Boron diffusion in polycrystalline silicon layers

Abstract

Boron was diffused into the poly Si layers of 5·5 μm thickness with boron nitride and diborane as boron sources. The diffusion depth was found to be proportional to the square root of diffusion time. The boron diffusion in the poly Si layers can be expressed in the well known complementary error function. The diffusion coefficient of boron in the poly Si layers is larger when diborane is used than when boron nitride is used as a boron source and is 10–50 times larger than that in the single crystal silicon substrates in the experimental range. The diffusion coefficients of boron at 1050°C in the single crystal silicon substrates with diborane as a boron source in the poly Si layers with boron nitride and diborane as boron sources are 8·80 × 10 −14, 1·17 × 10 −12 and 1·95 × 10 −12 cm 2/sec, respectively. The activation energies of the diffusion coefficients of boron in the above each case are 3·42, 2·39 and 2·51 eV, respectively.