Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1999-11-03
2001-06-26
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Gas or vapor deposition
C118S7230IR, C204S298070, C156S345420
Reexamination Certificate
active
06251187
ABSTRACT:
BACKGROUND OF THE INVENTION
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. High density plasma CVD processes promote the disassociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive ionic species. The high reactivity of the released ionic species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such CVD processes.
In one design of high density plasma chemical vapor deposition (HDP-CVD) chambers, the vacuum chamber is generally defined by a planar substrate support, acting as a cathode, along the bottom, a planar anode along the top, a relatively short sidewall extending upwardly from the bottom, and a dielectric dome connecting the sidewall with the top. Inductive coils are mounted about the dome and are connected to a supply radio frequency generator. The anode and the cathode are typically coupled to bias radio frequency generators. A series of equally spaced gas distributors, typically nozzles, are mounted to the sidewall and extend into the region above the edge of the substrate support surface. The gas nozzles are all coupled to a common manifold which provides the gas nozzles with process gases, including gases such as argon, oxygen, silane, TEOS (tetraethoxysilane), silicon tetrafluoride (SiF
4
), etc., the composition of the gases depending primarily on what type of material is to be formed on the substrate. The nozzle tips have exits, typically orifices, positioned in a circumferential pattern spaced apart above the circumferential periphery of the substrate support and through which the process gases flow.
The thickness of the deposited film is ideally, but in practice is never, perfectly uniform. Deposition uniformity is very sensitive to source configuration, gas flow changes, source radio frequency generator current, bias radio frequency generator currents, the nozzle height above the substrate support and the lateral position of the nozzle relative to the substrate support. Improvements in this deposition uniformity are hindered by several factors. For example, it is often preferable that the height of the nozzles above the substrate support surface be greater than it is. However, for practical reasons it is not feasible to position the nozzles through the dielectric dome. Also, adjusting the height of the nozzles above the substrate for each process condition is not practical unless the substrate is movable vertically. Furthermore, while increasing the distance between nozzle orifices and the substrate tends to improve the deposition uniformity, it adversely affects the gas efficiency, that is requires the use of more gas or more time. In addition, argon is commonly directed through the manifold and nozzles as part of the process gases, argon flow contributing to the effectiveness of sputtering rate and sputtering uniformity. However, the use of argon restricts the flexibility one has in varying the flow rate of the process gases through the nozzles.
Another factor affecting deposition is related to the cleanliness of the nozzle orifices. Some process gases, such as silane, can thermally disassociate and deposit silica on the inside of the nozzle orifices. In addition, some oxygen may diffuse back into the nozzle orifices and react with the process gases to create a deposit on the inside of the nozzle orifices. Attempts to “dry clean” the chamber (by keeping the chamber closed and injecting a cleaning gas, such as fluorine compounds, into the chamber) can create additional problems. For example, fluorine gas can partially react with deposited silica and create a porous material which expands and clogs up the orifices even worse.
SUMMARY OF THE INVENTION
The present invention is directed to an improved deposition chamber which uses a supplemental or second gas distributor, typically a nozzle, centered above the substrate support surface to enhance deposition thickness uniformity. Deposition thickness uniformity is also enhanced by equalizing the pressure of the process gases supplied to a series of gas distributors, also typically nozzles, fed by a common manifold.
The improved deposition chamber includes a housing defining a vacuum chamber. A substrate support is housed within the vacuum chamber. A plurality, typically 12, of first gas distributors, typically nozzles, have their orifices or other exits opening into the vacuum chamber in a circumferential pattern spaced apart from and generally overlying the circumferential periphery of the substrate support surface, as is conventional. With the invention, a second gas distributor is used and is positioned spaced apart from and generally overlying the center of the substrate support surface. The use of the second gas distributor to inject process gases into the vacuum chamber helps to improve deposition thickness uniformity over that which is achieved without the use of the second gas distributor.
Deposition thickness uniformity is also improved by supplying the process gases to the manifold at a plurality of positions. The supply of the process gases to the manifold is done in a manner so that the process gases are supplied to the gas distributors at the same pressure. This is done to ensure an equal flow rate from each of the first gas distributors.
The exits of the gas distributors are preferably sized to permit effective dry cleaning operations. In some situations dry cleaning operations may not be effective to clean the inside surfaces of the exits. In such situations enhanced cleaning of the gas distributors can be achieved by selectively connecting a vacuum pump to the gas distributors and slowly drawing the cleaning gas within the vacuum chamber in a reverse flow direction from the chamber, through the gas distributors and from the system through the vacuum pump.
A primary advantage of the invention is that by independently supplying process gases to the second (or upper) gas distributor, a more uniform deposition thickness can be achieved under a variety of operating conditions, which result in a change in the distribution of the process gases through the first or lower gas distributors.
It has been found that a second gas distributor with a single exit is effective for use with 8-inch (20 cm) substrates. However, for larger substrates, such as 12-inch (30 cm) substrates, one or more second gas distributors having a plurality of exits will likely provide the best deposition thickness uniformity.
Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.
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patent
Ishikawa Tetsuya
Li Shijian
Redeker Fred C.
Applied Materials Inc.
Lund Jeffrie R.
Townsend & Townsend & Crew
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