Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With radio frequency antenna or inductive coil gas...
Reexamination Certificate
2000-10-12
2003-01-28
Mills, Gregory (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With radio frequency antenna or inductive coil gas...
C156S345540, C156S345440, C118S7230AN, C118S7230IR, C118S729000, C118S7230ER
Reexamination Certificate
active
06511577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a reduced-impedance chamber for use in plasma processing applications and more particularly to a chamber that can be used in repeatable and controllable plasma processing applications.
2. Description of Related Art
A conventional chamber, as shown in
FIG. 1
, includes a process chamber
10
having a chamber wall
12
. A chuck assembly
14
is mounted on a bellows
13
that is mounted on a chuck mount ring
16
. Chuck mount ring
16
includes spokes
18
through which chuck mount ring
16
is connected to chuck assembly
14
. A workpiece, such as a semiconductor wafer
15
, is mounted on chuck assembly
14
. RF energy can be applied to chuck assembly
14
through a chuck impedance matching assembly
20
. A plasma source
24
and an injection assembly
21
through which operational gases are injected into chamber
10
are above chuck assembly
14
. A turbo-molecular pump
26
for evacuating operational gases is below chuck assembly
14
. A gate valve
25
between chuck assembly
14
and turbo-molecular pump
26
provides selective isolation of turbo-molecular pump
26
from chamber
10
to enable detection of leaks by monitoring the leak up rate and to enable regulation of chamber pressure by varying the conductance to turbo-molecular pump
26
. Coil
28
is provided in plasma source
24
to create a plasma therein. RF energy is supplied to coil
28
through fast match assembly
22
.
The chamber illustrated in
FIG. 1
operates as follows. First bellows
13
is lowered. Then wafer
15
is introduced through a slot valve (not shown) in the side of process chamber
10
usually below the operating position of chuck assembly
14
. Wafer
15
comes in on a blade (not shown) which has slots to allow for typically three pins (not shown) in chuck assembly
14
. The pins are able to move up and down by a mechanism internal to chuck assembly
14
. Once wafer
15
is over chuck assembly
14
, the pins lift wafer
15
off the blade, and the blade is then removed. After the blade is removed, the pins are lowered so that wafer
15
rests on chuck assembly
14
, and bellows
13
is raised.
A relatively high DC voltage is then applied at chuck assembly
14
to fix wafer
15
to chuck assembly
14
. Wafer
15
is electrically isolated from chuck assembly
14
. In one common version, chuck assembly
14
is anodized, usually by a special process with additional post coating to improve dielectric properties. In a second version a conductive material is positioned between polyamide sheets. The conductive material receives the clamping voltage. Chuck assembly
14
is not held at the electrostatic voltage but is at the DC ground. The chuck achieves a potentially high negative DC voltage through self-bias and leakage current. Since the chuck is capacitively coupled, it can achieve a DC voltage.
Operational gases are injected into chamber
10
through injection assembly
21
. RF energy is applied to coil
28
to create a plasma, and RF energy is applied to chuck assembly
14
through matching network
20
to generate a negative voltage on the wafer by means of self-bias. The self bias phenomenon results from the greater mobility of electrons as compared with the ions. For the ions to be drawn to the wafer surface at the same rate per RF cycle as the electrons, the wafer surface must generate the negative voltage. This is important for the process because it allows the ions to be accelerated to the wafer surface at an energy determined by the chuck RF voltage and the plasma parameters. After the process is completed, the injection of reactive gases is halted, the RF chuck power is removed, the wafer clamping DC voltage is removed or slightly reversed, the RF plasma energy is stopped, bellows
13
is lowered, and wafer
15
is removed.
If chuck assembly
14
is monopolar, then there is no means to deliver charge to wafer
15
through chuck assembly
14
during the clamping and unclamping of wafer
15
. Wafer
15
must accumulate charge opposite to the chuck electrostatic electrode. The plasma is the most common means to complete the clamping circuit to wafer
15
since the plasma is a sufficiently good conductor even at low power levels. Usually the plasma is kept on at low power levels during clamping and unclamping operations.
The plasma completes a circuit path between the driven electrode at chuck assembly
14
(i.e., plasma cathode) and the typically grounded counter electrode (i.e., plasma anode). The counter electrode is usually injection assembly
21
. In many systems, there are areas of the chamber wall that function as the counter electrode; if these walls are too close to the wafer, then they generate process uniformity problems or non-normal ion-accelerating electric fields. With the normal positioning of chuck assembly
14
in chamber
10
, the counter electrode conducts to ground through the following path: (1) from injection assembly
21
; (2) through plasma source
24
; (3) along inner wall
12
of chamber
10
; (4) through spokes
18
to the outer diameter of bellows
13
; (5) through bellows
13
; and (6) to the base of chuck assembly
14
. The combination of chamber
10
, bellows
13
, spokes
18
, plasma source
24
and injection assembly
21
represents a relatively high impedance as compared with the plasma bulk and sheath impedance.
FIG. 2
shows the equivalent circuit of the conventional chamber of FIG.
1
. Chuck assembly
14
, which is modeled by an inductor
100
, a resistor
102
, a capacitor
104
, a capacitor
106
and an inductor
140
, is adjacent to the position in the circuit corresponding to wafer
15
. Proximate to wafer
15
are a capacitor
108
and a resistor
110
, which are used to model the RF current that bypasses the sheath and heats the plasma. The rest of the model for the plasma includes a resistor
136
, a resistor
138
and a current source
135
, where current source
135
produces a current related to plasma parameters at wafer
15
. As discussed above, the path to ground from injection assembly
21
is through plasma source
24
, modeled by a capacitor
130
, an inductor
132
and an inductor
134
, wall
12
(including the electrostatic shield), modeled by a capacitor
124
, an inductor
126
and an inductor
128
, spokes
18
, modeled by a capacitor
118
, an inductor
120
and an inductor
122
, and bellows
13
, modeled by a capacitor
112
, an inductor
114
and an inductor
116
. An RF power supply
139
, which is modeled as a voltage source
148
and a resistor
150
, is connected to chuck assembly
14
through matching network
20
, which is modeled as a capacitor
142
, a capacitor
144
and an inductor
146
.
All of these components contribute to the impedance in the ground path. Typically, the connection to the chuck can have an inductance of 50 nh and a capacitance to ground of 200 pf; the bellows can have an inductance of 250 nh and a capacitance of 100 pf, the spokes can have an inductance of 33 nh and a capacitance of 50 pf; the wall can have an inductance of 40 nh and a capacitance of 100 pf; and the plasma source can have an inductance of 40 nh and a capacitance of 100 pf.
In this model the plasma impedance is fixed. The plasma current source uses Langmuir probe data to determine the parameters of the current. These effects together produce harmonics. The generally nonlinear impedances of the elements described above result in the generation of higher order harmonics in the plasma voltage at the workpiece whereby the processing is difficult to control.
For the circuit in
FIG. 2
,
FIG. 3
illustrates the predicted waveform of the voltage across the plasma sheath from the plasma anode to the plasma cathode. In this model the voltage across the bulk of the plasma is ignored. This voltage accelerates the ions to the wafer and controls the energy of the ions arriving at the wafer. The model assumes a perfect match for the fundamental of the RF energy at the input to the matching network
20
.
FIG. 4
shows the corresponding frequency spectra of the voltage
Mills Gregory
Tokyo Electron Limited
Zervigon Rudy
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