Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
1999-02-24
2001-10-09
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S509000
Reexamination Certificate
active
06300255
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the processing of large diameter semiconductive wafers into integrated circuits (and similar devices) wherein the wafers are put through a series of processing steps, one or more of which steps involve depositing on an exposed surface of each wafer a thin, uniform insulating layer or layers of silicon oxide (SiO
2
) by means of chemical reactions of mixed gasses (well known in the art) to which the wafers are exposed. A commonly used process is known as sub-atmospheric chemical vapor deposition (SACVD)™.
BACKGROUND OF THE INVENTION
The processing of semiconductive wafers (e.g., thin discs of single-crystal silicon) into various integrated circuits (and similar devices) is well known in the art. To this end manufacturers offer throughout the world various makes and designs of equipment for this purpose. Because of the precision in construction and of operation required of such equipment, and the uniformity in processing necessary to obtain a high yield within specifications of devices being produced, the equipment is expensive to build and to operate. It is highly desirable therefore that the capital and operating costs of such equipment, for a given production throughput, be reduced as much as possible.
Recently semiconductive wafers with a diameter of 300 mm (0.3 meter) have become available to the manufacturers of integrated circuits. Compared to previously available 200 mm wafers (or even smaller ones), a 300 mm wafer offers a potential gain in productivity of more than two to one. Use of 300 mm wafers is thus highly attractive from a cost standpoint.
In a SACVD™ process step where silicon oxide is being deposited as insulation on a wafer, reactive gasses (well known in the art such as an organic vapor in helium or nitrogen, and ozone) are separately mixed together very close to where they will be used, then immediately introduced into a hermetically sealed chamber. The mixed gasses flow into a chamber at desired pressure and flow rate and are continuously exhausted from the chamber by a pump. A wafer within the chamber is held at a desired temperature (e.g., in the range of 200 to 800° C.) while the reactive gasses flow over an exposed surface of the wafer and in so doing deposit thereon a thin layer of silicon oxide insulation. Since the layer of silicon oxide being deposited onto the wafer should be as uniform as possible over the entire wafer surface from center to rim, the reactive gas stream should have its component gasses thoroughly mixed together before impinging on the wafer, and the mixed gasses should flow with perfect, or near perfect, uniformity over the entire area of the exposed surface of the wafer.
Non-uniformity in mixing and/or flow of the reactive gasses results in an insulating layer (SiO
2
) being deposited unevenly onto the wafer. The resulting layer is thus thicker, or thinner, in some places than in others. When even small peaks and/or valleys begin to show up in an insulating layer the integrated circuits (or similar devices) which are being produced on the wafer can be rendered defective and thus become scrap. It becomes however, more and more difficult to achieve absolute uniformity in the mixing and flowing of larger volumes of the reactive gasses as the area of a wafer is made larger and larger (e.g., from a diameter of 200 mm to a diameter of 300 mm or greater). Thus, in practical effect, processing apparatus intended for 200 mm wafers cannot merely be scaled up in size so that it is big enough to handle 300 mm wafers and still produce integrated circuits having zero, or nearly zero defects. Substantial modifications in the apparatus are required. The present invention in one of its aspects provides an effective and economical solution to this problem of achieving uniform processing in chambers for large diameter wafer (e.g., 300 mm).
Previously, where wafer diameters were much smaller, there have been attempts to combine two wafer-processing chamber cavites into a single piece of equipment. Thus common usage could be made of certain elements of equipment such as housing, platform, gas supplies, control circuits, etc. The provision of dual-cavity chamber equipment would therefore offer increased production throughput along with substantial savings in capital cost. But problems of uniform processing, as discussed above have, among other reasons, precluded dual-cavity chamber equipment suitable for 300 mm wafers. The present invention in another of its aspects makes possible dual-cavity chamber apparatus capable of processing two such semiconductor wafers simultaneously.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided a method of mixing together two separate streams of gasses which react together, and then promptly flowing them into a wafer-processing chamber in such a way that the reacting gasses will result in the deposition of a highly uniform layer of silicon oxide insulation onto a large diameter semiconductive wafer within the chamber. The wafer lies upon a heating element in the chamber and is maintained at a suitable elevated temperature while the walls of the chamber are kept at a much lower temperature by coolant fluid pumped around and within the walls thereof.
To achieve immediate and intimate mixing of the gasses in the separate streams, one stream is injected tangentially into a mixing block having a small vertical cavity, and the other stream is injected tangentially into the cavity in the opposite direction. This results in a vigorous stirring and mixing of the two gas streams as they enter the cavity. The now-mixed reactive gasses continually flow out of the mixing cavity down through a plurality of perforated gas dispersion plates, which evenly spread the gasses into a highly uniform mixture flowing over an area slightly larger than the area of the wafer. The dispersion plates are specially configured and mounted with respect to each other, the mixing cavity, and a wafer in order to obtain gas flow over the wafer with the necessary high degree of uniformity. The reactive gasses flow down upon and over an exposed upper surface of the wafer and are exhausted from the bottom of the chamber by an evacuation pump. After an insulating layer of desired thickness (and virtually perfect uniformity) has been deposited on the wafer, the wafer is removed from the chamber by an automatic mechanism (well known in the art) and cleaning gas is pumped into the chamber. The cleaning gas passes through the mixing cavity, the gas dispersion plates, and down through and out of the chamber. Chemical residues left over from a previous processing step or steps of forming an insulating layer are thus removed from the passages and walls of the chamber, and the equipment is thus readied for another wafer-processing step.
Viewed from one process aspect, the present invention is directed to a method of forming a layer of uniform thickness on a surface of a semiconductive wafer by chemical vapor deposition from a mixture of reactive gasses. The method comprises the steps of: forming from separate streams of first and second gases a whirlpool-like swirling mixture of the gases in close proximity to the semiconductive wafer on which a layer of uniform thickness is to be deposited; and forming from the mixture of gases a uniform mixture of the reactive gasses; and flowing the mixed reactive gasses over and upon the surface of the wafer so as to form a layer of uniform thickness on the surface of the semiconductive wafer.
Viewed from one apparatus aspect, the present invention is directed to apparatus for forming a layer of uniform thickness on a surface of a semiconductive wafer from reactive gasses. The apparatus comprises a housing defining a chamber therein configured to contain a semiconductive wafer during processing and a mixing block defining a gas mixing cavity. A first entrance of the mixing cavity receives a first reactive gas in one direction tangentially into the mixing cavity. A second entrance of the mixing cavity receives a second reactive gas into the m
Hendrickson Scott
Nguyen Son T.
Shmurun Inna
Venkataranan Shankar
Applied Materials Inc.
Dang Phuc T.
Nelms David
Ostroff & Associates
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