GB2419957A

GB2419957A - Mass flow controller with embedded web server

Info

Publication number: GB2419957A
Application number: GB0526343A
Authority: GB
Inventors: Ali Shajii; Nicholas Kottenstette; Jesse Ambrosina; John A Smith
Original assignee: MKS Instruments Inc
Current assignee: MKS Instruments Inc
Priority date: 2002-06-24
Filing date: 2003-06-24
Publication date: 2006-05-10
Anticipated expiration: 2023-06-24
Also published as: GB2404028A8; GB2404028B; GB2419422B8; GB0526337D0; GB2419421A; GB2419422A8; GB2419420B8; GB2419420B; GB2419422B; GB2419676A; GB2419422A; GB2419677A; GB2419958B8; GB2419421A8; GB2419420A8; GB0526346D0; GB2404028A; GB2419676A8; GB2419958A; GB2404028B8

Abstract

A mass flow controller 604 comprises a mass flow sensor (202) configured to produce a mass flow signal representative of a gas flow through the mass flow controller 604, an electronic controller (210) and an outlet valve (220). Based on the signal from the mass flow sensor (202), the electronic controller (210) produces a control signal for the outlet valve (220). The electronic controller (210) is also configured to operate as a web server 602 and provides access to the World Wide Web to allow the display of pages related to the operation and configuration of the mass flow controller.

Description

MASS FLOW CONTROLLER

The present invention relates to mass flow sensing and control systems.

Capilla tube thermal mass flow sensors exploit the fact that heat transfer to a fluid flowing in a larnillar tube from the tube walls is a nction of mass flow rate of the fluid, the differejce between the fluid temperature and the wafl temperature and the specific heat of the fluid. Mass flow controllers employ a variety ofnass flow sensor conguratjorjs For example, one type of constructjn involves a stainless steel flow Seflscr tube with one, and more typically two or 1 0 more, resistive elements in thermally conductive contact with the sensor tube, The resistiVe elemejits are typically Composed of a material having a high temperature Coefficient of Jesistance Each of the elements can act as a healer, a detector or both. One or more of the elements is energicd with electrical current to supply heat to the fluid strcaiii t- ough the tube. If the healers are supplied 1 5 with constant current the rate of fluid mass flow tin-ough time tube can be derived fi omim emperatLire differences in the eleiflejits Fluid mass flow rates can also be derived by varying the current tlaougli the heaters to nmaintain a colistant temperatui-e profile.

Such thermal mass flow sensors may be attached as a i of a mass flow contj oiler, with fluid from the controller's main channel feeding the capillary tube (also referred to herein as the sensor tube). The portion of the main channel to which the inlet and outlet of the sensor tube arc aaciicd is ofien referred to as the "bypass" of the flow Sensor. Many applications employ a plurality of mass flow Controllers to relate the supply of fluid tlough a supply line, and a plurality of the supply lines may he "tapped off' a main fluid supply line. A sudden change in flow to one of the controllers may create pressure fluctuations at the inlet to one or more of the other controllers tapped off time main supply line. Such pressure fluctuations create differences beteen the flow rate at the inlet and outlet of an affected mass flow controller Because thermal mass flow sensors measure flow at the inlet of a. mass flow controller, but puLlet flow from the controller is the critical parameter for process control, such inlet/oiitlet flow' discrepancies can lead to significant process control errors.

In a semiconductor processing application, a process tool may include a plurality of chambers with each chamber having one or more mass flow controllers controlling the flow of gas into the chamber. Each of the mass flow controllers is typically re-calibrated evei-y two weeks. The recalibration process is described, for example, in U.S. Patent 6,332,348 Bi, issued to Yelveion et aL December 25, 2001, which is hereby incorporated by reference. In the course of such an "In Situ" calibration coflventjoia! methods require a technician to connect a mass flow meter in line with each of the mass flow controllers, flow gas through the mass flow meter and mass flow controller, compare the mass flow controller reading to that of the mass flow meter and adjust calibration constants, as necessary. Such painstaking operations can Iequire a great deal of time aiid, due to labor costs and the unavailability of process tools, with which the mass flow corilrollej-s operaLe, can he very costly.

A mass flow sensor that substantially eliminates sensitivity to pressure variations would therefore be highly desirable. A convenient calibration method and apparatus for mass flow controllers would also be highly desirable. More flexible access to a mass flow controller would also he highly desirable.

Apparatus and method for increasing the control performance of a mass flow controller would also be highly desirable.

Summary of the Invention

According to the present invention there is provided a mass flow controller and a system, defining a flow path heeen a gas inlet and an outlet of the system as set forth in the appended claims.

Brif Description of Drawings

Figure 1 is a block diagram of a system that includes a mass flow sensor; Figure 2 is a sectional view of a mass flow controller that employs a mass flow sensor.

Figure 3 is a sectional view of an illustrative themial mass flow sensor as used in conjunction with a pressure sensor to produce a compensated indication of mass flow through a mass flow controller; Figure 4 is a block diagram of the control electronics employed by an illustrative embodiment of a mass flow sensor.

Figure 5 is a flow chad of the process of compensating a thermal mass flow sensor signal.

Figure 6 is a conceptual block diagram of a web-enabled mass flow controller.

Figure 7 is a conceptual block diagram of calibrator such as may be employed with a mass flow controller.

Figure 8 is a block diagram of a self-calibrating mass flow controller.

Figure 9 is a graphical representation of flow and pressure curves corresponding to the process of calibrating a mass flow controller.

Figure 1 0 is a conceptual block diagram of a dual processor configuration such as may be used in a mass flow controller.

Figure 11 is a flow chart of the general operation of a mass flow controller's non- deterministic processor.

Figures 12A and 12B are flow charts of the general operation of a mass flow controller's deterministic processor, and Figures 1 3A through 1 3E are screen shots of web pages such as may he employed by a web server embedded within a mass flow controller.

Detailed Description of Disclosure

A mass flow sensor employs a thermal mass flow sensor to sense and provide a measure of the flow of fluid into an inlet of a fluid flow device, such as a mass flow controller. The mass flow sensor uses a pressure sensor to compensate the inlet flow measure provided by the thermal mass flow sensor to thereby provide an indicator that more accurately reflects the fluid flow at the outlet of the associated mass flow controller.

A system 100 that benefits from and includes the use of a mass flow sensor is shown in the illustrative block diagram of Figure 1.

A plurality of mass flow controllers MFC1, MFC2, ... MFCn receive gas from main gas supply lines 102, 103. The mass flow controllers, MFCI, MFC2 MFCn are respectively connected through inlet supply lines 1 04, 106, .. 109 to a main gas supply line 102, 103 and through respective outlet supply lines 110, 112, . . .115 to chambers Cl, C2, Cii. In this illustrative embodiment the term "chamber" is used in a broad sense, and each of the chambers may be used for any of a variety of applications, including, hut not limited to, reactions involved in the production of semiconductor components. Generally, users of the chambers are interested in knowing and controlling the amount of each gas supplied to each of the chambers Cl, C2, ...Cn. Each chamber Cl, C2, ... Cn may also include one or more additional inlet lines for the supply of another type of gas. Outflow from the chambers may be routed through lines (not shown) for recycling or disposal.

The mass flow controllers, MFC1, MFC2,. . .MFCn, include respective mass flow sensors MFS1, MFS2, . . .MFSn, electronic controllers Ed, EC2, . . . Ecn and outlet control valves OCV1, OCV2, .. .OCVn. At least one of the mass flow sensors is, and, for ease of description, assume all are, compensated mass flow sensors. Each mass flow sensor senses the mass of gas flowing into the mass flow controller and provides a signal indicative of the sensed value to a corresponding electronic controller. The electronic controller compares the indication of mass flow as indicated by the sensed value provided b the mass flow sensor to a set point and operates the outlet control valve to minimize any difference between the set point and the sensed value provided by the mass flow sensor.

Typically, the set point may be entered manually, at the mass flow controller, or downloaded to the mass flow controller. The set point may be adjusted, as warranted, through the interventjoii of a human operator or automatic control system. Each of the inlet supply lines 104, 106, . . 109 may be of a different gauge, and/or may handle any of a variety of flow rates into the mass flow controller. A single electronic controller, such as electronic controller Ed, may he linked to and operate a plurality of mass flow sensor/outlet control valve combinations. That is, for example, any number of the illustrated electronic controllers EC2 through Ecn may be eliminated with the corresponding mass flow sensors and outlet control valves linked to the electronic controller EC 1 for operation.

An abrupt change of flow rate, due to a change in set point for example, into any of the mass flow controllers may he reflected as an abrupt pressure change at the inlet of one or more of the other mass flow controllers. This unwanted side effect may he more pronounced in a relatively low flow rate mass flow controller if the abrupt change occurs in a high flow-rate mass flow controller. Because the mass flow sensors in this illustrative embodiment are thermal mass flow sensors positioned to sense flow in the mass flow controller at the inlet to the mass flow controller, the mass flow sensed by the thermal mass flow sensor may not accurately reflect the flow at the outlet of the controller. In order to compensate for this discrepancy, a mass flow sensor includes a pressure sensor positioned to provide an indication of the pressure within the volume between the inlet and outlet of the mass flow controller. In an illustrative embodiment, the pressure sensor is located in the "dead volume" between the thermal mass flow sensor's bypass and the outlet control valve. An thctroic controller employs the indication of pressure provided by the pressure sensor to compensate the measure of mass flow provided by the thermal mass flow sensor.

The resultant, a compensa mass flow indication, more accurately reflects the flow at the outlet of the mn flow controller and, consequently, this indication may be employed to advantage by a mass flow controller in the operation of its outlet control valve. A display may be included to display the sensed pressure. The display may be local, attached to or supported by the mass flow controller, or it may be remote at a gas box control panel, for example, connected to the mass flow controller through a data link.

In a semiconductor processing application, a process tool may include a plurality of chambers with each chamber having a plurality of mass flow controllers respectively controlling the flow of constituent gases into the chamber. Each of the mass flow controllers is typically re-calibrated every two weeks. Thc re-calibration process is dcscribed, for example, in US Patent 6,332,348 Dl, issued to Yelverton et al. December 25, 2001, which is hereby incorporated by reference. In the course of such an "In Situ" calibration, conventional methods require a technician to connect a mass flow meter in line with each of the mass flow controllers, flow gas through the mass flow meter and mass flow controller, compare the mass flow controller reading to that of the mass flow meter and adjust calibration constants, as necessary. Such painstaking operations can require a great deal of time and, due to labour costs and the unavailability of process tools with which the mass flow controllers operate, can be very costly. In an illustrative embodiment described in greater detail in the discussion related to Figure 7, a mass flow controller includes a self-calibrating mechanism that substantially eliminates such tedious and costly chores.

The sectional view of Figure 2 provides an illustration of a mass flow controller 200 that employs a mass flow sensor 202. The mass flow sensor 202 includes a thennal mass flow sensor 204, a pressure sensor 206, a temperature sensor 208 and an electronic controller 210. A laminar flow element 212 establishes a pressure drop across the capillary tube of the thermal mass flow sensor 204, as will be described in greater detail in the discussion related to Figure 3. In operation, a fluid that is introduced to the mass flow controller 200 through the inlet 214 proceeds through the bypass channel 216 containing the laminar flow element 212. A relatively small amount of the fluid is diverted through the thermal mass flow sensor 204 and re-enters the bypass channel 216 downstream of the laminar flow element 212. The electronic controller 210 provides a signal to the control valve actuator 218 to thereby operate the outlet control valve 220 in a way that provides a controlled mass flow of fluid to the outlet 222. The pressure sensor 206 senses the pressure within the volume within the bypass channel 216 between the laminar flow element 212 and the outlet control valve 220, refen-ed to herein as the "dead volume 216a".

As will be described in greater detail in the discussion related to Figure 5, the electronic controller 210 employs the pressure sensed within the dead volume 216a by the sensor 206 1 5 to compensate the inlet flow rate sensed by the thermal mass flow sensor 204. This conipciisated inlet flow rate figure more closely reflects the outlet flow rate, which is the ultimate target of control. In particular, a mass flow sensor is a combination sensor that employs the time rate of change of pressure within a known volume 216a to provide a precise measure of mass flow during pressure transients and a thermal mass flow sensor that may be "corrected" using the pressure-derived mass flow measurement. Both the thermally.sensed and pressure derived mass flow measurements are available for processing. The temperature sensor 208 senses the temperature of the fluid within the dead volume. In an illustrative embodimeiit the temperature sensor 208 senses the temperature of a wall of the controller, as an approximation of the temperature of the fluid within the dead volume 216a.

The volume 216a of the dead volume is determined, during manufacturing or a calibration process, for example, and may be stored or downloaded for use by the electronic controller 210. By taking sequential readings from the pressure sensor output 206 and operating on that data, the electronic controller 210 determines the time rate of change of pressure within the dead volume 216a. Given the dead volume, the temperature of the fluid within the dead volume, the input flow rate sensed by the thermal tnsss flow sensor 204, and the time rate of change of pressure within the dead volume, the elecironic controller 210 approximates the fluid flow rate at the output 222 of the mass flow controller 200. As previously noted, this approximation may also be viewed as compensating thc mass flow rate figure produced by the thermal mass flow sensor 204.

The electronic controller 210 employs this computed output fluid flow rate in a closed loop control system to control the opening of the mass flow controller outlet control valve 220.

In an illustrative embodiment, the value of the pressure sensed by the pressure sensor 206 may also be displayed locally, (that is, at the pressure sensor) and/or remotely (at a control panel or through a network interface, for example). In a self-calibrating process described hereinafter in the discussion related to Figure 7, the electronic controller 210 may take the time derivative of the pressure signal when the flowrate varies in the mass flow controller and thereby derive the actual flow rate into the mass flow controller.

The actual flow rate may then he used to calibrate the mass flow controller.

The sectional view of Figure 3 provides a more detailed view of a thermal mass flow sensor 204, such as may be employed in conjunction with a pressure sensor to produce a compensated mass flow indication that is, in a digital implementation a multi-bit digital value. The multi-bit digital value provides a closer approxirnatjoj to the actual mass flow at the outlet of a mass flow controller than an uncompensated mass flow sensor would, particularly during pressure transients on the mass flow controller inlet lines. The thermal mass flow sensor 204 includes laminar flow element 212, which rests within the bypass channel 216 and provides a pressure drop across the bypass channel 216 for the thermal mass flow sensor 204 and drives a portion of the gas through the sensor capillary tube 320 of the thermal mass flow sensor 204. The mass flow sensor 202 includes circuitry that senses the rate of flow of gas through the controller and controls operation of the control valve 220 accordingly. The thermal niass flow sensor assembly 204 is attached to a waIl 322 of the mass flow controller 200 that forms a boundary of the bypass channel 216 Input 324 and output 326 apertures in the wall 322 provide access to the thermal mass flow sensor assembly 204 for a gas travelling through the thermal mass flow controller and it is the portion of this passageway between the input and output that typically defines the bypass channel. In this illustrative embodiment the mass flow sensor assembly 204 includes a baseplate 328 for attachment to the wall 322. The baseplate 328 may de attached to the wall arid to the remainder of the sensor assembly using threaded hole and mating bolt combinations, for example.

Input 330 and output 332 legs of the sensor tube 320 ettend through respective input 334 and output 336 apertures of the baseplate 328 and, through apertures 324 and 326, the mass flow controller wall 322.

The mass flow sensor assembly preferably includes top 338 and bortom 340 sections that, when joined form a thermal clamp 341 that holds both ends of the sensor tube 320 active area (that is, the area defined by the extremes of resistive elements in thermal contact with the sensor tube) at substantially the Same temperature. The thermal clamp also forms a chamber 342 around the active area of the Sensor tube 320. That is, the segment of the mass flow sensor tube within th chamber 342 is in thermal communication with two or more resistive elements 344, 346, each of which may act as a heater, a detector, or both One or more of the elemejits is energized with electrical current to supply heat to the fluid as it streams thiougli the tube 320. The thermal clamp 341, which is typically fabricated from a material characterized by a high thermal conductivity relative to the thermal conductivity of the sensor tube, makes good thermally conductive contact with the portion of the sensor tube just downstream ftoni the resistive element 344 and with the portion of the sensor tube just upstream from the resistive element 346. The thermal clamp thereby encloses and protects the resistive element 344 and 346 and the sensor tube 320. Additionally, the thermal clamp 341 thermally "anchors' those portions of the sensor tube with which it makes contact at, or near, the ambient temperature. in order to eliminate even minute errors due to teinperatiii-e difièrertjajs, the sensui tube may be moved within the thermal clamp to insure that any difference between the resistance of the two coils is due to fluid flow through the sensor tube, not to temperature gradients imposed upon the coils from the environment.

In this illustrative embodinjent each of the resistive elements 344 and 346 includes a thermally sensitive resistive conductor that is wound around a respective portion of the Sensor tube 320. Each of the resistive elements extends along respetive portions of the sensor tube 320 along an axis defined by the operational segment of the sensor tube 320 Downstream resistive element 346 is disposed downstream of the resistive element 344 The elements abut one another or are separated by a small gap for manufacturing convenience and are preferably electrically connected at the center of the tube. Each resistive element 344,346 provides an electrical resistance that varies as a function of its temperature. The temperature of each resistive element varies as a function of the electrical current S flowing tIough its resistive conductor and the mass flow rate within the sensor tube 320. In this way, each of the resistive elements operates as both a heater and a sensor. That is, the element acts as a heater that generates heat as a frmnction of the current through the element and, at the same time, the element acts as a sensor, allowing the temperature of the element to be measured as a ftmnction of JO its electrical resistance The thermal mass flow sensoi 204 may employ any of a variety of electronic circuits, typically in a Wheatstone bridge arrangement, to apply energy to the resistive elements 346 and 344, to measure the temperature dependent resistance changes in the element and, thereby, the mass flow rate of fluid passing through the sensor tube 320. Circuits employed for this purpose are disclosed, for example, in U.S. Patent 5,461,913, issued to FIiide et al and U.S. Patent 5,410,912 issued to Suzuki, both of which are hereby incorporated by reference in their entirety In operation, fluid Flows from the inlet 214 to the outlet 222 and a portion of the fluid flows through the restrictive laminar flow element 212. The remaining and propoijona1 amount of fluid flows through the sensor tube 320.

The circuif (not shown here) causes an electrical current to flow through the resistive elements 344 and 346 so that the resistive elements 344 and 346 generate and apply heat to the sensor tube 320 and, thereby, to the fluid flowing through the sensor tube 320. Because the upstream resistive element 346 transfers heat to the fluid befci-e the fluid reaches the portion of the sensor tube 320 enclosed by the downstream resistive element 344, the fluid conducts more heat awa.y from the upsti earn resistive element 346 than it does from the downstream resistive clement 344. The differejce in the amount of heat conducted away from the two resistive elements is proportional to the mass flow rate of fluid within the sensor tube and, by extension, the total mass flow rate through the mass flow rate controller 200 from the input port 214 through the output port 222. The circuit measures this difference by sensing the respective electrical resistances of resistive elements 344,346 and generates an output signal that is representative of the mass flow rate through the sensor tube 320.

The conceptual block diagram of Figure 4 illustrates the architecture of an electronic controller 400 such as may be used in a mass flow sensor. In this illustrative embodiment, the controller 400 includes sensor 402 and actuator 404 interface. Among the sensor interfaces 402, a flow sensor interface 408 operates in conjunction with a mass flow sensor to produce a digital representation of the rate of mass flow into an associated mass flow controller. The controller 400 may include various other sensor interfaces, such as a pressure sensor interface 410 or a temperature sensor interface 411. One or more actuator drivers 412 are employed by the controller 400 to control, for example, the opening of an associated mass flOW controller's output control valve. The actuator may be any type of actuator, such as, 1 5 for example, a current-driven solenoid or a voltage-driven piezoelectric actuator.

The controller 400 operates in conjunction with a mass flow controller to produce a digital representation of the rate of mass flow into an associated mass flow controller. A thermal mass flow controller, such as described in the discussion related to Figure 3, i-nay be employed to produce the mass flow nieasuieineut. The controller 400 i-nay employ a pressure sensor interface 410 to monitor the pi-essure of fluid within an associated mass flow controller In an illustrative embodiment, a pressure sensor, such as the pressure sensor 206 of Figure 2, provides a measure of the pressure within the mass flow controller.

More specifically, in this illustrative embodiment, the semisor measures the pressure within dead volume of the mass flow controller. In an illustrative embodiment, the mass flow ontroller pressure thus measured may be displayed, at the pressure sensor 206 or at the controller housing, for example, or some other location.

The controller 400 may convert the pressure measurement to digital form and employ it in analysis or other functions For example, if the mass flow controller employs a thermal mass flow sensor, the controller 400 may use the mass flow controller pressure rneasur?ement to compensate for inlet pressure transiet though a temperature sensor inteace may be used to obtain a temperature reading from a ternperElture sensor aachd, for example, to the wall of a mass flow controller a separate temperature sensor may not be required for each mass flow controller For example, mass flow controllers are oflen employed as described in greater detail in the discussion related to Fire 1, in 1 0 conjunction with a semiconductor processing tool that includes a number of mass flow controllers and other devices that are all linked to a controller such as a workstation The processing tool is operated within a carefiully controlled enviroflmeiit that features a relatively stable temperature. Because the temperafjre of the fluid within the mass flow controller is very iiearly equal to 1 5 that of the wall of the enclosure and the wall of the enclosure is very nearly the temperai ure of the room within which the tool is housed, a temperature meas1re1eit fi-orn, for example the workstation that controls the tool, may provide a sufficient]y accurate estimate of the gas temperature within the mass flow controller Consequently in addition to, or instead of, employing a separate temperature sensor on each mass flow controller, the temperature may be obtained from another seijs within the same environment as the mass flow controljei- one located at a workstation for example.

The Controller 400 includes a local user inteace 416 that may be used with one or more input devices such as a keypad, keyboard, mouse, trackball, joy stick, buttons touch screei.s, dual inline packaged (Dif') or thumb-wheel switches, for example, to accept input from users, such as technicians who operate a mass flow controller The local user interface 414 may also include one or more outputs suitable for driving one or more devices, such as a display, which may be an indicator light, a character alphanumeric or apliic display, or an audio ol.Jtpijt device used to comrnL11jcate informatj0 From a mass flow contloller to a user, for example. A communications interface 416 permits a mass flow controller to communicate with one or more other instruments, and/or with a local controller, such as a workstation that controls a tool that employs a plurality of mass flow controllers and/or other devices in the production of integrated circuits, for example.

In this illustrative example, the communications interface 414 includes a DeviceNet interface. DevjceNet is known and discussed, for example, in U. S. Patent No. 6,343,617 Bi issued to Tinsley et a!. February 5, 2002, which is hereby incorporated by reference. The controller 400 also includes storage 418 in the form, for example, of electrically erasable programmable read only memory (BEPROM) that may be used to store calibration data, mass flow controller identification, or code for operating the mass flow controller, for example.

Various other forms of storage, such as random access memory (RAM), may he employed. The storage can take many forms, and, for example, may be distributed, with portions physically located on a controller "chip" (integrated circuit) aiicl other portions located off-chip. The controller 400 employs a data processor 420, which rnighl. take the form of an arithmetic logic unit (ALU) in a general lurpose microprocessor for example, to reduce data, For example, the data processor 420 may average readings received at the sensor inputs, determine the number of times a sensor reading has exceeded one or more threshold values, recoi cl the time a sensor reading remains beyond a tin eslioid value, uf pifui i other forms of data logging.

PFessure transients on the inlet supply line to a mass flow controller 200 that employs a thermal mass flow sensor 204 may create erroneous mass flow readings, Erroneous mass flow readings may lead, in turn, to improper control of a mass flow Controllers outlet valve, which could damage ordestroy articles being processed with gasses under control of the mass flow controller. The digital representation of mass flow may take the forni of one or more data values and is subject to fluctuations due to Pressure transients on the inlet line of the mass flow sensor. L an illustrative embodiment the controller 400 employs data obtained at the pressure sensor interface 410 to compensate for fluctuations induced in a thermal mass flow sensor 204 by pressure transients on the mass flow sensor inlet line 214. In this illustrative embodiment, the controller 400 obtains temperature information through a temperature interface 411. The controller 400 employs the temperature, pressure, and mass flow readings obtained from the respective interfaces, to produce a compensated mass flow reading that more closely reflects the mass flow at the outlet of the mass flow sensor than a reading from the thermal mass flow sensor alone provides, The controller 400 also provides control to sensors, as necessary, through flow sensor interface, pressure sensor interface, and temperature interfaces, 408, 410, and 411, respectively.

The controller 400 also includes a valve actuator interface 404, which the controller 400 employs to control the position of a valve, such as the valve 220 of Figure 2, to thereby control the rate of fluid flow through a mass flow controller, such as the mass flow controller 200, in a closed -loop control process. The valve 1 5 actuator may he a solenoid-driven actuator or peizo-electric actuator, for example. The controller 400 must be capable of operating with sufficient speed to read the various sensor outputs, compensate as necessary, and adjust' the mass flow controller outlet control valve 220 to produce a predetermined flow rate.

The flow rate is Predetermined in the sense that it is "desired" in some sense. [t is not predetermined in the sense that it must he a static setting. That is, the predetermined flow rate may he sct by an operator using a mechanical means, such as a dial setting, or may be downloaded from another controller, such as a workstation, for example, and may be updated.

In an illustrative embodiment the controller 400 employs readings Doom the pressure interface 410 to compensate flow measurements obtained at the mass flow interface 408 fi'oni thermal mass flow sensor 204 that senses mass flow at the inlet 214 to mass flow controller 200. The compensated flow measurement more accurately depicts the flow at the outlet 222 of the mass flow controller 200.

This outlet flow is the flow being directly controlled by the mass flow controller 200 and typically is the flow of interest to end users. Employing a pressure- compensated flow measurement in accordance with the principles of the present invention imprdves the accuracy of a mass flow sensor's outlet flow reading and thereby permits a mass flow controller to more accurately control the flow of fluids. That is, at equilibrium mass flow at a mass flow controller's inlet is equal to the mass flow at the outlet of the mass flow controller, but during inlet or outlet pressure transients, the flow rates differ, sometimes significantly. As a result, a mass flow controller that provides closed loop control using its inlet flow to control its outlet flow may commit substantial control errors.

The steady state mass flow in the capillary sensor tube 320 of a thermal mass flow sensor such as described in the discussion related to Figure 3 is generally described by the following equation: d2P(pp 32i R wh eie: dc capillary Lube inside diameter Lc = capillary tube length pi == the density of the gas at the inlet pR = the density othe gas at standard temperature and pressure = the gas viscosity Pi = the pressure at the inlet of the mass flow controller Po The pressure at the outlet of the mass flow controller P the pressure in the dead volume of the mass flow controller The total flow through the mass flow controller is related to that through the capillary sensor tube 320 through a split ratio: a QBP/Qc where QBP is the flow tlIbugh the bypass channel 216 and Qc is the flow through the capillary tube 320. The total flow Q at the mass flow Qcontroller inlet 214 is: Qi = QBP +Qc = (1+ a)Qc If flow remains laminar in both the bypass and capillary, the split ratio will remain constant. When the inlet pressure varies with time, the nature of the inlet pressure transient and the pressurization of the dead volume govern the flow at the inlet. Assuming that all thermodynamic events within the dead volume occur at a constant temperatui-e that is equal to the temperature of the enclosure that forms a l)a.rtial receptacle around the dead volume, the mass conservation within the dead volume may be described by: Q (i dt Where.

PR = pressure at standard temperature and pressure (760 Turr.) iS TR = temperature at statidaid temperature and pressure (273 K) Tw = wall temperature (temperature of the wall of the mass flow controller) V = volume of the dead volume = inlet; flow to the mass flow controller = outlet flow from the mass flow controller A. mass flow sensor employs the relationship of equation (2) to compensate a thermal mass flow sensor's mass flow signal and to thereby substantially reduce errors in mass flow readings during pressure transients.

The flow chart of Figure 5 depicts the process of compensating a thermal mass flow sensor reading.

The process begins in step 500 and proceeds from there to step 502 where a mass flow sensor's controller, such as the controller 400 of Figure 4, obtains a mass flow reading. This reading may be obtaincd from a thermal mass flow sensor through a flow interface, such as interface 408 of Figure 4, for example.

This flow measurement reflects the rate of mass flow at the inlet of a mass flow controller and, as previously described, may not adequately represent the mass flow rate at the outlet of the mass flow controller. The mass flow rate at the outlet of a mass flow controller is generally the rate of interest for use in control applications. Consequently, a mass flow controller compensates for the 1 0 inaccuracy inherent in assuming that the inlet flow rate to a mass flow controller is equal to the outlet flow rate from the mass flow controller. From step 502 the process proceeds to step 504 where the sensor controller 400 obtains the temperature of the flow within the bypass channel. The temperature could be obtained through a temperature interface such as interface 412 of Figure 4, or it 1 5 may be downloaded to the compensated mass flow sensor. The compensation process may safely assume that the gas temperature is equal the temperature of the enclosure of the mass flow controller. Additionally, in most applications, the temperature will remain relatively stable over a long period of time, so that a stored temperature value may be employed, with updates as necessary.

Afier c'hiaining tile gas temperature in step 504 the process proceeds to step 506 where the sensor controller obtains the volume of the dead volume. This value may have been stored during manufacturing, for example. From step 506 tile process proceeds to step 508 where the pressure within the dead volume is obtained over a period of time. The number of measurements and the time over which the measurements are made depend upon tile speed and duration of transients at the inlet of the mass flow controller. In step 510 the processor employs the pressure measurements made in step 508 to compute the time rate of change of pressure within the dead volume, After computing the time rate of change of pressure within the dead volume, the process proceeds to step 512 where a compeilsated outlet flow value is computed according to equation (2).

S Simpljficatjons may be made in the computational process. For example, the volume of the dead volume, standd temperature, and standard pressure may all be combined into a single constant for use with the inlet flow measurement and time rate of change of pressure within the dead volume to compute a / compensated outlet flow approxjnrntjon This simplification would yield an equation of the form: Qo = Qi - C1(V/f)(dP/dt) (3) Where: Qo = the compensated sensed outlet flow rate, Qi = the sensed inlet flow rate, Cl = a normalizing constajit relating the temperature and pressure to standard temperature and pres sure 1 5 V the volume between the Sensor bypass and the outlet flow control valve, T the temperature of the fluid within the volume, dP/dt time rate of change of pressure within the volume.

As previously noted, the volume V could be folded into the constant (:1.

From step 512 the process proceeds to step 514 where it continues, with the flow sensofs controller obtaining pressure temperature and flow readings and Computing a compensated outlet flow estimate, as described. The process proceeds from step 514 to end in step 5 16, for example, when the mass flow sensor is shut down.

Returning to the block diagram of Figure 4, in this illustrative embodjnent the controller 400 includes a diagnostic interface 422 that peflnjts an operator, such as a teclmician for example, to not only initiate, hut conduct diagnostic tests on the mass flew controller Fuherjnore the inteiface 422 permits the operator to conduct the diagnostics in a manner that requires no input from the local system controlier which may be a workstation, thai otheise normally controls the mass flow controller Such diagnostics are transparent to the local system controller which may not even be made aware of the diagnostics being performed and may, consequently continue its operations unabated, The diagnostic interface provides access to mass flow controller sensor measurements, control outputs and mass flow controller diagnostic inputs and outputs. These various inputs and outputs may be exercised and measured through the diagnostic interface with very little delay. In an illustrative dual- processor ernbodjnjeit described in greater detail in the description related to the discussion of FigLLi'e9 a deterministic processor may modify outputs and/or monitor inputs, from sensors or test points, for example During the execution of On-line diagnostics the controller continues to execute its process control functions unimpeded while at the same time, the controller may provide real- IS time interaction with a teclmicjan (i e, interactions wherein the delays are imperceptible to a human operator either locally or through a teleCofl]flljjrljcations Connection Using the diagnostic inl.erface 422, an operator can adjust control values, such as the set point, used to deternjie the mass flow controller's operation.

Additionally the operator may modify sensor output values in order to lest the mass flow Controller's response to specified sensor readings. That is, an upeiatur can modify the selisor readings a mass flow controller employs to control the flow of gasses through its outlet valve and, thereby, exercise the controller for diagnostic purposes. 1 Operator may read all sensor and test point inputs as well as inthrrnatjon stored regarding control (stored by the deterministic controller in the dual processor embodiment), read all sensor values, read test point values, read control informnatjo11 such as the desired set point Additionally, the operator may write to control outputs and test points and over-write stored values, such as sensor readings or set point information in order to fully test the controller through the diagnostic port.

In an illustrative embodiment, a mass flow controller may includ a web server. Such a web server may be included within the diagnostic interface, for example. In such an embodiment, the diagnostic interface includes a web-server that pennits the mass flow controller to be used in a system such as illustrated in the block diagram of Figure 6. In such a system, a user, such as a teclrnjcjan, may employ a web-enabled device 600 such as a personal computer, personal digital assistant, or cellular telephone that runs a web Browser (e.g. Netscape (RTM) or Explorer (RTM) to communicate with a server 602 embedded in the mass flow controller 604. The server 602 includes web pages that provide an interface for the user to the mass flow controller 604. The discussion related to Figures l3A through l3E provide greater detail related to the web server capability embedded in an illustrative embodiment of a mass flow controller Mass flow sensors are typically calibrated during their manufactung proce Because a mass flow sensor is usually incorporated into a mass flow Controller, this cliscus501l will center on mass flow controllers hut the methods and apparatus discussed herein are applicable to "standalone' mass flow sensors as well. The calibration process recjuii-es a technician to supply a gas at a known flow rate to the mass flow controller and correlale the mass flow sensor's flow igna1 to the known flow rate. For cxanlp!e in the case of a mass flow sensor that provides a voltage output coIrespondiig to flow, the technician maps the voltage output from the sensor into the actual flow rate. Tls process may be repeated for a plurality of flows in order to develop a set of voltage/flow correlations: for example, a 4Volt output indicates a 10 standard cubic centimeter per minute (50cm) flow, a 5 Volt output indicates a 50 sccm flow, etc. Flow rates that fall between calibration points may he interpolated using linear or polynomial interpretation techniques for example. This process may be repeated for several gases, Correlatioji tables that relate the signal from the mass flow sensor (which may be a voltage) to flow rates for various gases may thus be developed and stored. Such tables may be downloaded to a mass flow controller for use in the field", or may be stored within a mass flow controller, Often, technicians calibrate a mass flow controller using a relatively innocuous gas, such as N2, and provide calibration coefficients that may be used to correlate the flow of another gas to the calibration gas. These calibration coefficients may then be used in the field when a known gas is flowed" through the mass flow controller to compute the actual flow from the apparent flow. That is, the apparent flow may be a flow correlated to N2 and, if sine gas is sent through the mass flow controller the mass flow controller multiplies the apparent flow by an Arsine gas 1 0 calibration coefficient to obtain the actual flow. Additionally, once in the field, mass flow controllers may be re-calibrated on a regular basis to accommodate "drift", orientation, water coneiit of a gas the flow of which is being controlled, or to compensate for other factors. U S. Patent 6,332, 348 B1, issued on December 25, 2001 to Yelvertoii et al, which is hereby incorporated by reference, discusses these factors, and the unwieldy processes and equipment required to carry out these in-the-field calibrations in greater detail.

A calibration method and apparatus will he described in the discussion related to the conceptual block diaam of Figure 7. This calibration system and method may he employed in a manufacturing setting, or, in an illustrative embodiment, may be incorporated into a self-calibrating mass flow controller. The mass flow controller 700 includes a mass flow sensor 702 and an electronic controller 704 that receives a flow signal from the mass flow sensor 702. A calibrator 706 includes a variable flow gas source 708, a receptacle of predetermined volume 710, and a pressure differentiator 712. It should he noted that the lines separating different functional blocks are somewhat fluid. That is, in different embodiments, the function associated with one block may be subsumed by one or more other blocks. For example, in an Illustrative embodiment, the pressure differentiator 712 is implemented all, or in part, by the execution of code within the electronic controller 704. The variable flow gas source 708 provides a gas at proportional rates to both the receptacle of predeterinjiied volume and the mass flow sensor.

The flow rate to the mass flow sensor 702 may be equal to the flow rate to the receptacle of predetermined volume 710: i e., a propoftionality constant of 1, for example. The mass flow sensor 702 is configured to produce a mass flow signal indicative of the flow that it senses and, in this illustrative embodiment, this signal is sent to the electronic controller 704, The pressure differentiator 712 produces a signal correlated to the flow from the variable flow source 708 into the receptacle of predeterrniied volume 710 according to the relationship of equation 4: Qo = Qi - Cl (V/T)(dP/dt) (4) where' Qo = the outlet flow rate in standard cubic centimeters per minute, Qi the inlet how rate in standard cubic centimeters per minute, 1 5 Cl = a nornjaIjzjn constant relating the temperature and pressure to standard temperature and pressure V the predetermined volume of the receptacle in liters, T the Kelvin temperature of Ihe fluid within the receptacle dP/dt time rate of change of pressure within the receptacle in Ton/second In an illustrative embodiment, the receptacle is closed and gas flows into the receptacle until the pressure within the receptacle equals that of gas supplied by the variable flow Source 708. in such an illustrative embodiment the variable flow source may be a constant_prescufe source that, as pressure within the receptacle builds, supplies gas at an exponentially decreasing flow I-ate In such a case, the outlet flow Qo 0, and the inlet flow, Qis given by: Qi = Cl(V/T) (dp/dt) (5) The pressure differentjator 712 takes the time derivative of the pressure within the recetacJe 710 and, given the normalizing constant Cl, the predeternijned volume V, and the gas temperature within the receptacle, the differntjator (and/or the electronic controller 704) may determine the actual flow into the receptacle 710. Because the flow into the receptacle is proportional to the flow into the thermal mass flow sensor 702, the actual flow into the thermal mass flow sensor 702 may also be determined by a multiplying the actu flow into the receptacle by a proportionality constant (e.g., the proportionality constant is 1 if the flows are equal). The signal from the mass flow sensor is then correlated, by the electronic controller 704 for example, to the actual flow, determined as just described. Such correlation relates one or more signal levels from the mass flow sensor to the actual flows. The pressure differentjator 712 may include analog differentjator circuitry, for example, that takes the time derivative of the pressure signal. The differentjator output signal, a signal representative of the time 1 5 derivative of the pressure within the receptacle dP/dt, n-lay be sampled by an analog_to_digital converter (not shown) to permit the electronic controller 704, which may include a microprocessor DSP chip, or dual processors, for example to Operate on the time derivative signal. Alternatively, the pI-essure differentiator 712 may COIIVCI-t the pressure signal to digital form for processing by the electronic controller 704, which takes the time derivative of the pressure signal.

In such an enibodjrnent the electronic controller, in combination with diffci-entiator code, operates as the differentjator The controller employs at least two pressure differences divided by corresponding time inteals to compute the derivative. The gas may be supplied in parallel to the receptacle and mass flow sensor, or it may be supplied in series, as will be described in greater detail in the following dISCUSSjOII related to a self-calibrating mass flow controller.

In operation, a mass flow controller may he calibrated as just described, using a plurality of gases, with the correlation values (mappings of sensor output to actual flow) stored in tables Calibration coefficients, relating flow measurements of one gas to another may also be developed and stored. The tables and/or coefficients may be downloaded to a mass flow controller in the field for use by the controller in contol1ing the flow of a gas. Various lown interpolation techniques such as linear or polynomial interpolation may be employed in Conjunction with the calibration tables and/or coefficients. Additionally, such stored calibration tables and/or coefficients may be used as default values in a self-calibrating mass flow controller in accordance with the principles of the present invention A self-calibrating mass flow controller in accordance with the principles of the present invention includes a calibrator 706 and a mass flow Sensor 702 which may be employed to calibrate the mass flow controller in a manner as just described In the case of a self-calibrating mass flow controller, though, the calibratjoii can be performed In Situ, in the field just as readily as in a manufactwjno settjn.

C)nce installed in the field, on a seuiiconducf or processing tool as in the system 100 of Figure 1, for example, the mass flow controller can calibrate itself using the gas that is to be used during the selnicoriductor processing By using the gas that is to he used in processing, the mass flow controller may provide a more accurate how measuremejt, because it will automatically accommodate variations such as moisture content, for example. Additionally a new processing gas may be used just as readily as a convelltjc)nal gas, since the self-calibrating mass flow controller may calibrate itself (that is, correlate mass flow signal levels to actual flow levels determined by the pressure differentiator, on the gas to he used, not in relatioj to another, standard gas, such as N2. Because the mass flow controller is calibrated in the orientEltjon in which it will be used, discrepancies due to reorientation of the mass flow controller in the field relative to the pocitioi in which it was calibrated during manufacturing will be substantially eliminated I the mass flow controllej-s within a system such as system 100 of Figure 1 may be calibrated aul:oiiiatically and simultaneously within moments.

This is in contrast to the cumbersome painstaking process employed for conventional mass flow controllers which are typically individually calibrated by a technician employing multiple mass flow meters, going from mass flow controller to mass flow controller As will be described in greater detail in the description related to the discussion of Figure 8, a mass flow controller that includes a thermal mass flow sensor and a pressure transducer may shut its outlet valve to create a varying gas flow into it's dead volume. By taking the time derivative of the pressure the actual flow into the dead volume receptacle may be determined The mass flow controller's correlation of the actual value of the flow to the thermal mass flow sensor signal acts as the mass flow controller's calibration.

Figure 8 is a conceptual block diagram of a self-calibrating mass flow controller 800. Tn this illustrative, series-flow, embodiment, a gas flows through a thermal sensor 802 into a receptacle of predetermined volume 804, then through an outlet valve 806.

The outlet flow Qo would normally be a controlled flow into a chamber, such as a chall1ber within an integrated circuit processing tool. An electronic controller 808, which, in this illustrative embodiment, executes code to perform the differentiation required to obtain actual flow, as described in the discussion related to Figure 7, is in communication with the thermal sensor 802, pressure sensor of 805 and the outlet valve 806. Tn an illustrative process, the electronic controller 808 operates in conjunction with the outlet valve 806 to form a variable-flow gas supply, That is, the electronic controller shuts the outlet valve, which causes the flow to decrease exporieiilially. The pressure within the dead volume increases, and the electronic controller differentiates this signal a number of times in order to obtain actual flow readings to correlate to the mass flow sensor signal values over a relatively broad range of flows. Additionally, in order to extend the period of time during which the flow is varying and to obtain actual flow values for correlation with the thermal mass flow signal values over a broad range, the electronic controller may open the outlet valve to a flilly open position before closing it.

The pressure and flow profiles associated with such a process are illustrated conceptually in the graph of Figure 9 At an initial time t the pressure difference between gas at the inlet to the mass flow controller Pin and the pressure Pr downstreani in the receptacle 804 forces gas to flow through the mass flow controller at a rate Qin. In this example, the inlet pressure P, pressure within the receptacle PR, ad flow through the input of the mass flow controller Q are constant, At time t0 the controller shuts the outlet valve, thereby reducing outlet flow Qo to zero. Gas continues to flow into the receptacle as long as there is a pressure difference between the receptacle and the iiet. As the pressure P within the receptacle rises exponentially toward an equilibrium state of equality with the inlet pressure Pj, the inlet flow Q decreases. By taking the derivative of the pressure change within the receptacle (also referred to herein as dead volume" in asocjatjoi with an illustrative embodiment of the invention), the electronic controller may determine the actual flow into the receptacle, as previously described The electronic controller may correlate a plurality of simultaneous 1 5 readings produced by the thermal mass flow sensor, to thereby calibrate the mass flow sensor That is, once this process is completed for a specific gas, flow readings from the thermal mass flow sensor may be correlated to actual flow rates. The results may he employed by the electronic controller 808 to control the opening of the valve 806 in a closed loop control system in order to deliver a selected flow downstreaii hi order to increase the period of time t0 from when the controller shuts the valve, to the lime at which the flow becomes undetectable, and to thereby increase the number and precision of pressure measurements that may be made, the controller may open the valve completely before shutting it at time t. Additionally, one or more flow restrictors may be placed in the flow path between the iniet to the thermal mass flow sensor and the inlet to the receptacle $04.

The conceptual block diagram of Figure 1 0 illustrates the architecture of a dual-processor embodiment of an electronic controller 1000 such as may be used in a mass flow sensor in accordance with the principles of the present invention.

In this illusftatj\e embodiment the controller includes two processors 1002, 1004. One of the processors 1002 is dedicated to "real time" processes and the other processor 1004 is dedicated to non-eal time processes. By "real time" we mean processes that require a specified level of service within a bounded response time, In this sense, the processes are deterministic and the processor 1002 will be referred to herein as the deterministic processor. The objective of the dual processor architecture is to reduce the number of interrupts and manage asynchronous event responses in a predictable way. The non-detern-iinistic processor 1004 may handle event-driven interrupts, such as responding to input from a user. The deterministic processor 1002 handles only frame-driven, that is, regularly scheduled, interrupts. In an illustrative embodiment, the nondeterministic processor is a general purpose processor 1 004, suitcd for a variety of tasks, such as user-interface, and other, miscellaneous tasks, rather than a specialized co-processor, such as a math- or communications - coprocessor. In particular, a TMS320VC547] available from Texas instruments, Inc., may he employed in a dual-processor embodiment in accordance with the principles. The TMS320VC5471 is described in a data manual, available at http://www- s.ti.com/sc/ds/tm5320vc5471pdf which is hereby incorporated by reference.

A processor interface 1006 provides for inter-processor communications.

The deterministic processor 1002, includes sensor and actuator interfaces Among the sensor intci-faces a flow sensor inteiface 1005 operates in conjunction with a mass flow sensor to piuduee a digital lepresentation of the rate of mass flow in an associated mass flow controller One or moreactuator interfaces 1010 are employed by the deterministic processor 1002 to control the opening of an associated mass flow controller's output control valve or drive a diagnostic test point, for example. The actuator may be a. current-driven solenoid or a voltage- driven piezo-electrjc actuator, for example. As will be described in greater detail in the discussion related to the flow chart of Figure 9, aer initialization, the deterministic processor 1002 loops through a control sequence, gathering sensor data, gathering setting information (for example, a desired mass flow setting), providing status information, and controlling the state of the outlet valve.

Because non_detemijiijstic tasks are offloaded to the non-deterministic processor 1004, the deterministic processor's control loop may be very compact.

Consequently control tasks may be executed within a minimal period of time and control readings and drive signals may be updated more frequently than posible if time were set aside for seicing non- deterministic tasks.

The controller 1000 operates in conjunction with a thermal mass flow sensor as generally described in the discussion related to Figure 3 to produce a digital representation of the rate of mass flow into an associated mass flow contioller The digital represelltatjon may take the form of one or more data values and is subject to fluctuatjors due to pressure transients at the input of the mass flow sensor. The controller IOOO, and more specifically, the deterministic processor 1002 may employ data obtained at the pressure sensor interface 1006 to compensate fbr fiuctjtjon5 induced in the thermal mass flow sensor by pressure transjeiils on the mass flow sensor inlet line. In this illustrative embodiment the deterministic processor 1002 employs the temperature, pressure, and mass flow readings obtained from the lespectjve I C)08, 1007, and 1005 inteifaces, to produce a compensaled mass flow reading that more closely reflects the mass flow at the outlet of the mass flow sensor than a reading from the thermal mass flow Sensor alone The dcterijijnistjc processor 1002 also provides control to sensors, as neccssaiy through thermal flow 1005, pressume 1007, and temperature 1008 sen,cr,r inteaces Thic Lumpensation process will be described in grealer detail in the discussjoi related to Figure Ii. The deterministic processor 1002 also includes a valve actuator inteace 1010, which the deterministic processor employs to control the position of a valve, such as the valve 220 of Figure 2, 10 thereby control the rate of fluid flow through a mass low controller, such as the mass flow controller 200, in a closed -loop control process.

The deterministic processor 1002 is devoted to the closed-loop valve control process, and, co11sequejt1y must be capable of operating with sufficient speed Ia read the various sensor outputs Compensate as necessary, and adjust the valve to produce a predetermined flow rate. The flow rate is predetermjjed in the sense that it is tdesiredll in sonic sense, and it need not be a static setting. That is, the predetermined flow rate may be set by an perator using a mechanical means, such as a dial setting, or may be downloaded from another controller, such as a workstation for example, and updated frequently. Typically, gas flow control, and in this case, compensated gas flow control, requires relatively high-speed operation. Various types of processors such as reduced instmctjon set math coprocessor, or digital signal processors (DSPs) may be suitable for such high_speed operation The computational, signal conditioning, and inteacing capabilities of a DSP make it particularly suitable for operation as the deterministic processor 1002, As will be described in greater detail in the description of the control process related to the discussion of Figure 9, the function performed by the deterministic processor 1002 is delermin.istic in the sense that certain operations are completed in a timely and regular manner in order to avoid errors, and possible instabilities in the control process. The deterministic 1002 and non-deterministic 1004 processors communicate via the inler-process interface 1006 in a manner that does not inipede the deterministic operatioji of the determjijstjc PrOcessor 1002. Interprocessor comnlunicatjons are discussed in greater detail in the discussion related to Figure 9.

The non-determjiijstjc processor 1004 includes a local user inteace 1016 thut may he used with one 01. more input devices such as a keypad, keyboard, mouse, trackhall, joy stick, buttons, touch screens, dual inline packaged (T)IP) or thumb-wheel switches for example to accept input from users, such as technicians who operate a mass flow controller associated with the non- dletcrn1jnjstic processor 1004 The local user inteace 1016 also includes one or more outputs suitable for driving one or more devices, such as a display, which may he a character, alphanumeric or graphic display, for example, indicator light, or audio output device used to communicate information from a mass flow controller to a user. A Colni mnicatjojs inteace 1018 permits a mass flow controller to communicate with one or more other instiments and/or with a local controller such as a workstatioi that controls a tool that employs a plurality of mass flow controllers and/or other devices in, the productioi of integrated circuits, for example, In this illustrative example, the cornmucations interface 1018 includes a DevjceNet interface, A diagnostic interface 1020 provides an interface for a te1rnician to n diagnostics as previously described in relation to the diagnostic interface 422 of Figure 4. In an illustrative embodiment, the diagnostic interface includes an Ethernet inteace and a web server.

The compactness of code for the deterministic processor 1002 permits the deterministic processor to be highly responsive to input changes and to quickly modify actuator signals in response to those changes. This partitioning of operations between deterministic and non-determiristic processors also eases the initial development of code, for both the deterministic and non-deterministic processors, For example, the deterjijnistjc code needn't respond to unscheduled events, such as "mirroring" a user's requests on a display at a user interface, and the nofl-detciinjiistjc code needn't break away from providing such user feedback 1 5 in order to adjust an outlet valve control setting every fifty bus cycles. The partitioning betweeni deterministic and non-cIeterrnjnjsj also permits relatively simple revisioj and upgrades. If the code for one processor must he revised or upgraded the code for the other may require no revisions or only minor revisions, in particular, the code for the deterministic processor may be more "mature", or fixed than that fur the non-defernjnistjc processor; user interfaces, cumrnunljcaLjons nn.d other similar functions tend to he upgraded more frequenLly than the detej- mjnjstjc mass flow control, functions.

Using this llustratj\fe dual-processor embodiment, a user interface may be updated without any impact on the control function code, fur example, Revision and majiltenajice of nhied-mode code (deterministic and nondeternijnjstic code) would be a much more complicated and costly proposition than code partitioned in a manner in accordance with the principles of the present invention, In an illustrative embodiment the dual-processor controller 1000 may by a hybrid processor that incorporates two processors on one integrates circuit An integrated circuit such as the TMS320C5471 hybrid processor available from Texas Instruments (RIM) may be employed as the dual pocessors in accordance with the principles of, the present iflvCntjon The digital signal processing (DSP) subsystem of the chip, due to its math capabilities would be more suitable as the deterministic processor in such an application The IC's dual-poked memo may he employed as the inter- processor interface with the processors dting to and reading from memory locations set aside to a as mail boxes" for the transfer of information, including data, commands and command responses.

Such an interprocessor interface permits the deternjstjc processor to continue operating in a frame_driven mode while, at the same time, allowing the deternnjstjc processor to play a role in diagnostics and calibration. y request for sensor data from the non-detcriiijiiistjc processor may be picked up from the mailbox on one pass of the deteinjstic processor's control loop, with the readings deposited in the mailbox the very nex time through the loop. Diagnostic outputs may be modi-fied simil&Jy The deterministic processor may also operate in other, flprocess orieiited modes. For example, during a seff-calibratjon process such as previously described the deterministic processor would no longer operate to maintain a set flow through the mass flow controller. In such a mode the determjiijstjc processor would be occupied by shutting the mass flow Controller's outlet valve, tang a plum-ality of time derivatives of the pressure within the dead volum; Computing the corresponding actual flow in the mass flow controller and correlating the actual flow to the flow signal produced by a them-mI mass flow sensor.

The flow chart of Figure Ii outlines the process of sensing and Controlling the flow of gas through a dual processor mass flow controller.

The process begins in step 11 00 arid proceeds from there to step 11 02 where the controller iS initialized This initialjzatioii step may include the uploading of caiibratjoii values or a calibration sequence itself Additionally, operating code for both the detemijnjstic and flondetennijiistjc processors 1004 may be uploaded at this point. In an illustrative embodiment, the non-detennjiuistjc processor 1004 may upload its own code and begin operating then upload code for the deterministic processor 1002. In the process of Uploading code for the deterministi processor 1002, the non-detejnjstjc processor 1004 may select among a plurality of executable code sts to up]oadto the deterministic processor 1002, thereby tailoring the operation of the deterministic processor 1002. The non- detejnjstjc processor 1004 may base this se1ectjoi on switch settings, commands from a local controller (e.g., a workstation controlling the operation of a semiconductor process tool), or settings stored in non-volatile storage, for example. Such a selection permfits a mass flow controller to be tailored to different flow control operations For example, a technician may, by selecting among code sets, choose to operate the controller in a pressure controller" niode rather than a "mass flow controller" mode, and this selection may be made locally or remotely (i C. through a telecorr1Ifu1jcatjons link).

In step 1104 the non-deterministic processor] 004 passes operating code and initial control settings to the deternmjiijstjc processor 1002 which then begins operating in a manner described generally in connection with the flow chatt of Figure 12. From step 1104, the process proceeds to step 1106 where the non- deterministic processor 1004 seIices the local input/out interface. Such scicing may include reading various inputs, including keyboard, switch, or mouse inputs, and displaying informnjtjon locally, through LEDS, alphanumeric displays, or graphical displays From step 1106 the process proceeds to s(cp I IU where the non-detern njstjc processor 1004 se1jces the communications interface This seTicing may include the steps of uploading control and sensor data to a workstation that operates as the local controller of a semiconductor process tool, for example. Additionally the nofl-de[ermjijstjc processor 1002 may download updated settings from the local controller From step 1108 the process proceeds to step 1110 where the non- deterministic processor 1004 seices the diagnostic interface. Various diagnostic operatjois such as set fotth in the description related to the discussion of Figure 4, may be performed in this step. In an illustrative embodiment, the mass flow controller includes a web server, which permits an operator to run diagnostics through a network such as the world wide web." Fiom step 1110 the process proceeds to step 1112 where the non- deterministic processor 1004 services the inter-processor interface 1006. During tnormali!, non-diagnostic.

operation, the non-deterministic processor 1004 obtains readings from the deterministic processor 1002 and passes control information, such as a flow setting obtained through the communications interface, to the deterministic processor. From step 1112, the process proceeds to continue the processes just set forth in step 1114. The process proceeds to end in step 1116 when the mass flow controller is turned off for example.

As previously noted, the steps set forth in this and other flow charts herein need not he sequential and, in fact, a number of functions performed by the non- deterministic Processor 1 004 may be event-interrupt-driven and no predictable sequence may he ascribed to the non-deterministic processor's operation. Other processes, such as data-loggizig may be performed at regular intervals. The nondeterministic Processor can support a two-way socket connection to the deterministic processor through an Ethernet network interface, for example, to provide a relatively direct connection between a remote user arid the deterministic processor.

The flow chart of Figure 12A-12B depicts the operation of the deterministic processor of a dual processor mass flow controller. In the context of this flow chart, it is assumed that an initialization process has taken place and that the deterministic processor is cycling through its control loop. The process begins in step 1200, Figure 12A, and proceeds from there to step 1202 where the deterministic processor determines whether it is to operate in its "normal" control capacity or whether it is to operate in an alternative mode, such as a manual diagnostic mode or an automatic diagnostic mode, for example.

The deterministic processor bases this decision on information it obtains from the inter- processor interface 1006. The deterministic processor services frame- driven, rather than even-driven interrupts, consequently, it regularly polls the inter-processor interface to obtain information such as this.

If the deterministic processor is to operate in its normal mode, the process proceeds from step 1202 to step 1204, where the deterministic processor obtains information from the inter-processor interface regarding the desired control settings. This information may be in the form of a desired flow rate received from a local controller, from a front panel user interface, or through the diagnostic port 1020 for example, The deterministic processor may also transfer information, such as sensor data, for example, to the non-deterministic processor through the inter-processor interface during this step. From step 1204 the process proceeds to slep 1206 where the deterministic processor gathers data, fI'orn a variety or sensors for example. The sensors from which the deterministic processor obtains data may include a mass flow sensor (thermal or other type), a temperature sensor, or a pressure sensor, for example, From step 1206 the process proceeds to step 1208, where the deterministic processor computes the flow rate of material through the mass flow controller. In an illustrative embodiment, the mass flow controller includes a Lherinal mass flow sensor and a pressui-e sensor configured to measure the pressure within the dead volume between the thermal mass how sensor's bypass and the mass flow controller outlet valve, step 1212. In this embodiment, the deterministic Pmccssor may employ the niethoci described in relation to the disáussjon of Figure 5 to compensate a flow rate measured by a thermal mass flow sensor at the inlet of the controller to more closely approximate the flow rate at the outlet of the controller In an embodiment in which the flow rate obtained from the sensor is not compensated, the process would proceed directly from step 1206 to step 1210, skipping the computational process of step 1208.

In step 1210 the deterministic processor determines whether the flow rate computed in step 1208 (or read in step 1206) is equal to the desired flow rate indicated by the setting information obtained from the nondeterministic processor via the interprocessor interface in step 1204. If the values are equal the deterministic processor continues tle opertjon as just described, as indicated by the "contjIjLJC" block 1224 (i.e., the deterministic processor returns to step 1202 and Continues to cycle through the loop). If the values re not equal, the deterministic processor computes an error signal and employs the error signal to adjust the drive signal to the mass flow controller's outlet valve. From step 1212 the process proceeds to continue in step 1214. The process proceeds from step 1214 to end in step 1216 when the mass flow controller is shut down or reset, for

example.

I in step 1202 the deterministic processor concludes that it is not to operate in tile normal mode, the process proceeds through Connecting box A to step 1218, Figure 12B, where the deterministic processor determines whether it is to operate in a diagnostic mode. The deterministic processor may obtain this information from the inter-processor i11tcace if the deterministic processor ig to operate in a diagnc>stic mode, the process Proceeds to step 1220. In step 1220 the detcrmjiiigij processor dcl.errfljl)es which diagnostic mode it is to operate in.

Once again, this information may he passed to the deterministic processor through the inter-processor interface in an "automatic' mode, the deterministic Processor acquires a sequence of diagnostic values from the inter_processor interface The sequence of values is available at the interface for acquisition by the deermjTjtjC processor The diagnostjc valucs may be cnntroj outputs fur seing the opening of the mass flow controller outlet valve or for setting test point drive values, for example, or the diagnostic values may indicate desired sensor readings or readings from test points, for example. The diagnostic values may also indicate the sequence in winch the values are to be employed, in order to set test point driver values, then read test point outputs, for example In a manual mode diagnostic values are made a\Taiiable to the deterministic processor through the interproc50 inteace one at a time. In an embodiment in which the mass flow controller includes a web server, a technician ma' use a web- enabled workstatiofl to contact the sen;er in the mass flow controller Once linked to the server, the technician may enter a valve setting command, by typing, selectiig from a pull down menu or clicking on icon, for example. This single, setting, command would be received by the non- deterministic processor through its diagnostic po and passed to the deterministic processor through the inter- processor interface.

in the manual diagnostic mode the deterministic processor executes through whatever diagnostic values are available at the inter-processor interface, then returns to its normal control loop. This could "override' a single control loop cycle it for example, a single diagnostic value, such as a test point drive value, is presented to the deterministic processor or, if a sequence of diagnostic values is presented to the deterministic processor, a number of control loop cycles may be overridden In the automatic diagnostic mode a number of diagnostic values may be exchanged through the inter-processor interface in a period con- esponding to a few control loop cycles, with a substantial number, on the order of at lest ten times as many, control loop cycles intervening between automatic diagnostic exchanges. Diagnostic modes may be combined, for example, to produce an aulomatic active on-line diagnostic mode, for example. In an illustrative embodiment a mass flow controller in accordance with the principles of the present invention operates on a one- millisecond control loop cycle, during which it provides one percent of fill-scale accuracy.

Keeping the various diagnostic modes in mind, and keeping in mind that processes illustrated through the use of flow charts may not be strictly linear processes and alternaLive flows may be implemented within the sccpe of the invention, the diagnostic process will be described generally iii relation to steps 1220 through 1226. In step 1220 the deterministic processor acquires diagnostic values from the inter-processor inteace As previously noted, these values may be for the deterministic processor to use as control outputs or they may indicate data that is to be acquired by the deterministic processor, from a sensor, for example. From step 1220 the process proceeds to step 1222 where the deterministic processor Processes the values acquired in step 1220, by changing an outlet valve acthator drive signal or transferring a sensor reading to the interprocessbr interface for example.

From step 1222 the process proceeds to step 1224 where the detenninistjc process determines whether it has completed its diagnostic tasks. If it has not S comple its diagnostic tasks, for example if it is operating in the automatic diagnostic mode and there are more values in a sequence of values to be retrieved from the inter_processor interface the process returns to step 1222 and from there as Previously described I in step 1224 the deterministic processor concludes that it has completed its diagnostic task, the process returns through connecting box B to step 1214 of Figure 12A. If the deterministic processor determines that it is not to operate in a diagnostic mode, the process proceeds from step 1218 where Processor peiforms functions such as routine background operations, then proceeds to return through connectiiig block B to step 1214 and from there as previously described is The screen shots of Figures 13A through 13 illusti-ate a user interface such as may be made available for access to a mass flow controller in accordaice with the principles of the present irIvel]tjon that includes a web server interface, such as the inteiface 608 of Figure 6. In an illustrative embodiment the mass flow colllrc)Ilcr includes a web server, such as the server 602 of Figure 6. A user may employ the seer locally, througJ a local controller or remotely, from a web- cijabled device, such as the device 600 of Figure 6. Tn this manner, the same user interface may be employed for both remote and local interactions with the mass flow coiltroller Detailed information regarding a mass flow controller such as modej number, range, and n1aflufacturij setup parameters may be displayed to a user and Sep paramete may be displayed as well. Different display techniques may he employed If there are only a limited number of acceptable values, they may be displayed and chosen from a pulldown menu, for example. As previously described a user, such as a techthcian can change set point values, Open or Close a valve, or monitor flow output, for example through this interface Additionafly \hiIe the mass flow controller is operating under a process control application, a user may induce he server to plot and log parameter values obtained from the mass flow controller.

The screen shot of Figure 13A illustrates the display a user may encounter when first accessing a mass flow controller in accordance with the principles of the present invention Over the web. The display prompts the user to choose a COmmucations protocol through use of the pulidown window 1300. The "que devices" link 1302 allows the user to initiate a process whereby his browser attempts to locate all devices that it recognizes.

Basic inforrnatioii may be downloaded through the server. Information related to the mass flow controller are displayed in the screen of fire 13B. Such screens may be expanded or collapsed. A user may choose to view i1ormation related to a subset of the displayed mass flow controllers. Based on the model number, serial number and intenially stored codes, product specificatioj3s for the mass flow Controller are displayed along with user-selectable parameters, which may be displayed in a list, for example. A user may employ this screen to download calibration data to or from a nias flow controller and to enter calibration tables. A user may also alter set points through this interface and monitor the repotted flow through the corresponding mass flow controller.

Additionally, a user may override settings and open or close a mass flow controller's outlet control valve. Each mass flow controller's specifications may be viewed, as illustrated by the screen of Figure 13C. Illustrative user-selectable parameters are displayed in the screexi shot of Figure 13D and calibratioi data such as a user may download from a mass flow controller is illusliaLed in the screen shot of Figure 13E.

A Soware implementation of the above described embodiment(s) may comprise a series of computer instictjons either fixed on a tangible medium, such as a computer readable media, e g. diskette, CD-ROM, ROM, or fixed disc, or transmittable to a computer system, via a modem or other inteace device, such as Communications adapter connccted to the network over a medium.

Medium can be either a tangible medium, including but not limited to, optical or analog cornmunjcatjns lines, or may be implemented with wireless techniques, including but not limited to microwave, infrared or other transmission techniques.

The series of computer insti-iictjons embodies all or part of the functionality previously described herein with respect to the invention. Those skilled in the art will appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Further, such instructions may he stored using any memory technology, present or future, including, but not limited to, semiconductor, magnetic, optical 1 0 or other memory devices, or transmitted using any communications technology, present or future, including but not limited to optical, infrared, microwave, or other transmission technologies. It is contemplated that such a computer program product may be distributed as a removable media with accompanying printed or electronic documentation e g, shrink wrapped software, preloaded with a 1 5 computer system, e g., on system ROM or fixed disc, or distributed from a server or electronic bulletin board over a network, e g., the Internet or World Wide Web.

Althoinh various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve sonic of the advantages of the Invent ion without dcpasting from the scope of the invention. It will be apParent to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. Further, the methods of the invention may be aclueved in either all software implementations, using the appropriate object or processor instructions or in hybrid implementations that utilize a combination of hardware logic, software logic and/or firmware to achieve the same results, Processes illustrated through the use of flow charts may not be strictly linear processes and alternative flows may be implemented within the scope of the invention. The specific configuration of logic and/or instructions utilized to achieve a particular function, as well as other modifications to the inventive concept are intended to be covered by the appended claims.

The foregoing description of speci& embodiments of the invention has been presented for the purpose's of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaclngs. The embodiments were chosen and described to best explain the principles of the invention and its practical application, and to thereby enable others skilled in the a to best utilize the inventjoii It is intended that the scope of the invention be limited only by the claims appended hereto.

Claims

1. A mass flow controller comprising: a mass flow sensor configured to produce a mass flow signal representative of a gas flow through the mass flow controller; and an electronic controller configured to produce a closed loop control signal for an outlet valve based on said mass flow signal, wherein said electronic controller is also configured to operate as a web server.

2. The mass flow controller of claim I, wherein said electronic controller is configured to display web pages related to the mass flow controller.

3. The mass flow controller of claim 2, wherein said electronic controller is configured to display web pages related to the status of the mass flow controller.

4. The mass flow controller of claim 2, wherein said electronic controller is configured to display configuration data related to the mass flow controller.

5. The mass flow controller of claim 2, wherein said electronic controller is configured to accept user input through interaction with a displayed web page.

6. The mass flow controller of claim 5, wherein said user input includes commands to change the configuration of the mass flow controller.

7. The mass flow controller of claim 6, wherein said web server is also configured to operate with active diagnostics code to permit the execution of mass flow controller active diagnostics from a web-enabled device.

8. The mass flow controller of claim 7, wherein active diagnostics code operational with the mass flow controller's electronic controller includes code to enable the manipulation of operational signals from a device connected to the network.

9. The mass flow controller of claim 7, wherein active diagnostics code operational with the mass flow controller's electronic controller includes code to enable the manipulation of diagnostic signals from a device connected to the network.

10. The mass flow controller of claim 7, wherein active diagnostics code operational with the mass flow controller's electronic controller includes code to enable the monitoring of operational signals from a device connected to the network.

11. The mass flow controller of claim 7, wherein active diagnostics code operational with the mass flow controller's electronic controller includes code to enable the monitoring of diagnostic signals from a device connected to the network.

12. The mass flow controller of claim 7, further comprising: on-line diagnostics code operational with the mass flow controller's electronic controller that enables on-line monitoring of operational signals from a web-enabled device connected to an interworking network.

13. The mass flow controller of claim 7, further comprising: on-line diagnostics code operational with the mass flow controller's electronic controller that enables on-line monitoring of diagnostic signals from a web-enabled device connected to an interworking network.

14. The mass flow controller of claim 7, further comprising: on-line diagnostics code operational with the mass flow controller's electronic controller that enables on-line manipulation of diagnostic signals from a web-enabled device connected to an interworking network.

15. The mass flow controller of claim 7, further comprising: on-line diagnostics code operational with the mass flow controller's electronic controller that enables on-line manipulation of operational signals from a web-enabled device connected to an interworking network.