Abstract
In this dissertation, we propose a new VALFCP (variable amplitude low-frequency charge pumping) technique to characterize the nitride trap energy and spatial distributions in Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) flash memory cells. Besides, the VALFCP technique is utilized to investigate effects of P/E cycles on nitride/oxide trap properties. We also study the effects of dopant fluctuation on SONOS cell retention by using 2D TCAD simulations. In chapter 2, we propose a new VALFCP technique including a modified charge pumping measurement methodology and a generalized numerical model, which allows extracting the spatial and energy trap distributions from the charge pumping data. A numerical model based on Shockley-Read-Hall-like electron tunneling capture is used to correlate a charge pumping current with nitride trap energy and position. By changing frequency and pulse amplitude in charge pumping measurement, a nitride trap density as a function of trap position and energy can be extracted. In chapter 3, influences of program/erase (P/E) cycles on the defect generation in a SONOS flash memory cell are studied by using the VALFCP technique. We observe that P/E cycles would generate new oxide and nitride traps, and degraded cell retention is observed. Besides, the increase of oxide and nitride trap densities follows a power law behavior as a function of P/E cycles. We also observe that these stress-created oxide and nitride traps are unstable and will be eliminated rapidly during high temperature storage. In chapter 4, the effects of discrete dopant fluctuation in sub-45-nm SONOS flash memory cells are studied. In addition to the well-known fluctuation in threshold voltage, the wide threshold voltage distribution also affects cell retention, which results in a severe reliability problem in planar SONOS flash memory cells beyond the 22 nm generation. Similar discrete dopant effects are observed in the fin field-effect transistor (FinFET) structure. The FinFET SONOS flash memory cell having a nearly un-doped channel is shown to be promising for sub-22-nm SONOS technologies.