Container for semiconductor wafer sample and method of preparing

Details Container for semiconductor wafer sample and method of preparing Container for semiconductor wafer sample and method of preparing

1991-10-16

1994-02-08

Thomas, Tom

Fishing, trapping, and vermin destroying

437 8, 437228, H01L 2100, H01L 2102, H01L 2166

Patent

active

052848027

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a wafer container for easily and correctly evaluating the contamination of the surface of a semiconductor wafer and also to a method of preparing a sample for analyzing the surface of the wafer sample received in such a wafer container.
2. Background Art
Contamination of the surfaces of wafers is the worst situation in semiconductor fabrication process. Therefore, it is necessary to evaluate the contamination level in various manufacturing steps. For this purpose, a sample wafer must be conveyed into an evaluation room or analysis room without being contaminated. To permit this conveyance, a clean container is necessary which can be sealed and prevents the wafer held in it from moving during conveyance.
An individual wafer container used conventionally has a cover which is screwed off. The container includes an intermediate plate provided with legs which are held against the fringe of the face of the wafer to lock it. The airtightness of the container is unsatisfactory. Furthermore, the legs of the intermediate plate make frictional contact with the face of the wafer and so the face tends to be damaged or powder tends to be produced due to abrasion. Accordingly, it is the common practice to use a plastic container holding tens of wafers as a wafer container for evaluating the contamination. This kind of plastic container is employed by manufacturers of silicon wafers to deliver manufactured wafers.
Evaluation of the surface of a wafer depends either on measurement of the density of particulates on the surface of the wafer or on analysis of the contaminative impurity elements. Today, semiconductor devices are highly sophisticated. Therefore, where the latter method is adopted, if a wafer is contaminated with a trace amount of a harmful element such as a heavy metal or alkali element, e.g., on the order of 10.sup.11 atoms/cm.sup.2, then the manufacturing yield or the reliability is adversely affected. Nonetheless, conventional surface analysis apparatuses, such as AES, XPS, and EPMA, and even SIMS are not sensitive enough to analyze such a trace amount of element with certainty. Thus, a method of enriching the surface contamination is needed. Where the surface is coated with a film of an oxide, nitride, or the like, the film must be decomposed and then only the contaminative elements present in it must be enriched.
An excellent method of performing such an enrichment is disclosed in Japanese Patent Laid-Open No. 69531/1985. This method uses a sealed container in which a thin film is decomposed. Specifically, a container holding hydrofluoric acid, a wafer holder, and another container receiving liquid produced by decomposing the surface of the wafer with gaseous hydrofluoric acid evaporated from the hydrofluoric acid are installed in the sealed container. In this case, the amount of the liquid produced by the decomposition and existing in the sealed container is very small. In addition, the impurities contained in the hydrofluoric acid are not transferred into this liquid, because hydrofluoric acid in gas phase is utilized. Only the desired impurities excluding elements tending to less ionize such as Cu can be almost completely transferred into the liquid. That is, the impurities can be enriched into a trace amount of liquid. Flameless atomic absorption spectrometry is most adapted for the analysis of such liquid. Traces of impurities existing in the film on the surface are analyzed by this method.
In order to make such a surface analysis, the sample must be conveyed with a container as described above from the location where the sample is collected into an analysis room. Then, the container must be conveyed into a decomposition chamber. Thereafter, the sample must be transferred into the decomposition container.
During this conveyance, it is essential that the wafer be not contaminated. Therefore, it is necessary that the container used for the conveyance be not inferior in cleanliness to the decomposition container. Hence, the decomposition co

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