Use of an electrochemical sensor for controlling the etching of silicon dioxide films in aqueous HF processing baths

摘要

Abstract: It is shown that an appropriately selected point-of-use ionic conductivity sensor can be utilized to replace thermal oxide coated wafers for monitoring aqueous HF processing baths. The use of both conventional conductivity sensors which employ two or more electrodes contacting the solution and electrodeless, inductance based sensors are reviewed. The former type afford cost and versatility advantages, while the latter type possess desirable material properties. Ionic conductivity data for aqueous HF solutions as a function of composition and temperature is reported over a range of 0 to 5 wt% HF. The temperature coefficient was found to be nonlinear over this concentration range, but this parameter is very small relative to other common electrolyte solutions. A comparison with refractive index measurements shows ionic conductivity to be more sensitive.!9