Method for monitoring bubble formation and abnormal via defects in a spin-on-glass planarization, etchback process

Abstract

A method for monitoring bubble formation in and over a spin-on glass(SOG) layer during the CVD deposition of a superjacent insulative layer is described wherein a monitor wafer is processed either with or without a metal pattern. After a SOG layer has been deposited and cured, a layer of silicon oxide is deposited over it by CVD. If bubbles are formed during the silicon oxide deposition step as a result of out-gassing of the SOG layer, they are entrapped at or near the SOG/silicon oxide interface. The silicon oxide layer is then subjected to a buffered HF etch which exposes the bubbles either by opening them up by eroding the SOG layer underneath the oxide layer or by bringing the surface of the silicon oxide layer closer to the entrapped bubbles, thereby decorating them to make them visible to a white light scanning tool. The monitor wafer is initially scanned just prior to the SOG deposition to obtain a reference scan. A final scan is made after the deposited surface oxide layer has received the buffered HF etch. Bubbles formed over and in an improperly cured SOG layer, occur in clusters that reveal a swirling pattern, reflecting the spin deposition step. The monitor and method of use provides a convenient means for detecting problems with the SOG deposition and curing process, thereby permitting timely remedial action to re-center a deviate process.