Abstract
The degree to which deposited metals cover steps over topography is important to the yield and reliability of devices in very large scale integrations. In evaporated and sputtered films the most difficult steps to cover are those with straight walls. This is especially true with aluminum and its alloys. Via step coverage has been studied as a function of bias sputtering parameters. It was found that 1.3 μm diam, straight-walled vias 1 μm deep, are planarized (100% step coverage) under the same conditions that 60% coverage is achieved in 2.8 μm vias. Unbiased deposition results in only 20% coverage. The effects of target power, bias voltage, and anode voltage on bias current and step coverage were studied. The low power delivered to the substrate under conditions for planarization is not consistent with a mechanism involving backsputtering of aluminum; no significant change in the measured deposition rate was found when bias was introduced. Cross-sectional microscopy suggests a mechanism involving forward scattering of surface atoms at the via edge under bombardment by bias ions.
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