Plasma density and etch rate enhancing semiconductor...

Details Plasma density and etch rate enhancing semiconductor... Plasma density and etch rate enhancing semiconductor...

1998-08-12

2001-05-08

Mills, Gregory (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C118S7230AN, C118S7230ER, C118S715000

Reexamination Certificate

active

06228208

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to semiconductor processing chambers and, more particularly, the invention relates to gas distribution plates for a narrow gap chamber for deep trench etch.
2. Description of the Background Art
Integrated circuit (IC) wafer processing systems, particularly those which fabricate VLSI circuits on silicon wafers, can use many processes to form the circuit features in a die on a wafer. One of the more popular processes is magnetically enhanced reactive ion etching (MERIE) where a highly reactive plasma is used to react with the material on the wafer surface or an underlying substrate though a series of photoresist masks to produce the desired circuit features. A rotating magnetic field, produced by magnets mounted outside the chamber stirs the plasma. MERIE processes and reactors are described in detail in U.S. Pat. No. 5,215,619, issued Jun. 1, 1993 and U.S. Pat. No. 5,225,024, issued Jul. 6, 1993, both of which are incorporated herein by reference. A typical MERIE chamber has a pedestal for supporting a wafer. The pedestal typically includes a cathode and a mechanical or electrostatic chuck. Reactive gas enters the chamber through an aluminum gas distribution plate disposed above the pedestal. Typically, the gas distribution plate is attached to the underside of an aluminum lid that closes the top of the chamber. The gas distribution plate also includes a plastic blocker plate that occupies most of the space between an interior surface of the gas distribution plate and a bottom surface of the lid.
When MERIE is used to etch deep trenches in the surface of a semiconductor wafer, a narrow gap between the cathode and the gas distribution plate is often desirable. In this way the plasma is confined to a small volume within the narrow gap thereby increasing the plasma density without increasing the plasma power. The higher plasma density is desirable in a deep trench etch because it leads to a higher etch rate.
Prior art MERIE chambers have attempted to narrow this gap by mechanically changing the height of the pedestal. Such a height adjustable pedestal is expensive and time consuming to manufacture. As an alternative, the chamber lid may be designed such that the lid is indented. A MERIE chamber of the prior art is depicted in FIG.
1
. The chamber
100
has a set of walls
102
defining an internal volume. A wafer
104
(shown in phantom) rests on a pedestal
106
situated inside the chamber
100
. Lift pins
108
raise and lower the wafer relative to the pedestal
106
. The wafer
104
is introduced into the chamber
100
by a robot arm
110
(also shown in phantom). Plasma confining magnetic fields are produced by magnets
138
mounted outside the chamber.
The chamber
100
is covered by a lid assembly
112
. The lid assembly
112
includes an indented lid
114
that projects into the chamber
100
. The lid
114
has a radially projecting flange
117
. The lid
114
is supported on the chamber walls
102
by the flange
117
and secured thereto by bolts
116
. The lid
114
is typically sealed by an O-ring (not shown). The lid
114
has a lower surface
115
that is substantially flat. A gas distribution plate
118
is attached to the lower surface
115
of the lid
114
by a plurality of long bolts
128
that fit through a plurality of clearance holes
129
in the lid
114
and thread into a plurality of tapped holes
130
in an upper surface
119
of the gas distribution plate
118
. The indentation of the lid produces a narrow gap between a bottom surface of the gas distribution plate and the pedestal
106
that confines a plasma to a small volume within the chamber
102
.
A plastic blocker plate
120
fits in a recess
121
in the upper surface
119
of the gas distribution plate
118
. Reactive gas is fed into the chamber
100
through a gas feed line
122
which communicates with a passage
124
in the lid
114
and a matching hole
123
in the blocker plate
120
into the recess
121
. Gas enters the chamber through a plurality of orifices
126
in the gas distribution plate
118
that communicate between the recess
121
and the interior of the chamber
102
. A large diameter O-ring
132
is located radially outward of the clearance holes
129
. A small diameter O-ring
134
, located radially inward of the clearance holes
129
. As shown in
FIG. 1B
, the O-rings seal the gas distribution plate
118
when the chamber is at room temperature (approximately 20° C.). However, thermal stresses occur when the chamber is at its operating temperature of 70° C. to 90° C. These thermal stresses cause the lid
114
to bow downwardly at its center and upwardly at its rim as shown in FIG.
1
C. As a result, a downward stress is applied to the blocker plate
120
. The blocker plate
120
, in turn, presses down on the gas distribution plate
118
exerting a stress that tends to cause first the inner O-ring
132
then the outer O-ring
134
to fail.
The lid
114
and the gas distribution plate
118
join at an interface
131
that terminates inside the chamber
100
. A first vacuum leak path exists at the clearance holes
129
, along the interface
131
past the large diameter O-ring
132
. The interface
131
also communicates with the recess
121
, therefore a second leak path exists through the clearance holes
129
along the interface
131
past the small diameter O-ring
134
into the recess
121
and thence through the orifices
126
into the chamber. As such the space in between the O-rings
132
and
134
is essentially at atmospheric pressure and, therefore, likely to leak into the chamber. Consequently, the chamber takes a long time to pump down. Residual moisture and gas adversely affect the result of a deep trench etch. If the chamber is not pumped down long enough to remove residual moisture and gas, contaminant particles (such as silicon oxide) can be formed on the wafer during processing rendering one or more dies on the wafer defective. Furthermore, each time the chamber is opened, both the lid
114
and the gas distribution plate
118
must be wet cleaned which delays wafer production.
Therefore, a need exists in the art for a lid assembly for a narrow gap MERIE reactor that remains sealed under operating conditions.
SUMMARY OF THE INVENTION
The disadvantages associated with the prior art are overcome with the present invention of a semiconductor processing chamber with an inventive lid assembly. Specifically, the lid assembly comprises an indented lid and a gas distribution plate disposed below the lid. An upper surface of the gas distribution plate substantially conforms to the shape of a lower surface of the lid such that an edge of a joint between them lies outside the chamber. Preferably, both the lid and the gas distribution plate are U-shaped in cross section. The lid has a recess in a lower surface thereof. The recess is sealed from the atmosphere by an O-ring, disposed between the gas distribution plate and lid, located radially outward of the recess. An inventive blocker plate is disposed within the recess for evenly distributing gas flow. The blocker plate conforms to the lower surface of the lid when the lid assembly is heated. Preferably, the blocker plate has a concave upper surface.
The novel shape of the gas distribution plate reduces leaks. The novel gas distribution plate is sealed with only a single O-ring thereby reducing complexity of construction and number of components that may fail. Furthermore, the concave blocker plate compensates for the thermal stress due to the bowing of the gas distribution plate which might otherwise cause the O-ring to fail.


REFERENCES:
patent: 5215619 (1993-06-01), Cheng et al.
patent: 5225024 (1993-07-01), Hanley et al.
patent: 5728253 (1998-03-01), Saito et al.
patent: 5885356 (1999-03-01), Zhao et al.
patent: 5891350 (1999-04-01), Shan et al.
patent: 5950925 (1999-09-01), Fukunaga et al.
patent: 5964947 (1999-10-01), Zhao et al.
patent: 5976308 (1999-11-01), Fairbain et al.
patent: 6110556 (2000-08-01), Bang et al.
patent: 0 714 998 A2 (1

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