Post-etch residue removal with EKC® chemicals

Spray solvent tools are used in the post etch residual polymer removal process to clean the surface of wafers. EKC is a commonly used chemical in the process that employs two tanks. The process operating temperature of EKC is kept between 65 °C (149 °F) and 75 °C (167 °F). The actual residue removal takes place in the spray solvent tool where EKC is fed to, according to a pre-determined cycle of chemical recirculation and wafer run.

Chemical curve: Water in EKC R.I. per Conc% b.w. at Ref. Temp. of 20˚C

Two control strategies can be adopted with the aid of Vaisala K-PATENTS® Semicon Refractometer PR-33-S. The first one is to monitor water content in EKC, and the second is to maintain the water content at a constant level. The former allows for setting high and low alerts for the amount of water, which warrants safe wafer production. The latter has proved to provide a considerable reduction in the EKC consumption.

The recirculation starts when the wafer run in the spray solvent tool is over and the chemical is delivered to the EKC tank. The tank is partially drained of the chemical and refilled with fresh EKC and water. Water is evaporating through the exhaust system of the spray solvent tool during the spray run. 

The amount of water in EKC is maintained with automated chemical spiking after each wafer run. The chemical spiking is activated using the PR-33-S output signal. This arrangement provides the exact set point for water in the EKC concentration and helps to optimize and reduce EKC replenishment.

After EKC clean, there is an IPA/Dry process where IPA may get contaminated with EKC traces. The Semicon Refractometer can monitor the concentration of the chemicals to alert of possible mixes. The refractive index values of EKC and IPA differ substantially allowing a very reliable measurement of EKC traces in IPA.

• Silicon wafers