Applications of plasma cleaning for electron microscopy

Summary form only given. Specimen contamination and amorphous irradiation damage severely limit the ability to perform accurate electron microscope analysis of materials, especially as specimen areas of interest decrease in size. To analyze smaller areas of interest, electron probe sizes have decreased, while probe currents have increased. The combination of these two factors results in an increase in the amount of carbonaceous contamination formed on the specimen under the electron beam. Recent instrumentation developments have resulted in the application of a high frequency, low energy, reactive gas plasma that chemically removes hydrocarbon contamination from both the specimen holder and the specimen without altering the specimen properties. The gas plasma is created within a cylindrical chamber, where the specimen and specimen holder are contained. Gas dynamics analysis indicate an even distribution of plasma within the chamber and around the specimen contained in the specimen holder. A high frequency (HF) antenna, located external to the chamber, couples inductively the oscillating electromagnetic field through the quartz chamber walls and generates the plasma. A critical aspect of this low-energy form of plasma creation is that no components (i.e., electrodes) are located within the plasma, other than the specimen and specimen holder that are being processed. This enables effective cleaning with negligible specimen heating and eliminates the sputtering of electrode material onto the specimen and specimen holder. Critical aspects of the plasma generation, ion energy, electrode location, process gas, and vacuum technology are discussed in this presentation. The effect of plasma processing parameters on various materials research specimens will be presented.