Gari Harris

Phase transitions during solid‐state formation of cobalt germanide by rapid thermal annealing

Phase transitions that involve solid‐state reactions between cobalt and thin films of germanium have been investigated. Germanides are formed by reacting Co (300 A thick) with thin layers of Ge (∼2000 A thick) deposited on silicon substrates. Germanium was deposited on Si by rapid thermal chemical‐vapor deposition and cobalt was deposited onto Ge by evaporation. The Co/Ge/Si stacked structure samples were then rapid thermally annealed at atmospheric pressure in an inert ambient consisting of Ar. Using x‐ray‐diffraction spectroscopy, Co5Ge7 and CoGe2 are identified as the phases which form at 300 and 425 °C respectively. The sheet resistance was found to be a strong function of the annealing temperature and a minimum resistivity of approximately 35 μΩ cm is obtained after annealing at 425 °C. The minimum resistivity material corresponds to the CoGe2 phase with an orthorhombic crystal structure. Above 600 °C, the resistivity increases due to an instability of the solid‐phase reaction between Co and thin Ge ...

Growth Kinetics, Silicon Nucleation on Silicon Dioxide, and Selective Epitaxy Using Disilane and Hydrogen in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

Silicon nucleation on silicon dioxide and selective silicon epitaxial growth (SEG) were studied in an ultrahigh vaccuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor using 10% Si 2 H 6 diluted in H 2 . Silicon was deposited on SiO 2 patterned Si(100) substrates over a pressure range of 10-100 mTorr and a temperature range of 650 and 850 o C. Under these conditions, the growth rate ranged from 50 to 330 nm/minute, demonstrating compatibility with single wafer manufacturing throughput requirement. A pressure dependence in the activation energy in the surface reaction limited regime was observed and attributed to a variation in the steady-state hydrogen coverage on the growing surface

Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon onto (100) Silicon I . The Influence of Prebake on (Epitaxy/Substrate) Interfacial Oxygen and Carbon Levels

This investigation is concerned with the influence of a vacuum prebake on oxygen and carbon levels at epitaxial silicon/silicon (100) interfaces. The epitaxial layers are deposited in an ultrahigh vacuum, rapid thermal reactor using chemical vapor deposition techniques. Secondary ion mass spectroscopy (SIMS) is used to evaluate carbon and oxygen levels at the epitaxy/substrate interface. We show that a vacuum prebake can be effectively used following a standard ex situ clean that consists of an RCA clean, a dilute (5%) HF dip, and a rinse in deionized water. The results show that if epitaxial deposition is initiated by introducing the reactive gases into the chamber at the prebake temperature, oxygen and carbon levels below the sensitivity limits of secondary ion mass spectroscopy are obtained at the epitaxy/substrate interface. This result can be reproducibly achieved with a low thermal budget prebake of 750°C/15 s even after a relatively long rinse (∼300 s) in deionized water. We propose that the mechanism responsible for cleaning is thermal desorption of oxygen and hydrocarbons from the (100) surface of silicon. We show that the surface obtained with this ex situ clean is very stable and, hence, the wafer can be left in a clean ultrahigh vacuum environment for many hours without detectable changes in the oxygen and carbon levels. On the other hand, results indicate that when the prebake is terminated by cooling the wafer to the ambient temperature of the reactor, carbon is readsorbed on the silicon surface at a peak concentration of 3 to 6 x 10 18 cm -3 . We also show that when a small amount of hydrogen is introduced into the reactor during the prebake, a higher thermal budget is required to remove oxygen from the surface. This observation is attributed to a higher H 2 O background associated with the presence of hydrogen. It is concluded that vacuum prebake is an attractive surface preparation technique which effectively reduces oxygen and carbon levels on a silicon (100) surface below the SIMS sensitivity limits.

Low thermal budget in situ removal of oxygen and carbon on silicon for silicon epitaxy in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor

In this letter, we present experimental evidence on desorption of O and C from a Si surface resulting in impurity levels below the detection levels of secondary ion mass spectroscopy. We then propose a surface preperation method for silicon epitaxy that consists of an ex situ clean and an in situ low thermal budget prebake in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV‐RTCVD) reactor. The ex situ clean consists of a standard RCA clean followed by a dilute HF dip and rinse in de‐ionized water. The in situ clean is either carried out in vacuum or in a low partial pressure of 10% Si2H6 in H2. The experiments were conducted in an UHV‐RTCVD reactor equipped with oil‐free vacuum pumps. We propose that the responsible mechanism is desorption of oxygen and hydrocarbons from the Si surface due to the low partial pressures of these contaminants in the growth chamber. If Si2H6 is used during the prebake, a sufficiently low growth rate is required in order to provide sufficient time for desorptio...

Ultra-shallow raised p + -n junctions formed by diffusion from selectively deposited in-situ doped Si 0.7 Ge 0.3

In this paper, a novel raised p+−n junction formation technique is presented. The technique makes use ofin- situ doped, selectively deposited Si0.7Ge0.3 as a solid diffusion source. In this study, the films were deposited in a tungsten halogen lamp heated cold-walled rapid thermal processor using SiCl2H2, GeH4, and B2H6. The microstructure of the Si0.7Ge0.3 layer resembles that of a heavily defected epitaxial layer with a high density of misfit dislocations, micro-twins, and stacking faults. Conventional furnace annealing or rapid thermal annealing were used to drive the boron from thein- situ doped Si0.7Ge0.3 source into silicon to form ultra-shallow p+−n junctions. Segregation at the Si0.7Ge0.3/Si interface was observed resulting in an approximately 3:1 boron concentration discontinuity at the interface. Junction profiles as shallow as a few hundred angstroms were formed at a background concentration of 1017 cm−3.

Low thermal budget in situ cleaning and passivation for silicon epitaxy in a multichamber rapid thermal processing cluster tool

Abstract In this Letter, we report our results on surface preparation, involving in situ cleaning and passivation for low-temperature Si epitaxy in a multichamber cluster tool. The experiments were carried out in a three-chamber reactor which mimics a cluster tool. The results indicate that residual O on the dilute HF-treated Si surface (ex situ cleaned) can be reduced below the detection limit of secondary ion mass spectroscopy (SIMS) by in situ baking at 750°C for 15 s in an ultra-high vacuum environment or in H2 (pressure = 240 mTorr). We show that the extremely reactive Si surface can be passivated against recontamination by exposing it to a low-pressure Si2H6 environment at the ambient temperature immediately following the in situ clean. When the unpassivated samples are exposed to an air pressure of 10−6 Torr in the load-lock, O adsorbs on the surface up to 50% of a monolayer within 10 min. Under the same conditions, with passivation, the oxygen levels remain below the detection level of SIMS. Surface passivation will be extremely useful in applications that require wafer transfer between chambers such as in multichamber cluster tools.

Selective Removal of Silicon-Germanium: Chemical and Reactive Ion Etching

The use of both chemical and reactive ion etching for the selective removal of Si x Ge 1-x alloys with respect to both silicon and silicon dioxide has been investigated. We have found that a solution of NH4OH:H 2 O 2 :H 2 O is effective in selectively etching the Si x Ge 1-x films with respect to both of these materials. The chemical composition of the substrate surface after removal of insitu doped Si x Ge 1-x films was evaluated using EDS and SIMS. Diffusion from insitu doped Si 0.7 Ge 0.3 , followed by selective removal, was used to demonstrate self-aligned npn dopant profiles with narrow base widths. Reactive ion etching of Si x Ge 1-x alloys was investigated using SF 6 , CF 4 , and Cl 2 based chemistries. Pressure, power, and gas flow ratios were optimized to provide the least isotropic etch possible for Si x Ge 1-x films containing approximately 40% Ge. Selectivity and degree of anisotropic etching were determined as a function of Ge content for samples with 0% to 100% Ge. Samples were analyzed using SEM and ellipsometry. Highest selectivities were achieved using SF 6 and O 2 .

Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon on (100) Silicon II . Carbon Incorporation info Layers and at Interfaces of Multilayer Structures

In this study, we have investigated carbon incorporation in epitaxial Si layers and at interfaces of multilayer epitaxial structures due to desorption of hydrocarbons from chamber walls at elevated temperatures. The experiments were conducted in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor. We have investigated carbon contamination as a function of deposition temperature, film growth rate, and partial pressure of hydrocarbons. The results show that at higher deposition temperatures (750 and 800°C) carbon levels in epitaxial layers are lower compared to levels in layers grown at lower temperatures (650 and 700°C). It is proposed that at higher temperatures, the carbon concentration in Si is determined by the adsorption-desorption equilibrium and this results in a growth rate independent incorporation process. At lower temperatures, carbon incorporation is limited by the availability of sites for chemisorption. Site availability is determined by hydrogen coverage on Si during growth, and this produces a growth rate dependent incorporation process. Hydrocarbon desorption from the chamber walls increases with increasing hold time at elevated temperatures, resulting in a time dependent increase in the carbon level within epitaxial layers. Carbon contamination at interfaces of multilayer structures was found to depend strongly on the growth temperature. Higher interfacial carbon levels were obtained following growth at higher temperatures when temperature cycling was used to start and stop the growth processes. When gas switching was used for this purpose, interfacial carbon contamination was observed at lower temperatures (650 and 700°C). This is tentatively attributed to loss of hydrogen coverage when Si 2 H 6 is evacuated from the chamber for gas switching and inefficient desorption of physisorbed species from the surface at lower temperatures.

Cleaning during Initial Stages of Epitaxial Growth in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

In this paper, we report our results on surface preparation for the growth of epitaxial Si films. Hydrogen passivated surfaces are currently being investigated for application in Si epitaxy to eliminate the high temperature in-situ bake necessary to remove the native oxide. Hydrogen passivation is obtained by a dilute HF dip before the substrate is loaded in the process chamber. However the passivation is partially lost when the HF dip is followed by a water rinse which results in oxygen absorption on the substrate. It was found that the peak oxygen concentration at the epitaxy substrate interface increase by an order of magnitude due to a five minute water rinse. We report here that oxygen and carbon at the epitaxy substrate interface can be desorbed during initial stage of epitaxial growth by reducing epitaxial growth rate. In this work, epitaxial Si films were deposited over a wide range of growth rates obtained by varying Si 2 H 6 flow rates. The peak oxygen concentration decreases by an order of magnitude by changing the growth rate from 3000 to 700A/kminute for a deposition temperature of 800°C. We believe that at higher growth rates Si overgrows on absorbed oxygen maintaining epitaxial alignment reflected in the good electrical quality of the epitaxial films. However, at low growth rates oxygen has sufficient time to desorb before overgrowth can take place, improving the epitaxy substrate interface quality.