A.B. Joshi

Thickness uniformity and electrical properties of ultrathin gate oxides grown in N2O ambient by rapid thermal processing

Thickness uniformity of ultrathin (30–100 A) dielectric films grown on 4 in. silicon wafers in pure N2O ambient using a specially designed rapid thermal process reactor is studied. Excellent thickness uniformity in terms of percentage standard deviation (≤5%) is observed. Metal‐oxide‐semiconductor capacitors with these thin (∼100 A) dielectrics have been fabricated. Results show that N2O oxides exhibit comparable interface state density and slightly larger breakdown field, but significantly reduced interface state generation and charge trapping under constant current stressing compared to oxides grown in pure O2.

A comparison of radiation and hot-electron-induced damages in MOS capacitors with rapid thermally nitrided thin-gate oxides

Abstract We report an investigation of the degradation caused by ionizing radiation exposure and Fowler-Nordheim current injection in MOS capacitors with rapid thermally nitrided thin-gate oxides. The effect of nitridation conditions on the extent of the degradation was studied. It was observed that the damage caused by ionizing radiation and constant-current stressing are strongly dependent on the nitridation temperature and duration. Also, this dependence is different for the two cases. These observations are explained using some defect generation models and structural changes in oxide due to nitridation.

Mechanism of rapid thermal nitridation of thin oxides

The nitrogen/oxygen replacement reaction which occurs during rapid thermal nitridation (RTN) of oxides has been investigated by Auger electron spectroscopy and Fourier transform infrared spectroscopy techniques. Results have indicated that out‐diffusion rate of nitridation by‐products is responsible for the observed nitrogen profile in RTN oxides. Based on the results, an attempt has been made to describe the mechanism of the nitridation reaction. The proposed mechanism considers the diffusion of NHx species and nitridation by‐products along with the structural modifications in SiO2 during RTN. Electrical measurements on metal‐oxide‐semiconductor capacitors were used to further support the proposed mechanism for the nitridation process.

Chemically modified ultrathin oxides fabricated by rapid thermal processing

A comprehensive review of chemical composition and electrical properties is presented for thin gate oxides with small amounts of nitrogen or fluorine, incorporated by rapid thermal processing. Electrical properties of these chemically modified oxides are correlated with the changes in chemical composition and the resulting structural modifications. Qualitative models described in some of the earlier works are used to establish these correlations. It is concluded that the changes in chemical composition of Si02 can be controlled to realize superior gate dielectrics for application in ULSI MOS devices.

Performance and reliability of ultrathin reoxidized nitrided oxides fabricated by rapid thermal processing

In this paper we report a systematic and comprehensive study of the chemical and electrical properties of rapid thermally nitrided (RTN) and reoxidized nitrided (RTO) thin oxides and reliability of MOSFETs with these materials as gate dielectrics. The chemical properties of the RTN oxides are studied using AES and VFIR techniques. The nitridation mechanism is discussed and a model is proposed to explain the widely reported nitrogen and oxygen distribution in RTN oxides. Electrical properties of RTN oxides such as dielectric constant conduction mechanism fixed charge and interface state density charge trapping and hot electron and radiation hardness are investigated and are correlated with their chemical characteristics. Post nitridation anneals were performed on the nitrided oxides in 02 d N2 ambients. Charge trapping and hot electron and radiation hardness of the resulting films are studied and compared. Finally the MOSFETs with reoxidized nitrided oxides as gate dielectrics are fabricated and their performance and reliability are studied. 1.

High Quality Ultra-Thin Tunneling N2O Oxides Fabricated by Rtp

In this paper, a detailed reliability investigation is presented for ultra-thin tunneling (∼50 A) oxides grown in N 2 O ambient using rapid thermal processing (RTP). These N 2 Oss-oxides are compared with oxides of identical thickness grown in O 2 ambient by RTP. The reliability investigations include time-dependent dielectric breakdown as well as stress-induced leakage current in MOS capacitors with these gate dielectrics. Results show that ultra-thin N 2 O-oxides show much improved reliability as compared to oxide grown in O 2 ambient.

Comparison of -MOSFET lifetime estimates based on GIDL enhancement and transconductance degradation as criteria

Abstract A comparison of MOSFET lifetimes based on gate-induced drain leakage (GIDL) enhancement and transconductance degradation as criteria is presented. Analysis of damage mechanisms indicates that degradations related to interface state generation limit the MOSFET lifetime at reduced voltage operations. In conventional gate oxide MOSFETs, GIDL enhancement due to band-to-defect tunneling and transconductance degradation limit the lifetime at reduced voltage. For MOSFETs with reoxidized nitrided gate oxides, our results show that GIDL enhancement due to band-to-defect tunneling is a better reliability monitor than transconductance degradation at low operating voltages.

Time‐dependent breakdown of oxynitride gate dielectrics under unipolar ac stress

Time‐dependent dielectric breakdown under unipolar ac stress is investigated for control, nitrided, and reoxidized nitrided oxides, prepared by rapid thermal processing. All these gate dielectrics show longer time‐to‐breakdown under ac stress compared to constant voltage stress. Nevertheless, the extent of retardation of breakdown under ac stress is observed to be minimum for nitrided oxides and maximum for reoxidized nitrided oxides. Differences in detrapping behavior in these gate dielectrics are used to explain different improvement factors for breakdown under ac stress.