Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1999-06-01
2001-04-24
Dang, Thi (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C118S724000, C118S7230AN, C219S395000, C219S398000
Reexamination Certificate
active
06221203
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for controlling temperature of a chamber and more particularly, relates to an apparatus and method for controlling temperature of a semiconductor process chamber in which a plurality of heating elements are mounted juxtaposed to the chamber wall and controlled by a plurality of thermal sensors such that a more uniform chamber temperature control is achieved.
BACKGROUND OF THE INVENTION
In the continuing miniaturization of semiconductor devices, one of the keys to shrinking device geometries is the ability to construct very dense contact or interconnect structures such as that used in a multi-level metallization schemes. The critical processing step involves etching the contacts and interconnects to a dimension as small as 0.35 &mgr;m or even 0.25 &mgr;m in diameter in applications for a 64 or 256 megabit DRAMs or other high-density logic devices. To fully implement the process, high selectivity of oxide to the underlying polysilicon or silicide is a key requirement. A high-density plasma etch process utilizing fluorine chemistry is ideal for the high selectivity etch process. A suitable equipment to be used for the process is supplied by the Applied Materials, Inc. of Santa Clara, Calif. Under the tradename of Centura Omega™ dielectric etch system. For instance, an oxide etch process can be performed in such an equipment by etching 8,000 Å to 12,000 Å of doped oxide down to a nitride layer. The etch step uses a well-characterized C
2
F
6
or C
3
F
8
chemistry to etch the oxide and stopping at the nitride layer. In order to avoid or to minimize a polymer film deposition during the etch process, a high density plasma source powered by a 2 MHZ RF signal is used. The source generates an ion density of about 1×10
12
cm
−3
. Free fluorine atoms are removed or scavenged from the reaction chamber through the use of a heated silicon top plate.
Referring initially to
FIG. 1
, a cross-sectional view is shown of a typical plasma etch reactor equipped with a silicon ceiling as a scavenging surface. The silicon ceiling is a source of silicon atoms which scavenge fluorine out of the plasma to thereby provide a desired carbon-to-fluorine ratio forming a carbon-rich polymer impervious to the fluorine in the plasma over the non-oxide (i.e., polysilicon or silicon nitride) film. In a typical etching process, a reactant gas such as C
2
F
6
is excited sufficiently to generate a plasma inside the reactor chamber and to produce ions and free radicals of F and CF
3
. The F radicals etch any silicon dioxide film on the wafer, while carbon and fluorine atoms or ions in the plasma combine on the wafer surface to form a polymer.
The polymer disassociates when formed on silicon dioxide surfaces due to the effect of oxygen freed from the silicon dioxide film during the etch process, and due to the effect of fluorine in the plasma. However, when polymer is formed on non-oxide film (i.e., polysilicon or silicon nitride), the polymer accumulates due to the lack of oxygen in the underlying non-oxide film. This formation inhibits etching of the underlying non-oxide film and thereby provides a pronounced etch selectivity of the oxide film over the non-oxide film. The selectivity is of great importance when etching vias through a silicon dioxide layer overlying a non-oxide layer which is not to be etched. The selectively is limited if the polymer formed over the polysilicon layer contains more than 40% fluorine by weight, because such polymers are susceptible to being attacked by fluorine in the plasma, and therefore provide only limited protection to the underlying polysilicon layer.
FIG. 1
shows an inductively coupled plasma etch reactor of the type generally used. The reactor includes a vacuum chamber
10
enclosed by a cylindrical quartz sidewall
12
and a bottom
14
including a cathode assembly on which a silicon wafer
16
is held by a retractable annular holder
18
on a pedestal
19
. The ceiling
20
is made of crystalline silicon and heated by an overlying heating element
22
connected to a temperature controller (not shown). A cylindrical aluminum top wall
24
rests on the quartz sidewall
12
and supports an overlying cooling element
26
in which coolant is circulated through water jacket
28
as shown in FIG.
2
. This arrangement cools the quartz sidewall
12
through the aluminum cylindrical top wall
24
.
A helical cylindrical antenna coil
30
is wrapped around the cylindrical quartz sidewall
12
and is connected to an RF energy source
32
to inductively couple energy to the plasma in the chamber
10
. A ceramic cylindrical cover
34
made of materials such as Al
2
O
3
or Si
2
N
4
surrounds the antenna coil
30
.
A gate valve-vacuum pump assembly
36
draws gas from the chamber
10
through an opening in the chamber body
38
to maintain a vacuum in the chamber
10
through an opening in the chamber body
38
to maintain a vacuum in the chamber
10
determined by a pressure control device
40
. A gas feed
42
feeds reactant gases such as C
2
F
6
into the chamber
10
.
In order to maintain the temperature of the interior surface of the quartz sidewall
12
well above 170° C. a single heating element (not shown) rests in the interior of the ceramic cover
34
near the bottom of the quartz sidewall
12
and is connected to an electrical source (not shown). The temperature of the heating element is monitored by a thermal sensor
28
which feeds a signal to a controller (not shown).
The temperature of the silicon ceiling
20
determines the rate at which silicon atoms scavenge the plasma within the chamber
10
and therefore affects the carbon-to-flourine plasma ratio providing a polymer carbon content greater than 60% by weight. Such temperature control of the ceiling
20
is provided by a controller governing the ceiling heat source in accordance with a signal received from a thermocouple
44
attached to the silicon ceiling
20
. Heat conduction to the silicon ceiling
20
is set by a suitable air gap between the heater
22
and the ceiling
20
.
During an etching process, the RF power source
32
used is in the range of 2,000-3,000 watts at about 2 MHz. The bias RF power source
46
connected to the pedestal
19
is in the range of 500-1500 watts at 1.8 MHZ depending on the size of the wafer
16
. The silicon ceiling temperature is in the range of 200°-300° C., and is normally set at approximately 260° C. The quartz sidewall interior surface temperature is in the range of between 170° C. and 230° C, and is normally set at 220° C. The C
2
F
6
gas flow rate is between 20-50 standard cubic centimeters per minute and the chamber pressure is between 1-10 millitorr.
In a typical etching process for oxide films, a high density, low pressure plasma is used. The chemistry involved is the dissociation of C
2
F
6
into components of CF
2
F and C. The CF
2
is the active etching component of the gas, while F and C forms a fluorocarbon polymer that deposits on any surface that is relatively cool (i.e., at a temperature of 100° C. or below).
A cross-sectional view of the quartz sidewall
12
which contains the chamber cavity
10
for a conventional plasma etch chamber is shown in
FIG. 2. A
heating element
50
is contained in the interior of a ceramic cover (not shown) in-between the quartz sidewall
12
and the helical cylindrical antenna
30
. In a conventional etcher, or for most other semiconductor process chambers, a single heating element
50
is utilized with its temperature monitored by a single thermal sensor
28
. In the chamber cavity
10
, processing difficulties frequently occur due to a poor temperature uniformity achieved across the chamber cavity. For instance, during a plasma etching process, where the quartz sidewall
12
is maintained at a temperature well above 170° C. and normally at a temperature of about 220° C. a temperature variation as high as 30° C. within the chamber cavity
10
is observed. This creates a serious problem in a plasma etching process
Lin Ruey Horng
Wu Yi Lang
Dang Thi
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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