Wafer processing apparatus

Details Wafer processing apparatus Wafer processing apparatus

1999-07-16

2002-07-09

Mills, Gregory (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With workpiece support

C156S345520, C156S345240, C118S7230ER, C118S725000, C118S728000

Reexamination Certificate

active

06416618

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a wafer processing apparatus, and more particularly, to a wafer processing apparatus which holds a wafer on an electrostatic chuck such that the wafer is subjected to desired processing steps such as etching, ashing, film growth, sputtering, or doping.
2. Description of the Background Art
Electrostatic chuck techniques have recently come to be applied to many types of apparatus for subjecting a wafer to various processing steps; for example, a plasma etching apparatus and a film growth apparatus. With a wafer clamp which has conventionally been used (i.e., a clamp for holding the periphery of a wafer), impurities are likely to deposit on the periphery of the wafer, as well as the periphery of the wafer is unavailable for production. The electrostatic chuck is used for reasons of preventing deposition of impurities on the periphery of the wafer, rendering the outermost periphery of the wafer available for production, and resulting in improved product yield.
Further, use of the electrostatic chuck yields temperature uniformity which is more stable than that yielded by use of the wafer clamp. For this reason, the electrostatic chuck can ensure superior processing performance even when the diameter of the wafer is increased. Consequently, as the diameter of a wafer becomes larger, the electrostatic chuck technique will be more commonly employed for semiconductor manufacturing systems.
This electrostatic chuck involves many technical problems for practical use. For instance, high-temperature processing (at a temperature of more than 200° C.) of a wafer has recently been carried out frequently. When a wafer is chucked by a heated electrostatic chuck during the high-temperature processing, the wafer may be warped and damaged by thermal stress. For this reason, to ensure stable operation of the electrostatic chuck, there has been employed a manner in which a wafer heating means is specially provided, and a pre-heated wafer is conveyed to a electrostatic chuck so as to be subjected to desired wafer processing.
FIG. 1
is a schematic diagram showing the configuration of an electrostatic chucking apparatus described in Japanese Patent Application Laid-open No. Hei4-288062. The chucking apparatus shown in
FIG. 1
comprises a main chamber
10
and a sub-chamber
12
. An electrostatic chuck
14
having a heater is disposed within the main chamber
10
, and a resistance heating medium
16
is provided within the electrostatic chuck
14
. A wafer
18
is processed on the electrostatic chuck
14
while being heated by the resistance heating medium
16
.
A wafer support tool
20
is disposed within the sub-chamber
12
. The resistance heating medium
16
is provided within the wafer support tool
20
, as in the electrostatic chuck
14
. The wafer
18
is pre-heated within the sub-chamber
12
by the resistance heating medium
16
before being subjected to high temperature within the main chamber
10
.
Next, there will be given an explanation of how the wafer is damaged while being directly secured by a high-temperature electrostatic chuck.
FIGS. 2A and 2B
show a wafer processing apparatus having a commonly-employed electrostatic chuck. More particularly,
FIG. 2A
is a cross-sectional view of a conventional wafer processing apparatus taken along a plane A—A shown in
FIG. 2B
, and
FIG. 2B
is a front view of the conventional wafer processing apparatus. The electrostatic chuck shown in
FIGS. 2A and 2B
is of a well known two-electrode type.
In
FIGS. 2A and 2B
, reference numeral
22
designates a processing chamber for shielding the interior thereof from outside air;
24
designates a dielectric plate which is provided within the processing chamber
22
for generating electrostatic force;
26
designates a first electrode placed in the dielectric plate
24
;
28
designates a second electrode disposed concentrically with the first electrode
26
in the dielectric plate
24
;
30
designates a first variable D.C. power supply provided in order to apply a predetermined D.C. voltage to the first electrode
26
;
32
designates a second variable D.C. power supply provided in order to apply a predetermined D.C. voltage to the second electrode
28
;
34
designates a wafer which is held on the surface of the dielectric plate
24
so as to be subjected to predetermined processing;
36
designates a heater provided for heating the wafer
34
to a predetermined temperature by way of the dielectric plate
24
; and
38
designates a pusher which passes and receives the wafer to and from a transport robot (not shown) which is provided so as to convey the wafer
34
to the interior of the processing chamber
22
and place the wafer
34
on the surface of the dielectric plate
24
. The elements located within the region designated by reference numeral
40
correspond to the structure of a conventional common electrostatic chuck of two-electrode type.
FIG. 3
is a flowchart for explaining holding operation of the electrostatic chuck provided in the conventional wafer processing apparatus.
As shown in
FIG. 3
, in step S
1
, the wafer
34
is transported to the interior of the processing chamber
22
from an unillustrated transport robot.
In step S
2
, the pusher
38
is raised to receive the wafer
34
from the transport robot. The wafer
34
that is transported into the processing chamber
22
is passed from the transport robot to the pusher
38
that has been raised to a predetermined elevated position.
In step S
3
, the transport robot retracts from the processing chamber
22
. After retraction of the robot, the operation proceeds to step S
4
.
In step S
4
, the pusher
38
is lowered to place the wafer
34
on the dielectric plate
24
.
In step S
5
, desired voltages (a pair of reverse voltages employed in ordinary cases) are supplied from the first and second variable D.C. power supplies
30
and
32
to the first and second electrodes
26
and
28
embedded in the dielectric plate
24
. As a result, the wafer
34
is securely held on the dielectric plate
24
by an electrostatic force.
By reference to
FIGS. 4A
to
4
C, there will be described development of a fracture in the wafer
34
resulting from the holding action of the electrostatic chuck. In
FIGS. 4A
to
4
C, those elements which are the same as those shown in
FIGS. 2A and 2B
are assigned the same reference numerals, and repetition of their explanations is omitted here.
FIG. 4A
shows the wafer
34
immediately after having been placed on the dielectric plate
24
;
FIG. 4B
shows the state of the wafer
34
when it is heated; and
FIG. 4C
shows a fracture in the wafer
34
resulting from heating. In
FIGS. 4A
to
4
C, arrows depicted by reference numeral
42
indicate the direction in which the wafer
34
expands upon being heated, arrows depicted by reference numeral
44
indicate the direction of the electrostatic attraction force between the wafer
34
and the dielectric plate
24
, and the lengths of the arrows
44
indicate the magnitude of the electrostatic attraction force. Reference numeral
46
designates a warp arising in the wafer
34
during the course of a heating process, and reference numeral
48
designates a fracture in the wafer
34
resulting when the warp
46
becomes excessive.
The mechanism whereby the fracture
48
developing in the wafer
34
will now be described in detail. As shown in
FIG. 4A
, the wafer
34
placed on the dielectric plate
24
is secured on the same by application of a predetermined voltage to the first and second electrodes
26
and
28
.
The wafer placed on the dielectric plate
24
extends in the radial direction, i.e., in the direction designated by arrows
42
shown in
FIG. 4B
due to thermal stress, as being heated by the heater
36
.
However, the wafer
34
is fixedly held on the dielectric plate
24
by the electrostatic attraction force. Thus, expansion of the wafer
34
is hindered, thereby generating the warp
46
within the wafer
34
. Particularly, in the case of the electrostat

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