EFFECTS OF ION-INDUCED ELECTRON-EMISSION ON MAGNETRON PLASMA INSTABILITIES

Some magnetron sputtering systems experience rapid Oscillations in the current and voltage of the plasma discharge after several hours when equipped with certain targets. These oscillations often lead to the pl asma becoming extinguished, a condition known as ''flame-out.'' This a rticle details the study of two 90% W-10% Ti magnetron targets which d iffered in density. The higher density targets sometimes experienced f lame-out after approximately 3 h of sputtering. The less dense materia l could be sputtered for the entire 15 h life of the target. Scanning electron microscopy pictures and atomic composition depth profiles wer e obtained using Auger electron spectroscopy. In addition, a Colutron- based ion source with a high vacuum system was used to measure ion-ind uced secondary electron emission coefficients as a function of energy, ion specie, and gas coverage. Analysis of the sample from the group t hat suffers flame-out showed large regions of pure titanium in the int erior of the sample and higher levels of oxygen contamination. These o xide regions act as insulators in the material which cause the seconda ry electron emission to decrease, the plasma current to drop and the v oltage to rise. The less dense targets had a surface topography which helped overcome these decreases is electron emission. Experiments show ed that an increase in the voltage with respect to the surface signifi cantly increased electron emission, for the less dense targets, counte racting any drops in plasma current.