| 摘要 |
<p>This invention is directed to prevent step breakage and short-circuit of wires resulting from steps of isolation trenches formed in an SOI substrate. An oxide film for a pad is formed on a main plane of an SOI layer formed on an insulating substrate and furthermore, a silicon nitride film and an SiO2 film are sequentially formed. Thereafter, isolation trenches reaching the insulating substrate are formed by RIE using the SiO2 film as the mask. An insulating film is then formed on the inner wall of the isolation grooves by thermal oxidation, and polycrystalline silicon is filled into the insolation trenches. `This polycrystalline silicon is etched back while control is made so that the upper end of polycrystalline silicon inside the isolation trenches is above the upper end of the silicon nitride film, and the excessive polycrystalline silicon deposited on the substrate surface is removed. Next, polycrystalline silicon inside the isolation trenches and the silicon nitride film are used as an etching stopper to etch and remove the SiO2 film used as the mask at the time of the formation of the isolation trenches. Since this etching and removal of the SiO2 film used as the mask is carried out after polycrystalline silicon is filled into the isolation trenches, the oxide film for isolating the substrates inside the SOI substrate is not etched when the mask is removed. When the masking SiO2 film is etched and removed, polycrystalline silicon and the silicon nitride film inside the isolation trenches function as the etching stopper, and the oxide film for the pad as the lower layer and the insulating film formed on the inner wall of the trenches are prevented from being etched, and flatness in the trench portions is not lost. <IMAGE></p> |
