L.C. McIntyre

Cross sections for 170° backscattering of 4He from oxygen, aluminum and argon for 4He energies between 1.8 and 5.0 MeV

Abstract Cross sections for 170° backscattering of 4He ions incident on oxygen, aluminum and argon target atoms at energies in the range 1.8 to 5.0 MeV have been measured using 4He beams from a 6 MV Van de Graaff. The targets were thin (850, 1950 A) films of Ar-sputtered Al2O3 (on C substrates) which incorporated up to 6% Ar. Cross sections at a particular energy were determined by comparing the measured apparent thicknesses (in atoms/cm2) of O, Al and Ar in the film at the particular energy with those measured for 4He energy near 2 MeV (where the cross sections were assumed to be Rutherford). The cross sections were measured at maxium intervals of 50 keV, with uncertainties of ± 4%. The cross section for HeAr is nearly Rutherford over the entire range, that for HeAl shows small deviations from Rutherford above 4.2 MeV, while that for HeO is strongly non-Rutherford above 2.4 MeV. Results are presented in graphical and tabular form.

Non-Rutherford 4He cross sections for ion beam analysis

Abstract Increasing use of 4 He analysis beams with energies between 2 and 10 MeV for depth profiling and backscattering analysis of thin films and near-surface materials requires accurate measured values of non-Rutherford cross sections for scattering of 4 He by the lighter elements. Cross sections for scattering of 4 He through large angles deviate from Rutherford at 4 He laboratory energy ∼ 2.2 MeV for target nuclei 12 C and 16 O; deviations for target atomic numbers Z = 20 and 40 occur at 4 He energies of about 5 and 10 MeV, respectively. We review the experimental cross section data currently available for large angle scattering of 4 He from the light elements (4 ≤ Z ≤ 20) for incident 4 He laboratory energies 1.5–10 MeV. For each target element, we indicate energy regions with smooth cross section variation suitable for use for simple backscattering analysis as well as strong narrow resonances that may be used for depth profiling light elements in heavy-element matrices.

Determination of nitrogen using the 14N(α, p)17O nuclear reaction

Abstract A technique for quantifying nitrogen in thin films using the 14N(α, p)17O reaction is reported. An incident alpha particle beam with energy near 3.9 MeV is used and emitted protons are detected at a lab angle of 135°. A 15 μm Kapton foil is placed over the detector to stop elastically scattered alpha particles. A thin film containing a known areal density of nitrogen is used for calibration. We present relative yield data on protons from the 14N(α, p0)17)O reaction at 135° lab angle from 3.4 MeV to 4.0 MeV as well as an example of the application of this technique in determining nitrogen content in thin films. Possible interfering reactions, particularly 28Si(α, p)31, are also discussed.

MeV ion beam analysis of high-Tc superconducting films

Areal densities [at./cm2], average stoichiometric ratios, impurity concentrations and elemental depth profiles for high-Ec thin films may be determined by high-energy backscattering using 3–5 MeV 4He analysis beams. Accuracies of about ± 3% and ± 1% are obtained for areal densities and average stoichiometric ratios, respectively. We present results of the analysis for several YBaCuO films in the thickness range 2500–9000 A. We indicate the advantages of using the 3–5 MeV 4He analysis beams rather than the usual 1–2 MeV 4He beams used for Rutherford backscattering spectrometry.

Amorphization implants and low temperature rapid thermal processing to form low sheet resistance, shallow junction, boron implanted layers

The effects on Si wafers of (1) Ge or Si amorphization implants, (2) B or BF2 dopant implants at low energies (15 keV through 16 nm of screen oxide) and (3) rapid thermal processing (RTP) at 800–1050° have been systematically studied. Sheet resistance (Rs), spreading resistance probe (SRP), Rutherford backscattering (RBS) and ultrahigh vacuum secondary ion mass spectrometry (SIMS) have been used to study the resulting electrical and materials properties of these wafers. Values for Rs versus junction depth are below any results reported in the literature. The Rs maps show lower Rs and better uniformity in the wafers that were amorphized with Ge or Si and received a B rather than a BF2 implant. The effects of channeling, molecular breakup of BF2, B solid solubility, and annealer uniformity are discussed.

Cross sections for 170.5° backscattering of 4He by the isotopes of boron for 4He energies between 1.0 and 3.3 MeV

Elastic scattering cross sections for 4He on both isotopes of boron have been measured at a laboratory angle of 170.5° in the energy range 1–3.3 MeV to an accuracy of about 7%. Self-supporting targets of natural boron (18μgcm2) and 99% enriched 10B (6μgcm2) were used. The scattering was observed to be Rutherford between 1 and 1.3 MeV for both isotopes. Previously unreported elastic scattering anomalies were observed in 10B near 1.5 and 1.65 MeV and in 11B near 1.5 and 2.05 MeV. Results above 2.1 MeV are compared to previous measurements; discrepancies of up to 50% are noted. The major features in the cross sections above 2.1 MeV are broad resonances near 2.4 MeV in 10B and near 2.6 MeV in 11B. The cross section is found to be smooth and approximately Rutherford for 11B in the energy range 2.2 to 2.5 MeV.

Backscattering spectrometry with 4He, 14C, 14N, 40Ar and 84Kr analysis beams with energies 1.5–5.0 MeV

Abstract The resolution of a silicon surface-barrier detector (Ortec BA-14-25-100) has been measured for analysis beams of 4He, 12C, 14N, 40Ar and 84Kr (in the 1.5–5.0 MeV energy range) backscattered from a thin ( ∼ 30 A ) Ta film. These measured values of the detector resolution were used in the calculation of mass resolution vs target mass curves for analysis beam energies 2, 5 and 10 MeV. Tabulated values of energy loss for the analysis ions in the target material were used with the measured values of detector resolution to calculate depth resolution vs beam energy curves for target materials Ta, Ni and Nb. The results are generally disappointing; there appears to be no major advantage to be gained by use of these heavier-than-4He analysis beams in this energy region.

Quantification of beryllium in thin films using proton backscattering

Abstract The strong resonance in the 1H-9Be backscattering cross section near 1H laboratory energy 2525 keV has been used to determine 9Be areal densities in thin films with accuracies of about 6%. We report measured cross sections (for a 170.5° laboratory backscattering angle) for 1H on 9Be for 1H energies from 2400 to 2700 keV. The areal densities of the self-supporting Be foils used for the 1H-9Be measurements were determined from 4He-9Be backscattering measurements. We also report measured cross sections for 170.5° backscattering of 4He by 9Be for 4He laboratory energies of 500 to 4200 keV. Results of channeling measurements in epitaxial Be films on crystalline substrates are also discussed.

Determination of boron using the B(α,p)C nuclear reaction at incident energies near 3 MeV

Abstract A technique for determining boron content of thin films using the B(α,p)C reaction on both isotopes of boron is described. An incident alpha energy near 3 MeV is used and emitted protons are detected at 135° lab angle. A thin film containing a known areal density of boron is required for calibration. A comparison is made between this method and conventional elastic scattering of 4 He + ions for boron determination in thin films containing heavy elements or backings. We also present relative yield data on protons from the 10 B(α,p) 13 C and 11 B(α,p) 14 C reactinos at 135° lab angle between 1.4 and 3.3 MeV.

Depth profiling of phosphorus using resonances in the 31P(α, p)34S reaction

Abstract Several resonances in the 31 P α , p 34 S reaction were investigated for their use in depth-profiling 31 P in solids. Targets with uniform 31 P concentrations as well as those containing Gaussian depth distributions resulting from implantation at 30 and 200 keV were measured using a resonance at 3640 keV. Computer simulation of yield curves was used to treat cases where more than one resonance contributed.