JPS6481324A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce leak currents and to improve memory keeping characteristic by forming a polycrystalline silicon layer, thermally oxidizing it in an oxide atmosphere containing fluorine or compounds thereof, removing such thermally oxidized film by etching, and then forming a desired insulating film on the polycrystalline silicon layer. CONSTITUTION:The surface of a polysilicon film 8 formed on an oxide film is characterized by irregularities 20 due to an infinity of crystal grains, in the interior of which crystal grains 21 are present. When oxidizing the polysilicon film 8 in oxygen containing NF3, large quantities of fluorine atoms 23, being entrapped by an oxide film formed on the polysilicon film 8, plasticity of the oxide film 22 increases while stresses are relieved. By this reaction, the surface of the n<+>-type polysilicon film 8 is smoothly oxidized. At the same time, fluorine atoms 23 are infiltrating into the n<+>-type polysilicon film 8 and combined with non-combined Si atoms which are present at the boundary of the crystal grains 21. As a result, doner type impurities in the n<+>-type polysilicon film 8 are no longer precipitated at the boundary of the crystal grains. According to the constitution, the characteristic of a capacitor oxide film to be later formed can be improved. By removing the oxide film 22 by etching afterwards, an excellent film can be obtained.