Reliability of ultrathin nitrided oxides grown in low pressure N2O ambient

The influence of N₂O oxynitridation and oxidation pressure on reliability of ultrathin gate oxides from 4 down to 2.5 nm thickness was investigated. A set of different oxidation parameters was applied during oxide growth which comprised oxidation pressure and N₂O partial pressure during rapid thermal oxidation. The reliability of the oxides was tested by constant voltage stress. Evaluation of the resulting times to soft breakdown (t_sbd) for different stress voltages allows to predict a supply (gate) voltage V^10y,max providing an oxide lifetime of 10 years. For this extrapolation, t_sbd was assumed to increase exponentially as stress voltage is reduced. The slope of the extrapolation is found to become steeper as oxides become thinner, which implies higher V^10y,max and thus higher reliability for thinner oxides as under an assumption of a uniform slope for all thicknesses. Further, the results of this extrapolation demonstrate that oxidation in N₂O containing ambient can improve oxide reliability for ultrathin gate oxides.     

Effect of N2O nitridation on the electrical properties of MOS gate oxides

Furnace annealing in N₂O is a convenient technique for improving the reliability of thermal oxides without significant modifications of the process flow. We investigate the impact of N₂O nitridation on MOSFET device performance, assessing the various factors contributing to the observed degradation of electron mobility. Estimates based on low-frequency C-V and charge pumping measurements show that nitridation causes a significant increase of the interface trap density in the vicinity of the conduction band. Interface traps contribute a parasitic component to the gate-channel capacitance, thus leading to an overestimate of the inversion charge. This effect accounts for a substantial fraction of the mobility degradation which is observed for the nitrided devices. The remaining degradation can be ascribed to an enhancement of Coulomb scattering, maybe due to differences in dopant segregation, and to a change of the surface roughness characteristics.     

氮气或氧气气氛退火的氧化铪材料电荷泄漏情况研究

本文中, 使用开尔文探针显微镜,研究了不同退火气氛(氧气或氮气)情况下氧化铪材料的电子和空穴的电荷保持特性。与氮气退火器件相比,氧气退火可以使保持性能变好。横向扩散和纵向泄露在电荷泄露机制中都起了重要的作用。 并且,保持性能的改善与陷阱能级深度有关。氮气和氧气退火情况下,氧化铪存储结构的的电子分别为0.44 eV, 0.49 eV,空穴能级分别为0.34 eV, 0.36 eV。 最后得到,不同退火气氛存储器件的电学性能也与KFM结果一致。对于氧化铪作为存储层的存储器件而言,对存储特性的定性和定量分析,陷阱能级,还有泄漏机制研究是十分有意义的。     

Effects of N distribution on charge trapping and TDDBcharacteristics of N2O annealed wet oxide

Wet pyrogenic oxide of different thicknesses was annealed in N₂O ambient and the N concentration in the films was studied by using SIMS (secondary ion mass spectroscopy). It was found that for a certain annealing time and temperature, the N concentration (at %) increases with decreasing wet oxide thickness and the location of the peak of N is observed near the interface of nitrided oxide and Si substrate. On the contrary, after nitridation the concentration of H is higher in the thicker wet oxide of thickness 100 Å and also does not change much from the surface to the interface. For the thinner wet oxide of thickness 40 Å, the concentration of H is less and decreases toward the interface. Gate dielectrics were characterized using high-frequency and quasi-static measurements. After a constant current stress, a large distortion was observed for the N₂O annealed wet oxide of 98 Å whereas for the N₂O annealed wet oxide of 51 Å the distortion was small. With increasing stressing time, hole trap is followed by electron trapping for the wet oxide of 98 Å whereas for the N₂O annealed wet oxide of 51 Å, hole trapping increases a little at the beginning and then saturates. From the TDDB characteristics, a longer t_BD was observed for N₂O annealed wet oxide of 51 Å compared to 98 Å. From the experimental results, it can be suggested that the improved reliability of thin gate oxide is due to the large amount of N concentration near the interface only. Hence for the device fabrication process, if the wet oxide is nitrided in N₂O ambient, the reliability of gate oxide will be improved in the ultrathin region     

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     

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     

Investigation of 4H-SiC MOS capacitors annealed in diluted N2O at different temperatures

Thermally grown oxide on 4H-SiC has been post-annealed in diluted N₂O (10% N₂O in N₂) at different temperatures from 900 to 1100 °C. The quality of the nitrided oxide and the SiO₂/4H-SiC interface was investigated by AC conductance and high frequency C-V measurements based on Al/SiO₂/4H-SiC metal-insulator-semiconductor (MOS) structure. It is found that N₂O annealing at 1000 °C produces the lowest interface state density, though the difference is not so significant when compared to the other samples annealed at 900 and 1100 °C. These results can be explained by the high temperature dynamic decomposition process of N₂O. By fitting the AC conductance data, it is found that higher temperature nitridation increases the capture cross-section of the interface traps.     

Effects of N2O anneal and reoxidation on thermal oxidecharacteristics

The effects of post-oxidation N₂O anneal on conventional thermal oxide are studied. The oxide thickness increase resulting from N₂O anneal is found to be self-limiting and insensitive to initial oxide thickness, which makes the thickness of the resulting oxide easy to control. The N₂O anneal leads to increased resistance against injection-induced interface-state generation and to reduced hole trapping. No further quality improvement is found when the N₂O-annealed oxide is subject to an additional reoxidation. This finding confirms that nitrogen incorporation in the absence of hydrogen is responsible for improving the quality of the conventional oxides     

Uniform durable thin dielectrics prepared by rapid thermalprocessing in an N2O ambient

Thin dielectrics grown on silicon wafers by rapid thermal processing in an N₂O ambient at temperatures of 1100°C, 1150°C, and 1200°C are discussed. The resulting films, in conjunction with an O₂ ambient control were characterized by thickness measurements and electrical performance. Dielectrics formed in N₂O in this temperature range were all superior to that prepared in an O₂ ambient in terms of interface state generation and flatband voltage shift after constant current stressing. Although all N₂O prepared samples exhibited similar cross wafer electrical uniformity, higher growth temperatures favored thickness uniformity. The electrical behavior of the N₂O wafers was not strongly dependent on growth temperature; however, a 60-s 1100°C post-oxynitridation N₂ anneal was found to significantly reduce subsequent electrical performance. It is also demonstrated that under optimum process conditions, high-quality uniform dielectrics can be formed by RTP in N₂O     

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     

选频N_2O激光器

N_2O是线性非对称分子,它的激光工作能级为(001)和(100)振动态以及相联系的转动态,由于下工作能级(100)可以向基态(000)进行偶极跃迁,所以粒子数反转密度较低,加之N_2O气体在高温下容易分解,这些都会使激光功率低于CO_2激光。为了克服这些不利因素,我们采取流动工作气体方式获得连续的激光输出。 激光管长为2100毫米,放电长度为1800毫米,放电管内径20毫米。腔体的一端由NaCl布氏窗封密构成半外腔。金膜全反凹面镜曲率半径为10米,选频用的金属基底光栅为100条/毫米、闪耀波长10.6微米的原刻光栅。激光管装有进气口和出气口,分别与气源钢瓶和抽气泵相联,抽气速率8升/秒,折算管内流速25米/秒。     

The electrical characteristics of polysilicon oxide grown in pure N2O

N₂O was used to grow silicon polyoxide. It was found that the N₂O-grown polyoxide had a lower leakage current but a higher breakdown field when the top-electrode was positively biased. This is opposite to that of conventional O₂-grown polyoxide. Moreover, it had less electron trapping when stressed and a larger charge-to-breakdown     

Enhancement of integrity of polysilicon oxide by using acombination of N2O nitridation and CMP process

This work prepares and demonstrates, for the first time, a high-quality polysilicon oxide, by combing N₂O nitridation and chemical mechanical polishing (CMP) process. Our results demonstrate that capacitors with this process have an improved Q_hd (charge-to-breakdown) due to the planar surface and more concentrated nitrogen at the interface of polysilicon oxide     

Enhanced reliability for low-temperature gate dielectric of MOS devices by N2O or NO plasma nitridation

Silicon MOS capacitors fabricated solely by low-temperature processes (under 600 °C) are treated with nitridation using N₂O or NO plasma. Their properties are investigated at room temperature under high-field stress. It is found that both kinds of plasmas are effective in improving the gate-oxide hardness against stress-induced damage, which is characterized by a smaller shift in flatband voltage and smaller increase in interface states after the stress. Moreover, NO-nitrided device shows better performance than N₂O-nitrided one. These results show that plasma nitridation has positive effects on the reliability of low-temperature-fabricated devices, which play an important role in flat-panel display systems on glass.     

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     

Role of nitridation/reoxidation of NH3-nitrided gatedielectrics on the hot-carrier resistance of CMOS transistors

The effect of nitriding and reoxidizing conditions are examined on the hot-carrier (HC) properties of p-channel and n-channel transistors with reoxidized nitrided oxide gate dielectrics. Nitrogen was introduced into the gate dielectric by performing cyclical nitridation and reoxidation steps (one cycle versus four cycles of nit./reox.), keeping the same overall oxidation and nitridation times constant, It was found that there were considerable differences in hot-carrier hardness, of up to three orders of magnitude for p-channel transistors, but much less for n-channel devices. Nitrogen-content variations (a factor of 2) for these very similar conditions explain the n-channel hot-carrier results. In the case of the p-MOS transistors, it is suggested that changes in hydrogen concentration might be responsible for the hot-carrier behavior     

Nitrogen bonding configurations near the oxynitride/silicon interface after oxynitridation in N2O ambient of a thin SiO2 gate

The identification of the bonding environments and their progressive modifications upon reaching the oxynitride/silicon interface, in a SiO₂/SiO_xN_y/Si structure, have been investigated by means of X-ray photoemission spectroscopy (XPS). The SiO₂ film was grown at 850 °C by means of a mixed dry-steam process, followed by a 60 min, 950 °C furnace oxynitridation in N₂O gas. A depth profile analysis was carried out by a progressive chemical etching procedure, reaching a residual oxide thickness of about 1.2 nm. XPS analysis of the Si 2p and N 1s photoelectron peaks pointed out that the chemistry of the oxynitride layer is a rather complex one. Four different nitrogen bonding environments were envisaged. Both the overall nitrogen content, which rises up to 2.5%, and its bonding configurations are progressively changing while moving towards the silicon interface.     

Studies of CW lasing action in CO2-CO,N2O-CO, CO2-H2O, and N2O-H2O mixtures pumped by blackbody radiation

A proof of principle experiment to evaluate the efficacy of CO and H₂O in increasing the power output for N₂O and CO ₂ lasing mixtures has been conducted and theoretically analyzed for a blackbody radiation-pumped laser. The results for N₂ O-CO, CO₂-CO, N₂O-H₂O and CO₂-H₂O mixtures are presented. Additions of CO to the N₂O lasant increased power up to 28% for N₂O laser mixtures, whereas additions of CO to the CO₂ lasant, and the addition of H₂O to both the CO₂ and N₂O lasants, resulted in decreased output power     

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     

Effects of wet N2O oxidation on interface properties of6H-SiC MOS capacitors

Oxynitrides were grown on n- and p-type 6H-SiC by wet N₂O oxidation (bubbling N₂O gas through deionized water at 95°C) or dry N₂O oxidation followed by wet N₂O oxidation. Their oxide/SiC interfaces were investigated for fresh and stressed devices. It was found that both processes improve p-SiC/oxide but deteriorate n-SiC/oxide interface properties when compared to dry N₂O oxidation alone. The involved mechanism could be enhanced removal of unwanted carbon compounds near the interface due to the wet ambient, and hence a reduction of donor-like interface states for the p-type devices. As for the n-type devices, incorporation of hydrogen-related species near the interface under the wet ambient increases acceptor-like interface states. In summary, wet N ₂O oxidation can be used for providing comparable reliability for nand p-SiC MOS devices, and especially for obtaining high-quality oxide-SiC interfaces in p-type MOS devices