2-DIMENSIONAL PROFILING IN SILICON USING CONVENTIONAL AND ELECTROCHEMICAL SELECTIVE ETCHING

One of the methods to delineate a two-dimensional dopant profile in Si devices is the selective etching technique combined with imaging of t he doping dependent topography by atomic force microscopy. A major pro blem of the etching procedures reported so far is the critical control of the etch duration of only a few seconds as well as a limited sensi tivity and dynamic range. We report further improvements of the conven tional technique and compare it to an alternative approach. Etching ex periments were carried out in an electrolytic cell, whereby the etchin g is controlled potentiostatically. Better control of the dissolved vo lume is achieved through current integration. Buffered HF as the elect rolyte replaces the difficult nitrogen related chemistry of the classi cal approach. The etch rates thereby decrease by a factor of 10-100 th us allowing for a longer etch duration. The basic mechanisms, the sens itivity, and the dynamic range of the two techniques have been studied by using homogeneous samples and special test structures for calibrat ion and ultrashallow profiling. Two-dimensional profiling has been car ried out on cross sections of 0.25 mu m complementary metal-oxide-semi conductor devices with the classical and the electrochemical approache s. Problems of preparation, etching procedure, and imaging techniques are discussed in order to improve the quantification of the selective etching technique. (C) 1998 American Vacuum Society.