Thereafter, a low temperature baking or curing, such as below 400??? C., is performed on the insulating layer 210 for 30???60 min. [0018] Next, in FIG. 2d, after the low temperature baking, an optional polish process, such as chemical mechanical polishing (CMP), is performed on the SOG layer 210 using the pad nitride layer 204 as a etch stop layer.