Selective Chromate Conversion of Integrated Circuit Interconnecting Aluminization

The extremely small size of semiconductor integrated circuits introduces microanalytical problems not normally encountered. E. A. Corl1 at the 1964 Physics of Failure Symposium described an anion reaction for failure analysis of microcircuits. A similar non-destructive chemical process, chromate conversion of the interconnecting aluminization, has been stuided. The process will react selectively producing striking contrasts in the color of the aluminization. A number of factors both in the solution and the integrated circuit itself were found to influence the reaction rate. By the proper application and technique, chromate conversion can be used to locate sites of surface defects and attendant electrical failure. Variations and contrasts in the characteristic brown color will show whether an area is P or N, the relative doping level, areas of high Al2O3 concentration, the presence of pinholes in the oxide under the aluminum, breaks in the aluminum, and containants on the surface. The advantages of the process are simplicity, economy, sharp variations in color, and it is non-destructive. Compositions of the various solutions and the pertinent reaction parameters are described. A study of a number of factors within the integrated circuit affecting the reaction was also made. A proposed reaction mechanism is discussed. The process appears to have great utility as an analytical tool. It may also have an application as a process step for the protection of aluminum against oxidation and mechanical damage.