Single bit electrically erasable programmable read only memory fails: inline charge monitors for screening plasma damaged tunnel oxides
Gopalakrishna, Amit Kumbasi
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The purpose of this thesis is to inspect single-bit fails in electrically erasable programmable read-only memories (EEPROM). Single-bit fails is a failure mechanism in which data stored in the memory cell is lost. One or more bit lines have a cell that program to the required threshold voltage of a written cell whereas rest of the written cells in that line have a higher threshold value due to leakage of the data stored. However the data is not completely lost. Since Gate Oxide Integrity (GOI) is considered to be the source of data-retention problem of the memory, this thesis examines tunnel oxide and the process used in manufacturing EEPROM. The solution is to develop an in-line charge monitor that can screen the tunnel oxide at various stages in the process flow. The idea behind the thesis is to identify the damage to the tunnel oxide early in the flow so that further processing of the leaky oxide can be stopped thereby saving money. The first chapter, Semiconductor Memories, gives a brief introduction to different kind of memories available in the market and their evolution. Also working of different classification of memories is discussed. Chapter two, Non-Volatile Semiconductor Memory, gives an introduction on nonvolatile memory as EEPROM belongs to this family of memories. Various storage mechanisms, layout and physics of EEPROM are taken up. Failure modes in EEPROM and degradation mechanism are discussed in chapter three. Failure modes in EEPROM. Since plasma is considered to be the source for degradation of tunnel oxide, plasma physics and charging in plasma is discussed. Chapter four, Experimental approach - Charge Monitors, will include the design, process flow of the in-line monitor. The testing of the wafers followed by qualitative interpretation of the leakage curves is included in chapter five, Results and discussion. The quantitative analysis marks the end of this chapter. A physical model is developed for the charging of the antennas in chapter six, CONCLUSION AND FUTURE WORK which is followed by the future course of work.