Copper and copper alloy thin films: Evolution of resistivity and microstructure.

摘要

The impact of eleven alloying elements, at two nominal concentrations of 1.0 and 3.0 at%, on the grain structure, texture and resistivity of Cu was investigated. The alloying elements were Mg, Ti, In, Sri, Al, Ag, Co, Ir, Nb, W and B. The films were electron beam evaporated onto oxidized silicon wafers and had thicknesses in the range of 420 to 560 run. The ex situ annealing treatments were done at 400, 650 and 950°C. The temperature range for the in situ studies was 100 to 950°C. In the as-deposited state, the alloy films had a higher resistivity, a significantly finer grain size, and a weaker texture when compared to pure Cu. With some exceptions, ex situ annealing reduced the resistivity and strengthened the texture. In addition, it was found that the higher the annealing temperature, the lower the resistivity and the stronger the 111> component of the fiber texture. Apart from the two Co-containing films, the 400°C, 5 hr annealed alloy films had smaller grain sizes than the pure Cu film, and, additionally, the grain sizes for the nominally 3.0 at% films were smaller than those for the nominally 1.0 at% films. The ex situ and in situ studies showed a clear inverse correlation such that the higher the in situ grain growth temperature, the lower the grain size after the ex situ 400°C, 5 hr anneal. By contrast, the strength of texture after this anneal showed a direct correlation with the grain size. The notable exceptions, for which grain size and texture did not correlate, were Cu(1.0Nb) and Cu(2.4Nb). For the 400°C, 5 hr annealed films, Cu(0.4B) and Cu(1.0Ag) had the lowest resistivities at 2.0 and 2.1μΩ-cm, respectively, Cu(2.8Co) showed the largest average grain size at 1080 nm, and Cu(3.0Ti) had the strongest 111> fiber texture at 94.2 vol%. The resistivity, grain size and 111> vol% for the pure Cu film after the same anneal were 2.0μΩ-cm, 790 nm and 59.8, respectively. No alloy film simultaneously satisfied the requirements of a low resistivity, and a larger grain size and a stronger texture than pure Cu.