A new preferential etch of silicon (1 1 1) with ammonia system

Preferential etching is a simple and fast technique to evaluate the structural perfection of a simple crystal. For silicon crystals, this technique is widely used to delineate crystal defects generated during crystal growth, wafer preparation and processing. An investigation of the NH4OH–CH3COOH system shows that preferential etching of crystal defects on (1 1 1) silicon surface is very sensitive to the concentration ratio of NH4OH and CH3COOH. The investigation of this system leads to development of an improved etch. This etch consists of 80–90 parts of NH4OH and 20–10 parts of CH3COOH. The newly developed etch can delineate a wide variety of crystal defects with sharp definition, high resolution and minimum surface roughness, over a range of resistivities. A slow etch rate (0.35 μm/min) at 75 °C provides etch control. In most cases, the etch time required is about 15 min.