Investigation of the Radially Spreading Micro-Bubble Defect due to Contamination from SEM

An investigation into the origin and control strategies for a distinct defect characterized by radially spreading wafer maps was conducted during the spin-on hard-mask (SOH), photo resist (PR), and spin-on dielectric (SOD) coating processes. It was found that this defect is closely associated with wafer review or critical dimension (CD) measurements using a scanning electron microscope (SEM) prior to the coating process, and exists in the form of micro-bubbles. To determine the formation mechanism, surface contamination analysis, contact angle, and potential measurements were performed. The results indicated a mechanism for bubble formation resulting from locally inhomogeneous wafer surface hydrophobization caused by carbon compound-based contamination in a vacuum SEM chamber, leading to bubble nucleation and air entrapment during the acceleration coating stage. As preventive measures, the organic contamination source was reduced by cleaning the SEM chamber, and it was demonstrated that implementing enhanced reducing resist consumption (RRC) in the photo process and treatments such as pre-wet cleaning or O2 plasma ashing are effective solutions.