Selective resputtering of bismuth in sputtered Bi-Sr-Ca-Cu-O films

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Abstract
We present studies using a dc magnetron in an on‐axis configuration to sputter Bi‐Sr‐Ca‐Cu‐O films from a composite target. These studies show that bismuth can be preferentially resputtered. The influence of ozone, molecular oxygen, and total pressure on the resputtering of bismuth is investigated and discussed. Ozone, in low concentrations, can dramatically affect the degree of resputtering. By comparing the effects of molecular oxygen and ozone, some insight is gained regarding the possible mechanisms of negative ion formation in the magnetron environment. Based on our results we suggest that molecular oxygen can bring about resputtering primarily by forming O+2, which collides with the target to produce energetic negative oxygen ions. In contrast, ozone may form negative ions by electron impact in the dark space above the target, giving rise to lower‐energy negative ions, which can traverse the plasma unneutralized and can be stopped with an applied bias on the sample block. With no added oxidant, negative oxygen ions from the target oxygen may dominate the background resputtering. Similarity is found between our results and those for similar studies on Y‐Ba‐Cu‐O by other workers. Bismuth in Bi‐Sr‐Ca‐Cu‐O behaves as barium in Y‐Ba‐Cu‐O with regards to preferential resputtering; furthermore, the response of strontium, calcium, and copper to oxygen in sputtered Bi‐Sr‐Ca‐Cu‐O is similar to what is observed for copper in Y‐Ba‐Cu‐O.