Self-Assembled Patterning of Ultrathin Silicides by Local Oxidation
- PDF / 6,921,229 Bytes
- 5 Pages / 604.8 x 806.4 pts Page_size
- 34 Downloads / 152 Views
RS BULLETIN/AUGUST 1999
for reactive ion etching, as is the case for the technologically important silicide CoSi2- Thus we have recently proposed a new self-assembled patterning method based on a solid-state reaction, where we locally control the diffusion processes by stress.5-6 Oxidation of a silicide layer serves as the solid-state reaction and the stress is generated using a conventionally patterned Silicon nitride layer with minimum dimensions of 2 /um. Presently, the method allows the formation of thin epi taxial silicide lines with widths as narrow as 50 nm. Such nanoscale silicide structures pave the road to new nanoelectronic devices. 7,8 For completeness, we would like to mention that small silicide structures can also be made by ion-beam synthesis using either a hard implantation mask or a focused ion beam. 910 Ion-beam synthesis involving hot implantation and annealing allows the material to be selectively s y n t h e sized, mostly buried in the Substrate. In this article, we give a short intro duction to the materials aspects of selfassembly, explain the physical processes involved, compare the results with Monte Carlo simulations, and present instructive examples.
Transition-Metal Silicides Transition-metal silicides are routinely used for the metallization of microelectronic devices and for the formation of Schottky contacts for photodetectors. 1112 The most appropriate Compounds for contacts in deep submicron metal-oxidesemiconductor field-effect transistors (MOSFETs) are TiSi2 and CoSi2. If the di mensions approach 100 n m or less, the use of CoSi2 is preferred, because its re-
sistivity depends only weakly on the line width. 11 Therefore, there is currently a transition in the industry from the use of TiSi2 to CoSi2 metallization. Another im portant advantage of CoSi2 is its structural compatibility with Silicon. The cubic CaF 2 lattice is only 1.2% smaller than that of Silicon, allowing the growth of singlecrystalline layers.13 Such layers show superior thermal stability because of their excellent uniformity, their planar interfaces, and their lack of grain boundaries. All samples used for this contribution were grown by a special molecular-beam epitaxy process.14'15
Oxidation of TransitionMetal Silicides A remarkable property of silicides is their oxidation behavior. Oxidation leads to the formation of Si0 2 on top of the sili cide, but the silicide is not destroyed, only displaced into the Substrate, without metal oxide formation. 16 The oxidation process can be described as a sequence of diffusion and reaction Steps, similar to the oxidation of Silicon described by the model by Deal and Grove. 17 As illustrated in Figure 1, the oxidation process
Figure 1. Illustration of the oxidation mechanism of a silicide layer on Silicon. The numbers indicate the main diffusion and reaction steps. (1) Oxidant transfer into the Silicon dioxide layer and its diffusion through the layer; (2) dissociation of the silicide at the oxide-silicide Interface and the formation of Si02; (3) diffusion of the di
Data Loading...
