Reliability considerations in sealed SONOS nonvolatile memory devices

The memory characteristics and reliability of a SONGS nonvolatile memory device are determined, to a large extent, by the charge transport and trapping properties of its storage nitride film. In this payer we investigate carrier trapping phenomenon in a scaled SONGS transistor with an effective gate oxide thickness of 94 and a nit-ride storage layer deposited with LPCVD at 680 degrees C, Atomic Force Microscopy (AFM) has been employed to examine the surface quality of deposited nitride films. We have found that nitride film deposited at 680 degrees C shows the lowest surface roughness, as compared to the films formed at 725C and 650 degrees C. With a charge separation technique, we have demonstrated that the charge centroid is deep into the nitride layer at low injection levels and moves towards the center of the film as the injection level is increased. From our measurement, a trap density of 1.7 x 10(19) cm(-3) in the nitride has been determined. Devices with nitride (2.1 Angstrom RMS roughness) deposited at 680 degrees C show less degradation in data retention with respect to erase/write cycling when compared to devices with nitride (2.9 Angstrom RMS roughness) deposited at 725 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.