Abstract: RIE of metallization is achieved at low power and low pressure using Cl.sub.2 and HCl as reactant species by creating a transformer coupled plasma with power applied to electrodes positioned both above and below a substrate with metallization thereon to be etched. Three layer metallizations which include bulk aluminum or aluminum alloy sandwiched between barrier layers made from, for example, Ti/TiN, are etched in a three step process wherein relatively lower quantities of Cl.sub.2 are used in the plasma during etching of the barrier layers and relatively higher quantities of Cl.sub.2 are used during etching of the bulk aluminum or aluminum alloy layer. The ratio of etchants Cl.sub.2 and HCl and an inert gas, such as N.sub.2 are controlled in a manner such that a very thin side wall layer (10-100 .ANG.) of reaction byproducts created during RIE are deposited on the side walls of trenches formed in the metallization during etching.

Abstract: Disclosed is a method of forming in a monocrystalline silicon body an optimum recessed oxide isolation structure with reduced steepness of the bird's neck. Starting from a monocrystalline silicon body, there is formed thereon a layered structure of first silicon dioxide, polycrystalline silicon, second silicon dioxide and silicon nitride, in that order. The layers are patterned to form openings in the structure at the areas where it is desired to form the oxide isolation pattern within the silicon body. The exposed areas of the silicon body are anisotropically reactive ion etched to an initial portion of the desired depth obtaining the corresponding portion of the trench having substantially vertical walls. Then by chemical etching the trench is extended to a final portion of the desired depth obtaining inwardly sloped walls in the final portion. The body is then thermally oxidized until the desired oxide isolation penetrates to the desired depth within the silicon body.