S. R. Wilson

Dielectric functions of bulk 4H and 6H SiC and spectroscopic ellipsometry studies of thin SiC films on Si

Spectroscopic rotating-analyzer ellipsometry employing a compensator and optical transmission were used to measure the dielectric functions of bulk 4H and 6H SiC from 0.72 to 6.6 eV for light propagating nearly parallel to the hexagonal axis. The measurements below the band gap show the presence of a thin surface layer, which was modeled as SiO2. The data are similar to results for cubic (3C) and 6H SiC from the literature, but differences are notable, particularly above 4 eV. At 5.56 eV, we observe a critical point in 4H SiC, which is assigned to direct interband transitions along the U=M−L axis in the hexagonal Brillouin zone after comparison with band structure calculations. No evidence for direct transitions below 6.5 eV was found in 6H SiC. We apply our results to the analysis of a 4H SiC film on insulator (SiCOI) produced by high-dose hydrogen implantation and direct wafer bonding on Si. For comparison, we also studied a 1 μm thick epitaxial layer of 3C SiC on Si, where the interference oscillations...

Rapid isothermal annealing of As-, P-, and B-implanted silicon

Single‐crystal silicon wafers have been implanted with As, P, and B to doses of 1×1013–1×1016/cm2 and given a transient anneal using a Varian IA‐200 Rapid Isothermal Annealer. The system uses infrared radiation to heat the wafers to temperatures in excess of 1000 °C for times on the order of 10 sec. Sheet resistance and Hall measurements have been used to determine the effect of the anneal on the electrical properties of the wafers. Rutherford backscattering and secondary ion mass spectroscopy have been used to measure lattice damage and dopant profiles before and after annealing. As and P are lost during the anneal unless the wafer is capped. Complete activation can be achieved with very little dopant diffusion. Residual damage is minimal in (100) oriented wafers that had been implanted with As. However, for (111) wafers damage is less in (111) wafers implanted to doses ≥5.0×1015/cm2, than in (111) wafers implanted to doses ≤5.0×1015/cm2. The diffusion of As during this transient anneal has been modeled ...

Si implantation in GaAs

High‐resolution Rutherford backscattering, transmission electron microscopy, and proton‐induced x‐ray emission with channeling have been used to investigate the damage and lattice site location of Si‐implanted GaAs. Semi‐insulating Cr‐doped GaAs(100) crystals were implanted at room temperature with Si+ ions of single (120 keV) and multiple energies (50–400 keV). The total dose of implanted ions varies from 3×1015 cm−2 to 5×1015 cm−2. The residual damage and the lattice location of the implant are determined after 15 min annealing of the samples at 850 °C and 950 °C. It is shown that about 60%–70% of the Si atoms occupy substitutional lattice sites. The amount of precipitation has been evaluated and found to be very low (≤2%). For the dose of 5×1015 cm−2, microtwins lying on the (111) planes are found to be present after annealing at 850 °C in addition to the usual dislocation loops. However, after annealing at 950 °C, the primary residual damage consists of dislocation loops in addition to some small prec...

Damage annealing behavior of Se implanted GaAs

Abstract High resolution Rutherford backscattering-channeling (RBS-C) and transmission electron microscopy (TEM) have been used to investigate the annealing behavior of Se implanted Cr-doped GaAs layers. Two distinct annealing stages were observed; one at 250°C which is associated with amorphous zone annihilation and/or onset of solid phase epitaxial growth and the other at about 400–500°C, depending on the dose, that can be related to the dissociation of microtwins. Above 500°C, the residual defects are primarily dislocation loops and precipitates. The calculated number of atoms associated with the precipitates has been found to correspond closely to the number of implanted atoms, implying 100% precipitation for the cases studied in this work. This could explain the poor or nonexistent electrical activation of Se after low temperature annealing (600°C), even though good regrowth of the amorphous layer has taken place. Experiments with high purity GaAs produced the same result, as far as the observed residual damage was concerned, thus eliminating speculation about the involvement of Cr in the nucleation of microtwins. Transmission electron microscopy investigations of the amorphous-crystalline interface in the as-implanted samples failed to reveal any extended defects. In the present paper, we discuss various mechanisms that could be responsible for the formation of twins in low temperature annealed GaAs.

Characterization of buried SiO2 layers formed by ion implantation of oxygen

Oxygen has been ion implanted (200 keV) into silicon at doses ranging from 2E17/cm2 to 2E18/cm2. The peak oxygen concentration occurs at a depth of 0.5 μm. These doses produce peak oxygen concentrations which are below and above the concentrations necessary to form stoichiometric SiO2. If the oxygen concentration exceeds stoichiometry, a buried SiO2 layer is formed with a thin superficial silicon layer on the surface. This superficial silicon layer has been used as a seed for growing single crystal silicon epi. The resulting Silicon on Insulator (SOI) structure has been characterized by Rutherford backscattering, cross-sectional TEM, AES, optical microscopy, spreading resistance probe, Hall effect and infrared transmission measurements. The effects of dose, substrate temperature during the implant, and subsequent anneal conditions have been examined.

Rapid isothermal anneal of 75As implanted silicon

Silicon wafers implanted with 75As have been annealed with a Varian IA‐200 isothermal annealer. The anneal occurs in vacuum using radiation from a resistively heated sheet of graphite. The anneal quality depends on the graphite heater temperature and exposure time. If the anneal time is too short implantation damage remains and if the time is too long measurable losses of As occur causing the sheet resistance to increase. The loss of As can be prevented by depositing 0.05 μm of SiO2 on the wafer before annealing.

Grain growth during transient annealing of As‐implanted polycrystalline silicon films

Polycrystalline silicon films deposited on oxidized wafer surfaces were implanted with As and annealed on a Varian IA‐200 rapid thermal annealer. The effects of annealing conditions on resultant grain size of original as‐deposited columnar grains are presented with a modified model for interfacially driven grain growth. During an initial temperature rise to 910 °C the original grain size (39 nm) and dopant profile are not significantly altered. At 1145 °C the grains have grown to 90 nm and the As is uniformly distributed throughout the film. Additional annealing to 1300 °C in 20 s causes grains to grow to 260 nm. Further grain growth is retarded due to the 300‐nm film thickness. During annealing of unencapsulated films a substantial loss of As results in a lower rate of grain growth. When grain size increases, Hall mobility increases and resistivity decreases.

Deep-level transient spectroscopy study on double implanted n+–p and p+–n 4H-SiC diodes

Planar n+–p and p+–n junction diodes, fabricated in 4H-SiC epitaxial layers using a double-implantation technology (a deep-range acceptor followed by a shallow-range donor implantation and vice versa), are characterized using capacitance deep-level transient spectroscopy (DLTS) to detect deep levels, which may influence device electrical performance. Either Al or B was used as the acceptor, while N or P was used as the donor, with all implants performed at 700 °C and annealed at 1600–1650 °C with an AlN protection cap. Different traps were observed for the various dopants, which are believed to be related to different impurity-defect complexes. A trap at ∼EV+0.51 eV was observed in nitrogen-implanted samples, while an acceptor trap at ∼EV+0.28 eV and a donor trap at ∼EC−0.42 eV were observed in Al-implanted samples. A prominent boron-related D-center trap at ∼EV+0.63 eV is seen in the DLTS spectra of B-implanted diodes. In diodes with implanted phosphorus, three traps at ∼EV+0.6 eV, EV+0.7 eV, and EV+0.92...

Effects of irradiation temperature and dose on exfoliation of H+-implanted silicon carbide

H+ implantation of SiC is the basis for a thin-film transfer process, which when combined with oxidation and hydrophilic wafer bonding, can be exploited to produce silicon carbide-on-insulator material useful as a wide-band-gap semiconductor. This thin-film transfer process has been successfully applied to Si to produce a commercial silicon-on-insulator material. The efficacy of hydrogen to produce thin-film separation was studied by investigation of H+-induced exfoliation in implanted SiC. Results showed that the onset and degree of exfoliation of SiC depends initially upon the concentration of implanted H+. However, the dose dependence of exfoliation exhibits a rather marked retrograde behavior. The degree of exfoliation eventually starts to decrease with increasing ion dose until exfoliation is completely suppressed. This behavior is attributed to a competition between the positive effects of hydrogen on exfoliation and the negative effects of ion-induced damage. Experiments were done to isolate the ef...

Fast diffusion of As in polycrystalline silicon during rapid thermal annealing

The diffusion of As in polycrystalline silicon films subjected to rapid thermal annealing has been studied using sheet resistance and Rutherford backscattering. The polycrystalline Si films were deposited on oxidized silicon wafers, implanted with As, and annealed with a Varian IA‐200 isothermal annealer. Infrared radiation from a resistively heated sheet of graphite heats the wafer, in a vacuum, to temperatures >1000 °C for times on the order of a few seconds. The rate of diffusion and rate of loss of As from the polycrystalline Si is much faster than the diffusion rate and loss rate in single crystal Si annealed with identical conditions. Diffusion prior to grain growth agrees with previously reported results for As in polycrystalline Si. However, grain growth appears to enhance As diffusion.