The nature of residues following the ashing of arsenic implanted photoresist
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The nature of residues following the ashing of arsenic implanted photoresist Clifton W. Draper Bell Laboratories, P.O. Box 900, Princeton, New Jersey 08542
Chuck W. Pearce and Jere T. Glick Lucent Technologies, 555 Union Boulevard, Allentown, Pennsylvania 18103
Mike Gordon SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741
Gwen E. Olness and Steven L. Bernasek Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (Received 18 November 1996; accepted 8 May 1997)
Extensive analytical characterization indicates that the most significant contaminant following dry processing of As-implanted photoresist is not a carbon-based residue, but is in fact arsenic itself. The arsenic residue is an amorphous form of elemental arsenic, relatively free of oxygen or carbon, that is stable for long periods of time. Since arsenic is not particularly soluble in sulfuric acid, hydrogen peroxide, or their mixtures, it makes sense to pose questions regarding the optimum choice for post-dry processing wet chemical cleans.
I. INTRODUCTION
Ion-implanted photoresist represents one of the most challenging materials to remove effectively from a semiconductor wafer surface. Although oxides and nitrides of silicon are used as implant masks on occasion, hardbaked photoresist is the implantation mask of choice used in device manufacturing. The fact that this material choice presents implantation equipment manufacturers and the implant engineers with special problems is well recognized and has been discussed in industry trade journals such as the recent article by Burggraaf.1 The stopping of the high energy implant species within the photoresist is accompanied by significant conversion of particle kinetic energy to thermal energy and by direct atomic displacement in the cascade developed in the volume around the range profile of the implant ion.2 The uppermost region of the photoresist is frequently described as having become “carbonized,” and some work has identified this hardened layer as being akin to disordered graphite.3 Additional evidence for this material change comes from studies of the outgassing that occurs during implantation in work like that of Roche, Michaud, and Bruel,4 and from electron microscopy like that reported by Orvek and Huffman.5 The outgassing of hydrogen during high current implantation can cause the background pressure in the implanter vacuum chamber to increase by two orders of magnitude.1,6,7 Figure 1 is a scanning electron micrograph8 of implant-hardened KTI 820 (Kodak positive photoresist) that has been exposed to an acetone-water mixture and then nitric acid. This J. Mater. Res., Vol. 12, No. 10, Oct 1997
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wet chemical treatment dissolves away the bulk of the approximately 2 mm thick UV-treated, hard-baked, Asimplanted photoresist, thus undercutting the carbonized layer, making its roughly 0.2 mm thickness quantifiable. It is this layer of material that is often cited as the cause of diff
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