Method of making single-step trenches using resist fill and recess

Abstract

A trench capacitor with a buried plate is formed with a single etching process by the expedient of filling the trench so formed and lined with diffusion source material with resist by baking and reflowing the resist which also serves to adjust exposure sensitivity of the resist such that exposure and development of the resist removes the resist to a repeatable and uniform depth. Remaining resist allows etching of the diffusion source layer to a very accurate dimension. Thus only a readily formed oxide or TECS layer is needed to confine impurities during diffusion to form the buried plate. An isolation collar can be formed after recess of the fill to avoid formation of step corners and erosion of the isolation collar by repeated fill and etch back processes while permitting maximum capacitance to be achieved for a given trench 'footprint'.