Experimental measurements of spatial particle removal from silicon wafers by megasonic energy

An experimental study was conducted in a megasonic cleaning tank containing deionized water to determine the influence of acoustic power, cleaning time, water temperature and dissolved gas content on the local and total cleaning efficiency of 0.5 micron silicon particles deposited on silicon wafers. The experimental system included a 2.54 cm by 15.24 cm flat piezoelectric transducer mounted on the bottom of the tank that operated at 910 kHz. The water temperature was controlled using an electric emersion heater. A flow recirculation system contained a filter for particle removal and a degasser connected to vacuum to control the dissolved gas content. A dissolved oxygen meter was used to monitor the dissolved oxygen content and a model was developed to predict the total dissolved gas content of the water.; A statistical approach was used to design a factorial four-factor two-level experiment. Two values of each variable, power, time, temperature, and gas content, were used. Two wafers were used in each experiment and each test was replicated for a total of 64 wafers.; By performing an analysis of variance test, power, time and dissolved gas content had a significant effect on the cleaning results. Reduction in dissolved gas content and increasing the transducer power and cleaning time enhance the cleaning efficiency. A change of temperature from 25°C to 50°C had no significant effect on particle removal.; Cleaning was most pronounced in the center of the wafers located near the center of the acoustic beam above the transducer. Cleaning efficiency was negative in some locations near the perimeter indicating particle redeposition. Wafer damage is suspected for 8 wafers when the dissolved gas content was low, the water temperature was 50°C and the cleaning time was 10 minutes.