Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Reexamination Certificate
2001-12-04
2004-08-03
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C118S715000
Reexamination Certificate
active
06770145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an apparatus for carrying out a process for forming a metal film or a metallic compound film with the use of LPCVD method, also relates to a method for controlling the film formation process.
2. Description of the Related Art
Since chemical vapor deposition method (hereinafter referred to as CVD method) can be used to produce a uniform film, and since CVD method has an excellent capability called “step coverage” which can be effectively used to form a uniform film on an uneven surface, this method has become one of generally used thin film formation techniques for forming thin film electrodes in a semiconductor device.
A thin film formation process involved in the CVD method requires that after a raw material has been vaporized and moved to the surface of a substrate, the particles of the raw material are caused to react with one another on the substrate so as to be accumulated thereon. Particularly, in recent years, there has been in use a low pressure CVD method (hereinafter referred to as LPCVD method) which takes into account the manufacturing of a thin film at a lower temperature but with a higher efficiency, and enables the above reaction to be conducted in an atmosphere having a reduced pressure. Further, in order to reduce the reaction temperature, as a metallic compound for use as a raw material, there has been in use an organometallic compound.
Here, an apparatus for manufacturing a thin film using the LPCVD method, is comprised of a container for accommodating an organometallic compound as a raw material, a heating device for heating the container to vaporize the organometallic compound so as to obtain a raw material gas, and a reactor accommodating a substrate for precipitating a thin film, with all of them being communicated in a predetermined manner by virtue of various pipes. In addition, the LPCVD apparatus is equipped with an exhaust pump which is used to maintain a low pressure atmosphere within the reactor. Furthermore, in order for the exhaust pump to be kept at a high exhaust efficiency and in order to prevent any possible failure during the operation of the exhaust pump, there has been in use a trap (cold trap) for removing in advance some condensed components from the exhaust gas.
However, the inventors of the present invention have recently developed a recycle technique in order to solve an existing problem, i.e., the cost for manufacturing a thin film is relatively high because of a low efficiency in using the raw material compound in the CVD method. According to the improved recycle technique of the invention, the raw material used in the above reaction is recovered, and an un-reacted metallic compound is refined from the used and recovered raw material so that the un-reacted metallic compound can be processed into a reusable form. Moreover, the inventors of the present invention have found it effective to use a trap to recover the used raw material, because the use of the trap makes it easy to effect the recovery of the used raw material. Namely, a raw material compound (organometallic compound) used in the CVD method usually has a relatively low boiling point and a relatively low vapor pressure, so that such a raw material compound is easy to undergo a phase change at a relatively low temperature and thus it may be easily condensed from its gaseous phase into its liquid phase. Accordingly, if taking into account the original purpose of using a trap, a trap may be considered to be an excellent device for recovering the used raw material. Besides, since an LPCVD apparatus is usually equipped with a trap, it is not necessary to provide another trap to effect the recovery of the used raw material.
On the other hand, when using the recycle technique described in the above, it is usually desired to recover as much as possible the used raw material in order to be able to recycle as much as possible the metallic compound. Accordingly, in order to increase the recovery amount when recovering the used raw material, it is usual to consider increasing the capacity of a trap.
However, an increase in the capacity of a trap will undesirably cause an increase in the size of a CVD apparatus, thus causing an increase in the equipment cost. Moreover, an increase in the capacity of a trap can also reduce an exhaust efficiency of an exhaust pump, thus undesirably reducing the functions originally provided by the trap.
Accordingly, the present invention is to provide an improved LPCVD apparatus capable of recovering a larger amount of used raw material, without reducing its exhaust efficiency.
SUMMARY OF THE INVENTION
The inventors of the present invention, as a result of investigation for solving the above-described problems, have thought that in order to efficiently recover the used raw material, it is important to increase a cooling efficiency when cooling a used raw material in the trap. Further, as a method for putting such an idea into practical use, the inventors think it is appropriate to fill the gas flowing passage of the trap with an amount of solid fillers. In a commonly used conventional trap, the internal surfaces thereof can serve as effective cooling surfaces. However, since in such a conventional trap there is only a small contact area allowing a contact between a used material and the cooling surfaces, a sufficient cooling of the used raw material is almost impossible. In contrast to this, using an amount of fillers to fill the gas flowing passage of the trap can increase the contact area allowing the desired contact between a used material and the cooling surfaces, thereby ensuring an increased cooling efficiency in the trap.
On the other hand, for use as the fillers it is usual to employ pellet-like materials such as Raschig rings. As this time, in order to increase the cooling efficiency for cooling the used raw material, an amount of fillers are required to be loaded into the trap with a high density. However, if an amount of fillers are loaded into the trap with a high density, a pressure loss across the trap will be large, and this will make it difficult for an exhaust pump to carry out an exhaust operation. As a result, a pressure dropping speed in the reactor will be reduced, bringing about an undesired influence to the reaction in which a thin film is formed. For this reason, the commonly used pellet-like fillers are considered to be not appropriate for being loaded into the trap.
For the above reason, the inventors of the present invention think that it is preferable to use some cylindrical fillers having a honeycomb structure, which can server as the fillers capable of efficiently cooling the used raw material, without bringing about any unfavourable influence to the exhaust efficiency of the exhaust pump.
Namely, the present invention relates to an LPCVD apparatus which comprises a container for accommodating an organometallic compound serving as a raw material, a heating device for heating the container to vaporize the organometallic compound so as to obtain a raw material gas, and a reactor containing a substrate for precipitating a thin film, an exhaust pump for maintaining a low pressure atmosphere within the reactor, a cooling trap provided on the upstream side of the exhaust pump for cooling used raw material gas supplied from the reactor. In particular, the LPCVD apparatus is characterized in that a raw material flowing passage within the trap is filled with an amount of cylindrical fillers having a honeycomb structure.
The fillers having a honeycomb structure which can be suitably used in the present invention are so formed that the cross section of each filler has a plurality of holes formed therethrough, with these holes extending in the longitudinal direction (along which the used raw material gas flows) of each cylindrical filler. Therefore, if an amount of fillers to be used are those having such a honeycomb structure, it is possible to prevent an undesired increase in the pressure loss of the raw material gas passing therethrough.
Lund Jeffrie R.
Rothwell Figg Ernst & Manbeck
Tanaka Kikinzoku Kogyo K.K.
Zervigon Rudy
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