Abstract: The invention relates to a process for treating a portion of the surface of a substrate according to a first and second surface treatments which are different from each other and are intended respectively for a first group of regions and for a second group of regions of the surface portion, the two groups of regions being mutually complementary with respect to the surface portion, the process making it possible to use only a single operation of positioning a mask which differentiates the regions of the first and second groups of regions, using the same protective materials for the regions of each group of regions against the effects of the treatment intended for the regions of the other group of regions. Application to the fabrication of semiconductor products.

Abstract: In the manufacture of 16 Mbits DRAM chips, a polysilicon strap is used to provide an electrical contact between the drain region of the active NFET device and one electrode of the storage capacitor for each memory cell. The storage capacitor is formed in a trench etch in a silicon substrate which is partially filled with polysilicon. The substrate is conformally coated by a TEOS SiO.sub.2 collar layer having a non-uniform thickness. A chemistry having a high TEOS SiO.sub.2 /Si3N.sub.4 and polysilicon selectively (i.e. which etches TEOS SiO.sub.2 faster than Si.sub.3 N.sub.4 and polysilicon by a factor of at least 6) is used to anisotropically etch the collar layer. C.sub.4 F.sub.8 /Ar/C) mixtures which have selectivities of 9:1 and 15:1 are adequate. When the surface of the Si.sub.3 N.sub.