Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Application No. 61/743,748, filed Sep. 10, 2012, entitled PRESSURE BASED MASS FLOW CONTROLLER, by Daniel T. Mudd et al., the contents of which are hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to semiconductor processing, and more specifically, improved mass flow controllers (MFC). 
       BACKGROUND OF THE INVENTION 
       [0003]    Mass flow control has been one of the key technologies in semiconductor chip fabrication for forty years. As the technology of chip making has improved so has the demand on the mass flow controller (MFC). Initially chip manufacturing processes were courser than today. Process steps were longer and focus was on the control of steady state flow accuracies and repeatability. One could divert the gas flow or wait to strike a plasma until the system had stabilized at steady state and little attention was paid to the transients that occurred at the turn on or off of the gas flow. 
         [0004]    Problematically, as more refined manufacturing processes evolved with time, higher performance was needed from conventional thermal and pressure based MFCs. The stability and accuracies of the past devices were bottlenecking semiconductor fabrication process. Process step durations shortened to 5 second steps seen now verses 30 minutes process steps of the past. The relatively long transient time to change gas flow rates to the process once acceptable with the longer process steps is problematic with the shorter process steps. Further, MFCs are lagging to meet the demand for controlling gas flows over a wider flow range with more accuracy and less costly hardware. 
         [0005]    The pressure based MFC was introduced in the last decade and is now overtaking the use of the thermal MFC in critical etch applications. In 2002, Fugasity introduced a pressure base MFC called the Criterion. The pressure based MFC was an improvement on the thermal MFC and hence was a commercial success. However, those same forces that pushed the development of the Criterion, the demand for improved performance and reduced price, are still pushing to improve the design of the pressure based MFC. 
         [0006]    One of the issues common to thermal and pressure based MFCs is form factor. Space is very expensive in a modern semiconductor tool. The interface connecting the MFC to the other components in a gas box has been standardized by the industry to allow interchangeability of devices such as MFC and air operated shut off valve produce by a multiple different suppliers. The dominate interface standard in the industry is based on components being 1.1″ wide. MFC&#39;s are 1.1″ wide (28.6 mm) by 4.13″ (105 mm) in length with porting and other geometry details as describe in the Semi F82-0304 specification. Similarly a second interface specification, Semi F84-0304, defines the interface geometry for air operated valve as being 1.1″ wide by 1.1″ in length square interface. 
         [0007]    Independent of the device type or manufacturer the vast majority of components (air valves, filters, check valves, regulators, etc.) found in the gas box of a modern semiconductor fabrication tool will comply with the 1.1″ square interface. MFC and Electronic regulators will fit the 1.1″ X 4.13″ rectangular interface. 
         [0008]    These device interchangeability issues and the resulting interface standards have had the impact of preventing spontaneous component size reductions. About every 10 to 20 years the industry has seen a new smaller standard proposed and accepted, but in time periods between these adoptions, devices are, as a practical matter, forced to retain the external envelope defined by the standards. 
         [0009]    However, internal device design improvements that allow smaller internal components, while not affecting the external envelope, have had the beneficial effect of allowing more instrumentation and functionality to be placed into the standard external envelope. For example a supply pressure transducer, typically a 1.1″ square interface, had been traditionally place upstream of an MFC. Component size reduction of the pressure transducer and similar reduction in the MFC&#39;s internal components has allow the function of the supply pressure transducer to be integrated into the MFC thus eliminating the need for the 1.1″ square interface formerly used by the pressure transducer. 
         [0010]    What is needed is a robust MFC having various space-saving layouts that allows additional component integration within the standard envelope and which incorporates improved design, components and new functionalities to address the transient response issues and accuracy limitations inherent in the current devices. Additionally, a layout in an MFC allows for a smaller pressure based MFC package size that allow it to fit the smaller standard square interface envelope rather than requiring the larger rectangular interface that current MFCs require. 
       SUMMARY 
       [0011]    The present invention addresses these shortcomings by providing a pressure based mass flow controller (MFC) device, and methods therein, with space saving layouts and improved functionalities. 
         [0012]    In one embodiment, an MFC has a standard envelope with an enclosure and a corresponding base. A pressure transducer is communicatively coupled to a process gas in a proportional inlet valve without being physically coupled to the base. The space on the base, formerly occupied by the pressure transducer, is available for additional component integration. In one embodiment, a second pressure transducer is located remotely and shared by multiple MFCs. 
         [0013]    In another embodiment, an envelope is smaller than the standards. A pressure transducer is communicatively coupled to a process gas in an inlet valve without being physically coupled to the base. In this case, the components are arranged to be more compact in view of space formerly occupied by the pressure transducer. While this shorter embodiment does not fit the larger current interface standards it is obvious that making a device larger is easier than making one smaller and the smaller device might be readily expanded to fit current applications or be adopted as the new future interface standard that is periodically adopted. 
         [0014]    In an embodiment, an MFC utilizes a second pressure transducer that is remotely located downstream from the MFC. 
         [0015]    In yet another embodiment, an MFC has a self-relieving P1 pressure. 
         [0016]    In still another embodiment, an MFC has a first LFE and a second LFE configured in parallel to produce a wide-range MFC that maintains its accuracy over a range that previously required two separate MFCs. 
         [0017]    Additionally, a mini IGS style MFC, which utilizes the smaller square interface currently used by air valve, can have a pressure transducer communicatively coupled to a process gas in a proportional inlet valve without being physically coupled to a base. Optionally, a venting orifice can be provided. 
         [0018]    Advantageously, the MFC layout provides additional space on a standard MFC envelope, and the MFC layout allows a smaller MFC envelope. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the following drawings, like reference numbers are used to refer to like elements. Although the following figures depict various examples of the invention, the invention is not limited to the examples depicted in the figures. 
           [0020]      FIG. 1  is a schematic diagram illustrating a prior art layout of a pressure based mass flow controller (MFC) with a conventional P1 pressure transducer coupled to a base within a standard envelope, according to a prior art embodiment. 
           [0021]      FIG. 2A  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 pressure transducer decoupled from a base for a smaller envelope, according to an embodiment. 
           [0022]      FIG. 2B  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 decoupled from the base and with space for an additional component to be coupled to a base within a standard envelope, according to an embodiment. 
           [0023]      FIG. 3  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 pressure transducer decoupled from A base and a relief valve coupled to the base for rapidly reducing the pressure upstream of the restrictor, to within a standard envelope, according to an embodiment. 
           [0024]      FIG. 4  is a schematic diagram illustrating a layout for a pressure based MFC with A P2 pressure transducer decoupled from a base and located remote to the envelope, and a relief valve coupled to the base, according to an embodiment. 
           [0025]      FIG. 5  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 pressure transducer decoupled from a base and a second laminar flow element (LFE), which can be functionally active or inactive by the opening or closing of a high conductance valve in series with the LFE, according to an embodiment. 
           [0026]      FIG. 6  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 pressure transducer decoupled from a base and the second LFE, and a relief valve, according to an embodiment. 
           [0027]      FIG. 7  is a schematic diagram illustrating a layout for a pressure based MFC with a P1 pressure transducer decoupled from a base and a second LFE, and a relief valve, and a P2 pressure transducer decoupled from the base and located remote to the envelope, according to some embodiments. 
           [0028]      FIG. 8  is a layout for a schematic diagram illustrating a mini integrated gas system (IGS) with a P1 pressure transducer decoupled from the base, and a P2 pressure transducer remotely located, according to an embodiment. 
           [0029]      FIG. 9  is a layout for a schematic diagram illustrating a mini IGS with a P1 pressure transducer decoupled from a base, a venting orifice, and a P2 pressure transducer remotely-located, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    A mass flow controller (MFC) device, and methods therein, with various space saving layouts is described. 
         [0031]      FIG. 1  is a schematic diagram illustrating a prior art layout of a pressure based mass flow controller (MFC)  100  with a conventionally-located P1 pressure transducer  104  coupled to a base  220  within a standard envelope, according to a prior art embodiment. One example of the prior art MFC  100  is the device manufactured by Fugasity. The prior art MFC  100  can be 4.13″ long to fit industry standards. It consists of a proportional flow control valve  105  at an inlet  101  of the device, followed by the P1 pressure transducer  104  downstream of a proportional flow control valve  105 , followed by a characterized laminar flow element (LFE)  105  acting as a flow restrictor, and a P2 pressure transducer  106  near the outlet  102  of the device. The prior art MFC  100  also utilizes a printed control board (PCB) (not shown) containing supporting electronics, software and calibration coefficient for receiving, pressure signals, a temperature signal (e.g., from a temperature sensor  107  embedded in the device) and an external set point indicating the target flow. Given these inputs the PCB drives a voltage to the proportional inlet valve  105  until sufficient pressure was achieved in the volume between a poppet of a valve and the downstream restrictor, to achieve the needed flow through the restrictor. This particular pressurized volume is referred to herein as a P1 volume. Under the conventional paradigm, the P1 pressure transducer  105  is coupled to the base in order to monitor the pressure of P1 volume. 
         [0032]      FIG. 2A  is a schematic diagram illustrating a layout for a pressure based MFC  200 A with a P1 pressure transducer  210 A decoupled from a base  220 , according to an embodiment. Because the P1 pressure transducer  210 A no longer occupies space on the base  220 , the envelope can be reduced from the standard size of 4.13″ or the freed up space on the base can be used to add additional components and functionality. 
         [0033]    The inlet  211  of the MFC  200 A receives a process gas into a conduit (e.g., an inlet conduit). Nitrogen is an exemplary process gas, but any suitable gas or fluid could be substituted. The conduit can be any suitable tubing, plumbing or machined block, either rigid or flexible. A KS1 substrate block (not shown) as manufactured by Hytron Corporation, serves as an interconnecting platform for the base  220  of the MFC  200 A and other components for supplying gas to and receiving gas from the MFC  200 A. 
         [0034]    The proportional inlet valve  230 A can be a solenoid or other appropriate component physically coupled to the base  220  to control gas flow through an inlet  211  of the MFC  200 A. Process gas is received from the conduit (e.g., the inlet conduit) and sent back to the conduit after processing (e.g., the intermediate conduit). Rather than being directly connected to the base  220 , the P1 pressure transducer  210  is communicatively coupled to monitor process gas internally downstream of from the valve seat and poppet of proportional inlet valve  230 A. In some embodiments, the proportional inlet valve  230 A has a movable portion and a fixed portion, and the P1 pressure transducer  210 A is coupled to the fixed portion. 
         [0035]    More specifically, the proportional inlet valve  210 A has a solid upper pole rigidly attached to an outer tube, also rigidly attached to the base of the valve which is sealed to the base  220  of the MFC  200 A. The mechanism contains the pressurized gas flowing through the proportional inlet valve  230 A. Inside the outer tube a movable plunger is suspended via a radial spring. A conduit is bored through the fixed pole to communicate gas pressure to the P1 pressure transducer  210 A attach to an end of the fixed pole, on top of the proportional inlet valve  230 . As a result, the process gas and its associated pressure can communicate from the exits of the valve seat to the P1 pressure transducer  210 A allowing the P1 pressure upstream of the restrictor to be sensed and controlled. 
         [0036]    Details  201  and  204  are detail views showing the gas passages connecting the valve seat to the P1 pressure transducer  210 . Detail  201  shows the small passages that contain gas from the valve seat to the movable plunger. Detail  202  illustrates the flow passage in the area of the movable plunger and orifice valve seat. Detail  203  shows the gas passage past the radial spring and into the small annular gap between the movable plunger and the lower details of the fixed outer tube assembly. Detail  204  illustrates the annular gap passage between the top section of the fixed outer tube assembly and the movable plunger and a second passage between the gap between the movable plunger and the fixed core where it enters the bore drilled through the length of the fixed plunger. 
         [0037]    Although these passages are small, little flow is needed to pressurize or depressurize the small volume, hence, the pressure measured by the P1 pressure transducer  210  effectively represents the pressure at an outlet  212  of the valve seat and the inlet to the characterized restrictor. 
         [0038]    A P2 pressure transducer  240  measures process gas in the conduit (e.g., outlet conduit) between an LFE  225  and the outlet  212 . The outlet  212  delivers the process gas to a next conduit for eventual use by the process. In some embodiments, additional processing is performed on the process gas, such as mixing with other gases, or the like. A temperature sensor  245  provides temperature readings and a PCB  235  processes the temperature readings and other information in controlling the components on the MFC  200 A. 
         [0039]    In an embodiment of an IGS style MFC, due to arranging the P1 pressure transducer on top, the MFC functionality can be provided by a smaller envelope (e.g., see  FIGS. 8 and 9 ). In more detail, rather than complying with the traditional interface standard of Semi F82-0304 for a rectangular-shaped interface having a 4.13″ long base, the IGS style MFC can comply with the Semi F84-0304 standard for a square-shaped interface having a 1.1″ base. Both standard are hereby incorporated by reference in their entirety. 
         [0040]      FIG. 2B  is a schematic diagram illustrating a layout for a pressure based MFC  200 B with a P1 pressure transducer  210 B decoupled from the base an additional component coupled to the base within a standard envelope, according to an embodiment. 
         [0041]    Relative to  FIG. 2A , the newly available real estate along the base of MFC  200 B is utilized for integrating one or more additional components  270  within the standard size envelope rather than reducing the envelope (e.g., see  FIGS. 3-7  for examples of additional components). 
         [0042]      FIG. 3  is a schematic diagram illustrating a layout for a pressure based MFC  300  with a P1 pressure transducer  310  decoupled from the base and a relief valve  370  coupled to the base within a standard envelope, according to an embodiment. Space for the relief valve  370  is enabled by the relocation of the P1 pressure transducer. 
         [0043]    For MFCs having a small flow range, 500 sccm and below for example, the pressurized mass of gas between the valve seat of the proportional inlet valve and the inlet of the flow restrictor, the P1 volume, is significant compared to the desired flow rate to the process. Traditionally, when one gives the MFC a command to stop flow, via outputting a set point value of zero, the inlet proportional valve closes immediately but flow continues to bleed through the restrictor and to the process as the pressure in the P1 volume bleeds down to equalize with the pressure downstream of the restrictor. In the current pressure based MFC  300 , the mass at P1 pressures that correspond to 100% full scale flow is roughly 1 to 2 standard cubic centimeters (i.e., 1 scc=1 cc of gas at 0 C and 1 atm). If the MFC is relatively large, say 1000 sccm at full scale, FS, (i.e., 1000 scc per minute) then the mass in the P1 volume is insignificant compared to the working flow rate and it bleeds off relatively quickly. However, flow rates below 1 sccm are now being requested. If the MFC is a 1 sccm FS device the P1 mass is very significant and the time constant of bleeding off the P1 mass is 1 minute. If the process is 5 seconds in length, then having an MFC that continues to flow gas to the process minutes after the command to stop flow, is not an acceptable situation. As a practical matter, the traditional mechanical full scale of pressure based MFC are limited to be above 250 sccm, to avoid this issue. Pressure based MFCs, which are built and labeled with full scales below this value, typically have the large 250 sccm laminar flow element restrictor but operate in the lower range operation by electronically or numerically scaling the flow calculation so that although the device is mechanically large its full scale reading is much smaller. The larger restrictor lowers the P1 pressure and bleeds down the P1 volume quicker, however this method induces larger device calibration drift. 
         [0044]    The relief valve  370  of  FIG. 3 , by contrast, routes the P1 volume mass to a non-process abatements system via a vent or vacuum pump (also see  FIGS. 4 ,  6 ,  7  and  9 ). In operation, a PCB controls a proportional valve controlled by a PCB. When it is desired to reduce the flow from the MFC  300  faster than the natural bleed down time constant of the bleed off through the restrictor to the process, the proportional P1 relief valve will open and control the P1 pressure to a lesser pressure. The lesser pressure can be controlled to quickly reduce to a lower flow rate or to stop flow. In the IGS  900  of  FIG. 9 , an orifice  910  replaces the proportional valve for cost and space savings. The orifice  910  is sized to bleed off a mass flow rate typically between 50 and 500 sccm (give a 1 cc P1 volume) to allow the speedy depressurization, relative to the intended process time, of the P1 area. It is noted that an on/off valve might be placed downstream and in series with the vent line if it is desired to reduce the quantity of gas vented. In this case continuous venting is avoided and gas is only vented when it is desired to reduce the P1 pressure. 
         [0045]      FIG. 4  is a schematic diagram illustrating a layout for a pressure based MFC  400  with a P2 pressure transducer  440  decoupled from the base and located remote to the envelope, and a relief valve  470  coupled to the base, according to an embodiment. 
         [0046]    The gas box of a modern semiconductor fabrication tool controls and mixes the flows of multiple gas species. Typically these gases combine at a common header connected to the exhaust of each of different gas sticks contain the different MFCs. Although there is typically a shut off air valve at the end of each MFC, its conductance is sufficiently high compared to the flow rate of the MFC that the pressure of the common header is sufficiently indicative of the P2 pressure seen by the individual MFCs when the shut off air valve is open and gas is flowing from the MFC. As a result, the P2 pressure information from a single pressure transducer located on this exhaust header (via analog or digital connections) can be shared with the PCBs of the individual MFCs to provide the P2 pressure information without the need for individual P2 pressure transducers located on each MFC. Optionally the P2 information may be read by the tool controller and sent electronically to the MFCs. In this layout, space is gained by removing the second pressure transducer allowing a smaller envelope or additional integrated components. Moreover, cost savings is realized because P2 pressure transducers are not needed on each MFC. 
         [0047]    In one embodiment, as shown by  FIGS. 8 and 9 , the P2 pressure transducer  840 ,  940  can be located remotely to an IGS style MFC  800 ,  900 . In other embodiments, the P1 pressure transducer can be placed on top of the proportional inlet valve as described herein. Furthermore, other embodiments can add a second LFE or a self-relieving valve. 
         [0048]      FIG. 5  is a schematic diagram illustrating a layout for a pressure based MFC  500  with a P1 pressure transducer  510  decoupled from the base and a second LFE  525 B, according to an embodiment. In  FIG. 7 , the MFC with a P1 pressure transducer  710  decoupled from the base and a second LFE  725 B also has a remotely-located P2 pressure transducer  740 . 
         [0049]    Returning to  FIG. 5 , the second LFE  525 B is configured in series with a high conductance valve  575 . The high conductance valve  575  for this embodiment can be characterized by a pressure drop through the valve sufficiently small compared to a pressure drop across the second LFE  225 B, such that the flow calculation error induced by ignoring the valve pressure drop is acceptably small. For example, ignoring the pressure drop a standard ¾″ valve used in the industry in series with a LFE typically induces a 0.15% R error at 5,000 sccm flow of N2. It is noted that this error can be further reduced, or flow rates increased without loss of accuracy, by numerically correcting the flow calculation based on the characterization of the valve used. 
         [0050]    This additional LFE  525 B and valve are placed in parallel with the initial LFE  525 A. When the high conductance valve is closed the MFC  500  has the full scale of the single initial LFE. When the high conductance valve is open, the MFC  500  has the full scale of the two LFEs  525 A,  525 B in parallel. By making the added LFE  525 B markedly larger (i.e., much more flow at the same P1 and P2 pressures) than the initial LFE  525 A, the MFC  500  will have a markedly higher full scale flow capability. Effectively, the MFC  500  has the novel aspect of operating as a high flow and a low flow MFC that shares the same inlet valve, transducers and PCB in the same package size as a current conventional MFC. The MFC  500  allows the replacement of multiple gas lines and MFCs for a single gas species, a situation commonly seen in a modern gas box, by a single gas line and MFC saving both space and cost. 
         [0051]    The present MFC  500  meets dueling industry demands for accurate flow control and wider ranges than current MFCs can support. The O2 flow rates from 0.1 sccm to 10,000 sccm are now achievable on the same tool. Conventionally, separate O2 MFCs of different full scale values are configured to cover the desired flow range at the intended accuracy. The additional LFE  525 B with the high conductance on/off valve in series can cut the number of O2 (or other gas) MFCs in half, saving space and money. While the initial LFE  525 A of the pressure based MFC  500  can maintain 1% reading accuracy over a dynamic range of 20 to 1, the dual LFE operation of the MFC  500 , with the proper ratio between the LFE&#39;s  525 A,  525 B, can maintain a 1% of reading accuracy over a dynamic range of 20×20 to 1 or 400 to 1. One of ordinary skill in the art will recognize that a dynamic range of 20 to 1 and a reading accuracy of 1% are just examples that can be varied for different implementations. 
         [0052]    Optionally, the two LFEs  525 A,  525 B may be sized to focus on separate flow ranges that are not adjacent but that are further apart. For example, the smaller restrictor controlling flow accurately from 0.5 sccm to 10 sccm and the larger LFE sized to control flows from 200 sccm to 4000 when the high. 
         [0053]    In other embodiments a third or more LFEs can be added for additional range. 
         [0054]    In the layout embodiment of  FIG. 6 , a pressure based MFC  600  with a second LFE  625 B also includes a P1 pressure transducer  610  decoupled from the base, and a relief valve. Additionally, in the layout embodiment of  FIG. 7 , a pressure based MFC  700  with a second LFE with a P1 pressure transducer decoupled and a relief also includes a P2 pressure transducer decoupled from the base and located remote to the envelope. As described above, the P2 pressure transducer can be locate downstream, for example, at a common exhaust header shared by several MFCs. 
         [0055]    This description of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications. This description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications as are suited to a particular use. 
         [0056]    The scope of the invention is defined by the following claims.

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