Cleaning and liquid contact with solids – Processes – Including work heating or contact with combustion products
Reexamination Certificate
1999-03-03
2001-02-27
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including work heating or contact with combustion products
C134S021000, C134S022180, C438S905000
Reexamination Certificate
active
06193811
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor vacuum chambers, and more specifically to an improved method and apparatus for baking-out and cooling-down a semiconductor vacuum chamber.
BACKGROUND OF THE INVENTION
Many semiconductor device fabrication processes such as physical vapor deposition (PVD), high density plasma (HDP) deposition, etc., employ high vacuum chambers (e.g., base pressures before back filling with process gases of 10
−8
-10
−9
Torr) to affect the deposition of thin films on a semiconductor wafer. To reach such high vacuum levels after a vacuum chamber has been vented to atmosphere (e.g., for maintenance, cleaning, etc.) and to prevent film contamination due to the desorption of moisture and other gaseous elements and compounds (i.e., potential contaminants) from the chamber's interior surfaces (e.g., the chamber's shield, wafer pedestal, etc.) during elevated temperature processing, the vacuum chamber's interior surfaces must be heated to an elevated temperature (e.g., about 200° C.) for a time period sufficient to desorb the potential contaminants (i.e., chamber bake-out). Improper chamber bake-out manifests itself in a degraded pre-process or “idle” chamber pressure (i.e., base pressure), an enhanced rate of pressure rise from the base pressure when the chamber's vacuum pump is shut-off (i.e., rate of rise or “ROR”), and poor deposited film quality (e.g., poor film resistivity), as described below with reference to FIG.
1
.
FIG. 1
is a side diagrammatic illustration, in section, of the pertinent portions of one conventional high density plasma sputtering chamber
21
. The sputtering chamber
21
contains a wire coil
23
which is operatively coupled to a first RF power supply
25
. The wire coil
23
may comprise a plurality of coils, a single turn coil as shown in
FIG. 1
, a single turn material strip, or any other similar configuration. The wire coil
23
is positioned along the inner surface of the sputtering chamber
21
, between a sputtering target
27
and a wafer pedestal
29
. The wafer pedestal
29
is positioned in the lower portion of the sputtering chamber
21
and typically comprises a pedestal heater (not shown) for elevating the temperature of a semiconductor wafer supported by the wafer pedestal
29
during processing within the sputtering chamber
21
. The sputtering target
27
is mounted to a water cooled adapter
31
in the upper portion of the sputtering chamber
21
so as to face the substrate receiving surface of the wafer pedestal
29
. A cooling system
31
a
is coupled to the adapter
31
and delivers cooling fluid (e.g., water) thereto.
The sputtering chamber
21
generally includes a vacuum chamber enclosure wall
33
having at least one gas inlet
35
and having an exhaust outlet
37
operatively coupled to an exhaust pump
39
(e.g., a cryopump). A removable shield
41
that surrounds the wire coil
23
, the target
27
and the wafer pedestal
29
is provided within the sputtering chamber
21
. The shield
41
may be removed for cleaning during chamber maintenance, and the adapter
31
is coupled to the shield
41
(as shown). The sputtering chamber
21
also includes a plurality of bake-out lamps
49
located between the shield
41
and the chamber enclosure wall
33
for baking-out the sputtering chamber
21
as described below.
The sputtering target
27
and the wafer pedestal
29
are electrically isolated from the shield
41
. The shield
41
preferably is grounded so that a negative voltage (with respect to grounded shield
41
) may be applied to the sputtering target
27
via a DC power supply
43
operatively coupled between the target
27
and ground, and a negative bias may be applied to the wafer pedestal
29
via a second RF power supply
45
operatively coupled between the pedestal
29
and ground. A controller
47
is operatively coupled to the first RF power supply
25
, the DC power supply
43
, the second RF power supply
45
, the gas inlet
35
and the exhaust outlet
37
.
Although this is one chamber configuration, others, such as traditional magnetron sputter systems, which do not use a coil, or systems using hollow cathode sources, are specifically contemplated as useable with the invention herein. To bake-out the sputtering chamber
21
, conventionally the bake-out lamps
49
are switched on between about 90% to 100% power when the chamber is at high vacuum. The pedestal heater (not shown) of the wafer pedestal
29
is set at about 200° C., and the water supply to the adapter may or may not be shut-off. The chamber then is allowed to bake-out for about eight hours during which time degassed material will raise the chamber pressure.
For chambers in which titanium, titanium nitride or tantalum nitride are deposited, the above bake-out procedure is sufficient to produce a good base pressure (e.g., low 10
−8
Torr range), a low ROR (e.g., about 10 to 20 nTorr/min), and good deposited film quality.
The reason for the success of this bake-out procedure is that both titanium and tantalum are excellent gettering materials and, therefore, once deposited on the chamber surfaces during wafer processing, can absorb (or “getter”) moisture and other gaseous elements and compounds from the sputtering chamber's atmosphere. Typically, these gettered contaminants do not desorb, even during elevated temperature processing, so that the chamber's base pressure and ROR are not affected by the gettered contaminants. As well, the gettered contaminants do not significantly affect deposited film quality. An eight hour bake-out, however, results in significant process downtime for the chamber being baked-out, as well as for processing equipment upstream and downstream from the processing chamber. Overall fabrication throughput thereby is greatly degraded by conventional bake-out techniques.
When the conventional bake-out procedure is employed within a chamber for copper deposition (e.g., a copper HDP chamber) the results are less satisfactory due to copper's poor gettering properties. For instance, even after an eight hour bake-out, a high density plasma chamber for copper deposition can exhibit a high base pressure (e.g., low 10
−7
Torr), a rapid ROR (e.g., about 200 nTorr/min) and a poor deposited copper film quality (e.g., poor resistivity). Accordingly, a need exists for an improved bake-out method that can be performed more rapidly than conventional bake-out methods (e.g., so as to improve throughput), and that sufficiently bakes out even a chamber for copper deposition.
A process related to and often used in conjunction with processing chamber bake-out is processing chamber cooling or “cool-down”. Chamber cool-down is performed following high temperature processing or following chamber bake-out, and can result in significant process downtime for the processing chamber being cooled, as well as for processing equipment upstream and downstream from the processing chamber. For example, the time required to perform chamber maintenance and repair is initially determined by the temperature of the various chamber components which must be sufficiently cooled before handling. Opening a chamber at elevated temperatures exposes personnel to safety hazards and may result in oxidation and contamination of the chamber.
In order to mitigate the effects of contamination, chambers are typically cooled under high vacuum conditions. Because some processing chamber components are operated at temperatures in excess of 600° C., cool-down time may be on the order of hours. The exact time required to reach a desired temperature depends on the chamber. For example, chamber components having high thermal conductivity (such as aluminum components) are capable of cooling more rapidly than components having low thermal conductivity (such as stainless steel components).
FIG. 2
shows a cooling curve for a typical high density plasma chamber cooled according to current practice. The chamber was operated under normal conditions and then allowed to cool under vacuum. Th
Ding Peijun
Gogh James van
Saigal Dinesh
Sundarrajan Arvind
Applied Materials Inc.
Chaudhry Saeed
Dugan Valerie G.
Gulakowski Randy
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