<title>Time reduction of MCM-D prototype realization by process control and modeling</title>

Abstract

The evolution of advanced packaging techniques like Multi Chip Modules makes the realization of prototypes necessary. This can be a long and costly operation. Therefore we developed methods permitting time gains to be made in two of the steps of this operation. To avoid the use of physical masks we have experimented a laser beam set for direct writing of metal and insulating layers in microcircuits. To shorten preliminary tests, we propose a theoretical model of the interaction between the laser beam and the photoresist. It permits to predict the line widths etched in the photoresist and thus avoids the need oflong calibration processes. Electrical test lines of various widths have been used as a validation tool. The precision obtained is better than 5%. Polyimides (P1) meet most of the requirements for dielectric materials. As the curing process is crucial for the properties of the final P1 film, thermal treatment was subject of optimization leading however to process times up to more than 4 hours. We developed an interferometric control system in combination with a hot plate, in order to provide an automated and optimized curing process. Total curing time is reduced to 1-2 hours. Characterization and FTIR measurements were done for conventional and interferometrically controlled curing samples before and after aging in wet atmosphere: controlled samples are more crystalline, show comparable electrical and reliability properties, and seem less stressed.