A new process for tungsten gate metal oxide semiconductor (MOS) capacitors has been developed using chemical vapor deposition (CVD) of tungsten on a thin poly-Si layer of appropriate thickness. The poly-Si acts as a sacrificial layer and is consumed during the CVD of tungsten (W). This process yields a nearly pure W metal gate after SiH4 reduction of WF6 at 300°C. Compared with sputtered tungsten films, the CVD tungsten film has lower resistivity and lower intrinsic film stress. In addition, the CVD tungsten metal gate MOS capacitor has a lower interface state density (D18) and a higher charge-to-breakdown (Q84), than sputter-deposited tungsten gate MOS capacitors. InfroductionAs device dimensions continue to decrease for higher density and improved performance in integrated circuits, there is a growing demand for more highly conductive gate and interconnection materials. The poly-Si now used for this purpose in conventional processing has certain limitations, due mainly to limited conductivity. In addition, it is well known that the use of p-polygates has become indispensable for p-channel metal oxide semiconductor field effect transistors (MOSFET5) in the deep submicron regime. However; the penetration of boron impurities results in a shift of the threshold voltage, an increase in subthreshold swing and leakage current, and degradation of the gate oxide reliability.1-3 Metal silicides4' have been considered because their conductivities are higher than that of poly-Si by one order of magnitude. Furthermore, it is expected that materials with conductivities higher than those of silicides will be required in the future for very high density integrated circuits. Thngsten is considered a very promising gate material candidate because it makes gate implantation unnecessary. Furthermore, tungsten also provides low resistivity and near midgap work function.7 Tungsten gates have conventionally been prepared by sputtering,8 plasma-or laser-enhanced chemical vapor deposition (CVD).9"° However, conventional CVD of tungsten using silane or hydrogen reduction of WF, cannot deposit W on oxides at temperatures below 400°C. Although tungsten can be forced directly onto Si02 surfaces at temperatures above 400°C, the resulting films possess 3-type structures with high resistivity'2 and tend to peel off because of poor adhesion to the Si02. In this study, we developed a new process, in which CVD of tungsten was employed to deposit W on a thin sacrificial poly-Si layer deposited on a gate oxide prior to CVD of the W itself. The natural self-limiting Si consumption property of the chemical vapor deposition of tungsten,'3 the so-called Si reduction reaction, will cause the thin sacrificial poly-Si layer to be consumed, so that a nearly pure W metal-gate MOS capacitor will result at the low deposition temperature of 300°C. We introduce the first tungsten metal gate Electrochemical Society Active Member.(the poly-Si layer is completely consumed) MOS capacitor with the tungsten-gate formed by CVD process; this differs from conventional ...

A New Tungsten Gate Metal Oxide Semiconductor Capacitor Using a Chemical Vapor Deposition Process.-In the new W gate MOS process, tungsten is vapor deposited on a thin, sacrificial poly-Si layer which is completely consumed during the CVD process. The process yields a nearly pure W metal gate after SiH4 reduction of WF6 at 300 • C. Compared with sputterdeposited W gate MOS capacitors, the CVD capacitor has a lower resistivity gate, lower intrinsic tungsten film stress, lower interface state density, and a higher charge-to-breakdown value, which makes it promising for future VLSI application. -(YEH, W.-K.; SHIAU, Y.-C.; CHEN, M.-C.; J. Electrochem.