3 September 1998 Resolving localized oxide breakthrough during poly etch of nonvolatile floating gate structures
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Abstract
This paper discusses an unusual series of problems encountered in etching the poly 1 floating gates of an EEPROM device. Such devices feature two levels of polysilicon: a control gate composed of poly 2, and a 'floating gate' which consists of lightly doped poly 1. The failure modes originates as a result of the highly anisotropic nature of floating gate etch recipe, as well as the unusual implant doping scheme used with this particular device. We experienced a significant yield problem involving the definition of the floating gate which resulted in localized 'pitting' of the silicon adjacent to the floating gate structure. This pitting occurred as a result of an unusual behavior mode sometimes exhibited by etchant ions, and it caused the poly 2 control gate to short to the substrate. This short resulted in a byte failure. The initial solution to this problem eliminated the pitting, but introduce dan unintended degeneration of the side-wall profile of the poly 1 floating gate. This new failure modality generated bit failures. This paper presents a detailed description of both failure mechanisms and the sophisticated four-step etch recipe used to eliminate them. As the importance of non-volatile memory to the semiconductor industry increases, these failure modes will become more commonplace, and the solutions presented here of increasing value.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jerry T. Healey, Vibol Sim, Scott E. Rubel, "Resolving localized oxide breakthrough during poly etch of nonvolatile floating gate structures", Proc. SPIE 3507, Process, Equipment, and Materials Control in Integrated Circuit Manufacturing IV, (3 September 1998); doi: 10.1117/12.324362; https://doi.org/10.1117/12.324362
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