Cleaning with Carbon Dioxide Snow Inspection of a Cleaning Method

Today cleaning with carbon dioxide pellets similar to sand blasting is an established technology. It is used for cleaning buildings outsides, rusty contamination or even to remove paint from airplanes. In any of these cases, the treated contamination is of a rough and macroscopic character. For the cleaning challenges of the Semiconductor Industry of the Microelectromechanical Systems (MEMS) with submicron particle contamination and thin film contamination this process is not at all suitable. On the other hand, established cleaning methods for the above mentioned problems, such as wet cleaning with water or chemicals, are often inconvenient, costly and are followed by the necessary disposal of cleaning media. At the Fraunhofer IPA, Stuttgart, Germany, experiments have been performed to develop an optimized cleaning system with carbon dioxide snow. High purity carbon dioxide is highly compressed and afterwards expands through a specially formed nozzle. Like this the carbon dioxide creat es a mix of snowflakes and gas. The effect of cleaning is a result of an almost gentle but very effective momentum transfer by the snowflakes on the contamination and the resulting shock wave which is induced by the sublimating carbon dioxide. The main advantages of this cleaning method can be described as follows: - cleaning of hybrid structures with a very high local resolution - minimal consumption of carbon dioxide - dry cleaning - no contaminated cleaning media (compared to wet cleaning with water or chemicals - disposal-free cleaning - cleaning of particle and filmic contamination - effective cleaning of submicron contamination at a high performance. This paper describes the experiences and results from the experiences carried out at the Fraunhofer Society, Institute for Manufacturing Engineering and Automation (Fraunhofer IPA)