Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1999-10-04
2002-03-26
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S719000, C118S730000, C118S729000, C118S695000, C118S696000, C216S084000, C216S085000, C216S088000
Reexamination Certificate
active
06360687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wafer flattening system for locally etching projections on a wafer surface by an activated species gas to flatten the surface or locally etching relatively thick portions of a wafer to achieve a uniform distribution of thickness of the wafer.
2. Description of the Related Art
FIG. 25
is a schematic sectional view of an example of a wafer flattening technique of the related art.
In
FIG. 25
, reference numeral
100
is a plasma generator. Activated species gas G in the plasma generated by the plasma generator
100
is sprayed on the surface of a wafer W from a nozzle
101
.
The wafer W is placed and secured on a stage
120
. The stage
120
is made to move in the horizontal direction to guide a portion Wa relatively thicker than a prescribed thickness on the surface of the silicon wafer W (hereinafter referred to as a “relatively thick portion”) directly under the nozzle
101
.
The activated species gas G is then sprayed from the nozzle
101
to the projecting relatively thick portion Wa to locally etch the relatively thick portion Wa to achieve a uniform distribution of thickness of the surface of the wafer W and thereby flatten the surface of the wafer W.
The above wafer flattening technique of the related art, however, suffered from the following problem.
The ions in the plasma generated by the plasma generator
100
are accelerated by the potential difference applied between the plasma and wafer W in striking the wafer W. Only the portions struck by the ions are etched by large extent. Further, due to sputtering, the atoms of the surface of the wafer W are stripped away. Therefore, the surface of the wafer W becomes rough at the atomic order.
Further, particles floating around the wafer W and particles generated in the discharge tube forming the nozzle
101
deposit on the surface of the wafer W causing the etchability of the portions where the particles are deposited to decline. As a result, the amounts of etching at the portions where the particles are deposited and the portions where they are not deposited differ and the surface of the wafer W is again roughened.
Due to the above, when local etching is performed, the root mean square roughness (RMS) of the surface of the wafer W ends up becoming larger. When the surface of the wafer W was actually observed after local etching under an interatomic microscope, it was learned that when a wafer W having an RMS before local etching of less than 1 nm is locally etched by the above wafer flattening process, the RMS ends up deteriorating to as bad as about 10 nm.
Further, when transferring the wafer W from a previous step to the local etching step, an oxide film naturally forms on the surface of the wafer W. If the wafer is locally etched in a state with this natural oxide film left alone, white turbidity will form at the surface of the wafer W after the local etching and will cause a deterioration of the surface roughness of the wafer W.
SUMMARY OF THE INVENTION
The present invention was made to solve the above problems and has as its object to provide a wafer flattening system configured to continuously and automatically perform the removal of the natural oxide film of a wafer and the flattening and smoothing of the wafer so as to improve the surface roughness of the wafer and to increase the work efficiency.
To achieve the above object, according to the aspect of the invention, there is provided a wafer flattening system comprising: a natural oxide film removing device for removing a natural oxide film formed on a wafer surface; a first transport device for taking out a wafer from which the natural oxide film has been removed by the natural oxide film removing device and transporting it to a predetermined location; a local etching apparatus provided with a discharge tube with a nozzle facing the wafer transported by the first transport device and a plasma generator for causing plasma discharge of a gas of a fluorine compound or a mixed gas including a fluorine compound fed to the discharge tube so as to produce a predetermined activated species gas and spraying the activated species gas from the nozzle of the discharge tube to a relatively thick portion of the surface of the wafer to locally etch the relatively thick portion; a second transport device for taking out a wafer flattened by the local etching apparatus and transporting it to a predetermined location; and a smoothing apparatus for grinding off a projection on the surface of the wafer transported by the second transport device to smooth the wafer surface.
Due to this configuration, the natural oxide film formed on the wafer surface is removed by the natural oxide film removing device, then the wafer is transported by the first transport device to the local etching apparatus. Further, at the local etching apparatus, the plasma generator causes plasma discharge of the gas of the fluorine compound or the mixed gas including the fluorine compound fed into the discharge tube so as to produce the activated species gas. This being done, the activated species gas is sprayed from the nozzle of the discharge tube to relatively thick portions of the wafer, whereby the relatively thick portion is locally etched. Therefore, by successively locally etching the entire surface of the wafer, the entire wafer surface is flattened. Further, the flattened wafer is transported by the second transport device to the smoothing apparatus. The smoothing apparatus grinds off the projections on the surface of the wafer to smooth the wafer surface.
In particular, according to an embodiment of the invention, the first transport device and the second transport device are configured by a single transport device used for both purposes.
As an example of the natural oxide film removing device, according to an embodiment of the invention, the natural oxide film removing device is provided with a solution tank for storing a solution for removal of the natural oxide film of the wafer, a washer, and a third transport device for immersing the wafer in the solution tank and then transporting it to the washer.
Due to this configuration, the wafer is immersed by the third transport device in the solution tank storing the solution for removal of the natural oxide film. After the removal of the natural oxide film, the third transport device is used to transport the wafer to the washer where the solution and other unnecessary matter are washed off.
There are various types of solutions for removal of the natural oxide film, but as preferable examples, according to an embodiment of the invention, the solution for removal of the natural oxide film stored in the solution tank is an aqueous solution of hydrofluoric acid.
As another example of the natural oxide film removing device, according to an embodiment of the invention, the natural oxide film removing device is provided with a discharge tube for spraying a predetermined activated species gas over the entire surface of the wafer and a plasma generator for causing plasma discharge of a mixed gas including a fluorine compound and hydrogen in the discharge tube so as to produce the activated species gas.
Due to this configuration, the plasma generator causes plasma discharge of the mixed gas containing the fluorine compound and hydrogen in the discharge tube and the production of the activated species gas. This being done, the activated species gas is sprayed from the discharge tube over the entire surface of the wafer, whereby the natural oxide film on the wafer surface is etched by the activated species gas.
Note that as a preferable example of the ratio of mixture of the mixed gas, according to an embodiment of the invention, the ratio of the hydrogen to the fluorine compound in the mixed gas is from 0.1% to 50% by volume.
Further, it is preferable to position a flat or notch serving as a mark for identification of the crystallization direction of the wafer or wafer position at the time of the local etching processing. Therefore, according to an embodiment of the inventio
Horiike Yasuhiro
Iida Shinya
Sadohara Takeshi
Tanaka Chikai
Yanagisawa Michihiko
Burr & Brown
Mills Gregory
SpeedFam-IPEC Co., Ltd
Zervigon Rudy
LandOfFree
Wafer flattening system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wafer flattening system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wafer flattening system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2889787