JP2002231698A - Focus ring for plasma etching system, and plasma etching system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus ring for significantly reducing the productive yield for a semiconductor integrated circuit and a productive yield, immediately after the usage of the focus ring by preventing failure in etching for a silicon wafer, and provide a plasma etching system, using the focus ring. SOLUTION: In the focus ring for the plasma etching system, concentration of Fe measured in secondary ion mass spectrometry is 1×103 counts or lower, and the plasma etching system using the focus ring is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus ring used for a plasma etching apparatus in a semiconductor device manufacturing process and a plasma etching apparatus using the same.

[0002]

2. Description of the Related Art One of the manufacturing processes of a semiconductor device includes an etching process for forming a circuit pattern on a semiconductor wafer. Among these, a parallel plate type plasma etching apparatus arranges a semiconductor wafer on a lower electrode and places a semiconductor wafer on the lower electrode in parallel with an upper electrode having a large number of through holes for flowing a reaction gas. Plasma is generated to etch the wafer.

In this apparatus, a ring-shaped member called a focus ring is arranged outside the lower electrode in order to prevent the diffusion of plasma around the wafer and effectively cause reactive ions to enter the wafer. The focus ring uses glassy carbon in addition to quartz, silicon, and the like. Glassy carbon is a carbon material obtained by carbonizing and sintering a thermosetting resin.
It has a dense structure. This material has not only characteristics such as conductivity, chemical stability, heat resistance, and high purity, which are the characteristics of general carbon materials, but also excellent characteristics such that constituent particles do not fall off. For this reason, it is said that glassy carbon is suitable for semiconductor production members.

However, with the recent high integration of semiconductor integrated circuits, patterns on silicon wafers have been controlled with higher precision. For this reason, there is a demand for reducing impurities in device members that affect the yield of semiconductor integrated circuits. As a countermeasure, the focus ring made of glassy carbon was highly purified by RCA cleaning used for cleaning silicon wafers, but the production yield of semiconductor integrated circuits, especially immediately after the start of plasma etching, was reduced. It has not been improved significantly.

[0005]

According to the first and second aspects of the present invention, there is provided a plasma etching method capable of preventing a defective etching of a silicon wafer and greatly reducing the production yield of a semiconductor integrated circuit and the production yield immediately after the start of use of a focus ring. It is to provide a focus ring suitable for the device. A third aspect of the present invention is to provide a plasma etching apparatus capable of preventing a defective etching of a silicon wafer and significantly reducing a production yield of a semiconductor integrated circuit and a production yield immediately after starting use of a focus ring.

[0006]

The present invention relates to the following. (1) Fe concentration measured by secondary ion mass spectrometry is 1 ×
A focus ring for a plasma etching apparatus having a density of 10 ³ counts or less. (2) The focus ring for a plasma etching apparatus according to (1), wherein the focus ring is made of glassy carbon. (3) A plasma etching apparatus comprising the focus ring according to (1) or (2).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a focus ring of a plasma etching apparatus is generally a ring-shaped member. FIG. 1 shows an example of a state where the focus ring is mounted on a plasma etching apparatus. FIG. 1 is a schematic sectional view of a parallel plate type plasma etching apparatus. In FIG. 1, an upper electrode 2 and a lower electrode 3 are provided in a plasma etching apparatus 1, and a focus ring 4 is provided on the lower electrode. The wafer 5 is etched by an etching process gas blown from the upper electrode.

The shape of the focus ring may be a ring shape having a circular inner periphery and an outer periphery, a step having a step on the inner periphery, and an orientation flat (orientation flat) formed on the wafer in consideration of the orientation flat. The focus ring may be shaped to match the outer diameter of the wafer. The size of the focus ring differs depending on the mounted plasma etching apparatus and the size of the wafer to be etched. The size of the wafer is generally 6 inches, 8 inches, 12 inches, or the like.
The inner diameter of the focus ring is preferably equal to or smaller than the outer shape of the wafer, and more preferably 0.1 to 10 mm smaller than the outer shape of the wafer. Further, the width (that is, the difference between the inner diameter and the outer shape) of the focus ring is preferably 10 to 100 mm, and the thickness is preferably 1 to 7 mm.

In the focus ring of the present invention, the amount of Fe in the focus ring is determined by secondary ion mass spectrometry (SIM).
The value measured in S) is not more than 1 × 10 ³ counts. Here, the reason why the value of the Fe amount measured by SIMS is specified to be 1 × 10 ³ counts or less is that if the value exceeds the specified value, the silicon wafer as the material to be etched is scattered with the consumption of the focus ring during plasma etching. This is because the semiconductor integrated circuit formed on the silicon wafer becomes defective due to the contamination with Fe.

The method of measuring the purity of a member for a semiconductor manufacturing apparatus, such as a focus ring, a plasma etching electrode or the like, which is currently generally used and which requires particularly high purity, is as follows. (1) After assembling the members such as the focus ring, the amount of impurities in the ash is measured by ICP-MASS. (2) A member such as a focus ring is immersed in 10% hydrochloric acid to extract metal impurities attached to the surface, and then the amount of metal impurities in the extract is measured by ion chromatography. In the above measurement method, in the measurement method (1), although the purity of the bulk of the member can be measured, since the measurement sensitivity is low,
The correlation with the product yield of the semiconductor integrated circuit, particularly with the yield immediately after use, is unknown, and the measurement method (2) can measure only the amount of impurities adhering to the surface.

However, impurities adhering to the surface of the focus ring are almost completely removed by empty discharge (injection of a dummy silicon wafer and generation of plasma) performed at the time of attachment. Has little effect on the stay. Therefore, no correlation was found between the product yield and the amount of impurities. On the other hand, a correlation was found between the Fe amount measured by SIMS and the product yield. The reason is that when the amount of Fe measured by SIMS exceeds the specified value, the focus ring surface layer Fe scattered in the plasma enters the silicon wafer and is formed there along with the consumption of the focus ring. This is because the semiconductor integrated circuit becomes defective.

As the material of the focus ring of the present invention, glassy carbon, quartz, single crystal silicon, polycrystalline silicon, etc. can be mentioned. , And is preferably glassy carbon.
Here, the glassy carbon is an amorphous carbon material obtained by carbonizing and firing a cured thermosetting resin, and the thermosetting resin to be used is not particularly limited, but a phenol resin, an epoxy resin, Unsaturated polyester resin, furan resin, melamine resin, alkyd resin, xylene resin, etc.
Alternatively, a mixture of these resins can be used. Among them, a furan resin, a phenol resin, or a mixed resin thereof is preferable because glassy carbon having good characteristics can be obtained.

A curing agent is used depending on the type of the thermosetting resin. Examples of the curing agent include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, organic sulfonic acids such as p-toluenesulfonic acid and methanesulfonic acid, and carboxylic acids such as acetic acid and trichloroacetic acid. Examples of the alkali include ammonia, amine, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. The curing agent is preferably used in an amount of 0.001 to 20% by weight based on the thermosetting resin.

The thermosetting resin is molded by various molding methods according to the desired shape after the addition of the curing agent as required, and then cured. This curing is 50-300 ° C
It is preferable to carry out the heat treatment at the temperature described above. In order to obtain a stable resin plate, it is preferable that the molding and curing of the resin be performed under a heating condition and a heating rate in which the amount of catalyst for curing is set to an appropriate amount and condensed water and the like easily escape to the outside.

Next, after performing a predetermined process for forming the shape of the focus ring, using a jig and a furnace which have been subjected to a high-purification treatment, an inert gas (usually an inert gas such as helium, argon or the like) is used. About 900 in an oxygen-free atmosphere composed of at least one kind of non-oxidizing gas such as nitrogen, hydrogen, and halogen gas, under reduced pressure or vacuum, or in an atmosphere buried in graphite powder, carbon powder, or the like to shut off the atmosphere.
It is carbonized and fired at a temperature of at least 1000C, preferably at least 1000C. Thereafter, preferably from 1300 ° C to 3000 ° C
To perform high-temperature heat treatment to obtain glassy carbon.
In addition to the above method, the glass-like carbon material plate may be formed into a focus ring shape by a known method such as drilling, electric discharge machining, or ultrasonic machining.

After processing the inner and outer diameter portions of the focus ring, polishing and washing are performed to form the focus ring. However, the present invention is not limited by the above-mentioned starting materials and manufacturing steps. In order to keep the measured value of Fe by SIMS within the range of the present invention, the plasma etching electrode is washed with a strong acid such as hydrofluoric nitric acid, concentrated sulfuric acid, aqua regia or the like added with a surfactant, or in a HCI gas atmosphere at a high temperature. And the like, but any method is not limited in order to achieve the object of the present invention. The SIMS measurement of the present invention was performed using a Hitachi IMA-3 type under the conditions of a primary ion species: O ₂ +, a primary ion acceleration voltage: 20 KV, and a primary ion current: 300 nA.

[0017]

Embodiments of the present invention will be described below. Example 1 A phenol resin (manufactured by Hitachi Chemical Co., Ltd., trade name: VP-112N) was used as a raw material resin, and 8% by weight of trichloroacetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added thereto as a curing agent.
Under heating at 70 ° C., the mixture was cast into an aluminum petri dish having a diameter of 500 mm to obtain a resin plate. This resin plate was heated at 70 ° C for 3 days for 9 days.
After heating and hardening at 0 ° C. for 3 days, carbonization and firing were performed at a rate of 1 ° C./min at a maximum of 900 ° C., and then heat-treated at a rate of 5 ° C./min at a maximum of 3000 ° C. to obtain glassy carbon. . After the obtained glassy carbon flat plate was processed into a required ring shape by electric discharge machining, the surface was finished with lap and polish to form a focus ring. Next, ultrasonic cleaning was performed by immersing in a 5: 5: 1 mixture of hydrofluoric acid having a concentration of 26%, nitric acid having a concentration of 60%, and a surfactant (trade name, manufactured by Asahi Glass). The focus ring of the present invention was obtained by measurement by SIMS with various ultrasonic cleaning times.

The above-mentioned focus ring was attached to a plasma etching apparatus, and trifluoromethane and fluorinated methane were supplied as reaction gases at a flow rate of 20 SCCM each.
00 KHz, gas pressure in the reaction chamber 0.05 Torr
The silicon wafer was etched under the condition of r.
Next, the amount of Fe contamination on the surface of the silicon wafer was measured using a total reflection type fluorescent x-ray analyzer (Model TREX610, manufactured by Technos).
T). Table 1 shows the measurement results.

Comparative Example 1 A phenol resin (product name: VP-112N, manufactured by Hitachi Chemical Co., Ltd.) was used as a raw material resin, and 8% by weight of trichloroacetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a curing agent. In addition,
Under heating at 70 ° C., the mixture was cast into an aluminum petri dish having a diameter of 500 mm to obtain a resin plate. This resin plate was heated at 70 ° C for 3 days for 9 days.
After heat curing at 0 ° C. for 3 days, carbonization and firing were performed at a rate of 1 ° C./min at a maximum of 900 ° C., and then heat-treated at a rate of 5 ° C./min at a maximum of 3000 ° C. to obtain glassy carbon. . After the obtained glassy carbon flat plate was processed into a required ring shape by electric discharge machining, the surface was finished with lap and polish to obtain a focus ring. Then, add 3% hydrochloric acid (concentration 10%).
After ultrasonic cleaning for 0 minutes, the substrate was further washed with pure water for 30 minutes.
This was measured by SIMS to obtain a plasma etching electrode outside the range of the present invention.

The above-mentioned focus ring was attached to a plasma etching apparatus in the same manner as in the embodiment, and trifluoromethane and fluorinated methane were flowed at a flow rate of 20 SCCM each as a reaction gas.
The silicon wafer was etched under the conditions of a power supply frequency of 400 KHz and a gas pressure in the reaction chamber of 0.05 Torr. Then, the amount of Fe contamination on the surface of the silicon wafer was measured by a total reflection X-ray fluorescence spectrometer (Model T, manufactured by Technos).
REX610T). Table 1 shows the measurement results.
In addition, the measurement result of the Fe contamination amount in Table 1 shows an average value of five points in a plane of a 6-inch wafer.

[0021]

[Table 1]

[0022]

According to the first and second aspects of the present invention, there is provided a plasma etching apparatus capable of preventing a defective etching of a silicon wafer and significantly reducing the production yield of a semiconductor integrated circuit and the production yield immediately after the start of use of the focus ring. can do. The plasma etching apparatus according to the third aspect is industrially extremely suitable because it can prevent the defective etching of the silicon wafer and significantly reduce the production yield of the semiconductor integrated circuit and the production yield immediately after the start of use of the focus ring.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a parallel plate type plasma etching apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma etching apparatus 2 Upper electrode 3 Lower electrode 4 Focus ring 5 Silicon wafer

Continued on the front page (72) Inventor Makoto Ishii 3-3-1 Ayukawacho, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Office F-term (reference) 4G032 AA07 AA14 BA04 GA11 GA19 4G075 AA24 AA30 BC06 BD03 BD14 CA47 DA01 EA01 EB01 EB42 EC21 EE02 FB03 5F004 BA04 BB23 BB29 BC03 CA02 CA03

Claims (3)

[Claims] 1. A focus ring for a plasma etching apparatus, wherein the Fe concentration measured by secondary ion mass spectrometry is 1 × 10 ³ counts or less. 2. The focus ring for a plasma etching apparatus according to claim 1, wherein the focus ring is made of glassy carbon. 3. A plasma etching apparatus comprising the focus ring according to claim 1.