I have a 740 nm thick metal stack with TiN as the topmost layer (the TiN is an anti-reflective coating layer) sitting on top of a bare Si wafer. The 1500 nm spin-on-glass (SOG) covers the entirety of the wafer acting as a planarizer. I need to etch-back the SOG to a height of 740 nm without etching the TiN. The gas mixture to be used is CF4/CHF3/O2/Ar. But, the problem is this gas mixture would also etch TiN. Is there any way I can use the same mixture but avoid etching the TiN?

I have attached the datasheet for the SOG if needed.