NH3 Nitridation Research Articles

Electrical Characteristics of TaOxNy for High-k MOS Gate Dielectric Applications

ABSTRACTIn this paper, we report a process for the preparation of high quality amorphous tantalum oxynitride (TaOxNy) via ammonia annealing of Ta2O5 followed by wet reoxidation for use in gate dielectric applications. Compared with tantalum oxide(Ta2O5), a significant improvement in the dielectric constant was obtained by the ammonia treatment followed by light reoxidation in a wet ambient. We confirmed nitrogen incorporation in the tantalum oxynitride (TaOxNy) by Auger Electron Spectroscopy. By optimizing the nitridation and reoxidation process, we obtained an equivalent oxide thickness of less than 1.6nm and a leakage current of less than 10mA/cm2 at -1.5V. Compared with NH3 nitridation, nitridation of Ta2O5 in ND3 improve charge trapping and charge-to-breakdown characteristics of tantalum oxynitride.

Dopant Diffusion in Silicon Substrate during Oxynitride Process

AbstractWe found an anomalous behavior of dopant diffusion in Si substrate during the oxynitride process. SIMS measurements showed a notably enhanced diffusion during the NO and N2O oxynitride process. The considerably enhanced diffusion was also observed in re-oxidation of oxynitride film grown by the NO annealing or NH3 nitridation of a SiO2 film. In order to simulate the enhanced diffusion, an enhancement coefficient was introduced, showing that the simulation results are in reasonable agreement with the experimental ones. We applied the diffusion model to the simulations of MOSFETs fabricated under various conditions of the oxynitride process. The device characteristics of MOSFETs were successfully reproduced by adopting a suitable dependence of nitrogen concentration CN on the surface recombination rate of interstitial Si at the oxynitride/Si substrate interface.

The effects of thermal nitridation and reoxidation on the interfacial stress and structure of silicon dioxide gate dielectrics

Electron spin resonance spectroscopy is used to study the effects of thermal NH3 nitridation and subsequent reoxidation on the structure of the dielectric/silicon interface. This is accomplished by study of the Pb center, an interfacial point defect. The values of g⊥ in Pb spectra observed in the nitrided oxide and reoxidized nitrided oxide systems differ from Si/SiO2 systems, suggesting that the average value of the tensile stress in the silicon substrate increases upon nitridation while reoxidation acts to return the interfacial stress to prenitridation levels. The implications of these structural changes upon device performance are discussed.

Comparison of defect structure in N2O- and NH3-nitrided oxide dielectrics

Electron spin resonance spectroscopy is used to identify and compare point defects in N2O-nitrided, NH3-nitrided, and conventional SiO2 films. We detect only three types of defects in these dielectrics. Pb centers, the primary source of interface states in Si/SiO2 systems under all technologically significant circumstances, appear in all three dielectrics. Both N2O and NH3 nitridation result in higher as-processed Pb interface defect densities, but lower radiation-induced Pb defect generation. Thus N2O nitridation appears capable, as does NH3 nitridation, of providing reduced radiation-induced interface state generation. In addition, both nitridations appear capable of lowering the number of radiation-induced E′ centers, the dominant hole trap in conventional thermal oxides. NH3 nitridation, however, appears to offer greater resistance to radiation-induced generation of these traps. NH3 nitridation also results in a large number of bridging nitrogen centers, and strong evidence indicates that the bridging nitrogen centers are the dominant electron trap in NH3-nitrided and -reoxidized nitrided oxide films. These defects are absent in N2O-nitrided films, which are known to exhibit reduced levels of electron trapping.

Effects of NH3 nitridation on oxides grown in pure N2O ambient

Effects of NH3 nitridation on the chemical and electrical properties of N2O oxides have been studied. Compared with NH3-nitrided SiO2, NH3 nitridation does not degrade the electrical properties of N2O oxides, thus resulting in superior impurity diffusion barrier properties, while preserving excellent interface immunity to hot-carrier injection and much lower charge trapping. Correlation studies between the chemical and electrical properties of NH3-nitrided N2O and NH3-nitrided SiO2 have been done to explain these results.

Effect of NH3 nitridation on time-dependent dielectric breakdown characteristics of heavily oxynitrided tunnel oxide films

The effects of NH/sub 3/ nitridation temperature (800-1000 degrees C) and time (15-90 s) in a dry oxidation NH/sub 3/-nitridation-N/sub 2/O oxynitridation sequence on the time-dependent dielectric breakdown (TDDB) characteristics of oxynitrided SiO/sub 2/ films are investigated. It is found that high-temperature (1000 degrees C) and short-time (30 sec) NH/sub 3/ nitridation gives excellent TDDB characteristics. >

Fabrication of High Quality Mos Devices for Application in Hazardous Environments Based on Rtp Gate Dielectrics With in Situ Rtcvd of Polysilicon Gates

ABSTRACTProcess modules for MOS gate fabrication were developed which can be completed subsequently in one RTP reactor: atmospheric process sequences for gate oxides and oxynitrides as well as low pressure chemical vapor deposition of polysilicon (RTCVD). Prior to the Rapid Thermal Oxidation (RTO), the wafers were treated with a Rapid Thermal Cleaning process (RTC) in H2/Ar ambient. After the desoxidation step the RTO was done in O2/H2/Ar followed by an anneal (RTA) for the gate oxide or a nitridation in NH3 (RTN) and reoxidation for the oxynitrides, respectively. The polysilicon gate electrode was fabricated either by RTCVD in situ or in a conventional furnace reactor. The two-step RTCVD process resulted in a very good thickness uniformity for the polysilicon layers of 3% (3mm from the edge). The influence of the process variations on breakdown field, fixed oxide charge, interface state density, flatband voltage, and threshold voltage of the different types of gate dielectrics was investigated. The charges and voltages were determined by LF-HF CV measurements. In order to characterize the radiation tolerance of electronic devices, radiation induced flatband and threshold voltage shifts as well as the build up of interface charges were determined. The irradiation was performed at a Co - 60 gamma source. Breakdown fields in the range of 19 MV/cm, interface state densities of less than 109 eV−2cm−2, and radiation induced threshold voltage shifts below 0.1 V after 1.5 Mrad(Si) were obtained.

Fabrication of High Quality MOS Devices for Application in Hazardous Environments Based on RTP Gate Dielectrics with In Situ RTCVD of Polysilicon Gates

ABSTRACTProcess modules for MOS gate fabrication were developed which can be completed subsequently in one RTP reactor: atmospheric process sequences for gate oxides and oxynitrides as well as low pressure chemical vapor deposition of polysilicon (RTCVD). Prior to the Rapid Thermal Oxidation (RTO), the wafers were treated with a Rapid Thermal Cleaning process (RTC) in H2/Ar ambient. After the desoxidation step the RTO was done in O2/H2/Ar followed by an anneal (RTA) for the gate oxide or a nitridation in NH3 (RTN) and reoxidation for the oxynitrides, respectively. The polysilicon gate electrode was fabricated either by RTCVD in situ or in a conventional furnace reactor. The two-step RTCVD process resulted in a very good thickness uniformity for the polysilicon layers of 3% (3mm from the edge). The influence of the process variations on breakdown field, fixed oxide charge, interface state density, flatband voltage, and threshold voltage of the different types of gate dielectrics was investigated. The charges and voltages were determined by LF-HF CV measurements. In order to characterize the radiation tolerance of electronic devices, radiation induced flatband and threshold voltage shifts as well as the build up of interface charges were determined. The irradiation was performed at a Co - 60 gamma source. Breakdown fields in the range of 19 MV/cm, interface state densities of less than 109 eV−1cm−2, and radiation induced threshold voltage shifts below 0.1 V after 1.5 Mrad(Si) were obtained.

Metal-oxide-semiconductor characteristics of rapid thermal nitrided thin oxides

The electrical properties of thin nitrided oxide (∼100 Å) formed by rapid thermal nitridation (RTN) in pure NH3 have been studied. It is found that the current-voltage characteristic of RTN oxides follows a Fowler–Nordheim tunneling behavior with modifications caused by electron trapping processes at the oxide surface and interface. The trapping density is dependent on the RTN conditions. At the interface, both fixed charge (Nf) and interface state (Dit) densities exhibit turnaround phenomena when the RTN process proceeds. The maximum values of Nf and Dit at the turnaround points are lower for the higher temperature RTN, suggesting a viscous flow related strain relieving mechanism associated with RTN of thin oxides. Films with superior endurance behavior (QBD=20.4 C/cm2 compared with QBD=5.1 C/cm2 of thermal oxide under 10 mA/cm2 constant current stress) have been obtained by RTN at 1000 °C, 10 s.