Method of performing plain etching treatment and apparatus therefor

Disclosed herein are a dry etching method and a dry etching apparatus. The method comprises a step of applying an etching inhibiting gas to that portion of a workpiece where etching speed is high, while the workpiece is being etched with reactive-gas plasma. The apparatus comprises functions for holding a reactive etching gas, a first electrode located within the gas-holding functions, for supporting a workpiece, a second electrode located within the gas-holding functions and spaced apart from the first electrode by a predetermined distance, functions for supplying high-frequency power, thereby to convert the reactive etching gas into a plasma in the space between the first and second electrodes, and functions for supplying an etching inhibiting gas to that portion of the workpiece where etching speed is high.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a dry etching method of forming a fine 
pattern in manufacturing, for example, a semiconductor device, and also to 
a dry etching apparatus for forming such a fine pattern. 
2. Description of the Related Art 
Known as micro-process techniques for manufacturing semiconductor devices 
are microwave plasma etching, reactive ion etching, and the like. The 
reactive ion etching includes a method using parallel flat electrodes, a 
method utilizing electron cyclotron resonance (ECR), and the like. 
In a conventional reactive ion etching apparatus, the upper electrode is 
mounted on the top of the reaction chamber, and the lower electrode, which 
extends parallel to the upper electrode, is located within the reaction 
chamber. The upper electrode has a hollow and is grounded. A gas pipe is 
connected to the upper surface of the upper electrode, for introducing a 
reaction gas into the hollow. The upper electrode has a plurality of 
through holes in its lower surface, through which to supply the reaction 
gas into the reaction chamber. A workpiece, such as a silicon wafer, is 
mounted on the lower electrode. The lower electrode is connected by a 
blocking capacitor to a high-frequency power supply. The lower electrode 
is surround by a baffle plate which is located within the reaction 
chamber, as well. The baffle plate has a plurality of through holes. An 
exhaust pipe is connected to the side of the reaction chamber, for 
exhausting the reaction gas from the reaction chamber. 
To etch the workpiece, the reaction gas is introduced into the reaction 
chamber through the holes made in the lower surface of the upper 
electrode. The gas is exhausted from the chamber through the exhaust pipe, 
10 thereby controlling the gas pressure within the reaction chamber. At 
the same time, a high-frequency power is supplied from the high-frequency 
power supply to the lower electrode, generating a plasma in the space 
between the upper and lower electrodes. The plasma thus generated is 
applied to the workpiece, whereby the target film formed on the workpiece 
is etched. 
During the etching process, the reaction gas is introduced into the chamber 
through the holes of the upper electrode and is exhausted from the chamber 
through the exhaust pipe. Part of this gas reacts with the plasma and 
changes into a reaction-product gas. The reaction-produce gas is exhausted 
from the chamber through the exhaust pipe. That part of the 
reaction-product gas which has been generated at the periphery of the 
workpiece is immediately exhausted, but that part of the gas which has 
been generated at the center portion of the workpiece is hard to exhaust. 
Thus, less reaction-product gas accumulates on the edge portion of the 
workpiece than on the center portion thereof. As a consequence, the edge 
portion of the workpiece is etched faster than the center portion of the 
workpiece. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a dry etching method and 
a dry etching apparatus, which can etch every portion of a silicon wafer 
(including a center portion and an edge portion) at sufficiently uniform 
speed. 
According to the invention, there is provided a dry etching method 
comprising a step of applying an etching inhibiting gas to that portion of 
a workpiece where etching speed is high, while the workpiece is being 
etched with reactive-gas plasma etching of the workpiece. 
Also, according to the invention, there is provided a dry etching apparatus 
comprising: means for holding a reactive etching gas; a first electrode 
located within the gas-holding means, for supporting a workpiece; a second 
electrode located within the gas-holding means and spaced apart from the 
first electrode by a predetermined distance; means for supplying 
high-frequency power, thereby to convert the reactive etching gas into a 
plasma in the space between the first and second electrodes; and means for 
supplying an etching inhibiting gas to that portion of the workpiece where 
etching speed is high. 
The etching method of this invention solves the problem with the 
conventional method in which the portions of a workpiece cannot be etched 
at the same speed. To be more specific, the etching inhibiting gas is 
applied in a prescribed amount to the edge portion of the workpiece, thus 
inhibiting the etching of the edge portion on which no reaction-product 
gas accumulates. The edge portion which should otherwise be etched too 
fast is, therefore, etched at substantially the same speed as the other 
portion, such as the center portion, on which the reaction-product gas 
accumulates. As a result, every portion of the workpiece can be etched 
uniformly. 
The dry etching apparatus of the invention, described above, is designed to 
perform this drying etching method. In the apparatus, the etching 
inhibiting gas is applied in a prescribed amount to that portion of a 
workpiece which may be etched excessively, thus inhibiting the etching of 
the this portion, whereby every portion of the workpiece can be etched 
uniformly. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will now be described with reference 
to the accompanying drawings. 
As shown in FIG. 1, a plasma etching apparatus of the invention comprises a 
reaction chamber 21, which is made of aluminum and has its inner surface 
alumite-treated. An upper electrode 22 is mounted on the top of the 
reaction chamber 21, and a lower electrode 23 is held within the chamber 
21. The electrodes 22 and 23 are flat plates located in parallel to each 
other. The upper electrode 22 is a hollow member which has through holes 
made in its lower surface. A first gas pipe 24 is connected to the top of 
the upper electrode 22, for introducing a reaction gas into the reaction 
chamber 21 through the holes of the upper electrode 22. 
A workpiece 26, such as a silicon wafer, is placed on the lower electrode 
23. The workpiece 26 is held by means of a mechanism (not shown) fixed to 
the lower electrode 23. The lower electrode 23 is connected by a blocking 
capacitor 27 to a high-frequency power supply 28. In the reaction chamber 
21, the lower electrode 23 is surrounded by a baffle plate 29, which has a 
plurality of through holes 30. An exhaust pipe 31 is connected to one side 
of the reaction chamber 11. 
The apparatus further comprises a second gas pipe 32. The second gas pipe 
32 extends into the reaction chamber 21. As is shown in FIG. 2A, it has a 
loop at its inner end, which surrounds the workpiece 26. The loop has a 
plurality of nozzles 32a, through which to apply at least one gas onto the 
edge portion of the workpiece 26, said gas being similar to a 
reaction-product gas. Alternatively, as shown in FIG. 2B, the loop may 
have a number of holes 34 so that the gas can be applied more uniformly 
onto the edge portion of the workpiece 26. 
If the workpiece 26 has a WSi film to be etched, a reaction gas, which is a 
mixture of Cl.sub.2 and SF.sub.6, is introduced into the reaction chamber 
21 through the upper electrode 22, and reaction-product gases, which are 
WF.sub.6, and SiCl.sub.4, and the like will be generated in the chamber 
21. In this case, WF.sub.6 gas, for example, is introduced as etching 
inhibiting gas into the chamber 21 through the second gas pipe 32. 
To etch the WSi film on the workpiece 26, the reaction gases Cl.sub.2 and 
SF.sub.6 are supplied into the chamber 21 through the holes 25 of the 
upper electrode 22. Simultaneously, the etching inhibiting gas WF.sub.6 is 
introduced into the chamber 21 through the second gas pipe 32. This 
etching inhibiting gas is supplied in an amount equal to that of the 
reaction-product gas being generated at the center portion of the 
workpiece 26. The reaction-product gases and the etching inhibiting gas 
are discharged from the chamber 21 through the exhaust pipe 31, thereby 
controlling the pressure within the reaction chamber 21. At the same time, 
the high-frequency power supply 28 supplies high-frequency power to the 
lower electrode 23, generating a plasma in the gap between the electrodes 
22 and 23. The plasma is applied onto the SWi film, thus etching this 
film. 
As the reaction gases are supplied into the chamber 21, gradually etching 
the SWi film on the workpiece 26, the reaction-product gas generated 
through the reaction accumulates on the workpiece 26, more at the center 
portion than in the edge portion. Nonetheless, the SWi film is uniformly 
etched, or etched at the same speed at the center portion and the edge 
portion. This is because the etching inhibiting gas (i.e., WF.sub.6 gas), 
which is similar to the reaction-product gas, is applied onto the edge 
portion of the workpiece 26 in an amount substantially equal to that of 
the reaction-product gas being generated at the center portion of the work 
piece 26. 
The etching inhibiting gas is not necessarily be one similar to the 
reaction-product gases. Whatever gas that can inhibit the etching reaction 
can be used instead, to etch the WSi film uniformly. 
The broken line in FIG. 3 represents the relation between the speed at 
which the embodiment of FIG. 1 etches a portion of the WSi film and the 
distance at which this portion is located from the center of the workpiece 
26. On the other hand, the solid line shown in FIG. 3 illustrates the 
relation between the speed at which a conventional plasma etching 
apparatus etches a portion of a WSi film formed on a workpiece and the 
distance at which this portion is located from the center of the 
workpiece. As is evident from FIG. 3, the plasma etching apparatus of the 
invention, shown in FIG. 1 and FIG. 2A (or FIG. 2B), can etch a WSi film 
uniformly--that is, to the same extent at the center portion and the edge 
portion. 
Let us consider, here, the yield of integrated circuits formed on a 
semiconductor wafer subjected to plasma etching. In the conventional 
plasma etching apparatus, the etching speed at the center portion of the 
wafer differs by more than 10% from the etching speed at the edge portion 
thereof. Consequently, the yield of the integrated circuits formed on the 
wafer is only about 36% at best. By contrast, in the apparatus of the 
present invention, the etching speed at the center portion of the wafer 
differs by 10% or less from that at the edge portion thereof. As a result, 
the yield of the integrated circuits formed on the wafer can be about 
100%. 
As may be understood from FIG. 1, both electrodes 22 and 23 are of the same 
type employed in the conventional plasma etching apparatus. Hence, the 
apparatus of the invention can be manufactured easily. 
FIGS. 4 and 5 show the second and the third embodiment of the present 
invention, in which a second gas pipe is located in part within a reaction 
chamber. The components identical to those of the apparatus shown in FIG. 
1 are denoted at the same reference numerals and will not be described in 
detail. 
In the second embodiment of FIG. 4, the looped portion of the second gas 
pipe 32 is arranged within an upper electrode 22 and has nozzles. The 
nozzles extend downwards, made in the lower surface of the upper electrode 
22, and located in a circle around the through holes 25 cut in the lower 
surface of the electrode 22. In the second embodiment of FIG. 4, the 
looped portion of the second gas pipe 32 is formed within a lower 
electrode 23 and has nozzles. The nozzles extend horizontally, made in the 
upper peripheral portion the lower electrode 23, and opens in the 
periphery of the upper portion of the lower electrode 23. 
The embodiments of FIGS. 4 and 5 can perform plasma etching on the center 
and edge portions of a workpiece 26 at the same speed, as well. 
As has been indicated, the etching speed at the edge portion of the 
workpiece 26 is reduced to the etching speed at the center portion, i.e., 
the low etching speed. This does not matter at all, because the etching 
speed at the center portion can be increased by raising the temperature 
within the reaction chamber 21. 
FIG. 6 is a table showing various combinations of a film to etch, a 
reaction gas and a etching inhibiting gas. Any one of the combinations 
shown can be employed in the present invention. As has been pointed out, 
the etching inhibiting gas is not necessarily be one similar to the 
reaction-product gases; any gas able to inhibit etching reaction and free 
of chemical influence of another gas whatever can be applied instead, to 
achieve the same result. 
In the first to third embodiments, as has been described, the second gas 
pipe 32 has its gas-applying unit in the vicinity of the edge portion of 
the workpiece 26. Instead, the pipe 32 may be so positioned as to apply 
the etching inhibiting gas to any portion of the workpiece 26 that should 
otherwise be etched at higher speed than other portions. 
All embodiments described above are plasma etching apparatuses. 
Nevertheless, this invention is not limited to this type of a dry etching 
apparatus. It can be applied to a barrel-type etching apparatus, a 
downflow type etching apparatus, an ECR plasma etching apparatus, and the 
like. 
Moreover, various changes and modification can of course be made, without 
departing the scope and spirit of the present invention. 
As described above, the present invention can provide a dry etching method 
and a dry etching apparatus, which can etch every portion of a silicon 
wafer (including a center portion and an edge portion) at sufficiently 
uniform speed. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described herein. Accordingly, various modifications may be made 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.