METHODS AND APPARATUS FOR CLEANING A SUBSTRATE EDGE USING CHEMICAL AND MECHANICAL POLISHING

Abstract

Methods and apparatus are provided for concurrently chemically and mechanically polishing a substrate edge. The invention includes a substrate support adapted to rotate a substrate; a polishing head adapted to contact an edge of the substrate, the polishing head including a first channel adapted to apply a first fluid to the edge of the substrate; a second channel adapted to direct a second fluid onto a major surface of the rotating substrate; and a third channel adapted to direct a third fluid at the major surface of the substrate and to prevent the second fluid from diluting the first fluid. Numerous other aspects are provided.

Description

FIELD OF THE INVENTION

The present invention relates generally to electronic device processing, and more particularly to methods and apparatus for cleaning an edge of a substrate.

BACKGROUND OF THE INVENTION

During electronic device manufacturing, undesirable materials may build up on the edge of a substrate. The materials may include dielectrics, photoresist and metals used in IC manufacture. Therefore, it may be desirable to clean or polish the bevel and edge of the substrate to remove these materials. What is needed are systems, methods and apparatus for cleaning the edge of substrates without damaging the major surfaces of the substrates.

SUMMARY OF THE INVENTION

In aspects of the invention, an apparatus is provided for concurrently chemically and mechanically polishing a substrate edge. The apparatus comprises a substrate support adapted to rotate a substrate; a polishing head adapted to contact an edge of the substrate, the polishing head including a first channel adapted to apply a first fluid to the edge of the substrate; a second channel adapted to direct a second fluid onto a major surface of the rotating substrate; and a third channel adapted to direct a third fluid at the major surface of the substrate and to prevent the second fluid from diluting the first fluid.

In other aspects of the invention, a system is provided for concurrently chemically and mechanically polishing a substrate edge. The system comprises a substrate support adapted to rotate a substrate; a polishing head, adapted to contact an edge of a substrate, the polishing head including a first channel adapted to apply a first fluid to the edge of the substrate; a second channel adapted to direct a second fluid onto a major surface of the rotating substrate; a third channel adapted to direct a third fluid at the major surface of the substrate and to prevent the second fluid from diluting the first fluid; and a controller adapted to operate the concurrent chemical and mechanical polishing of the edge of the substrate.

In yet other aspects of the invention a method is provided for concurrently chemically and mechanically polishing a substrate edge. The method includes the steps of (1) rotating a substrate; (2) contacting an edge of the substrate with a polishing head; (3) applying a first fluid to the edge of the substrate via the polishing head; (4) directing a second fluid onto a major surface of the rotating substrate; and (5) directing a third fluid at the major surface of the substrate, wherein the third fluid prevents the second fluid from diluting the first fluid.

Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of a cross-section of a portion of a substrate.

FIG. 2 is a schematic illustration depicting an example embodiment of an edge cleaning system according to the present invention.

FIG. 3 is a perspective view depicting another example embodiment of an edge cleaning system according to the present invention.

FIG. 4 is a side view of a polishing unit according to the present invention.

FIG. 5 is a front view of a polishing unit according to the present invention.

FIG. 6 is a flow chart depicting an example application method of embodiments of an edge cleaning system according to the present invention.

DETAILED DESCRIPTION

The present invention provides improved methods and apparatus for cleaning and/or polishing the edge of a substrate. The edge of a substrate may be polished by application of an abrasive polishing pad or film contacting the substrate edge via a polishing head and by application of chemicals onto the substrate edge, as the substrate is rotated or otherwise moved (e.g., oscillated). As the substrate rotates, deionized water (hereinafter “DI water”) may be applied to the major surface (non-beveled and non-edge surface) of the substrate to prevent potential contamination and to remove material that accumulates as a result of polishing/cleaning. However, it may be undesirable for the DI water to contact the polishing head or dilute the chemicals. According to the present invention, a curtain of fluid, and in a preferred embodiment a gas, such as N₂, is directed at the major surface of the substrate such that the gas prevents the DI water from contacting the polishing head and/or diluting the polishing chemicals. In some embodiments the curtain of gas may be curbed to form an arc surrounding the area on the substrate to be polished, such that the interior of the arc faces the polishing head. In some embodiments, the interior of the arc may face the DI water supply to contain the DI water and push it away from the polishing head.

Turning to FIG. 1, a substrate 100 may include two major surfaces 102, 102′, and an edge 104. Each major surface 102, 102′ of the substrate 100 may include a device region 106, 106′, and an exclusion region 108, 108′. (Typically however, only one of the two major surfaces 102, 102′ will include a device region and an exclusion region.) The exclusion regions 108, 108′ may serve as buffers between the device regions 106, 106′ and the edge 104. The edge 104 of a substrate 100 may include an outer edge 110 and bevels 112, 114. The bevels 112, 114 may be located between the outer edge 110 and the exclusion regions 108, 108′ of the two major surfaces 102, 102′. The present invention is adapted to clean and/or polish the outer edge 110 and at least one bevel 112, 114 of a substrate 100 without affecting the device regions 106, 106′. In some embodiments, all or part of the exclusion regions 108, 108′ may be cleaned or polished as well.

Turning to FIG. 2, a schematic illustration of an example embodiment of a polishing head system 200, including a polishing head 201, adapted to polish the edge 104 of a substrate 100 is provided. The substrate 100 may be held or supported and rotated by a vacuum chuck 202, for example. Other suitable substrate support and rotation means may be used. For example, the substrate 100 may be rotated by driver rollers and guide rollers, etc. The polishing head 201 may include a backing pad 204, a roller, and/or an inflatable pad. In either case, the pad, roller and/or inflatable pad may be soft and/or include or develop contours to conform to the shape of the substrate edge 104. In some embodiments, the backing pad 204 may also include abrasive particles and be used to polish the substrate edge 104. Additionally or alternatively, the backing pad 204 may be pressed against a polishing tape 206, used to polish the substrate edge 104. The system 200 may further include an actuator 208 (e.g., a pneumatic slide, hydraulic ram, servo motor driven pusher, etc.). As the substrate 100 rotates, the actuator 208 may press the backing pad 204, and hence the polishing tape 206, against the substrate edge 104. Alternatively or additionally, the actuator 208 may be adjustable, and may also be used to push the entire head 201 towards the substrate 100. Alternatively, a biasing device (e.g., a spring) may be employed to mount the pad 204 to the head 201, to provide flexible/dynamic counter pressure to the pad 204. In some embodiments, the substrate 100 may be in contact with the polishing tape 206 for about 15 to 150 seconds depending on the type of tape used, the grit of the tape, the rate of rotation, the amount of polishing required, etc. More or less time may be used. The contact between the polishing tape 206, and the substrate edge 104, as the polishing tape 206 is pressed against the substrate edge 104 by the backing pad 204, combined with the particular rotational speed of the substrate 100, may provide relative movement between the polishing tape 206 and the substrate edge 104, resulting in polishing the substrate edge 104. Depending on the amount of force applied by the actuator 208, the resiliency of the pad 204 selected, the amount of inflation of an inflatable pad, and/or the amount of tension on the polishing tape 206, a controlled amount of pressure may be applied to polish the substrate edge 104. Thus, the system 200 may provide precise control of an edge polish process, which may be used to compensate for different edge geometries and changes in the substrate 100 as material is removed from the substrate edge 104.

The pad 204 may be made of material such as, for example, an acetal resin (e.g., Delrin® manufactured by DuPont Corporation), PVDF, polyurethane closed cell foam, silicon rubber, etc. Other suitable materials may be used. Such materials may have resilience or an ability to conform that is a function of the thickness or density of the pad 204. The material may be selected based upon its resilience. The desired resilience may be selected based upon the type of polishing required.

In some embodiments, the degree to which the pad 204 may conform to the substrate edge 104 may be adjustable. For example, the pad 204 may be, or include, an inflatable bladder, as described in Application Ser. No. 60/939,333 (Attorney Docket No. 11567/L), cited above, which may be inflatable by air, liquid or other fluid. The amount of fluid filling the pad 204 may be adjusted, such that the pad 204 may suitably conform to the substrate edge 104.

The substrate 100 may be rotated, for example, in a horizontal plane. The substrate edge 104 may be aligned with, or normal to, the polishing tape 206, pad 204 and/or polishing head 201. In additional or alternative embodiments, the substrate 100 may be rotated in a vertical plane, other non-horizontal plane, and/or be moved between different planes of rotation.

In the embodiment described herein, as the substrate 100 rotates, the polishing head 201 may rock around the substrate edge 104 to polish the entire edge 104. The angle of rocking may include, for example, plus or minus 90 degrees. Other rocking angles may be used. In operation, this is achieved by angularly translating the head 201, and consequently the backing pad 204 and polishing tape 206 in contact with, and contoured to, the substrate edge 104, around an axis that is tangential to the outer edge 110 of the substrate 100 as it is rotated. In some embodiments, the head 201 may be adapted to continuously or intermittently oscillate between the various positions. The head 201 may be moved by drivers (not shown) under the direction of a programmed or user operated controller 210 (shown in FIG. 3). Alternatively, the head 201 may be fixed and/or only adjusted while the substrate 100 is not being rotated. In yet other embodiments, the substrate 100 may be held fixed while the head 201 is oscillated (as described above), as well as rotated circumferentially around the substrate 100. In some embodiments, the key parameters to control the edge polishing area may be the angle of rocking, the center of rotation for rocking, and the contour of the backing pad.

In some embodiments, fluids or chemicals may be used to aid in the polishing or washing away of accumulated particles, and may be delivered to the substrate edge 104, as further described below with respect to FIG. 4.

As described above, in some embodiments, the controller 210 (shown in FIG. 3), (e.g., a programmed computer, a programmed processor, a gate array, a logic circuit, an operator directed valve system, an embedded real time processor, etc.) may control the driver(s) used to rotate the substrate 100 and the actuator 208 used to push the pad 204 against the substrate edge 104. Note that the controller 210 may be coupled (e.g., electrically, mechanically, pneumatically, hydraulically, etc.) to each of a plurality of actuators 208. Likewise, operation of the fluid channels, described below with respect to FIG. 4, may also be under the direction of the controller 210. Under direction of the controller 210, various fluids may be selectively delivered to the pads 204 and/or the substrate edge 104 via the fluid channels. The controller 210 may be adapted to receive feedback signals from the driver and/or actuator 208, that indicate the amount of energy being exerted to drive the substrate 100 (e.g., rotate a vacuum chuck holding the substrate 100) and/or actuate the actuator 208 to push the pad 204, respectively. These feedback signals may be employed to determine when a particular layer of film has been removed and/or whether a sufficient amount of polishing has occurred.

FIG. 3 is a perspective view depicting an example embodiment of a substrate polishing system 300 according to the present invention. The substrate polishing system 300 shown herein includes three heads 302. Any number and type of heads 302 may be used in any practicable combination. In addition, in such multi-head embodiments, each head 302 may use a differently contoured backing pad 204 (e.g., different contours of the strip, etc.). Any number of heads 302 may be used concurrently, individually, and/or in a sequence. The heads 302 may be disposed in different positions and in different orientations (e.g., aligned with the substrate edge 104, normal to the substrate edge 104, angled relative to the substrate edge 104, etc.) to allow the pads 204 and/or polishing tape 206 to polish different portions of the edge 104 of the rotating substrate 100. The heads 302 may be adapted to be oscillated or moved (e.g., angularly translated about a tangential axis of the substrate 100 and/or circumferentially relative to the substrate 100) around or along the substrate edge 104 by any suitable means so as to polish different portions of the substrate edge 104. Different heads 302 may be used for different substrates 100 or different types of substrates 100.

Turning to FIG. 4, a side view of a polishing unit 400 according to the present invention is depicted. In the example embodiment shown herein, the polishing unit 400 includes a polishing head 402. The polishing head 402 may include a backing plate 404, covered by a backing pad 406. In some embodiments the backing plate may be shaped to mimic the shape of the substrate while in other embodiments the backing plate may conform to the shape of the substrate. In some embodiments the backing plate 404 may be coupled to the polishing head 402, while in other embodiments the backing plate 404 may be integrally formed with the polishing head 402. The backing pad 406 may be used to mechanically polish the substrate edge 104. In some embodiments, as described above, polishing tape 206 may be used to polish the substrate edge 104, and the backing pad 406 (or roller) may press the polishing tape 206 against the substrate edge 104. The polishing unit 400 may also include a nozzle 408, disposed at the substrate edge 104. The nozzle 408 may be shaped as a thin curved slit. Other nozzle shapes may be used. As described above, as the substrate 100 rotates, a deionized water supply may direct deionized water onto the major surface 102, 102 of the substrate 100, via a deionized water channel 410, and the deionized water may be centrifugally pushed out to the rest of the major surface 102, 102 of the substrate 100. Additionally, while the substrate 100 rotates, the nozzle 408 may dispense a curtain of fluid, such as N₂ (whereby the curtain of fluid is hereinafter referred to as “N₂”). Other gases or fluids may be used. For example, other inert gases may be used. The shape of the thin slit nozzle 408 may provide a curtain of N₂ between the substrate edge 104 and the polishing head 402 and pad 406. In some embodiments the shape of the nozzle 408 may provide a curtain of N₂ that may be curved or arced, such that the area of the substrate 100 being polished, and a portion of the major surface 102 of the substrate 100, is surrounded by the N₂ curtain. This N₂ curtain may prevent the deionized water from contacting, and potentially damaging, the polishing head 402. Additionally, the N₂ curtain may also prevent the deionized water from mixing with, and diluting, the chemicals (described below and with respect to FIG. 5) used to clean and polish the substrate edge 104. Alternatively, the N₂ curtain may prevent the chemicals (e.g., polishing chemicals) from contacting the major surface 102 of the substrate 100. The chemicals may include, for example, surfactant and/or other known cleaning chemistries.

While in the exemplary embodiment shown here, the nozzle 408 is positioned at a 90 degree angle with respect to the major surface 102 of the substrate 100, in alternate embodiments the nozzle may be positioned at a different angle with respect to the major surface 102 of the substrate 100. For example, when the nozzle 408 is perpendicular (or 90 degrees) to the major surface 102 of the substrate 100, the N₂ curtain may also flow in a perpendicular direction to the major surface 102 of the substrate 100. When the N₂ curtain contacts with the major surface of the substrate 100, it may flow towards both the polishing head 402 and the DI water, thereby essentially pushing both the chemicals from the DI water to keep them separate. In another exemplary embodiment, the nozzle 408 may be angled towards the DI water, such that the N₂ curtain pushes the DI water away from the polishing head 402, further preventing chemical dilution, but may have no effect on the chemicals contacting the substrate edge 104. In yet another exemplary embodiment, the nozzle 408 may be angled towards the polishing head 402, such that the DI water may be allowed to flow towards the polishing head 402, to a certain extent, but the chemicals are prevented from contacting the major surface 102 of the substrate 100.

In some embodiments the chemicals may be applied to and/or through the tape 206 and/or the pad 406 or roller. The backing plate 404 may include one or more channels 502 adapted to drip or spray the fluid directly onto or into the pads 204, 406. Alternatively, the pad 406 may be inflatable and may include a bladder (not shown) with a semi-permeable membrane that allows fluid to be slowly released and transmitted to the polishing tape 206 (e.g., through the pad). In such embodiments, the pad 204, 406 may be covered by, made of, and/or include, material that absorbs and/or retains the fluids used (e.g., polyvinyl alcohol (PVA), etc.). In other embodiments, the chemicals may be sprayed directly onto the substrate 100.

In an alternative embodiment, instead of a polishing pad 406 and/or in combination with the polishing pad 406, heating elements (not shown) may be used to provide temperature assistance to enhance the wet etch rate of the chemicals used to polish/clean the substrate edge 104. The applied heat may be controlled at different locations to control the resulting material removal profile. As with the backing plate, the materials that enclose the heating elements may be flexible/pliable materials such as rubber, polyimide, etc.

Turning to FIG. 5, a front view of the polishing unit 400 described in FIG. 4, according to the present invention is depicted. In some embodiments, the polishing unit 400 may also include one or more sponges 500. The sponges 500 may be affixed to the backing plate 404 and separated by the polishing pad 406. Any suitable fixation means may be used. Other orientations may be used. Additionally, more or fewer sponges 500 may be used. The backing plate 404, as described above, may include one or more channels 502 adapted to supply a cleaning/polishing chemical to one or more of the sponges 500. In the particular example depicted herein, each sponge 500 is coupled to a separate channel 502. In some embodiments, for example, a single channel 502 may supply chemicals to multiple sponges 500, or an individual sponge 500 may receive chemicals from multiple channels 502. The chemicals may be the same type or a different type. Different chemicals may be used to more effectively clean/polish the substrate. In either case, the sponge 500 may receive different chemicals in sequence, for example. In other words, in the case of an individual sponge 500 and a single channel 502, a first chemical may flow through the channel 502 and then a second, different chemical may flow through the channel 502. In the case of the individual sponge 500 and multiple channels 502, for example, a first chemical may flow through a first channel 502 and then a second chemical may flow through a second channel 502. In the case of the individual sponge 500 with multiple channels 502, the sponge 500 may alternatively receive the chemicals from the multiple channels 502 at the same time. In some embodiments, the same chemicals may be flowed through the multiple channels 502 into the individual sponge 500 to increase the flow of chemicals to the sponge 500 and subsequently the substrate 100. In some embodiments, the same chemicals may be flowed through multiple channels 502 into multiple sponges 500. Alternatively, each sponge 500 may receive a different chemical. Additionally, the amount of chemicals supplied to the sponges 500 may be controlled by the controller 210 or operator. The sponges 500 may contact and apply chemicals to the substrate edge 104 during the cleaning/polishing process. Additionally, as described above, the polishing pad 406, similarly to the polishing tape described above, may include abrasive materials of various minerals and grit sizes, which provide a mechanical polishing action. The thin curved slit nozzle 408 may be disposed at the substrate edge 104, between the substrate edge 104 and the sponges 500 and polishing pad 406. While the substrate 100 rotates, as indicated by the central curved arrow, and the deionized water is dispersed, the nozzle 408 may dispense a curtain of N₂, or other suitable gas (e.g., an inert gas). As described above, the curtain of N₂ is applied between the substrate edge 104 and the sponges 500 and polishing pad 406, and may prevent the deionized water from contacting and potentially damaging the polishing head 402. Additionally, the N₂ curtain may also prevent the deionized water from mixing with and diluting the chemicals used to clean and polish the substrate edge 104. Additionally, the N₂ curtain may also prevent the chemicals from contacting the major surface of the substrate.

Additionally, the present invention may employ gravity or suction to cause the runoff not to contaminate or contact other parts of the substrate 100 or system 200. Further, the substrate edge 104 may be cleaned/polished by energy (e.g., megasonic energy), which may be applied to the substrate edge 104 via fluid carrying such energy.

Turning to FIG. 6, a flow chart illustrating an exemplary method 100 of the present invention is depicted. Although five discrete sequential steps are depicted, it should be understood that any number of steps, sub-steps, and/or super-steps may be combined or divided out and performed in different orders and/or concurrently. The particular sequence depicted is merely exemplarily and not necessarily required to perform various method embodiments of the present invention. In other words, for example, in some embodiments, all or some of the steps may be performed concurrently or in reverse order. In step S102, a substrate is rotated in a chuck, for example. In step S104, an edge of the substrate is contacted with a polishing head. A first fluid, such as a cleaning chemical, is applied to the edge of the substrate via the polishing head in step S106. The chemical may be applied by sponges included in the polishing head. In step S108 a second fluid is directed onto a major surface of the rotating substrate. The second fluid may be deionized water. As described above, as the substrate rotates, the water may be centrifugally pushed out to the rest of the major surface of the substrate. In step S110 a third fluid is directed at the major surface of the substrate, such that the third fluid prevents the second fluid from diluting the first fluid. The third fluid may be a curtain of N2. As described above, the curtain of N₂ is applied between the substrate edge 104 and the polishing head 402, and may prevent the deionized water from contacting and potentially damaging the polishing head 402. Additionally, the N₂ curtain may also prevent the deionized water from mixing with and diluting the chemicals used to clean and polish the substrate edge 104. Additionally, the N₂ curtain may also prevent the chemicals from contacting the major surface of the substrate.

It should be understood that the inventive edge polishing apparatus described herein may be employed in apparatuses other than those adapted for bevel and edge polishing and/or removal of films on substrates. Further, as will be apparent to those of ordinary skill in the art, the apparatus describe herein may be employed to polish and/or remove films on an edge of a substrate supported in any orientation (e.g., horizontal, vertical, diagonal, etc).

Further, it should be understood that although only examples of cleaning a round substrate are disclosed, the present invention could be modified to clean substrates having other shapes (e.g., a glass or polymer plate for flat panel displays). Further, although processing of a single substrate by the apparatus is shown above, in some embodiments, the apparatus may process a plurality of substrates concurrently.

The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.

Claims

1. An apparatus for concurrently chemically and mechanically polishing a substrate edge, the apparatus comprising: a substrate support adapted to rotate a substrate;a polishing head adapted to contact an edge of the substrate, the polishing head including a first channel adapted to apply a first fluid to the edge of the substrate;a second channel adapted to direct a second fluid onto a major surface of the rotating substrate; anda third channel adapted to direct a third fluid at the major surface of the substrate and to prevent the second fluid from diluting the first fluid.

2. The apparatus of claim 1 wherein the first channel is further adapted to apply the first fluid to the edge of the substrate where the polishing head contacts the edge.

3. The apparatus of claim 1 wherein the polishing head includes one or more sponges adapted to contact the edge of the substrate.

4. The apparatus of claim 3 wherein the first channel provides the first fluid to the one or more sponges.

5. The apparatus of claim 1 wherein the polishing head includes a pad.

6. The apparatus of claim 1 wherein the polishing head includes a polishing tape.

7. The apparatus of claim 1 wherein the polishing head includes a conformal backing plate.

8. The apparatus of claim 1 wherein the polishing head includes a shaped backing plate.

9. The apparatus of claim 1 wherein the second fluid is deionized water.

10. The apparatus of claim 1 wherein the shape of the third fluid forms an arc surrounding the edge of the substrate contacted by the polishing head and a portion of the major surface of the substrate.

11. A system for concurrently chemically and mechanically polishing a substrate edge, the system comprising: a substrate support adapted to rotate a substrate;a polishing head adapted to contact an edge of a substrate,the polishing head including a first channel adapted to apply a first fluid to the edge of the substrate;a second channel adapted to direct a second fluid onto a major surface of the rotating substrate;a third channel adapted to direct a third fluid at the major surface of the substrate and to prevent the second fluid from diluting the first fluid; anda controller adapted to operate the concurrent chemical and mechanical polishing of the edge of the substrate.

12. The system of claim 11 wherein the shape of the third fluid forms an arc surrounding the edge of the substrate contacted by the polishing head and a portion of the major surface of the substrate.

13. The system of claim 12, further comprising a thin curved slit nozzle adapted to form the arc shape of the third fluid.

14. The system of claim 11 wherein the third fluid is N2.

15. The system of claim 11 wherein the controller is adapted to operate the direction of at least one of the second and third fluids.

16. The system of claim 11 wherein the controller is adapted to operate the application of the first fluid to the edge of the substrate.

17. The system of claim 11 wherein the first channel is further adapted to apply the first fluid to the edge of the substrate where the polishing head contacts the edge.

18. The system of claim 11 wherein the polishing head includes one or more sponges adapted to contact the edge of the substrate.

19. The system of claim 18 wherein the first channel provides the first fluid to the one or more sponges.

20. A method for concurrently chemically and mechanically polishing a substrate edge, the method comprising: rotating a substrate;contacting an edge of the substrate with a polishing head;applying a first fluid to the edge of the substrate via the polishing head;directing a second fluid onto a major surface of the rotating substrate; anddirecting a third fluid at the major surface of the substrate, wherein the third fluid prevents the second fluid from diluting the first fluid.

21. The method of claim 20 further comprising: arcing the third fluid such that the arc surrounds the edge of the substrate contacted by the polishing head and a portion of the major surface of the substrate.

22. The method of claim 20 further comprising: rocking the polishing head about the edge of the substrate.

23. The method of claim 20 further comprising: pressing a polishing tape against the edge of the substrate via the polishing head.

24. The method of claim 20 further comprising: pressing a polishing pad against the edge of the substrate via the polishing head.

25. The method of claim 20 wherein the polishing head includes at least one sponge, and the first fluid is applied to the edge of the substrate via the at least one sponge.