Damage-to-dose ratio after low energy silicon ion implantation into crystalline silicon
- PDF / 423,665 Bytes
- 5 Pages / 576 x 792 pts Page_size
- 57 Downloads / 223 Views
S. Dunham Electrical, Computer and Systems Engineering Department, Boston University, Boston, Massachusetts 02215 (Received 23 June 1992; accepted 28 April 1993)
In this work, we develop a model describing the diffusion of vacancies and self-interstitials and their recombination during ion implantation. The model includes the effect of the moving surface due to regrowth and the defect generation rate as a function of depth based on Monte Carlo simulations. The results are compared to experimental measurements of the damage-to-dose ratio (DDR) after low energy, 40 eV, silicon ion implantation into silicon at 300 and 685 K. We have derived an analytic approximation which agrees with the results of the computational model, implemented on a CM-2 parallel computer. We find that the calculated effective diffusivity, the main adjustable parameter in the simulations, is much lower than predicted based on extrapolation from experiments at higher temperatures. We attribute this difference to the aggregation of self-interstitials. We also find that the effect of interstitial-vacancy recombination on DDR is negligible under the experimental conditions considered; however, the crystal surface motion has a significant impact on the results.
I. INTRODUCTION Observations of damage in crystalline silicon following low energy silicon ion bombardment1'2 show that, after deposition, the interstitials tend to accumulate well beyond the crystal region where they have been produced. The total number of these interstitials has been measured by ion channeling,1 and the results are shown in Table I. In order to interpret these measurements, we have developed a model to calculate the number of interstitials (damage) remaining in the silicon following the implantation and the ratio of this damage to implant dose (DDR). The model includes interstitials and vacancies, their recombination, the surface motion of the growing crystal, and a constant source of interstitials and vacancies. The source is calculated using a modified TRIM code, TRIMCSR (TRansport of Ions in Matter including Collision cascade, Sputtering, and Replacement events).3*4 In the analytical version of the model, the upper bounds for the effective interstitial diffusion coefficients that could be responsible for the DDR in Table I were estimated analytically. The computational version of the model was performed on a CM-2 massively parallel computer.5 The concentration profiles of interstitials and vacancies were represented by a single 2 X n array with n = 1024 or n = 2048, representing the discretization J. Mater. Res., Vol. 8, No. 9, Sep 1993
http://journals.cambridge.org
Downloaded: 18 Mar 2015
TABLE I. Experimentally measured damage obtained by silicon ion scattering and cross-sectional TEM on ion beam deposited layers of Si on (110) Si. The damage-to-dose ratio (DDR) is listed as a function of temperature and dose at silicon ion energy of 40 eV.1 Dose (at./cm2 X 1016)
Temp.
Implant time
(K)
(s)
DDR
13.0
300 685 685 685 685 685 685 685 685
13000 5700 6100 6200 6
Data Loading...
