J. A. Borders

FORMATION OF SiC IN SILICON BY ION IMPLANTATION

The production of SiC in single‐crystal silicon by C12+ implantation to fluences of 1017/cm2‐side followed by annealing has been detected by the characteristic infrared absorption of the TO phonon of SiC. Immediately following room‐temperature implantation and after 20‐min isochronal anneals up to temperatures ≤ 825°C, a previously unreported broad absorption band centered at 700–725 cm−1 is observed. SiC is observed to form at temperatures ≈ 850°C. For anneals ≥ 850°C, most of the broad absorption band shifts into the SiC‐TO phonon absorption band. From the infrared absorption measurements together with the results of He+ backscattering, we conclude that about half of the implanted atoms are incorporated into microregions of SiC which are surrounded by bulk silicon.

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.

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...

Ion implantation as an ultrafast quenching technique for metastable alloy production: The Ag‐Cu system

Substitutional solid solutions of Ag in Cu have been formed by ion implanting Ag at concentrations up to 16 at.%. The physical states of the implanted alloys were deduced by ion channeling and transmission electron microscopy and their stability was examined by annealing to 400 °C. The implantation results are compared with those obtained previously by conventional rapid quenching techniques.

The physical state of implanted tungsten in copper

The physical state of W implanted in Cu has been studied by 4He+ ion channeling and transmission electron microscopy. At implant concentrations ≲1 at.%, W is in solid solution but may form elemental bcc precipitates on annealing to ≳450 °C. For implant concentrations of ∼10 at.%, a disordered layer of Cu and W is formed with the W occupying no regular lattice sites; on annealing W precipitates are formed with dimensions of a few hundred angstroms.

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.

Metastable alloy layers produced by implantation of Ag and Ta + ions into Cu crystals

Abstract Transmission electron microscopy and MeV 4He+ ion channelling have been used to study alloy layers formed by Ag+ and Ta+ ion implantation into Cu. The Ag-Cu layers, for concentrations up to 17 at.%, are metastable solid solutions similar to those produced by conventional rapid quenching techniques. However, the Ta-Cu layers undergo a transition from metastable solid solutions to essentially non-crystalline alloys for increasing Ta concentration, this occurring at about 10 at. % Ta. The formation of such metastable layers is attributed to rapid quenching during thermal spike decay. The structure difference between the high concentration Ta-Cu and Ag-Cu alloys is correlated with concepts of equilibrium solubility and impurity interactions. Thermal annealing of the Ag-Cu alloys gives rise to aligned Ag precipitates for temperatures below 400°C, whereas the Ta-Cu non-crystalline layers are relatively stable at temperatures up to ∼ 600°C.

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.

Helium ion stopping cross sections in gold

Abstract The stopping cross section of He ions in gold has been measured at incident energies from 0.4 MeV–1.9 MeV. A backscattering technique was used to measure the energy loss in gold films which had been vacuum evaporated on sapphire substrates. The stopping cross section results are compared with the previous data of Wilcox, Gobeli and Nakata. Brices semi-empirical formula has been fit to the data with a resultant root-mean-square percentage deviation of 0.6 per cent.