Abstract:
An improved system and method for obtaining data related to the operation of a processing system which converts from analog measurement data, usually obtained from meters and gages, to digital data. Visual images of various types of measuring instruments are collected and used for measuring a process functionality. An image sensor provides an image of a first feature of the measuring instrument. The image data is processed by an image processor, which is operable to detect a first feature and determine its position relative to a second feature of the measuring instrument. The difference in the relative positions (measured distance) can then be compared to a predetermined or expected value. If the measured and expected values are not substantially the same, a signal can be generated which instructs a controller to adjust the process functionality until the measured value reaches the expected value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a data conversion system and method, and more particularly, to a system and method for converting analog data to digital data using visual images. 
     2. Description of the Related Art 
     In the processing industry it is generally important to be able to monitor on-going processes. Specifically, in the semiconductor processing industry, it is important to monitor, such parameters as temperature, pressure, and mass flow rate. 
     In a typical semiconductor processing system, a mass flow controller, for example, is a well-known instrument used to maintain a preselected mass flow rate. A typical mass flow controller operates on the principle of adding heat energy to a flowing fluid and measuring a heat transfer function and or thermal mass transport function in two sensors spaced in or near the flowing fluid. The measure of the temperature difference between the sensors is a function of fluid mass flow. When the fluid at one temperature having passed by the first upstream sensor is then heated to a higher temperature, the resistivity of the downstream second sensor is changed, the measured temperature difference between the sensors being the measure of flow. In a gas, the rise in temperature is a function of the amount of heat added, the sensor geometry and conductivity, the mass flow rate and the properties of the gas. 
     In FIG. 1, an example of a typical mass flow controller  10  is shown, which includes a horizontal bypass sensor tube  12  with upstream and downstream sensors  14  and  16 , respectively, exterior of the tube and a heater element  18  similarly wound between sensors  14  and  16  on the tube exterior. When fluid (liquid or gas) is flowing in tube  12 , heat is transferred along the line of flow from upstream sensor  14  to downstream sensor  16  producing a signal. Each sensor  14  and  16  form part of a bridge and amplifier circuit, which can detect the temperature difference caused by the greater heat input to the downstream sensor  16 , and can produce a signal proportional to the gas flow rate. The flow rate signal is compared to a command voltage from a potentiometer or the like, which generates an error signal. The error signal causes a valve to change the flow rate until a predetermined flow rate has been reached. 
     Unfortunately, the mass flow controller, thus described, has several drawbacks. For example, heat conduction is through the tube wall, which may result in relatively long response times. To provide satisfactory performance, this type of mass flow controller generally requires heating of the fluid up to about 100° -200° C. greater than the ambient temperature of the incoming fluid. In many gaseous applications, this may be above the safe temperature limit of the gas or cause decomposition of the gas or reaction with contaminants. Moreover, the heater element requires greater amounts of power. Further, for each gas composition and flow range, the instrument must be calibrated because of nonlinearities and inconsistent correction factors. 
     For this reason, what is needed is an improved system and method for obtaining data related to the operation of a processing system, which is less complex to implement, less expensive to put into practice, and more reliable than currently existing systems and methods. The system and method should include the ability to convert analog data obtained from various meters and gages, to a digital data signal useable for operating various control devices. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved system and method for obtaining data related to the operation of a processing system, such as a semiconductor processing system. Advantageously, the present invention provides conversion from analog measurement data, usually obtained from meters and gages, to digital data, which is typically more useful for operating various control devices. 
     The present invention provides a system for collecting visual images of various types of measuring instruments, which are used for measuring a process functionality, such as mass flow rate, temperature, pressure, and the like. An image sensor is included in the system for providing an image of a first feature of the measuring instrument. The image data is processed by an image processor, which is operable to detect the first feature and determine its position relative to a second feature of the measuring instrument, which is the measured value. The measured value can then be compared to a predetermined or expected value. If the measured and expected values are not substantially the same (within an acceptable limit), a signal can be generated which instructs a controller to adjust the process functionality until the measured value reaches the expected value. 
     The present invention compares digitally formatted data rather than, for example, temperature differences (see FIG. 1) and is therefore less complex to implement, less costly to put into practice, and more reliable then typical mass flow controllers. Advantageously, the present invention may provide uninterrupted measurement using readily available and easily implemented conventional measuring instruments. The application of the present invention is flexible in that the invention can be used to monitor measuring instruments that currently exist on processing systems without having to change out the instruments. 
    
    
     Other uses, advantages, and variations of the present invention will be apparent to one of ordinary skill in the art upon reading this disclosure and accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified illustration of a typical mass flow controller; 
     FIG. 2 is a simplified diagram of a data collecting system in accordance with an embodiment of the present invention; 
     FIGS. 3A-3C are simplified illustrations of embodiments of measuring devices in accordance with the present invention; 
     FIG. 4 is a flow diagram of the operation of the present invention; and 
     FIGS. 5A-5C are simplified illustrations of images in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides a system and associated method for collecting analog measurement data and converting the data to digital data for use with various control mechanisms. The invention may be used with a variety of applications including the manufacturing process of semiconductor devices, hard disks, and liquid crystal displays. By way of example, the invention can be used with etching, deposition, chemical-mechanical planarization, and rapid thermal processing systems. 
     FIG. 2 is a simplified diagram of a data collection system  100  in accordance with an embodiment of the present invention. Data collection system  100  may include a measuring instrument  102  or, alternatively a plurality of measuring instruments (not shown), which are used to verify the operating conditions of a processing system. System  100  also includes an image sensor  104 , an image processor  106 , a controller  108 , and a control mechanism  110 . 
     Measuring instrument  102  may be any device used to determine the value or magnitude of a quantity or variable. Of interest, are those quantities or variables that help to define or describe an object, a system, or a process. For example, in an industrial process, specifically a semiconductor manufacturing process, measurement and control of variables, such as temperature, pressure, time, velocity, and flow rate, determine quality and efficiency of production. 
     Measuring instrument  102  may include, but is not limited to any instrument which can provide a real-time viewing capability, such as a thermometer, a manometer, a barometer, a dial gage, and a flow meter, optionally, measuring instrument  102  can have a liquid crystal display, (LCD), which gives an alphanumeric indication of the value of a quantity or variable. 
     As illustrated in the embodiments shown in FIGS. 3A-3C, measuring instrument  102  includes a minimum value indicator  112 , a maximum value indicator  114 , and a present value indicator  116  (e.g. a metering float in a flow meter). Each indicator  112 ,  114 , and  116  is a feature that can be imaged by image sensor  104 . Accordingly, features  112 , 114  and  116  must provide contrast, such that its location or position can be determined relative to the location or position of each other feature  112 , 114  and  116 . For example, as illustrated in FIG. 3A, measuring instrument  102  includes lines or calibrations (i.e. features  112  and  114 ) drawn, etched or formed on instrument  102  at specific locations, which represent a particular value. The lines are sized and colored, such that they provide a contrast with faceplate  117  of instrument  102 , so that image sensor  104  can detect the lines. For example, faceplate  117  may provide a black background while indicators  112  and  114  are thick white lines. 
     FIG. 3A illustrates one embodiment of measuring instrument  102 , which is a mass flow meter. In operation, a substance (liquid or gas) enters a flow tube  120  at a first end  122  and exits at a second end  124 . By applying well known volumetric flow science, the action of the substance flowing through tube  120  causes present value indicator  116  to rise (or fall) between minimum indicator  112  and maximum indicator  114 . 
     FIG. 3B illustrates an embodiment in which measuring instrument  102  is a dial gage, such as a well known Bourdon-tube gage. The dial gage operates in a well-known fashion to convert linear into rotary motion to move a pointer over a calibrated scale. As before, by action of pressure P flowing through tube  120 , present value indicator  116  can be made to rotate between minimum indicator  112  and maximum indicator  114 . 
     FIG. 3C illustrates an embodiment in which measuring instrument  102  is a thermometer. Again, applying well known volumetric flow science, by action of the temperature of a substance flowing through tube  120 , present value indicator  116  can rise (or fall) between minimum indicator  112  and maximum indicator  114 . 
     Referring again to FIG. 2, image sensor  104  may be mounted near measuring instrument  102  using conventional mounting techniques. The conventional mounting allows for precision positioning of image sensor  104 . In one embodiment, image sensor  104  can be positioned with a view angle θ relative to a line of sight axis  130  of between 0° (e.g. directly along axis  130 ) and 30°; preferably between about 0° and 5° from axis  130 . Once an image is acquired, conventional image processing techniques can be used to digitally “tilt” or to “zoom” to a specific portion of the acquired image to accommodate the differences in various camera mount configurations. 
     The image of measuring instrument  102  acquired by image sensor  104  is used to provide the position of present level indicator  116  between minimum indicator  112  and maximum indicator  114 . 
     For the purpose of acquiring this image, image sensor  104  may be any conventional camera, such as a CCD camera, a video camera, a photographic camera, or a digital camera, which can record an image of a target object as digital image data upon a recording medium such as a memory card. In one embodiment, camera  104  may be a QUICKCAM™ Home camera from Logitech Corporation of Fremont, Calif. As will be described in greater detail below, the image acquired using camera  104  is provided to image processor  106  for subsequent image processing. The Logitech QUICKCAM™ Home camera provides digitized image output, which can be provided to image processor  106  via a Universal Serial Bus (“USB”) (not shown). Optionally, the image acquired using a non-digital camera  104  is first digitized using a conventional digitizer before the image is processed in image processor  106 . As described below, the output signals from camera  104  are applied as input to image processor  106  for use in computing the relative position of indicators  112 ,  114 ,and  116 . 
     The output from image processor  106  is applied to controller  108 . Controller  108  controls the operation of control mechanism  110 , which may include drive motors, valves, solenoids, actuators, and the like. Control mechanism  110  enables the adjustment of the processing functionality being monitored (e.g. mass flow, temperature, pressure, and the like). Details of the control circuitry are conventional and can be readily tailored by those of usual skill in the art to a particular function. 
     FIG. 4 is a flow diagram  200  of the process using the system of the present invention. Referring to FIGS. 2,  4  and  5 A- 5 C, the operation of the present invention begins by acquiring an image ( 202 ) of measuring instrument  102 . Light from measuring instrument  102  is focused by a photographic lens upon a photoelectric conversion element in an imaging section. Analog image data, which is photoelectrically converted by the photoelectric conversion element, is converted into digital data by an A/D conversion device. Various forms of signal processing are performed upon this digital image data, and the data is then temporarily stored in a buffer memory. 
     In one embodiment, the digitized image output signal from image sensor  104  may be stored as a bitmap. Bitmaps are known in the art. Generally, a bitmap can be thought of as an array of pixels, each pixel representing a point on the digitized image. By knowing the resolution of the bitmap, the number of pixels in each row and the number of pixels in each column of the bitmap are also known. For example, a 640×480 bitmap has 480 rows and 640 columns of pixels. Each pixel in a selected column is extracted and converted to units of red, green, and blue (“RGB”) intensity or normal gray scale intensity. The resulting intensity values of all pixels in the selected column can be loaded into a spreadsheet or application program for processing. The invention can be performed using any pixel or image format. For example, each pixel in the selected column can also be converted to the so-called HSV format. 
     The digital image data is directed to image processor  106  for image processing ( 204 ). Image processor  106  receives the digital image data to perform a well-known digital image processing technique, such as those described generally in R. Gonzales and R. Woods, “Digital Image Processing”, Addison-Wesley Publishing Co., 1993, pgs. 518-560, and as generally described in G. Baxes, “Digital Image Processing: Principles and Applications,” Wiley and Sons, Inc. 1994, which are herein incorporated by reference for all purposes. 
     In one embodiment, shown in FIG. 5A, the image processing techniques extract image components that are useful in the representation and description of shape boundaries and the like, and are used herein to detect indicators  112 ,  114 , and  116 . For example, each indicator is a boundary between two regions with relatively distinct gray-level properties. The indicator is detected by distinguishing discontinuities in the gray-level where the transition between two regions occurs. A map can be created from the detection of the line. The map is an intrinsic image, which contains the likelihood that a pixel belongs to an indicator line. Typically, a small neighborhood of pixels, such as a 3×3 or 5×5 array of pixels, is analyzed. All points that are similar are linked forming a boundary of pixels that share common properties, such as strength and direction. Using the well known concept of using the gradient for image differentiation, the gradient is defined as:          ∇              f     =       [           G   x               G   y           ]     =     [             ∂   f     /     ∂   x                   ∂   f     /     ∂   y             ]                              
     and 
     
       
         ∇ƒ= mag (∇ f )=[ G   x   2   +G   y   2 ] ½   
       
     
     Thus a line coordinate (x′, y′) in the neighborhood of (x, y) is similar in magnitude to the pixel at (x, y) if: 
     
       
         |∇ƒ( x, y )−∇ƒ( x′,y ′)|≦ T   
       
     
     where T is a nonnegative threshold. The direction of the gradient vector is given by: 
     
       
         α( x, y )=tan −1 ( G   y   /G   x ) 
       
     
     Thus, a line pixel at (x′, y′) in the neighborhood at (x, y) has a similar angle to the pixel (x, y) if: 
     
       
         |α( x, y )−α( x′, y′ )|&lt; A   
       
     
     where A is an angle threshold. 
     General purpose image processing software can be used to perform many of the tasks described above. One such software package is SHERLOCK, available from iMAGING Technology, Inc. of Bedford, Mass. Another image processing application for use with the present invention is DT Vision Foundary™, available from Data Translation, Inc. of Marlboro, Mass. 
     Once indicators  112 ,  114 , and  116  are known, image processor  106  can use well-known mathematical relationships to estimate the relative distance between minimum level indicator  112  and present level indicator  116 , referenced as D 1 . Optionally, the relative distance between maximum level indicator  114  and present level indicator  116 , referenced as D 2 , can also be determined. In one embodiment, present level indicator  116  may be a metering float or other device, which has a thickness greater than a single line (see FIG.  5 A). In this embodiment, image processor  106  can detect a first edge  132  and a second edge  134  using the technique described above. Once these edges are known the distance between them D 3  can be calculated. By dividing this distance in half, the center of the indicator can be determined for use in calculating distances D, and D 2 . 
     After distances D 1  and D 2  are known, the distances are compared to a preselected reference distance to determine whether the system requires adjustment ( 206 ). If the measured distance is different from the reference distance beyond a predetermined limit, the image processor generates a signal ( 208 ). The signal is a direction, which is sent to controller  108 . Controller  108  receives the signal, which instructs controller  108  to perform a function. For example, using the mass flow meter embodiment of FIG. 3A, if it is found that the distance between present level indicator  116  and minimum level indicator  112  is too low, controller  108  is instructed to direct valve mechanism  110  to increase the flow rate. As soon as the distance between indicator  112  and  116  is within a predetermined range, controller  108  is instructed to adjust valve  110  accordingly. The process is repeated ( 210 ) to maintain the proper flow rate. 
     In another embodiment, shown in FIG. 5B, by using the techniques described above, indicators  112 ,  114 , and  116  may be found on the image of a dial gage (see FIG.  3 B). In this embodiment, image processor  106  can use well-known mathematical relationships to estimate the relative angle between minimum level indicator  112  and present level indicator  116 , referenced as λ 1 . Optionally, the relative angle between maximum level indicator  114  and present level indicator  116 , referenced as λ 2 , can also be determined. After angles λ 1  and/or λ 2  are known, the values are compared to a preselected reference value, which corresponds to a desired operational value, to determine whether the system requires adjustment. If the measured angle is different from the reference angle beyond a predetermined limit, the image processor generates a signal. The signal is a direction, which is sent to controller  108 . Controller  108  receives the signal, which instructs controller  108  to perform a function. For example, using the pressure meter embodiment of FIG. 3B, if it is found that the angle between present level indicator  116  and minimum level indicator  112  is too shallow, controller  108  is instructed to direct pressure regulator  110  to increase the pressure to the system. As soon as the angle between indicator  112  and  116  is back within a predetermined range, the controller is instructed to adjust pressure regulator  110  accordingly to maintain the proper pressure in the system. 
     In yet another embodiment, shown in FIG. 5C, by using the techniques described above, indicators  112 ,  114 , and  116  may be found on the image of a thermometer (see FIG.  3 C). In this embodiment, the thermometer presents a column shaped indicator  140 , which has a leading edge  142  that defines present level indicator  116 . As before, image processor  106  can use well-known mathematical relationships to estimate the relative distance between minimum level indicator  112  and present level indicator  116 , referenced as F 1 . Optionally, the relative distance between maximum level indicator  114  and present level indicator  116 , referenced as F 2 , can be determined. After values F 1  and F 2  and/or known, the values are compared to a preselected reference value, which corresponds to a desired operational temperature, to determine whether the system requires adjustment. If the measured distances F 1  and/or F 2  are different from the reference value beyond a predetermined limit, the image processor generates a signal. The signal is a direction, which is sent to controller  108 . Controller  108  receives the signal, which instructs controller  108  to perform a function. For example, using the thermometer embodiment of FIG. 3C, if it is found that the distance between present level indicator  116  and minimum level indicator  112  is too large, controller  108  is instructed to direct temperature regulator  110  to decrease the temperature to the system. As soon as the distance between indicator  112  and  116  is back within a predetermined range, the controller is instructed to adjust temperature regulator  110  accordingly to maintain the proper temperature in the system. 
     Flow meters, pressure gages, thermometers, as well as other types of measuring instruments, may have additional calibrations or other extraneous features, other than the minimum, maximum, and present level indicators. To reduce confusion that may occur as to the proper reference point to be used in the image processing calculations described above, these calibrations and extraneous features should be ignored. Accordingly, an initial calibration image can be made of the desired measuring instrument. Features that are to be used in calculating the measured values are selected, while the remaining features are ignored. Thus, during operation of the present invention, the non-desired features can be filtered from the image. 
     The description of the invention given above is provided for purposes of illustration and is not intended to be limiting. The invention is set forth in the following claims.