Patent Application
20080216901
Pressure controllers for processing tools, such as semiconductor processing tools, typically perform pressure control in one or more vacuum chambers in the tool so, in response to measurements of the actual pressure. Currently, analog communication links are used to communicate pressure signals between these pressure controllers and the pressure sensors that actually perform the pressure measurements.
When analog communication links are used to transmit pressure signals, filtering is required at the receiving end of the analog signal. This reduces the bandwidth of the system, which in turn can limit pressure control performance, in particular in vacuum systems with a fast time constant. Noise due to non-ideal grounding can also be a problem when analog signals are exchanged between the pressure sensor and the pressure controller in a pressure control system.
There is a need for pressure control systems and methods that can avoid these adverse effects.
A pressure control system for a tool includes a digital communication network between a pressure sensor and a pressure controller. The digital communication network is configured to communicate signals between the pressure sensor and the pressure controller. The pressure sensor is configured to measure pressure within a vacuum chamber in the tool. The pressure controller is responsive to pressure measurements, made by the pressure sensor and communicated to the pressure controller through the digital communication network, to control the pressure within the vacuum chamber so as to maintain the pressure in the vacuum chamber at a pressure set point received from the tool.
A method of controlling pressure in a vacuum chamber in a tool may include: measuring pressure in the vacuum chamber, receiving from the tool a pressure set point for the vacuum chamber, and communicating the pressure measurement and the pressure set point to a pressure controller through a digital communication network. The method may further include controlling the pressure in the vacuum chamber in response to the received pressure measurement and pressure set point, so as to maintain pressure in the vacuum chamber at the pressure set point.
Systems and methods for vacuum pressure control are disclosed in which a digital communication link is provided between a pressure sensor that makes measurements of pressure, and a pressure controller that controls the pressure to a desired set point in response to these pressure measurements. By using a digital communication link to communicate pressure signals between the pressure sensor and the pressure controller, immunity may be acquired from ground noise that is often present in systems such as semiconductor processing tools, and that would adversely affect pressure control. Further, the effective dynamic range for the pressure measurement and control may be increased.
The digital communication network 150 may be a bi-direction (or two-way) network that enables two-way communication of pressure-related signals and messages between the pressure sensor 130 and the pressure controller 140. Alternatively, the communication network 150 may be a one-way network, in which pressure-related communications may occur along one direction only, while transmissions along the other direction are reserved solely for housekeeping functions such as zeroing and error status.
The pressure sensor 130 measures pressure within one or more vacuum chambers in the tool 120. The pressure sensor 130 may be a capacitance-based pressure transducer, in one embodiment of the present disclosure, although other types of pressure transducers are also within the scope of the present disclosure. For example, the pressure sensor 130 may be a baratron manufactured by MKS Instruments, Inc.
The pressure controller 140 receives from the pressure sensor 130, through the digital communication network 150, signals containing the pressure measurements by the pressure sensor 130. The pressure controller 140 also receives desired pressure set points from the tool 120, typically sent by a tool controller (not shown) within the tool 120. In response to the received pressure measurement signals and pressure set points, the pressure controller 140 controls pressure in the vacuum chamber(s) in the tool 120 so as to maintain the pressure at the desired pressure set points received from the tool 120. Typically, the pressure controller 140 includes a valve that opens and closes so as to control the flow rate of fluid into or out of the vacuum chamber and thereby controlling the pressure in the vacuum chamber.
The digital communication network 150 enables closed loop sensor feedback for pressure control by the system 100. The digital communication network 150 may be a private network, such as CAN (Control Area Network) by way of example. Private digital networks generally allow for highly reliable packet transmission at regular, periodic intervals. It is desirable that the CAN network enable signal communication at an update rate of about 10 msec or higher.
For purposes of the pressure control system 100, it is desirable that the digital communication network 150 be an isolated network that can communicate signals with substantially no interference from any other networks and any other processes going on in these networks. In this way, the digital communication network 150 would be able to deterministically transmit signals that are substantially noise-free.
While an isolated and private digital communication network 150 such as a CAN may be desirable, in some embodiments the digital communication network 150 may include one or more of the following: Ethernet TCP (Transmission Control Protocol)/IP (Internet Protocol); DeviceNet; CAN (Controller Area Network); UDP/IP (User Datagram Protocol/Internet Protocol); RS (Recommended Standard)-232; and RS (Recommended Standard)-485.
The pressure controller 140 may receive control signals (such as the pressure set point) from the tool 120 over a tool level communication link 180. This link 180 may be implemented using systems that may include, but are not limited to: Dnet; RS232; and Ethernet.
Communications between the pressure sensor 130 and the tool 120 may also occur over a separate tool level communication link 170. While
These signals may contain information and/or commands that include, but are not limited to, the following: calibration and/or zeroing of the pressure sensor 130; dynamic range of the pressure sensor 130; and diagnostic information for the pressure control system 100. Diagnostic information may relate to factors that include, but are not limited to: heater temperature of the pressure sensor; shorting of a diaphragm in the pressure sensor 130; internal failure of the pressure sensor 130; cumulative drift of the pressure sensor 130; zeroing range of the pressure sensor; and the exceeding of the full scale range by the pressure sensor 130.
The closed loop sensor feedback system described above may also be configured to support additional sensor input, in addition to supporting input from the pressure sensor 130. For example, the pressure control system 100 may be configured to receive the output from an FRC (flow ratio controller) that provides a flow change feedforward signal to the pressure controller 140.
Signals other than pressure measurement signals, for example diagnostics information described above, could also be communicated between the pressure sensor 130 and the pressure controller 140 through the digital communication network 170, in one embodiment of the present disclosure.
In an embodiment in which the digital communication network is a CAN network, the packet transmission for signals containing pressure measurement, diagnostics, and other information, may occur in one or more ways, as described below.
In one example, the pressure sensor(s) may send out a message to the pressure controller. An exemplary protocol may technically consist of a CAN Group 1 message ID 0, broadcast from the pressure sensors every 10 ms. The message identifier may be an unsigned long, with the lowest six bits being the MacID of the sending pressure sensor (illustrated as 230-1 and 230-2). All other bits, which are unused, may be set to zero. This may produce a group 1 message that should take priority over any normal (group 2) Device net communications if present. This may also assure that the arbitration between the pressure sensor's messages will be handled by a lower level driver without additional work.
In this example, a packet in the message may contain a message ID, a data length of 9, followed by the data itself. The reading in Torr may be represented as a four byte floating point number. The full scale in Torr may be represented as a four byte floating point number. The status may be represented as an eight bit unsigned integer.
The status indicator bits may include, but are not limited to, the following:
0) heater at control temperature;
1) pressure within zeroing range;
2) diaphragm shorted;
3) e-Baratron over 110% of full-scale range;
4) zero adjustment over 20% (further zeroing not allowed);
5) e-Baratron internal failure (for reasons such as heater circuit failure, and power supply out of spec);
6) cumulative drift out of range; and
7) unused at this time.
0 & 1 bits may be required for zeroing.
DeviceNet drivers at the pressure control valve may be modified to disable normal MacID filtering. Messages that don't have the valve's MacID may normally be dropped when received. In this example, messages with other MacIDs are readings from the baratrons. The MacIDs are used to determine which pressure sensor is the high range channel and which is the low. Messages with unused MacIDs are dropped. For example, defaults at the valve may be MacID 1 for low channel, and MacID 2 for high channel. These values can be changed in the valve and on the pressure sensors.
Data may be read on the pressure control valve and used instead of reading the ADC (analog-to-digital converter). The ADC calibration data may be used to convert Torr pressure/range readings into simulated ADC raw counts.
The full scale range may be updated automatically if the valve's range for a transducer does not match the contents of a packet. The crossover point may also be adjusted appropriately.
In another situation, a message may be generated by a valve in the pressure controller 140, for example to initiate zeroing of one or more of the pressure sensors. The message identifier may be an unsigned long, with the lowest six bits being the commanded baratron's MacID. Bit 6 may be set to 1 but all other (unused) bits may be set to zero. This produces a group 1 message ID 1. The pressure sensor with the MacID that matches the message may do a zero. A default target value of 0% may be provided even if a traditional zero (0% assumed) is needed.
In this example, the message packets may contain a message ID, a data length of 4, then the data itself. The zero target may be represented in percent of full scale as a four byte floating point number.
In the above example, commands to be added to the baratron's interface may include, but are not limited to:
Enter digital baratron mode;
Get/Set MacID of baratron;
Commands to be added to the control valve's serial interface may include, but are not limited to:
Enter digital baratron mode;
Get/Set MacID of high or low channel pressure sensor;
Report status of high or low channel pressure sensor; and
Execute zero on high or low channel pressure sensor with or without a target.
In sum, systems and methods have been described in which a digital communication link is provided between one or more pressure sensors and a pressure controller, so that noise-free and high dynamic range signals are provided between the pressure sensors and the pressure controller, at an update rate of 10 msec or higher. The digital communication link allows improved pressure control stability and dynamic range.
While certain embodiments have been described of systems and methods for controlling pressure in the vacuum processing system, it is to be understood that the concepts implicit in these embodiments may be used in other embodiments as well. The protection of this application is limited solely to the claims that now follow.
In these claims, reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference, and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public, regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
