Formation and Facet Less Immersion of Discrete Al-Si Areas on Unpolished Wafers in Silicon Thermomigration Technology

The paper considers the technology of thermal migration for the formation of a through-layer insulation of individual crystals in the manufacture of power electronics devices. The initial Al-Si layer for the thermal migration process is formed in SiO₂ windows from the Al melt and the surface disordered Si layer dissolved in it. Selective dissolution of Si occurs when the surface of the moving wafer sequentially contacts the Al melt ribbon, where the convection flows of the melt remove the dissolved Si atoms to the melt volume. In the process, it is possible to control the thickness of the Al-Si melt formed in the SiO₂ windows. The formation of the p⁺-Si*(Al) layer, which is deposited during recrystallization from the Al-Si melt during the cooling of the wafers, the high concentration of Si and the homogeneity of the Al-Si layer ensure the isotropic nature of the dissolution process and, accordingly, the faceless immersion of the discrete zone during the subsequent thermal migration process. The observed change in the polarity of the brightness contrast of the surfaces of the discrete zone and adjacent silicon in the temperature range of 1100-1130°C allows us to control the beginning of the high-temperature immersion process. The article also shows the dependence of the thickness of the Al-Si layer on the parameters of its formation process.