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     

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     

Time-dependent dielectric breakdown characteristics ofN2O oxide under dynamic stressing

Time-dependent dielectric breakdown (TDDB) characteristics of MOS capacitors with thin (120-Å) N₂O gate oxide under dynamic unipolar and bipolar stress have been studied and compared to those with control thermal gate oxide of identical thickness. Results show that N₂O oxide has significant improvement in t _BD (2×under-V_g unipolar stress, 20×under+V_g unipolar stress, and 10×under bipolar stress). The improvement of t_BD in N₂O oxide is attributed to the suppressed electron trapping and enhanced hole detrapping due to the nitrogen incorporation at the SiO₂/Si interface     

Reduction of RIE-damage by N2O-anneal of thermal gateoxide

We have investigated RIE-induced damage in MOS devices with thermal oxide as well as N₂O-annealed oxide as gate dielectrics. A systematic improvement in robustness against RIE-induced damage is seen when N₂O flow rate and/or N₂O anneal temperature are increased. We have demonstrated a N₂O anneal process at 900°C, which provides a robust SiO₂/Si interface against plasma damage and hot carrier stress     

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)     

Reduction of leakage current in chemical-vapor-deposited Ta2O5 thin films by furnace N2O annealing

In this brief, we present a post-deposition annealing technique that employs furnace annealing in N₂O (FN₂O) to reduce the leakage current of chemical-vapor-deposited tantalum penta-oxide (CVD Ta₂O₅) thin films. Compared with furnace annealing in O₂ (FO) and rapid thermal annealing in N ₂O (N₂O), FN₂O annealing proved to have the lowest leakage current and the most reliable time-dependent dielectric breakdown (TDDB)     

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     

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     

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     

AC hot-carrier effects in MOSFETs with furnaceN2O-nitrided gate oxides

AC hot-carrier effects in n-MOSFETs with thin (~85 Å) N₂O-nitrided gate oxides have been studied and compared with control devices with gate oxides grown in O₂. Results show that furnace N₂O-nitrided oxide devices exhibit significantly reduced AC-stress-induced degradation. In addition, they show weaker dependences of device degradation on applied gate pulse frequency and pulse width. Results suggest that the improved AC-hot-carrier immunity of the N₂O-nitrided oxide device may be due to the significantly suppressed interface state generation and neutral electron trap generation during stressing     

Effects of post-deposition anneal on the electrical properties ofSi3N4 gate dielectric

The effects of postdeposition anneal of chemical vapor deposited silicon nitride are studied. The Si₃N₄ films were in situ annealed in either H₂(2%)/O₂ at 950°C or N₂O at 950°C in a rapid thermal oxidation system. It is found that an interfacial oxide was grown at the Si₃N₄/Si interface by both postdeposition anneal conditions. This was confirmed by thickness measurement and X-ray photoelectronic spectroscopy (XPS) analysis. The devices with H₂ (2%)/O₂ anneal exhibit a lower gate leakage current and improved reliability compared to that of N₂O anneal. This improvement is attributed to a greater efficiency of generating atomic oxygen in the presence of a small amount of hydrogen, leading to the elimination of structural defects in the as-deposited Si₃N ₄ film by the atomic oxygen. Good drivability is also demonstrated on a 0.12 μm n-MOSFET device     

The TEOS oxide deposited on phosphorus in-situ/POCl3doped polysilicon with rapid thermal annealing in N2O

This work presents a TEOS oxide deposited on the phosphorus-in-situ doped polysilicon with rapid thermal N₂O annealing. The oxide exhibits good electron trapping characteristics with a charge-to-breakdown (Q_bd) up to 110 C/cm². It is due to the good polysilicon/oxide interface morphology obtained by replacing POCl₃ doping with in-situ doping and the rapid thermal annealing in N₂O. In addition, the N₂O annealing densifies the deposited oxide and incorporates nitrogen into the oxide and at the polysilicon/oxide interface, thus improving the electrical characteristics     

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     

High-performance polycrystalline SiGe thin-film transistors usingAl2O3 gate insulators

The use of aluminum oxide as the gate insulator for low temperature (600°C) polycrystalline SiGe thin-film transistors (TFTs) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N₂O plasma. The composition of the deposited aluminum oxide was found to be almost stoichiometric (i.e., Al₂O₃), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured an devices with 50-nm-thick Al₂O₃ gate dielectric layers. Typically, a field effect mobility of 47 cm²/Vs, a threshold voltage of 3 V, a subthreshold slope of 0.44 V/decade, and an on/off ratio above 3×10⁵ at a drain voltage of 0.1 V can be obtained. These results indicate that the direct interface between the Al₂ O₃ and the SiGe channel layer is sufficiently passivated to make Al₂O₃ a better alternative to grown or deposited SiO₂ for SiGe field effect devices     

Interface properties of NO-annealed N2O-grown oxynitride

The oxide/Si interface properties of gate dielectric prepared by annealing N₂O-grown oxide in an NO ambient are intensively investigated and compared to those of O₂-grown oxide with the same annealing conditions. Hot-carrier stressings show that the former has a harder oxide/Si interface and near-interface oxide than the latter. As confirmed by SIMS analysis, this is associated with a higher nitrogen peak concentration near the oxide/Si interface and a larger total nitrogen content in the former, both arising from the initial oxidation in N₂O instead of O₂     

Leakage current reduction in chemical-vapor-depositedTa2O5 films by rapid thermal annealing in N2O

This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) Ta₂ O₅, films by developing a new post-deposition single-step annealing technique. Experimental results indicate that excited oxygen atoms generated by N₂O decomposition can effectively repair the oxygen vacancies in the as-deposited CVD Ta₂ O₅ film, thereby resulting in a remarkable reduction of the film's leakage current. Two other post-deposition annealing conditions are compared: rapid thermal O₂ annealing and furnace dry-O₂ annealing. The comparison reveals that RTN₂O annealing has the lowest leakage current, superior thermal stability of electrical characteristics and the best time-dependent dielectric breakdown (TDDB) reliability     

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     

High quality interpoly-oxynitride grown by NH3nitridation and N2O RTA treatment

In this letter, a method to grow high quality interpolysilicon-oxynitride (interpoly-oxynitride) film is proposed. Samples, nitridized by NH₃ with additional N₂O annealing and CVD TEOS deposited on poly-oxynitride (poly-I) with RTA N ₂O oxidation, show excellent electrical properties in terms of very high electric breakdown field, low leakage current, high charge to breakdown, and low electron trapping rate. This novel film is a good candidate for an interpoly dielectric of future high density EEPROM and flash memory devices     

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     

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