Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With radio frequency antenna or inductive coil gas...
Reexamination Certificate
2001-11-28
2004-03-16
Alejandro-Mulero, Luz (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With radio frequency antenna or inductive coil gas...
C118S7230IR
Reexamination Certificate
active
06706142
ABSTRACT:
BACKGROUND
1. Field of the Invention
Embodiments of the present invention relate to novel systems and methods for processing semiconductor substrates. More specifically, aspects of the present invention relate to systems and methods for enhancing plasma processing of a semiconductor substrate.
2. Description of the Related Art
Plasma-generating reactors have been used extensively in processes for fabricating integrated circuit and microelectromechanical (MEM) devices on or from a substrate such as a silicon wafer. One particularly useful reactor is the inductively-coupled plasma-generating (ICP) reactor, which inductively (and to some extent capacitively) couples radio frequency (RF) power into a gas contained within the reactor to generate a plasma. The plasma contains species such as ions, free radicals, and excited atoms and molecules that may be used to process the substrate and ultimately produce integrated circuit or MEM devices.
An ICP reactor may be used to carry out a variety of processes to fabricate integrated circuit devices on a semiconductor substrate, including anisotropic and isotropic etching and chemical vapor deposition (CVD). For anisotropic etching, an ICP reactor may be used to produce a plasma with a high ion density. Generally, a low pressure and high RF power are used which favor the production of ions. The ions are accelerated perpendicularly toward the surface of the substrate by an electric field which is typically induced by an RF bias applied to the substrate support. The ions bombard the substrate and physically and/or chemically etch the substrate and any materials deposited thereon, such as polysilicon (poly), silica (SiO
2
, silicon oxide, or oxide), silicon nitride (Si
3
N
4
or nitride), photoresist (resist), or metals. Such anisotropic etching processes are useful for forming integrated circuit features having substantially vertical sidewalls.
ICP reactors are also useful for producing reactive species for isotropic etching, particularly for stripping photoresist from the surface of a semiconductor substrate. Sufficient energy is coupled into the gas in the plasma generation chamber to form a plasma containing a high density of atomic and molecular free radicals that chemically react with the polymeric photoresist to facilitate its removal. For example, a plasma may be used to dissociate oxygen gas into atomic oxygen that reacts with polymeric photoresist to form CO and CO
2
, which evolve and are carried away by the process gas into the exhaust system of the reactor. In such processes, in contrast to anisotropic etching, it is often desirable to reduce or eliminate ion bombardment which may damage the surface of the substrate.
ICP reactors are also useful for CVD of a material onto the surface of a substrate. For many CVD processes, the process is enhanced by ion bombardment and may be carried out at lower temperatures with higher deposition rates by exposing the substrate directly to the plasma (this process is called plasma-enhanced or plasma-assisted CVD). In plasma-enhanced chemical vapor deposition (PECVD), sufficient energy is coupled to the gas in the plasma generation chamber to form a plasma containing a high density of atomic and molecular free radicals and energetic species that interact with the surface of the substrate to form a deposited layer. For example, silane (SiH
4
) releases hydrogen and can be used to deposit a layer of polysilicon onto a substrate. In addition, silane or tetraethoxysilane (TEOS) can be added to an oxygen plasma to deposit a layer of silicon dioxide on a substrate, which in turn can be used as an etch mask during reactive-ion etching or as an insulating layer in circuit devices.
In each of the above processes, processing uniformity can be a critical factor in determining integrated circuit quality, yield, and production rate. Uniform etching, stripping, or chemical deposition over the surface of a wafer assures that structures fabricated at the center of the substrate's surface have essentially the same dimensions as structures fabricated near the edge of the substrate. Thus, the yield of chips from a wafer depends, at least in part, on the etch, strip, or deposition uniformity across the wafer's surface. Higher yield also contributes to a higher production rate.
Processing uniformity may be affected by the density and distribution of reactive species in the plasma and by the plasma potential across the substrate's surface. Processing may occur at higher rates in areas of the wafer surface where there is a higher density of reactive species. Further, for ion enhanced processes, any variance in the plasma potential across the wafer's surface will cause a corresponding variance in ion bombardment energies which may, for example, lead to nonuniform ion etch or ion enhanced deposition.
A number of different inductively-coupled reactor configurations have been used to produce plasmas for the processing of a variety of substrate sizes. In an effort to increase chip production rates, however, integrated circuit manufacturers have moved from small-diameter substrates to substrates of ever-increasing diameters. At one time, 100 millimeter (mm) silicon wafers were the norm. These wafers were subsequently replaced by 150 mm and then 200 mm wafers; most sizes are currently being replaced by 300 mm wafers that will undoubtedly become conventional for high volume and high complexity computer chips in the near future. In time, it is expected that even larger wafers will be developed.
With larger diameter substrates, it becomes difficult to produce a plasma with highly uniform properties in a conventional reactor chamber. For ion enhanced processes, the flux of ions at locations across the wafer surface may become nonuniform.
FIG. 1
illustrates a typical cylindrical ICP reactor, generally indicated at
100
. In reactor
100
, gas is provided to the reactor chamber
102
through an inlet
104
. A helical induction coil
106
surrounds the chamber and inductively couples power into the gas in reactor chamber
102
to produce a plasma. Ions or neutral activated species then flow to a wafer surface
108
for processing. In addition, an RF bias may be applied to the wafer to accelerate ions toward the wafer surface for ion enhanced processing.
The dashed line
110
in
FIG. 1
represents a maximum potential surface (MPS) for a plasma produced in reactor
100
. An MPS is a geometric construction of the maximum values of the DC plasma potential along arbitrary lines drawn from the substrate to points on the interior surfaces of chamber
102
. An ion which is created above the MPS senses an electrostatic potential that tends to drive it toward the interior walls of the chamber. An ion created within the MPS senses an electrostatic potential that tends to push it toward the substrate. A higher percentage of ions near the edges of the wafer are driven to the walls than near the center of the wafer as illustrated by the dome-like MPS
110
. The difference in the ion flux between the edges and the center of the wafer may be significant and lead to nonuniform processing.
The shape of the MPS may be influenced by the configuration of reaction chamber
102
.
FIG. 2
illustrates a schematic diagram showing the plasma properties in a reactor that contains a conically-shaped section
202
above a vertical-walled section
204
of a reactor generally indicated at
200
. The dashed line
210
in
FIG. 2
represents the MPS for a plasma produced in reactor
200
. Also shown in
FIG. 2
is an induction coil
220
positioned along conically-shaped section
202
of the reactor. This configuration produces regions of “hot electrons” generally indicated at
225
in the chamber, with the hot electrons producing a particularly high rate of ionization of the processing gas in these regions of the chamber. The high rate of ionization helps to counteract the natural tendency of the MPS to drop off near the sidewalls of the reactor. The result is the development of a flatter MPS in the chamber than would have been attained in
Kinder Ronald L.
Kushner Mark J.
Savas Stephen E.
Zajac John
Alejandro-Mulero Luz
Mattson Technology Inc.
Wilson Sonsini Goodrich & Rosati
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