Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2000-03-30
2001-11-13
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C156S345420, C216S069000, C438S729000
Reexamination Certificate
active
06316369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an corrosion-resistant system and method for a plasma etching apparatus in which a relatively thick portion(s) on a surface of an object to be etched are locally etched.
2. Description of the Related Art
FIG. 5
is a cross section showing an example of a known plasma etching apparatus, and
FIG. 6
is a diagram showing the state of oscillation of a micro wave.
The plasma etching apparatus performs plasma-discharge using a micro wave. A mixed gas containing a halogen-based gas such as CF
4
(carbon tetrafluoride) is supplied to a quartz discharge tube
110
which is mounted on an upper surface of a chamber
100
. As shown in
FIG. 6
, the micro wave M of about 500W is generated or oscillated continuously by a micro wave oscillator
120
toward a wave guide
121
, so that the mixed gas in the quartz discharge tube
110
is made into a plasma state, thus producing active species such as fluorine radicals which contribute to etching a silicon wafer W.
On the other hand, the silicon wafer W is fixedly mounted on a stage
101
which is driven to move in an X-Y direction (i.e., the right and left direction as well as the front and rear direction of the sheet of
FIG. 5
) by means of an X-Y drive mechanism
130
.
Specifically, a movable stand
132
carrying thereon a stage
101
is driven to move in an X-axis direction by means of a drive motor
131
and in a Y-axis direction by means of a drive motor
133
mounted on the movable stand
132
.
With this construction, the active species such as fluorine radicals generated by the plasma discharge is jetted from an ejection opening
110
a
of a quartz discharge tube
110
onto a silicon wafer W. At the same time, the X-Y drive mechanism
130
moves a relatively thick portion of the silicon wafer W (i.e., a portion which forms a surface of the silicon wafer W is formed, and which is relatively thicker than a specified thickness) right under the ejection opening
110
a
of the quartz discharge tube
110
so that the relatively thick portion can be partially or locally etched.
Here, it is to be noted that during such partial or localized etching, part of the active species gas G jetted from the ejection opening
110
a
might diffuse to etch an inner wall of the chamber
100
as well as the X-Y drive mechanism
130
.
To avoid this, the plasma etching apparatus employs an corrosion-resistant technique.
That is, the inner wall of the chamber
100
and the X-Y drive mechanism
130
are subjected to corrosion-resistant coating so that they can be prevented from being etched by the active species gas G. Furthermore, even if those portions such as threaded portions, rails, bearings of the X-Y drive mechanism
130
, rotation shafts of the drive motors
131
,
133
and so on, which are in sliding contact with other elements, are applied with corrosion-resistant coatings, such corrosion-resistant coatings would be liable to be peeled off during a long period of use. Thus, those contacting and sliding portions are coated with a corrosion-resistant oil which does not flake off due to repeated sliding actions.
The above-mentioned plasma etching apparatus and corrosion-resistant technique have the following problems.
A first problem is that since the plasma etching apparatus is constructed such that a micro wave M is oscillated or generated continuously so as to produce plasma discharge, as illustrated in
FIG. 6
, the effective period or life time of the quartz discharge tube
110
is short and the etching rate with respect to the silicon wafer W is low, and the silicon wafer W during etching is liable to be contaminated.
FIG. 7
is a cross section showing the state of corrosion of the quartz discharge tube
110
.
If a mixed gas containing a CF
4
(carbon tetrafluoride) gas for instance is plasma-discharged, there will be generated an active species gas G which contains CF
3
radicals, F radicals, CF
3
cations or positive ions, F anions or negative ions, etc. These radials, positive and negative ions contribute to the localized etching of the silicon wafer W.
However, when plasma discharging is continuously conducted, the quartz discharge tube
110
continuously absorbs the micro wave, resulting in a rapid rise of the heating temperature of the quartz discharge tube
110
. As a consequence, the reaction of the active species gas G and a SiO
2
(silicon dioxide) component of the quartz discharge tube
110
is promoted, as shown in
FIG. 7
, so that the inner wall of the quartz discharge tube
110
is subjected to corrosion, thus forming a hole or holes through the quartz discharge tube
110
in a relatively short period of time.
Furthermore, when the corrosion of the quartz discharge tube
110
has been made, the active species gas G reacts with the quartz discharge tube
110
to turn into a SiF
4
(silicon tetrafluoride) gas, thereby reducing the density of the active species gas G ejected to the silicon wafer W to lower the etching rate of the silicon wafer W.
In addition, during the etching of the quartz discharge tube
110
, there are generated particles of impurities contained in the quartz discharge tube
110
itself. These particles might be jetted to the surface of the silicon wafer W, thus contaminating the silicon wafer W.
A second problem is that the above-mentioned corrosion-resistant technique does not provide a satisfactory corrosion resistant effect.
Specifically, it is impossible to completely provide all the exposed portions of the chamber
100
, the X-Y drive mechanism
130
and the like with corrosion-resistant coatings. Especially, the X-Y drive mechanism
130
is constructed of various members assembled, so it is impossible to coat every component member with a corrosion-resistant oil.
Further, the corrosion-resistant oil applied to the sliding portions gradually evaporates so that the base portions underlying the corrosion-resistant coatings are exposed during a long period of use. In order to avoid this, it is necessary to disassemble the chamber
100
and the X-Y drive mechanism
130
regularly or at a predetermined interval and re-coat them with the corrosion-resistant oil.
SUMMARY OF THE INVENTION
In view of the above, the present invention is intended to obviate the above-described problems, and has for its object to provide a corrosion-resistant system and a corrosion-resistant method for a plasma etching apparatus which are capable of reducing or improving the corrosion or erosion phenomena of a discharge tube of the plasma etching apparatus, other equipment or elements in a chamber used for localized etching.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a corrosion-resistant system for a plasma etching apparatus in which a reactive gas in a discharge tube is plasma-discharged by using a micro wave or a high-frequency wave to produce an active species gas by means of which a relatively thick portion of an object to be etched is locally etched,
the corrosion-resistant system comprising:
oscillation means for continuously oscillating the micro wave or the high frequency wave; and
oscillation control means for controlling the oscillation means in an on-off manner so that a pulsed micro wave or a pulsed high-frequency wave is oscillated from the oscillation means.
With this arrangement, the micro wave or the high-frequency wave is oscillated from the oscillation means under the control of the oscillation control means, so that a temperature rise of the discharge tube is decreased in comparison with a continuous oscillation, accordingly suppressing reactions between active species in a plasma and the discharge tube.
In a preferred form of the corrosion-resistant system for a plasma etching apparatus according to the first aspect of the invention, the duty ratio of the pulsed micro wave or high-frequency wave is set to 75% or less, and the pulse frequency of the pulsed micro wave or high-frequency wave is set to 10 kHz or more.
With this arrangement, the pulsed micro wave or high-f
Horiike Yasuhiro
Iida Shinya
Yanagisawa Michihiko
Fitch Even Tabin & Flannery
Powell William A.
SpeedFam Co., Ltd
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