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MOTOROLA INC. Technical Developments Volume 13 July 1991
INTERFACE HARDENING BY IMPLANTING F OR CL INTO SACRIFICIAL OXIDE
by Hsing-Huang Tseng, Bich-Yen Nguyen and Jim Pfiester
DEFINITION OF THE PROBLEM
Device degradation by hot-carrier injection (HCI) is one of the most serious problems in short-channel MOSFET reliability.
Reason: Because the device dimension has been
scaled down without reducing the supply voltage, the high electric field near the drain region causes the hot- carrier injection problem.
POSSIBLE APPROACHES
1. Drain structures: E.G. LDD ETC.
2. Improvement of gate dielectric and silicon sub- strate interface characteristics to reduce the amount of trapping centers or the bond break- age rate during hot-carrier injection.
3. Incorporation of fluorine or chlorine at the gate dielectric and si-substrate interface.
PRIOR ART
Incorporation of fluorine at the gate dielectric and si-substrate interface by implanting fluorine into the surface region of polycrystalline-silicon gate and sub- sequently annealing to drive the fluorine atom into the gate SI02 toward the SIO2/SI interface. This was not addressing the present problem.
OUR SOLUTION TO THE PROBLEM
1. Grow sacrificial oxide on the silicon substrate.
2. Deposit thin silicon nitride on the sacrificial
oxide to prevent fluorine out-diffusion.
3. Implant fluorine through the silicon nitride and into the sacrificial oxide.
4. Anneal and drive the fluorine.
5. Strip nitride and sacrificial oxide (ON0 ET...
