Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2001-06-13
2003-12-02
Mancene, Gene (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S010000, C137S624120, C700S282000
Reexamination Certificate
active
06655408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to mass flow controllers used in semiconductor processing systems.
2. Description of the Related Art
Conventional semiconductor manufacturing techniques may include advanced chemical and/or thermal reactions that are extremely sensitive to the processing conditions within the processing chamber. In a dry etching-type process, for example, the flow of etch gases supplied to a dry etch chamber having a semiconductor wafer positioned therein must be carefully controlled if the desired etch characteristics are to be obtained. Further, in nucleation processes that may be implemented prior to depositing tungsten monolayers in a chemical vapor deposition process (CVD), for example, the deposition chemical reaction generally begins immediately upon the reactant gases being supplied to the processing chamber. Therefore, if the flow of the reactant gases into the processing chamber is not initiated at or very near a calculated optimal flow rate for the particular chemical reaction, then the chemical reaction often yields undesirable and/or unpredictable results that may substantially reduce the device yield from the process.
In an attempt to precisely control gas flow into processing chambers and/or processing environments, conventional semiconductor processing systems have generally implemented one or more mass flow controllers (MFCs) to regulate and/or control the flow of reactant gasses into the processing environment. These MFCs generally operate by receiving a gas supply at an MFC input and outputting a regulated gas supply at an MFC output. The MFC output is generally in communication with the processing chamber/environment, and therefore, are generally used to supply a reactant processing gas thereto.
In operation, conventional MFCs generally regulate and/or control the pressure and/or volume of the gas supply at the MFC output in accordance with at least one input received from a user.
FIG. 1
illustrates a conventional MFC
10
that may be implemented in a semiconductor processing system in order to control reactant gas flow into the processing system. The conventional MFC
10
may receive a reactant gas, which may be a single gas or a combination of gases, at a primary side input
11
to MFC
10
. The reactant gas flowing into the MFC
10
from the primary side is generally divided into two portions, wherein a first portion flows through a restriction device
12
and the second portion flows through a flow sensor bypass tube
13
. Within the flow sensor bypass tube
13
the mass flow of the gas passing therethrough is cooperatively determined by temperature sensors
14
, heater
23
, and a bridge circuit device
15
in communication with the temperature sensors
14
. Heater
23
, which may be positioned equidistant from each of temperature sensors
14
, heats a constant percentage of the MFC gas flow. With no gas flow, the heat reaching each of sensors
14
is equal. With increasing flow, the gas flow stream carries heat away from the upstream temperature sensor
14
and towards the downstream temperature sensor
14
. This temperature difference may be measured and is representative of the gas flow in the bypass tube
13
. Therefore, since the flow of gas through bypass tube
13
is proportional to the total flow of gas through MFC
10
, then the total flow of gas through MFC
10
may be determined from the mas flow of gas traveling through bypass tube
13
. The determined temperature change may be converted into representative electrical signals through a bridge circuit device
15
, and thereafter, the representative electrical signals communicated to an amplifier circuit
16
. Amplifier circuit
16
operates to amplify the electrical signals and then communicates the representative electrical signals to a user display device
17
, which may convert the signals into a format that may be viewed and analyzed by the user. Additionally, the amplifier circuit may communicate the amplified electrical signals to a control circuit
19
within MFC
10
.
Control circuit
19
generally operates to control the position of the primary MFC valve
21
, which essentially operates to allow gas to flow through MFC
10
, via a valve driver
20
in communication with the control circuit
19
. Control circuit
19
also receives an input from a user input device
18
that may operate to indicate to control circuit
19
the user's desired flow rate. Thus, control circuit
19
may compare a measured flow rate, which is indicated by the representative electrical signals received from amplifier circuit
16
, with a desired flow rate received from user input device
18
. Thereafter, the control circuit
19
may adjust the position of valve
21
to increase or decrease the gas flow through MFC
10
such that wherein the increase or decrease is calculated to adjust the gas flow through the MFC closer to the desired gas flow. This process is generally termed a ranging in-type process, as the MFC valve position is adjusted towards the desired position in a dampened oscillatory manner so that the oscillation of the valve position is calculated to decrease to the desired position within a predetermined amount of time. Therefore, if the gas flow is to be increased, for example, then the control circuit would communicate to valve driver
20
to actuate valve
21
in the direction shown by arrow “A”. This increases the spacing between the terminating end of valve
21
and the wall of MFC
10
so that additional gas may be allowed to flow through MFC
10
in the direction indicated by arrow “B”. The gas passing through MFC
10
is outputted through an MFC output
22
, which is generally in communication with a processing chamber or processing environment.
Although conventional MFCs are generally effective in maintaining a relatively constant gas flow once the flow is initiated, the implementation of a control circuit receiving an input from an amplifier circuit and adjusting the valve position in order to obtain a desired gas flow is generally ineffective in generating an accurate and/or predictable gas flow at startup conditions. In particular, the combination of a sensing device transmitting a signal to a valve control device results in a “ranging in” type of operation in order to obtain the desired flow rate. Ranging-in operations, as are known in the art, generally include a process of measuring a current flow and adjusting the current flow in the direction of a desired flow. If the difference between the current flow and desired flow is substantial, then the adjustment, which is generally calculated, may also be substantial. Ranging-type operations are effective when the actual gas flow is proximate the desired flow, as the control circuit generally only has to make a minor valve adjustment to obtain the desired flow. However, in situations where the actual gas flow is not proximate the desired gas flow, then the control circuit generally attempts to substantially alter the valve position in order to bring the current flow rate to a level that is proximate the desired level. This substantial alteration in turn causes a return reaction in the control circuit, which initiates a dampened oscillatory condition that eventually results in the MFC ranging the valve position into a position that yields the desired flow rate. This condition is generally caused by a lack of gas pressure on a flow control valve during a flow startup process. The lack of gas pressure at flow startup generally operates to cause the MFC flow controller to open the flow control valve farther in an attempt to initiate gas flow at the desired rate. However, with no gas resident at the flow control valve upon startup of flow, the controller attempts to increase flow by further operating the flow control valve. Therefore, once gas arrives, the valve is too far open and the controller must compensate in the opposite direction. This effect results in the ranging in and/or oscillation conditions.
FIG. 2
illustrates an exemplary graph of the volt
Applied Materials Inc.
Krishnamurthy Ramesh
Mancene Gene
Moser Patterson & Sheridan
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