AC hot-carrier-induced degradation in NMOSFETs withN2O-based gate dielectrics

Frequency-dependent ac-stress-induced degradation in MMOSFETs with N₂O-grown and N₂O-nitrided gate oxides was investigated. Suppressed device degradation is observed in both N₂ O-based devices as compared to SiO₂ device for frequency up to 100 kHz, which is attributed to nitrogen incorporation in the gate oxides, Moreover, when comparing the two N₂O-based oxides, N₂O-grown oxide device exhibits enhanced degradation than N₂O-nitrided oxide device. Charge pumping measurements reveal that N₂O-nitrided oxide has better immunity to interface-state and neutral-electron-trap generation under dynamic stress     

Improved hot-carrier immunity in CMOS analog device with N2O-nitrided gate oxides

The authors report on the hot-carrier effects on analog device performance parameters in CMOS devices with N₂O-nitrided gate oxides. The hot-carrier-induced degradation has been studied in terms of drain output resistance, voltage gain, differential offset voltage, and voltage swings. Results show that, N₂O nitridation significantly improves the hot-carrier immunity in these aspects, especially for n-channel MOSFETs. Analog and digital device performance degradations have been compared     

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     

Improved immunity to plasma damage in ultrathin nitrided oxides[CMOS technology]

Plasma-induced damage in various 3-nm thick gate oxides (i.e., pure O₂ and N₂O-nitrided oxides) was investigated by subjecting both nMOS and pMOS antenna devices to a photoresist ashing step after metal pad definition. Gate leakage current measurements indicated that large leakage current occurs at the wafer center as well as at the wafer edge for pMOS devices, while it occurs only at the wafer center for nWOS devices. These interesting observations could be explained by the polarity dependence of ultrathin oxides in charge-to-breakdown measurements. Additionally, ultrathin N₂O-nitrided oxides show superior immunity to charging damage, especially for pMOS devices     

Improved performance and reliability of N2O-grownoxynitride on 6H-SiC

This letter reports, for the first time, N₂O-grown oxides on both n-type and p-type 6H-SiC wafers. It is demonstrated that the N₂O-grown technique leads to not only greatly improved SiC/SiO₂ interface and oxide qualities, but also considerably enhanced device reliabilities as compared to N₂O-nitrided and conventional thermally oxidized devices. These improvements are especially obvious for p-type SiC MOS devices, indicating that N₂ O oxidation could be a promising technique for fabricating enhancement-type n-channel SiC MOSFETs     

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     

Plasma-induced charging damage in ultrathin (3-nm) gate oxides

Plasma-induced damage in various 3-nm-thick gate oxides (i.e., pure oxides and N₂O-nitrided oxides) was investigated by subjecting both nMOS and pMOS antenna devices to a photoresist ashing step after metal pad definition. Both charge-to-breakdown and gate leakage current measurements indicated that large leakage current occurs at the wafer center as well as the wafer edge for pMOS devices, while only at the wafer center for nMOS devices. These interesting observations could be explained by the strong polarity dependence of ultra thin oxides in charge-to-breakdown measurements of nMOS devices. In addition, pMOS devices were found to be more susceptible to charging damage, which can be attributed to the intrinsic polarity dependence in tunneling current between nand p-MOSFETs. More importantly, our experimental results demonstrated that stress-induced leakage current (SILC) caused by plasma damage can be significantly suppressed in N₂O-nitrided oxides, compared to pure oxides, especially for pMOS devices. Finally, nitrided oxides were also found to be more robust when subjected to high temperature stressing. Therefore, nitrided oxides appear to be very promising for reducing plasma charging damage in future ULSI technologies employing ultrathin gate oxides     

P-channel MOSFET's with ultrathin N2O gate oxides

The performance and reliability of p-channel MOSFETs utilizing ultrathin (~62 Å) gate dielectrics grown in pure N₂O ambient are reported. Unlike (reoxidized) NH₃-nitrided oxide devices, p-MOSFETs with N₂O-grown oxides show improved performance in both linear and saturation regions compared to control devices with gate oxides grown in O₂. Because both electron and hole trapping are suppressed in N₂O-grown oxides, the resulting p-MOSFETs show considerably enhanced immunity to channel hot-electron and -hole-induced degradation (e.g., hot-electron-induced punchthrough)     

Enhanced off-state leakage currents in n-channel MOSFETs withN2O-grown gate dielectric

This paper reports on the off-state drain (GIDL) and gate current (Ig) characteristics of n-channel MOSFETs using thin thermal oxide (OX), N₂O-nitrided oxide (N2ON), and N₂O-grown oxide (N20G) as gate dielectrics. Important phenomena observed in N20G devices are enhanced GIDL and Ig in the low-field region as compared to the OX and N20N devices. They are attributed to heavy-nitridation-induced junction leakage and shallow-electron-trap-assisted tunneling mechanisms, respectively. Therefore, N2ON oxide is superior to N20G oxide in leakage-sensitive applications     

Dependence of hot-carrier immunity on channel length and channelwidth in MOSFETs with N2O-grown gate oxides

The authors report on the channel length (0.5-5 μm) and width (0.6-10 μm) dependence of hot-carrier immunity in n-MOSFETs with N ₂O-grown gate oxides (~85 Å). While channel hot-carrier-induced degradation has a strong dependence on channel geometry in control devices, the degradation and its channel geometric dependences are greatly suppressed in devices with N₂O-gate oxides. Under Fowler-Nordheim injection stress, the control device shows an enhanced degradation with decreasing channel length and increasing channel width, whereas N₂O device exhibits a less dependence on channel geometry     

MOS characteristics of ultrathin SiO2 prepared byoxidizing Si in N2O

MOS characteristics of ultrathin gate oxides prepared by furnace oxidizing Si in N₂O have been studied. Compared to control oxides grown in O₂, N₂O oxides exhibit significantly improved resistance to charge trapping and interface state generation under hot-carrier stressing. In addition, both charge to breakdown and time to breakdown are improved considerably. MOSFETs with N₂O gate dielectrics exhibit enhanced current drivability and improved resistance to g_m degradation during channel hot-electron stressing     

Effects of residual surface nitrogen on the dielectric breakdowncharacteristics of regrown oxides

Effects of residual surface nitrogen, remaining on the Si surface after stripping off tunneling oxynitrides (N₂O-grown or NH ₃-nitrided oxides), on the quality of the regrown gate oxides are studied. Residual surface nitrogen is observed to reduce the breakdown field and degrade the time-dependent dielectric breakdown (TDDB) characteristics of the subsequently grown gate oxides. Results show that oxide regrowth in N₂O, rather than O₂, can significantly suppress these undesirable effects     

High-field breakdown in thin oxides grown in N2O ambient

A detailed study of time-dependent dielectric breakdown (TDDB) in N₂O-grown thin (47-120 Å) silicon oxides is reported. A significant degradation in breakdown properties was observed with increasing oxide growth temperatures. A physical model based on undulations at the Si/SiO₂ interface is proposed to account for the degradation. Accelerated breakdown for higher operating temperatures and higher oxide fields as well as thickness dependence of TDDB are studied under both polarities of injection. Breakdown under unipolar and bipolar stress in N₂O oxides is compared with DC breakdown. An asymmetric improvement in time-to-breakdown under positive versus negative gate unipolar stress is observed and attributed to charge detrapping behavior in N₂O oxides. A large reduction in time-to-breakdown is observed under bipolar stress when the thickness is scaled below 60 Å. A physical model is suggested to explain this behavior. Overall, N₂O oxides show improved breakdown properties compared with pure SiO₂     

High-field-induced leakage in ultrathin N2O oxides

Stress-induced leakage current (SILC) is studied in ultrathin (~50 Å) gate oxides grown in N₂O or O₂ ambient, using rapid thermal processing (N₂O oxide or control oxide, respectively). MOS capacitors with N₂O oxides exhibit much suppressed SILC compared to the control oxide for successive ramp-up, constant voltage DC, and AC (bipolar and unipolar) stresses. The mechanism for SILC is discussed, and the suppressed SILC in N₂O oxide is attributed to suppressed interface state generation due to nitrogen incorporation at the Si/SUO₂ interface during N₂O oxidation     

Reliable fluorinated thin gate oxides prepared by liquid phasedeposition following rapid thermal process

A reliable fluorinated thin gate oxide prepared by liquid phase deposition (LPD) following rapid thermal oxidation (RTO) in O₂ or nitridation (RTN) in N₂O ambient was reported. Fluorine (F) atoms incorporated into the oxides during LPD process are found to be helpful to the improvement of oxide quality. It is observed that these fluorinated gate oxides show good properties in radiation hardness, charge to breakdown (Q_bd), and oxide breakdown field (E_ox) endurances. Interestingly, the Q_bd 's for the fluorinated gate oxides are 10 times larger than those for the gate oxides prepared by RTO in O₂ or RTN in N₂ O directly. Some of the E_ox's are even higher than 17 MV/cm for the samples investigated in this work     

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     

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     

Degradation of N2O-annealed MOSFET characteristics inresponse to dynamic oxide stressing

The performance of n-MOSFETs with furnace N₂O-annealed gate oxides under dynamic Fowler-Nordheim bipolar stress was studied and compared with that of conventional oxide (OX). Time-dependent dielectric breakdown at high frequency was shown to be improved for the N₂ O-annealed devices compared with that for devices with OX. In addition, a smaller V_t shift after stress was found for nitrided samples. The shift decreased with increasing stressing frequency and annealing temperature. Measurements of both G_m and D_it revealed a peak frequency at which the degradation was the worst. A hole trapping/migration model has been proposed to explain this     

Hot-carrier-induced degradation in reoxidized-nitrided-oxiden-MOSFETs under mixed AC-DC stressing

Reduced degradation rate can be observed for reoxidized-nitrided-oxide (RNO) n-MOSFETs under dynamic stressing versus the corresponding static stressing. A new degradation mechanism is proposed in which trapped holes in gate oxide are neutralized by the hot-electron injection, with no significant generation of interface states because of the hardening on the Si-SiO₂ interface by nitridation/reoxidation steps. The RNO device degradation during AC stressing arises mainly from the charge trapping in the gate oxide rather than the generation of interface states. Moreover, the AC-stressed RNO devices are significantly inferior to the fresh RNO devices in terms of DC stressing, possibly due to lots of neutral electron traps in the gate oxide resulting from the AC stressing     

Effects of growth temperature on TDDB characteristics of N2O-grown oxides

Effects of oxide growth temperature on time-dependent dielectric breakdown (TDDB) characteristics of thin (115 Å) N₂O-grown oxides are investigated and compared with those for conventional O₂-grown SiO₂ films with identical thickness. Results show that TDDB characteristics of N₂O oxides are strongly dependent on the growth temperature and, unlike conventional SiO₂, TDDB properties are much degraded for N ₂O oxides with an increase in growth temperature. Large undulations at the Si/SiO₂ interface, caused by locally retarded oxide growth due to interfacial nitrogen, are suggested as a likely cause of degradation of TDDB characteristics in N₂O oxides grown at higher temperatures