Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
2002-03-04
2004-01-13
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
C438S015000, C438S016000, C438S401000, C355S072000
Reexamination Certificate
active
06677167
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor manufacturing technology, and in particular to temperature control for a wafer, which is required for processing a semiconductor wafer in a semiconductor manufacturing apparatus.
These years, the diameter of a wafer to be processed by a semiconductor manufacturing technique, becomes larger and larger so as to fall in a range from 8 to 12 inches. This is because a number of chips, which are available from a single wafer, is to be increased so as to reduce the manufacturing cost. However, as a result, this fact has forced manufacturers of semiconductor equipments into development of an apparatus capable of manufacturing large diameter wafers with enormous investments.
However, on one hand, in view of the relationship to other apparatus in an ordinal manufacturing line, since there is raised such a problem, as an actual circumstance, that all apparatus ordered by clients are not always those which can cope with large diameter wafers, and accordingly, it is required to design, evaluate and produce a new apparatus for every size of wafers desired by a client, resulting in a heavy task to the manufacturer of semiconductor equipments.
Further, due to highly increased integration of semiconductor chips, these years, required machining accuracy has becomes more and more severe, and accordingly, the control of the temperature of a wafer during processing has been more and more important. For example, in order to materialize anisotropic etching in an etching process which requires a high aspect ratio, a process in which etching is made while a side wall is protected by organic polymer is used, but in this process, the degree of formation of the organic polymer serving as a protecting film is changed in dependence upon a temperature.
Accordingly, if the distribution of temperature of a wafer on processing is not uniform, the degree of formation of the protection film on a side wall becomes uneven within the surface of the wafer, and as a result, there is raised a problem of unevenness in an etching shape. Further, in addition to this fact, since the diameter of the wafer becomes larger and larger, as mentioned above, so that the input heat to the wafer tends to be more and more large, that is, for example, a bias power applied to an wafer in a process of etching an inter-layer-dielectric on a manufacturing line for 12 inch diameter wafers becomes higher up to 3 kW, and accordingly, to uniform the temperature distribution in the surface of the wafer causes a very important technical task.
By the way, during plasma processing, a wafer is electrostatically attracted and held to a stage by means of an electrostatic chuck, at this stage, in order to ensure heat transfer between the wafer and the stage, a method in which gas for heat transfer (usually helium is used) is introduced for cooling, has been conventionally used. Further, although the structure of the electrostatic chuck should be changed variously, depending upon a specification of an apparatus, in a typical example, a high thermal conductive metal such as aluminum which is covered on its outer surface with a ceramic film having a thickness of not greater than about 1 mm is used as a base, and a temperature adjusting medium controlled by an external temperature adjusting unit is circulated through the base in order to adjust the temperature.
At this stage, the range of temperature to be controlled is various in dependence upon a process to be used. As to the temperature of the stage for holding the wafer, stable operation is required over a wide range from, for example, −40 deg.C. to a high temperature up to about 100 deg.C. That is, severe requirements have been imposed such that even though heat is inputted to a wafer stage in a plasma processing apparatus in a wide range from a low temperature to a high temperature, a uniform temperature distribution should be materialized over a wafer having a large diameter.
By the way, in an actual electrostatic chuck structure, it is, in general, overhanged from the outer periphery of a wafer by several millimeters, and accordingly, cooling in the vicinity of the outer periphery of the wafer is insufficient, resulting in main cause of deterioration of the temperature distribution over the surface of the wafer. Thus, several ideas for optimizing a method of introduction of helium gas passing between the electrostatic chuck and the back-side surface of the wafer, and the pressure thereof have been conventionally proposed.
However, in a certain method which has been conventionally proposed, since the chuck has a specific structure which is optimized for wafers having a specific size, redesigning has to be additionally made for the electrostatic chuck and the structure of the lower part of the apparatus to which the chuck is mounted, as a whole. Thus, it has been extremely ineffective.
It is noted that a method of improving the temperature distribution over the surface of a wafer is disclosed as a conventional example in JP-A-7-249586 which discloses such a structure that first and second gas passages which are opened at the outer surface of a lower electrode in the vicinity of its outer periphery, and at a plurality of positions therein, and both gas passages in dual systems are connected thereto with first and second gas supply and discharge means, respectively, so as to supply helium gas to the gas passages, independent from each other, in order to cool a semiconductor wafer.
It cannot be safely said that consideration is sufficiently made as to variation of the wafer processing function, and it is raised a problem in view of restraining the cost.
That is, in the conventional technology, since the structure is optimized for a wafer having a certain specific size, it becomes extremely inefficient if the structure is used for wafers having different sizes, and as a result, there is raised such a problem that the cost cannot be restrained from increasing.
Further, since the conventional technology requires the gas supply and discharge means which are independent from each other between the position in the vicinity of the outer periphery of the wafer and the inner periphery thereof, the change of the wafer processing function is complicated and expensive.
Further, in the conventional technology, it is required to set the pressure of helium gas to be fed in the vicinity of the outer periphery of the wafer to a high value, up to about 30 Torr, and accordingly, the attracting force of the electrostatic chuck has to be set to a value which can match with the pressure. As a result, the cost is further increased. It is here estimated that erroneous attraction occurs. The wafer on processing is greatly corrupted, and accordingly, there is raised such a problem that the burden caused by recovery works becomes heavier. Thus, it is inevitable to increase the attraction force.
Detailed explanation will be hereinafter made of the problems inherent to the conventional technology with reference to
FIGS. 9 and 10
of which
FIG. 9
shows an example of a prior art wafer processing apparatus which are formed for processing a 8 inch wafer and
FIG. 10
is an example of a water processing apparatus for processing a 12 inch wafer. At first the prior art shown in
FIG. 9
will be explained. In the apparatus shown in
FIG. 9
, etching gas is introduced into a vacuum chamber
9
, as shown, and the pressure in the chamber
9
is set to an appropriate value by adjusting the opening degree of a valve
12
provided upstream of a turbo-molecular pump
13
.
Further, a parallel planar type upper electrode
100
is laid in the upper part of the vacuum chamber
9
and is connected to a high frequency power source
8
so as to be applied thereto with a high frequency voltage having a frequency of, for example, 13.56 MHz in order to generate plasma
6
to which a wafer
1
is exposed so as to subject the wafer
1
to an etching process.
Here, in the case of
FIG. 9
, the diameter of the wafer
1
is 8 inches, and is set on convex part formed on a w
Kanai Saburou
Kanno Seiichiro
Kawahara Hironobu
Masuda Toshio
Suehiro Mitsuru
Hitachi High-Technologies Corporation
Luk Olivia
Niebling John F.
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