PROCESS FOR FABRICATING GLASS TOOLING

Abstract: Process for fabricating glass tooling with a featured surface. The method entails the steps of coating a polished surface of a glass blank with a continuous metal coating. A photoresist is applied, exposed, and developed in a desired pattern. Uncovered metal is etched away and the remaining metal provides a mask. The uncovered glass is plasma etched to feature the surface of the glass blank.

Description: -1- PROCESS FOR FABRICATING GLASS TOOLING This invention relates generally to a process for fabricating glass tooling such as molds with featured surfaces. A known process for making tooling with a featured surface is shown in Figs, la to lg. A polished glass blank 22. Fig. la, is coated with a layer of photoresist 24, Fig. lb. A latent image is written onto the photoresist layer by means of modulated laser light focused by an optical system 26 (Fig. lc) so that it is registered in the form of a pattern of voids in the developed photoresist layer (Fig. Id). After application of a release layer, a thin nickel layer 28 (Fig. le) is electrochemically deposited onto the patterned side of the glass blank and is then removed to form a single metal negative copy of the vulnerable master which is destroyed in the process, this copy being referred to in the industry as the "father." Electrochemical copying of the father produces a limited number (six or so) of "mother" copies 30 (Fig. If) before the father has deteriorated to the point that the resolution of additional mothers would be unsatisfactory. The mothers are positive copies of the master, and are themselves copied a limited number of times to produce negative "son" copies 32, shown in Fig. lg. The sons are used as tooling having a featured surface. This "family" process is necessary so that many production tools may be made from a single glass master mold. The problem of the known process, and that to be solved by this invention, is that each generation of the family, and each succeeding member of the same generation, suffers increasing resolution degradation. -2- The solution of this problem is a novel process for fabricating tooling with a featured surface by coating a polished surface of a glass blank with a continuous metal coating, applying a photoresist layer. exposing the photoresist in a desired pattern, developing the photoresist, etching away metal uncovered by the photoresist such that the remaining metal provides a mask, and plasma etching the glass in regions unprotected by the mask. The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below. The description of preferred embodiments refers to the attached drawings wherein: Figs, la to lg are a series of sectional fragmental views of a prior art manufacturing process for molds; Figs. 2a to 2h are a series of sectional fragmental views of a manufacturing process for tools in accordance with the present invention; and Figs. 3a to 3e are a series of sectional fragmental views of a manufacturing process for using tooling made in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method described herein presents a process for making a clear glass tooling from a polished, flat glass plate. Figs. 2a to 2h schematically show a preferred manufacturing process for the tooling. Fig. 2a illustrates a glass blank 36 which has been selected for its light transmission properties, absence of internal voids, and polishability. One surface 38 of blank 36 has been ground and polished. -3- preferably to a finish with defects no larger than about 10 A to 15 A RMS and scratches of widths less than 0.025mm. Referring to Fig. 2b, a thin layer 40 of metal (preferably chromium) has been deposited on polished o surface 38. Preferably the chromium layer is from 800 A o to 1000 A RMS thick and may be deposited by standard vacuum coating techniques. Other coating methods will readily occur to those skilled in the art. A positive working photoresist layer 42. such as Eastman Kodak Company resist KPR-820. is applied to the chromium layer such as by spin coating. The photoresist is dried and post-baked in accordance with usual application techniques. As shown in Fig. 2c. latent images are formed in the photoresist layer by focused light, i.e. laser light. The latent image contains the pattern which is to be etched into glass blank 36. Various chemicals well known in the art are usable to develop resist 42 as shown in Fig. 2d. After the resist is developed, the portion of chromium layer 40 not protected by resist is chemically etched down to glass blank 36 (Fig. 2e). Fig. 2f shows the glass and chromium pattern following removal of unexposed photoresist by a suitable solvent. The glass blank with the chromium pattern (Fig. 2f) is placed in a vacuum coater. A plasma is established using argon gas at approximately 1.2 x 10 torr. Radio frequency power is applied to the gas at 500 watts and 400-500 volts. Chromium is a sacrificial mask for plasma etching gas. and the plasma erodes away the glass and the chromium mask. Pattern depth is controlled by the thickness of the mask, the power, and the duration o of etch. Depths of approximately 1000 A RMS can be -4- obtained with an etch time of one hour and a chromium o thickness of 800 A RMS. The rate at which the chromium erodes is about 1/3 to 1/2 slower than that of glass. Fig. 2g shows the etched glass blank and chromium coating. Fig. 2h shows the glass after chromium removal by a conventional acid. After the chromium has been removed, the master is optically clear and can transmit ultraviolet light. Glass tooling made in accordance with the present invention may be used in a molding process for making optical disks as shown in Figs. 3a to 3c. A rigid metal substrate 44 (Fig. 3a) is aligned with and spaced from featured glass tooling 46 which has been prepared in accordance with the process illustrated in Figs. 2a to 2h. The gap between substrate 44 and tooling 46 is filled with a liquid molding resin 48 (Fig. 3b) which is radiation polymerizable. As shown in Fig. 3b, the resin is polymerized by ultraviolet light through transparent tooling 46. The light source may be a mercury-vapor lamp 54 having a wave length of about 330nm to 450nm. If featured, the resultant sub-layer has a resolution on the order of 0.0013mm. and shrinkage is less than two percent. The polymerized resin 48 adheres to the substrate 44 but not to the glass tooling 46, which can be parted from the resin as shown in Fig. 3c. The featured surface of the resin can be coated with various layers such as a metal mirror or record layer 50 (Fig. 3d) and a protective transparent layer 52 (Fig. 3e). The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims: AMENDED CLAIMS [received by the International Bureau on 12 September 1986 (12.09.86); original claims 1—6 unchanged; new claims 7—10 added (1 page)] 7. (New) The process claimed in any of claims 1, 2 or 3, wherein the surface (38) of the glass blank (36) has been ground and polished to a finish with defects no larger than o o about 10 A to 15 A and scratches of widths less than 0.025-μm. 8. (New) The process claimed in any of claims 1, 2 or 3, wherein the photoresist layer (42) is a positive working material applied by spin coating. 9. (New) The process claimed in any of claims 1. 2 or 3. wherein the exposing step is done by focused laser light. 10. (New) The process claimed in any of claims 1, 2 or 3. wherein those portions of the photoresist layer (42) remaining on the metal pattern are removed before the plasma etching step, and that portion of the metal pattern remaining on the glass is removed after the plasma etching step.

Inventors: FISTER ROBERT VIRGIL, PLEDGER JAMES RONNIE, FISTER, ROBERT, VIRGIL, PLEDGER, JAMES, RONNIE
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1986
Main classification: G11B23
IPC codes: C03C15, G03F7, G11B7