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There are several planarization techniques used in wafer fabrication. There are two categories for planarization techniques, namely, local planarization and global planarization. Local planarization refers to smoothing techniques that increase planarity over small areas. Global planarization consist of techniques that decrease long-range variations in wafer surface topology, especially those that occur over the entire image field of the stepper. Planarization techniques include: • oxidation; • chemical etching; • taper control by ion implant damage; • deposition of films of low-melting point glass; • resputtering of deposited films to smooth them out; • use of polyimide films; • use of resins and low-viscosity liquid epoxies; • use of spin-on glass materials; • sacrificial etch-back; and • mechanical-chemical polishing of the wafer.

Contacts are then formed on the base diffusions. Ion-implanted resistors are suited for low-power digital and linear circuits because of their high sheet resistance. Thin-film resistors offer high precision and stability. They are fabricated by vacuum evaporation or sputtering of thin films of resistive materials directly on the substrate oxide layer. Materials used for thinfilm resistors include nichrome, sichrome, and a variety of refractory silicides. These materials exhibit good adhesion on the oxide as thin films, and are usually built with a film thickness of about 10nm to 100 nm.

The chamber is heated and taken to a low pressure, and then filled with a positively charged plasma of the reactive gas. The opposing electrical charges cause the rapidly moving plasma molecules to align themselves and strike the wafer surface vertically, thereby reacting with and volatizing the exposed metal layer. 10. v. Alloying and Annealing. After the metallised interconnections have been deposited and etched, a final step of alloying and annealing may be performed. To perform alloying, the metallised substrate is placed in a low-temperature diffusion furnace.