Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2001-04-03
2003-08-26
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S001000, C556S043000, C556S052000, C556S053000, C556S058000, C556S110000, C427S248100, C427S593000
Reexamination Certificate
active
06610873
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a method for purifying an organometallic compound in a reusable state from an exhaust gas after thin film formation in the CVD method using an organometallic compound as a raw material.
2. Description of the Related Art
Since the chemical vapor deposition method (hereinafter referred to as CVD method) has the advantages that it can easily prepare uniform thin films and it is superior in step coverage, the method is one of the thin film-forming technologies generally employed for production of film electrodes in semiconductor devices. The CVD method is considered to become a major process for preparation of film electrodes in the future because the method can provide further densification required of recent circuits and electronic parts.
The CVD method is a preparation method of a thin film of a metal or a metal oxide, which involves vaporizing a raw metal compound to transport the same to the surface of a substrate, reacting the transported raw material particle on the substrate to accumulate as a metal or a metal oxide to form a thin film. As a raw material of metal compound, in particular, organometallic compounds, which have low melting points and are easy to handle, are used (the CVD method using an organometallic compound is hereinafter referred to as MOCVD).
Incidentally, the production costs of thin films by the MOCVD method depend on the prices of organometallic compounds which are raw materials and the ratio of the amount of the organometallic compounds consumed in the reaction to the amount of the compound introduced on the surface of a substrate, i.e., the utilization ratio, and the utilization ratio in the conventional MOCVD method is 10% or lower, which means most of the introduced source gas is actually disposed as an exhaust gas. Therefore, the production costs of thin films with such low utilization ratios are strongly influenced by the prices of organometallic compounds.
In this connection, the prices of organometallic compounds are generally high because their synthesis require multiple steps. For example, copper itself is not expensive as a metal but the price significantly increases when an organometallic compound thereof is synthesized. Therefore, it is considered that the high costs of forming thin films according to the conventional MOCVD method with low utilization ratios cannot be avoided due to the high prices of organometallic compounds.
Specifically, thin films of precious metals such as ruthenium and iridium are being employed recently for higher performance of film electrodes and since precious metals are trace metals and are expensive themselves, organometallic compounds thereof are significantly expensive. Therefore, the production costs of thin films of precious metals according to the conventional MOCVD method are expected to be extremely high.
As described earlier, the organometallic compounds are easy to handle and capable of forming thin films efficiently and they are expected to be increasingly employed. Therefore, if demand for the organometallic compounds increases, the conventional MOCVD method with low utilization ratios has the disadvantages relating to the production costs of thin films and about deletion of resources due to a huge lose of the materials.
The applicant developed a recycling method of organometallic compounds for MOCVD wherein an unreacted organometallic compound component is extracted from a used raw material which was conventionally discarded and then purified to a reusable state, as a method for reducing the production costs of thin films and avoiding depletion of resources, and filed a patent application for an MOCVD thin film production process incorporating this recycling technology (application number 2000-96359). This recycling technology involves purification and extraction of organometallic compounds by passing the raw material after the thin film formation, for example, through a cold trap to cool and condense to recover the same in a liquid state and distilling the recovered material under appropriate conditions. This technology can avoid wasting organometallic compounds and hence reduce the production costs of thin films.
Although the main point of the above-mentioned MOCVD thin film production process resides in the recycling technology, the recycling technology needs some improvements. The recycled organometallic compounds should have substantially as high purity as the virgin material in order to produce thin films with comparable properties to those made from the virgin material. It is also required that as much organometallic compounds as possible be extracted from a used raw material in order to reduce the production costs of thin films. In particular, the purity is extremely important for organometallic compounds for use as a raw material for MOCVD and if an organometallic compound containing a trace amount of impurities is used as a raw material for MOCVD, the purity of the thin film also decreases, which may affect the electric characteristics and influence the morphology of the film.
The present invention has been made under these situations and proposes an improved recycling method of organometallic compounds in which an unreacted organometallic compound is extracted from a used raw material which has undergone the CVD steps and recycled, wherein the organometallic compound of high purity is extracted efficiently.
SUMMARY OF THE INVENTION
The inventor has examined improvements in order to improve the above-mentioned recycling technology. As a result, the inventor has conceived the idea that it is necessary to assess the possibility that reaction products formed by the thin film formation reaction and its side reaction are present in a used raw material, and their properties and effects in order to complete a superior recycling technology.
In view of the effects of reaction products here, if the reaction products can be removed by normal reparation methods such as distillation, they do not signify aside from a reduction in the yield. In this connection, the inventor has thought the reaction products already identified in the conventional researches do not matter. The reason is that the impurities identified in these conventional researches include low molecular weight compounds such as water, carbon dioxide, aldehydes, and formic acid, which are originated from decomposed organometallic compounds due to leaving of metal atoms and these low molecular weight compounds have significantly different properties from those of the organometallic compounds from which they are to be separated and thus can be easily separated by normal separation methods such as distillation. Therefore, it is considered if the actual CVD thin film formation process produces only these compounds, the above-mentioned conventional recycling technology can sufficiently cope with the compounds.
However, the inventor has examined a used raw material after the thin film formation reaction in detail, and found that the actual CVD thin film formation process produces the above-mentioned low molecular weight compounds as reaction products, but also produces other reaction products due to unreported side reactions.
In this connection, a case is taken as an example for illustration in which a ruthenium thin film is produced with diethylruthenocene represented by Formula 1, which is recently receiving attention as a raw material for ruthenium thin films, and its used raw material is recycled.
Diethylruthenocene, represented by Formula 1, is a compound composed of a ruthenium atom as a metal atom and two ethyl derivatives of cyclopentadiene coordinating to the metal as ligands. The CVD thin film formation process with diethylruthenocene involves a decomposition reaction of diethylruthenocene on a substrate to accumulate ruthenium.
The inventor has fully examined the composition of the used raw material after the thin film formation with diethylruthenocene and found the used raw material contains predominantly unreacted diethylruthenocene but the followin
Nazario-Gonzalez Porfirio
Rothwell Figg Ernst & Manbeck
Tanaka Kikinzoku Kogyo K.K.
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