Etching Bath Analysis

Measuring Hydrofluoric Acid in an Etching Bath

Wafers are immersed in a bath of etchant solution—often diluted hydroflouric acid—to remove SiO2 or other extremely thin layers from the surface. The HF etch rate, described in Å/sec, must be held constant to avoid scrapped wafers, but the rate varies with HF concentration in the solution. Errors in etchant dilution ratio stem from improper initial mixing, residual water from previous rinses, and using a single bath with multiple acid ratios for different production recipes.

Solution: the OMA continuously monitors HF concentration in the etching agent solution and provides an alarm output for when the sample ranges outside of specification.