A damascene process is used to fabricate a tungsten via through a SiO2 dielectric layer. First the SiO2 dielectric layer is deposited, with a thickness of 1 p.m.
A via hole is etched in the SiO2, and W is blanket deposited by CVD. Right after the W deposition. the Degree of Planarization (DOI;) equals 1.0. and the thickness of the W directly above the dielectric layer is equal to 0.8 µm.
A plasma etch back of the W layer is now done to remove the W that covers the top of the dielectric layer, and leaving the W only in the via hole.
If the etch rate of the W in the etch-back process is 5.0 nm sec;, and the etch selectivity of W with respect to SiO2 is 4:1, what is the profile of the structure after 180 sec of etching? Specify the heights of the W and SiO2 layers in am.
(Neglect any variations in thicknesses or etch rate.)