Charge decay characteristics of silicon-oxide-nitride-oxide-silicon structure at elevated temperatures and extraction of the nitride trap density distribution

Abstract

We investigated the charge decay characteristics of a silicon-oxide-nitride-oxide-silicon type nonvolatile memory at elevated temperatures. Based on the amphoteric trap model and the thermal emission model of the trapped charge, we propose an advanced charge decay model which includes the effect of the bottom oxide, and apply it to extraction of the trap density distribution in energy levels of the nitride layer. The samples prepared have nitride films deposited simultaneously and are classified into two groups according to the thickness of the bottom oxide. The trap density distributions extracted from two groups showed good consistency.

Dependence of Electrons Loss Behavior on the Nitride Thickness and Temperature for Charge Trap Flash Memory Applications

“…Also, a reasonable nitride thickness range was obtained through electrical characteristic measurements. Four charge loss mechanisms [11,12] are involved in the data retention state for scaled CTF memory devices: trapped electrons tunnel from traps to the silicon conduction band (T-B), trapped electrons tunnel from traps to the Si/SiO 2 interface traps state (T-T), holes tunnel from the silicon valence band to nitride traps (B-T) and thermal excited trapped electrons from the traps to the nitride conduction band followed by tunneling through the tunnel oxide (T-E), as shown in Fig. 1.…”

Charge loss behavior of a metal-alumina-nitride-oxide-silicon-type flash memory cell with different levels of charge injection

“…4͑b͔͒. 2,8 However, it should be noted that the fixed charge in Al 2 O 3 , 13 the Si 3 N 4 / Al 2 O 3 interfacial layer, 9 and the physical location of X c ͑Refs. 1 and 12͒ could be responsible for different banding bending of the TPO and BTO.…”

“…According to Kim et al 2 and Tzeng and Gwo, 8 the tunneling rate of thermal emission followed by oxide tunneling ͑e th e ox ͒ can be written as tunneling rate = 1/e ox e th = 1/e ox,0 AT 2…”

“…6 Recently, electron detrapping via thermal emission and subsequent oxide tunneling was proposed as a possible charge loss mechanism. 2,5,8 However, it is still difficult to determine the direction of the charge loss path. Unlike program and erase operations, the state of the device during retention is completely different in terms of the electric field.…”

“…[1][2][3][4][5][6][7] Among the possible charge loss mechanisms in silicon-oxide-nitride-oxide-silicon-type flash memory devices with a thin bottom oxide ͑Ͻ3 nm, BTO͒, several authors have reported both direct tunneling across the BTO and thermal emission as the main charge loss mechanisms. 4,7 However, since a high-k material ͑i.e., Al 2 O 3 ͒ was used as a top oxide ͑TPO͒, the charge loss through the BTO could be negligible due to a thicker BTO.…”