ABSTRACT

Proximity rapid thermal diffusion (RTD) has been investigated as a doping technique for p-type boron doped junctions. The efficiency of RTD has been studied as a function of process variables (temperature, time, and ambient) and evaluated based on sheet resistance measurements, secondary ion mass spectroscopy (SIMS), spreading resistance (SR), and Fourier transmission infrared absorption (FTIR) in a spin-on-dopant source (SOD). The doping efficiency in source wafers is controlled by different mechanism than in processed wafers. Strong influence of dopant incorporation in the processed wafers on oxygen content in the diffusion ambient is observed especially at low diffusion temperatures.

We investigated effects of surface preparation in doping silicon wafers using proximity rapid thermal diffusion (RTD). This process uses a spin-on-dopant (SOD) as an evaporating source for doping processed wafers. Various cleaning processes were used to study formation of the dopant glass on the silicon wafers during RTD. Doping was evaluated by sheet resistance measurements, dopant profiling using SIMS analyses, carrier distributions using spreading resistance profiling (SRP) or anodic oxidation, and was complemented by the composition analyses of the SOD deposited on the source wafers and of the dopant glass formed on the target wafers using Fourier Transform Infrared Spectroscopy (FTIR) in the transmission and reflection modes, respectively. It was found that the influence of the cleaning steps is much stronger in low temperature doping processes than at high temperatures. In addition, the temperature effect related to the wafer size was also an important factor in determining the doping efficiency in this RTDs.