Process Reliability Considerations of Planarization with Spin-on-Glass

The paper reports on the process and reliability aspects of double-metal structures with spin-on-glass (SOG) for electronic circuits made by very large scale integration (VLSI) technology. The electrical and physical properties of structures made of metal/CVD oxide + SOG/metal, where both metals are connected by vias which are plasma-etched through the insulator, were investigated using special test structures. Structures with CVD oxide combined with SOG tended to fail in higher percentage than similar structures with only CVD oxide. Two apparent failures, specific to structures with SOG, were investigated: open-circuit during contact continuity test and high-resistivity during contact resistance test. Electrical measurements and Auger electron spectroscopy analysis of plasma-etched multilayer oxide with SOG indicated the formation of a residual amorphous layer containing metal, oxygen, fluorine and carbon. The residual layer formed for structures with CVD oxide and SOG was found to be thicker than that for similar structures with CVD oxide only. These residual layers between the two metals could be removed by argon ion sputtering; otherwise it caused electrical failures.