Ultrasonic sputtering for polishing in semiconductor industry

In the article, authors discover the reasons, which decrease efficiency of very important process in semiconductor industry - chemical mechanical polishing (CMP). It is shown that decreasing of final product quality is caused by nonuniform distribution of polishing liquid on a surface. After analysis of different fluid supply ways it was suggested to use the fine-disperse ultrasonic sputtering of polishing liquid to polishing wheel surface. Proposed technology implements uniform sputtering of polishing liquid to polishing wheel surface and therefore it provides: 1. uniform pressure fluctuations, that effect on wafer roughness, 2. uniform distribution of chemical agent on polishing surface. The results of studies that provide the developing of ultrasonic oscillatory system for practical realization of suggested technology and technical solutions are presented. The oscillatory system was built as a half-wave system, based on piezoelectric transducer and concentrator with step-exponential coupling. Resonant frequency at 40 kHz was selected taking to account following requirements: liquid flow is from 0,2 to 1,2 milliliters per second, average drop diameter is 18 micrometers, that prevent a fog occurrence. For providing a maximal jet width, some studies of sputtering process from different form sputtering surfaces were carried out. Optimal form of working tool sprayer was found. The optimal working tool of oscillatory system has elliptic shape and has axisymmetricaly located additional channels. This form produces atomization jet more than 65 millimeters wide and at distance 40 millimeters from working end. Description of electronic generator, which products ultrasound frequency AC current for supplying oscillatory system, is presented. Key features of sputtering devices are summarized in conclusion.