Introduction to Plasma Cleaning

Introduction to Plasma Cleaning By Enrico Malatesta CEO SCI Automation Pte. Ltd. Singapore

Cleaning, Surface Modification, and Etching Process Plasma cleaning is defined as a process that uses an ionized gas to interact with a substrate in order to remove contamination and/or modify its surface. Plasma cleaning, therefore is much more than just a cleaning process, it is also a surface modification process and an etching process. In a more general way, we can say that most plasma cleaning applications are methods to promote adhesion between two items: • • • • • • by simple decontamination of their interfacing surfaces by generating a modified surface condition such as increasing the surface roughness by increasing the surface energy by rendering the surface hydrophilic By rendering the surface hydrophobic By removing metal oxides by physical and/or chemical interaction

Plasma Cleaning and Wire Bonding Yield For example, in the Semiconductor Industry, a typical application is preparing the surface of a leadframe and the dies mounted on it, with plasma cleaning. This is typically done prior to the wire bonding process with the purpose of increasing the bonding yield. It is also done before the molding process to ensure the removal of voids and delamination, thus increasing the package yield. Semiconductor manufacturing processes are intended to build each individual die so that it performs according to specification. However, manufacturing issues during processing, variation in the process variables and cross contamination from other processes may cause some die to fail due to a phenomenon called NSOP (Non Stick on Pad). NSOP defines the event detected by the wire bonder when it senses that the bond just created was unsuccessful (no adhesion between the wire and the die’s pad surface).

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An example (1) of how plasma cleaning can help solve this problem comes from an...