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  Partial edge bead removal to allow improved grounding during e-beam mask writingUSPTO Application #: 20060130969Title: Partial edge bead removal to allow improved grounding during e-beam mask writing Abstract: A method to provide a ground point for second, or subsequent, e-beam mask-writing steps by selectively removing the photoresist edge bead of a photomask substrate to expose the underlying chrome layer. The selective removal leaves at least one tab of photoresist edge bead over the chrome layer. After the first e-beam mask writing step and subsequent etch, the tab can be removed to expose a portion of the chromium layer that can act as a new ground point for a second e-beam etch. Also, a nozzle for use in selectively removing the edge bead to leave a tab of photoresist edge bead. (end of abstract) Agent: Whyte Hirschboeck Dudek S.c. - Milwaukee, WI, US Inventor: J. Brett Rolfson USPTO Applicaton #: 20060130969 - Class: 156345220 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060130969. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a divisional of U.S. Ser. No. 10/614,529, filed Jul. 7, 2003. BACKGROUND OF THE INVENTION [0002] The present invention relates to fabricating a photomask used in a photolithography process and, more specifically, to a method and apparatus for removing an edge bead from a photomask. [0003] A photomask may be used to transfer a pattern onto a semiconductor wafer. The pattern which is to be transferred onto the wafer may be formed on a material, such as glass or quartz, which is substantially transparent. The material of the photomask may also include thin films of metal or other nontransparent material that prevent light from passing through selected portions of the photomask. In typical photomasks, the nontransparent material is opaque chrome. [0004] Due to limitations imposed by the wavelength of light used to transfer the pattern, resolution degrades at the edges of the patterns of the photomask. Phase-shifting photomasks increase the resolution of patterns by creating phase-shifting regions in the transparent areas of a photomask. One type of phase-shifting mask is known as an "attenuated" or "half-tone" phase-shift mask. In this type of mask, the transparent regions transmit approximately 100% of the incident radiation, similar to the strong phase-shifting mask. However, the transparent areas are in-phase. The "phase-shifting" feature of an attenuated phase-shift mask is due to the fact that the opaque regions of the hard shifters are replaced with areas that are slightly transmissive, and act to shift light transmitted by 180.degree.. Transmission of this incident radiation is typically in the 6-9% range for these masks. [0005] Depending on the process used, an attenuating phase-shift mask may only require a single maskwriting step (similar to a binary mask). However, other processes may be used which require two or more maskwriting steps in order to create desired features, such as an opaque border region. At the present time, single-write processes, without the opaque border, have not been successful in photolithography steppers which use longer wavelengths for alignment or reticle identification, due to the material constraints of the pattern material. [0006] Several methods of fabricating a photomask having an opaque layer on the border of the mask are known in the art. One process requires two mask-writing steps. First, a primary mask pattern is written and etched to the underlying substrate of the mask blank, the photoresist is stripped, and the mask blank is re-coated. Second, an opaque layer is written onto the border of the mask. [0007] One drawback of the two mask-writing steps process is that the first chromium etch removes all exposed chrome. The subsequent lack of exposed chrome makes obtaining a good ground for the second e-beam write difficult without extensive write tool modification. Therefore, there is a need for a two mask-writing steps process that facilitates grounding the e-beam for the second mask-writing step. BRIEF SUMMARY OF THE INVENTION [0008] The current invention is a method for facilitating second, and subsequent, mask-writing steps by protecting potential grounding points from etching. The invention also includes a nozzle tool useful in conducting the method. [0009] In one preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; selectively removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0010] In another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle adapted to apply a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle adapted to apply a solvent to the edge of the workpiece; a third nozzle adapted to apply a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first, second and third nozzles to selectively apply solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0011] In another preferred embodiment a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: means to apply a solvent to the top surface of the workpiece adjacent to the periphery; means to remove the solvent from the edge of the workpiece; and means to apply the solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each means to apply and remove a solvent may be independently controlled; selectively applying and removing solvent by means of the nozzle tool to the top surface and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0012] In another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle and vacuum means adapted to apply and remove a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle and vacuum means adapted to apply and remove a solvent to the edge of the workpiece; a third nozzle and vacuum means adapted to apply and remove a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first nozzle and vacuum means, the second nozzle and vacuum means and the third nozzle and vacuum means to selectively apply and remove solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0013] A method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle adapted to apply a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle adapted to apply a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first and second nozzles to selectively apply solvent to the top surface and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0014] In another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; selectively removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0015] A method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle adapted to apply a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle adapted to apply a solvent to the bottom surface of the workpiece; a vacuum means adapted to remove a solvent from the edge of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first nozzle, the second nozzle and the vacuum means to selectively apply and remove solvent to the top surface and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; removing the exposed chrome layer; removing the tab of photoresist material, or removing at least one tab if more than one tab is present; and removing the exposed chrome layer. [0016] In still another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: means to apply and remove a solvent to the top surface of the workpiece adjacent to the periphery; means to apply and remove the solvent from the edge of the workpiece; and means to apply and remove the solvent from the bottom surface of the workpiece adjacent to the periphery, wherein each means to apply and remove a solvent may be independently controlled; selectively applying and removing solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0017] A method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: means to apply a solvent to the top surface of the workpiece adjacent to the periphery; means to remove the solvent from the edge of the workpiece; and means to apply the solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each means to apply and remove a solvent may be independently controlled; selectively applying solvent to the top surface and bottom surface of the workpiece and removing the solvent from the edge of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0018] In yet another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle adapted to apply a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle adapted to apply a solvent to the edge of the workpiece; a third nozzle adapted to apply a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first, second and third nozzles to selectively apply solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0019] A method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising a first nozzle adapted to apply a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle adapted to remove the solvent from the edge of the workpiece; a third nozzle adapted to apply a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first, second and third nozzles to selectively apply and remove solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0020] In another preferred embodiment, the invention is a method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising: a first nozzle and vacuum means adapted to apply and remove a solvent to the top surface of the workpiece adjacent to the periphery; a second nozzle and vacuum means adapted to apply and remove a solvent to the edge of the workpiece; a third nozzle and vacuum means adapted to apply and remove a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first nozzle and vacuum means, the second nozzle and vacuum means and the third nozzle and vacuum means to selectively apply and remove solvent to the top surface, edge and bottom surface of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. [0021] A method for making a photomask, the method comprising the steps of providing a workpiece comprising a substrate having a top surface, a bottom surface opposed to the top surface and an edge connecting the top surface and the bottom surface, the edge defining a periphery of the substrate, wherein a layer of chrome superimposes the top surface and a layer of a photoresist material superimposes the chrome layer; providing a nozzle tool comprising a first nozzle adapted to apply and remove a solvent to the top surface of the workpiece adjacent to the periphery; a vacuum means adapted to remove a solvent to the edge of the workpiece; a second nozzle and vacuum means adapted to apply a solvent to the bottom surface of the workpiece adjacent to the periphery, wherein each nozzle may be independently controlled; controlling the first nozzle, the second nozzle and the vacuum means to selectively apply solvent to the top surface and bottom surface of the workpiece and remove solvent from the edge of the workpiece thereby removing the photoresist material from portions of the workpiece adjacent to the periphery to expose the chrome layer while leaving at least one tab of photoresist material covering the chrome layer adjacent to the periphery; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a first pattern; removing the exposed chrome layer; removing the tab of photoresist material, or removing one tab if more than one tab is present; selectively removing photoresist material nonadjacent to the periphery to expose the chrome layer in a second pattern; and removing the exposed chrome layer. 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