A polycrystalline-Si/sub 1-x/Ge/sub x/-gate CMOS technology

Abstract

A new polycrystalline silicon-germanium gate CMOS process has been developed for a submicron CMOS technology. The incorporation of germanium into a heavilydoped p-type polycrystalline-silicon (P+ poly-Si) gate material causes the gate workfunction to be reduced (more than 300 mV for a 60% Ge material), so that both NMOS and PMOS surfacechannel devices may be achieved. In addition, it improves the gate sheet resistance by increasing dopant activation. Whereas pure Ge is not suitable for use as a gate material due to its low melting point and its lack of a stable oxide, poly-Si 1 -,Ge, films with Ge mole fractions up to 0.6 were found to be completely compatible with standard VLSI fabrication processes, in regard to deposition and patterning techniques, high-temperature chemical and mechanical stability, and electrical stability and uniformity.

The influence of poly‐Si/SiGe gate in CMOS transistors for RF and microwave circuit applications

“…We demonstrate that a reduction in the gate depletion improves the DC characteristics for poly-SiGe gate as compared with poly-Si gate in agreement with literature [5], [6], [7] which uses a single p + doped, poly-Si 1-x Ge x gate material. It is well understood that the conventional single p + doped or dual doped poly-Si gate has the problem of Boron penetration from gate through gate oxide layer [8], so for this study, our local CMOS process uses a single n + doped, poly-Si 1-x Ge x gate material to achieve both n + doped gate n-MOS and n + doped gate p-MOS devices.…”

High-performance deep submicron CMOS technologies with polycrystalline-SiGe gates

“…For example, PMOS capacitors with 30% Ge content show an eV shift in the workfunction as compared to poly-Si. There is essentially no change in for n-type poly-SiGe [2], [6]. We have outlined in this section the material properties of poly-SiGe relating to its integration into a standard MOS processing flow.…”

“…Fig. 1 summarizes the impact of the Ge mole fraction change in the p-type poly-SiGe gate on the gate-semiconductor workfunction difference based on the data available from literature [2], [6], [7] and our own measurements. The change in is usually measured from the flatband voltage dependence on the gate oxide thickness, assuming that density of the interface states stays constant [8].…”

“…Recently, there have been quite a number of reports on the properties of heavily doped poly-SiGe films [2]- [6], [11]- [13].…”

High-performance polycrystalline SiGe thin-film transistors using Al2O3 gate insulators

“…In bipolar transistors, it has been used to form narrow bandgap base regions [1]. In field effect devices, it has been used to form variable workfunction gate electrodes [2]. In large-area electronics such as flat panel displays, its advantages include lower solid-state crystallization temperature and potentially higher mobility [3].…”