JPH0488656A - Graphite wafer holding jig - Google Patents

Abstract

PURPOSE:To prevent graphite particles from falling off from a graphite material, to protect a wafer against contaminant, and to make the most of the merits of graphite by a method wherein a coating film of thermal decomposition carbon is formed on the surface of the graphite material. CONSTITUTION:A thermal decomposition carbon coating film 14 is formed on the surface of component members such as a support 11 and the like formed of graphite material, whereby all the surface of a wafer support jig 10 is covered with the thermal decomposition carbon coating film 14. The graphite material located inside the coating film 14 is formed in an aggregate of particle as an organizational structure, and on the other hand the coating film 14 is of dense structure different from the aggregate of particle. The film 14 is provided with few voids, large in density, and as low in gas permeability as glass. Therefore, the film 14 is free from the effect of such a heat cycle that it is heated in an oven and put back in a room temperature state again, and graphite particles are prevented from falling off. Gas discharged from a graphite holding jig of this design in operation is very little. By this setup, the holding jig is prevented from contaminating a wafer 20 and able to make the most of the merits of graphite.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a wafer holding jig for holding a raw material wafer for semiconductor devices and inserting it into a furnace. The present invention relates to the formed wafer holding jig.

(Prior art) In the process of manufacturing semiconductor devices, wafer holding jigs are used to form a large number of oxide films on wafers made of silicon, etc., which are the raw materials. It is inserted into a high-temperature furnace while holding the wafer. In the process of forming an oxide film on the wafer, an oxide film is also formed on the jig at the same time, but if this jig is used repeatedly, the oxide film will gradually become thicker.
This peels off during use and has a negative impact on the wafer.
It is necessary to periodically clean the oxide film with hydrofluoric acid.

This type of wafer holding jig is generally made of quartz material, but since this quartz material is sensitive to hydrofluoric acid, repeated hydrofluoric acid cleaning may cause the wafer holding jig made of this quartz material to The jig had poor durability because it became thin and unusable.

Therefore, it has been considered to form this type of wafer holding jig using ceramics that are resistant to hydrofluoric acid, but with recent technological advances, the diameter of the wafer 1 itself has become larger. Therefore, it has become extremely difficult to form a large wafer holding jig while taking into consideration the firing shrinkage of ceramics. In particular, ceramics have extremely poor workability due to their excellent hardness, and dimensional accuracy also deteriorates as the size increases. Above all, ceramics are fired using a firing aid, but this firing aid remains as an impurity after firing, and this residual impurity poses a problem when used as a wafer holding jig. It is.

Currently, there have been proposals using graphite materials, which have many advantages as materials for composing wafer holding jigs, such as heat resistance, easy workability, and chemical resistance. However, if a wafer holding jig made of graphite material is used repeatedly, some of the graphite material may fall off in the form of fine particles, which can cause contamination of the wafer. Something happened.

In other words, high-density graphite, which is used as a material for such wafer holding jigs, has excellent chemical stability and can be easily increased in density, making it an extremely suitable material in terms of characteristics. be.

However, this high-density graphite is graphitized by forming fine powder of coke or carbon into a high density together with a binder component such as tar pitch and then firing it. Because of this, wear and tear occurs due to particles falling off. Further, there are disadvantages in that the fallen graphite particles contaminate the upper surface of the wafer.

Furthermore, since high-density graphite has pores in its organizational structure, when a graphite jig is cleaned with hydrofluoric acid, the hydrofluoric acid enters the pores and is difficult to remove.

Development and development of this type of wafer holding jig as described above.
As a result of a detailed study of the improvement process, the inventors of the present invention concluded that graphite material is an excellent material for constructing this type of wafer holding jig, considering all aspects. However, in order to use graphite material, the above-mentioned problems had to be solved. Therefore, the present inventors have conducted various studies on how to prevent particles from falling off from graphite materials, and how to prevent hydrofluoric acid from entering during hydrofluoric acid cleaning. They realized that using decomposed carbon would produce good results, and completed the present invention.

(Issues to be solved by the invention!) The present invention has been made based on the above-mentioned circumstances, and the problem to be solved is the problem of falling off of graphite particles when the wafer holding jig is formed of graphite material. be.

It is an object of the present invention to provide a wafer holding jig that can fully utilize the advantages of graphite material while preventing graphite particles from falling off the graphite material and solving the problem of contamination of wafers. There is a particular thing.

(Means for Solving the Problems) In order to solve the above problems, the means taken by the present invention are as follows. This is a wafer holding jig (10) J characterized in that a coating made of pyrolytic carbon is formed on the surface of a graphite material.

(Operation of the invention) The wafer holding jig (1
0) is explained as follows.

First, since the wafer holding jig (10) according to the present invention has its support base (11), shelf rod (12), and other constituent members made of graphite material, it is easy to process. It is not only durable but also has excellent dimensional accuracy, which allows it to sufficiently withstand the temperature at which an oxide film is formed on the wafer (20) it holds.

The wafer holding jig (lO) according to the present invention has a pyrolytic carbon film (14) formed on the surface of each component such as the support base (11) formed of graphite material, so that the entire surface is heated. It is covered with a decomposed carbon film (14). This pyrolytic carbon coating (14) has a dense structure different from that of a particle aggregate, whereas the graphite material located inside it has a structure as an aggregate of particles. . In other words, this pyrolytic carbon film (14) has almost no pores, has a high density, and has a very low gas permeability comparable to that of glass.

Since the outer metal surface of the wafer holding jig (10) is coated with the pyrolytic carbon film (14) having the above properties as shown in FIG. ) is placed in a furnace as shown in Figure 3, heated, and then exposed to room temperature conditions many times during a heat cycle, the pyrolytic carbon coating on the surface of the wafer holding jig (10) , it is not affected by the heat cycle described above, and particles do not fall off like in the case of ζ graphite material. In addition, since there are almost no pores, even when it is taken out of the furnace and exposed to the atmosphere, it does not absorb moisture or gas, and the amount of gas released during use is extremely small. Therefore, by using this wafer holding jig (10), contamination of the wafer (20) can be avoided. In addition, pyrolytic carbon film (14
) It is possible to suppress the total ash content contained in the wafer (20) to 10 ppm or less, as shown in the examples below.
contamination is completely negligible.

In addition, since the pyrolytic carbon coating (14) itself has excellent corrosion resistance against hydrofluoric acid, no matter how many times the wafer holding jig (10) coated with it is washed with hydrofluoric acid, This also allows the wafer holding jig (10
), it never wears out.

Therefore, this wafer holding jig (10) has excellent durability. Furthermore, the pyrolytic carbon film has a dense structure different from that of graphite material, which has a structure as a particle aggregate, and has almost no pores, so there is no inconvenience that hydrofluoric acid enters and is difficult to escape.

(Example) Next, the wafer holding jig (10) according to the present invention will be explained according to the embodiment shown in the drawings.As shown in FIG. Support stand (11
) The shelf rods (12) having a large number of holding grooves (13) between them are connected and integrated, and these support stands (1 piece)
and the shelf rod (12) has isotropy and has high density (1, 7 to
2, Og/cm”) and high purity (total ash content: 10
ppm or less) graphite material. As shown in FIG.
A pyrolytic carbon film (14) of about 0.00 μm was formed.

This wafer holding jig (10) is formed as follows in this embodiment. First, each support (11) and shelf rod (12) are formed using the graphite material as described above. Of course, each shelf rod (12) has a holding groove (13) formed in advance. After these were assembled in the state shown in Figure 1, a pyrolytic carbon coating (14) was formed on the entire surface.

As a method for forming the pyrolytic carbon coating (14) on the surface of the graphite substrate, there are various commonly used chemical vapor deposition methods (CVD).
) on the graphite base material.
The graphite substrate is heated to 0° C., and a hydrocarbon or halogenated hydrocarbon is brought into contact with the substrate in the presence of hydrogen gas to form a dense layer of pyrolytic carbon on the graphite substrate having many pores. These reactions are preferably carried out under normal pressure or reduced pressure, or, in view of the uniformity and smoothness of the pyrolytic carbon film, under reduced pressure, particularly at 300 Torr or less. Moreover, the thickness of the pyrolytic carbon surface layer is preferably 10 μm to 500 μm. The reason for this is that if the thickness is 10 μm or less, sufficient wear resistance cannot be obtained, and if the thickness is 500 μm or more, there is a high possibility that cracks will occur in the coating due to the difference in thermal expansion with the base material.

Of course, the pyrolytic carbon itself formed as described above is of high purity, but the graphite base material used to laminate it contains various impurities, such as iron, nickel, cobalt,
Vanadium may be mixed in, and these may remain on the pyrolytic carbon side. Possible routes for impurities to enter pyrolytic carbon include impurities in the graphite base material mentioned above, diffusion during the formation of pyrolytic carbon, and impurities mixed in the supply gas. It will be done.

These impurities are prevented from being mixed into the pyrolytic carbon by using a high-purity graphite base material and the purity of the supply gas (selecting the structure and materials of gas supply parts, supply pipes, reaction vessels, etc.) It is something that can be done. By such a method, the amount of total components (impurities such as iron) in the pyrolytic carbon coating (14) can be reduced to 10 ppm or less.

Hydrocarbon gas such as methane, propane or benzene from which impurities have been sufficiently removed is used as the raw material gas for forming the pyrolytic carbon film (14), and hydrogen gas and argon gas are used as carrier gases to adjust the concentration. It was used. As a result, the raw material gas became pyrolytic carbon and was deposited on the surface of the support base (11) etc. which was at a high temperature due to decomposition, bonding, etc.

Although the wafer holding jig (10) shown in FIG. 1 is of a so-called horizontal type, the present invention can also be applied to a vertical type wafer holding jig (10) as shown in FIG. Needless to say.

(Effects of the Invention) As described in detail above, in the present invention, as exemplified in the above embodiments, "the raw material wafer for semiconductor devices is The wafer holding jig (10) is characterized by forming a coating made of pyrolytic carbon on the surface of the graphite material, which allows graphite particles to be removed from the graphite material. It is possible to provide a wafer holding jig that can take full advantage of the advantages of the graphite material while preventing it from peeling off and solving the problem of contamination of the sea urchin/1.

FIG. 1 is a perspective view showing a state in which a wafer is held by a horizontal wafer holding jig according to the present invention, and FIG. 2 is a partially enlarged sectional view showing a pyrolytic carbon coating formed on the surface of the wafer holding jig. FIG. 3 is a sectional view of the wafer holding jig in use, and FIG. 4 is a perspective view of the vertical wafer holding jig.

Explanation of symbols 10... Wafer holding jig, 11... Support stand, 12...
... Shelf rod, 13... Holding groove, 14... Pyrolytic carbon coating, 20... Wafer.

that's all

Claims (1)

[Scope of Claims] A wafer holding jig for holding raw material wafers for semiconductor devices, the whole being formed of an isotropic high-density, high-purity graphite material, wherein the surface of the graphite material has a pyrolyzable A wafer holding jig characterized by forming a film made of carbon.