High resolution measurements of two-dimensional dopant diffusion in silicon

We report detailed experimental results on the electrochemical selective et ching of doped Si. By using transmission electron microscopy analyses and s preading resistance measurements we investigated the dependence of the etch ing selectivity on the different parameters of the electrochemical cell, i. e., bias voltage and chemical solution. In B-doped samples immersed in buff ered HF, the increase of bias voltage from 0.5 to 1 V produces a slight imp rovement of the etching selectivity and a B concentration as low as 1 x 10( 17) cm(-3) can be successfully delineated at 1 V. A further improvement is achieved by using HF:HNO3:CH3COOH or HF:HCl chemical mixtures for which the delineation sensitivity approaches the value of 1 x 10(16) cm(-3). In buff ered HF As-doped regions can be delineated to a concentration of 2 x 10(17) cm(-3), independently of the bias voltage, in the range 2-4 V. These resul ts were used to measure the 2D doping diffusion profiles in silicon wafers patterned with polycrystalline Si strips and implanted with As or B, by usi ng different tilt and twist angles. The high resolution of the electrochemi cal delineation allowed us to evaluate very accurately the effects of the i mplant angles on the lateral doping distribution.