D. B. Aldrich

Stability of C54 titanium germanosilicide on a silicon‐germanium alloy substrate

The stability of C54 Ti(Si1−yGey)2 films in contact with Si1−xGex substrates was investigated. The C54 Ti(Si1−yGey)2 films were formed from the Ti‐Si1−xGex solid phase metallization reaction. It was determined that initially C54 Ti(Si1−yGey)2 forms with a Ge index y approximately the same as the Ge index x of the Si1−xGex substrate (i.e., y≊x). After the formation of the C54 titanium germanosilicide, Si and Ge from the Si1−xGex substrate continue to diffuse into the C54 layer, presumably via lattice and grain boundary diffusion. Some of the Si diffusing into the C54 lattice replaces Ge on the C54 lattice and the Ge index of the C54 Ti(Si1−yGey)2 decreases (i.e., y<x). We propose that this process is driven by a reduction in C54 crystal energy which accompanies the replacement of Ge with Si on the C54 lattice. The excess Ge diffuses to the C54 grain boundaries where it combines with Si1−xGex from the substrate and precipitates as Si1−zGez which is Ge‐rich relative to the substrate (z≳x). This segregation a...

Silicide formation and stability of Ti SiGe and Co SiGe

Abstract The formation and stability of the products of Ti and Co reacting with Si1 − x Gex substrates were investigated. For the Ti SiGe system, when a C54 Ti(Si1 − yGey)2 layer forms, the Ge index y is initially the same as the Ge index of the Si1−xGex substrate (i.e. y = x). Thereafter Si1 − xGex from the substrate continues to diffuse into the C54 layer via lattice and grain-boundary diffusion. Some of the Si which diffuses into the C54 lattice replaces Ge in the lattice, and the C54 Ti(Si1 − yGey)2 becomes silicon enriched (i.e. y Co SiGe system, it was determined that a silicon-enriched Co(Si1 − yGey) layer was formed at ~ 400 °C. As the annealing temperature was increased, the reacted layer became even more Si enriched. For both materials systems, Ge-enriched Si1 − zGe(z > x) islands were observed. It was found that for Co Si 1 − xe x the reacted layer consisted of CoSi2 and Si1 − zGez, after high-temperature annealing (≈700 °C). We propose that these processes are driven by a reduction in the crystal energy of the C54 Ti(Si1 − yGey)2 phase in the Ti SiGe system and the Co(Si1 − yGey) phase in the Co SiGe system which accompanies the replacement of Ge with Si.

Film thickness effects in the Ti–Si1−xGex solid phase reaction

The effects of film thickness on the Ti–Si1−xGex solid phase reaction were investigated. Thin C49 TiM2 (M=Si1−yGey) films were formed from the solid phase reaction of 400 A Ti or 100 A Ti with Si1−xGex alloys. It was determined that for films formed from 400 A Ti, the nucleation barrier of the C49‐to‐C54 transformation decreases with increasing germanium content, for alloy compositions with up to ≊40 at. % germanium (i.e., x≤0.40). It was also observed that germanium segregates out of the TiM2 lattice, for both the C49 and C54 phases, and is replaced on the TiM2 lattice with Si from the substrate. The germanium segregation changes the Ge index y of the Ti(Si1−yGey)2. For films formed from a 100 A Ti layer it was observed that the C54 TiSi2 nucleation temperature was increased by ≥125 °C. The addition of germanium to the silicon increased the agglomeration of the C49 phase and caused the C54 TiM2 nucleation barrier to increase further. The results also indicate that the increased temperature required for t...

Electrical and structural properties of zirconium germanosilicide formed by a bilayer solid state reaction of Zr with strained Si1−xGex alloys

The effects of alloy composition on the electrical and structural properties of zirconium germanosilicide (Zr–Si–Ge) films formed during the Zr/Si1−xGex solid state reaction were investigated. Thin films of Zr(Si1−yGey) and C49 Zr(Si1−yGey)2 were formed from the solid phase reaction of Zr and Si1−xGex bilayer structures. The thicknesses of the Zr and Si1−xGex layers were 100 and 500 A, respectively. It was observed that Zr reacts uniformly with the Si1−xGex alloy and that C49 Zr(Si1−yGey)2 with y=x is the final phase of the Zr/Si1−xGex solid phase reaction for all compositions examined. The sheet resistance of the Zr(Si1−yGey)2 thin films was higher than the sheet resistance of similarly prepared ZrSi2 films. The stability of Zr(Si1−yGey)2 in contact with Si1−xGex was investigated and compared to the stability of Ti(Si1−yGey)2 in contact with Si1−xGex. The Ti(Si1−yGey)2/Si1−xGex structure is unstable when annealed for 10 min at 700 °C, with Ge segregating from Ti(Si1−yGey)2 and forming Ge-rich Si1−zGez pr...

Raman Scattering Study of Interface Reactions of Co/SiGe

Raman scattering measurements are used to characterize Co/Si, Co/Ge and CO/Si 0.8 Ge 0.2 thin film reactions. For Co/Si samples, the phase transitions Co--CoSi--CoSi 2 are identified by Raman spectroscopy. For Co/Ge samples, Raman features associated with Co5Ge 7 and CoGe 2 phases were observed. For CO/Si 0.8 Ge 0.2 samples, only CoSi was identified along with Ge enriched SiGe alloy peaks. No features associated with CoGe or Co(SiGe) were found.

X-Ray Absorption Studies of Titanium Silicide Formation at the Interface of Ti Deposited on Si

Near edge X-ray absorption spectra (XANES) have been obtained from the Ti K-edge for several series of titanium silicide samples produced by different techniques. Samples were fabricated by depositing Ti on silicon wafers and subsequently annealing them up to temperatures from 100°C to 900°C in UHV, vacuum furnace, or in a Rapid Thermal Annealing system. Measurements were done in the fluorescence and total electron yield modes. The XANES measurements were correlated with Raman scattering measurements. The XANES data of several reference compounds were obtained, and the data showed a high sensitivity to changes in the film structure. Ti metallic bonding and Ti-Si bonds can be distinguished and their evolution as a function of annealing is related to previous results. For the samples with increased impurities, Ti regions were stable at higher temperatures. The XANES spectra of samples annealed under N 2 indicate the formation of a surface nitride.

XAFS Study of Some Titanium Silicon and Germanium Compounds

It has been shown that, across the full range of Si-Ge alloy compositions, C54 Ti(SiyGe1-y)2 will form from the reaction of Ti with SixGe1-x. An increase in the silicon fraction (i.e., y>x)was seen with the formation of Titanium Germanosilicide which may be due, in part, to the relative diffusion rates of Si and Ge in Ti. In C54 Ti(SiyGe1-y)2 the Si and Ge atoms occupy sites equivalent to the Si in C54 TiSi2. Within error, these atoms form shells about the Ti atoms, with Si and Ge occupancies indicative of the net Si and Ge atomic percents. The radial distances of the shells vary linearly, within error, between those of C54 TiSi2 and C54 TiGe2. The ability to vary the shell distances (and thus vary the lattice constants) of C54 Ti(SiyGe1-y)2 by varying Si and Ge content will prove useful in applications where lattice matching and epitaxy are of importance.

Investigation of Titanium Germanide Formation by Raman Scattering and X-Ray Absorption Spectroscopy

The reactions of titanium on germanium were studied using Raman spectroscopy and X-ray Absorption Spectroscopy (XAS). Samples used in this study were produced in a custom MBE system with dual E-gun sources, two filament sources, and base pressure −10 Torr. Ge(100) substrates were prepared by chemical cleaning and homoepitaxial deposition of 500A - 1000A Ge at 550°C. Ti was deposited and subsequently annealed at 50°C intervals from 500°C to 700°C. Raman and XANES spectra of the titanium germanides were obtained and used to examine the.evolution of the crystalline structures which form by the interface reactions of Ti on Ge. A low-order phase formed by diffusion controlled growth prior to the formation of TiGe 2 (isomorphous with TiSi 2 [C54]) by nucleation controlled growth.

Titanium Germanosilicide: Phase Formation, Segregation, and Morphology

The high temperature solid phase reaction of Ti with Si x Ge 1−x produces a low resistivity titanium germanosilicide which is isomorphic with the C54 phase of TiSi 2 and TiGe 2 . The composition of the final C54 Ti(Si y Ge 1−y ) 2 film is dependent on the composition of the initial Si-Ge alloy and on the annealing conditions. The intermediate phases of the Ti-Si and Ti-Ge reactions are C49 TiSi 2 and Ti 6 Ge 5 respectively. The reaction path of Ti - Si x Ge 1−x shifts from that of Ti-Si to that of Ti-Ge as the Si x Ge 1−x alloy composition changes (×=1→0). Phase separations were observed at low temperatures for Ti reactions with Si-Ge alloys and the C54 formation temperature was observed to decrease as the Si-Ge alloy composition approached Si .5 Ge .5 . Surface and interface morphologies were examined using SEM and TEM. The formation of smooth, large grain, low resistivity films has been observed for the reaction of Ti with low Ge content alloys (x≥0.7). As germanium content is increased the formation of faceted islands is observed. Reactions with high Ge content alloys (x≤0.3) produce films with morphologies similar to those of the Ti-Ge reaction.

Interface Stability of Ti(Sil−yGey)2 and Si1−x Gex Alloys

The stability of C54 Ti(Si 1−y Ge y ) 2 films in contact with Si 1−x Ge x substrates was investigated. The titanium germanosilicide films were formed from the Ti − Si 1−x Ge x solid phase metallization reaction. It was observed that Ti(Si 1−y Ge y ) 2 initially forms with the same germanium content as the Si 1−x Ge x substrate (i.e., y = x). Following the initial formation of TiM 2 (M = Si l−y Ge y ), silicon and germanium from the substrate diffuse into the TiM 2 layer, the composition of the TiM 2 changes, and Si 1−z Ge z precipitates form along the TiM 2 grain boundaries. The germanium content of the Ti(Si l−y Ge y ) 2 decreases, and the Si l−z Ge z precipitates are germanium rich such that y 2 film and the dynamics of the germanium segregation were examined using the Ti-Si-Ge ternary equilibrium diagram. The relevant region of the ternary diagram is the two phase domain limited by a Si-Ge solid solution and a TiSi 2 − TiGe 2 solid solution. In this study first approximation Ti(Si l−y Ge y ) 2 -to- Si l−x Ge x tie lines were calculated on the basis of classical thermodynamics. The tie line calculations indicate that for C54 Ti(Si l−y Ge y ) 2 to be stable in contact with Si l−x Ge x , the compositions of the two phases in equilibrium must be such that y x . The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamic processes by which the Ti(Si 1−y Ge y ) 2 /Si 1−x . Ge x , system progresses from the as-formed state ( y = x ) to the equilibrium state ( y x ) can be predicted using the tie line calculations.