Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

Abstract

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated. Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation. The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5 , H 2 SO 4 pH = 5 , NaOH pH = 8 , NaOH pH = 10 , NaOH pH = 12 , deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H 2 SO 4 pH = 3 at 50°C and HCl pH = 2 , H 2 SO 4 pH = 3 , and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5 , NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H 2 SO 4 pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H 2 SO 4 pH = 2 , H 2 SO 4 pH = 5 , NaOH pH = 10 , NaOH pH = 12 , citric acid, Micro-90 and deionized water at 50 °C and HCl pH = 3 , H 2 SO 4 pH = 5 , NaOH pH = 8 , NaOH pH = 10 , NaOH pH = 12 , Micro-90 and Alfred tap water at 90°C.