CHEMICAL ETCHING OF SILICON - SMOOTH, ROUGH, AND GLOWING SURFACES

Scanning Force Microscope images of silicon surface morphology are pre sented for samples exposed to various oxidizing environments followed by oxide removal. These are contrasted with samples exposed to HNO3/HF solutions. The former samples consistently produced surface roughness on the order of a few nanometers, while the latter solution exhibited surface roughness of several hundred to over a thousand nanometers. T his cough surface is photoluminescent and is known as porous silicon. Careful observation of the onset of the reaction (which is preceeded b y a concentration dependent induction period) suggests that the reacti on mechanism is autocatalytic; some etchant product species catalyzes the further attack of the surface. Surface features of co-existing flu orescing and non-fluorescing regions emphasize the heavy etching prese nt in the porous silicon region. Local control of the porous silicon f ormation by a photoinduced etching process is reported for the first t ime suggesting the possibility of a non-resist lithographic procedure.