Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With etchant gas supply or exhaust structure located outside...
Reexamination Certificate
2002-05-08
2004-05-11
Lund, Jeffrie R. (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With etchant gas supply or exhaust structure located outside...
C118S715000, C204S298070, C204S298330
Reexamination Certificate
active
06733621
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for venting pressure from closed systems. More particularly, the invention relates to an apparatus and method for venting vacuum pressure from a semiconductor wafer etcher in order to prevent damage to a turbo pump in the etcher.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, particularly sub-micron scale semiconductor devices, profiles obtained in the etching process are very important. Careful control of a surface etch process is therefore necessary to ensure directional etching. In conducting an etching process, when an etch rate is considerably higher in one direction than in the other directions, the process is called anisotropic. A reactive ion etching (RIE) process assisted by plasma is frequently used in an anisotropic etching of various material layers on top of semiconductor substrate. In plasma enhanced etching processes, the etch rate of a semiconductor material is frequently larger than the sum of the individual etch rates for ion sputtering and individual etching due to a synergy in which chemical etching is enhanced by ion bombardment.
To avoid subjecting a semiconductor wafer to high-energy ion bombardment, the wafer may also be placed downstream from the plasma and outside the discharge area. Downstream plasma etches more in an isotropic manner since there are no ions to induce directional etching. The downstream reactors are frequently used for removing resist or other layers of material where patterning is not critical. In a downstream reactor, radio frequency may be used to generate long-lived radioactive species for transporting to a wafer surface located remote from the plasma. Temperature control problems and radiation damage are therefore significantly reduced in a downstream reactor. Furthermore, the wafer holder can be heated to a precise temperature to increase the chemical reaction rate, independent of the plasma.
In a downstream reactor, an electrostatic wafer holding device known as an electrostatic chuck is frequently used. The electrostatic chuck attracts and holds a wafer positioned on top electrostatically. The electrostatic chuck method for holding a wafer is highly desirable in the vacuum handling and processing of wafers. An electrostatic chuck device can hold and move wafers with a force equivalent to several tens of Torr pressure, in contrast to a conventional method of holding wafers by a mechanical clamping method.
Referring initially to
FIG. 1
, a conventional inductively coupled plasma etched chamber
10
is shown. In the etch chamber
10
, which typically represents one that is commercially available as a LAM TCP etcher, the plasma source is a transformer-coupled source that generates a high density, low pressure plasma away from a wafer surface. The plasma source allows an independent control of ion flux and ion energy. The plasma can be generated by a flat spiral coil (not shown), i.e., an inductive coil separated from the plasma by a dielectric plate
12
which is normally fabricated of a ceramic material with a gas inlet
14
provided therein. The dielectric plate
12
may be a dielectric window made of a substantially transparent material such as quartz to facilitate visual observation of a middle chamber
20
. The middle chamber
20
is further formed by a bottom ceramic plate
16
equipped with an opening
18
for allowing a plasma to pass thereto. The sidewall
22
of the middle chamber
20
is normally formed of a metallic material, such as aluminum, with an anodized aluminum surface. The top ceramic plate
12
, the bottom ceramic plate
16
and the metallic sidewall
22
form a self-contained chamber, i.e., the middle chamber
20
which has a first cavity
24
therein.
A wafer
30
is positioned on an electrostatic chuck (or ESC)
26
, inside the chamber interior
33
of the main chamber
32
, sufficiently away from the RF coil (not shown) such that it is not affected by the electromagnetic field generated by the RF coil. A typical LAM TCP plasma etcher enables a high density plasma to be produced and a high etch rate to be achieved. In a typical inductively coupled RF plasma etcher
10
, an inductive supply and a bias supply are further used to generate the necessary plasma field. In a typical inductively coupled RF plasma etcher
10
, shown in
FIG. 1
, a source frequency of 13.5 MHZ and a substrate bias frequency of 13.5 MHZ are utilized such that ion density of about 0.5-2.0×10
2
cm
3
is obtained at the wafer level, while electron temperature of about 3.5-6.0 eV and a chamber pressure of 1-25 mTorr are achieved.
In the plasma chamber
10
, after the wafer
30
is etched in a main chamber
32
, etchant gas is normally evacuated from the middle chamber
20
and from the main chamber
32
by a turbo pump
34
controlled by a gate valve
36
. The turbo pump
34
is further connected to a dry pump
38
through an isolation valve
42
and connecting conduits
40
and
44
. Opening of the isolation valve
42
allows the etchant gas to be evacuated from the turbo pump
34
by the dry pump
38
. Simultaneous with the etchant gas pumping process, an inert purge gas such as nitrogen is introduced into the middle chamber
20
and the main chamber
32
through the gas inlet
14
to further facilitate the removal of residual etchant gas from the chamber interiors
24
and
33
, respectively.
In the conventional plasma chamber
10
, over time etchant gas flowing through the main chamber
32
, the middle chamber
20
and the gate valve
36
frequently causes corrosion of the internal components of these elements. Accordingly, the internal components of the main chamber
32
, the middle chamber
20
and the gate valve
36
must periodically be cleaned and repaired for routine maintainence of the plasma etch chamber
10
. This is accomplished by initially closing the gate valve
36
in order to vent residual etchant gas from the plasma etch chamber
10
typically by operation of a chamber auto-vent
28
, manually opened and closed by a lever
29
. This action causes atmospheric or ambient air to enter the chamber interior
24
of the middle chamber
20
and the chamber interior
33
of the main chamber
32
, and the air pressure in the chamber interiors
24
,
33
equalizes with the atmospheric or ambient air. Simultaneously, the turbo pump
34
generates an internal vacuum pressure which is isolated by the closed gate valve
36
and the isolation valve
42
. After maintenance of the main chamber
32
, the middle chamber
20
and/or the gate valve
36
, the gate valve
36
is manually re-opened to equalize pressure between the middle chamber
20
and the turbo pump
34
. Due to the relatively large difference in pressure between the chamber interiors
24
,
33
and the internal vacuum generated by the turbo pump
34
, typically about 760 Torr, air contained in the chamber interiors
24
,
33
rushes through the now-open gate valve
36
and into the turbo pump
34
, which is prone to damage due to the rushing air. Therefore, an apparatus is needed for equalizing pressure between the chamber interior
24
of the middle chamber
20
and the turbo pump
34
prior to opening the gate valve
36
in order to prevent damage to the turbo pump
34
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an apparatus and method for preventing vacuum-induced damage to a turbo pump in a plasma etch chamber or system for semiconductors.
Another object of the present invention is to provide an apparatus and method for venting pressure from a closed system.
Another object of the present invention is to provide an apparatus and method for dispelling or reducing pressure differentials in a system.
Still another object of the present invention is to provide an apparatus and method for reducing a pressure differential between a chamber and a pump separated from the chamber by a valve before opening the valve.
Yet another object of the present invention is to provide an apparatus and method for gradually dispelli
Lund Jeffrie R.
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
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