Measurements of charge on submicron particles generated in a sputtering process

The concentration and charge of a submicron aerosol were measured during the venting cycles of a quartz sputtering system. The concentration of submicron particles in the aerosol measured after the plasma was turned off and the chamber vented was of order 20/cm3. A Faraday cup was used to collect the particles by filtration and the total electrical current was measured with an electrometer. From these measurements, the average charge on each particle was estimated to be 1.4×104 negative elementary charges. Mutual electrostatic repulsion rates of the gas-borne particles revealed the charges on 0.4 and 0.6 μm particles to be proportional to the diameter squared. No agglomerates were seen in the scanning electron microscope images of these submicron particles collected on a filter, even when the surface density was extremely high. This also suggests that particles were highly charged during the collection process.