Non-Contact Electrical Doping Profiling

Monitoring of dopant concentration in the near surface region is very important in semiconductor manufacturing, especially for epi-technology and ion implantation. Two relevant techniques which have been used are Mercury probe and Elastic probe. Both of them allow profiling of dopant concentration by measuring the capacitance of the depletion layer, CD, versus the applied bias. These techniques are contact in nature. In addition Mercury probe uses Hg, which may be considered undesirable in cleanroom environment.The method being presented is non-contact and non-destructive. A deep depletion layer is created by corona charging of the wafer surface. This depletion layer decays to an equilibrium value due to thermal generation of minority carriers. Two transients are simultaneously monitored during this process: 1) the small signal ac surface photovoltage that measures the depletion layer capacitance, and 2) the contact potential difference that measures the voltage drop across the depletion layer. The set of corresponding C-V data is used to calculate the dopant concentration profile. In silicon, the technique is applicable for dopant concentrations in the range from 1e14 to 1e18 cm(-3). The probing depth is limited at the upper end by avalanche breakdown in the semiconductor and at the lower end by the minimum surface barrier. Measurements of dopant profiles on bare and oxidized surfaces using this technique are presented for epitaxial p/p+ and n/n+ substrates, n/p structures, and implanted wafers, covering probing depths from 0.05 mum to 7 mum. This non-contact technique can be realized in a simple configuration that may be of interest for universities and research and development centers.