Growth and Characterization of Titanium Zirconium Disilicide Thin Films on Silicon
Abstract
Titanium disilicide (C54 TiSi_2 ) has been conventionally used as contacts in the source and drain regions of metal oxide semiconductor devices to reduce the series resistance. Thin film of C54 TiSi _2s are formed at the shallow junctions at the source and drain regions in a self-aligned silicide (SALICIDE) process. As device dimensions are scaled down, the C54 TiSi_2 films formed at the shallow junctions are required to be thinner (several hundred angstroms). However, for a thin TiSi_2 film, the film agglomerates when it is annealed at high temperatures ({~}800 ^circC). The agglomerated C54 TiSi _2 thin films result in significantly increased sheet resistance. The objective of this work is to find an alternative material which exhibits improved thermal stability at high temperatures compared to C54 TiSi_2. Our approach is to stabilize the metastable C49 phase of TiSi _2 thin films on silicon substrates at high temperatures by co-evaporation of Ti with a small amount of Zr during the deposition. In this study, thin films of Ti, Zr, and Ti-Zr alloy were deposited on atomically clean Si (100) and (111) surfaces in an ultra high vacuum (UHV) deposition system, and the films were annealed in UHV to form silicide. In -situ Raman and ex-situ x-ray diffraction experiments were performed to identify the phases of these thin film samples. A quantitative x-ray absorption structural analysis was performed to study the local environments around the Ti or (and) Zr atom(s) in the Ti/Si, Zr/Si, and rm Ti _{1-x}Zr_{x}/Si samples. The surface and interface morphologies were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross section transmission electron microscopy (TEM). Sheet resistances of these films were obtained using a four point probe. The contact resistivities of the silicide/Si samples were measured using a transmission line model (TLM) method. The C49-to-C54 phase transition temperature of (rm Ti_{1-x}Zr_{x })Si_2 increases with Zr content, x. When x > 10%, the (rm Ti_ {1-x}Zr_{x})Si^2 thin films are stable in the C49 phase at annealing temperatures up to 1000^circC. This is proposed to be a result of the nucleation energy barrier for a C54 nucleus to form increasing with Zr content, x. The local structural analysis also suggests that C49 ( rm Ti_{1-x}Zr_{x})Si _2 rearranges structuraly to compensate for the strain energy introduced by Zr atoms. The C49 ( rm Ti_{1-x}Zr_{x})Si _2 thin films exhibit larger substrate coverages than the C54 TiSi_2 films. The surface roughness and sheet resistance of the C49 ( rm Ti_{1-x}Zr_{x})Si _2 films are lower than those of the C54 TiSi_2 films at high annealing temperatures (>800^circC). The C49 (rm Ti_{x}Zr_ {1-x})Si_2 thin films exhibit increased resistance to agglomeration compared to the C54 structure because the C49 phase has lower surface and interface free energies than the C54 phase. The contact resistivity of the C49 ({rm Ti_{1-x}Zr _{x})Si_2}/n^+ -Si contact is similar to those of the C54 TiSi _2/n^+-Si and C49 ZrSi_2/n ^+-Si contacts. The C49 (rm Ti_{1-x}Zr_{x})Si_2 thin films can also be selectively formed in the Si regions of the SiO_2-Si patterned substrates using a conventional SALICIDE process. Therefore, C49 (Ti_{1 -x}Zr_{x})Si_2 may be a good candidate as a contact material, which can be used as contacts in the source and drain regions of future MOSFETs.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT.......114D
- Keywords:
-
- TITANIUM;
- ZIRCONIUM;
- SILICON;
- CONTACT MATERIALS;
- Physics: Condensed Matter; Engineering: Metallurgy; Engineering: Materials Science; Engineering: Electronics and Electrical