Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
1999-03-18
2001-02-27
Bueker, Richard (Department: 1763)
Coating processes
Coating by vapor, gas, or smoke
C118S715000
Reexamination Certificate
active
06194030
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for low pressure chemical vapor deposition (LPCVD) of thin films onto a substrate, and more particularly to a method and apparatus for improving the thin film uniformity by controlling the velocity of gas within the LPCVD apparatus.
BACKGROUND OF THE INVENTION
LPCVD is a technique for forming thin film layers on substrates. In particular, LPCVD is used to form metal films (e.g., for wiring), semiconductor films (e.g., for doping to form active areas) and insulating films (e.g., for insulating the metal wires) on silicon wafers in fabricating semiconductor devices such as integrated circuits.
Briefly, a typical prior art LPCVD apparatus includes a heated chamber within which is held one or more wafers on which a thin film is to be deposited. A gas inflow system at one end of the chamber inflows a reactive gas into the chamber. The chamber is kept at low pressure so that the reactive gas flows through the chamber and flows over the surfaces of the one or more wafers. The combination of temperature, pressure and the particular type of reactive gas results in a film being deposited on the surface of each of the one or more wafers. A gas exhaust system removes the reactive gas, as well as other gaseous compounds formed by the reactive process.
In semiconductor manufacturing, it is highly advantageous to deposit thin films on a plurality of wafers in one deposition process because it increases throughput and allows for better process control. However, a major disadvantage with this approach using prior art LPCVD apparatus is that the uniformity of the films deposited on each wafer can vary over each wafer and amongst the wafers due to uneven gas flow velocity between the wafers. This is because the deposition rate of the film is related to the uniformity of the gas flow velocity between the wafers. In particular, it has been observed that the wafers closest the gas input end typically have non-uniform thin films. This is problematic, since in the art of semiconductor manufacturing, it is known that uniform films are an important aspect of successfully fabricating semiconductor devices.
Most prior art apparatus are capable of altering the gas flow within the chamber only by altering the amount of exhaust using a vacuum pump, or by altering the gas inflow at the gas inflow end of the chamber. For example, U.S. Pat. No. 4,699,805 to Seelbach et al. discloses an LPCVD process and apparatus for enhancing the gas flow within the chamber by providing a U-shaped gas injection tube. The tube is coupled to a vacuum pump which controls the pressure within the chamber. Another example of external chamber pressure control is described in U.S. Pat. No. 5,653,810 to Kataoka et al., which discloses an apparatus and process for forming a metal film in a CVD apparatus, wherein the pressure inside the liner tube is controlled by a control valve in an external exhaust unit.
Other prior art CVD apparatus are capable of altering the flow of gas within the chamber, but are limited to forming a film on a single wafer. For example, U.S. Pat. No. 5,362,526 to Wang et al. discloses a high-pressure single wafer CVD apparatus having a uniform radial-pumping gas apparatus which enables uniform reactant gas flow across the wafer. The gas apparatus includes a gas distributor plate in close proximity to the wafer. While the distributor plate is directed to the general idea of directing the gas flow in relation to the wafer, the direction of the flow radial. In addition, the distributor plate is designed for use in a high-pressure, single wafer CVD apparatus, and does not appear to be applicable to a low-pressure, multi-wafer CVD apparatus. Similarly, U.S. Pat. No. 4,798,165 to deBoer discloses an improved technique for providing deposition materials to a growth surface by passing a reactive gas through a plate having a plurality of apertures, the plate being arranged in close proximity to the surface on which deposition is to be carried out. However, the aperture plate is limited to affecting the air flow around in the vicinity of the single surface. Moreover, the plate is required to be substantially the size of the single surface.
SUMMARY OF THE INVENTION
The present invention relates to methods and apparatus for LPCVD of thin films onto a substrate, and more particularly to a method and apparatus for improving the thin film uniformity by controlling the velocity of gas within the LPCVD apparatus.
A first aspect of the invention is an apparatus for depositing a thin film on each surface of a plurality of substrates. The apparatus comprises a liner tube having a first end, a second end and an interior capable of accommodating the substrates between the first and second ends. A gas supply system provides a reactive gas to the interior at or near the first end. A gas exhaust system with an exhaust cross-sectional area, exhausts the gas emerging from the second end. A gas flow restrictor is arranged at the second end and is designed so as to restrict the flow of the gas at the second end.
A second aspect of the invention is a gas flow restrictor, suitable for use in the apparatus described above, in the form of a restrictor plate having apertures therein. The restrictor plate apertures preferably have a collective area substantially the same as the exhaust cross-sectional area. Also, the plate is preferably curved and fits over the second end of the liner tube as a removable cap. The plate can also be integral with the liner tube.
A third aspect of the invention is a method of depositing a thin film on the surface of each of a plurality of substrates in a LPCVD apparatus having a liner tube with a first end, a second end and an interior capable of accommodating the plurality of substrates between the first and second ends, and a gas exhaust cross-section. The method comprises the steps of first, flowing a reactive gas into the liner tube through the first end at a first velocity, and then restricting the flow of the gas only at the second end so as to make the flow of gas at the second end have a second velocity that is substantially the same as the first velocity.
A sixth aspect of the invention is a method as described above, wherein the step of restricting the flow of gas includes the step of adding a gas flow restrictor, as described above, at the second end.
REFERENCES:
patent: 3603284 (1971-09-01), Garnache
patent: 4699805 (1987-10-01), Seelbach et al.
patent: 4793283 (1988-12-01), Sarkozy
patent: 4798165 (1989-01-01), deBoer et al.
patent: 4892753 (1990-01-01), Wang et al.
patent: 4986216 (1991-01-01), Ohmori
patent: 4992044 (1991-02-01), Philipossian
patent: 5000113 (1991-03-01), Wang et al.
patent: 5121705 (1992-06-01), Sugino
patent: 5127365 (1992-07-01), Koyama
patent: 5279670 (1994-01-01), Watanabe
patent: 5354715 (1994-10-01), Wang et al.
patent: 5362526 (1994-11-01), Wang et al.
patent: 5447568 (1995-09-01), Hayakawa et al.
patent: 5484484 (1996-01-01), Yamaga
patent: 5571333 (1996-11-01), Kanaga
patent: 5653810 (1997-08-01), Kataoka et al.
patent: 58206119 (1982-05-01), None
patent: 60-202937 (1985-10-01), None
patent: 1-309315 (1989-12-01), None
patent: 2-58825 (1990-02-01), None
patent: 3-211823 (1991-09-01), None
patent: 6224129 (1994-08-01), None
Bueker Richard
Downs Rachlin & Martin PLLC
International Business Machines - Corporation
LandOfFree
Chemical vapor deposition velocity control apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chemical vapor deposition velocity control apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemical vapor deposition velocity control apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2564363