Deposition of copper by using self-sputtering

A magnetron sputtering source using sustained self-sputtering has been developed for uniform deposition of copper on large wafers (200 mm in diameter). Usually, Ar gas is used in sputter deposition. In sustained self-sputtering, no Ar gas was used for deposition, the sputtered Cu atoms were ionized in the magnetron plasma, and some Cu ions were accelerated to sputter more Cu atoms out of the target. In this work, the magnetron was optimized to allow sustained self-sputter deposition of Cu on 200 mm wafers with: reasonable power (9-12 kW). When sputtering a target of 325 mm in diameter, the minimum power density to sustain plasma without using Ar gas was found to be 10.8 W/cm(2). This was much lower than the threshold power density reported in the literature. A chamber employing a large spacing between the target and wafer (16 cm) was used. The resulting deposition rate was about 320 nm/min, when a 12 kW of de power was applied. The standard deviation in film thickness was less than 2.5% in our limited experiments. The pressure during sputtering was less than 4 x 10(-4) Pa. In comparison with Ar sputtering at an Ar pressure of 0.13 Pa, the bottom coverage, defined by the ratio of film thickness on the trench bottom to the film thickness on the open field area, was increased by about 20% by using sustained self-sputtering. The bottom coverage can be further increased when the throw distance is increased. However, we did not observe significant enhancement of bottom coverage by applying de and rf biases to the wafer during sustained self-sputtering, although about 20% of Cu species arriving at the wafers was ionized. (C) 1999 American Vacuum Society. [S0734-2101(99)10905-9].