phosphosilicate glass deposited by chemical vapor deposition cvd the second layer was silicon dioxide deposited by cvd from teos the combined thickness of the two layers was approximately 900 nm then a photoresist layer not shown was deposited and patterned photolithographically to define a via 464 in some embodiments the mask opening defining the via was round in top view with a diameter of 0 18 u03bcm the via was formed in layer 110 with a plasma etch the photoresist was removed and another layer of photoresist not shown was deposited and patterned photolithographically to define a trench 470 in dielectric 110 for a tungsten interconnect the length of the trench was normally at least 2 u03bcm in some embodiments the trench length was approximately 1 mm the trench width was then 0 22 u03bcm the trench was etched with a timed etch to a depth of approximately 250 nm via 464 was fully exposed at the bottom of the trench then the top surface of the structure was exposed to rf plasma in argon atmosphere for 10 seconds the argon flow was 5 sccm standard cubic centimeters per minute the rf power was 315 w this operation removed native oxide from layer 120 also this operation smoothened rounded top edges 480 of trench 470 and via 464 i e the respective perimetrical top edges formed by the perimeters of trench 470 and via 464 along the surfaces into which they extend the rounded perimetrical top edges are desirable to reduce stress in titanium nitride 150 fig5 at these edges so as to reduce the risk of volcano formation the rf plasma operation was performed in a system of type endura available from applied materials of santa clara calif.