Etching a substrate: processes – Planarizing a nonplanar surface
Reexamination Certificate
1999-06-18
2001-08-28
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Planarizing a nonplanar surface
C216S067000, C216S079000, C438S697000, C438S706000, C438S707000
Reexamination Certificate
active
06280645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wafer flattening process for etching and flattening projecting portions of a wafer surface locally by an activated species gas or locally etching relative thick portions of a wafer to achieve a uniform distribution of thickness of the wafer and to a system for the same.
2. Description of the Related Art
FIG. 11
is a schematic cross-sectional view of an example of a wafer flattening process of the related art.
In
FIG. 11
, reference numeral
100
is a plasma generation unit. Activated species gas G in the plasma generated by the plasma generator unit
100
is sprayed on the front surface of a wafer W from a nozzle
101
.
The wafer W is placed and fixed on a stage
120
. The stage
120
is made to move in the horizontal direction to guide a portion relatively thicker than a prescribed thickness on the front surface of the 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 and achieve a uniform distribution of thickness of the front surface of the wafer W.
The thickness of the relatively thick portion Wa of the wafer W is not however uniform but is diverse.
Therefore, a technique has been devised for controlling the relative speed of the nozzle
101
with respect to the wafer W to match with the thickness of the relatively thick portion Wa (for example, the technology disclosed in Japanese Patent Laid-Open No. 9-27482).
This technique calls for measuring the positions and thicknesses of relatively thick portions Wa over the entire surface of the wafer W by a wafer flatness measurement apparatus to create two-dimensional position-thickness data. This data is converted to position-relative speed data showing the positions of the relatively thick portions Wa and the relative speeds of the nozzle
101
for making the relatively thick portions Wa a desired flatness after the etching.
Next, the stage
120
is controlled based on the position-relative speed data to make the nozzle
101
directly over predetermined relatively thick portions Wa to etch the entire surface of the wafer W.
That is, at a relatively thick portion Wa with a large thickness, the relative speed of the nozzle
101
is reduced to increase the amount of etching, while at a relatively thin portion Wa with a small thickness, the relative speed of the nozzle
101
is increased to reduce the amount of etching so as to thereby flatten the entire surface of the wafer W.
In the above wafer flattening process of the related art, however, there were the following problems.
Since the ions in the plasma generated at the plasma generation unit
100
are accelerated by the potential difference applied between the plasma and the wafer W and strike the wafer W, just the portions which the ions strike are etched to a large degree. Further, the atoms of the surface of the wafer W are removed by the sputtering. Therefore, the surface of the wafer W is roughened on an atomic order.
Further, the particles floating around the wafer W and the particles generated in the discharge tube forming the nozzle
101
deposit on the front surface of the wafer W. The etching characteristics of the portions where the particles are deposited decline. As a result, the amounts of etching of the portions where the particles are deposited and the portions where they are not deposited become different and the front surface of the wafer W becomes rough.
Due to the above reasons, local etching ends up resulting in a larger mean squared roughness (hereinafter referred to as the “IRMS”) of the front surface of the wafer W. When the front surface of the wafer W after the local etching is observed by an interatomic microscope, it is seen that when a wafer W with an RMS before local etching smaller than 1 nm is locally etched by the above wafer flattening process, the RMS ends up deteriorating about 10 nm.
SUMMARY OF THE INVENTION
The present invention was made to solve the above problems and has as its object to provide a wafer flattening process and system enabling a reduction of the surface roughness of the wafer caused by local etching.
To achieve the above object, according to the aspect of the invention, there is provided a wafer flattening process comprising: a local etching step for spraying a first activated species gas, generated by causing a fluorine compound gas or a first mixed gas containing a fluorine compound to discharge and generate a plasma, from a nozzle portion of a first discharge tube to a relatively thick portion of the surface of the wafer to locally etch the relatively thick portion; and a smoothing step for spraying a second activated species gas, generated by making a second mixed gas containing carbon tetrafluoride and oxygen discharge to generate a plasma, over the entire surface of the wafer after the local etching step.
Due to this configuration, when a fluorine compound gas or first mixed gas is made to discharge to generate a plasma in the local etching step, a first activated species gas containing fluorine radicals is generated and the relatively thick portions of the wafer are locally etched by the fluorine radicals. Next, by spraying the second activated species gas over the entire surface of the wafer in the smoothing step, a predetermined reaction product is deposited by the oxygen radicals in the second activated species gas inside the fine recesses of the surface of the wafer causing surface roughness and therefore the entire surface of the wafer is smoothed.
The fluorine compound in the local etching step need only be able to generate fluorine radicals by discharge to generate plasma. As one example, the aspect of the invention, the fluorine compound in the local etching step is one of carbon tetrafluoride, sulfur hexafluoride, and nitrogen trifluoride.
On the other hand, the second mixed gas in the smoothing step is used for depositing reaction products in the fine recesses of the surface of the wafer caused by local etching to smooth the surface, so it is preferable that a ratio of mixture giving a second activated species gas containing a larger amount of oxygen radicals than fluorine radicals. The aspect of the invention, the ratio of oxygen to carbon tetrafluoride in the smoothing step is set to 200 to 400 percent.
In the smoothing step, any method may be used to spray the second activated species gas over the entire surface of the wafer, but as an example the invention, the smoothing step diffuses and sprays the second active species gas from the nozzle portion of the second discharge tube facing the front surface of the wafer a predetermined distance away from it to the entire front surface of the wafer.
Further, in the smoothing step, it is preferable that the second activated species gas uniformly strike the surface of the wafer when diffusing and spraying the second activated species gas from the nozzle portion of the second discharge tube to the entire front surface of the wafer. Therefore, the aspect of the invention, the center of the nozzle portion of the second discharge tube and the center of the wafer are substantially aligned and the wafer is made to rotate on the center. Further, the aspect of the invention, the center of the nozzle portion of the second discharge tube and the center of the wafer are offset and the wafer is made to revolve around the center of the nozzle portion.
Note that systems capable of specifically realizing the wafer flattening processes according to the invention, also stand as product inventions.
Therefore, the aspect of the invention, there is provided a wafer flattening system comprising: a local etching device provided with a first gas feed unit for supplying to a first discharge tube having an opening of a nozzle portion facing the front surface of the wafer a fluorine compound gas or a first mixed gas containing a fluorine compound, a first plasma generation unit for causing t
Horiike Yasuhiro
Iida Shinya
Yanagisawa Michihiko
Burr & Brown
Gulakowski Randy
Smetana J.
Yasuhiro Horiike and SpeedFam Co, Ltd.
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