Analysis of oxide bulk trapped charge distribution and densities from photo injection characteristics of oxide-nitride-oxide (ONO) structures
The thickness of ONO inter-poly dielectrics dominates the program and erase speed of a flash memory cell transistor with a stack gate structure. Therefore, as flash devices shrink, it is important to prevent the degradation in reliability while scaling down the thickness of the oxide. However, the thickness of the bottom oxide formed on a heavily doped poly-silicon cannot be easily reduced because of its high defect density due to a high concentration of dopants in the floating gate and an enhancement of the oxide thickness caused by oxidation of the doped polysilicon [1]. In order to overcome these problems, advanced LPCVD technology has been introduced, but the LPCVD oxide films still have many defect densities in comparison with thermal oxide films. In this work, the bulk trapped charges distribution and density in the bottom LPCVD oxide were quantitatively investigated by photocurrent-voltage characteristics. In addition, we found that the defect density and distribution in the bottom LPCVD oxide were remarkably decreased using post plasma oxidation.
Determination of insulator bulk trapped charge densities and centroids from photocurrent‐voltage charactersitcs of MOS structures
A new rapid technique for determining the density and centroid of trapped space charge in MOS structures is described. Photocurrent‐voltage characteristics for both the metal‐oxide and Si‐oxide interfaces are used to determine the internal fields due to bulk trapped charge and, hence, its density and centroid. An experimental example of this technique is shown for a MOWOS (metal‐SiO2‐W‐SiO2‐Si) structure where a layer of approximately 1014 W atoms/cm2 deposited 80 or 42 A from the Si‐SiO2 interface and charged by internal photoemission is investigated. This technique is compared to others in terms of its direct, rapid, minimally perturbing, low‐current and low‐field characteristics.
Photocurent spectroscopy in thin-film insulators: Voltage dependence of the external-circuit current
Abstract : An analytical model for trapping state photodepopulation measurements in conductor-thin film insulator-conductor structures is presented. The external circuit current dependence on applied voltage is determined, and it is shown that moments of the spatial distribution of trapped charge in the insulator can be extracted from collected charge vs. applied field characteristic curves. The photodepopulation technique is compared with more widely used differential capacitance and photoemission current techniques.