Time-dependent positive charge generation in very thin silicon oxide dielectrics

Abstract

We have studied the rate at which positive charge is generated starting near the oxide-silicon interface when electrons are injected from the gate through the very thin oxide layer in metal-oxide-(p)silicon tunnel diodes. By varying the oxide thickness, we find that the charging rate is not strongly controlled by the flux of tunneling electrons over a five order of magnitude range in current density. This implies that if the tunneling electrons do participate, then the charge generation in these oxides is at least a two-step process. A comparison of charge generation in aluminum and polycrystalline silicon gate devices suggests that the process does not involve aluminum-related defects. Measurements of the charging rate versus temperature, T, show that it is weakly dependent on T below 150–200 K and apparently thermally activated above this temperature range.

Oxide Wearout, Breakdown, and Reliability

“…This dependence is needed when using trap generation data and statistical models to calculate the TDDB distributions for different oxide thicknesses and fields [48,49,562,697,698]. The time dependence of trap generation has been reported by several workers [48,506,530,588,605,621,[700][701][702][703]. In general, the trap generation rate is fast initially and becomes slower as the density of traps increases, in agreement with a model of trap generation based on breaking the bridging oxygen bond, as described in Figures 21 and 22.…”

Improved charge injection in Si nanocrystal non-volatile memories

“…The idea of having a metal-insulator-semiconductor structure with Si nanocrystals (Si-nc) as a charge storage elements embedded in the insulator has become very attractive for several reasons: (i) the non-continuity of the layer prevents from charge loss through lateral paths; (ii) it shows small writing times at lower injection voltages; (iii) long retention times; (iv) reliability is improved as charge is injected by direct tunnel and (v) it shows inherent scalability even down to single electron devices [2].…”

Charge storage in Si nanocrystals embedded in SiO 2 with enhanced C-AFM

“…Therefore, tunnel oxide thickness can be further scaled down and, consequently, charge can be injected by direct tunneling instead of by hot carriers, leading to a reduction of the degradation of the dielectric properties of the oxide. Other advantages related to the decrease of the tunneling oxide thickness are the use of smaller programming voltages (reducing the power consumption), a significant increase of the writing/erasure speed (in the µs range [4]), an easy integration to silicon technology and inherent scalability even down to single electron devices [8].…”

“…Si-nc are fabricated using various deposition techniques [1,8] or ion implantation and annealing [9]. The main challenge is producing nanocrystals close enough to the channel without compromising the integrity of the gate oxide and the quality of the interface with the substrate.…”