Polarization and Charge Motion in Metal-Al[sub 2]O[sub 3]-SiO[sub 2]-Si Structures

Abstract

An investigation of the flatband voltage shifts of double insulator (A1203-SiO2) MIS capacitors under bias temperature stress has been performed in order to assess and characterize the stability of double insulator IGFET's. These shifts were opposite to the applied bias voltage ("ionic" direction), and it was found that they are composed of two components: (a) A "fast" component which is linear with gate bias voltage and symmetric with bias polarity. Most of the shift occurs in less than 1 rain at all temperatures used in this work (65~176 Its magnitude is temperature activated (0.15 eV). This part of the flatband voltage shift is explained by a bulk polarization of the A1203 layer with a polarizability that is independent of A1203 thickness. (b) A "slow" component which is observed under positive bias. It is characterized by a linear dependence of flatband voltage shift on the logarithm of stress time for times larger than a delay time, which is thermally activated (1.2 eV). This component is interpreted to be due to motion of mobile, ionic charge, such as sodium, across the A1203 and SiO2 layers. This charge motion is greatly reduced by increasing the A1203 thickness.A low threshold voltage p-channel MIS (metalinsulator-semiconductor) technology in which a double dielectric sandwich of 1000A of SiO2 and 500A of A120~ is used as the gate insulator (1,2) has received considerable interest in the past. Devices made with this gate structure and a Ti-Pd-Au metallization (3, 4) have a nominal threshold voltage of --1.0V if a 10 ohm-cm, <100>, n-type silicon substrate is used.One of the advantages of this technology is the excellent threshold voltage control and the inherently good stability of the threshold voltage under bias-temperature (BT) stress conditions.A discussion of control of the initial threshold voltage is given by Clemens and Labuda (5). The question whether the inherently stable devices show any residual threshold voltage shifts during their operating life has been treated by Lampi and Labuda (6) who performed a reliability study by bias temperature aging discrete MIS transistors. They found that under negative gate bias two apparently independent types of drifts can cause small threshold voltage shifts. One is a rapid drift which shifts the threshold voltage to more positive values, and the other one is a long term drift which shifts the threshold voltage to more negative values. The latter type, referred to as "slow trapping," was shown because of its large activation energy to be negligible at normal operating temperatures and biases and can be neglected for most applications. The first type is potentially more important because it occurs at lower temperatures and in shorter times. On the basis of experimental evidence it can be interpreted to be due to polarization of the A1203 layer and charge motion across the insulator structure (7). The purpose of this work is to investigate and characterize this rapid initial threshold voltage shift for both negative and positive bias and to evaluate its effec...

Characterization of Silicon Nitride and Silicon Carbonitride Layers from 1,1,3,3,5,5‐Hexamethylcyclotrisilazane Plasmas

“…6 (dashed curve). The directional dependence of the C-V curve shifts is typical of either bulk polarization instabilities or mobile ionic (H § or Na +) charge (49,51), while the distortion and hysteretic behavior is attributable to either fast surface states near the conduction band at the silicon interface (49,52) and/or to a nonuniform lateral distribution of mo- bile ionic charge (53,54). The interface states are probably related to C and Si dangling bonds in the silicon nitride film.…”

Passivation Coatings on Silicon Devices

“…In some high-reliability devices, silicon nitride (Si3N4), which serves as both a getter and an effective alkali barrier (322,65,100,41), is applied over the thermally grown SiO2 prior to metallization. Aluminum oxide (A12Q), which is also an alkali ion barrier (329,330), has been ,used in some MOS devices (49,174,105). Examples of devices with ion barriers inc]ude nitride-passivated bipolar devices (195,279), beam-lead sealed-junction devices (279,239), and MNOS devices (262).…”