Abstract:
A pressure sensor includes a diaphragm having a displaceable elastic inner portion, wherein the inner portion displaces in response to a pressure difference between first and second sides of the diaphragm. A radiation source may be configured to transmit first and second beams of radiation. A light receiver may be configured to receive the first beam of radiation directly from the radiation source and the second beam of radiation after it reflects from the first side of the diaphragm. A control system may be coupled to the radiation source and light receiver and adapted to determine the pressure difference from the displacement of the diaphragm.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/812,098, filed Mar. 30, 2004, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to high sensitivity, high bandwidth, low pressure sensors and, more particularly, to the application of these devices in air gauges for use in, for example, lithography devices.  
         [0004]     2. Related Art  
         [0005]     Conventional low pressure air gauges utilize mass flow sensors, which have relatively long response times, or low bandwidths, typically in the range of a tens of Hz. The relatively low bandwidths are not suitable for higher speed operations, such as, for example, lithography scanning applications.  
         [0006]     What are needed therefore are high sensitivity, low pressure air gauges having higher bandwidths than are presently available.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to high sensitivity, low pressure air gauges having higher bandwidths than are presently available.  
         [0008]     A pressure sensor in accordance with the invention includes a diaphragm having a substantially rigid outer portion and a displaceable inner portion that displaces in response to a pressure difference between first and second sides of the diaphragm. The pressure gauge further includes a sensor located proximate to the diaphragm and adapted to sense the displacement of the diaphragm inner portion. The pressure gauge further includes a monitor and control systems coupled to the sensor (wired or wireless), and adapted to determine the pressure difference from the displacement of the diaphragm.  
         [0009]     The present invention provides a variety of optional sensing designs including, without limitation, optical sensing designs and capacitive sensing designs.  
         [0010]     For low pressure applications, such as nanometer proximity sensors used in lithography applications, the operational pressure range of the sensor is approximately 0.1 to 0.5 inches of water. The resolution of the gauge pressure sensor is preferably approx. ˜0.001 Pa, this is approx. ˜4×10 −5  inches H 2 O. This would allow the gauge to resolve a few nanometers. Note that 1 (one) inch H 2 O=254 Pascals.  
         [0011]     The diaphragm and sensor have a relatively high bandwidth and can thus be implemented in relatively high speed applications. The invention can be implemented in, for example, lithography proximity sensing equipment and lithography topographical mapping equipment.  
         [0012]     Additional features and advantages of the invention will be set forth in the description that follows. Yet further features and advantages will be apparent to a person skilled in the art based on the description set forth herein or may be learned by practice of the invention. The advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0013]     It is to be understood that both the foregoing summary and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES  
       [0014]     The present invention will be described with reference to the accompanying drawings, wherein like reference numbers indicate identical or functionally similar elements. Also, the leftmost digit(s) of the reference numbers identify the drawings in which the associated elements are first introduced.  
         [0015]      FIG. 1  is a side plan view of a pressure sensor  100 , including a diaphragm  102  and a sensor  104 .  
         [0016]      FIG. 2A . is a front plan view of the diaphragm  102 .  
         [0017]      FIG. 2B  is a side plan view of a substantially rigid outer portion  202  of the diaphragm  102 .  
         [0018]      FIG. 2C  is a side plan view of the diaphragm  102 , including the substantially rigid outer portion  202 , an inner portion  204 , and a proximity sensor surface  206  shown distended as if under a differential pressure condition.  
         [0019]      FIG. 3  is a side perspective view of the pressure sensor  100 , wherein the sensor  104  and a monitor and control system  106  are implemented with a white-light interferometer.  
         [0020]      FIG. 4  is a side plan view of the pressure sensor  100 , wherein the sensor  104  and the monitor and control system  106  are implemented with an optical grazing angle sensor.  
         [0021]      FIG. 5  is a side plan view of the pressure sensor  100 , wherein the sensor  104  includes a capacitive sensor  502 , and the proximity surface  206  includes a grounded plate  504 .  
         [0022]      FIG. 6  is a side plan view of an air system  600 , including a first leg  602  and a second leg  604 , and the pressure sensor  100  positioned in a bridge therebetween.  
         [0023]      FIG. 7  is a side plan view of the pressure sensor  100  implemented in a proximity sensor  700  used in, for example, lithography.  
         [0024]      FIG. 8  is a side plan view of the pressure sensor  100  implemented in a proximity sensor  800 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0000]     I. Introduction  
         [0025]     The present invention is directed to low pressure air gauges having higher bandwidths than are presently available. The present invention can be used in, for example, and without limitation, lithography proximity sensing and lithography topographical mapping.  
         [0000]     II High Bandwidth, Low Differential Pressure Sensing  
         [0026]      FIG. 1  is a side plan view of a pressure sensor  100  including a flexing plate or diaphragm  102 , a diaphragm displacement sensor  104  (hereinafter “sensor”  104 ) located proximate to the diaphragm  102 , and a monitor and control system  106  electrically coupled (wired or wireless) to the sensor  104 . The sensor  104  is proximate to the diaphragm, but not necessarily in physical contact with the diaphragm.  
         [0027]     The diaphragm  102  and the sensor  104  are positioned within a body  108 , between a first area  110  and a second area  112 . The pressure sensor  100  determines a pressure difference between the first area  110  and the second area  112 .  
         [0028]      FIG. 2A  is a front plan view of the diaphragm  102 . The diaphragm  102  includes a substantially rigid outer portion  202 , for coupling the diaphragm  102  to an inner wall  114  ( FIG. 1 ) of the body  108 .  FIG. 2B  is a side plan view of the substantially rigid outer portion  202 . The substantially rigid outer portion  202  is made from metal, plastic, or other suitable substantially rigid material, or combinations thereof.  
         [0029]     Referring back to  FIG. 2A , the diaphragm  102  further includes a displaceable inner portion  204  that displaces in response to a pressure difference between the first and second areas  110  and  112  ( FIG. 1 ).  
         [0030]     The inner portion  204  is a flexing-plate, membrane-based portion constructed of a semi-elastic material, such as, for example and without limitation, mylar, kapton, rubber, and/or combinations thereof. The inner portion  204  expands in the direction of low pressure. The inner portion  204  is designed to respond to ultra low differential pressure in the range of, for example, and without limitation, approximately 0.1 to 0.5 inches of water. Alternatively, the inner portion  204  is designed to respond to other pressure differential ranges.  
         [0031]     The inner portion  204  is attached to the substantially rigid outer portion  202  in one or more of a variety of manners including, without limitation, glue, integrally forming, heat sealing, chemical bonding, and the like.  
         [0032]     The inner portion  204  optionally includes a proximity sensor surface  206 , wherein the sensor  104  ( FIG. 1 ) is sensitive to movement of the proximity sensor surface  206 . The proximity sensor surface  206  can be the inner portion  204  or a coating or impregnation thereof. Example coatings and impregnations are disclosed in one or more sections below.  
         [0033]      FIG. 2C  is a side plan view of the diaphragm  102 , including the substantially rigid outer portion  202 , the inner portion  204 , and the proximity sensor surface  206  shown distended as if under a differential pressure condition.  
         [0034]     In the example of  FIGS. 1 and 2 A, the body  108  has a cylindrical shape, thus the outer portion  202  has a complementary circular shape. The invention is not, however, limited to the example circular shape illustrated herein. One skilled in the relevant art(s) will understand that other shapes can be utilized as well, including, without limitation, oval, elliptical, and polygon.  
         [0035]     The sensor  104  and the proximity sensor surface  206  can be implemented with one or more of a variety of technologies. Example implementations of the sensor  104  and the proximity sensor surface  206  are disclosed below. The invention is not, however, limited to these example implementations. Based on the teachings herein, one skilled in the relevant art(s) will understand that the sensor  104  and the proximity sensor surface  206  can be implemented with other technologies as well, which are within the scope of the present invention.  
         [0036]     The pressure sensor  100  is a relatively high bandwidth device. Depending upon the materials and circuitry employed, the pressure sensor can have a bandwidth in the several thousands of Hz. The present invention is thus useful in both relatively low speed applications, such as, for example, lithography proximity sensing, and in relatively higher speed applications, such as, for example, lithography topography mapping.  
         [0000]     III. Interferometer Based Proximity Sensing  
         [0037]      FIG. 3  is a side perspective view of the pressure sensor  100 , wherein the sensor  104  and the monitor and control system  106  are implemented with an interferometer. The interferometer utilizes the proximity surface  206  as a reflecting target. Changes in the deflection of the proximity surface  206  result in corresponding changes to reflected light patterns received by the sensor  104 . A decoder within the monitor and control system  106  determines the relative deflection of the proximity surface  206 . The monitor and control system  106  then converts the deflection measurement of the proximity surface  206  to a pressure difference between the first and second areas  110  and  112 .  
         [0038]     The interferometer can be implemented with an off-the-shelf interferometer, including, but not limited to, a white light interferometer.  
         [0000]     IV. Optical Grazing Angle Proximity Sensing  
         [0039]      FIG. 4  is a side plan view of the pressure sensor  100 , wherein the sensor  104  and the monitor and control system  106  are implemented with an optical grazing angle sensor as taught in, for example, T. Qui, “Fiber Optics Focus Sensors: Theoretical Model,” MIT Report, 2000, incorporated herein by reference in its entirety.  
         [0040]     In operation, first and second optical paths  402  and  404 , respectively, are formed between transmitting and receiving fibers  406  and  408 , respectively. The first optical path  402  is between the transmitting fiber  406  and the receiving fiber  408 . The second optical path  404  is output from the transmitting fiber  406  and reflects off the proximity surface  206  before being received by the receiving fiber  408 . A first beam of light transmitted from the transmitting fiber  406  and received by the receiving fiber  408 , via the first optical path  402 , and a second beam of light transmitted from the transmitting fiber  406  and received by the receiving fiber  408 , via the second optical path  404 , form a spatial diffraction pattern. The pattern is a function of the relative position of the proximity surface  206 .  
         [0041]     When the proximity surface  206  deflects, illustrated in  FIG. 4  as “diaphragm deflection”  410 , the receiving fiber  408  receives intensity-modulated light from the second path  404 . A decoder in the monitor and control system  106  decodes the modulation and determines a relative deflection of the proximity surface  206 . The monitor and control system  106  then converts the deflection measurement of the proximity surface  206  (i.e., diaphragm deflection”  410 ) to a pressure difference between the first and second areas  110  and  112 .  
         [0042]     In the example of  FIG. 4 , the transmitting fiber  406  includes optics that split a light from a light source into the first and second paths  402  and  404 . Alternatively, two transmitting fibers are used with acoustically shifted wavelengths. The resulting interference pattern at the receiving fiber  408  constantly shifts or moves. When the proximity surface  206  is motionless, the interference pattern moves with a constant speed. When the proximity surface  206  moves, the speed of the corresponding shifting interference pattern changes. A counter in the monitor and control system  106  decodes the relative deflection of the diaphragm based on the pattern changes. The monitor and control system  106  then converts the deflection measurement of the proximity surface  206  to a pressure difference between the first and second areas  110  and  112 .  
         [0000]     V. Capacitive Proximity Sensing  
         [0043]      FIG. 5  is a side plan view of the pressure sensor  100 , wherein the sensor  104  includes a capacitive sensor  502 , and the proximity surface  206  includes a grounded plate  504 . The grounded plate  504  is made, at least in part, from conductive material such as metal. The capacitive sensor  502  is optionally located approximately 300 to 500 micrometers from the grounded plate  504 . Gas, such as air, acts as a dielectric between the capacitive sensor  502  and the grounded plate  504 , thus forming a capacitor. The capacitance is a function of the distance of the grounded plate  504  from the capacitive sensor  502 . Changes in the deflection of the diaphragm  102  result in changes to the capacitance. The monitor and control system  106  include circuitry, such as a tank circuit, for example, which generate an oscillation or modulation corresponding to the capacitive changes. The oscillation or modulation is then converted to a relative deflection measurement for the grounded plate  504 . The monitor and control system  106  then converts the deflection measurement of the grounded plate  504  to a pressure difference between the first and second areas  110  and  112 .  
         [0044]     Capacitive sensors are well known and commercially available, although they are not known by the present inventors to have been used in conjunction with pressure sensors.  
         [0000]     VI. The Pressure Gauge as an Air Gauge  
         [0045]     The pressure sensor  100  is optionally implemented as an air gauge that measures pressure changes caused by air flow. Such an air gauge is useful in, for example and without limitation, proximity sensors for lithography and topographical mapping for lithography.  
         [0046]      FIG. 6  is a front plan view of an air system  600 , including a first leg  602  and a second leg  604 . The pressure sensor  100  is positioned in the body  108 , which forms a bridge between the first and second legs  602  and  604 . The bridge  108  is coupled to the first and second legs by respective T-connections.  
         [0047]     In the example of  FIG. 6 , the T-connections are essentially right angle T-connections. The invention is not, however, limited to right angle T-connections. Based on the description herein, one skilled in the relevant art(s) will understand that other angle connections can be used.  
         [0048]     Air flow through the first and second legs  602  and  604  are illustrated with arrows. The air flow results in reduced pressure in areas  110  and  112 . When the air flow in leg  602  differs from the air flow in leg  604 , the resulting pressure difference between areas  110  and  112  will cause the diaphragm  102  to deflect toward the area of lower pressure. Based on an initial calibration, the monitor and control system  106  determines relative differences in air flow between the first and second legs  602  and  604 . The relative difference in air flow can be used, for example, in lithography proximity sensing, as described below.  
         [0000]     VII. Lithography Proximity Sensing  
         [0049]      FIG. 7  is a front plan view of a proximity sensor  700  used in, for example, lithography. Lithography proximity sensors are described in, for example, U.S. patent application Ser. No. 10/322,768, titled, “High-Resolution Gas Gauge Proximity Sensor,” filed Dec. 19, 2002, incorporated herein by reference in its entirety. An air gauge sensor is also taught in U.S. Pat. No. 4,953,388, titled, “Air Gauge Sensor,” issued Sep. 4, 1990, to Barada, incorporated herein by reference in its entirety.  
         [0050]     In  FIG. 7 , the proximity sensor  700  includes the first and second legs  602  and  604 . The first leg  602  is coupled to a measurement probe  702 . The second leg  604  is coupled to a reference probe  708 . The first leg  602  is a measurement leg, and the second leg  604  is a reference leg. The measurement probe is adjacent to a wafer or other work surface  704 , with a measurement gap  706  therebetween. The reference probe is adjacent to a reference surface  704 , with a reference gap  712  therebetween.  
         [0051]     The air flow in the first and second legs  602  and  604  are initially balanced, resulting in no air pressure difference between areas  110  and  112 . When the measurement gap  706  changes relative to the reference gap  712 , the air flow in the first leg  602  changes relative to the air flow in the second leg  604 , causing a corresponding pressure change in area  110  relative to the area  112 . The pressure change is sensed by the pressure sensor  100 , as described in sections above.  
         [0052]     Alternatively, the reference leg  604  and the reference probe  708  are replaced with a reference pressure. For example,  FIG. 8  is a side plan view of a proximity sensor  800 , in which the reference leg  604  is replaced with a reference pressure  802 . The reference pressure  802  can be an ambient pressure or a controlled pressure.  
         [0000]     VIII. Conclusion  
         [0053]     The present invention has been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Any such alternate boundaries are thus within the scope and spirit of the claimed invention. One skilled in the art will recognize that these functional building blocks can be implemented by discrete components, application specific integrated circuits, processors executing appropriate software and the like and combinations thereof.  
         [0054]     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.