Optimized dry etching procedure, using an oxygen containing ambient, for small diameter contact holes

A method for fabricating a MOSFET device, on a semiconductor substrate, using a small diameter SAC opening in an insulator layer, in a first region of said semiconductor substrate, to expose a source and drain region of said MOSFET device, with said small diameter SAC opening created via a RIE procedure, using oxygen as part of the RIE ambient, and monitoring the RIE end point of said small diameter SAC opening, using optical ellipsometry procedures, performed on a large area test site, in a second region of said semiconductor substrate, comprising the steps of:

• forming field oxide regions in said semiconductor substrate;
• growing a gate insulator layer on said semiconductor substrate;
• depositing an in situ doped, first polysilicon layer, on said gate insulator layer;
• depositing a first tungsten silicide layer, on said first polysilicon layer;
• depositing a first silicon oxide layer on said first tungsten silicide layer;
• patterning of said first silicon oxide layer, of said first tungsten silicide layer, and of said first polysilicon layer, to from polycide gate structures on underlying, said gate insulator layer in said first region of said semiconductor substrate;
• ion implanting a first conductivity imparting dopant into said first region of said semiconductor substrate, not covered by said polycide gate structures, to form a lightly doped source and drain region;
• depositing a second silicon oxide layer;
• anisotropic etching of said second silicon oxide layer to form silicon oxide spacers on the sides of said polycide gate structures;
• ion implanting a second conductivity imparting dopant into said first region of said semiconductor substrate, not covered by said polycide gate structures, and not covered by said silicon oxide spacers, to form said heavily doped source and drain region in region between said polycide gate structures;
• depositing a third silicon oxide layer;
• forming a photoresist shape on said third silicon oxide layer, comprised of a first opening, with a diameter between about 0.4 to 0.6 uM, exposing a region of said third silicon oxide layer, residing in said first region of said semiconductor substrate, and comprised of a second opening, with a diameter between about 40 to 50 uM, exposing a region of said third silicon oxide layer, residing in said second region of said semiconductor substrate:
• performing an initial phase of a reactive ion etching procedure, using C.sub.4 F.sub.8 --CO--Ar, with the addition of between about 1 to 20 sccm of oxygen, resulting in a first polymer layer, comprised of carbon and fluorine, deposited on said third silicon oxide layer, exposed in said first opening, in said photoresist shape, and depositing a second polymer layer, comprised of carbon and fluorine, on said third silicon oxide layer, exposed in said second opening, in said photoresist shape, with the thickness of said second polymer layer, equal to the thickness of said first polymer layer;
• performing a final phase of said reactive ion procedure, using C.sub.4 F.sub.8 --CO--Ar, with the addition of between about 1 to 20 sccm of oxygen, to simultaneously remove said first polymer layer, and said third silicon oxide layer, exposed in said first opening, in said photoresist shape, creating said small diameter SAC opening, between about 0.4 to 0.6 uM in diameter, in said first region of said semiconductor substrate, exposing said heavily doped source and drain region, and removing said second polymer layer, and said third silicon oxide layer, exposed in said second opening in said photoresist shape, creating a large opening between about 40 to 50 uM in diameter, in said second region of said semiconductor substrate, used for ellipsometric measurements to determine said RIE endpoint;
• removal of said photoresist shape;
• depositing a second polysilicon layer, including deposition on said heavily doped source and drain region, exposed in said small diameter SAC opening;
• deposition of a second tungsten silicide layer on said second polysilicon layer;
• and
• patterning of said second tungsten silicide layer, and of said second polysilicon layer, to create a polycide, self-aligned contact, (SAC), structure, completely overlying said small diameter SAC opening, and with said polycide SAC structure partially overlying a portion of said polysilicon gate structures, in regions where said polycide gate structures are adjacent to said small diameter, SAC opening.