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Browse Prior Art Database

Semiconductor Contact Hole Fabricating

IP.com Disclosure Number: IPCOM000046631D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Dockerty, RC: AUTHOR

Abstract

This is an improved technique of fabricating contact holes in double polysilicon (DPS) or single polysilicon/metal conductor structures where contact holes are required through different thicknesses of insulating material. In a DPS structure, contact holes must be etched to the source/ drain N+ regions, to the substrate, and to the poly I and poly II conductors. The contact holes are etched through overlying oxide layers masked by photoresist. A problem arises because different thicknesses of oxide cover the different contact areas. For example, the poly I must be oxidized prior to the deposition of poly II. The subsequent oxidation of the poly II causes an additional thickness of oxide over the poly I (cumulative to the previous poly I oxide coating) which will be thicker than the oxide layer over the poly II.

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Semiconductor Contact Hole Fabricating

This is an improved technique of fabricating contact holes in double polysilicon (DPS) or single polysilicon/metal conductor structures where contact holes are required through different thicknesses of insulating material. In a DPS structure, contact holes must be etched to the source/ drain N+ regions, to the substrate, and to the poly I and poly II conductors. The contact holes are etched through overlying oxide layers masked by photoresist. A problem arises because different thicknesses of oxide cover the different contact areas. For example, the poly I must be oxidized prior to the deposition of poly II. The subsequent oxidation of the poly II causes an additional thickness of oxide over the poly I (cumulative to the previous poly I oxide coating) which will be thicker than the oxide layer over the poly II. Furthermore, the contact to the substrate should be made through the field oxide which is significantly thicker than the oxide over the poly I. If all these contact holes are etched in a single etching step, substantial overetching is required through the shallower oxide in order to assure a complete etch through the thicker oxide. This need for overetching is inherently undesirable because it causes oversized contact holes. Fig. 1 shows a conventionally processed N channel DPS structure prior to contact hole etching. The illustrated structure is etched by two separate contact mask steps. The mask for contact 1 (CI) is used to open the substrate contact (SX) through the thick (8000 ~) field oxide. Contact mask (CII) is then used to open holes to the N+ diffusion contact areas, the polysilicon I (PI) contact areas and the polysilicon II (PII) contact areas, as shown. By using two masks, the overetch problem is eliminated with respect to the formation of the substrate contact. Nevertheless, the N+ diffusion contacts and PII contacts must be slightly overetched to ass...