Study of HKMG Stack Interface Engineer Applicable to 22nm/16nm Finfet Mosfet

Abstract

Since Intel announced that they had made a great breakthrough in 22nm node[1][2]on May 4, 2011, FinFET Transistor structures had almost controlled CMOS technology beyond 22nm node. In this node, with the development of lithography, silicide process was switched to the back end. This huge change bring benefit to the formation of HKMG stack interface engineer. Before the silicide step switched, limited by the already formed silicide, the growth temperature of interfacial oxide layer couldn’t be higher than 600°C for NiSi unstability at high temperature, but now 800°C or 850°C will also be allowed. So we could adopt thermal oxide as HKMG stack interface layer. In this paper, as interface layer of HKMG stack, chemical and thermal oxide were all studied. In 32nm/22nm node Bulk Planar CMOS technology, chemical oxide was grown through spraying DI water diluted Ozone on bare silicon substrate which was generally used in industry. It’s advantage was low thermal budget and the disadvantage was thermal unstability of Chemical ox during ALD HfOX growth. ChemOX would diffuse into HK dielectric, referred to Fig 1(b). It could also be observed very clearly at Si/ChemOX/RTCVD SIN structure , referred to Fig 2(b). From Fig 1(a) and Fig 2(a) , we had no doubt about the stability of thermal oxide interface layer. In this article, We chose three different thermal oxidation methods which were RTO, ISSG alone, ISSG with plasma nitridation[3][4]respectively. Considering the state of silicon substrate surface would severely affect the quality of ultrathin interface oxide layer, we also chose two different cleaning process which were HF 100:1 and BOE 100:1 last.In conclusion, in order to improve HKMG stack characteristic in FinFET Transistor structures, different interface layer and cleaning process had been studied. Considering the thermal unstability of Chemical oxidation method currently used in industry, we plan to take high quality thermal ultrathin interface oxide into 22nm node and beyond.