Silicides for Highly Integrated Memory and Logic Circuits
- PDF / 456,931 Bytes
- 10 Pages / 414.72 x 648 pts Page_size
- 90 Downloads / 221 Views
JOSEF WINNERL Siemens AG, Semiconductor Group, Otto-Hahn-Ring 6, 81739 Munich, Germany
ABSTRACT State of the art DRAM and logic processes widely make use of silicides formed by refractory metals like Ta, Mo, W, Ti, Co, or others. The methods for silicide formation range from sputtering, reaction with predeposited metal, to selective CVD deposition. The most common application of silicides in state of the art CMOS processes is to use them as a conducting layer that can withstand high temperature processes and that has a significantly lower sheet resistivity than doped mono or poly crystalline silicon. Besides their role as a temperature stable conductor silicides have further interesting properties when using them as a diffusion source for impurities to generate shallow junctions, or as an alternative gate material with a work function in the middle of the silicon band gap. Based on the example of the self aligned silicidation with titanium silicide the limitations of the state of the art technology will be shown and requirements for future applications will be discussed.
INTRODUCTION Refractory metals and their silicides have become inevitable elements of state of the art silicon processes. Especially in CMOS processes they are widely used in production and are subject of research and development work. The main reason for introducing silicides is their substantially lower resisitivity compared to doped mono and poly crystalline silicon and the high temperature stability compared to conventional interconnect materials like aluminum. After the deposition of the silicides processes like thermal oxidation, deposition of insulating layers like oxide or nitride, or planarization of BPSG layers by thermal reflow can be performed. Table I reviews basic properties of some popular silicides addressed in this paper '. Obviously there is a trade off between the temperature stability and the achievable sheet resisitivity. Generally the cosputtered silicides (TaSi 2 , MoSi 2 , WSi 2 ) show a higher temperature stability, whereas silicides formed by tempering a predeposited metal on silicon (TiSi 2 , CoSi 2 , NiSi 2 , PtSi) have a lower resistivity. 37 Mat. Res. Soc. Symp. Proc. Vol. 320. @1994 Materials Research Society
Table 1.Basic properties of most popular silicides '(Table III and VII) Silicide
Lowest eutectic temperature (C)
TiSi 2 TaSi 2 MoSi 2 WSi 2 CoSi2 NiSi 2 PtSi
1330 1385 1410 1440 1195 966 830
Silicide formation Metal on poly Cosputtering Cosputtering Cosputtering Metal on poly Metal on poly Metal on poly
Si
Si Si Si
Sintering temperature (C)
Resisitivity (go-cm)
900 1000 1000 1000 900
13 -16 50 - 55 ~100 - 70 18 - 20
900 600-800
-50 18 - 35
SILICIDES IN DRAMS The increasing complexity of dynamic memories is still the driving force for the rapid progress in CMOS technology development. Every three years the number of bits in DRAMs increases by a factor of four. Today the 4 Mbit DRAM is in mass production, production of 16 Mbit DRAMs is starting, and 64 Mbit samples are available. Fig. I schematical
Data Loading...
