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CPU evolution in performancelcost continues to drive the packaging technology. The limitations of wire bonded interconnects and traditional C4ICeramic flip chip have resulted in development of a new paradigm for CPU packaging involving area array solder bump connections to a high density organic multi layer LGA package. This paper describes some of the key reasons behind this transition. It introduces the key aspects of the new assembly process architecture, associated process flows and key yieldreliability issues addressed during the development.

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The gate bias polarity dependence of charge trapping and time-dependent dielectric breakdown (TDDB) in nitrided and reoxidized nitrided silicon dioxides prepared by rapid thermal processing (RTP) is reported here for the first time. Charge trapping during high-field injection can be reduced by rapid thermal nitridation for both substrate and gate injection. Whie reoxidation of nitrided oxides shows further reduction in charge trapping for substrate injection, degradation is observed for gate injection. Similar effects are observed for TDDB: reoxidized nitrided oxides show charge-to-breakdown in excess of 300 C/ cm2 for substrate injection, but 'less than 30 C/cm2 for gate injection. These effects are related to the nitrogen and hydrogen profiies in the oxides.

A new model for explaining the initial rapid oxidation of silicon in dry oxygen has been proposed. Creation of an oxygen-diffused zone near the Si-SiO2 interface is postulated. Our model takes into account the heretofore ignored phenomenon of diffusion of oxidizing species into the silicon substrate during initial exposure to such species. This occurs because of the low diffusion resistance offered by the ultrathin oxide films to the oxidizing species. The oxidizing species diffuses in such large amounts that not all of it is consumed at the Si-SiO2 interface; instead, a part of it diffuses into the substrate creating an oxygen-diffused zone in silicon. The reaction occurs over this zone instead of occurring just at the interface. As the oxide thickness builds up, the concentration of the oxidizing species at the Si-SiO2 interface decreases due to the increase in the diffusion resistance offered by the growing oxide film. Once the oxide becomes sufficiently thick all of the oxidizing species reaching the Si-SiO2 interface is consumed by the reaction at the interface, and the zone disappears. The occurrence of the reaction over a zone instead of occurring at the interface alone leads to an enhancement in the oxidation rate in the ultrathin-film regime. This enhancement has been formulated, and new oxide thickness-time relationships have been derived. This model explains all phenomena observed in silicon oxidation, and the Deal-Grove model is found to be a special case at larger thicknesses.