Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
2000-04-27
2002-04-02
Mills, Gregory (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C118S7230IR
Reexamination Certificate
active
06364995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to reactors for performing radio frequency (RF) plasma chemical vapor deposition (CVD) and sputter etch processes and particularly to such reactors for performing both processes simultaneously.
2. Background Art
CVD formation of a thin silicon dioxide film on an integrated circuit structure having small (0.5 &mgr;m or less) features with high aspect ratios (i.e., a large value of the ratio of channel depth to channel width, e.g., greater than two) is nearly impossible to accomplish without formation of voids between the metal lines. As shown in
FIG. 1A
, in depositing a dielectric material
10
on a device having a very narrow channel
12
(i.e., an aspect ratio greater than 2) separating two metal lines
14
a
,
14
b
, relatively little of the dielectric material
10
reaches the bottom of the channel
12
, leaving a void
15
. This is because dielectric material
10
is deposited more quickly at the corners
16
of the metal lines
14
than elsewhere along the vertical walls of the metal lines
14
, thus at least nearly sealing off the bottom of the channel
12
during the deposition process. A solution to this problem is to simultaneously etch the dielectric material
10
from the corners while depositing using an RF sputter etch process that uses ions impinging vertically on the surface, thus preventing pinching off of the channel
12
. This process can be used for spaces with aspect ratios greater than two, unlike currently-used sequential deposition and sputtering which fails below 0.5 &mgr;m.
As illustrated in the graph of
FIG. 1B
, an RF sputter etch process has a maximum etch rate for surfaces disposed at a 45° angle relative to the incoming ions. By directing the ions to impinge in a perpendicular direction relative to the wafer surface, the sputter etch process quickly etches angled surfaces formed by the simultaneous deposition process (such as dielectric surfaces formed over the corners
16
) and etches other surfaces (i.e., horizontal and vertical surfaces) much more slowly, thus preventing the blockage of the channel
12
and formation of the void
15
shown in FIG.
1
A. This permits deposition of dielectric material preferentially at the bottom of the channel
12
and on top of the lines
14
, relative to the side walls and corners
16
, as illustrated in FIG.
1
C.
In order to accomplish the foregoing, the RF plasma sputter etch rate near the corners
16
must be on the order of the deposition rate. High plasma density is required to meet the requirement of high sputtering rate (production throughput) without electrical damage to the semiconductor devices. In order to achieve such a sputter etch rate across an entire wafer (such as an eight inch Silicon wafer), the plasma ion density must be sufficiently high and uniform across the entire wafer. Such uniformity is readily accomplished using a plasma consisting almost entirely of argon ions. However, it will be remembered that the sputter etch process desired here is ancillary to a CVD process requiring species other than argon to be present. Specifically, in a CVD process employing silane (SiH
4
) in which the dielectric material
10
is SiO
2
, oxygen must be present in significant quantities, the oxygen being ionized in the plasma. The oxygen ions have a relatively short lifetime and are highly susceptible to quenching. It is very difficult to attain a dense and very uniform distribution of oxygen ions across the wafer surface, particularly 8-inch diameter wafers of the type now currently in use.
While the plasma may be generated with electron cyclotron resonance (ECR), ECR apparatus has limited commercial attractiveness due to design complexity, size and cost. Moreover, since the plasma is generated remotely from the wafer, scaling the ECR reactor up to accommodate an 8-inch wafer diameter is difficult and requires simultaneous use of complex magnetic fields.
Application of inductively coupled plasmas to high-rate sputter etching in CVD systems is disclosed in application Ser. No. 07/941,507 filed Sep. 8, 1992 by Collins et al. entitled “Plasma Reactor Using Electromagnetic RF Coupling and Processes” and assigned to the assignee of the present application, the disclosure of which is hereby incorporated by reference in its entirety into the present specification. An earlier version of this work is described in European patent publication EP 0,520,519 A1. As described therein, one advantage of inductively coupled plasmas over capacitively coupled plasmas is that the inductively coupled plasma is generated with a much smaller bias voltage on the wafer (reducing the likelihood of damage thereto) even in the presence of a greater plasma density. In the silicon oxide deposition disclosed in the referenced patent application, silane, mostly un-ionized, provides the silicon and a gaseous oxygen species provides the oxygen for the formation of silicon dioxide by CVD. Argon ions accelerated across the sheath adjacent the wafer are used for sputter etching.
FIG. 2
illustrates a CVD vacuum chamber
20
and RF antenna
22
for generating an inductively coupled plasma of the general type disclosed in the above-referenced application, although that particular chamber had a top-hat shape. The RF antenna
22
is a coiled conductor wound as a solenoid around the cylindrical vertical side wall
24
of the vacuum chamber
20
. The source chamber wall adjacent the coil antenna is an insulator while the ceiling
26
and the process chamber walls are preferably grounded, the flat ceiling
26
functioning as a grounded electrode.
The cylindrical coil of the referenced application non-resonantly couples the RF energy in the coil antenna into the plasma source region via an induced azimuthal electric field. Even in free space, the electric field falls to zero at the center of the chamber. When a plasma is present, the electric field falls off even more quickly away from the chamber walls. The electric field accelerates electrons present in the plasma, which then further ionize atoms into ions or break up molecules into atoms or radicals. Because the coupling is not tuned to a plasma resonance, the coupling is much less dependent on frequency, pressure and local geometries. The plasma source region is designed to be spaced apart from the wafers, and the ions and atoms or radicals generated in the source region diffuse to the wafer.
The chamber of the above-referenced application is primarily designed for etching at relatively low chamber pressures, at which the electrons have mean free paths on the order of centimeters. Therefore, we believe the electrons, even though primarily generated near the chamber walls, diffuse toward the center and tend to homogenize the plasma across a significant diameter of the source region. As a result, the diffusion of ions and atoms or radicals to the wafer tend to be relatively uniform across the wafer.
We believe the reactor of the above-referenced application has a problem when it is used for CVD deposition and sputter etching, particularly involving oxygen. For CVD, the chamber pressure tends to be somewhat higher, reducing the electron mean free path and resulting in a nonuniform plasma density with the peak density occurring in an outer annulus of the plasma. Furthermore, oxygen ions or radicals are subject to many recombination paths so that their diffusion lengths are relatively limited. Thus, the wafer center is farther from the plasma source region than the wafer edges, and the oxygen ion and radical density is less near the center of the wafer
28
than it is at the edges thereof, as illustrated in the solid line curve of ion density of FIG.
3
. The lack of oxygen ions near the wafer center reduces the sputter etch rate relative to the CVD deposition rate, leading to formation of the void
15
as illustrated in
FIG. 1A
in spaces or channels near the wafer center (e.g., the channel
12
of FIG.
1
A), while spaces near the wafer periphery have the desired ratio between sputtering and deposition rates.
One possible s
Fairbairn Kevin
Nowak Romuald
Alejandro Luz
Applied Materials Inc.
Michaelson & Wallace
Mills Gregory
LandOfFree
Dome-shaped inductive coupling wall having a plurality of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dome-shaped inductive coupling wall having a plurality of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dome-shaped inductive coupling wall having a plurality of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2846034