Solvent Free Post Metal Etch Veil Removal Process Development

Abstract

As the feature size of advanced integrated circuits decrease, it has become necessary for the semiconductor industry to start investigating advanced methods of polymer residual removal. When metal lines shrink to 0.25um and beyond, the switching speed of the device becomes the limiting factor. In order to shrink the dimensions of the metal lines, advanced photo resist technologies such as the use of deep-UV photo resist are used which creates different post metal etch residuals. Residual polymers which are formed during metal etch processing prove to be more difficult to remove with these advanced photo resists. These residuals, commonly known as veils, become increasingly difficult to remove with the conventional wet chemical solvent systems. A new technology has emerged that moves away from wet chemical processing. The objective of this engineering project was to qualify this new technology. The qualification included tool purchase inputs and development of the new process. The Ulvac Enviro was the tool of choice for this process development. The Enviro provides a unique system which combines the chemistry of a very low-bias reactive ion etch and remote microwave plasma and fluorine gases resulting in enhancing the solubility of residues in solvents, acids or de-ionized water. The Enviro not only provides a solution to the removal of the residual polymers it also has a lower cost of ownership and fewer concerns with chemical waste disposal. A two step microwave/RF process was developed using an Enviro. The process consisted of the following gas flows; NF3, N2/H2(5%) and O2. These gases along with the microwave and RF parameters were the significant factors for this deveil process. A balance between fluorination, oxidation and physical ion bombardment was developed using the Enviro system. Corrosion, veil removal and metal line profiles were among the main factors that were measured and compared against a standard wet chemical cleaning process. The experimental work done with this new Enviro process proved to either match or exceed the existing chemical deveil process. The Enviro process actually showed an improved performance over the standard based on corrosion results. The Enviro also provided more than a 50% reduction in wafer processing cost, by completely eliminating the need for solvent processing. As a result it was determined that the Ulvac Enviro can provide an excellent alternative to the conventional chemical deveil process.