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Options and oportunities with inorganic photoresist systemsS.A. Lis, J.M. Lavine, G.M. Goldberg, and J.I. MastersPhotomaterials Research Group, GCA Corporation209 Burlington Road, Bedford, MA 01730AbstractThe submicron lithographic capability of several compositions of GeSe have been mostconclusively shown by Tai and his co- workers.- Others2,304 have shown that As2S3 and someof the other chalcogenides exhibit similar potential. In this paper we shall report onan extensive investigation of As2S3, As2Se3 and GeSe2 used in conjunction with a varietyof Ag- bearing materials such as evaporated Ag, Ag2S, Ag2Se and Ag2Te as well as withchemically applied Ag- bearing layers. We shall describe both wet and dry processing tech-niques used with these materials. We shall assess the submicron lithographic capabilities,processing latitudes and results obtained with the matrix combinations of these materialsand show our experimental results.IntroductionThe amorphous chalcogenide glasses are under consideration as high contrast inorganicresists because of a number of fundamental advantages they posses over currently availableorganic polymer resists. A small number of workers have already begun to explore thesematerials in terms of specific procedures for providing sub -micron features optically, and500 to 1,000 A features using electron and ion beam exposure techniques. Of special in-terest is their possible application to optical projection lithography using step andrepeat systems where the high contrast and possible edge sharpening phenomena could providesub -micron capabilities at throughput rates competitive with conventional organic resists.Much of the previous work has focused on the use of silver sensitized Ge -Se glasses withcompositions ranging from GeSe2 to GeSe9. The pioneering work of Tai et all has demon-strated many of the fundamentally attractive features of these materials plus the un-expected edge sharpening effect which has attracted much attention. Other workers havealso examined silver sensitized As2S32 as an alternative material and have obtained resultsof similar lithographic interest. Also, some early work was done which demonstrated somecapability in terms of dry development of the two materials in CF43,4.The results we present here are from a study with a more broadly -based approach to thesematerials and their lithographic capabilities. We have explored both wet and dry deposi-tion and development of As2S3, GeSe2, and an additional new material As2Se3. The silversensitization methods were also explored using the more familiar wet -chemical dippingtechniques and the direct evaporation of silver bearing layers (such as Ag, Ag2S, Ag2Se andAg2Te) onto the chalcogenide surface.The fundamental film structure we are most interested in is shown in Figure 1. Thesurface topography is planarized by an organic polymer such as photoresist or polyimide.The cholcogenide is then overcoated on to the polymer to a thickness of between 600 to3,000 A. The chalcogenide film may then be silver sensitized by an overcoating which isgenerally only 100 A thick. Upon exposure the actinic radiation is absorbed in the Agsensitizing layer and Ag ions migrate into the top few hundred Angstroms of the chalcoge-nide. The resist image is essentially contained in this thin layer of Ag doped material.The basic intent of the development process is to utilize and transfer this image faith-fully to the wafer surface. The marked chemical effects of this Ag photodoping processare critical in providing these materials with high contrast and high resolution capa-bilities.Processing approachesThe general process sequence needed to deposit, expose and develop these chalcogenidesis shown in Figure 2. Since the structure used has three layers, each layer must bedeposited and removed, and so far, each step must be accomplished indepencently andefficiently. Most of the major steps have both wet and dry alternatives.The planarization layer is simply a spun -on organic polymer with properties which maysuit the users needs in terms of chemical resistance or photosensitivity. Consideringthe high quality of the planarization by this (wet) method it is questionable whethersimilar or superior quality might be accomplished by any dry deposition method. Most ofour results were obtained on subbing layers of hardbaked photoresist or polyimide. |
