 shows the flow rate of each gas.

  The graphite substrate was removed from the obtained two CVD-SiCs by grinding, and further processed into an annular shape having an outer diameter of 350 mm, an inner diameter of 300 mm, and a thickness of 4 mm to obtain a focus ring.

The conductivity of the two focus rings obtained was measured. The conductivity at 4 points of 5 mm distance from the outer periphery as the outer periphery, 4 points at 5 mm distance from the inner periphery as the inner periphery, and 4 points of intermediate points between the outer periphery and the inner periphery by the 4-probe method, respectively. It was measured. The measurement results of the two focus rings coincided within the error range. Table 1 shows the conductivity σ1 of the outer peripheral portion, the conductivity σ2 of the inner peripheral portion, and the ratio σ1 / σ2. Sample No. In 1 and 2, the conductivity σ3 at the midpoint between the outer periphery and the inner periphery was smaller than σ1 and larger than σ2. Sample No. 3 is the same as σ1 and σ2, and sample no. In 4, it was σ1 <σ3 <σ2. In addition, the electrical conductivity of the silicon wafer used for the plasma etching test mentioned later was 10 S / m.

  The dopant concentration of one focus ring was measured using secondary ion mass spectrometry (SIMS). The measurement was performed on a part (D1) having a distance of 5 mm from the outer periphery and a part (D2) having a distance of 5 mm from the inner periphery. Table 1 shows the average value of the dopant concentration D1 in the outer peripheral portion, the average value of the dopant concentration D2 in the inner peripheral portion, and the ratio LogD1 / LogD2.

The other focus ring was installed in a plasma etching apparatus together with a silicon wafer having a diameter of 300 mm, and a plasma etching test of the silicon wafer was performed. In the etching process, CF ₄ gas was introduced into the etching chamber, and a high frequency of 13.56 MHz was introduced at an output of 0.8 W / cm ² to generate plasma for 4 hours.

  The silicon wafer was used as a mask by applying polyimide tape from the center to the outer periphery before the etching process. After the plasma treatment, the polyimide tape was removed from the silicon wafer, and after cleaning, the level difference between the mask portion and the non-mask portion was measured to calculate the etching rate. The measurement locations were eight points with a distance of 10 mm from the wafer center as the wafer central portion, and eight points with a distance from the outer periphery of the wafer of 10 mm as the wafer outer peripheral portion. Table 1 shows Re / Rc, which is the ratio of Re at the outer peripheral portion to Rc at the central portion, where Rc is the average etching rate at the central portion and Re is the average etching rate at the outer peripheral portion.

  Sample No. In 1 and 2, since the outer peripheral portion D1 is larger than the inner peripheral portion D2, the etching rate ratio Re / Rc of the silicon wafer is close to 1.0, and a uniform etching process is performed. On the other hand, Sample No. In 3 and 4, since D1 is D2 or less, the plasma becomes non-uniform near the outer periphery of the silicon wafer, and the etching rate ratio Re / Rc of the silicon wafer is large.

1: Silicon carbide member 2: Outer circumference 2a: Outer circumference 3: Inner circumference 3a: Inner circumference 4: Base 5: Gas introduction nozzle

Claims (5)

The main component is silicon carbide containing a dopant,
Having an annular shape having an outer periphery and an inner periphery;
The dopant concentration in the outer peripheral portion D1atoms / cm ^3, when the dopant concentration of the inner peripheral portion was D2atoms / cm ^3, D1 is greater than D2, the silicon carbide member.   The silicon carbide member according to claim 1, wherein the D1 and the D2 satisfy a relationship LogD1 / LogD2 ≧ 1.01. When the conductivity of the outer periphery is σ1, and the conductivity of the inner periphery is σ2,
The silicon carbide member according to claim 1 or 2, wherein σ1 / σ2 that is a ratio of σ1 to σ2 is 5 or more.   The silicon carbide member according to claim 1, wherein the conductivity continuously increases from the inner peripheral portion toward the outer peripheral portion.   The silicon carbide member according to claim 1, wherein the dopant is nitrogen.

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