Plasma etching apparatus

Details Plasma etching apparatus Plasma etching apparatus

1999-11-08

2001-10-23

Utech, Benjamin L. (Department: 1765)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

Reexamination Certificate

active

06306245

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma etching method and apparatus for locally etching convex portions on a surface of an object to be treated.
2. Description of the Related Art
For a surface etching technology for etching a surface of an object such as a silicon wafer, there have been proposed a variety of techniques in which an object to be etched is exposed to a plasma-excited active species gas atmosphere so as to grind and polish the entire surface of the object, or in which an object to be etched is partially masked with a non-masked portion thereof being etched by means of an active species gas to form a circuit pattern.
In recent years, in place of the technique of etching the entire surface of an object, new technologies such as a TTV (Total Thickness Variation) technique, an LTV (Local Thickness Variation) technique and the like have been proposed in which convexes on a surface of an object to be etched such as a silicon wafer, a silicon-on-insulator device (SOI) and the like are subjected to localized etching, to thereby thin the etched object, or flatten the surface to improve variations in shaping or configuration of the object (for example, see Japanese Patent Laid-Open No. 6-5571).
FIG. 14
schematically shows the principle of such conventional techniques. In this figure, a reference numeral
100
designates a plasma generator which generates a plasma gas containing an active species gas G which is injected to a surface of an object to be etched in the form of a wafer
110
by means of a nozzle
101
through its opening
102
.
The wafer
110
is disposed on and fixed to a stage
120
so that the stage
120
can be moved in horizontal directions to guide a convex portion
111
of the wafer
110
into a position just under the opening
102
of the nozzle
101
. Then, the active species gas G is ejected to the convex portion
111
of the wafer
110
to locally etching the convex portion
111
to thereby flatten the surface of the wafer
110
.
In the above-mentioned conventional techniques, however, there arise the following problems. The sizes or dimensions of respective convexes of the convex portion
111
are varying, that is, for example with a silicon wafer having a diameter of 8 inches, there is a first one having an angle-shaped configuration with a highest or thickest near-center portion and a lower peripheral portion, a second one having a cone-shaped bottom configuration with a highest or thickest peripheral portion and a lowest or thinnest central portion, a third one having a multitude of small convexes and concaves each having a diameter of less than several millimeters, and a fourth one of mixed type having a mixed configuration with at least two of the above types being superposed or mixed with each other. In this manner, the convexes on the surface of the wafer are not uniform in size or dimensions thereof and not of the single type, but varying in size and type thereof.
On the other hand, since the active species gas is ejected from the nozzle
101
, the diameter D of the opening
102
of the nozzle
101
is substantially the same as the diameter of an area to be etched of the wafer
110
, so that the area of the wafer
110
is uniformly etched by means of the active species gas G. Accordingly, in the case where the wafer
110
has a multitude of convexes
111
of varying diameters on a surface thereof, the diameter D of the nozzle opening
102
has to be set so as to meet the diameter of the smallest one of the convexes, as shown in FIG.
15
. This is because if the diameter D of the nozzle opening
102
is set to a value corresponding to that of a larger convex
111
b
, concaves
112
near and around small convexes
111
a
are to be etched when etching the small convexes
111
a
. However, with the technique in which the diameter D of the nozzle opening
102
is matched to that of the smallest convex
111
a
, upon etching a larger convex
111
b
, a number of (i.e., from several to tens) etching treatments are required, thus prolonging the time necessary for one surface flattening operation.
For this reason, in order to carry out such a surface flattening operation in a short period of time using the above-mentioned conventional technique, it is generally required that a plurality (e.g., two in the illustrated example) of plasma generators
100
-
1
,
100
-
2
having different diameters of nozzle openings be provided for respective treatment chambers A, B so as to etch the wafer
110
by means of the plasma generators
100
-
1
,
100
-
2
in sequence. For example, the treatment chamber A is constructed such that it is equipped with the plasma generator
100
-
1
having a nozzle
101
with its opening of 30 mm, and the treatment chamber B is constructed such that it is equipped with the plasma generator
100
-
2
having a nozzle
101
with its opening of 7 mm. A wafer
110
is first supplied to the treatment chamber A in which relatively large convexes
111
b
on a surface of the wafer
110
each having a diameter equal to or greater than 30 mm are subjected to plasma etching. The wafer
110
thus treated is then transported to the treatment chamber B in which convexes
111
a
each having a diameter less than 30 mm are plasma etched.
With such a technique, however, the surface flattening time is in fact shortened, but at least two treatment chambers A, B equipped with the plasma generators
100
-
1
,
100
-
2
are required, resulting in a substantial increase in the cost of equipment. Moreover, the wafer
110
has to be transported from the treatment chamber A to the treatment chamber B. thus prolonging the time of the entire etching treatments required.
SUMMARY OF THE INVENTION
In view of the above, the present invention is intended to provide a novel and improved plasma etching method and apparatus in which a distance between an ejection opening in a plasma generator for ejecting an active species gas and a surface of an object to be etched can be changed to thereby shorten the time required for a surface flattening operation and reduce the cost of equipment as well.
In order to achieve the above object, according to one aspect of the present invention, there is provided a plasma etching method comprising the steps of:
disposing an ejection opening of a predetermined diameter in plasma generating means in confrontation with a prescribed convex of an object to be etched; and
ejecting an active species gas from the ejection opening to the convex to thereby flatten it through etching;
wherein a distance between the ejection opening and the convex is changed to provide an etching area corresponding to an area of said convex.
With the above method, the active species gas is ejected from the ejection opening of the predetermined diameter in the plasma generating means toward the convex, whereby the convex is etched and flattened.
In the case of the convex being large, the distance between the ejection opening and the convex is increased, whereas in the case of the convex being small, the distance is decreased, so that there is ensured an etching area corresponding to the varying size or area of the convex, whether large or small, thus flattening the convex in an effective manner.
In a preferred form of the plasma etching method of the invention, a period of time of ejecting the active species gas is controlled in accordance with the area of the convex. Thus, the ejection time of the active species gas can be increased so as to flatten the convex having a large area in a reliable manner. On the other hand, the ejection time of the active species gas can be shortened so as to flatten the convex having a small area in a reliable and effective manner.
In a further preferred form of the plasma etching method of the invention, a density of the active species gas is controlled in accordance with the area of the convex. Thus, the density of the active species gas can be increased so as to flatten the convex having a large area in a reliable and effective manner. On the other hand, the density of the acti

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