Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-08-03
2001-05-15
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C156S345420, C438S726000
Reexamination Certificate
active
06232236
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The present invention is generally related to semiconductor wafer processing equipment and, more particularly, to an improved apparatus and method for controlling plasma uniformity in a semiconductor wafer processing system.
2. Description of the Related Art
Traditionally, plasma-enhanced reactive ion etching systems contain an anode and cathode within a vacuum chamber. The cathode typically forms a pedestal for supporting a semiconductor wafer within the chamber and the anode is formed of the walls and/or top of the chamber. To process a wafer, a reactive gas is pumped into the vacuum chamber and the anode and cathode are driven by a single sinusoidal frequency (RF) source to excite the reactive gas into a plasma. The single frequency is typically 13.56 MHz, although frequencies from 100 kHz to 2.45 GHz are often used, with the occasional use of other frequencies. More specifically, a single frequency, sinusoidal RF signal is generally applied to the reactive gas within the chamber at a relatively high-power level, e.g., 3 kilowatts. The RF power excites the reactive gas, producing a plasma within the chamber proximate to the semiconductor wafer being processed. Such plasma-enhanced reactive ion processing has been used, for example, in etch and chemical vapor deposition processes.
The uniformity of the etch process that results from the forgoing etch chamber is poor. As such, an improved version of this etch chamber adds four magnetic coils about the outside of the chamber, i.e., one vertically oriented toroidal coil for each side of the chamber. These coils when driven with an AC signal magnetically control the plasma to facilitate a more uniform etch process. This form of chamber is generally known as a magnetically enhanced reactive ion etch (MERIE) chamber. One such MERIE chamber is manufactured by Applied Materials, inc. of Santa Clara Calif. as they model MxP
+
chamber. This chamber is described in commonly assigned U.S. Pat. No. 5,215,619 issued Jun. 1, 1993 to Cheng et al. and U.S. Pat. No. 5,891,350 issued Apr. 6, 1999 to Shan et al., which are herein incorporated by reference.
FIG. 1
is a schematic diagram of a MERIE system
100
of the prior art. The system
100
includes a processing chamber
101
. The chamber
101
comprises a set of side-walls
102
, a floor
104
and a lid
106
, defining an enclosed volume. A gas panel
110
supplies reactive gases (an etch chemistry) to the enclosed volume defined by the chamber
101
. The system
100
further includes an RF power supply
122
and a matching circuit
120
that drives a pedestal assembly
108
such that an electric field is established between the pedestal assembly
108
and the chamber walls
102
and lid
106
. A set of coils
124
are arranged about the sides
102
of the chamber
101
to facilitate magnetic control of the plasma
124
.
A pedestal assembly
108
comprises a pedestal
114
centrally mounted within the chamber
101
to a cathode
112
and surrounded by a collar
118
. The pedestal retains a workpiece
116
such as a semiconductor wafer which is to be processed in the chamber
101
. The plasma reaction chamber
101
employs capacitively coupled RF power to generate and maintain a high density, low energy plasma
124
. RF power, is coupled from the RF power supply
122
producing one or more RF frequencies through matching network
120
. The lid
106
and walls
102
are grounded and serves as a ground reference (anode) for the RF power. With the configuration shown in
FIG. 1
, plasma density is controlled by the RF power provided by the power supply
122
via the matching circuit
120
.
In semiconductor wafer processing, the cathode
112
is typically fabricated from a conductive material such as aluminum. The pedestal
114
is typically fabricated from a polymer such as polyimide or a ceramic material such as aluminum nitride or boron nitride. The workpiece
116
(i.e., a semiconductor wafer) is typically made of silicon. The electric field that couples to the plasma passes through both the workpiece and the pedestal. Since the cathode is made of a different materials than the workpiece, the different materials have different effects on the plasma. Consequently, there is an abrupt change of plasma parameters, and process uniformity, at the wafer edge
126
. To improve process uniformity at the wafer edge, a collar
118
, surrounds and partially overlaps the pedestal and pedestal
114
. The collar
118
(also known as a process kit) is typically made of a material such as quartz.
Although magnetic enhancement provides a substantial improvement in etch uniformity, the existence of a magnetic field in the chamber causes a phenomenon known as E×B drift where the electrons in the plasma tend to accumulate on one side of the chamber. Such drift causes non-uniform etching. To combat E×B drift, the phase of the AC signal that drives each coil is rotated such that the B field is magnetically rotated. This lessens the E×B drift problem but does not eliminate it. Additionally, non-uniformity of ion energy and radical component density causes non-uniform etching of a wafer.
Therefore, there is a need in the art for an apparatus and method for improved control of the plasma uniformity as well as ion energy and radical component uniformity across the wafer surface to provide for more uniform and repeatable etching of wafers.
SUMMARY OF THE INVENTION
The disadvantages associated with the prior art are overcome by the present invention of an apparatus and method for controlling a uniformity of a plasma, including ion energy uniformity and radical component density within a semiconductor wafer processing system such as an etch reactor. The apparatus comprises a wafer support, a conductive process kit surrounding the wafer support and an RF supply coupled to the process kit. The process kit or collar is biased by an RF signal having a frequency that can be the same as a cathode drive signal or a different frequency. The apparatus establishes a primary plasma in response to the cathode drive signal and a secondary plasma in response to the process kit drive signal. The secondary plasma is established proximate the process kit and, as such, it circumscribes the primary plasma which is located central to the reactor, above the wafer. The secondary plasma supplies electrons to the periphery of the primary such that the primary plasma is substantially uniform over the entire wafer surface. The secondary plasma also facilitates a uniform distribution of ion energy and radical components.
The method and apparatus of the present invention includes a computerized control system for establishing the primary and secondary plasmas with the reactor. The control apparatus also provides for utilizing various waveforms, frequencies and combinations of frequencies to establish and maintain the plasmas such that optimal wafer processing is obtained.
REFERENCES:
patent: 4464223 (1984-08-01), Gorin
patent: 4859908 (1989-08-01), Yoshida et al.
patent: 5215619 (1993-06-01), Cheng et al.
patent: 5271963 (1993-12-01), Eichman et al.
patent: 5607542 (1997-03-01), Wu et al.
patent: 5891350 (1999-04-01), Shan et al.
patent: 6095084 (2000-08-01), Shamouilian et al.
patent: 0 552 491 A1 (1993-07-01), None
patent: 0 742 577 A2 (1996-11-01), None
patent: 0 776 991 A1 (1997-06-01), None
patent: WO 95/32315 (1995-11-01), None
Bjorkman Claes
Luscher Paul
Mett Richard
Shan Hongqing
Welch Michael
Applied Materials Inc.
Powell William
Thomason, Moser & Patterso
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