The microstructure of Si thin films, deposited on in-situ cleaned Si(100) surfaces by remote plasma-enhanced chemical-vapor deposition (RPECVD), is dependent on the process pressure, substrate temperature and H2 flow rate. Surface characterization by on-line low energy electron diffraction, LEED, has been used to detect changes in the character of the deposited films which can either be amorphous, microcrystalline or crystalline, hereafter designated as a-Si, µc-Si, and c-Si, respectively. We have used these results to generate phase diagrams for the Si microstructure as a function of the process pressure and substrate temperature, including the flow rate of H2 as an additional deposition parameter.

The time/temperature dependencies of the surface roughness, subsurface extended defect formation, and minority-carrier lifetime are reported for n-type (100) silicon wafers exposed to a hydrogen ion beam. Surface roughness is assessed from atomic force microscopy, the distribution and nature of extended defects are determined from transmission electron microscopy, and the minority-carrier lifetime is evaluated by a non-contact laser-microwave technique. The surface roughness exhibits a weak dependence on ion-beam exposure time for the temperature range studied, whereas the distribution of extended defects may depend on exposure time at a given wafer temperature. The surface and bulk components of the minority-carrier lifetimes are consistent with these surface and subsurface properties. Transmission electron microscopy analyses demonstrate that the associated strain field of the extended defects is compressive in nature.

The effect of Si1−xGex alloy composition on the titanium germanosilicide phase formation sequence during the Ti-Si1−xGex solid phase reaction was examined. For the Ti-Si reaction the initial formation of C49 TiSi2 is followed, at higher temperatures, by the formation of C54 TiSi2. For the Ti-Ge reaction the initial formation of Ti6Ge5 is followed, at higher temperatures, by the formation of C54 TiGe2. It was determined that the Ti-Si1−xGex reaction follows three different reaction paths depending on the composition of the initial Si1−xGex alloy. For Si rich Si1−xGexalloys the Ti-Si1−xGex reaction follows a “Ti-Si like” reaction path (Ti+M ⇒ C49 TiM2 ⇒ C54 TiM2, where M = Si1−xGex). For Ge rich Si1−xGex alloys the reaction follows a “Ti-Ge like” reaction path (Ti+M ⇒ Ti6M5 ⇒ C54 TiM2). Both Ti6M5 and C49 TiM2 form during the reaction of titanium with Si1−xGex alloys in an intermediate composition range. Properties of the final C54 phase were observed to be strongly dependent on the phase formation sequence. Smooth continuous C54 titanium germanosilicide forms during the “Ti-Si like” reaction and discontinuous islanded C54 titanium germanosilicide forms during the “Ti-Ge like” reaction. An optimum Si1−xGex alloy composition range of 0.00 ≤ x ≤ 0.36 was determined for the formation of continuous- low-resistivity- C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy.

This study demonstrates the cleaning of Si(100) surfaces with a remote H2/SiH4 plasma. The surfaces were prepared with a chemical oxide the remains after an RCA clean. The plasma cleaning process was designed to remove contaminants such as C, F, and SiO2. The key to successful removal of the oxide is to have the plasma chemistry in a neutral deposition regime. The neutral deposition process regime is a balance between the deposition of Si by SiH4 and the etching of the deposited Si by atomic H. During the neutral deposition mode the SiO2 was removed without deposition of Si on the SiO2 surface. Once the SiO2 layer is removed, theunderlying Si surface is exposed to the H2/SiH4 plasma and a thin epitaxial film may be deposited. The final Si surface configuration after plasma cleaning is a 2×1 hydrogen terminated surface. The characterization of the interface and epitaxial film were investigated using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM).

The effects of Si1−xGex alloy composition on the Ti-Si1−xGex solid phase reaction have been examined. Specifically, effects on the titanium gcrmanosilicide phase formation sequence. C54 Ti(Si1−yGey)2 nucleation temperature, and C54 Ti(Si1−yGey)2 morphology were examined. It was determined that the Ti-Si1−xGex reaction follows a “Ti-Si-like” reaction path for Si-rich Si1−xGex alloys and follows a “Ti-Ge-like” reaction path for Ge-rich Si1−xGex alloys. The coexistence of multiple titanium germanosilicide phases was observed during Ti-Si1−xGex reactions for Si1−xGex alloys in an intermediate composition range. The morphology and stability of the resulting C54 germanosilicides were directly correlated to the Ti-Si1−xGex reaction path. Smooth continuous C54 titanium germanosilicide was formed for samples with Si1−xGex compositions in the “Ti-Si-like” regime. Discontinuous islanded C54 germanosilicides were formed for samples with Si1−xGex compositions in the mixed phase and “Ti-Ge-like” regimes. Using rapid thermal annealing techniques, it was found that the C54 titanium germanosilicides were stable to higher temperatures. This indicated that the morphological degradation occurs after C54 phase formation. The C54 Ti(Si1−xGex)2 formation temperature was examined as a function of alloy composition and was found to decrease by ≍ 70 °C as the composition approached x ≍ 0.5. An optimum Si1−xGex alloy composition range of 0 ⋚ x ⋚ 0.36 was determined for the formation of stable-continuous-low-resistivity-C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy. The results were described in terms of the relevant nucleation processes.

Remote H-plasma and H2/SiH4 plasma processes were studied as potential dry cleaning processes following reactive ion etching (RIE). The processes were compared to a process of UV/ozone followed by an HF dip. The native oxide from Si(100) substrates was removed with an RIE etch of CHF3/Ar. The RIE process produced ∼150Å of a continuous fluorocarbon (CFx) passivation layer on the Si surface. For the post-RIE-cleaning three approaches were studied and compared including (1) uv-ozone exposure followed by an HF dip, (2) remote H-plasma exposure, and (3) remote H2/SiH4 plasma exposure. Auger electron spectroscopy (AES) was used to investigate the surface chemical composition, and AFM was used to measure changes in surface roughness. All three processes showed substantial removal of the passivation layer. The CF× polymer was completely removed in less than 1 min for samples exposed to a 100W remote H-plasma at 15mTorr and 450°C. With the addition of ∼0.1% of SiH4, the remote H2/SiH4 plasma also showed increased removal of residual oxygen contamination. The surface roughness of the plasma processed surfaces increased slightly.

Actuable microelectromechanical systems (MEMS), fabricated by direct “writing” of deformable membranes on indium tin oxide/copper phthalocyanine (CuPc)/Al microstructures using 130 fs laser pulses, are described. The pulses locally ablate the CuPc without requiring micromachined release holes, demonstrating a novel material release mechanism. The direct-write procedure therefore requires fewer processing steps than traditional MEMS approaches. Using it, we fabricated optical modulators with phase modulation depths >π, intensity modulation amplitudes >50%, and bandwidths >100 kHz, at 5–10 V drive voltage. Fabrication of numerous microstructures and nanostructures can be envisioned, including photonic crystals and optical phased-array gratings.

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

The formation and stability of the products of Ti and Co reacting with Si1 − x Gex substrates were investigated. For the TiSiGe 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 < x). For the CoSiGe 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 CoSi1 − xex 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 TiSiGe system and the Co(Si1 − yGey) phase in the CoSiGe system which accompanies the replacement of Ge with Si.

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 Å Ti or 100 Å Ti with Si1−xGex alloys. It was determined that for films formed from 400 Å 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 Å 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 the transition to the C54 phase, for the 100 Å films, leads to an increased rate of germanium segregation.

This study addresses the formation of roughness and near surface defects on Si(100) surfaces that are exposed to a remotely excited H plasma. The remote H plasma processing can be employed for in situ wafer cleaning. Atomic force microscopy, transmission electron microscopy, and residual gas analysis are used to measure the surface roughness, the near surface defects, and the etching, respectively. For remote H plasma exposures at substrate temperatures ≤300 °C, etching is observed along with a significant increase in the surface roughness and the formation of platelet defects in the near surface region. As the substrate temperature is increased to above 450 °C, etching is significantly reduced and no subsurface defects or increases in surface roughness are observed.

The effects of Si1-xGex alloy composition on the Ti-Si1-xGex solid phase reaction have been examined. Specifically, effects on the titanium germanosilicide phase formation sequence, C54 Ti(Si1-yGey)(2) nucleation temperature, and C54 Ti(Si1-yGey)(2) morphology were examined. It was determined that the Ti-Si1-xGex reaction follows a "Ti-Si-like" reaction path for Si-rich Si1-xGex alloys and fellows a "Ti-Ge-like" reaction path for Ge-rich Si1-xGex alloys. The coexistence of multiple titanium germanosilicide phases was observed during Ti-Si1-xGex reactions for Si1-xGex alloys in an intermediate composition range, The morphology and stability of the resulting C54 germanosilicides were directly correlated to the Ti-Si1-xGex reaction path. Smooth continuous C54 titanium germanosilicide was formed for samples with Si1-xGex compositions in the "Ti-Si-like" regime. Discontinuous islanded C54 germanosilicides were formed for samples with Si1-xGex compositions in the mixed phase and "Ti-Ge-like" regimes. Using rapid thermal annealing techniques, it was found that the C54 titanium germanosilicides were stable to higher temperatures, This indicated that the morphological degradation occurs after C54 phase formation. The C54 Ti(Si1-xGex)(2) formation temperature was examined as a function of alloy composition and was found to decrease by approximate to 70 degrees C as the composition approached x approximate to 0.5. An optimum Si1-xGex alloy composition range of 0 less than or equal to x less than or equal to 0.36 was determined for the formation of stable-continuous-low-resistivity-C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1-xGex alloy. The results were described in terms of the relevant nucleation processes.

Oxide ferroelectric thin films are receiving considerable attention due to their potential application in a wide range of devices including ferroelectric nonvolatile memory, dynamic random access memory (DRAMs) electrooptic phase modulators, and laser light source frequency doublers. However, the complexity of the oxide materials has resulted in a relatively slow development of structureprocessing property relationships. In this paper, we review in turn how the microstructures of epitaxial KNbO3 and Pb(Zr Ti)O3 have been significantly improved over a period of time.In the case of epitaxial KNbO3 on oxide single crystal substrates, defect types which need to be controlled include 221-type misorientations, low angle boundaries, multiposition domains, and inversion domains. Several of these defect types are controlled via the substrate surface preparation. The role of lattice mismatch between film and substrate on the formation of the low angle boundaries remains an unresolved issue. We are currently comparing via TEM the KNbO3(100) films on (100)MgO, (100)MGAl2O4, (100)NdGaO3 and (100)KTaO3 substrates; these substrates covering a range of values of lattice mismatch between 0.1% and 5.0%.

Si(100) and (111) wafers were prepared by a standard RCA cleaning process followed by a treatment in HF/NH4F solutions with different pH values. SiO2/Si structures were formed on these surfaces by a two-step low-temperature, 200–300 °C, plasma-assisted oxidation/deposition process. The SiO2/Si(111) interface, subjected to a predeposition rinse in a 40 wt % NH4F solution, displayed a midgap interface trap density Dit of approximately 5×1010 cm−2 eV−1, which is significantly lower than is generally observed on thermally oxidized Si(111). The Dit values increased systematically up to about 2×1011 cm−2 eV−1 as the pH of the HF/NH4F treatment was decreased. For Si(100) wafers, the absolute level, and the energy distribution of Dit within the Si band gap, were essentially independent of the pH of the HF/NH4F treatment. The micromorphology and perfection of the H passivation of the Si surfaces after the HF/NH4F treatment were characterized by Auger electron spectroscopy and low-energy electron diffraction, and were correlated with the electrical properties of the resulting SiO2/Si structure. It was observed for the first time that the Si(100) surface partially reconstructs into a 2×1 structure after a rinse in 40 wt % NH4F that follows a traditional RCA cleaning treatment.

The high temperature solid phase reaction of Ti with SixGe1-x produces a low resistivity titanium germanosilicide which is isomorphic with the C54 phase of TiSi2 and TiGe2. The composition of the final C54 Ti(SiyGe1-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 TiSi2 and Ti6Ge5 respectively. The reaction path of Ti - SixGe1-x shifts from that of Ti-Si to that of Ti-Ge as the SixGei1-x alloy composition changes (x=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.5Ge.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.

The microstructure of undoped and phosphorus doped Si:H and Si,C:H films was analyzed by selected-area diffraction, conical dark-field imaging, energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy in transmission electron microscopes. Thin films were synthesized by remote plasma-enhanced chemical vapor deposition and characterized in terms of degree of crystallinity. The distribution of phosphorus in the Si:H and Si,C:H films, and carbon in the Si,C:H films was evaluated. The results indicate that i) the microstructure of a film may be two phase, consisting of silicon microcrystallites in an amorphous matrix, ii) phosphorus doping as well as the presence of carbon influences the degree of crystallinity by reducing the average size and volume fraction of microcrystallites, iii) the presence of carbon and phosphorus doping completely suppresses the crystalline phase, iv) phosphorus is distributed at approximately the same concentration in both the crystalline and amorphous phases of diphasic films, and v) carbon is detected in the amorphous phase of the Si,C:H films.

Phase formations in Co thin films (200Å in thickness) reacting with atomically clean Si(100), Ge(100), and Si0.80Ge0.20 epitaxial layer (800Å in thickness on Si(100) substrates) in UHV have been investigated. For the Co/Si system, it is found that CoSi (FeSi structure) is formed at 375°C through a very disordered CoSi phase, and the final CoSi2 phase is formed at 575°C. On the other hand, the CosGe7 phase was identified for the Co/Ge samples annealed at 300°C and 450°C and the final CoGe2 phase is formed at 600°C. For the Co/Si0.8Ge0.20 samples annealed from 400°C to 600°C, Co(Si1-yGey) phases with y-0.10 were detected, and for annealing at 700°C, only the CoSi2 phase was formed. These results indicate a preferential CoSi reaction when annealing the Co/SiGe structure. It was also found that the sheet resistance of the reacted thin films depend strongly on annealing temperature.

Low temperature (50–400°C) and low pressure (10–300 mTorr) processing conditions for remote H-plasma cleaning of Si(100) substrates were investigated. After plasma exposure, ordered surfaces were obtained which displayed 2×1, 3×1 and 1×1 LEED diffraction patterns. The surface phases following the H-plasma clean were dependent on temperature and pressure. The electronic states of the surfaces were explored with angle resolved uv-photoemission spectroscopy (ARUPS) and states due to Si-H bonding were identified. The atomic interactions at the surface were modeled in terms of several processes including Eley-Rideal abstraction, thermally activated desorption and a physisorbed weakly bound state. The kinetic model was able to describe the transitions observed in the processing results. Suitability of the cleaning process for low temperature epitaxy was demonstrated by low temperature MBE epi-growth on an H-terminated 2×1 surface. The initial oxide formation on the H-terminated surfaces were studied by ARUPS.

The microstructure and electrical properties of μc-Si and μc-Si,C prepared by remote plasma-enhanced chemical-vapor deposition, PECVD, are reviewed. The microstructure has been characterized by transmission electron microscopy, TEM, infrared, IR, absorption and Raman scattering. The electrical properties were characterized by temperature-dependent dark-conductivity measurements. These studies have explained significant quantitative differences between the carrier transport properties of μc-Si and μc-Si,C alloys in terms of a band offset model for the interfacial potential steps between the amorphous and crystalline constituents of these material systems.

Oxide-Nitride-Oxide, ONO, heterostructures, fabricated by low-temperature, 300°C, Remote Plasma Enhanced Chemical Vapor Deposition, have been used as gate dielectrics in metal insulator semiconductor devices. Analysis of C-V data for this devices indicates that higher levels of fixed charge are associated with the internal dielectric interfaces. A high-temperature, -900°C, Rapid Thermal Annealing, RTA, step has been inserted into the process sequence for fabricating ultra-thin, 4.7 nm SiO2 equivalent, device-quality ONO dielectric layers. The electrical properties of these ONO dielectrics, including the Si/SiO2 interfacial trap density, the flat band voltage, the charge to breakdown and the reliability under electron injection are comparable to those of high temperature, thermally-grown oxides.