D.K. Brice

Partitioning of ion-induced surface and bulk displacements☆

Abstract An analytical method is described to determine the number and partitioning of displacements of surface and bulk atoms by low energy ions incident on a solid. Results are presented for Ge, Si and C (diamond and graphite). For Ge the results are compared with Monte Carlo calculations using the computer code TRIMRC. Good agreement is found in this comparison, thereby verifying the adequacy of several approximations introduced into the formalism. Displacement threshold and surface-to-bulk displacement ratio contours are presented as a function of ion mass and energy based on our analytic calculations. Comparison of these contours with recent experimental results for Si suggests that this approach provides a global framework for understanding and optimizing the effects of low-energy ions on semiconductor expitaxial growth.

Spatial distribution of energy deposited into atomic processes in ion-implanted silicon

Abstract A method is given for calculating the spatial distribution of the production of a quantity, Q, averaged over many ions incident randomly on a solid for any energy dependent interaction between the ions and target atoms. The method is basically a two step method. First, the spatial distribution of the ions in the solid is followed as the ions lose energy. Then, at each intermediate energy the spatial distribution of Q-production is obtained and the result is integrated over the range of intermediate energies assumed by the ions. Saturation effects are ignored in the procedure so that explicit consideration must be given to saturation effects when applying the method to high dose cases. Annealing and diffusion effects are also ignored, and the method is restricted in applicability to experimental conditions where annealing and diffusion are unimportant. Results of calculations by this method are presented of the depth distribution of energy ultimately deposited into atomic processes for Li7, B11, C...

Recoil contribution to ion‐implantation energy‐deposition distributions

A previous method for directly calculating the spatial distribution of energy deposition into damage or ionization for ions implanted into solid targets is extended to account for energy transport by recoiling target atoms. The new calculations extend the applicability of the method to lower incident ion energies. In addition, an intermediate step in the calculations provides information on the spectrum of target recoil atoms. Good agreement is obtained between experiment and theory using the improved procedure. Calculated damage energy distributions are presented for 10‐keV–1‐MeV B, P, As, and Sb ions incident on silicon.

Modeling of enhanced diffusion under ion irradiation

The differential equations which govern enhanced diffusion under ion irradiation are solved using recently developed numerical techniques. Accurate time‐dependent profiles for vacancies, interstitials, and diffusing atoms are generated thereby with minimal computer time. The theoretical description is improved further by incorporating refined calculations of the atomic displacement rate by energetic ions. Three representative cases of enhanced diffusion are treated in detail: Al diffusion in Al under 100‐keV Al irradiation, Al diffusion in Al under uniform irradiation, and W diffusion in W under 100‐keV proton irradiation. It is shown that more information may be obtained from the diffused atomic profiles if the irradiation damage rate varies with depth in a known way over the diffusion region. Under this condition, both the shape and the time dependence of the atomic profile are sensitive to the rate coefficient for point‐defect annihilation. When the annihilation coefficient is so determined, the point‐...

Theoretical analysis of the energy spectra of back-scattered ions

Abstract An equation is derived which governs the energy spectrum of ions backscattered from a target whose composition varies continuously with depth. The equation also includes the effects of path length straggling on the energy spectrum through integrations over the depth distributions of both the incident and the back-scattered ions. When path length straggling is negligible, the equation reduces to a simple form, not involving integrations. The general equation is used together with model ion depth distribution functions to investigate the effects of the shape of the ion distribution on the predicted back-scattered spectrum. Delta functions, gaussian and several skewed distributions are used for this investigation. The predicted back-scattering spectra from these different distributions show little difference except at the energies corresponding to the back edge of a thick film target. At these energies the gaussian distribution provides some spreading of the observed edge, and skewing produces additional broadening and some tailing. For realistic skewing of the ion distributions the predicted tailing is not sufficient to account for the low energy tails observed in many experiments. These results suggest that accurate spatial ion distributions will be required before detailed analysis can be carried out on the sharp features of thick target spectra. In the last section of the paper the simplified form of the general equation is used together with an iterative procedure to obtain the depth distribution of target composition from a complex experimental spectrum.

The analysis of elastic recoil detection data

Abstract The physical concepts involved in elastic recoil detection (ERD) are reviewed in order to facilitate more quantitative use of this powerful ion beam analysis technique. Analytical expressions analogous to those developed for Rutherford backscattering are provided and recommendations are given for the optimization of depth resolution. Examples involving the concentration depth profiling of light elements are used to illustrate the analysis.

Steady state hydrogen transport in solids

Abstract The analytical formalism for evaluating the steady state hydrogen (tritium) inventory, recycle and permeation rate and recycle time for surfaces exposed to the plasma of an operating magnetic confinement fusion reactor is reviewed and new material relevant to the application of this theory is presented. The formalism includes hydrogen trapping, diffusion, and effects of thermal gradients (e.g., Ludwig-Soret effect), and is applicable for all orders of release kinetics at the inner and outer surfaces. The problem is formulated in terms of a unitless transport parameter, W=(Rφ/D)(k1/φ)l/r, where r is the order of the release kinetics, R is the range of the implant, φ is the penetrating part of the incident flux, kl is the recombination coefficient and D is the diffusion coefficient. The steady state analytical theory is applied to several materials of interest to controlled fusion.

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 DEPTH DISTRIBUTIONS: ENERGY DEPOSITION INTO ATOMIC PROCESSES AND ION LOCATIONS

A useful method of calculating the energy/unit depth deposited in atomic processes by energetic ions in solids is presented. The calculated energy density is shown to correlate well with previous Monte Carlo calculations of the vacancy concentration resulting from ion bombardment and recent experimental measurements of the depth distribution of ion damage. The method also provides the depth distribution of ions in the solid as a function of their energy during the stopping process. This information would allow, for example, calculation of the location and rate of various energy‐dependent interactions between incident ions and host atoms.

In situ measurements of hydrogen motion and bonding in silicon

Hydrogenation of both n‐ and p‐type metal/thin oxide/silicon diodes has been studied using high frequency capacitance profiling. In situ observations of donor and acceptor passivation were made while H ions were implanted through thin gate metallizations at various energies and fluxes. TRIM code simulations of the implantation process as well as studies of the energy, dose, and flux dependence of capacitance data lead us to conclude that irradiation of 400 A Al gated diodes with 800–1400 eV H ions rapidly establishes a time‐independent near‐surface H concentration which is proportional to both the ion flux and the implantation depth, and inversely proportional to the hydrogen diffusivity. While direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, modeling of low and high field data in both n‐ and p‐type samples is consistent with the notion that the positive charge state is occupied only 1/10 of the time. The time dependenc...