JPH0814033B2 - Electrode plate for plasma etching - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plasma etching electrode plate made of high-purity glassy carbon.

2. Description of the Related Art Generally, a glass-like carbon material is obtained by carbonizing a cured product of a thermosetting resin having an insoluble and infusible property in an inert atmosphere. This glassy carbon material is excellent in gas impermeability, has high hardness, and has an isotropic structure. Furthermore, this glassy carbon material generally has a light weight, heat resistance, high electrical conductivity, candy resistance, high thermal conductivity that a carbon material has, and in addition to its excellent mechanical strength and lubricity, It also has the characteristics of homogeneity and the characteristics of not producing carbon powder such as cutting chips when it is slidably used. Recently, focusing on the characteristics of such glassy carbon material, plasma treatment of glassy carbon material was performed. Utilization as an etching electrode plate is under study.

The glassy carbon currently commercialized is mainly manufactured by the following method.

A thermosetting resin is used as a raw material, and a substrate having a predetermined shape is thinly applied with a brush, spray, centrifugal method or the like, and then the operation is repeated to cure the resin.

The aggregate itself is made into a resin powder, which is molded and then fired to obtain glassy carbon.

Conventionally, a graphitizable carbon material using pitch or the like as a raw material, coke is crushed to produce a powdery carbon material, an appropriate binder is added to the powdery carbon material, and the mixture is kneaded. It has been manufactured by molding a material to form a molded body, firing the molded body, and graphitizing the fired body by heat treatment.

Japanese Unexamined Patent Publication (Kokai) No. 62-252942 discloses a plasma etching electrode plate made of high-purity glassy carbon. The production method is as follows: Liquid furan-based resin, phenol-based resin, or a mixed resin thereof, or a mixture of curable resin powders of the same kind added and mixed into a flat plate and then cured to form a resin. A plate is made, and then the resin plate is calcined and carbonized at 800 ° C in an inert atmosphere, further graphitized at 3000 ° C if necessary, and then deashed and highly purified. A large number of through holes having a diameter of 0.8 mm are formed at intervals of 2 mm or the like on the electrode plate manufactured in this manner. The thickness of the electrode plate is 3 mm. The physical properties of the electrode plate are a bulk specific gravity of 1.45 g / cm ³ , a porosity of 3%, a Shore hardness of 75, a bending strength of 580 kgf / cm ² , and an elastic modulus of 2430 kgf / cm ² .

Problems to be Solved by the Invention According to the above-described manufacturing method, a large number of pores having a relatively large diameter (about 2 μm) are generated due to voids during molding, dissipation of volatile components during heat treatment, and the like.

Further, the size and distribution of pores differ depending on the size of aggregate particles, the type of binder, the manufacturing process, and the like. for that reason,
The physical properties associated with pores become very complicated.

When the conventional glass-like carbon electrode plate for plasma etching is observed with an electron microscope, as shown in FIG. 7, there are open pores with a large diameter (about 2 μm) on the surface. In addition, closed pores having a large diameter (about 2 μm) also exist inside the electrode plate.

In this way, due to the open pores peculiar to glassy carbon,
The phenomenon that the specific surface area increases and the acidic characteristics and strength decrease is derived.

If not only open pores but also closed pores are present in the electrode plate, internal closed pores will appear on the surface when polishing and become open pores, and the same phenomenon as the above problem will occur.

The method described in detail as a conventional technique is inconvenient in that many open pores and closed pores are present in the laminated portion of the resin after firing. However, the characteristics such as mechanical strength and porosity are inferior to those of ordinary glassy carbon, and carbon particles are likely to fall off during use or during mouth washing.

In order to prevent this phenomenon of carbon particles falling off, a method of forming a glassy carbon film or a pyrolytic carbon film on the surface of the electrode plate has been proposed, but the mechanical strength of the film itself is weak and the problem of film peeling There was a point.

OBJECT OF THE INVENTION An object of the present invention is to provide an electrode plate for plasma etching, which has good plasma stability and excellent durability.

SUMMARY OF THE INVENTION The gist of the present invention resides in the electrode plate for plasma etching described in the claims.

Means for Solving Problems The electrode plate for plasma etching of the present invention is a plate-like body having a thickness of 2 mm or more and made of high-purity glassy carbon, and grain boundaries are not substantially present on the surface and the internal structure. The maximum pore diameter is 1 μm or less.

Preferably, the glassy carbon has an impurity content of 5 ppm.
Open porosity below 0.2% and maximum pore size below 0.5
It is less than μm. Furthermore, open porosity is 0.01%, maximum pore size
It is best to make it 0.1 μm or less.

EXAMPLE FIGS. 1 and 2 show an example of a glass-like carbon electrode plate for plasma etching according to the present invention. Electrode plate 10
Is a disk as a whole, a large number of small through holes 13 (Fig. 3) are formed in the circular opening 11 at the center, and eight large through holes 14 are formed at regular intervals in the periphery. Has been formed.

The through hole 14 is intended for attachment to the plasma etching apparatus, and has a small diameter portion and a large diameter portion, and has a two-step shape.

Although only a part is shown in FIG. 2, a large number of through holes 13 are densely formed in the entire opening 11. These through holes 13 are for the purpose of uniformly etching the wafer by causing the etching gas to flow uniformly, and as shown in FIG. 3, they are arranged at regular intervals in the vertical and horizontal directions. The three through holes 13 adjacent to each other are located at the vertices of an equilateral triangle.

The outer diameter of the electrode plate 10 is 10 inches, and the diameter of the opening 11 is set to 8 inches corresponding to the diameter of the processing wafer (not shown). Of course, other durability may be adopted. For example, the outer diameter of the electrode plate 10 is 12 inches,
The diameter of 11 may be 10 inches. The diameter of the opening 11 is preferably the same as or larger than the diameter of the wafer to be processed.

The arrangement density of the through holes 13 in the opening portion 11 is about 98 in the example of FIG.
It is preferable that the number is pieces / cm ² . In this illustrated example, 1733 through holes 13 are formed in the opening portion 11 having a diameter of 8 inches. The diameter of each through hole 13 is preferably 0.5 to 1 mm.

It should be noted that the arrangement density of the through holes 13 in the illustrated example is determined by the opening portions
Although the distribution is uniform throughout, the present invention is not limited to this example. For example, the arrangement density may be such that the central portions of the openings 11 are dense and the outer peripheral portions are sparse.

The thickness of the electrode plate 10 is set to 2 mm or more because the mechanical strength is increased and the service life is improved. The electrode plate 10 in the illustrated example has a thickness of 3 mm.

The electrode plate 10 is made of glassy carbon whose impurity content is controlled to 1/10 to 1/10 or less (for example, 5 ppm or less) of the conventional content.

The outline of a preferred method for producing the electrode plate of the present invention will be described below.

The process of adding a small amount of organic sulfonic acid to the thermosetting resin and polymerizing at room temperature is repeated. Then, the polymerized resin is poured into a mold to form a disk, and the temperature is slowly raised to cure the resin. A large number of through holes with a diameter of 0.8 mm are provided in the center of the thus hardened disc. After that, the disc is gradually heated and carbonized at 800 to 1200 ° C. It is surface-treated and further purified at 2000-2500 ° C.

The glassy carbon constituting the electrode plate of the present invention is preferably made by using a liquid thermosetting resin having fluidity as a starting material. This is because it becomes easy to obtain a glassy carbon material which does not include pores of 1 μm or more and has an open porosity of 0.2% or less.

4 to 8 show the surface texture of the electrode plate observed by an electron microscope.

The electrode plate structure made of the glassy carbon of the present invention shown in the electron micrograph of FIG. 4 has only a few open pores of about 0.2 μm or less. The open porosity of this example is 0.1%.

When a fluid thermosetting resin is used as a starting material, grain boundaries do not occur. Aggregate itself is made into resin powder,
When fired after molding, grain boundaries are likely to exist between particles, and properties such as mechanical strength and porosity deteriorate.

The thermosetting resin should be hardened and then cured in an inert atmosphere (oxygen free, usually helium, argon, nitrogen, hydrogen,
Carbonization and calcination are performed at a slow temperature increase rate in an atmosphere of at least one gas selected from the group consisting of an inert gas such as halogen, under reduced pressure or vacuum, or in an atmosphere in which the atmosphere is shut off.

The open porosity of the glassy carbon is preferably 0.2% or less. If the open porosity exceeds 0.2 wt%, when glassy carbon is used as an electrode plate for plasma etching, the electrode plate will be consumed by etching, the closed pores will be exposed, and the surface area will increase, resulting in etching and carbon particles. Dropout is accelerated. As a result, life is shortened. Further, when the carbon particles fall off, they adhere to the silicon wafer for semiconductor devices and deteriorate the physical properties of the wafer. As a result, the yield is reduced.

Examples of the thermosetting resin include furan resin, phenol resin, epoxy resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, and xylene resin. Such resins are used alone or by blending or modifying. Among them, modified furan resin is preferable.

Experimental Examples 1-3 p-trienesulfonic acid was added to furfuryl alcohol in an amount of 0.1.
Stir-mix up to 4 parts by weight explosion limit and polymerize, 1000-400
A flowable polymer having a viscosity of 0 cp (centipoise) was obtained.

After defoaming the produced frifryl alcohol polymerization solution,
A disk having a diameter of 300 mm and a thickness of 10 mm was molded in a molding die and cured in a dryer at a temperature rising rate of 1 ° C./hr.

The obtained cured product was heated in a nitrogen atmosphere at a heating rate of 2 ° C / h.
The temperature was raised to 1000 ° C., firing was performed, and finally a purification treatment was performed at 2300 ° C. to obtain glassy carbon.

Comparative Examples 1 to 3 An acid catalyst of p-toluenesulfonic acid was added to the furan resin, followed by defoaming treatment, and after molding, the temperature was gently raised to 200 ° C. to cure. The cured product thus obtained was pulverized to obtain a resin powder having an average particle size of 30 to 50 μm. This resin powder was mixed with the same type of furan resin, and the mixture was defoamed, then molded into a disk shape with a diameter of 200 mm and a thickness of 3 mm, and then cured. The obtained cured product was heated to 1000 ° C. at a heating rate of 2 ° C./h in a nitrogen atmosphere and baked, and finally purified at 2300 ° C. to obtain glassy carbon.

Table 1 shows the open porosity, the life and the amount of released gas for the glassy carbons of Experimental Examples 1 to 3 and Comparative Examples 1 to 3.

A silicon wafer was placed on a disk-shaped glassy carbon electrode plate, and a mixed gas of CF ₄ , Ar, and O ₂ was caused to flow, and plasma was generated to etch the silicon wafer. then,
The glassy carbon was also etched and consumed by the flowing oxidizing gas and the generated plasma. The initial thickness of the glassy carbon electrode plate was processed to be 3 mm, and the residual thickness was 0.8.
The life end was reached when it reached mm.

In addition, in Table 1, the amount of released gas is the amount of CO ₂ , H adsorbed on the surface of the glassy carbon when heated to 950 ° C.
₂ Indicates the amount of released gas such as CO.

As shown in Table 1, the glassy carbon electrode plate of the present invention had a significantly improved life under oxygen-containing conditions as compared with the comparative example.

In this experiment, the life end was determined when the thickness of the electrode plate was changed from 3 mm to 0.8 mm, but in reality there are many open pores in the glassy carbon electrode plate of the comparative example. Etching is not uniform, and when observed with an electron microscope, remarkable unevenness occurs as shown in FIG. Therefore, the plasma generated for etching the silicon wafer becomes unstable, and the etching rate of the silicon wafer is different in each part of the silicon wafer. Therefore, in reality, the life when used as a glassy carbon electrode plate for etching is considered to be shorter than the life shown in Table 1.

In addition, in the current small-diameter silicon wafer, the variation in the etching rate is within the specified range, but when considering the etching process of the large-diameter silicon wafer in the future, the variation in the etching rate in the comparative example is extremely large. It seems to be a big problem.

Furthermore, if the electrode plate is etched in an uneven shape as shown in FIG. 8, particles are likely to be generated. In the current semiconductor industry, the degree of integration has moved from 4M to 16M, and the line width of pattern etching has advanced to submicron. Therefore, the largest influence on the yield of silicon wafers is 0.1-
It is a particle of 0.3 μm. Reducing such particles greatly contributes to the yield of silicon wafers. For this reason, the glassy carbon of the comparative example does not cause many problems in the initial stage of use, but as the use time elapses, the surface is etched in an uneven shape, thereby roughening the surface and generating particles.

In addition, since the amount of released gas is large, the adsorbed gas is released during use, and the high-purity silicon wafer is adversely affected along with the generated plasma.

As shown in the electron micrographs of Figures 5-6,
The electrode plate of the present invention is uniformly etched and does not have large unevenness after etching unlike the comparative example.

[Brief description of drawings]

FIG. 1 is a schematic view of an electrode plate for plasma etching according to the present invention, FIG. 2 is a schematic cross-sectional view taken along line 2-2 of FIG. 1, and FIG. 3 is an enlarged view of a part of the opening portion of FIG. 4 is a plan view, FIG. 4 is an electron micrograph showing a metallographic structure of an example of the electrode plate for plasma etching according to the present invention at 1000 times magnification, and FIG. 5 is plasma etching of the electrode plate for plasma etching according to the present invention. An electron micrograph showing the subsequent metal structure at a magnification of 1000 times, and FIG. 6 is an electron micrograph showing the metal structure after the plasma etching of the present invention at a magnification of 15000,
FIG. 7 is an electron micrograph showing the metallographic structure of the conventional plasma etching electrode plate before use at a magnification of 1000 times, and FIG. 8 is the metallographic structure of the conventional plasma etching electrode plate after use at a magnification of 1000 times. It is an electron micrograph shown by. 10 …… Electrode plate 11 …… Open hole 13 …… Through hole 14 …… Through hole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasumi Sasaki 378 Oguni Town, Oguni Town, Nishiokitama-gun, Yamagata Prefecture Oguni Factory, Toshiba Ceramics Co., Ltd. (72) Kazuo Ito 30 Soya, Hadano, Kanagawa Prefecture Toshiba Ceramics Co., Ltd. Central Research Laboratory (72) Inventor Kazunori Meguro, Oguni Town, Oguni Town, Nishikitama District, Yamagata Prefecture, 378 Oguni Town, Toshiba Ceramics Co., Ltd. (56) Reference JP 62-252942 (JP, A) 170762 (JP, U)

Claims (1)

[Claims] 1. A thickness of 2 m made of high-purity glassy carbon.
An electrode plate for plasma etching, which is a plate having a size of m or more, substantially free of grain boundaries on the surface and internal structure, and having a maximum pore diameter of 1 μm or less.