Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – By reaction with substrate
Reexamination Certificate
1999-03-17
2001-02-20
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
By reaction with substrate
C438S787000
Reexamination Certificate
active
06191051
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a semiconductor wafer storing technology and, more particularly, to a wafer storing system having a vessel coated with ozone-proof material and a method of storing a semiconductor wafer.
DESCRIPTION OF THE RELATED ART
A field effect transistor is an important circuit component used in a semiconductor integrated circuit device, and a large number of field effect transistors are fabricated on a semiconductor wafer. When the field effect transistor is fabricated on the semiconductor wafer, a thin gate oxide layer is grown on active areas in the major surface through a thermal oxidation, and conductive material such as polysilicon is deposited over the thin gate oxide layer. The conductive layer is patterned into gate electrodes by using a photo-lithography and an etching, and dopant impurity is ion implanted into the active areas in a self-aligned manner with the gate electrodes.
Thus, the semiconductor wafer is firstly placed into a thermal oxidizing apparatus, and, thereafter, is moved from the thermal oxidizing apparatus to a reaction chamber of a deposition system. While the semiconductor wafer is being conveyed from the thermal oxidizing apparatus to the reaction chamber of the deposition system, there is a possibility that the thin gate oxide layer is contaminated. Although the thermally oxidizing apparatus and the deposition system are installed in a clean room, contaminant is not perfectly avoidable, and the semiconductor wafer is exposed to the contaminant.
Dust particles of metal and organic compound are typical examples of the contaminant. If the gate oxide layer is contaminated by the metal particles and the organic compound particles, the conductive material is deposited over the contaminated gate oxide layer, and is left between the gate oxide layer and the gate electrode. The contaminant deteriorates the electric properties of the gate oxide layer as reported by Kimura et. al. in “Time Dependent Dielectric Breakdown Phenomena Caused by Carbon Organic Contaminants”, Proceedings of 1994 Autumn Meeting of Society of Applied Physics, 19p-ZC-4. The paper teaches that the time dependent dielectric breakdown is increased due to carbon organic contaminants absorbed in the natural oxide grown on a silicon layer.
In order to eliminate the dust, particles from the clean room, a high efficiency particular air filtering system or an ultra low penetration air filtering system is installed in the clean room. The air filtering system decreases the dust particles in the clean room. However, the air filtering system hardly eliminates organic compound particles from the air, and the gate oxide layer is liable to be contaminated by the organic compound particles.
Japanese Patent Publication of Unexamined Application No. 5-259445 discloses a storing technology for a semiconductor wafer. The Japanese Patent Publication of Unexamined Application proposes to store a semiconductor wafer in vacuum or inert gas such as nitrogen gas.
The prior art storing technology disclosed in the Japanese Patent Publication of Unexamined Application is effective against the contamination in so far as the semiconductor wafer is placed in the vacuum or the inert gas immediately after the growth of the gate oxide layer. However, if the semiconductor wafer is exposed to the atmosphere in the clean room, the time dependent dielectric breakdown still takes place at a high percentage.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide a wafer storing technology which is effective against the contamination by the organic compound particles.
The present inventor contemplated the problem inherent in the prior art wafer storing technologies, and noticed that the prior art wafer storing ambience merely sealed a semiconductor wafer in dust-free atmosphere. If a wafer storing ambience attacked the organic compound particles, the wafer storing ambience would clean the semiconductor wafer by decomposing the organic compound. The present inventor stored a semiconductor wafer in ozone, and evaluated the cleaning capability of ozone as follows.
The present inventor prepared samples where silicon oxide had been grown to 80 angstroms on semiconductor wafers. Conductive material was deposited over the silicon oxide layer of the first sample group within an hour after the growth. The second sample group was stored in a clean room for a week, and, thereafter, the conductive material was deposited over the silicon oxide layer. The third sample group was stored in the nitrogen ambience for a week, and, thereafter, the conductive material was deposited over the silicon oxide layer. The fourth sample group was stored in ozone sealed in a vessel formed of teflon or polytetrafluoroethylene for a week, and, thereafter, the conductive material was deposited over the silicon oxide layer.
The present inventor evaluated the data storing technologies for the first to fourth sample groups from the aspect of the time dependent dielectric breakdown. The present inventor applied potential across the silicon oxide layers of the first to fourth sample groups, and investigated the cumulative percent defective of each sample group in terms of the breakdown charge. The potential was applied to 1 square millimeter, and the injection current density was 0.1 ampere/cm
2
.
The cumulative percentage defective of each group was plotted in FIG.
1
. Plots PL
1
, PL
2
, PL
3
and PL
4
represented the first sample group, the second sample group, the third sample group and the fourth sample group, respectively. The wafer storing technology in ozone did not drastically improve the cumulative percent defective.
The present inventor investigated why the ozone did not improve the cumulative percent defective. The present inventor found that ozone had decomposed the teflon. Although ozone decomposed the organic compound particles adhered to the semiconductor wafer before the entry into the teflon vessel, the teflon newly supplied organic compound particles to the semiconductor wafer, and the semiconductor wafer was contaminated, again.
Although a quartz vessel disclosed in Japanese Patent Publication of Unexamined Application No. 60-32315 or 61-39524 was effective against ozone, it was difficult to form a quartz vessel large enough to store a plurality of semiconductor wafers without a special facility. Moreover, the quartz was so heavy that operators suffered from an inability to easily manipulate the vessel.
To accomplish the object, the present invention proposes to coat a sealing vessel with material hardly decomposed by ozone.
In accordance with one aspect of the present invention, there is provided a wafer storing system for storing at least one semiconductor wafer comprising: a vessel having an inner wall formed of ozone-proof material and defining an airtight chamber so as to accommodate the at least one semiconductor wafer; and a source of ozone supplying ozone to the airtight chamber.
In accordance with another aspect of the present invention, there is provided a method of storing at least one semiconductor wafer, comprising the steps of: a) preparing a vessel having an inner wall formed of ozone-proof material and defining an airtight chamber; b) placing at least one semiconductor wafer in the airtight chamber; c) sealing the at least one semiconductor wafer in the airtight chamber; and d) creating ozonic atmosphere in the airtight chamber.
REFERENCES:
patent: 5944193 (1999-08-01), Shimizu
patent: 5972802 (1999-10-01), Nakano et al.
patent: 08083783 (1996-03-01), None
Ghyka Alexander G.
NEC Corporation
Niebling John F.
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