Melt and flow behavior of Al into micron size features using incoherent radiation

Summary form only given. High-aspect-ratio via filling by rapid thermal melting of Al has been achieved, but with two major drawbacks. Pure or 0.5%-Cu-doped Al films 0.5- to 1.5-μm thick were deposited on two types of wafer. Some wafers were patterned with 0.75- to 2-μm-deep windows formed into deposited SiO while others have no topography. The Al films were deposited on 90-nm TiN or TiW layers. TiN, TiW or SiO₂ capping was used on some wafers. By melting Al deposited on several substrates the authors found that molten Al did not wet TiN. The Al balled up and pulled away from the surface. It seemed to wet W:Ti, however, along with a metallurgical reaction between Al, W, and Si resulting in the formation of several alloys of W and Al, as well as W:(Si,Al)₂. Although Al melts at 660°C it did not flow until temperatures above 800°C were achieved. However, even at these temperatures via-filling was not observed in 0.5-μm-thick Al films. The authors found that Al thickness of 1 μm or more was required for filling micron-size vias. The high temperature required for the Al flow which causes junction degradation and the agglomeration of Al film are two severe drawbacks for using the RTA technique in Al planarization