Experimental evaluation of depth-dependent lateral standard deviation for various ions in a-Si from one-dimensional tilted implantation profiles

Abstract

This paper presents an experimental evaluation of the lateral standard deviation for various ions implanted in amorphous silicon (a-Si) with a simple extraction method using no complicated structures. First, we derive a model for the tilted implantation profile as a function of both tilt angle and lateral standard deviation, assuming a Gaussian lateral distribution function. This model is based on the assumption that two-dimensional (2-D) ion implantation profiles can be constructed from lateral and vertical distribution functions which are independent of each other, and it enables us to extract lateral standard deviation by only evaluating one-dimensional (1-D) (vertical) impurity profiles. Next, we systematically measure the ion implantation depth profiles at various tilts (0-60/spl deg/) with high resolution using secondary ion mass spectrometry (SIMS) and apply our proposed model for arsenic (As), phosphorus (P), antimony (Sb), and boron (B) ion implantations in a-Si over a wide energy range (20-160 keV) with a fixed dose of 1/spl times/10/sup 14/ cm/sup -2/. We successfully estimated not only average lateral standard deviation but also its depth dependence. Despite the simplicity of the model, the extracted depth-dependent lateral standard deviation shows good agreement over a wide energy range with the reported data calculated by theory or simulations. It is also shown that the lateral standard deviation has a linear depth dependence, and the lateral spread increases with the increase of depth for As, P, and Sb; on the other hand, it decreases for B, which reflects the difference of atomic mass between the incident ions and the target atoms.