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A novel nondestructive measurement technique is proposed to electrically monitor the depth of a trench etched in silicon for the purpose of process control in a manufacturing environment. A simple bipolar npn transistor can be constructed, the gain of which is shown to relate to the trench depth. The ratio of the injected emitter current to the captured collector current has demonstrated the ability to resolve variations in trench depth of less than 0.2 μm. The proposed structure is studied using two-dimensional simulations and experiments. A case study of two different silicon reactive ion etch tools is offered to demonstrate the effectiveness of the proposed technique.