Coating apparatus – Gas or vapor deposition – With treating means
Utility Patent
1999-01-12
2001-01-02
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S724000, C156S345420
Utility Patent
active
06167837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and apparatus for plasma enhanced chemical vapor deposition (PECVD), and more particularly to a method and apparatus for PECVD in a single wafer reactor that provides control of reactant gas over the surface of a wafer for more uniform processing, and provides for introduction of added dopant gases, and for wafer susceptor biasing to control the rate of ion incident on a wafer
2. Brief Description of the Prior Art
There are a large number of plasma enhanced chemical vapor deposition processes that are performed inside of enclosed chambers wherein the pressure, temperature, composition gases and application of radio frequency (RF) power are controlled to produce the desired thin film deposition of various materials onto substrates such as semiconductor wafers, flat panel displays and others. For convenience, the term “wafer” will be used in the following disclosure with the understanding that it also applies to the manufacture of flat panel and other types of substrates or devices wherein PECVD processes are employed. For example, silicon nitride is typically deposited via plasma enhanced chemical vapor deposition (PECVD) on top of metal layers on a semiconductor wafer.
A main feature of the PECVD process is that it can be carried out at low substrate temperatures as described by S. Wolf and R. N. Tauber, “Silicon Processing for the VLSI Era”, Volume 1—Process Technology, Lattice Press, 1986, pp. 171-174.
FIG. 1
shows a prior art chamber
10
having a rotating susceptor
12
capable of holding a plurality of substrates
14
. RF energy is applied to an upper electrode
16
to create a plasma (glow discharge), creating free electrons within the plasma region. The electrons gain sufficient energy from the electric field so that when they collide with gas molecules, gas-phase dissociation and ionization of the reactant gases (e.g. silane and nitrogen) occurs. The energetic species are then absorbed on the film surface of the wafers.
There are a variety of single wafer PECVD chamber designs available in the marketplace. There are also a variety of commercially available multiple wafer chambers, similar to the one shown in
FIG. 1
, wherein the wafers are all supported by a susceptor on a single horizontal plane.
The single wafer and horizontal multiple wafer PECVD chamber designs of the prior art, as described above, are problematic for numerous reasons. Single wafer designs suffer from the need to operate at relatively high pressures (>0.8 Torr) in order to achieve acceptable deposition rates and uniform film thickness across a wafer. Multiple wafer horizontal designs pose extreme difficulties in connection with the incorporation of automatic robotic wafer loading and unloading. Also, horizontal multiple wafer designs can process only a limited number of wafers before the chamber becomes so large in area that it becomes very difficult to maintain the necessary plasma uniformity and gas flow control.
It is apparent from the above description of the prior art that there is a need for a PECVD chamber that provides an improved material deposition rate and uniform thickness across a wafer, as well as facility for automatic robotic wafer loading and unloading.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a PECVD reactor yielding improved uniformity of material deposition across a wafer.
It is a further object of the present invention to provide a PECVD reactor having provision for application of RF energy for plasma enhancement, and provision for retarding incident ions on a wafer.
It is a still further objective of the present invention to provide a PECVD reactor having provision for introducing a controlled concentration of dopant across a wafer.
Briefly, a preferred embodiment of the present invention includes a PECVD reactor providing enhanced uniformity of deposition on a single wafer. The reactor has a susceptor for holding a wafer horizontally, and an apparatus for lifting the wafer from the susceptor for loading and unloading. A horizontally positioned thermal plate is positioned above the susceptor for uniform transfer of radiant heat energy from heat lamps to the wafer. The thermal plate also serves as an RF plate, being constructed of an electrically conductive material and connected to an RF transmission line and connector for receiving RF energy from an RF generator, for the purpose of providing an RF field for plasma enhancement. The thermal plate is configured thinner near its edges, so as to space the plate further from the susceptor and thicker near the center, placing it closer to the susceptor. The result of this variation is an increase in gas velocity as the gas moves toward the center of the susceptor and therefore wafer, decreasing the boundary layer between the reactant gas and the wafer surface wherein reactant products accumulate, overcoming gas depletion effects at the wafer center, and achieving a more uniform deposition or a wafer surface. The thermal plate also has small diameter holes drilled through to allow injection of dopant gases toward a wafer. Further control of deposition is achieved by applying an electrical bias on the susceptor for controlling the rate of incidence of ions on a wafer.
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Bueker Richard
Hassanzadeh P.
Jaffer David H.
Pillsbury Madison & Sutro
Torrex Equipment Corp.
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