Bipolar electrode bubble detection method and apparatus

A bubble detection method includes flowing a fluid through a conduit containing at least one bipolar electrode, applying an electric field across the fluid in the conduit, and detecting a presence of a bubble in the fluid when the bubble flows around or through the bipolar electrode by detecting a current or voltage output from the at least one bipolar electrode.

FIELD

The present disclosure relates generally to the field of semiconductor device manufacturing, and specifically to bipolar electrode containing apparatuses configured to detect bubbles in a fluid, such as a photoresist fluid, and methods of operating the same.

BACKGROUND

Photoresist layers are used as masks during fabrication (e.g., layer etching, etc.) of semiconductor devices. Photoresist layers are typically deposited on a semiconductor device in a solvent (e.g., as a solution or suspension) from reservoir through a pipe. However, bubbles in the photoresist solution or suspension may cause incomplete or defective photoresist mask patterns on the semiconductor devices, which may lead to defects in the semiconductor devices. The larger the bubbles size, the higher the likelihood of a major defect being created in the semiconductor device. Prior art methods for detecting bubbles in a photoresist fluid moving through a pipe typically use an optical sensor or a capacitor sensor. However, determining the size of the bubbles in the prior art sensors is difficult.

SUMMARY

According to an aspect of the present disclosure, a bubble detection apparatus comprises a container configured to flow a fluid therein, a pair of driving electrodes located on opposite sides of the container and configured to be exposed to the fluid, a bias circuit configured to apply a driving potential across the pair of driving electrodes to generate an electric field, multiple bipolar detection units located in the container and configured to be immersed in the fluid, wherein each of the multiple bipolar detection units comprises a respective first detection electrode and a respective second detection electrode that are spaced apart along a direction of the electric field within the fluid, and a current or voltage detection device configured to detect a current or voltage between the first detection electrode and the second detection electrode, and a computing unit configured to receive output currents or voltages from the current or voltage detection devices of the multiple bipolar detection units and detect presence of a bubble within the fluid when one or more of the output currents or voltages from the current or voltage detection devices of one or more of the multiple bipolar detection units drop below a respective reference level.

According to another aspect of the present disclosure, a bubble detection method includes flowing a fluid through a conduit containing at least one bipolar electrode, applying an electric field across the fluid in the conduit, and detecting a presence of a bubble in the fluid when the bubble flows around or through the bipolar electrode by detecting a current or voltage output from the at least one bipolar electrode.

DETAILED DESCRIPTION

A bipolar electrode (BPE) is conductor located in fluid (e.g., liquid, such as a solution or suspension). The conductor becomes an electrode having an anode and a cathode (e.g., a positive end and a negative end) by the action of an external electric field applied across the fluid from driving electrodes. In one embodiment, the presence of bubbles and/or the size of the bubbles can be detected by a change in measured voltage or current on the BPE caused by the bubbles blocking the external electric field as they pass around or through the bipolar electrode. Thus, when the driving electrodes are biased, a potential difference develops between the anode and cathode of the BPE based on the position and size of the bubble passing around or through the BPE.

The drawings are not drawn to scale. Multiple instances of an element may be duplicated where a single instance of the element is illustrated, unless absence of duplication of elements is expressly described or clearly indicated otherwise. Ordinals such as “first,” “second,” and “third” are employed merely to identify similar elements, and different ordinals may be employed across the specification and the claims of the instant disclosure. As used herein, a first element located “on” a second element can be located on the exterior side of a surface of the second element or on the interior side of the second element. As used herein, a first element is located “directly on” a second element if there exist a physical contact between a surface of the first element and a surface of the second element. Disclosure of an embodiment in which a first element comprises a second element herein also discloses another embodiment in which the first element consists essentially of, or consists of, the second element except for cases in which presence of an additional element is inherently implied.

Referring toFIGS.1A and1B, an exemplary bubble detection apparatus of the present disclosure is provided, which comprises a container6that contains a fluid5therein, a pair of driving electrodes (such as a driving anode90and a driving cathode10) located on opposite sides of the container6and exposed to the fluid5, and a bias circuit4configured to apply a driving potential across the pair of driving electrodes (90,10). For example, the bias circuit4may be a voltage source configured to apply a positive voltage to the driving anode90and a negative voltage to the driving cathode10. The bubble detection apparatus may be used to detect bubbles (e.g., small air bubbles, such as microbubbles) in any fluid. One example of the fluid is a photoresist fluid, such as a photoresist solution or suspension travelling through a pipe to be dispensed onto a semiconductor device to form a photoresist mask. The container6may be a conduit, such as a pipe or a manifold through which the liquid flows, such as a photoresist fluid flowing from a photoresist fluid reservoir (e.g., tank) to a nozzle positioned over a susceptor holding a substrate of a semiconductor device. A pump (not shown) may be used to pump the fluid from the reservoir to the nozzle. Other fluids, such as a spin-on glass suspension may be used instead of the photoresist fluid.

At least one bipolar detection unit50is immersed in the fluid5. For example, one of multiple bipolar detection units50is expressly illustrated inFIGS.1A and1B. Each bipolar detection unit50comprises a respective first detection electrode60(which is also referred to as a detection anode) and a respective second detection electrode40(which is also referred to as a detection cathode) that are spaced apart along a direction of electric field E within the fluid5(e.g., direction from the driving anode90to the driving cathode10). Further, each of the multiple bipolar detection units50comprises is electrically connected to a current or voltage detection device55, such as a voltmeter (represented by a symbol including the letter “V’ and a circle therearound) configured to detect a voltage across the first detection electrode60and the second detection electrode40. In an alternative embodiment, the current or voltage detection device55may comprise an ammeter. The first and second detection electrodes (60,40) may comprise physically separate electrically conductive electrodes which are electrically connected to opposite input terminals of the voltmeter or ammeter, or they may comprise opposing ends of a single electrically conductive electrode which are electrically connected to opposite input terminals of the voltmeter or ammeter.

A diagram inFIG.1Billustrates the mechanism for a voltage differential between a pair of detection electrodes (60,40) of a bipolar detection unit50. The potential as a function of distance V(D) between the driving anode90(of which the location is symbolically represented by a “+” sign) and the driving cathode10(of which the location is symbolically represented by a “−” sign) generally decreases linearly. If the lateral spacing between the driving anode90and the driving cathode10is D and if the potential difference between the driving anode90and the driving cathode10is V(D), then the potential difference as a function of distance V(d) between a first detection electrode60and a second detection electrode40of a bipolar detection unit50having an electrode spacing of d and laterally spaced apart along the direction of an electric field E is given by: V(d)=V(D)×(d/D).

WhileFIGS.1A and1Billustrate an embodiment in which the first detection electrode60is more proximal to the driving anode90than the second detection electrode40is to the driving anode90within each bipolar detection unit50, embodiments are expressly contemplated herein in which the first detection electrode60is more distal from the driving anode90than the second detection electrode40is from the driving anode90within each bipolar detection unit50or within a subset of multiple bipolar detection units50. Thus, embodiments in which one of more of the multiple bipolar detection units are disposed in a flipped configuration in which positions of the first detection electrode60and the second detection electrode40are reversed in a bipolar detection unit50are included in the scope of the present disclosure.

Referring toFIG.2and according to an embodiment of the present disclosure, multiple types of bipolar detection units50can be concurrently employed within the exemplary bubble detection apparatus. In one embodiment, first-type bipolar detection units50can have a respective first detection electrode60and a respective second detection electrode40that are spaced apart along the direction of the electric field E by a first electrode spacing d1. Each of the first detection electrodes60and the second detection electrodes40in the first-type bipolar detection units50can have a first width w1along a direction that is perpendicular to the direction of the electric field E. Second-type bipolar detection units50can have a respective first detection electrode60and a respective second detection electrode40that are spaced apart along the direction of the electric field E by a second electrode spacing d2. Each of the first detection electrodes60and the second detection electrodes40in the second-type bipolar detection units50can have a second width w2along a direction that is perpendicular to the direction of the electric field E. Third-type bipolar detection units50can have a respective first detection electrode60and a respective second detection electrode40that are spaced apart along the direction of the electric field E by a third electrode spacing d3. Each of the first detection electrodes60and the second detection electrodes40in the third-type bipolar detection units50can have a third width w3along a direction that is perpendicular to the direction of the electric field E. Additional types of bipolar detection units50having a respective electrode spacing between a pair of a first detection electrode60and a second detection electrode40, and having a respective width for the first detection electrode60and the second detection electrode40, may be provided in some embodiments.

In one embodiment, the first electrode spacing d1, the second electrode spacing d2, and the third electrode spacing d3may be the same. The first width w1can be greater than the second width w2, and the second width w2can be greater than the third width w3, etc. In this case, the first potential difference V(d1) in the first-type bipolar detection units50, the second potential difference V(d2) in the second-type bipolar detection units50, and the third potential difference V(d3) in the third-type bipolar detection units can be the same irrespective of the differences between the first width w1, the second width w2, and the third width w3. In other words, different types of bipolar detection units50measures a same potential difference irrespective of the widths if the electrode spacing between the first detection electrode60and the second detection electrode40is the same in the direction of the electric field, and if the different types of bipolar detection units50are oriented in the same direction within the fluid5.

Generally, the lateral dimension (such as a width along a direction perpendicular to the electric field E) of each bipolar detection unit50may be in the range of the diameter of spherical bubbles to be detected. For example, the lateral dimension (such as a width along a direction perpendicular to the electric field E) of each bipolar detection unit50may be in a range from 1 microns to 10 mm, such as from 10 microns to 1 mm, although lesser and greater dimensions may also be employed.

Referring toFIG.3and according to an embodiment of the present disclosure, the multiple types of bipolar detection units50can be advantageously employed to detect presence and the size (e.g., diameter) of a bubble7within the fluid5. Generally, bubbles7can float along within the fluid5in the general direction of flow of the fluid5within the container6. The bubbles generate a locally inhomogeneous environment within the fluid5, and generate defects in the dispensed fluid (e.g., in the dispensed photoresist). Thus, detection of the presence and/or the density of bubbles7in the fluid5can indicate whether the dispensed fluid (e.g., photoresist) is suitable for use (e.g., as a mask on a semiconductor device) or if it should be discarded and a different volume of photoresist used as a mask on the semiconductor device. Further, the bubble detection apparatus of the embodiments present disclosure allows measurement of lateral dimensions (such as the diameter) of the bubbles as will be described below. Thus, the apparatus can determine if the bubble size is sufficiently large to cause unacceptable defects in the dispensed fluid (e.g., in the photoresist mask), in which the fluid is discarded, or are sufficiently small as not to cause unacceptable defects in the dispensed fluid, in which case the fluid is used for its intended purpose (e.g., the dispensed photoresist can be used as a mask or the dispensed spin-on glass can be used as a dielectric layer in the semiconductor device).

In an embodiment in which a spherical bubble (e.g., air bubble)7has a diameter that is less than the first width w1and is greater than the second width w2and the third width w3, the spherical bubble cannot completely electrically isolate from the fluid5the first detection electrode60and the second detection electrode40of the first-type bipolar detection unit50because at least a portion of the first detection electrode60and at least a portion of the second detection electrode40are in contact with the fluid5all the time, i.e., even when a bubble passes through or around (i.e., envelops) the first-type bipolar detection unit50. As discussed with reference toFIG.2, the potential difference between the first detection electrode60and the second detection electrode40is V(d1) irrespective of the lateral dimensions of portions of the first detection electrode60and the second detection electrode40that are in contact with the fluid5.

However, when the bubble passes through or around the second-type bipolar detection unit50or the third-type bipolar detection unit50, at least one of the first detection electrode60and the second detection electrode40of the second-type bipolar detection unit50or the third-type bipolar detection unit50can be completely enveloped within the bubble7and thus electrically isolated from the fluid5. In other words, direct contact between a first detection electrode60and the fluid5, or direct contact between a second detection electrode40and the fluid5, can be lost during transit of the bubble7through or around the second-type bipolar detection unit50or the third-type bipolar detection unit50. When the direct contact between the fluid5and either of the first detection electrodes60and the second detection electrodes40is lost, the bubble7shields the electrodes from the electric field. In this case, the voltage between a pair of a first detection electrode60and a second detection electrode40can be decreased from V(d1) to a lower value, such as zero volts, and the second-type bipolar detection unit50or the third-type bipolar detection unit50measures presence of a bubble that is at least as big as the width (i.e., w2or w3) of a respective bipolar detection unit50.

The three graphs in the lower portion ofFIG.3illustrate changes in the electrical potential (i.e., measured voltage) for three bipolar detection units50when the same bubble7sequentially passes through or around a first-type bipolar detection unit50, a second-type bipolar detection unit50, and a third-type bipolar detection unit50. Therefore, the existence and the approximate size of bubbles can be determined by monitoring changes in the output (e.g., output voltage) of the multiple types of bipolar detection units50of the present disclosure. If the measured voltage from a unit50drops below the reference voltage (e.g., V(d1)), then a bubble7having a diameter that is at least equal to the width of the electrode(s) (40and/or60) is detected.

According to an embodiment of the present disclosure, the multiple types of bipolar detection units50comprise first-type bipolar detection units50having a respective first-type first detection electrode60and a respective first-type second detection electrode40, and second-type bipolar detection units50having a respective second-type first detection electrode60and a respective second-type second detection electrode40, and optionally additional types of bipolar detection units50. Each of the second-type first detection electrodes60differs from each of the first-type first detection electrodes60by at least one dimension, such as a width along a direction that is perpendicular to the direction of the electric field E. If present, the detection electrodes (60,40) of the additional types of bipolar detection units50can differ from the detection electrodes (60,40) of the first-type bipolar detection units50and the second second-type bipolar detection units50by at least one dimension, such as a width along a direction that is perpendicular to the direction of the electric field E.

In one embodiment, each of the first-type first detection electrodes60has a first lateral dimension (such as a first width w1) along a direction that is perpendicular to the direction of the electric field E, and each of the second-type first detection electrodes60has a second lateral dimension (such as a second width w2) along the direction that is perpendicular to the direction of electrical filed E. The second lateral dimension is different from the first lateral dimension.

In one embodiment, a first electrode spacing d1between the respective first-type first detection electrode60and the respective first-type second detection electrode40in a first-type bipolar detection unit50is the same as a second electrode spacing d2between the respective second-type first detection electrode60and the respective second-type second detection electrode40. If present, the detection electrodes (60,40) of the additional types of bipolar detection units50can have the same electrode spacing between a respective pair of a first detection electrode60and a second detection electrode40as the first electrode spacing d1and the second electrode spacing d2.

Referring toFIGS.4A and4B, a first configuration of the exemplary bubble detection apparatus of the present disclosure is illustrated. The bubble detection apparatus includes a container6that contains a fluid5therein, a pair of driving electrodes (such as a driving anode90and a driving cathode10) located on opposite sides of the container6and exposed to the fluid5, a bias circuit (not expressly shown for clarity, the same as the bias circuit4inFIG.1) configured to apply a driving potential across the pair of driving electrodes (90,10), and multiple bipolar detection units50immersed in the fluid5. Each of the multiple bipolar detection units50comprises a respective first detection electrode60and a respective second detection electrode40that are spaced apart along a direction of the electric field E within the fluid5and comprises a voltmeter configured to detect a voltage across the first detection electrode60and the second detection electrode40. According to an aspect of the present disclosure, the first configuration of the exemplary bubble detection apparatus comprises a computing unit200(such as a special or general processor, for example a computer loaded with a specialized program for processing data from the multiple bipolar detection units50) configured to receive output voltages (wirelessly or via a wire) from the voltmeters55of the multiple bipolar detection units50and detect presence of a bubble7within the fluid5when one or more of the output voltages from the voltmeters55of the multiple bipolar detection units50drop below a respective reference level (e.g., V(d1)), e.g., to zero volts.

In one embodiment, the multiple bipolar detection units50may be arranged along the direction of the liquid5flow path (i.e., channel)9in the container6(e.g., pipe or manifold). In one embodiment, the liquid flow path9may be parallel to the direction of the electric field E. The bipolar detection units50can be placed between the driving electrodes (90,10). The fluid5may be continuously supplied from an inlet2of the container6, and may be continuously dispensed out at an outlet8of the container6, which may be connected to a drainage mechanism (such as a nozzle, mechanical pump and/or a conduit that causes a gravity-induced flow).

As discussed above, the multiple types of bipolar detection units50comprise first-type bipolar detection units50having a respective first-type first detection electrode60and a respective first-type second detection electrode40, and second-type bipolar detection units50having a respective second-type first detection electrode60and a respective second-type second detection electrode40, and optionally additional types of bipolar detection units50. Each of the second-type first detection electrodes60differs from each of the first-type first detection electrodes60by at least one dimension, such as a width along a direction that is perpendicular to the direction of the electric field E. If present, the detection electrodes (60,40) of the additional types of bipolar detection units50can differ from the detection electrodes (60,40) of the first-type bipolar detection units50and the second second-type bipolar detection units50by at least one dimension, such as a width along a direction that is perpendicular to the direction of the electric field E.

In one embodiment, the dimension that varies among the multiple types of bipolar detection units50may change in stages. In one embodiment, different types of bipolar detection units50may be arranged as respective arrays (A1, A2, A3, A4, A5) of bipolar detection units50that are located at different distances from one of the driving electrodes (90,10) (such as the driving anode90). For example, a first array A1of first-type bipolar detection units can be located at a first distance from the driving electrode90, a second array A2of second-type bipolar detection units can be located at a second distance greater than the first distance from the driving electrode90, a third array A3of third-type bipolar detection units can be located at a third distance greater than the second distance from the driving electrode90, a fourth array A4of fourth-type bipolar detection units can be located at a fourth distance greater than the third distance from the driving electrode90, and a fifth array A5of fifth-type bipolar detection units can be located at a fifth distance greater than the fourth distance from the driving electrode90. In one embodiment, the width of each type of bipolar detection units50may have a respective width that is different from the width of a bipolar detection unit50of any other type.

In one embodiment, the first-type bipolar detection units50may be arranged as a first array A1of first-type bipolar detection units50located on a first plane that is perpendicular to the direction of the electric field E and laterally spaced from the driving anode90by a first distance, and the second-type bipolar detection units50may be arranged as a second array A2of second-type bipolar detection units50located on a second plane that is perpendicular to the direction of the electric field E and laterally spaced from the first plane.

In one embodiment, the container6comprises a tubular enclosure (e.g., pipe or manifold) configured to confine the fluid5along directions that are perpendicular to the direction of the electric field E. In one embodiment shown inFIG.4B, the area laterally surrounded by inner sidewalls of the tubular enclosure within a plane that is perpendicular to the direction of the electric field E may be invariant with a lateral distance from one of the pair of driving electrodes (90,10) (such as the driving anode90) along the direction of the electric field E. In other words, the container6may comprise a pipe having a uniform inner diameter along its axis. In another embodiment shown inFIG.4C, the area laterally surrounded by inner sidewalls of the tubular enclosure within a plane that is perpendicular to the direction of the electric field E may vary with a lateral distance from one of the pair of driving electrodes (90,10) (such as the driving anode90) along the direction of the electric field E. In other words, the container6may comprise a pipe having a non-uniform inner diameter which increases or decreases continuously or in a stepwise manner along the axis of the pipe.

While the container6may comprise a cylindrical pipe in the embodiment described above, in alternative embodiments, the container6may comprise a tubular enclosure (e.g., pipe or manifold) having a vertical cross-sectional shape other than a circle, such as a rectangle, a rounded rectangle, an ellipse, or any generally curvilinear two-dimensional shape having a closed periphery within vertical planes that are perpendicular to the direction of the electric field E. In one embodiment, the vertical dimension (i.e., height) of the path of the fluid5may be the same or smaller than the width of bipolar detection units50of the narrowest-type in order to increase the probability of contact between the bipolar detection units50and the bubbles7, i.e., in order to increase the probability of detection of the smallest bubbles7.

In one embodiment, the multiple bipolar detection units50comprise a first array A1of bipolar detection units50including a first subset of the multiple bipolar detection units50arranged within a first plane that is perpendicular to the direction of the electric field E and located at a first distance from one of the pair of driving electrodes (90,10) (such as the driving anode90), and a second array A2of bipolar detection units50including a second subset of the multiple bipolar detection units50arranged within a second plane that is perpendicular to the direction of the electric field E and located at a second distance from the one of the pair of driving electrodes. The second distance is different from the first distance.

Generally, a plurality of arrays (A1, A2, A3, A4, A5) of bipolar detection units50including a respective type of bipolar detection units50can be provided. Each type of bipolar detection units50may have different dimensions along a direction that is perpendicular to the direction of the electric field E, such as a width along the direction that is perpendicular to the direction of the electric field E. Each array (A1, A2, A3, A4, A5) of bipolar detection units can be laterally spaced from the driving anode90by different distances.

In one embodiment, the bubble detection apparatus of the embodiments present disclosure may comprise an inlet2configured to receive a flow of the fluid5into the container6, and an outlet8configured to dispense the fluid5from the container6therethrough. The inlet2and the outlet8may be spaced apart along a separation direction between the pair of driving electrodes (90,10).

Referring toFIG.4C, a first alternative embodiment of the first configuration of the bubble detection apparatus ofFIGS.4A and4Bis illustrated. In this case, the diameter or height of the channel9(i.e., the area laterally surrounded by inner sidewalls of the tubular enclosure of the container6within a plane that is perpendicular to the direction of the electric field E) can change as a function of the lateral distance from one of the pair of driving electrodes (90,10) (such as the driving anode90) along the direction of the electric field E. For example, the height of the conductive path for the fluid5may change continuously or stepwise as a function of the lateral distance from one of the pair of driving electrodes (90,10) (such as the driving anode90) along the direction of the electric field E. In one embodiment, the height of the conductive path for the fluid5may be greater over an array of bipolar detection units50having a greater width than over another array of bipolar detection units50having a lesser width.

Referring toFIG.4D, a second alternative embodiment of the first configuration of the bubble detection apparatus can be derived from the first configuration of the bubble detection apparatus ofFIGS.4A and4Bby providing arrays of bipolar detection units50on a pair of surfaces of the tubular enclosure that face each other, such as a top surface and a bottom surface. The probability of detection of bubbles7increases through use of a pair of arrays of bipolar detection units50on a pair of opposing surfaces instead of a single array of bipolar detection units50located on a single surface.

Referring toFIG.4E, a third alternative embodiment of the first configuration of the bubble detection apparatus can be derived from the first alternative embodiment of the first configuration of the bubble detection apparatus ofFIG.4Cby providing arrays of bipolar detection units50on a pair of surfaces of the tubular enclosure that face each other, such as a top surface and a bottom surface. The probability of detection of bubbles7increases through use of a pair of arrays of bipolar detection units50on a pair of opposing surfaces instead of a single array of bipolar detection units50located on a single surface.

Referring toFIGS.5A and5B, a second configuration of the exemplary bubble detection apparatus can be derived from the first configuration of the exemplary bubble detection apparatus by providing lateral offsets in a direction perpendicular to the electric field direction among the multiple arrays of bipolar detection units50, and by employing a same width for each bipolar detection unit50within the multiple arrays of bipolar detection units50. In one embodiment, a first array A1of bipolar detection units50can be located at a first distance from the driving anode90, and a second array A2of bipolar detection units50can be located at a second distance from the driving anode90. The first array of bipolar detection units50and the second array of bipolar detection units50can be periodic one-dimensional arrays having a uniform pitch along a lateral direction that is parallel to the first plane and the second plane. In one embodiment, the second array A2of bipolar detection units50can be laterally offset from the first array A1of bipolar detection units50along the lateral direction by a lateral offset distance that is in a range from 10% to 90% of the uniform pitch.

In configurations in which the lateral offset among the arrays (A1, A2, A3, A4, A5) of bipolar detection units50is zero, a significant fraction of spherical bubbles7having a diameter that is less than the maximum lateral extent of a neighboring pair of bipolar detection units50along the direction perpendicular to the flow of the fluid5may pass through the arrays (A1, A2, A3, A4, A5) of bipolar detection units50without detection by passing through the gap between the neighboring pair of bipolar detection units50.

Referring toFIG.5B, staggering of the arrays (A1, A2, A3, A4, A5) of bipolar detection units50along the direction that is perpendicular to the flow of the fluid5and perpendicular to the electric field direction with lateral offsets can increase the probability of detection of the bubbles7. For example, the bubble7is not detected in array A1, but is detected in array A2which is laterally offset from array A1. The lateral offset distance between a pair of arrays (A1, A2, A3, A4, A5) may be in a range from 10% to 90% of the uniform pitch. Thus, the efficiency of bubble detection can be increases by laterally staggering the multiple arrays (A1, A2, A3, A4, A5) of bipolar detection units50.

Referring toFIG.6, a third configuration of the exemplary bubble detection apparatus of the present disclosure may be derived from the first configuration or the second configuration by interlacing the detection electrodes (60,40) of different arrays (A1, A2, A3, A4, A5) of bipolar detection units50. In this case, the electrode spacing between a first detection electrode60and a second detection electrode40within each bipolar detection unit50may be about the same as in the first and second configurations, or may be greater than the electrode spacing in the first and second configurations.

In one embodiment, the first array A1of bipolar detection units50including a first subset of the multiple bipolar detection units50can be arranged within a first plane that is perpendicular to the direction of electric field E and is located at a first distance DIST_1from one of the pair of driving electrodes (90,10), and a second array A2of bipolar detection units50including a second subset of the multiple bipolar detection units50can be arranged within a second plane that is perpendicular to the direction of electric field E and is located at a second distance DIST_2from the one of the pair of driving electrodes. The second distance DIST_2can be different from the first distance DIST_1. For example, a first array A1of bipolar detection units50may be located in a first plane located at a first distance DIST_1from the driving anode90, and a second array A2of bipolar detection units50may be located in a second plane located at a second distance DIST_2from the driving anode90.

In one embodiment, an electrode spacing within the first subset of the multiple bipolar detection units50, and/or within each of the multiple bipolar detection units50, can be greater than the distance between the first plane and the second plane, i.e., the difference between the second distance DIST_2and the first distance DIST_1. In this case, second detection electrodes40within the first subset (such as the first array A1) of the multiple bipolar detection units50are more distal from the one of the pair of driving electrodes (90,10) (such as the driving anode90) than first detection electrodes60within the second subset (such as the second array A2) of the multiple bipolar detection units50are from the one of the pair of driving electrodes (90,10).

Referring toFIG.7, a fourth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from any of the first, second, and third configurations of the exemplary bubble detection apparatus. In the fourth configuration, two or more neighboring first detection electrodes60located within a same array (A1, A2, A3, A4, A5) can be merged to provide a respective larger first detection electrode60. Wiring on the first detection electrodes60can be simplified, and a more compact design can be provided. A bubble7can be detected when the bubble7envelops a second detection electrode40.

In one embodiment, an electrode spacing within a first subset (such as a first array A1) of the multiple bipolar detection units50is greater than a distance between the first plane and the second plane (i.e., the difference between the first distance DIST_1and the second distance DIST_2), and second detection electrodes40within the first subset of the multiple bipolar detection units50are more distal from the one of the pair of driving electrodes (which may be the driving anode90or the driving cathode10) than first detection electrodes60within a second subset (such as a second array A2) of the multiple bipolar detection units50are from the one of the pair of driving electrodes.

In one embodiment, a maximum lateral dimension (such as a width along a direction that is perpendicular to the direction of the electric field E) of each of the first detection electrodes60of a subset (such as any of the arrays (A1, A2, A3, A4, A5)) of the multiple bipolar detection units50within a plane (such as the first plane located at the first distance DIST_1) that is perpendicular to the direction of the electric field E is greater than a maximum lateral dimension (such as a width) of each of the second detection electrodes40of the subset of the multiple bipolar detection units within another plane that is perpendicular to the direction of the electric field E (and containing surfaces of the second detection electrodes40). In other words, the first detection electrode60may be wider than the second detection electrodes40within one, and/or more, and/or each, of the arrays (A1, A2, A3, A4, A5) of the multiple bipolar detection units50.

In one embodiment, each of the first detection electrodes60in the multiple bipolar detection units50can be connected to a respective set of multiple second detection electrodes40through a respective plurality of voltmeters. Each of the second detection electrodes40within the multiple bipolar detection units50can be connected to only a respective single one of the first detection electrodes60in the multiple bipolar detection units50. For example, N bipolar detection units50may include a single first detection electrode60and N second detection electrodes40, in which N is an integer greater than 1.

Referring toFIGS.8A and8B, a fifth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from any of the first, second, third, and fourth configurations of the exemplary bubble detection apparatus. In the fifth configuration, two or more neighboring second detection electrodes40located within a same array (A1, A2, A3, A4, A5) can be merged to provide a respective larger second detection electrode40. Wiring on the second detection electrodes40can be simplified, and a more compact design can be provided. A bubble7can be detected when the bubble7envelops a first detection electrode60.

In one embodiment, the first detection electrodes60of a subset (such as an array (A1, A2, A3, A4, or A5)) of the multiple bipolar detection units50are arranged as an array of discrete first detection electrodes60arranged within a plane that is perpendicular to the direction of the electric field E, and a set of at least two second detection electrodes40of the subset of the multiple bipolar detection units50is embodied as a common second detection electrode40. In one embodiment, N bipolar detection units50may comprise N first detection electrodes60and a common second detection electrode40. The common second detection electrode40may have a width that is greater than N times the width of a first detection electrode60within the N bipolar detection units50.

FIG.9is a schematic top-down view of a sixth configuration of the exemplary bubble detection apparatus of the present disclosure. In this embodiment, each of the first detection electrodes60in the multiple bipolar detection units50can be connected to a respective set of multiple second detection electrodes40through a respective plurality of voltmeters. Each of the second detection electrodes40within the multiple bipolar detection units50can be connected to only a respective single one of the first detection electrodes60in the multiple bipolar detection units50. For example, N bipolar detection units50may include a single first detection electrode60and N second detection electrodes40, in which N is an integer greater than 1. In one embodiment, each of the N second detection electrode40and the first detection electrode60in a bipolar detection unit50may have a same lateral dimension (such as a width) along a direction that is perpendicular to the direction of the electric field E.

In one embodiment, the respective set of multiple second detection electrodes40comprises a respective plurality of second detection electrodes40that are laterally spaced by different distances from one of the pair of driving electrodes (90,10) along the direction of electric field E. In one embodiment, the respective set of multiple second detection electrodes40comprises a respective plurality of second detection electrodes40having the same lateral dimension (such as a width) along a lateral direction that is perpendicular to the direction of the electric field E. In the sixth configuration of the exemplary bubble detection apparatus, the potential difference between a first detection electrode60and a second detection electrode40of a bipolar detection unit50varies depending on the electrode spacing between the first detection electrode60and the second detection electrode40.

Referring toFIG.10, a seventh configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from the sixth configuration of the exemplary bubble detection apparatus. In one embodiment, the respective set of multiple second detection electrodes40connected to a common first detection electrode60comprises a respective plurality of second detection electrodes40having different lateral dimensions (such as widths) along a lateral direction that is perpendicular to the direction of the electric field E. In one embodiment, multiple types of second detection electrodes40having different widths can be connected to a common first detection electrode60. In one embodiment, the multiple types of second detection electrodes40can have different electrode spacings from the first detection electrode60. For example, first-type second detection electrode40may have a first width and a first electrode spacing from the first detection electrode60, second-type second detection electrode40may have a second width and a second electrode spacing from the first detection electrode60, etc.

Referring toFIG.11, an eighth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from any of the previously described configurations of the exemplary bubble detection apparatus of the present disclosure by positioning the driving electrodes (90,10) along a direction that is not parallel to the flow direction of the fluid5. For example, the separation direction between the driving anode90and the driving cathode10can be perpendicular to the direction of the flow of the fluid5, and/or the lateral separation direction between an inlet2and an outlet8. Bubbles7can be detected when a bubble envelops any of the first detection electrodes60or the second detection electrodes40. In this configuration, the bubble detection apparatus may comprise an inlet2configured to receive a flow of the fluid5into the container6, and an outlet8configured to dispense the fluid5from the container6therethrough. The inlet2and the outlet8are spaced apart along a direction that is perpendicular to a separation direction between the pair of driving electrodes (90,10). In one embodiment, the bipolar detection units50may be arranged as a two-dimensional rectangular array of bipolar detection units50having a uniform or non-uniform pitch along the separation direction between the driving anode90and the driving cathode10, and having a uniform or non-uniform pitch along the separation direction between the inlet2and the outlet8.

Referring toFIG.12, a ninth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from the eighth configuration of the bubble detection apparatus of the present disclosure by positioning the bipolar detection units50in a non-rectangular array. In some embodiments, columns of bipolar detection units50arranged along the separation direction between the driving electrodes (90,10) may be laterally offset along the separation direction between the driving electrodes (90,10) from column to column. In some embodiments, rows of bipolar detection units50arranged along the flow direction may be laterally offset along the flow direction from row to row.

Referring toFIG.13A, a tenth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from any of the previously described configurations of the exemplary bubble detection apparatus by arranging a plurality of bipolar detection units50as a periodic array, such as a rectangular periodic array, having a first periodicity along a first direction and having a second periodicity along a second direction. In one embodiment, the first direction may be parallel to the direction of the electric field E, and the second direction may be perpendicular to the direction of the electric field E. In another embodiment, the first direction and the second direction may be orthogonal directions that are perpendicular to the direction of the electric field E.

Referring toFIGS.13B and13Cand according to an aspect of the present disclosure, the periodic array of bipolar detection units50may be connected to the computing unit200. The potential difference between a first detection electrode60and a second detection electrode40within each bipolar detection unit50can be continuously monitored. The outputs from the array of voltmeters55of the array of bipolar detection units50are mapped into an output array that replicates the physical locations of the bipolar detection units50in a virtual coordinate system. When no bubble7passes through the array of bipolar detection units50, all outputs of the array of the voltmeters can be non-zero, which are translated into an array of “l's” within the digitized output map, as illustrated in FIG.13B. When a bubble7passes through the array of bipolar detection units50, a subset of the outputs from the array of the voltmeters55can be zero volts, which is translated into logical “0's” within the digitized output map illustrated inFIG.13C. The areas the “0's” within the digitized output map can be employed to estimate the size of the detected bubble7. The frequency detection of bubbles7measures the bubble density within the fluid5. The exemplary bubble detection apparatus of the present disclosure can simultaneously measure the size distribution and the density of bubbles7within the fluid5.

Referring toFIG.14, an eleventh configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from any of the previously described configurations of the exemplary structure by employing a row of driving anodes90in lieu of a driving anode90, and/or by employing a column of driving cathodes10in lieu of a driving cathode10. Optionally, a plurality of flow channels9may be provided in lieu of a single flow channel9to facilitate flow of the fluid5therethrough. In one embodiment, a one-dimensional array or a two-dimensional array of bipolar detection units50may be provided on a sidewall of each flow channel9.

Referring toFIG.15, a twelfth configuration of the exemplary bubble detection apparatus of the present disclosure may be derived from the eleventh configuration of the exemplary bubble detection apparatus by positioning at least one driving anode90on a sidewall of the container6(e.g., on a sidewall of the inlet2) in a manner that does not impede the flow of the fluid5, and/or by positioning at least one driving cathode10on a sidewall of the container6(e.g., On a sidewall of the outlet9) in a manner that does not impede the flow of the fluid5.

Referring toFIGS.16A-16C, a thirteenth configuration of the exemplary bubble detection apparatus of the present disclosure may be derived from any of the previously described configurations of the exemplary bubble detection apparatus by providing at least one perforated flow blocking structure30including an array of openings31configured to guide flow of the fluid5therethrough. Each of the at least one perforated flow blocking structure30may comprise a respective perforated plate blocking the flow of the fluid5within the container6of the bubble detection apparatus, and including a one-dimensional array of openings31therethrough or a two-dimensional array of openings31therethrough.

In one embodiment, multiple bipolar detection units50can be formed on, or around, the openings in the perforated flow blocking structure(s)30. In one embodiment, the multiple bipolar detection units50may comprise a respective pair of a first detection electrode60and a second detection electrode40and a voltmeter55connecting the pair of the first detection electrode60and the second detection electrode40. In one embodiment, the first detection electrode60and the second detection electrodes40may be located on surfaces of the openings (such as tubular surfaces) through the perforated flow blocking structure(s)30. Specifically, the first and second detection electrodes (60,40) may be coated on the respective front and back sides of the perforated flow blocking structure30around the openings31if the perforated flow blocking structure30is electrically insulating (e.g., made of a glass, plastic or ceramic material).

In one embodiment, the multiple bipolar detection units50may comprise a one-dimensional array of the multiple bipolar detection units50located within a one-dimensional array of openings31within a perforated flow blocking structure30, such as a first perforated flow blocking structure30A. Further, the multiple bipolar detection units50may comprise two-dimensional arrays of the multiple bipolar detection units50located within a respective two-dimensional array of openings31within a respective perforated flow blocking structure30, such as a second perforated flow blocking structure30B or a third perforated flow blocking structure30C.

In one embodiment, a subset of the multiple bipolar detection units50comprises a two-dimensional array of bipolar detection units located on a two-dimensional array of openings31within a perforated flow blocking structure (30B,30C) that are configured to guide flow of the fluid5therethrough, and the first detection electrodes60and the second detection electrodes40of the two-dimensional periodic array of bipolar detection units50can be physically exposed to a respective opening31in the two-dimensional array of openings.

In one embodiment, the multiple bipolar detection units50may comprise an array of bipolar detection units50having a first pitch along a first direction and a second pitch along a second direction. For example, the second perforated flow blocking structure30B may comprise a two-dimensional array of openings31therethrough, and the two-dimensional array of openings31in the second perforated flow blocking structure30B may have the first pitch along the first direction and the second pitch along the second direction. The first direction and the second direction may be perpendicular to the direction of the flow of the fluid5. In one embodiment, the first direction may be perpendicular to the direction of the electric field E, and the second direction may be perpendicular to the direction of electric field E and perpendicular to the first direction.

In one embodiment, an additional perforated flow blocking structure, such as the third perforated flow blocking structure30C, can be provided. The third perforated flow blocking structure30C may be spaced from the second perforated flow blocking structure30B, and may have a respective two-dimensional array of openings31therethrough. Additional bipolar detection units50comprising an additional array of bipolar detection units50can be located on the two-dimensional array of openings in the third perforated flow blocking structure30C. The additional array of bipolar detection units50and the two-dimensional array of openings in the third perforated flow blocking structure30C may have a third pitch along the first direction and a fourth pitch along the second direction. The third pitch is less than the first pitch and the fourth pitch is less than the second pitch. In this case, the size (e.g., diameter) of the openings31through the third perforated flow blocking structure30C can be smaller than the size of the openings31through the second perforated flow blocking structure30B.

In one embodiment, the first detection electrode60and the second detection electrode40of each bipolar detection unit50can be located on a same side of a surface of an opening31in a respective perforated flow blocking structure30. For example, the first detection electrode60and the second detection electrode40of a bipolar detection unit50may be located on a bottom surface of an opening31(but on opposite sides of the structure30) in a perforated flow blocking structure30, on a top surface of an opening in a perforated flow blocking structure30, or on a sidewall of an opening in a perforated flow blocking structure30.

Referring toFIGS.17and18, fourteenth and fifteenth configurations of the exemplary bubble detection apparatus of the present disclosure can be derived from the thirteenth configuration of the bubble detection apparatus be employing a combination of a front perforated flow blocking structure32and a backside perforated flow blocking structure34in lieu of a perforated flow blocking structure30. For example, a first perforated flow blocking structure30A in the thirteenth configuration of the exemplary bubble detection apparatus may be replaced with a combination of a first front perforated flow blocking structure32A and a first backside perforated flow blocking structure34A, and a second perforated flow blocking structure30B in the thirteenth configuration of the exemplary bubble detection apparatus may be replaced with a combination of a second front perforated flow blocking structure32B and a second backside perforated flow blocking structure34B, and so forth. For each pair of a front perforated flow blocking structure32and a backside perforated flow blocking structure34, an array of first detection electrodes60for multiple bipolar detection units50can be provided on openings through the front perforated flow blocking structure32, and an array of second detection electrodes40for the multiple bipolar detection units50can be provided on openings through the backside perforated flow blocking structure34.

The number of the openings31in the front perforated flow blocking structure32may, or may not be, the same as the number of openings through the backside perforated flow blocking structure34within a pair of the front perforated flow blocking structure32and the backside perforated flow blocking structure34. The number of the first detection electrodes60on the front perforated flow blocking structure34may be the same as (as shown inFIG.17), or may be different from (as shown inFIG.18) the number of second detection electrodes40on the backside perforated flow blocking structure34within a pair of the front perforated flow blocking structure32and the backside perforated flow blocking structure34. In these configurations, the distance between a first detection electrode60and a second detection electrode40within each bipolar detection unit50can be determined primarily by the separation distance between the front perforated flow blocking structure32and the backside perforated flow blocking structure34. Generally, a bubble7can be detected when the bubble covers the entirety of a physically exposed surface of a first detection electrode60or a second detection electrode40.

Referring toFIGS.19A-19C, a sixteenth configuration of the exemplary bubble detection apparatus of the present disclosure can be derived from the thirteenth configuration of the exemplary bubble detection apparatus by positioning a first detection electrode60and a second detection electrode40of at least one bipolar detection unit50within different openings of a perforated flow blocking structure30, or on different surfaces (such as a top surface and a bottom surface) of a same opening31but on opposite sides of the perforated flow blocking structure30. Multiple perforated flow blocking structures30having openings of different sizes and/or of different periodicity may be employed. A bubble7can be detected when the bubble covers the entirety of a physically exposed surface of a first detection electrode60or a second detection electrode40.

FIG.20Aillustrates an array of bipolar detection units50prior to, and during, detection of a bubble7according to an embodiment of the present disclosure. Generally, each of the previously described configurations of the bubble detection apparatus, such as the configurations containing the perforated flow blocking structure30of the present disclosure may include a plurality of bipolar detection units50arranged as a periodic array, such as a rectangular periodic array. For example, a rectangular periodic array of bipolar detection units50may have a first periodicity along a first direction and a second periodicity along a second direction. In one embodiment, the first direction and the second direction may be orthogonal to each other, and may be perpendicular to the direction of the electric field E or may be perpendicular to the direction of flow of the fluid. A bubble7having a size that is greater than the first periodicity (i.e., a first pitch) and/or the second periodicity (i.e., a second pitch) can cover the entire area of at least one first detection electrode60and/or at least one second detection electrode40while passing through the periodic array of bipolar detection units50(e.g., while passing through plural openings31of the perforated flow blocking structure30). For example, as shown on the right side ofFIG.20A, one large bubble7may pass through several openings31of the perforated flow blocking structure30at the same time.

Referring toFIG.20Band according to an aspect of the present disclosure, the periodic array of bipolar detection units50may be wired or wirelessly connected to the computing unit200. The potential difference between a first detection electrode60and a second detection electrode40within each bipolar detection unit50can be continuously monitored. The outputs from the array of voltmeters55of the array of bipolar detection units50are mapped into an output array that replicates the physical locations of the bipolar detection units50in a virtual coordinate system. When no bubble7passes through the array of bipolar detection units50, all outputs of the array of the voltmeters can be non-zero, which are translated into an array of “1's” within a digitized output map. When a bubble7passes through the array of bipolar detection units50, a subset of the outputs from the array of the voltmeters can be zero volt, which is translated into logical “0's” within the digitized output map illustrated inFIG.20B. The areas the “0's” within the digitized output map can be employed to estimate the size of the detected bubble7. In other words, the “0's” represent the output of the bipolar detection units50adjacent to openings31of the perforated flow blocking structure30through which the bubble7is passing, while the “1's” represent the output of the bipolar detection units50adjacent to openings31of the perforated flow blocking structure30through which no bubble7is passing. The size of the bubble7may be determined by determining the number of adjacent bipolar detection units50that output a “0” signal. The frequency detection of bubbles7measures the bubble density within the fluid5. The exemplary bubble detection apparatus of the present disclosure can simultaneously measure the size distribution and the density of bubbles7within the fluid5.

Referring toFIG.21, a circuit for sequentially addressing selected pairs of a first detection electrode60and a second detection electrode40is illustrated according to an embodiment of the present disclosure. A common voltmeter55may be employed for multiple pairs of a first detection electrode60and a second detection electrode40located within a same row of pairs of a respective first detections electrode60and a respective second detection electrode40, i.e., within a same row of detection electrode pairs (60,40). Transistors70located the voltmeter55connector lines72may be used to select a specific electrode (60,40). The transistors70may be controlled by a controller (or computing device200) via gate lines74which are electrically connected to transistor gate electrodes80and which turn the transistors70on and off. Use of the circuit allows use of a single voltmeter55for each row of pairs of a first detection electrode60and a second detection electrode40, and facilitates manufacture of a two-dimensional M×N array of detection electrode pairs (60,40) sharing M voltmeters55. Each row of detection electrode pairs (60,40) may include N detection electrode pairs (60,40), and M rows of detection electrode pairs (60,40) may be provided within the two-dimensional M×N array. The number of N may be in a range from 2 to 1,024. The number M may be in a range from 2 to 1,024. N may be larger than M.

FIG.22Ais a top-down view of a region of a row of detection electrode pairs (60,40) and a circuit ofFIG.21according to an embodiment of the present disclosure.FIG.22Bis a side cross sectional view of the circuit ofFIG.22Aalong broken plane B-B′ inFIG.22A.FIG.22Cside cross sectional view of the circuit ofFIG.22Aalong plane C-C′ inFIG.22A. Field effect transistors70containing gate electrodes80and active regions82(e.g., doped semiconductor source and drain regions) located in a semiconductor (e.g., silicon) substrate84may be employed to provide electrical switching for the various detection electrodes (60,40) within the two-dimensional M×N array of detection electrode pairs (60,40) sharing M voltmeters55.

Referring collectively toFIGS.21and22A-22C, the bubble detection apparatus of the present disclosure may comprise a circuit configured to sequentially select a voltmeter55from the multiple voltmeters of the multiple bipolar detection units50by sequentially turning on a respective semiconductor switch (e.g., transistor70) selected from an array of semiconductor switches70, and to sequentially measure a voltage across the sequentially selected voltmeters55. The computing unit200can be configured to estimate a size of the bubble7based on the locations at which measured voltages of the voltmeters55are below the respective reference level.

Referring to all drawings and according to various embodiments of the present disclosure, a bubble detection apparatus comprises a container6configured to flow a fluid5therein; a pair of driving electrodes (90,10) located on opposite sides of the container6and configured to be exposed to the fluid5; a bias circuit4configured to apply a driving potential across the pair of driving electrodes (90,10) to generate an electric field; multiple bipolar detection units50located in the container6and configured to be immersed in the fluid5, wherein each of the multiple bipolar detection units50comprises a respective first detection electrode60and a respective second detection electrode40that are spaced apart along a direction of electric field within the fluid5and comprises a current or voltage detection device configured to detect a current or voltage across the first detection electrode60and the second detection electrode40; and a computing unit200configured to receive output currents or voltages from the current or voltage detection devices of one or more of the multiple bipolar detection units50and detect presence of a bubble7within the fluid5when one or more of the output voltages from the voltmeters of the multiple bipolar detection units50drop below a respective reference level.

Referring to all drawings and according to various embodiments of the present disclosure, a bubble detection method includes flowing a fluid5through a conduit6containing at least one bipolar electrode (40,60), applying an electric field E across the fluid5in the conduit6, and detecting a presence of a bubble7in the fluid5when the bubble flows around or through the bipolar electrode by detecting a current or voltage output from the at least one bipolar electrode.

In one embodiment, the at least one bipolar electrode comprises plural bipolar electrodes located in the conduit6. The step of detecting the current or voltage output from the at least one bipolar electrode comprises detecting the voltage output from the plural bipolar electrodes (40,60) using a voltmeter55. In one embodiment, the method further comprises determining a size of the bubble7when the bubble flows around or through plural bipolar electrodes in the conduit6.

In one embodiment, a first bipolar electrode (40,60) of the plural bipolar electrodes has at least one different dimension from a second bipolar (40,60) electrode of the plural bipolar electrodes. In another embodiment, each of the plural bipolar electrodes is located adjacent to one or more openings31in at least one perforated plate30located in the conduit6.

In one embodiment, the step of detecting the presence of the bubble7in the fluid5comprises detecting when a current or voltage output from the at least one bipolar electrode drops below a reference level, and the fluid5comprises a photoresist fluid flowing from a photoresist reservoir through the conduit6to a nozzle located over a semiconductor device.

The various embodiments of the present disclosure can be employed to monitor the presence, density and the size distribution of bubbles7within the fluid5of a bubble detection apparatus, and to determine the suitability of the fluid5for its intended use based on the presence, density and/or size of the bubbles7.