Frederick L. Vook

DIRECT EVIDENCE OF DIVACANCY FORMATION IN SILICON BY ION IMPLANTATION

The production of divacancies in Si by 400‐keV oxygen ion implantation (ΦI = 1.75 × 1014 cm−2, two sides) was detected by the characteristic divacancy optical absorption band at 1.8 μ. This band has been previously correlated with the presence of divacancies in electron‐ and neutron‐irradiated silicon. Ion‐produced divacancy annealing near 200°C was observed to correlate with neutron‐produced divacancy annealing. Detailed comparisons of the annealing of electron‐, neutron‐, and ion‐produced divacancies suggest that the ion‐produced divacancies anneal primarily in regions with sink concentrations ≥ 1019 cm−3.

Ionization, thermal, and flux dependences of implantation disorder in silicon

Abstract Proton channeling effect measurements were used to study the implantation lattice disorder in silicon as a function of ion flux (dose-rate), fluence, implant temperature, ion mass, and the presence of ionizing radiation. For both O+ and Sb+ implantation at 87°K the lattice disorder production is the same for equal total energy into atomic processes/cm3 at a fixed rate of energy into atomic processes/cm3-sec. The disorder production for both light (O+)and heavy (Sb+) ions exhibits a flux dependence at low temperatures and at room temperature. At low temperatures an increase in disorder is observed for increasing flux at constant fluences; however, for low fluence Sb implantation at 300°K, lower disorder is observed with increasing flux. The lattice disorder increases for all ions with decreasing implant temperature from 300°K down to temperatures as low as 38°K, but the variation with temperature is greater for lighter ions. The stimulation of lattice disorder annealing (typically ≍ 10 per cent) b...

Infrared studies of the crystallinity of ion-implanted Si

Abstract The crystallinity of ion-implanted silicon has been investigated using ion mass and ion fluence dependences of divacancy formation as measured by the characteristic 1.8 μ absorption band. Room temperature, nonchanneled implants of 400-keV B11, Zn64, and Sb121 ions were performed to maximum fluences of 1014 ions/crn2 for Sb and Zn and to 2 × 1015 ions/cm2 for B. The results are interpreted on the basis of ion energy spent in atomic processes per unit volume, e, within the implanted layer. For e ≤ 1019 keV/cm3 the energy to form a divacancy (1.5 ± 0.5 keV) is nearly ion independent. Maxima appear in the divacancy densities at ∼1013 Sb ions/cm2 and ∼2 × 1013 Zn ions/cm2 where e ≤ 1020 keV/cm3. The divacancy density for B implantation did not exhibit a distinct maximum at E = 1020 keV/cm3, but continued to increase with fluence. The B results are attributed to defect motion because divacancies are observed beyond the calculated depth for energy deposition after a high fluence B implant. In addition t...

Low temperature channeling measurements of ion implantation lattice disorder in GaAs

Abstract Lattice disorder resulting from 140 keV Zn and 151 keV Xe implantations below 100 °K was studied by channeling effect analysis using 400 keV protons. Implantations and analyses were performed in the same system without warmup. Isochronal anneal curves show significant annealing of disorder below room temperature for low temperature, low fluence implants. The annealing is similar for both Zn and Xe implants and also is similar to previous measurements of the annealing of thermal conductivity following low temperature electron irradiation. For 298 °K implants, the disorder production is strongly dose rate dependent and increases significantly with increasing dose rate. For dose rates used in these measurements, the disorder production at 298 °K was greatly reduced from that for the low temperature implantations.

ELECTRON PARAMAGNETIC RESONANCE OF DEFECTS IN ION‐IMPLANTED SILICON

The first EPR measurements of the identity of defects in an ion‐implanted layer (< 15 000 A) are reported. The Si–P3 center is the dominant paramagnetic defect produced at room temperature by 400‐keV O+ implantation in Al‐ and B‐doped Lopex Si, and it anneals below 200°C. The Si–P1 center is the dominant defect remaining above 200°C, and it anneals near 350°C. Interstitial Al++ (Si–G18) are observed in the Al‐doped sample; their number indicate that Si interstitials do not migrate over large distances into the unirradiated Si. Comparison of EPR and infrared data indicates that the Si divacancy is produced in the diamagnetic neutral charge state.

Evidence for vacancy motion in low temperature ion-planted Si

Abstract Recent results have reported a strong implantation-temperature dependence between 125°K and room temperature for lattice disorder produced by 200-keV B implantation into Si. Using our previous annealing model incorporating implant temperature and dose rate, we have calculated a characteristic defect annealing time at the threshold of the crystalline to amorphous transition at 173°K for 1 μA/cm2 and find that it agrees very closely with that for neutral vacancy annealing. In addition, we have made measurements of the 1.8μ infrared absorption band, characteristic of the Si divacancy, following room temperature and 85°K implants of 400-keV B11 or Sb121 ions. Very few divacancies are observed immediately after 85°K implants, but annealing growth of divacancies occurs between 150 and 300°K yielding a density almost equal to that for the same ion Ruence at 300°K. These results strongly suggest that below 300°K neutral vacancy motion and trapping control both the implantation-temperature dependence of l...

DEPTH DISTRIBUTION OF DIVACANCIES IN 400‐keV O+ ION‐IMPLANTED SILICON

The integral depth distribution for divacancies produced in silicon at room temperature by 400‐keV O+ion implantation has been measured. The divacancy distribution was determined from repeated measurements of the characteristic 1. 8μ absorption band following successive anodizations and strippings of the implanted layer. Most of the divacancies are located between 4500 and 12 000 A with a half‐value at ∼ 7500 A and a concentration of ∼ 4 × 1019 cm−3 near the center of the distribution. The measured integral depth distribution for the ion‐produced divacancies is proportional within experimental error to theoretical calculations by Brice for the integral depth distribution of ion energy spent in atomic processes.

DEPTH DISTRIBUTION OF EPR CENTERS IN 400‐keV O+ ION‐IMPLANTED SILICON

The depth distribution of Si‐P3 centers in 400‐keV O+ ion‐implanted silicon was determined using EPR measurements in conjunction with anodization and stripping of the implanted layer. The depth distribution of the EPR centers compares favorably to theoretical calculations by Brice for the depth distribution of the energy deposited into atomic processes and with infrared absorption measurements of the depth distribution of divacancies by Stein, Vook, and Borders. The combined EPR and infrared measurements indicate that the Fermi level in the damaged layer lies between Ec − 0.21 eV and Ev + 0.25 eV.

MULTILAYER THIN‐FILM ANALYSIS BY ION BACKSCATTERING

Multilayer polycrystalline Er, Sc, or V layers, 500–20 000 A thick, on Kovar or sapphire substrates were studied using 2‐MeV He+ ion backscattering. Underlying, as well as surface layer, average thicknesses were measured with a sensitivity of 200 A. In addition, results were obtained on interfacial diffusion, film thickness variations, and the depth distribution of heavy impurities.

INFRARED ABSORPTION BANDS IN CARBON‐ AND OXYGEN‐DOPED SILICON

Infrared absorption measurements were made before and after low‐temperature electron irradiations of silicon samples which contained either dispersed oxygen, carbon, or carbon plus oxygen. Two distinctly different centers are formed upon low‐temperature irradiation depending upon the carbon and oxygen content. One center is the well‐known vacancy‐oxygen A‐center defect (836 cm−1) and is formed in oxygen‐containing silicon with a magnitude which is independent of the carbon content. The other center (922 and 932 cm−1) is formed only in silicon crystals which contain both oxygen and carbon. The results indicate that this center is formed by the trapping of a silicon interstitial at a carbon‐oxygen complex.