Overetching

Overetching is the continuation of an etching process beyond the intended boundary or depth, resulting in the removal of material outside the target area or deeper than planned. It can occur in both wet chemical etching and in dry processes such as plasma or reactive ion etching. In some cases, an overetch step is deliberate to ensure complete pattern transfer or residue removal, but uncontrolled overetch can damage underlying layers and degrade device performance.

Causes of overetching include insufficient masking, excessive etch duration, high etch rates, poor selectivity between mask and substrate, high temperatures, nonuniform plasma or chemical concentrations, and loading effects that create etch-rate variations across a wafer. End-point detection errors and process variability can also contribute.

The consequences of overetching range from loss of pattern fidelity and undercutting of the masking layer to trenching, thinning of underlying films, increased sidewall roughness, and potential electrical leakage or device failure in microfabricated components. In sensitive structures, overetching can compromise structural integrity or introduce defects.

Prevention and control strategies include using adequate masking with margins or hard masks to resist etchants, optimizing etch chemistries for higher selectivity, and implementing accurate end-point detection to halt etching at the correct stage. Process controls such as temperature, pressure, and gas flow should be stabilized, and etching can be limited by reducing power or using pulsed/segmented approaches. In some processes, protective sidewall passivation steps or controlled overetch durations are employed to balance complete pattern transfer with minimal damage, followed by thorough metrology to verify critical dimensions and uniformity.