Gari S. Harris

Formation of titanium and cobalt germanides on Si (100) using rapid thermal processing

Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid thermal annealing in either Ar or N2 ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The sheet resistance was found to be dependent on annealing ambient (Ar or N2) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides were found to be 20 µΩ-cm and 35.3µΩ-cm, corresponding to TiGe2 and Co2Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti6Ge5 phase forms prior to TiGe2. The TiGe2 phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures (425° C); however, the stability of the material is poor at elevated temperatures.

Influence of dry and wet cleaning on the properties of rapid thermal grown and deposited gate dielectrics

Various silicon surface cleaning processes for rapid thermal in-situ polysilicon/ oxide/silicon stacked gate structures have been evaluated. Metal-oxide-semiconductor capacitors were fabricated to assess the effects of cleaning on the quality of gate oxide structures produced by both rapid thermal oxidation (RTO) and rapid thermal chemical vapor deposition (RTCVD). Excellent electrical properties have been achieved for both RTO and RTCVD gate oxides formed on silicon wafers using either an ultraviole/zone (UV/O3) treatment or a modified RCA clean. On the contrary, poor electrical properties have been observed for RTO and RTCVD gate oxides formed on silicon wafers using a high temperature bake in Ar, H2, or high vacuum ambient. It has also been found that the electrical properties of the RTCVD gate oxides exhibit less dependence upon cleaning conditions than those of RTO gate oxides. This work demonstrates that initial surface condition prior to gate oxide formation plays an important role in determining the quality of RTO and RTCVD gate oxides.

Thin oxynitride film metal‐oxide‐semiconductor transistors prepared by low‐pressure rapid thermal chemical vapor deposition

Thin silicon oxynitride (Si‐O‐N) films have been deposited using low‐pressure rapid thermal chemical vapor deposition (RTCVD) with silane (SiH4), nitrous oxide (N2O), and ammonia (NH3) as the reactive gases. Metal‐oxide‐semiconductor transistor transconductance measurements showed decreasing peak gm values but improved high field degradation characteristics. This is consistent with previous work on thermally nitrided oxides and suggests that the films are perhaps under tensile stress. Hot carrier stress at maximum substrate current was performed with the Si‐O‐N films displaying larger threshold voltage shifts when compared to furnace SiO2 indicating the possible existence of hydrogen related traps.

Effects of oxygen doping on properties of microcrystalline silicon film grown using rapid thermal chemical vapor deposition

An oxygen doped microcrystalline silicon (μc-Si) deposition process is developed by mixing small amounts of nitrous oxide (N2O) with silane (SiH4) in a rapid thermal chemical vapor deposition (RTCVD) reactor. The effects of oxygen doping on the properties of RTCVD μc-Si films are studied. Experimental results show that the RTCVD process provides high deposition rates for μc-Si and polycrystalline silicon (polySi) films at elevated deposition temperatures and pressures. The surface roughness of the RTCVD μc-Si films can be significantly reduced compared to that of conventional LPCVD polySi films. Steep side walls can be realized due to the small grain size of the μc-Si films. The sheet resistance of BF2 doped μc-Si films is slightly higher than that of BF2 doped polySi films, whereas sheet resistances of P and As doped μc-Si films are much higher than those of the corresponding P and As doped polySi films. Measurements of the catastrophic breakdown strength of metal-oxide-semiconductor (MOS) capacitors indicate that the quality of gate electrodes fabricated using μc-Si is improved relative to that of MOS capacitors fabricated using polySi gate electrodes.

A study of self-aligned formation of C54 Ti(Si 1−y Ge y ) 2 to p + and n + Si 0.7 Ge 0.3 alloys using rapid ther mal annealing

In this paper, solid state reactions of titanium with boron and phosphorus doped Si0.7Ge0.3 alloys have been investigated for application in a self-aligned germanosilicide process. Wet chemical etching of the germanosilicide with respect to unreacted Ti in a solution of 1:1:5 NH4OH:H2O2:H2O has been investigated. Characterization was performed using four-point probe sheet resistance measurements, x-ray diffraction, cross-sectional transmission electron microscopy, Nomarski optical imaging, and scanning electron microscopy. The C54 Ti(Si1−yGey)2 phase was observed to form for reactions on both boron and phosphorus doped Si0.7Ge0.3 alloys. Grain structures of the C54 phases were found to be similar to grain structures of intrinsic alloy reactions with lateral grain dimensions on the order of 0.3 Μm. Resistivities of 22 ΜΩ-cm have been determined for the boron and phosphorus reactions. Although the germanosilicide phases were observed to etch slowly in 1:1:5 NH4OH:H2O2:H2O, which is conventionally used in the self-aligned titanium silicide process, the much higher etch rate of titanium nitride compounds and unreacted Ti provided for a self-aligned germanosilicide process. A first anneal in a nitrogen ambient was found to be necessary to eliminate lateral silicidation over surrounding oxide during self-aligned germanosilicide formation.

Characterization of Oxygen-Doped and Non-Oxygen-Doped Polysilicon Films Prepared by Rapid Thermal Chemical Vapor Deposition

PolySi films deposited with and without oxygen doping using rapid thermal chemical vapor deposition (RTCVD) have been investigated. Experimental results show that RTCVD systems can be used to provide high deposition rates ( 900-1000 A/min at 700 °C) for both oxygen-doped and non-oxygen-doped polySi films. The surface roughness of the RTCVD polySi film is about half that of conventional LPCVD polySi films. The surface roughness and grain size of the RTCVD polySi film can be further reduced using oxygen doping. The catastrophic breakdown strength for capacitors using oxygen-doped polySi electrodes are improved compared with the breakdown strength for capacitors using non-oxygen-doped polySi electrodes. Electrical resistivities of B, P and As doped samples of polySi films with oxygen doping are found to be larger than those of polySi films without oxygen doping. Resistivities of silicides formed on the oxygen-doped polySi samples are approximately the same for those of silicides formed on non-oxygen-doped polySi samples.

Fabrication of Ultra-Shallow P+-N and N+-P Junctions by Diffusion From Selectively Deposited, Ion-Implanted and In-Situ Doped Si0.7Ge0.3

Selectively deposited Si 0.7 Ge 0.3 has been investigated as a potential diffusion source for fabricating ultra-shallow junctions in Si. Rapid thermal chemical vapor deposition (RTCVD) was used to selectively deposit Si 0.7 Ge 0.3 on Si using SiH 2 C1 2 , GeH 4 , and H 2 . Both ionimplanted and in-situ doped Si 0.7 Ge 0.3 were considered as a diffusion source for fabricating ultra-shallow junctions. In-situ doping was achieved with B 2 H 6 and PH 3 for p-type and n-type doping, respectively. Boron and phosphorus diffusion in ion-implanted Si 0.7 Ge 0.3 was investigated and modeled using SSUPREM4. Diffusion from implanted and in-situ doped Si 0.7 Ge 0.3 in Si was also studied and modeled. Boron diffusivities in Si 0.7 Ge 0.3 were found to be approximately 10 times greater than in Si, while phosphorus diffusivities were over 100 times greater in Si 0.7 Ge 0.3 . The faster dopant diffusivities in Si 0.7 Ge 0.3 allow high surface concentration, abrupt diffusion profiles to be formed in Si. Gated, p-n junction diodes with junction depths as shallow as 140A were fabricated and tested to study the quality of the diffusions from Si 0.7 Ge 0.3 .