Frenkel-Poole (FP) trap energies of atomic layer deposited Al2O3 and HfxAlyO thin films with various Hf∕Al compositions have been extracted. Using a method based on the field and temperature dependence of FP conduction, intrinsic trap energies under zero electric field can be extrapolated. Results indicate that FP trap energies increase from 0.56to1.48eV when adding more and more Al to HfO2. The trap energy seems to be inversely proportional to the square of the dielectric constant of the film, suggesting that traps may originate from the same type of defect, whose energy level is mediated by the dielectric constant.

Stress engineering of thin titanium nitride (TiN) films is of considerable importance to the memory industry, where these thin films are free to deform and need to be structurally robust to the deposition of overlying films and processing steps that are a part of the fabrication flow. TiN films in the thickness range of 50 to 100 Å are deposited at 425 °C using atomic layer deposition and are tensile in nature. The as-deposited films are partially surface oxidized due to exposure to atmosphere. The films are subsequently oxidized in an ozone/oxygen ambient at temperatures lower than 275 °C to form a surface oxide layer comprising of titanium dioxide (TiO2) and titanium oxynitride (TiOxNy). Volumetric expansion associated with oxide formation is found to induce compressive stress in the film, while oxidation had the undesirable effect of increasing film resistivity. A dilute hydrofluoric acid solution is used to etch the surface TiO2 layer, while a thin TiOxNy layer remains intact on the film surface. The removal of surface TiO2 results in restoring the resistivity of the films to values comparable to that of as-deposited TiN, while maintaining the compressive stress induced by film oxidation. X-ray photoelectron spectroscopy shows that the processing scheme results in increasing the amount of TiOxNy in the near-surface region of the films. The authors postulate that the higher molar volume TiOxNy layer exerts a compressive force on the underlying TiN film, and prevents a full relaxation of the films to their original tensile stress state. Further, the authors show that by controlling the oxidation conditions, it is possible to modulate the film stress in the range of −750 to +750 MPa. The processing scheme thus allows for stress engineering of thin TiN films at processing temperatures lower than 275 °C.

Low-voltage program/erase (P/E) operations of a NAND-type flash cell have been demonstrated using a multi-layer tunnel barrier. The concept is to achieve low voltage P/E operations similar to a scaled tunnel barrier without compromising retention by exploiting a multi-layer tunnel oxide consisting of a low-k, high-k and low k material. In this study, barrier engineered tunnel oxides of SiO 2 -HfO x -SiO 2 and SiO 2 -ZrO x -SiO 2 were explored using a Metal-Insulator-Nitride-OxideSilicon (MINOS) capacitor with a TiN gate electrode. The device programmed/erased at 16/-22V for 1ms and it had a memory window of 6V. The cell showed less than 2V charge loss after 27 hours when programmed to a 5V initial window. The proposed high-κ tunnel barrier is a promising alternative for tunnel oxide for sub-35 nm NAND Flash technology.Index Terms-High-κ dielectric, NAND Flash cell, tunnel oxide, low voltage programming/erasing.