A New Mechanism of Poly-silicon Crater Defect Induced from Al Tiny Particle Charging Effect during Water Rinse in Oxide Patterning Process

Poly-silicon crater defect generated in large plate of n+ poly-silicon on p-type substrate that resulted in gate oxide integrity (GOI) failure in 0.15mum silicon process is investigated. Al tiny particle accidentally introduced from PECVD resistance protection oxide (RPO) deposition is found to be able to translate into such poly-silicon crater defect in the test structure during subsequent oxide photo-resist patterning and oxide wet etching. The defect size can correlate to DI water rinse time of photo-resist developing in RPO oxide patterning. The longer time of water rinse, the larger size of the craters. This paper describes observation of n+ poly-silicon crater formation. A new mechanism of Al tiny particle induced n+ poly-silicon charging effect during high speed spinning water rinse in oxide patterning process is proposed. After water rinse completion in the process, the charges stored in poly-silicon are unable to be discharged immediately due to enough large capacitance of gate oxide in discharging path of the test structure. Charged poly-silicon is then quickly attacked in diluted 0.5w%HF immersion of RPO oxide wet etching by galvanic corrosion to form a crater. To eliminate poly-silicon crater formation, efforts could be put into eliminating the presence of aluminum particles in oxide deposition or optimization of water rinse condition. Oxide dry etching is also one of possible improvements can be evaluated