The evolution of hydrogen from plastic molding compound and it's effect on the yield and reliability of ferroelectric memories

Abstract

Degraded performance and reduced yields of semiconductor devices have been attributed to gaseous microcontamination during wafer processing. In particular, hydrogen contamination can degrade the performance of both Si and GaAs-based devices. Hydrogen is therefore maintained at concentrations below 10 ppb (parts-per-billion) in all UHP gases supplied to process tools. When compared to wafer processing, microcontamination-related yield losses during back-end processing are relatively unknown. Plastic packaging assembly is one of the more likely back-end processes leading to yield loss based on the elevated temperature and chemical exposure of the die during molding. Such yield losses are known to occur in the manufacture of ferroelectric memory devices and have potentially been attributed to: (1) thermal budget, (2) stress, and (3) thin film reduction by hydrogen. Thermal bakes at temperatures below the Curie point degrade the ferroelectric capacitor as a result of relaxation and aging. Stress from the assembly and molding process can also degrade the capacitors by altering the tetragonality of the perovskite lattice. Hydrogen can chemically reduce the ferroelectric film and destroy the adhesion between the ferroelectric and the electrode. This study focuses on determining the hydrogen evolved from plastic packaging materials during molding and past mold cure and its effect on the yield and retention reliability of ferroelectric memory devices.