Electrical and Reliability Characteristics of 12- Å Oxynitride Gate Dielectrics by Different Processing Treatments

Various ultrathin oxynitride gate dielectrics of similar thickness (~1.2 nm) fabricated by a combination of an in situ steam generated and remote plasma nitridation treatment (RPN), an RPN with rapid thermal NO annealing (RPN-NO), and an RPN with rapid thermal O₂ annealing (RPN-O₂) are reported in this paper. The RPN-NO gate dielectric films show superior interface properties including relatively high nitrogen concentration near the poly-Si/oxide interface and smooth interfaces, excellent electrical characteristics in terms of lower leakage current, better electron and hole channel mobility, higher drive current, and significantly improved reliability such as stress-induced leakage current, hot carrier injection, and negative bias temperature instability, compared to other gate dielectrics fabricated by different processes.     

Ultra-thin decoupled plasma nitridation (DPN) oxynitride gate dielectric for 80-nm advanced technology

Balancing gate leakage reduction, device performance, and gate dielectric reliability is a major challenge for oxynitride used as a gate dielectric for advanced technology. As compared to RTONO oxynitride, pMOSFET threshold voltage shift and transconductance degradation have been problematic for devices using remote plasma nitridation (RPN) or decoupled plasma nitridation (DPN) process due to non-optimal nitrogen profile in the film. In this paper, we report that the nitrogen profile of DPN gate dielectric can be engineered primarily by tuning the plasma pressure after optimizing other DPN process parameters to solve these problems. An EOT of 15 /spl Aring/ (23-/spl Aring/ NMOS CETinv) DPN oxynitride is demonstrated to have an acceptable pMOS Vt, comparable transconductance, significantly (/spl sim/30/spl times/) longer pMOS time-to-breakdown reliability for packaged devices, and 5/spl times/ gate leakage reduction relative to a high quality RTONO used in industry. The high quality ultrathin DPN film is fabricated in a commercially available system, which is compatible with standard CMOS processing technology. These encouraging results make high-pressure DPN oxynitride an attractive gate dielectric candidate for 80-nm advanced technology and beyond.     

Oxynitride gate dielectric grown in nitric oxide (NO): the effectof reoxidation on dielectric reliability of the active edge

Reoxidation of an oxynitride gate dielectric grown by NO anneal of thermal oxide has been studied. This process has demonstrated ~3-5X improvement of Q_BD of active edge intensive capacitors in comparison to thermal oxide, N₂O and NO oxynitride. This improvement is believed to be due to the reduction of local thinning of the gate dielectric at the field oxide edge which also reduces local build-up of positive charge near the gate electrode at the isolation edges     

Electrical properties of MOSFET's with N2O-nitridedLPCVD SiO2 gate dielectrics

Electrical properties of MOSFETs with gate dielectrics of low-pressure chemical-vapor-deposited (LPCVD) SiO₂ nitrided in N₂O ambient are compared to those with control thermal gate oxide. N₂O nitridation of CVD oxide, combines the advantages of interfacial oxynitride growth and the defectless nature of CVD oxide. As a result, devices with N₂O-nitrided CVD oxide show considerably enhanced performance (higher effective electron mobility), improved reliability (reduced charge trapping, interface state generation, and transconductance degradation), and better time-dependent dielectric breakdown (TDDB) properties (t_BD ) compared to devices with control thermal oxide     

Hot-carrier degradation of LDD MOSFET's with gate oxynitride grownin N2O

Hot carrier immunity (HCI) of single drain (SD) and lightly doped drain (LDD) n-MOSFET's with gate oxide and N₂O gate oxynitride was compared. Gate oxynitride shows better HCI than gate oxide in SD devices but comparable in LDD devices. We show that oxide grown during the poly-silicon oxidation process after gate poly-silicon definition plays an important role in determining the hot carrier resistance of LDD n-MOSFET's with N₂O gate oxynitride     

Characterization of ultrathin oxynitride (18-21 A) gate dielectricsby NH3 nitridation and N2O RTA treatment

In this paper, we developed a new method to grow robust ultrathin oxynitride (E_OT=18 A) film with effective dielectric constant of 7.15. By NH₃-nitridation of Si substrate, grown ultrathin Si₃N₄ With N₂O annealing shows excellent electrical properties in terms of significant lower leakage current, very low bulk trap density and trap generation rate, and high endurance in stressing. In addition, this oxynitride film exhibits relatively weak temperature dependence due to a Fowler-Nordheim (FN) tunneling mechanism. This dielectric film appears to be promising for future ultralarge scale integrated (ULSI) devices     

Investigation of hole-tunneling current through ultrathinoxynitride/oxide stack gate dielectrics in p-MOSFETs

The systematic investigation of hole tunneling current through ultrathin oxide, oxynitride, oxynitride/oxide (N/O) and oxide/oxynitride/oxide (ONO) gate dielectrics in p-MOSFETs using a physical model is reported for the first time. The validity of the model is corroborated by the good agreement between the simulated and experimental results. Under typical inversion biases (|VG|<2 V), hole tunneling current is lower through oxynitride and oxynitride/oxide with about 33 at.% N than through pure oxide and nitride gate dielectrics. This is attributed to the competitive effects of the increase in the dielectric constant, and hence dielectric thickness, and decrease in the hole barrier height at the dielectric/Si interface with increasing with N concentration for a given electrical oxide thickness (EOT). For a N/O stack film with the same N concentration in the oxynitride, the hole tunneling current decreases monotonically with oxynitride thickness under the typical inversion biases. For minimum gate leakage current and maintaining an acceptable dielectric/Si interfacial quality, an N/O stack structure consisting of an oxynitride layer with 33 at.% N and a 3 Å oxide layer is proposed. For a p-MOSFET at an operating voltage of -0.9 V, which is applicable to the 0.7 μm technology node, this structure could be scaled to EOT=12 Å if the maximum allowed gate leakage current is 1 A/cm² and EOT=9 Å if the maximum allowed gate leakage current is 100 A/cm²     

Robust ultrathin oxynitride dielectrics by NH3nitridation and N2O RTA treatment

In this paper, a method to grow robust ultrathin (E_OT=28 Å) oxynitride film with effective dielectric constant of 5.7 is proposed. Samples, nitridized by NH₃ with additional N₂O annealing, show excellent electrical properties in terms of very low bulk trap density, low trap generation rate, and high endurance in stressing. This novel dielectric appears to be very promising for future ULSI devices     

Oxynitride gate dielectrics for p+-polysilicon gate MOSdevices

Different oxynitride gate dielectrics (NH₃-nitrided, reoxidized NH₃-nitrided, N₂-annealed NH₃-nitrided, and N₂O grown oxides) are investigated for use in p⁺-polysilicon gate MOS devices. The comparison is based on flatband voltage shift as well as decrease in inversion capacitance. Results show that NH₃-nitrided and N ₂-annealed NH₃-nitrided oxides best suppress the boron penetration and, consequently, these two undesirable effects. These findings are explained on the basis of the distribution of nitrogen in various oxynitride dielectrics     

Improved reliability characteristics of submicrometer nMOSFETs withoxynitride gate dielectric prepared by rapid thermal oxidation inN2O

Submicrometer MOSFETs with ultrathin oxynitride gate dielectric grown in pure N₂O ambient were studied. The peak mobility of oxynitride is 5% lower than that of control oxide. However, the oxynitride shows 10% less mobility degradation under high normal field. Compared with the control oxide device, the oxynitride device shows significantly less degradation under channel hot-electron stress. The lifetime of the oxynitride device is approximately one order of magnitude longer than that of the control oxide sample. Significant improvement of device reliability is due to the nitrogen incorporation during the oxidation process     

Plasma-charging effects on submicron MOS devices

Plasma-charging damage on gate dielectrics of MOS devices is an important issue because of shrinking dimension, plasma nonuniformity, and effects on high-k gate dielectrics. A comprehensive study of plasma-charging effects on the electrical properties of MOS devices was investigated in this work. Shunt diodes were used to estimate the charging polarity distribution. For high-frequency application, the 1/f noise was found to be a promising index for assessing plasma-charging damage. Gate oxynitride formed by two-step nitridation was demonstrated to have better electrical reliability as compared to the conventional one-step nitridation, especially accompanied by amorphous silicon gate electrode. This improvement could be attributed to the relaxation of interface stress by amorphous silicon gate electrode and the suppression of hydrogen effects by gate oxynitride using two-step nitridation. Plasma-charging damage on Si₃N₄ and Ta₂O₅ gate dielectrics with high dielectric constant was also investigated. For MOS devices with Si₃N₄ film, the leakier characteristic and shorter time to breakdown reveal its inferior reliability. For MOS devices with Ta₂O₅ gate dielectric, the trap-assisted current mechanism makes a thicker physical thickness of Ta₂O₅ film more susceptible to plasma-charging-induced damage. Smaller physical thickness of Ta₂O₅ film in MOS devices is favorable due to the better reliability and comparable plasma-induced electrical degradation     

Furnace nitridation of thermal SiO2 in pureN2O ambient for ULSI MOS applications

Furnace nitridation of thermal SiO₂ in pure N₂ O ambient for MOS gate dielectric application is presented. N₂O-nitrided thermal SiO₂ shows much tighter distribution in time-dependent dielectric breakdown (TDDB) characteristics than thermal oxide. MOSFETs with gate dielectric prepared by this method show improved initial performance and enhanced device reliability compared to those with thermal gate oxide. These improvements are attributed to the incorporation of a small amount of nitrogen (~1.5 at.%) at the Si-SiO₂ interface without introducing H-related species during N₂O nitridation     

Effects of Oxynitride Buffer Layer on the Electrical Characteristics of Poly-Silicon TFTs Using $hbox{Pr}_{2}hbox{O}_{3}$ Gate Dielectric

In this paper, we have developed high-k Pr₂O₃ poly-Si thin-film transistors (TFTs) using different N₂O plasma power treatments. High-k Pr₂O₃ poly-Si TFT devices using a 200-W plasma power exhibited better electrical characteristics in terms of high effective carrier mobility, high driving current, small subthreshold slope, and high I_ON/I_OFF current ratio. This result is attributed to the smooth Pr₂O₃/poly-Si interface and low interface trap density. Pr₂O₃ poly-Si TFT with a 200-W N₂O plasma power also enhanced electrical reliabilities such as hot carrier and positive bias temperature instability. All of these results suggest that a high-k Pr₂O₃ gate dielectric with the oxynitride buffer layer is a good candidate for high-performance low-temperature poly-Si TFTs.     

Gate quality ultrathin (2.5 nm) PECVD deposited oxynitride andnitrided oxide dielectrics

Ultrathin oxynitride using plasma assisted deposition was evaluated against thermal oxide and nitrided thermal oxide as an alternative direct tunneling gate dielectric to thermal oxide in the 2.5-nm regime. The oxynitride showed an enhanced high field effective mobility relative to the thermal oxide although the low field mobility was slightly depressed. The N₂O nitrided oxide showed an enhanced high field effective mobility with no degradation in low field mobility. The interface state density of the oxynitride was equivalent to that of the thermal and nitrided thermal oxides; a very welcome observation for this deposition chemistry and anneal conditions     

High field stressing effects on the split N2O grown thingate dielectric by rapid thermal processing

Highly reliable thin oxynitride layers of very good Si-SiO₂ interface endurance were grown on silicon wafers with a split N ₂O cycle (N₂O/O₂/N₂O) employing rapid thermal processing (RTP). Excellent electrical characteristics with reduced positive charge generation, electron trapping and/or interface state generation were achieved under high field stressing compared to pure N₂O dielectric     

Low-frequency noise characterization of n- and p-MOSFET's withultrathin oxynitride gate films

MOSFET's with ultrathin (5 to 8.5 nm) silicon oxynitride gate film prepared by low-pressure rapid thermal chemical vapor deposition (RTCVD) using SiH₄, N₂O and NH₃ gases, are studied by low-frequency noise measurements (1 Hz up to 5 kHz). The analysis takes into account the correlated mobility fluctuations induced by those of the interfacial oxide charge. The nitrogen concentration, determined from SIMS analysis, varies from 0 to 11% atomic percentage. A comparison of the electrical properties between thermal and silicon oxynitride films is presented. The increasing LF noise signal with nitrogen atomic percentage indicates the presence of a higher density of slow interface traps with increasing nitrogen incorporation. Besides, a higher Coulomb scattering rate due to the nitridation induced interface charge explains reasonably well the degradation of the low field mobility after nitridation     

A novel technique of N2O-treatment onNH3-nitrided oxide as gate dielectric for nMOS transistors

A novel technique of N₂O treatment on NH₃-nitrided oxide is used to prepare thin gate oxide. Experiments on MOS capacitors and nMOSFET's with this kind of gate dielectric show that N₂O treatment is superior to conventional reoxidation step in suppressing both electron and hole trappings and interface trap creation under high-field stress. Interface hardness against hot-carrier bombardment and neutral electron trap generation are also improved. Thus, N₂O treatment on NH₃ -nitrided oxide shows excellent electrical and reliability properties, while maintaining sufficiently high nitrogen concentration in gate oxide which offers good resistance to dopant penetration     

Electrical Properties of Ultra Thin Nitride/Oxynitride Stack Dielectrics pMOS Capacitor with Refractory Metal Gate

Electrical properties of high quality ultra thin nitride/oxynitride（N/O）stack dielectrics pMOS capacitor with refractory metal gate electrode are investigated，and ultra thin (＜2 nm＝ N/O stack gate dielectrics with significant low leakage current and high resistance to boron penetration are fabricated.Experiment results show that the stack gate dielectric of nitride/oxynitride combined with improved sputtered tungsten/titanium nitride (W/TiN) gate electrode is one of the candidates for deep sub-micron metal gate CMOS devices.     

Low-pressure rapid thermal chemical vapor deposition of oxynitridegate dielectrics for n-channel and p-channel MOSFETs

The properties of oxynitride gate dielectrics formed using a low-pressure, rapid thermal chemical vapor deposition (RTCVD) process with SiH₄, NH₃, and N₂O as the reactive gases are presented. Material analyses show an increase of uniform nitrogen and interfacial hydrogen content with increasing NH₃/N₂O flow rate ratio. MOS capacitors with both n-type and p-type substrates and both n-channel and p-channel MOSFETs were analyzed electrically. The results show increasing fixed oxide charge and interface state density with increasing nitrogen and hydrogen content in the film. A decrease in peak transconductance and improved high-field transconductance was observed for n-channel MOSFETs. Improved resistance to hot-carrier interface state generation was also observed with increasing nitrogen concentration in the films. The results suggest that an optimal nitrogen concentration of approximately 3 at.% can be considered for further development of this technology     

High quality gate dielectrics grown by rapid thermal processingusing split-N2O technique onstrained-Si0.91Ge0.09 films

Thermal stability and strain relaxation temperature of strained Si _0.91Ge_0.09 layers has been investigated using double crystal x-ray diffraction (DCXRD). High quality gate oxynitride layers rapid thermally grown on strained Si_0.91Ge_0.09 using N₂O and the split N₂O cycle technique below the strained relaxed temperature is reported. A positive fixed oxide charge density was observed for N₂O and split-N₂ O grown films. The O₂ grown films exhibit a negative fixed oxide charge. The excellent improvements in the leakage current, breakdown field and charge-to-breakdown value of the N₂O or split-N₂O grown films were achieved compared to pure O₂ grown films