Diamond coated parts in a plasma reactor

Details Diamond coated parts in a plasma reactor Diamond coated parts in a plasma reactor

1999-08-16

2003-01-21

Dang, Thi (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C118S7230AN, C118S7230IR

Reexamination Certificate

active

06508911

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to plasma reactors and their operation. In particular, the invention relates to the composition of parts of the chamber facing the plasma in a plasma etch reactor.
BACKGROUND ART
Dry plasma etching is the preferred process for etching features on a silicon wafer being fabricated into semiconductor integrated circuits. Typically, one or more planar layers are deposited over the previously defined substrate, and a layer of photoresist mask or a hard mask is deposited over the planar layers and patterned to leave apertures exposing portions of the planar layers. An etching gas admitted into the etching reactor is then excited into a plasma state, and it acts on the portions of the planar layers exposed by the mask to remove those exposed portions. The dry plasma etching process has proved to be very effective at defining extremely small features with low production of deleterious particles.
The field of plasma etching is typically divided among silicon etching, oxide etching (typically of SiO
2
), and metal etching. Each uses its preferred chemistry and presents its own problems. However, many problems are common among them, and the etching chambers dedicated to different ones of the uses tend to resemble each other.
The most prevalent use of metal etching is to define interconnects (and accompanying contacts or vias) in a layer of aluminum or aluminum alloy deposited over an interlayer dielectric. Recently, copper interconnects have been developed. Once the generally planar aluminum layer has been deposited over the interlayer dielectric and into the contact or via holes, a photomask is deposited and defined over the aluminum layer. Then, an etching gas is admitted into the plasma etch chamber and excited into the plasma state. A typical etching gas is a halide-containing gas, usually F, Cl, or Br. The halogen reacts with the material being etched to typically form a volatile byproduct. It has long been known that a chlorine-based chemistry is effective at etching aluminum. See, for example, U.S. Pat. No. 5,387,556 to Xiaobing et al. Gaseous hydrochloric acid (HCl) is the prototypical chlorine-based etchant. However, HCl is no longer considered the optimum aluminum etchant.
Aluminum quickly forms an overlying layer of a native oxide of alumina (Al
2
O
3
) and related materials forming a residue over the metallic aluminum being etched. Alumina is a relatively stable material and resistant to reductive breakdown, even by HCl. For these reasons, a plasma etch of boron trichloride (BCl
3
), often in conjunction with HCl or Cl
2
, is typically used for etching aluminum and its alloys. Wang et al. in U.S. Pat. No. 5,219,485 use a similar chemistry to etch silicides in order to avoid residues from the silicide etch.
However, the use of a powerful chlorine-based etchant like BCl
3
introduces a problem originating from the fact that the chamber body is most economically made of aluminum, for example the alloy A16061-T6, and the chamber dome is usually made of alumina. The seminal problem is that a chamber having an aluminum body and which is used for etching aluminum must balance the etching of the aluminum portion of the substrate against the etching of the chamber body. Typically, the aluminum chamber body is anodized, that is, electrochemically processed to be covered with a moderately thin coating of alumina, to provide some protection for the aluminum. Nonetheless, though usually to a lesser extent, a chlorine-based etchant can also attack the alumina, whether in the dome or the thin anodized layer on the chamber body. The physical integrity of the aluminum chamber and alumina dome are important, but a more important problem arises from the fact that the etching of these parts is likely to produce aluminum-based particles that deleteriously fall on the wafer and reduces the yield of functioning integrated circuits. As a result, the chamber wall in a plasma reactor intended for aluminum etching advantageously should not be composed of aluminum, even with a coating of alumina. Alumina is relatively resistant to a chlorine-based etch, though not impregnable. However, as will be explained later, fluorine is often also used, which more readily etches alumina.
In U.S. patent application Ser. No. 08/770,092 filed Dec. 19, 1996, Shih et al. (including the two present inventors plus others) describe a protective coating of boron carbide (nominally B
4
C) applied to the aluminum chamber walls. A similar disclosure appears in European Patent Application EP-849,767-A2. This patent application is incorporated herein by reference in its entirety. The boron carbide coating has been applied to a high-density plasma reactor, known as the Decoupled Plasma Source (DPS) Metal Etch Chamber available from Applied Materials, Inc. of Santa Clara, Calif.
A schematic representation of the commercial DPS chamber is illustrated in the cross-sectional view of FIG.
1
. An upper, main processing compartment
10
is bounded by a curved ceramic dome
12
typically of alumina, an upper housing
14
typically of aluminum to which the ceramic dome
12
is sealed, and a movable pedestal wall
16
that is vertically movable to engage and seal within an inwardly extending annular shelf
18
of the upper housing
14
. The upper housing
14
rests on and is sealed to a lower housing
20
, and a bellows
22
is sealed to the bottom of the lower housing
20
and to a stem
24
extending downwardly from the pedestal wall
16
. An electrode
19
may be included at the center of the dome
12
. A lower compartment
26
is defined generally by the walls of the lower housing
20
and the lower edge of the annular shelf
18
. During plasma processing, the movable pedestal wall
16
seals the upper compartment
10
from the lower compartment
22
by engaging and sealing itself to the annular shelf
18
of the upper housing
14
.
A vertical actuator
28
connected to the bottom of the stem
24
can move the pedestal wall
16
into and out of engagement with the annular shelf
18
. An unillustrated robot blade can transfer a wafer
30
into the lower compartment through a loadlock slit
32
in the lower housing
20
and its unillustrated slit valve when the vertical actuator
28
has lowered the pedestal wall
16
to a position to receive the wafer
30
on its upper surface. The pedestal wall
16
typically includes an electrostatic chuck to selectively hold the wafer
30
by electrostatic attraction exerted by an electrical signal applied to the chuck. After the wafer has been placed on the pedestal wall
16
, the vertical actuator
28
raises the pedestal wall
16
so that it seals the upper compartment
10
and places the wafer within the upper compartment
10
.
The upper housing
14
also includes a turbo port
38
connecting to an integral pumping stack
40
. A vacuum pumping system
42
mated with the bottom of a pumping stack
40
pumps the upper compartment
10
as well as the lower compartment
26
when it is opened to the upper compartment
10
. A poppet valve
44
fixed to the upper housing
14
over the pumping stack
40
can selectively isolate the upper compartment
10
from the vacuum pumping system
42
.
Processing gas, which for etching aluminum typically includes BCl
3
and Cl
2
as well as possibly CF
4
, CHF
3
, N
2
, Ar, etc., is injected into the sealed upper compartment
10
through a plurality, typically four, of unillustrated gas nozzles fixed to the radially inner ends of respective gas orifices
46
penetrating the upper housing
14
near its top. RF power is applied to an inductive coil
48
wrapped around the curved dome
12
so as to create a high-density plasma of the processing gas within the upper compartment
10
. RF power is also applied to the wafer pedestal
16
and possibly to an unillustrated counter electrode fixed in middle of the curved dome
12
so as to bias the plasma to effect the desired etching of the wafer.
According to Shih et al., a coating of boron carbide is plasma sprayed onto the inside of the aluminum chamber housing
14

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