Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-04-17
2001-10-16
Zarabian, Amir (Department: 2824)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S670000, C438S610000, C137S003000, C137S088000, C137S607000, C137S624160
Reexamination Certificate
active
06303501
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the manufacture of integrated circuits. In particular, the present invention is directed to apparatus, systems, and methods for thoroughly mixing a plurality of gases to be used in a semiconductor wafer manufacturing process. More particularly, the present invention relates to thorough gas mixing for the formation of polycide films using. materials such as tungsten silicide (WSi
x
) on a semiconductor wafer.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two-year/half-size rule (often called “Moore's Law”) which means that the number of devices which will fit on a chip doubles every two years. Today's wafer fabrication plants are routinely producing 0.5 &mgr;m and even 0.35 &mgr;m feature size devices, and tomorrow's plants soon will be producing devices having even smaller feature sizes.
One of the primary steps in fabricating modern semiconductor devices involves the formation of a dielectric, metal, or insulating layers over a semiconductor substrate. As is well known, such layers can be deposited by chemical vapor deposition (CVD). CVD processes are particularly suitable for use with high integration devices because CVD layers provide superior step coverage and post-annealing qualities to those layers formed by sputtering or other conventional deposition methods. In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions (homogeneous or heterogeneous) take place to produce a desired film. In a plasma enhanced chemical vapor deposition (PECVD) process, the flowing gas may be excited to a plasma state. A controlled plasma is formed to decompose and/or energize reactive species to produce the desired film. The process of depositing layers on a semiconductor wafer (or substrate) usually involves heating the substrate and holding it a short distance from the source of a stream of deposition (or process) gas flowing towards the substrate. In general, reaction rates in thermal and plasma processes may be controlled by controlling one or more of the following: temperature, pressure, and reactant gas characteristics.
In the quest to achieve ever smaller devices, increasingly stringent process requirements are being imposed on integrated device manufacturing processes. One such requirement is the thorough mixture of process gases prior to introduction of the gases into a CVD chamber. A thorough mixture of the process gases is typically necessary to achieve a uniform deposition pattern on the semiconductor substrate. If the quality of the mixing achieved by the plurality of gases is insufficient, the CVD process using the gases will provide an uneven deposition pattern, which may result in variance of the sheet resistance of the deposited film, delamination during annealing, or other undesirable qualities which may degrade device performance.
A thorough gas mixre is particularly desirable in the formation of a tungsten silicide (WSi
x
) film. To overcome heat generation and heat dissipation problems associated with using conventional polysilicon films and scaled down device dimensions, “polycide” films using tungsten silicide have been formed by depositing a metal silicide layer over a layer of conventional polysilicon. Such polycide films have lower resistivities than polysilicon films and thus reduce heat generation and heat dissipation problems. The preferred method for forming tungsten silicide layers comprises chemical vapor deposition (CVD) of dichlorosilane (DCS) and tungsten hexafluoride (WF
6
) over a semiconductor substrate.
Unfornmately, despite the improved film characteristics of the DCS and WF
6
process, the CVD process using these two gases is particularly sensitive to gas flow and mixture parameters. Conventional gas mixers adapted to provide adequate levels of gas mixing are costly to manufacture and sensitive to minor flaws associated with manufacturing. Conventional mixers typically only use one mixing step and rely on a mixer that is difficult to test prior to actual use in a semiconductor system. Hence, it would be desirable to provide an improved gas mixing apparatus that would provide reliable and thorough gas mixing. It would further be desirable to provide a gas mixing apparatus that facilitates manufacturing and would be less sensitive to minor flaws that may occur during manufacturing.
SUMMARY OF THE INVENTION
The present invention is related to semiconductor wafer processing. More specifically, the present invention is directed to apparatus, systems, and methods for reliable and thorough gas mixing. The present invention uses a mixing procedure that is more tolerant of flaws which may occur during manufacturing and thus increases the robustness of the resulting gas mixing apparatus. Due in part to the design associated with this improved gas mixing apparatus, the present invention allows for easier access to portions of the apparatus involved in fluid mixing. This facilitates manufacturing and also improves device testing prior to installation of the gas mixing apparatus into a wafer processing system.
According to the present invention, a gas mixing apparatus for use with a semiconductor wafer processing chamber comprises a gas mixer housing having a gas inlet for fluidly coupling to a plurality of gas sources. The housing includes a fluid flow channel fluidly coupled to the gas inlet. The fluid flow channel comprises one or more fluid separators for separating the gas into two or more gas portions and one or more fluid collectors for allowing the gas portions to collide with each other to combine and form a mixed gas. The mixed gas exits the mixing apparatus through a gas outlet fluidly connected to the fluid flow channel, typically for flowing the mixed gas into a processing chamber. The fluid flow channel can allow for repeated separating and colliding of the gas portions to ensure a more complete gas mixture.
In one embodiment of the gas mixing apparatus, the fluid separators comprise a first carrier channel having a channel surface that redirects the process gases into two or more gas portions flowing away from one another in the channel. The fluid collector comprises an impinging channel that intersects the first carrier channel at a location where a plurality of gas portions are colliding. The impinging channel may then further intersect a second carrier channel to release the mixed gas into the second carrier channel which separates the mixed gas into a plurality of gas portions.
In further embodiments of the gas mixing apparatus, the fluid flow channel of the gas mixer housing may be provided on an insert slidably fitted within an insert recess of the housing. Having the channel on a removable insert simplifies manufacturing of the fluid flow channel and also facilitates inspection of the part. The fluid flow channel is typically incorporated on the surface of the insert. In certain embodiments, the insert may also be attached to a portion of the housing in the form of a protrusion. In this embodiment, the present invention provides a gas mixer housing comprising a first portion and a second portion. The first portion has a protrusion incorporating the fluid flow channel on the surface of the protrusion and the second portion has a protrusion recess for slidably receiving the protrusion.
In still further embodiments of the gas mixing apparatus, the fluid flow path may be provided directly on the gas mixer housing. In this embodiment, the gas mixer housing comprises a first portion and a second portion where the fluid flow channel is incorporated on the surface of the second portion. This allows a fluid flow channel to be formed in the housing without the use of an insert. The flow channel remains accessible to inspection as the portions of the housing may be separated from one another.
According to the present invention, a method for fabricating an integrated
Chen Aihua
Chen Chen-An
Nakanishi Koji
Applied Materials Inc.
Luu Pho
Townsend & Townsend & Crew
Zarabian Amir
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