Wafer Level Characterization of the Sacrificial HDP Oxide Lateral Etching by Anhydrous Vapor HF with Ethanol Vapor for SiGe MEMS Structures

Abstract

In this work, the lateral etching of the sacrificial high density plasma (HDP) oxide by anhydrous vapor HF (AVHF) together with ethanol vapor is characterized for SiGe microelectro-mechanical systems (MEMS) structures. An extensive design of experiment (DOE) is carried out to study the impact of the process conditions on etch rate (ER) and within wafer uniformity (UWiW). Two wafer level automated techniques, critical dimension scanning electron microscopy (CD SEM) and high resolution profiler (HRP), are compared to replace the manual inspection method performed at die level. It is found that each 25Torr increment in process pressure doubles the ER in the 75 Torr - 125 Torr range. Each 150sccm increment in AVHF flow rate increases the ER 1.3~1.5 times in the 300 sccm - 600 sccm range. Based on the reproducible ER (~80 nm/min) and the UWiW (~10%) of the process of record (POR) as measured by CD SEM, a statistical process control (SPC) is set up for this process condition.