High temperature process chamber having improved heat endurance

Details High temperature process chamber having improved heat endurance High temperature process chamber having improved heat endurance

2000-04-20

2002-11-26

Bueker, Richard (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With workpiece support

C156S345480, C118S724000, C118S7230IR, C118S729000

Reexamination Certificate

active

06485605

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a high temperature process chamber and a method for using the chamber and more particularly, relates to a high temperature process chamber that has improved heat endurance and a method for improving the heat endurance a process chamber.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, dry chemical etching occurs when a chemical reaction takes place between a gas and a wafer surface, with or without a plasma, while the resulting volatile product is pumped away. The dry etching process is typically selective and non-directional. In a plasma-assisted chemical etching process, the major role of the plasma is to maintain a supply of reactive species in the form of free radicals and excited neutrals.
In plasma-assisted chemical etching, material is selectively removed by a reactive gas created near or within a glow discharge from an initially non-reactive gas mixture. In most plasma etching systems, the injected gas itself rarely reacts with the surface that has been etched while free radicals are believed to be the major reactant species. The gas mixture is selected to produce reactive species by molecular dissociation into radicals and excitation of neutrals in the plasma. Because of the absence of physical enhancement or ion bombardment, plasma-assisted chemical etching is essentially isotropic and very selective. The plasma assisted chemical etching is therefore widely used when isotropic etching is required or when dimensional control is not critical. The most common example of plasma assisted chemical etching is the removal of a photoresist layer in an oxygen plasma, sometimes referred to as a plasma ashing technique.
The plasma ashing technique is an isotropic etch process of an organic photoresist material in an oxygen glow discharge where atomic oxygen is produced together with electrons. The oxygen atoms then react with the organic material to form the volatile products of CO, CO
2
and H
2
O. It has been found that since most of the underlying film materials are not attacked by an oxygen plasma, over etching is frequently used to ensure that all resist materials are removed without residues. For instance, a wafer that is coated with 1 &mgr;m photoresist material can be processed between 5 and 10 minutes. The plasma ashing process can also be used for descumming of wafers, i.e. removal of residual layers of photoresist or other organic material following a resist developing and hard baking processes. Typically, the residues can be removed in a 1 minute exposure to an oxygen plasma.
The plasma ashing process reduces costs and potential hazards of a wet chemical etching. It has therefore become an important etching step to remove photoresist materials, particularly those which have become insoluble in wet solvents. For instance, when the photoresist material has been exposed to a flourine or a chlorine dry etch environment during a polysilicon or oxide etching or to high current ion implantation. After a hardened top layer of the photoresist has been removed, a plasma etching or wet chemical etching process can be used to remove the remainder of the photoresist material. A plasma ashing process can also be followed by a cleaning step to remove ions and heavy metals which are not volatilized by the oxygen plasma process.
A typical inductively coupled plasma etch chamber
10
is shown in FIG.
1
. In the etch chamber
10
, the plasma source is a transformer coupled plasma source which generates a high density, low pressure plasma
12
decoupled from the wafer
14
. The plasma source allows an independent control of ion flux and ion energy. Plasma
12
is generated by a flat spiral coil,
16
, i.e. an inductive coil separated from the plasma by a dielectric plate
18
, or a dielectric window on top of the reactor chamber
20
. The wafer
14
is positioned sufficiently away from the coil
16
so that it is not affected by the electromagnetic field generated by the coil
16
. There is very little plasma density loss since plasma
12
is generated only a few mean-free-path away from the wafer surface. The plasma etcher
10
enables a high density plasma an high etch rates to be achieved. In the etcher
10
, and inductive supply
22
and a bias supply
24
are used to generate the necessary plasma field. Multi-pole magnets
26
are used for surrounding plasma
12
generated. A wafer chuck
28
which moves up-and-down by shaft
32
is used to hold wafer
14
during the etching process. A ground
30
is provided to one end of the inductive coil
16
.
In a typical inductively coupled RF plasma etcher
10
, a source frequency of 13.5 MHZ and a substrate bias frequency of 13.5 MHZ are utilized. An ion density of approximately 0.5~2.0×10
12
/m
3
, an electron temperature of 3.5~6.0 eV, and a chamber pressure of 1~25 mTorr are used.
In the plasma ashing chamber
10
of
FIG. 1
, the wafer stage
28
operates at a typical high temperature of about 250° C. in a photoresist stripping process. A lift cylinder
34
is installed under the support
36
, as shown in
FIGS. 2A
,
2
B,
3
A and
3
B. The support
36
is fastened to a bottom chamber wall
38
, as shown in
FIG. 3B
by a plurality of screws
40
. The lift cylinder
34
is operated by compressed airfed through an inlet needle valve
42
and an outlet needle valve
44
. The shaft
32
is further supported and guided by a support cylinder
46
. An upper support cylinder
48
, as shown in
FIG. 3A
, is used to support and guide the shaft
32
located inside the plasma process chamber when the support
36
is fastened to the bottom chamber wall
38
of the plasma process chamber
10
.
In the conventional plasma ashing chamber
10
, the lift cylinder
34
which is operated by the needle valves
42
,
44
is mounted directly to the support
36
in close proximity of the plasma process chamber
10
, i.e. by mounting directly to the bottom process chamber wall
38
. Since the wafer stage
28
in the plasma process chamber
10
is kept at 250° C. during a photoresist stripping process, the lift cylinder
34
operates at a temperature of about 70° C. from the heat conduction through the support
36
and the support cylinder
46
. Commercially available lift cylinders are not designed to operate at such high temperature and furthermore, are not equipped with anti-friction O-ring to function properly on a long term basis. The control elements, such as the needle valves
42
,
44
are also likely to fail when exposed to such high operating temperature. It has been found that there is a 65% failure rate of the lift cylinder during a four year running period on a plasma process chamber.
Numerous equipment problems have therefore been encountered in the conventional plasma process chamber
10
. These include a loss of accurate speed control of the wafer stage
28
by the lift cylinder
34
due to failure in the needle valves
42
,
44
. When the needle valves
42
,
44
are worn after extended exposure to high operating temperature, the control of compressed air flow through the needle valves
42
,
44
is no longer accurate and frequently results in too fast a speed in the upward movement of the wafer stage
28
. Furthermore, after a failure in the lift cylinder
34
has occurred, the plasma process chamber must be opened in order to change the lift cylinder. During a preventive maintenance procedure, the temperature of the plasma process chamber must also be dropped to room temperature in order to carry out the procedure. When the operation of the chamber is resumed, the O-ring on the left cylinder does not seal properly since the seal has not expanded to its supposed volume at 70° C. resulting in leaks through the seal. The conventional lift cylinder can only function properly for about six months which is impossible in maintaining a high throughput in the fabrication process.
It is therefore an object of the present invention to provide a high temperature process chamber that does not have the drawbacks or shortcomings of the conventional high temperature

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