VACUUM PRESSURE SENSOR INCLUDING CONTAMINATION SHIELDING

Abstract

A vacuum pressure sensor includes an electrode and a diaphragm forming a capacitive structure. The sensor further includes a housing defining a sensor cavity and including a support structure configured to support the capacitive structure within the sensor cavity. The diaphragm is located in a diaphragm plane, and the electrode extends substantially parallel to the diaphragm on a first side of the diaphragm plane. The housing further includes an inlet disposed on a second side of the diaphragm plane and configured to be in fluid communication with a measurement environment.The sensor further comprises a contamination shield disposed in the sensor cavity between the inlet and the capacitive structure, wherein the contamination shield is configured to provide at least one fluid communication path from the inlet to the membrane, and wherein each of the at least one fluid communication paths crosses the membrane plane at least twice.

Description

REGIONThe present disclosure relates generally to vacuum pressure sensors, and more particularly to a vacuum pressure sensor having a contamination shield.BACKGROUNDIndustrial Systems and Processes for Depositing Materials on a Base Substrate and Removing Materials from a Base Substrate, e.g..Semiconductor fabrication processes often require vacuum chambers with strictly controlled environments to provide the required reactive gases at controlled concentrations, pressures, temperatures and flow rates. Examples of such applications and processes include various types of deposition and etching processes, as well as sterilization processes.In these industrial systems, sensors are needed to measure process parameters such as pressure, temperature, and gas flow rate. For example, capacitive diaphragm gauges are known in the art and simplified examples thereof are illustrated in FIGS. 1 and 2. Referring to FIG. 1, a vacuum pressure sensor 100 includes a housing 102 defining a sensor cavity 104 in which a capacitive structure 108 is disposed. A conduit forms an inlet 106 and is air tightly connected to the housing 102 and allows fluid communication for media as illustrated by the thick arrows from a sensing environment (e.g., a vacuum chamber, not shown) to the sensor cavity 104. The capacitive structure 108 includes a conductive, flexible membrane 108 that is held at a fixed distance from an electrode 110 located in a permanently sealed vacuum environment 112 and thus forms a capacitor. In a nominal state (i.e., non-deflected), the diaphragm 108 lies within a plane 114 bisecting the sensor cavity 104, such that the capacitive structure 108 has a known capacitance value. When the diaphragm 108 is exposed to different pressures from the sensing environment, the diaphragm 108 deflects to a different extent, thereby changing the capacitance of the capacitive structure. Using known components and circuitry, such changes in capacitance may be measured so that the pressure in the measured environment may be determined.The aforementioned industrial systems often generate reaction byproducts such as vapors and particles, which migrate into the cavity of a sensor, spread there, and contaminate and / or corrode sensor elements arranged there. These contaminants are often in the form of deposited films and particles that deposit on the sensor element, such as the sensor diaphragm 108 of a capacitive sensor. When such process contaminants accumulate on the sensor element of a sensor or may corrode, measurement accuracy and stability of the sensor output deteriorate over time. In order to ensure proper performance and reliability of the measurement results of the sensor, it is important to prevent process contamination of such sensor elements, and various techniques for minimizing such contamination are known in the art.For example, heated vacuum manometers are frequently used in which the temperature of the sensor is controlled high enough to prevent vapor condensation in the sensor cavity. While this method is extremely effective in preventing condensation contaminants, such heated manometers are more expensive than unheated manometers and do not prevent particulate contaminants from entering and affecting the sensor element.Another example is the use of discrete inline filters to trap particulate contaminants in the lines leading to the sensors. However, such filters require additional system components and may not efficiently condense vapors before they reach the sensing element of the sensor.Moreover, routine maintenance work has been performed to remove contaminants in the sensor cavity by solvent rinsing. However, in this technique, the system must be shut down to perform maintenance, the effectiveness of this technique being highly dependent on the specific solvent and the technique used for rinsing. Damage or degradation to the sensor may also occur when improper or improper solvents are used or an improper flushing technique is employed.The use of a shield barrier or a plasma shield is a common technique for protecting the sensor membrane from direct exposure to process contaminants, examples of which are illustrated in FIGS. 1 and 2. In FIG. 1, a disk-like shield 120 is inserted within the sensor cavity 104 and is configured to prevent visual communication of incoming fluid media from the conduit 106 to the membrane. Similarly, in FIG. 2, the sensor 200 (having substantially the same housing, conduit and sensor structure as in FIG. 1 ) includes a helical shield 220 inserted within the inlet conduit that in turn prevents line-of-sight access from the sensing environment to the sensor cavity. Although these shields 120, 220 provide a type of protection as a primary barrier and block most contaminants, they still leave substantial paths around these shields that can result in a secondary exposure of sensitive membrane regions to contamination.Thus, techniques that overcome the above-mentioned deficiencies of the prior art techniques would be a justified addition to the technique.SUMMARYThe above-described shortcomings are solved by providing a vacuum pressure sensor according to the present disclosure. In one embodiment, such a sensor comprises an electrode and a membrane forming a capacitive structure. The sensor further comprises a housing defining a sensor cavity and comprising a support structure configured to support the capacitive structure within the sensor cavity. The membrane is located in a membrane plane and the electrode extends substantially parallel to the membrane on a first side of the membrane plane. The housing further includes an inlet disposed on a second side of the membrane plane and configured to be in fluid communication with a measurement environment. The sensor further comprises a contamination shield disposed in the sensor cavity between the inlet and the capacitive structure, wherein the contamination shield is configured to provide at least one fluid communication path from the inlet to the membrane, and wherein each of the at least one fluid communication paths crosses the membrane plane at least twice.In one embodiment, the housing and contamination shield are formed from corrosion resistant material such as INCONEL or 316L stainless steel.In one embodiment, the contamination shield is mounted to the support structure.In one embodiment, each of the at least one fluid communication path is partially provided by an opening formed in the contamination shield on the first side of the membrane plane.In one embodiment, the contamination shield includes a bottom wall extending substantially parallel to and on the second side of the membrane plane, and further includes a side wall extending from the bottom wall such that a distal edge of the side wall terminates on the first side of the membrane plane.In an embodiment, the support structure comprises an undercut region extending substantially parallel to the membrane plane and on the first side thereof to define a rear surface of the support structure. In addition to this embodiment, the contamination shield may include a bottom wall extending substantially parallel to and on the second side of the membrane plane, a side wall extending from the bottom wall to the first side of the membrane plane, and a top wall extending from the side wall substantially parallel to the membrane plane, wherein the top wall is disposed between the housing and the back surface of the support structure, and wherein the top wall includes at least one opening defining the at least one fluid communication path. Still referring to this embodiment of one, the contamination sensor may be formed of upper and lower shield portions, wherein the upper shield portion is provided as part of the support structure or wherein the upper shield portion comprises the upper wall. Moreover, the upper shield portion may include at least a part of the side wall.In an embodiment, a fluid communication path of the at least one fluid communication path includes at least one labyrinth feature that partially blocks the fluid communication path. The at least one labyrinth feature may be disposed on the housing and / or on the contamination shield.BRIEF DESCRIPTION OF THE DRAWINGSThe foregoing and other features and advantages will be more fully described in the following, non-limiting description of specific embodiments taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic cross-sectional view illustrating a first embodiment of a vacuum pressure sensor with a contamination shield according to the prior art; FIG. 2 is a schematic cross-sectional view illustrating a second embodiment of a vacuum pressure sensor with a contamination shield according to the prior art; FIG. 3 is a schematic cross-sectional view illustrating a first embodiment of a vacuum pressure sensor with a contamination shield according to the present disclosure; FIG. 4 is a schematic cross-sectional view illustrating a second embodiment of a vacuum pressure sensor with a contamination shield according to the present disclosure; FIG. 5 is a schematic cross-sectional view illustrating a third embodiment of a vacuum pressure sensor with a contamination shield according to the present disclosure; and FIG. 6 is a schematic cross-sectional view illustrating a fourth embodiment of a vacuum pressure sensor with a contamination shield according to the present disclosure.DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTSAs used herein, terms substantially similar to "at least one of A, B, or C" are to be interpreted disjunctionally, i.e., they require A or B or C, or any combination thereof, unless the context indicates or implies otherwise. Further, terms substantially similar to "at least one of A, B, and C" are to be interpreted conjunctivally, i.e., they require at least one of A, at least one of B, and at least one of C, unless the context indicates or implies otherwise. Further, the term "substantially" or similar terms requiring subjective comparison are to be understood as "within manufacturing tolerances" unless the context indicates or implies otherwise.As used herein, the term "operably connected" refers to at least one functional relationship between two elements and may encompass configurations in which the two elements are directly connected to one another, i.e., without intervening elements, or are indirectly connected to one another, i.e., with intervening elements.As used herein, the term "fluid communication" refers to a configuration between two or more members in which fluid can flow between those members in at least one direction.All vacuum pressure sensors illustrated in the accompanying figures are not drawn to scale. Moreover, as is known in the art, the various sensors illustrated in the figures generally have a cylindrical shape about a longitudinal axis.Referring to FIG. 3, a simplified illustration of a first embodiment of a vacuum pressure sensor 300 including a contamination shield according to the present disclosure is shown. The sensor 300 includes a housing 302 mounted on a support structure 304 so as to form an airtight sensor cavity 306 therebetween. The materials used for the housing 302 and the mounting structure 304 are the same as materials commonly used in the art. A conduit that has an airtight connection to the housing 302 forms a fluid inlet 308 to the sensor cavity 306. According to known techniques, the support structure 304 is configured to support a capacitive structure 310 comprising a membrane 312 and an electrode 314 within the sensor cavity 306. In a nominal non-deflected state, the diaphragm 312 lies within a diaphragm plane 316. Throughout the present disclosure, regions above the membrane planes as depicted in the present figures are considered a first side of the membrane plane, while regions below the membrane planes as depicted in the present figures are considered a second side of the membrane plane.It should be noted once again that the structures illustrated in FIG. 3 are not drawn to scale; for example, for a membrane 312 having a diameter of 1 inch (25.4 mm), the distance between the membrane 312 and the electrode 314 is about 0.005 inch (0.13 mm). Components and circuitry that provide the electrical connection to the diaphragm 312 and the electrode 314 are well known in the art and are not shown in FIG. 3 for ease of illustration.The sensor 300 further includes a contamination shield 320 disposed within the sensor cavity 306 between the inlet 308 and the capacitive structure 310 to interfere with line-of-sight communication as well as fluid communication between the inlet 308 and the capacitive structure 310. The contamination shield 320 is configured to provide at least one fluid communication path from the inlet 308 to the membrane 312 while ensuring that the at least one fluid communication path is convoluted, thereby reducing the likelihood that contaminants will reach the membrane 312. In the context of the present disclosure, the term "entanglement" means that a contamination shield according to all embodiments of the present disclosure is configured to ensure that the at least one fluid communication path provided thereby crosses the membrane plane at least twice, as described in more detail below. Such a configuration tends to substantially surround or isolate capacitive structure 310 from inlet 308, thereby making capacitive structure 310 more difficult to reach for contaminants, while still providing a relatively compact structure for sensor 300. Such a configuration further has the further advantage that the capacitive structure 310 is isolated from environmental factors (e.g., barometric pressure, thermal transients, etc.), thereby improving accuracy and consistency of the sensor 300. In the various embodiments described herein, various examples of contamination shields that meet these criteria are illustrated.In general, contamination shields according to the present disclosure are preferably made from corrosion resistant materials (particularly materials resistant to the specific chemicals and contaminants in industrial processes to which they are likely to be exposed). Examples of such materials include the "INCONEL" alloy or 316L stainless steel. Other materials suitable for this purpose are known to those skilled in the art.In the first embodiment of FIG. 3, the contamination shield 320 is formed as a cup-like structure having a bottom wall 322 and an annular side wall 324 extending substantially perpendicularly from a periphery of the bottom wall 322. The diameter of the contamination shield 320 is such that it is greater than an outer diameter of the capacitive structure 310 but less than an inner diameter of the housing 302, thereby forming flow paths, as described in more detail below. As shown in FIG. 3, the contamination shield 320 is mounted to the support structure 304 using known techniques (e.g., welding), although this is not a prerequisite, i.e., in an alternative embodiment, the contamination shield 320 could be mounted to the housing 302 via suitable support struts or the like, for example. In the illustrated embodiment, the bottom and side walls 322, 324 are integrally formed as a single unit. As further shown, bottom wall 322 is configured to extend substantially parallel to membrane plane 316. A feature of the contamination shield 320 is that the bottom wall 322 is disposed on the second (bottom) side of the membrane plane 316, while the side wall 324 extends from the bottom wall 322 across the membrane plane 316 and has a distal edge (relative to the bottom wall 322) terminating at a point on the first side of the membrane plane 316. In this manner, the configuration, placement, and sizing of the contamination shield 320 relative to the configuration, placement, and sizing of the housing 302 and the capacitive structure 310 results in the creation of fluid communication paths that are forced to cross the membrane plane 316 at least twice.In conjunction with the housing 302, the bottom and side walls 322, 324 form a first horizontal flow path 326 and a first (annular) vertical flow path 328. Similarly, and in conjunction with the support structure 304 and the capacitive structure 310, the bottom and side walls 322, 324 also form a second (annular) vertical flow path 330 and a second horizontal flow path 332. In the illustrated embodiment, the sidewall 324 includes at least one opening 334 that establishes, though restricted, fluid communication between the respective vertical flow paths 328, 330. In this way, the fluid communication between the horizontal flow paths 326, 332, the vertical flow paths 328, 330, and at least one opening 334 creates at least one fluid communication path from the inlet 308 to the diaphragm 312. As shown by the thick arrows, media from the measurement environment may thus flow through the inlet 308 into the first horizontal flow path 326, and thereafter into the first vertical flow path 328, thereby traversing the membrane plane 316 a first time. The medium may continue to flow through the openings 334 into the second vertical flow path 330 and into the second horizontal flow path 332, traversing the membrane plane 316 a second time. Media present in the second horizontal flow path 332 impinges on the diaphragm 312 thereby allowing measurement of the pressure within the measurement environment. The at least one fluid communication path thus formed from the inlet 308 to the diaphragm 312 provides a relatively long path and surfaces that provide a greater possibility for particulates and condensates to accumulate before encountering the diaphragm 312.As further illustrated in FIG. 3, the support structure 304 may optionally include an undercut region 340 formed therein such that the undercut region 340 extends behind the capacitive structure 310 and forms a back surface 342 of the capacitive structure 310. Techniques for forming such an undercut region are known to those skilled in the art. The presence of the undercut region 340 may provide an additional surface upon which particles or condensates may come to rest before encountering the membrane 312.Moreover, in further embodiments described below, undercut region 340 may be configured to receive a portion of the contamination shield.Referring to FIG. 4, a simplified illustration of a second embodiment of a vacuum pressure sensor 400 including a contamination shield according to the present disclosure is shown. In FIG. 4, like reference numerals refer to like structures as compared to FIG. 3 In this second embodiment, the sensor cavity 306 is defined by an upper housing 450 in addition to the housing 302 and the support structure 404. Here, the support structure 404 is altered to provide a larger undercut region 440 such that a back surface 442 of the support structure 404 is further within the sensor cavity 306 compared to the first embodiment 300 of FIG. 3.The upper housing 450 spans the diameter of an opening (opposite the inlet 308) formed by the housing 302 and is air tightly secured to a terminal edge of the housing 302 using known techniques. An opening is formed centrally in the upper housing 450 such that the support structure 404 can be air tightly secured to the upper housing 450 using known techniques. The upper housing 450 further includes a flange 452 that extends into the undercut region 440 opposite the back surface 442 of the support structure 404. An annular portion 454 of the flange 452 extends downwardly (as shown in FIG. 4 ) and a radially extending portion 456 of the flange 452 extends substantially parallel to the diaphragm plane 316 such that a peripheral edge of the radially extending portion 456 has a diameter greater than an outermost diameter of the support structure 404 but less than an inner diameter of the housing 302. In this manner, the flange 452 provides a third horizontal flow path 460 and further provides a fourth horizontal flow path 462 in cooperation with the back surface 442 of the support structure 404.In addition, the flange 452 has at least one opening 434 formed therein that provides fluid communication between the third and fourth horizontal flow paths 460, 462. In the illustrated embodiment, the at least one aperture 434 is formed in the annular portion 454 of the flange 452. However, this is not a prerequisite, since the at least one opening 434 can instead also be formed in the radially extending section 456 of the flange 452.The contamination shield 420 in this embodiment again has a cup-like shape and comprises a lower wall 422 arranged on a second side of the membrane plane 316 and a side wall 424 starting therefrom and extending to the first side of the membrane plane 316. Unlike the first embodiment of FIG. 3, no openings are formed in the side wall 424. In addition, the contamination shield 420 is mounted to the radially extending portion 456 of the flange 452. In this manner, the radially extending portion 456 effectively serves as the top wall of the contamination shield.In this configuration, the at least one created fluid communication path includes (in order from inlet 308 to diaphragm 312) the first horizontal flow path 326, the first vertical flow path 328, the third horizontal flow path 460, the at least one opening 434, the fourth horizontal flow path 462, the second vertical flow path 330, and the second horizontal flow path 332. The addition of the third and fourth horizontal flow paths 460, 462 substantially increases the overall length of the at least one fluid communication path, thereby providing additional isolation of the capacitive structure 310 from the inlet 308 as well as even greater opportunities for the accumulation of particles and condensates prior to encountering the membrane 312.Referring to FIG. 5, a simplified illustration of a third embodiment of a vacuum pressure sensor 500 including a contamination shield according to the present disclosure is shown. In FIG. 5, like reference numerals refer to like structures as compared to FIG. 3, and in this third embodiment, a case 302 again has a cup-like structure. In this case, however, the housing 302 is inverted so as to be mounted on a housing base 503 on which the inlet 308 is in turn mounted. Thus, the sensor cavity 306 is defined by the housing base 503, the housing 502, and a support structure 504 mounted to the housing 502 (in a central opening formed in the housing 502). Again, the support structure 504 is altered (as compared to FIG. 3 ) to provide a larger undercut region 540 such that a back surface 542 of the support structure 504 is further within the sensor cavity 306 as compared to the first embodiment 300 of FIG. 3.In the third embodiment, the contamination shield 520 includes a bottom wall 522 and a side wall 524 substantially similar to those described above with respect to FIGS. 3 and 4. However, in this case, the contamination shield also includes a top wall 526 that extends radially inward from the top of the side wall 524. The top wall 526 has a central opening configured to receive a portion of the support structure 504, such that the top wall 526 is airtightly secured to the support structure 504 using known techniques. The top wall 526 also includes at least one opening 534.As further shown in FIG. 5, the contamination shield 520 is formed from two sections, a bottom shield section 570 and a top shield section 572, which sections can be air tightly secured together using known techniques. As shown, the upper shield portion 572 provides the 526 and a portion of the sidewall 524, while the lower shield portion 570 provides another portion of the sidewall 524 and the bottom wall 522. However, it is understood that the upper and lower shield portions 570, 572 could be constructed to provide different portions of the various walls 522, 524, 526, respectively, that define the contamination shield 520.Nevertheless, such a compartmentalized construction of the contamination shield 520 simplifies the assembly of the sensor 500 because the upper shield portion 572 can be first attached to the support structure 504. Subsequently, the lower shield portion 570 is attached to the upper shield portion 572 such that the contamination shield 520 substantially surrounds the capacitive structure 310. Subsequently, the assembly comprising the support structure 504 and the contamination shield 520 is mounted on the housing 502, which is then attached to the housing base 503.In the third embodiment of FIG. 5, similar to the embodiment of FIG. 4, the at least one fluid communication path (in order from the inlet 308 to the diaphragm 312) includes the first horizontal flow path 326, the first vertical flow path 328, a third horizontal flow path 560, the at least one opening 534, a fourth horizontal flow path 562, the second vertical flow path 330, and the second horizontal flow path 332. The addition of the third and fourth horizontal flow paths 560, 562 substantially increases the overall length of the at least one fluid communication path once again, thereby providing additional isolation of the capacitive structure 310 from the inlet 308 as well as even greater opportunities for the accumulation of particles and condensates prior to encountering the membrane 312.Referring to FIG. 6, a fourth embodiment of a vacuum pressure sensor 600 is shown, which is substantially similar to the third embodiment of FIG. 6. However, in this fourth embodiment, obstacles in the form of labyrinth features 680 are partially disposed within the first horizontal flow path 326. Although illustrated within the first horizontal flow path 326, it should be appreciated that such labyrinth features 680 may alternatively or additionally be disposed in any of the other horizontal or vertical flow paths described in any of the embodiments disclosed herein. In the illustrated example, each of the labyrinth features 680 includes a pair of upwardly extending protrusions 682 formed in the housing base 503 and a downwardly extending protrusion 684 formed in the bottom wall 522 of the contamination shield 620 and engaging between the upwardly extending protrusions 682. The labyrinth features 680 formed in this manner once again increase the overall distance of the at least one fluid communication path and provide additional surface area for collecting contaminants. It should be appreciated that although a shape of the labyrinth features 680 including a single spline is shown, this is not a prerequisite since each of the labyrinth features 680 may include multiple splines, e.g., three upwardly extending protrusions 682 with two downwardly extending protrusions 684 splined therebetween. As another alternative, each of the labyrinth features 680 may be simpler in design in that it includes only a single upwardly or downwardly extending protrusion 682, 684. Although the various embodiments according to the present disclosure have been described in connection with specific implementations thereof, it will be apparent that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, the various housing embodiments illustrated in FIGS. 3-6 may be interchanged as much as possible. Accordingly, the preferred embodiments of the invention set forth herein are intended to be illustrative only and not restrictive, so long as their variations are within the scope of the appended claims and their equivalents.

Claims

A vacuum pressure sensor comprising an electrode and a diaphragm forming a capacitive structure, the sensor comprising: a housing defining a sensor cavity and comprising a support structure configured to support the capacitive structure within the sensor cavity such that the diaphragm is in a diaphragm plane and the electrode extends substantially parallel to the diaphragm on a first side of the diaphragm plane, the housing further comprising an inlet disposed on a second side of the diaphragm plane and configured to be in fluid communication with a sensing environment; and a contamination shield disposed in the sensor cavity between the inlet and the capacitive structure, the contamination shield configured to provide at least one fluid communication path from the inlet to the diaphragm, each of the at least one fluid communication paths crossing the diaphragm plane at least twice.The vacuum pressure sensor of claim 1, wherein the housing and the contamination shield are formed of corrosion resistant material.The vacuum pressure sensor of claim 2, wherein the contamination shield comprises INCONEL or 316L stainless steel.The vacuum pressure sensor of claim 1, wherein the contamination shield is mounted on the support structure.The vacuum pressure sensor of claim 1, wherein each of the at least one fluid communication path is partially provided by an opening formed in the contamination shield on the first side of the membrane plane.The vacuum pressure sensor of claim 1, wherein the contamination shield comprises a bottom wall extending substantially parallel to and on the second side of the diaphragm plane, and further comprises a side wall extending from the bottom wall such that a distal edge of the side wall terminates on the first side of the diaphragm plane.The vacuum pressure sensor of claim 1, wherein the support structure comprises an undercut region extending substantially parallel to the diaphragm plane and on the first side thereof to define a back surface of the capacitive structure.The vacuum pressure sensor of claim 7, wherein the contamination shield comprises a bottom wall extending substantially parallel to and on the second side of the diaphragm plane, a side wall extending from the bottom wall to the first side of the diaphragm plane, and a top wall extending from the side wall substantially parallel to the diaphragm plane, wherein the top wall is disposed between the housing and the back surface of the support structure, and wherein the top wall comprises at least one opening defining the at least one fluid communication path.The vacuum pressure sensor according to claim 8, wherein the contamination sensor is formed of an upper shield portion and a lower shield portion.The vacuum pressure sensor according to claim 9, wherein the upper shield portion is provided as part of the support structure.The vacuum pressure sensor according to claim 9, wherein the upper shield portion comprises the upper wall.The vacuum pressure sensor of claim 11, wherein the upper shield portion comprises at least a portion of the sidewall.The vacuum pressure sensor of claim 1, wherein a fluid communication path of the at least one fluid communication path comprises at least one labyrinth feature that partially blocks the fluid communication path.The vacuum pressure sensor of claim 13, wherein the at least one labyrinth feature is disposed on the housing.The vacuum pressure sensor of claim 13, wherein the at least one labyrinth feature is disposed on the contamination shield.

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