DIELECTRIC BARRIER DISCHARGE PLASMA GENERATOR

A dielectric barrier discharge plasma generator includes a ground electrode and a high voltage electrode which are configured to form a circuit to receive a power input for plasma generation, a dielectric barrier having a first surface attached to the high voltage electrode, and a second surface facing the ground electrode, and discharge gap being formed between the second surface of the dielectric barrier and the ground electrode for plasma generation, and a resiliently deformable mechanism operative to bias the high voltage electrode against the first surface of the dielectric barrier.

FIELD OF THE INVENTION

The invention generally relates to plasma generation, and more specifically to a dielectric barrier discharge (DBD) plasma generator.

BACKGROUND

Atmospheric pressure plasma has been used for many applications in the electronics and semiconductor industries. Atmospheric pressure plasma may be generated with various electrical discharge technologies, including corona discharge, glow discharge, gliding arc, and dielectric barrier discharge (DBD), etc. Among these techniques, the DBD is adopted in more applications due to its high efficiency, high cost-effectiveness, and simple geometrical configurations.

However, in conventional DBD plasma generators, ineffective discharge may be caused due to air gaps between high voltage electrodes of the DBD plasma generators and dielectric barriers attached thereto. Specifically, ineffective discharge between high voltage electrodes and dielectric barriers will reduce the generation of plasma in discharge gaps and cause overheating of the high voltage electrodes and dielectric barriers.

It would therefore be beneficial to provide a solution for reducing ineffective discharge caused by the air gaps between electrodes and dielectric barriers attached to the electrodes of the DBD plasma generators so as to improve the discharge efficiency of DBD plasma generators

SUMMARY OF THE INVENTION

It is thus an object of the invention to seek to provide an improved DBD plasma generator that includes a resilient mechanism designed for reducing the air gap between a high voltage electrode and a dielectric barrier of the DBD plasma generator. With this improved DBD plasma generator, the ineffective discharge caused by the said air gap present between the high voltage electrode and the dielectric barrier can be significantly reduced, thereby greatly improving the discharge efficiency of the DBD plasma generator.

According to various embodiments of the present invention, there is provided a dielectric barrier discharge plasma generator. The plasma generator comprises a ground electrode and a high voltage electrode, which are configured to form a circuit to receive a power input for plasma generation, a dielectric barrier having a first surface in contact with the high voltage electrode and a second surface facing the ground electrode, and a discharge gap being formed between the second surface of the dielectric barrier and the ground electrode for generating plasma, and a resiliently deformable mechanism operative to bias the high voltage electrode against the first surface of the dielectric barrier.

In some embodiments, the high voltage electrode may include a first conductive part and a second conductive part which are physically separated from each other, wherein the resiliently deformable mechanism includes a resilient member disposed between the first conductive part and the second conductive part, the resilient member being operative to apply a biasing force to the first and the second conductive parts to bias the first and second conductive parts against the first surface of the dielectric barrier. Specifically, the first and second conductive parts are biased to fully contact different parts of the first surface of the dielectric barrier.

In some embodiments, the resilient member may include a compression spring disposed between the two conductive parts. The two conductive parts may include two separate semi-cylindrical structures or two cuboid-shaped structures.

In some embodiments, the resilient member may include at least one deformable sheet metal plate. For example, the resilient member may include two curved deformable sheet metal plates, each having a first edge and a second edge on opposing sides of the sheet metal plate, the first and second edges of each sheet metal plate being respectively coupled to two opposite ends of the first and second conductive parts. The first and second conductive parts may include two separate planar or curved metal plates.

In some embodiments, the resiliently deformable mechanism may include a slot formed on the high voltage electrode such that the high voltage electrode is deformable to provide a biasing force to bias an external surface of the high voltage electrode against the first surface of the dielectric barrier. In one embodiment, the slot is formed and oriented along a direction parallel to a longitudinal axis of the high voltage electrode. The high voltage electrode may be made of a metal plate and have a cylindrical or cuboid shape. In other words, the high voltage electrode may include a cylindrically shaped or cuboid-shaped metal plate.

In some embodiments, the dielectric barrier includes a tubular structure that encloses the high voltage electrode in order to avoid the high voltage electrode from being in contact with reactive gas entering into the discharge gap.

In the present invention, the plasma generator may be a cylindrical-type or planar-type plasma generator. If the plasma generator is a cylindrical-type plasma generator, the dielectric barrier includes a cylindrical structure, the first surface of the dielectric barrier includes an inner cylindrical surface of the dielectric barrier and the second surface of the dielectric barrier includes an outer cylindrical surface of the dielectric barrier. If the plasma generator is a planar-type plasma generator, the dielectric barrier has a rectangular cross-section, and the first surface of the dielectric barrier includes two opposing side inner faces of the dielectric barrier.

In order to avoid overheating of the high voltage electrode and dielectric barrier, the plasma generator may further comprise a cooling air inlet formed on a top cover of the plasma generator to allow cooling air to enter the space for enclosing the high voltage electrode and an air outlet formed on the top cover. The top cover may be made from a non-conductive material, e.g., plastic.

The plasma generator further includes a plasma outlet formed at one end of the ground electrode for discharging or releasing the plasma generated in the discharge gap, and at least one reactive gas inlet formed on the ground electrode to allow reactive gas to enter the discharge gap. The plasma outlet may include at least one opening located at a bottom end of the ground electrode. The number and cross-section shape of the opening(s) may be adjusted according to the requirements of actual applications.

With the dielectric barrier discharge plasma generator provided in embodiments of the invention, the air gap between the high voltage electrode and the dielectric barrier can be significantly reduced or avoided. Thus, the ineffective discharge caused by this air gap can be effectively reduced or avoided, and the discharge efficiency of the dielectric barrier discharge plasma generator is greatly improved.

These and other features, aspects, and advantages will become better understood with regard to the description section, appended claims, and accompanying drawings.

In the drawings, like parts are denoted by like reference numerals.

FIG.1is a schematic cross-sectional view of a dielectric barrier discharge plasma generator100according to some embodiments of the invention. As shown inFIG.1, the dielectric barrier discharge plasma generator100includes a ground electrode101, a high voltage electrode102, a dielectric barrier103, and a resiliently deformable mechanism104. The ground electrode101and the high voltage electrode102are configured to form an electrical circuit to receive a power input for plasma generation.

Referring toFIG.1, the ground electrode101forms a casing of the plasma generator100. The dielectric barrier103is fixedly located within the casing formed by the ground electrode101and configured to form a space to enclose the high voltage electrode102. The dielectric barrier103has a first surface103aattached to the high voltage electrode102for covering a contact surface102A of the high voltage electrode102, and a second surface103bfacing an internal surface of the ground electrode101, and a discharge gap G for plasma generation is formed between the second surface103bof the dielectric barrier103and the internal surface of the ground electrode101. The resiliently deformable mechanism104is operative to bias the contact surface102A of the high voltage electrode102against the first surface103aof the dielectric barrier103, thereby reducing or even eliminating any air gap between the contact surface102A of the high voltage electrode102and the first surface103aof the dielectric barrier103.

The plasma generator100also includes at least one reactive gas inlet105which is configured to allow the reactive gas for plasma generation to enter the discharge gap G. Although inFIG.1, only one gas inlet105is located in the side wall of the ground electrode101, it should be appreciated by a person skilled in the art that the number and position of the reactive gas inlets in other embodiments of the invention may be adjusted according to the actual design and requirements of the plasma generator as long as the reactive gas can be guided to enter the discharge gap by the reactive gas inlet(s). For example, there may be two reactive gas inlets, with both or only one gas inlet being located on the top wall or side wall of the ground electrode101.

Referring toFIG.1, the plasma generator100may further include a cooling air inlet106aand an air outlet106bwhich are configured to establish a cooling air circulation for efficiently lowering the temperature of the high voltage electrode102and the dielectric barrier103in order to avoid overheating thereof. The cooling air inlet106a, and air outlet106bare located on a top cover of the plasma generator100, the former being arranged to allow the cooling air to enter a space enclosed by the dielectric barrier103in which the high voltage electrode102is located and the latter being arranged to discharge air from the space.

The plasma generator100also includes a plasma outlet107as shown inFIG.1. The plasma outlet107may be provided at a bottom end of the ground electrode101for allowing the plasma generated in the discharge gap to be discharged or released and applied to an electronic component sample, e.g., a wafer, located below the plasma generator100. It should be noted that the shape and position of the plasma outlet107may be adjusted to meet the requirements of various applications.

In use, the ground electrode101is configured to establish a direct connection to the ground, and both the ground electrode101and the high voltage electrode102are removably connected to a high-voltage alternating current (AC) generator (not shown inFIG.1) which is configured to provide a high-voltage and high-frequency output to the plasma generator100, such that electrical breakdown of a reactive gas entering the discharge gap through the reactive gas inlet105occurs in the plasma generator100for plasma generation. The high voltage electrode102is enclosed in a space formed by the dielectric barrier103so as to prevent the high voltage electrode102from being in contact with the reactive gas in the plasma generator100. Also, even if there is any undesired discharge due to an air gap between the high voltage electrode102and the dielectric barrier103, it will not affect plasma treatment of an electronic component placed below the plasma outlet107since the undesired discharge occurs in a space enclosed by the dielectric barrier103, i.e., an enclosed space formed by the dielectric barrier103.

In various embodiments of the invention, the plasma generator may be a cylindrical-type or a planar-type dielectric barrier discharge plasma generator. Detailed structures of some plasma generators according to certain embodiments of the invention will be described below. The common features of these plasma generators which have been described above with reference to the plasma generator100that is shown inFIG.1will not be repeated below.

FIG.2AandFIG.2Brespectively show a perspective cut-away view and a cross-sectional view of a cylindrical-type dielectric barrier discharge plasma generator200according to a first embodiment of the invention. Referring toFIG.2AandFIG.2B, the plasma generator200includes a ground electrode201in the form of a cylindrical casing with a frusto-conical bottom, a dielectric barrier203fixedly located within the cylindrical casing (the dielectric barrier203being in the form of a tubular structure with a circular cross-sectional shape), a high voltage electrode202having two separate conductive parts and being enclosed in the space formed by the dielectric barrier203, and a resiliently deformable mechanism204in the form of a compression spring which is disposed between the two separate conductive parts of the high voltage electrode202.

FIG.2Cshows a perspective view of the high voltage electrode202and the resiliently deformable mechanism204in the form of a compression spring of the plasma generator200according to the first embodiment. As shown inFIG.2C, the high voltage electrode202includes a first semi-cylindrical conductive part202awith a first or external surface202a-1and a second or internal surface202a-2, and a second semi-cylindrical conductive part202bwith a first or external surface202b-1and a second surface202b-2. The first and second conductive parts are physically separated from each other and the compression spring204is located between the first and second conductive parts202a,202b. Specifically, two ends of the compressing spring204are respectively coupled to the two opposing second surfaces202a-2,202b-2such that when the high voltage electrode202and the compression spring204are installed in the plasma generator200, the compression spring204is compressed, which in turn applies a biasing force to the first and second conductive parts202a,202bso as to bias the first conductive part202aand the second conductive part202bagainst the internal surface203aof the dielectric barrier203. Specifically, when the high voltage electrode202and the compression spring204are installed in the plasma generator200, the first surface202a-1of the first conductive part202ais biased to fully contact a first part of the internal surface203aof the dielectric barrier203, and the first surface202b-1of the second conductive part202bis biased to fully contact a second part of the internal surface203aof the dielectric barrier203. The first part of the internal surface203ais separate from the second part of the internal surface203a. A discharge gap G around the cylindrical dielectric barrier203is formed between the external surface203bof the dielectric barrier203and the ground electrode201. It should be noted that the discharge gap G is only formed between portions of the dielectric barrier203which contact the first surfaces202a-1,202b-1of the high voltage electrode202and the opposing portions of the ground electrode201.

Referring toFIG.2AandFIG.2B, in the first embodiment, the plasma generator200also includes a first reactive gas inlet205aand a second reactive gas inlet205bwhich are located in the side wall of the ground electrode201to allow reactive gas to enter the discharge gap between the ground electrode201and the dielectric barrier203. The first reactive gas inlet205ais arranged in the side wall of the ground electrode101opposite the first conductive part202aof the high voltage electrode202, and the second reactive gas inlet205bis arranged in the side wall of the ground electrode101opposite the second conductive part202bof the high voltage electrode202. It is to be appreciated by a person skilled in the art that the first and second reactive gas inlets205a,205bmay be located on the top wall of the ground electrode201in other embodiments, and the plasma generator200may include fewer or more than two reactive gas inlets.

As shown inFIG.2AandFIG.2B, the plasma generator200further includes a cooling air inlet206aand an air outlet206bformed on a top cover of the plasma generator200. Referring toFIG.2C, each of the first and second conductive parts202a,202bmay include a plurality of through-holes202cpassing through the conductive parts202a,202balong a direction parallel to a longitudinal axis of the high voltage electrode202. The through-holes202care provided to allow cooling air to enter them so as to accelerate the cooling of the high voltage electrode202. It should be noted that in some embodiments of the invention, the cooling air inlet206aand/or the air outlet206bmay be further extended such that one end thereof contacts a top surface of the high voltage electrode202or enters into a through-hole of the high voltage electrode202, so as to reduce the temperature of the high voltage electrode202faster.

As shown inFIG.2AandFIG.2B, the plasma generator200further includes a plasma outlet207having a circular cross-section which is an opening located at the bottom end of the ground electrode201. Alternatively, the plasma outlet207may be designed according to actual needs in different applications. For example, the plasma outlet207may include at least one slit opening provided on the bottom surface of the plasma generator200.FIG.2Dshows a first alternative design of the plasma outlet207′ according to the first embodiment of the invention. In this design, the plasma outlet207′ includes a slit opening located at the center of the circular bottom surface of the plasma generator200.FIG.2Eshows a second alternative design of the plasma outlet207″ which includes three curved slit openings evenly spaced along a circumference of a circle on the bottom surface of the plasma generator200.FIG.2Fshows a third alternative design of the plasma outlet207′″ which includes four separate straight slit openings respectively arranged along four edges of a rectangular or square. The plasma outlets with different shapes may be used in different applications to ensure that the plasma is applied specifically to required portions of electronic components located below the plasma generator200.

FIG.3Ashows a perspective cut-away view of a cylindrical-type dielectric barrier discharge plasma generator300according to a second embodiment of the invention. Compared to the plasma generator200in the first embodiment, the plasma generator300includes a different high voltage electrode302and a different resiliently deformable mechanism304. Other components of the plasma generator300which are the same as the plasma generator200, those will not be repeated here.

FIG.3Bshows a perspective view of the high voltage electrode302and the resiliently deformable mechanism304of the plasma generator300. Referring toFIG.3AandFIG.3B, the high voltage electrode302is in the form of a hollow cylindrical structure and the resiliently deformable mechanism304includes a slot formed on the hollow cylindrical structure such that the hollow cylindrical structure is deformable to provide a biasing force to bias the external surface of the hollow cylindrical structure against the internal surface303aof the dielectric barrier303. The hollow cylindrical structure may be made of a metal plate. To further increase the area of the internal surface of the high voltage electrode302for accelerating the cooling of the high voltage electrode302and the dielectric barrier303, the high voltage electrode302may include an uneven internal surface303ato increase the contact surface with cooling air entering the hollow space of the high voltage electrode302. For example, the internal surface303aof the high voltage electrode302may include a plurality of semi-cylindrical recesses which are equally-spaced around a longitudinal axis of the cylindrical structure as shown inFIG.3B. It should be noted that in other embodiments of the invention, the high voltage electrode302may have a smooth internal surface as shown inFIG.3C, or the slot304on the hollow cylindrical structure may be formed and oriented along a direction parallel to a longitudinal axis of the cylindrical structure, as shown inFIG.3D, in order to maximize the contact area between the high voltage electrode302and the dielectric barrier303, thereby maximizing the efficiency of plasma generation.

FIG.3Eshows a perspective cut-away view of a cylindrical-type dielectric barrier discharge plasma generator300′ according to a third embodiment of the invention. In the third embodiment, an additional dielectric barrier303′ is provided to cover an internal surface of the ground electrode301. Specifically, the additional dielectric barrier303′ is arranged to cover at least the part of the internal surface of the ground electrode301facing a part of the dielectric barrier303which covers or contacts the high voltage electrode302. Accordingly, in this embodiment, the discharge gap is formed between the dielectric barrier303covering the high voltage electrode302and the additional dielectric barrier303′ covering the ground electrode301.

In various embodiments of the invention, the dielectric barrier attached to the high voltage electrode, or the additional dielectric barrier attached to the ground electrode may be made of alumina or quartz and may have a thickness of approximately 1 mm to 5 mm.

FIG.4AandFIG.4Brespectively show perspective cut-away and cross-sectional views of a planar-type dielectric barrier discharge plasma generator400according to a fourth embodiment of the invention. Referring toFIG.4AandFIG.4B, the plasma generator400includes a ground electrode401in the form of a cuboid-shaped casing with a trapezoidal bottom, a dielectric barrier403located within the cuboid-shaped casing, the dielectric barrier403being in the form of a tubular structure with a rectangular cross-sectional shape, a high voltage electrode402having two separate cuboid-shaped conductive parts and being enclosed in a space formed by the dielectric barrier403, and a resiliently deformable mechanism404in the form of a compression spring which is disposed between the two separate conductive parts of the high voltage electrode402.

FIG.4Cshows a perspective view of the high voltage electrode402and the resiliently deformable mechanism404(in the form of a compression spring) of the plasma generator400according to the fourth embodiment. As shown inFIG.4C, the high voltage electrode402includes a first cuboid conductive part402awith two opposing side faces402a-1,402a-2and a second cuboid conductive part402bwith two opposing side faces402b-1,402b-2. The first and second conductive parts402a,402bare physically separated from each other, and the compression spring is located between the first conductive part402aand the second conductive part402b. Specifically, two ends of the compression spring are respectively coupled to the second side faces402a-2,402b-2of the two conductive parts402a,402bsuch that when the high voltage electrode402and the compression spring are installed in the plasma generator400, the compression spring is compressed to apply a biasing force to the first and second conductive parts402a,402bin order to bias the first and second conductive parts402a,402bagainst an internal surface403aof the dielectric barrier403. Specifically, when the high voltage electrode402and the compression spring are installed in the space formed by the dielectric barrier403, the first side face402a-1of the first conductive part402ais biased to fully contact a first internal face403a-1of the dielectric barrier403, and the first side face402b-1of the second conductive part402bis biased to fully contact a second internal face403a-2of the dielectric barrier403, the first and second internal faces403a-1,403a-2of the dielectric barrier403being opposite to each other.

Referring toFIG.4AandFIG.4B, the plasma generator400also includes a first reactive gas inlet405alocated in a first side wall401aof the ground electrode401, the first side wall401afacing a first external face403b-1of the dielectric barrier403, and a second reactive gas inlet405blocated in a second side wall401bof the ground electrode401, the second side wall401bfacing a second external face403b-2of the dielectric barrier403. The dielectric barrier403is designed to enclose the high voltage402to avoid the high voltage electrode from being in contact with the reactive gas for plasma generation. Alternatively, the first and second reactive gas inlets405a,405bmay be located on the top wall of the ground electrode401as long as the reactive gas can be guided to enter the discharge gap between the ground electrode401and the dielectric barrier403.

As shown inFIG.4AandFIG.4B, the plasma generator400further includes a cooling air inlet406aand an air outlet406bformed on a top cover of the plasma generator400. Referring toFIG.4C, each of the first and second conductive parts402a,402bmay include a plurality of through-holes402cpassing through the conductive parts402a,402balong a vertical height direction Z of the high voltage electrode402. The through-holes402care provided to allow cooling air to enter them so as to accelerate the cooling of the high voltage electrode402. It should be noted that in some embodiments of the invention, the cooling air inlet406aand/or the air outlet406bmay be further extended such that one end thereof contacts a top surface of the high voltage electrode402or enters into a through-hole of the high voltage electrode402, so as to reduce the temperature of the high voltage electrode402faster.

The plasma generator400also includes a plasma outlet407as shown inFIG.4AandFIG.4B. The plasma outlet407has a rectangular slot opening located at the bottom end of the plasma generator400. It should be noted that the shape of the opening is provided for illustrative purposes only, and is not intended to limit the scope of the invention. In other embodiments, the plasma generator400may have a plasma outlet with a different shape, e.g., a circular outlet or other outlet shapes such as those shown inFIG.2DtoFIG.2F.

FIG.5Ashows a perspective cut-away view of a planar-type dielectric barrier discharge plasma generator500according to a fifth embodiment of the invention. As shown inFIG.5A, the structure and components of the plasma generator500are similar to the plasma generator400in the fourth embodiment, except that the high voltage electrode502and resiliently deformable mechanism504used in the fifth embodiment are different. Components that are similar to those of the plasma generator400of the fourth embodiment, e.g., the ground electrode501, the dielectric barrier503, the reactive gas inlets505a,505b, the cooling air inlet506aand air outlet,506b, and the plasma outlet507will not be described in further detail.

FIG.5Bshows a perspective view of the high voltage electrode502and resiliently deformable mechanism504used in the fifth embodiment. As shown inFIG.5B, the high voltage electrode502includes a first conductive plate502aand a second conductive plate502bparallel to each other. Each conductive plate502a,502bhas first and second opposing edges. The resiliently deformable mechanism504includes first and second curved metal plates504a,504b. The first edges502a-1,502b-1of the two conductive plates502a,502bare connected by the first curved metal plate504aand the second edges502a-2,502b-2of the two conductive plates502a,502bare connected by the second curved metal plate504b. In this embodiment, the curved metal plates504a,504bof the resiliently deformable mechanism504may be in the form of arc-shaped metal plates. To further increase the contact area of cooling air in the high voltage electrode502, each conductive plate502a,502bmay have an uneven internal surface. For example, a plurality of semi-cylindrical recesses may be formed on the internal surface of each conductive plate502a,502bas shown inFIG.5B. It should be noted that in other embodiments of the invention, the first and second conductive plates502a,502bmay not be parallel to each other as long as the two conductive plates502a,502bare designed and arranged to be biased to fully contact the dielectric barrier.

FIG.5Cshows a perspective cut-away view of a planar-type dielectric barrier discharge plasma generator500′ according to a sixth embodiment of the invention. The only difference between the plasma generator500′ and the plasma generator500of the fifth embodiment is that the plasma generator500′ further includes an additional dielectric barrier503′ which covers at least a part of the internal surface of the ground electrode501, the said part of the internal surface facing the part of the dielectric barrier503which covers or contacts the high voltage electrode502. Accordingly, a discharge gap for plasma generation is formed between the dielectric barrier503which covers the high voltage electrode502and the additional dielectric barrier503′ which covers the internal surface of the ground electrode501.

It should be noted that the various embodiments described above are for illustrative purposes only and are not intended to be a limitation of this disclosure, as other configurations of the plasma generators are also possible. For example, the slot formed on the high voltage electrode may also be used as a resiliently deformable mechanism in a planar-type plasma generator, and the curved metal plates for connecting the first and second conductive parts of the high voltage electrode may also be used as a resiliently deformable mechanism in a cylindrical-type plasma generator.

As will be appreciated from the above description, the plasma generators provided in various embodiments of the invention are designed to discharge plasma along a cylindrical area or two sides of a planar dielectric barrier so as to improve the efficiency of plasma generation. Further, the proposed plasma generators include a resiliently deformable mechanism for offering a biasing force to bias the high voltage electrode of the plasma generator against the dielectric barrier so as to reduce or even eliminate an air gap between the high voltage electrode and the dielectric barrier attached thereto so as to avoid ineffective discharge, thereby improving the efficiency of plasma generation. The dielectric barrier is designed to enclose the high voltage electrode to prevent the high voltage electrode from contacting the reactive gas in the discharge gap for plasma generation. In addition, as the high voltage electrode is located in an enclosed space, even if any undesired discharge occurs due to an existing air gap between the high voltage electrode and the dielectric barrier, it will not affect the plasma treatment applied to the electronic component sample disposed below the plasma generator. The plasma generators further include a cooling air inlet and an air outlet to lower the temperature of the high voltage electrode faster.

Although the present invention has been described in considerable detail with reference to certain embodiments, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.