A Design of Experiments Approach to BCB Etch Uniformity Improvements

Nortel Networks GaInP/GaAs HBT process1,2 employs a bisbenzocyclobutene (BCB) intermetal dielectric, chosen for it’s excellent planarization and dielectric properties. During a 3 ” to 4” conversion of the GaAs HBT production facility, the existing 3 ” etch conditions for the BCB etch using CF4/O2 in an Ar carrier gas were found to produce inadequate uniformity control on the 4” wafers. A program was initiated to improve etch uniformity using a Design of Experiments (DOE) methodology. Since there was already a strong starting point for the experiments (the etch conditions used in the 3 ” process), the approach was to use a response surface method (RSM) to optimize the existing 3 ” conditions for 4 ” wafers, forgoing the screening type experiments that would normally be required for a new process. As a result of the experiments, etch uniformity improved from ~14 % to ~6%