Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2000-12-15
2004-11-09
Scherbel, David A. (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S487500, C137S553000, C118S715000, C251S129040
Reexamination Certificate
active
06814096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to automated pressure control and, more specifically, to an Improved Pressure Controller and Method.
2. Description of Related Art
The term, “semiconductor processing equipment,” refers to a seemingly infinite variety of large, highly expensive pieces of machinery that are used to conduct a variety of different processes that ultimately result in a completed semiconductor device. What is a common design aspect for many pieces of semiconductor processing equipment is the need for accurate, fast and reliable pressure control of the vacuum within the chamber where the process is taking place. If we look at
FIG. 1
, we can review how a conventional semiconductor processing tool system
10
is arranged today.
FIG. 1
is a depiction of a conventional semiconductor processing tool system
10
. As shown in
FIG. 1
, the processing tool
12
is typically supplied by gas that is transmitted from a gas supply
14
(such as the bottle shown) through a gas supply line
16
until it gets to the vicinity of (or inside of) the semiconductor processing tool
12
, where the actual flow of the gas to the chamber is controlled by a mass flow controller
18
. In this way, the tool
12
can regulate when and how much gas to inject into the processing chamber
20
.
There is generally a chamber pressure sensor
22
that provides an external signal via the pressure signal conduit
34
. This external pressure signal typically can be either analog or digital in form, and represents the pressure conditions within the chamber
20
. The signals are carried by a pressure signal conduit
34
to a conventional pressure control means
30
. Within the pressure control means
30
, the pressure signal is generally summed with a host tool logic signal later referred to as host tool pressure setpoint. The host tool pressure setpoint is generally generated by the tool logic controller
32
, with its content being an analog or digital pressure setpoint value. These tool logic signals are transmitted to the pressure control means
30
by a tool logic signal conduit
36
.
If we refer back to the tool
12
, we can also see that another important feature that is many times found within the tool
12
is a plasma generator unit
23
. This feature is important since plasma generators create sudden and sometimes large pressure deviations. Plasma generators essentially energize the gas molecules which splits them into ionized atoms and species. These ionized species are much more reactive than their molecular “parents” thus greatly speeding up and increasing the selectivity of processes such as etch and deposition. The instant the plasma is turned on, a fraction of the gas molecules split in to pieces thereby producing instant undesirable increases in chamber pressure. Similarly, the supply lines
16
(and the gas they transmit) also have an effect on the pressure within the chamber
20
. The chamber
20
is generally kept in a vacuum state in order to prevent impurities from contaminating the semiconductor process. The conventional arrangement for maintaining the vacuum condition in the chamber
20
is via a vacuum source
24
, such as the vacuum pump
24
shown. The vacuum pump
24
simply pumps to an exhaust
25
while drawing a vacuum on a vacuum transmission line
26
. Between the vacuum source
24
and the vacuum transmission line
26
is found a valve
28
. It is by actuation of this valve
28
that the pressure can be raised and lowered (usually in the sub-atmospheric range) within the chamber
20
.
Once the pressure signal and tool logic signal are summed in the pressure control means
30
, the resulting signal is sent to a motor driver circuit
42
via an external valve command conduit
38
. This conduit
38
is either hard wired via conventional cable, printed circuit board trace, or wire, however, it could also be wireless. The motor driver circuit
42
is actually a sub-component of a valve control assembly
40
. The other components of the valve control assembly
40
are an internal valve command conduit
44
and a motor/valve drive assembly means
46
for actuating the valve
28
. As should be appreciated, the signals generated by the pressure control means
30
are acted upon by the valve control assembly
40
to open and close the valve
28
such that the pressure in the chamber
20
is regulated. As described above, the pressure control system is influenced by external factors called states of the process, in particular, the turning on and off of gas inputs to the chamber and the initiation of RF events to create plasma are primary contributing factors. The pressure control algorithm (executed by the Pressure Control Means
30
) constantly works at maintaining the pressure regulated at the required value by actuating the valve in order to compensate and balance the pressure responsive to the changing states of the process. It is clear that the pressure regulation task can be performed only as well as the individual elements comprising the closed loop system permit. As such the valve control assembly (
40
) is an essential component in terms of its accuracy and speed of response to maintain quality and/or stability of the control system. If we now turn to
FIG. 2
, we can look more closely at the valve control assembly
40
of the conventional system.
FIG. 2
depicts a conventional valve control assembly
40
. As can be seen, the resultant signal of the summed commands from the pressure control means
30
in
FIG. 1
arrive at the motor driver circuit
42
via an external valve command conduit
38
. As discussed above, this is typically a cable that is run for whatever length necessary to extend between the pressure control means
30
and the motor driver circuit
42
. Between the motor driver circuit
42
and the motor/valve drive assembly means
46
is an internal valve command conduit
44
. In the conventional system, this conduit, too, is an external cable running between the motor driver circuit
42
and the motor/valve drive assembly means
46
. The motor/valve drive assembly means
46
conventionally comprises a motor drive
48
such as a conventional stepper motor, which in turn drives a required reduction gear, or other means of mechanical advantage
52
via a motor shaft
50
. In other forms, the motor drive
48
is connected to a valve stem
54
via belts and pulleys. In any case, it is conventional in the art that there not be a direct connection or coupling between the motor drive
48
and the valve means
28
without some method of mechanical advantage or reduction gearing having the effect of increasing the number of revolutions of the motor drive
48
needed to create a full open to close cycle of the valve means
28
. This mechanical advantage typically also has the beneficial effect of increasing the step resolution as many folds as the reduction factor of the mechanical reducer means. However, it also represents an actuation speed penalty of the same magnitude, as the motor has to travel farther for the same valve displacement. Additionally, the increased resolution is partially absorbed and degraded by the inherent nonlinearity (backlash) introduced by the mechanical reducer means. That actuation speed handicap has proved to be more detrimental to the quality of the pressure control dynamic characteristics and transient response performance than initially expected. A further note is that within the conventional internal valve command conduit
44
, there is typically one single unidirectional path that extends from the motor driver circuit
42
to the motor drive
48
with the exception of two limit switches that are normally used within the motor valve drive assembly to reference the open and closed valve positions. These switches return a binary logic signal that cannot resolve position continuously across the stroke of the valve but only at two discrete locations—in order to distinguish these limit-switch-generated signals from signals to be discussed later on in connection with
FIG. 4
, we shall re
Ballard William
Cederstav Per
Kruse David
Mallory Sean
Vyers Emmanuel
Krishnamurthy Ramesh
Nor-Cal Products, Inc.
Scherbel David A.
Steins & Associates, P.C.
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