Characteristics of polysilicon thin-film transistor with thin-gatedielectric grown by electron cyclotron resonance nitrous oxide plasma

Polysilicon thin-film transistors (poly-Si TFT's) with thin-gate oxide grown by electron cyclotron resonance (ECR) nitrous oxide (N₂ O)-plasma oxidation is presented. ECR N₂O-plasma oxidation successfully incorporates nitrogen atoms at the SiO₂/poly-Si interface, consequently forms a nitrogen-rich layer with Si≡N bonds at a binding energy of 397.8 eV. ECR N₂ O-plasma oxide grown on poly-Si films shows higher breakdown fields than thermal oxide. The fabricated poly-Si TFT's with N₂ O-plasma oxide show better performance than those with ECR O₂ -plasma oxide, which results not only from the smooth interface but also oxygen- and nitrogen-plasma passivation     

Highly reliable ECR N2O-plasma polyoxide grown on heavily phosphorus-doped polysilicon films

Reliability of polyoxide grown by electron cyclotron resonance (ECR) N₂O-plasma on heavily phosphorus-doped polysilicon has been investigated for the interpoly dielectrics (IPDs) of nonvolatile memories (NVMs). ECR N₂O-plasma polyoxide grown on polysilicon with phosphorus of 1 × 10²¹ cm⁻³ exhibits a significantly high breakdown field of 10 MV/cm and low electron trapping rate of 0.5 V, which are regardless of phosphorus concentration. The improvements are attributed to the smooth polyoxide/polysilicon interface, low phosphorus concentration, and nitrogen-rich layer with strong silicon-nitrogen bonds at the polyoxide/polysilicon interface.     

High-performance p-channel poly-Si TFT's using electron cyclotronresonance hydrogen plasma passivation

This letter presents a summary of the first detailed investigation of electron cyclotron resonance (ECR) hydrogen plasma exposure treatments of p-channel poly-Si thin film transistors (TFT's). It is shown that ECR hydrogenation can be much more efficient than RF hydrogenation. Poly-Si p-channel TFT's fabricated at low temperatures (⩽625°C) and passivated with the ECR hydrogenation treatment are shown to exhibit ON/OFF current ratios of 7.6×10⁷, subthreshold swings of 0.62 V/decade, threshold voltages of -4.6 V, and hole mobilities over 18 cm²/V.s     

Low-temperature polysilicon TFT with gate oxide grown byhigh-pressure oxidation

Polysilicon thin-film transistors (TFTs) were fabricated with the maximum processing temperature limited to 650°C. Best results were obtained when the gate oxide was grown by a two-step high-pressure oxidation process, using high-pressure steam and then dry oxygen both at 15 atm and 650°C. The TFTs exhibit a mobility of 34 cm²/V×s, threshold voltage of 3.5 V, leakage current below 0.01 pA/μm, subthreshold slope of 0.18 V/decade, and an ON/OFF ratio of over eight orders of magnitude. These values are comparable to those obtained with conventional polysilicon TFTs using high-temperature thermal oxidation     

Highly reliable ultrathin silicon oxide film formation at lowtemperature by oxygen radical generated in high-density krypton plasma

This paper focuses attention on electrical properties of silicon oxide films grown by oxygen radical generated in Kr/O₂ mixed high-density microwave-excited plasma at 400°C. They represent high growth rate, low activation energy, high dielectric strength, high charge-to-breakdown, and low interface trap density and bulk charge enough to replace thermally grown silicon oxide     

The characteristics of polysilicon oxide grown in pureN2O

This work reports on the characteristics of polysilicon oxide grown in pure N₂O (N₂O-grown polyoxide). The obtained polyoxide has a desirable polarity asymmetry of J-E characteristic, i.e., a lower leakage current and a higher breakdown electric field, which are ideal for the nonvolatile memory application, when the top electrode is positively biased. The asymmetry is due to the smoother surface of the N₂O-grown polyoxide. Comparing to conventional polyoxides, the N₂O-grown polyoxide has a lower electron trapping rate and a larger Q_bd, which are attributed to the incorporated nitrogen at the polyoxide/poly-1 interface. The centroids of trapped charges of the N₂O-grown polyoxide are more away from the polyoxide/poly-1 interface and this affects the polarity dependence of trapping     

Performance and reliability of low-temperature polysilicon TFT with a novel stack gate dielectric and stack optimization using PECVD nitrous oxide plasma

This paper proposes a novel tetraethylorthosilicate (TEOS)/oxynitride stack gate dielectric for low-temperature poly-Si thin-film transistors, composed of a plasma-enhanced chemical vapor deposition (PECVD) thick TEOS oxide/ultrathin oxynitride grown by PECVD N/sub 2/O plasma. The novel stack gate dielectric exhibits a very high electrical breakdown field of 8.5 MV/cm, which is approximately 3 MV/cm higher than traditional PECVD TEOS oxide. The novel stack oxide also has better interface quality, lower bulk-trap density, and higher long-term reliability than PECVD TEOS dielectrics. These improvements are attributed to the formation of strong Si/spl equiv/N bonds of high quality ultra-thin oxynitride grown by PECVD N/sub 2/O plasma, and the reduction in the trap density at the oxynitride/poly-Si interface.     

Improvement of polysilicon oxide characteristics by fluorineincorporation

The effect of fluorine on the polysilicon oxide (polyoxide) characteristics is investigated. It is found that the polyoxide leakage current and breakdown strength are improved as fluorine is incorporated into the oxide film. Experimental results show that the improvement is believed to be due to the oxide stress relaxation rather than the change of the polyoxide/polysilicon interface texture     

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     

Improvement of polysilicon oxide by growing on polished polysiliconfilm

This letter first reports the characteristics of polyoxide that was thermally grown on polished polysilicon film. Compared to conventional polyoxide, polyoxide grown on polished polysilicon film exhibits lower leakage current, higher dielectric breakdown field, larger effective barrier height, and higher charge-to-breakdown. This simple and well-operated process provides a very promising option for the interpolysilicon oxide     

Highly reliable MIS capacitors with plasma nitridation and doubled dielectric-constant tantalum pentoxide

We studied effective thinning of metal-insulator-semiconductor tantalum pentoxide capacitors experimentally for DRAM application. First, we investigated the dielectric constant of a tantalum pentoxide film deposited and crystallized on an oxidation-resistant thick silicon-nitride film. Dependence of electrically equivalent thickness on physical thickness of tantalum pentoxide revealed an increased dielectric constant of 60, whereas the films on a silicon-dioxide film had a dielectric constant of no more than 40. To apply this increased dielectric constant to DRAM capacitors, we applied novel plasma nitridation on the surface of polysilicon. The plasma-nitrided surface showed fair oxidation resistance up to 800/spl deg/C, at which a tantalum pentoxide film fully crystallizes. The temperature was 100/spl deg/C higher than that of a conventional treatment using rapid thermal nitridation (RTN). The improved oxidation resistance enabled the increased dielectric constant as well as suppression of silicon oxide between the film and polysilicon. Consequently, effective thinning by 10% was demonstrated even on rugged polysilicon without increase of leakage current. Time-dependent dielectric-breakdown measurements revealed that the tantalum pentoxide capacitors fabricated using plasma nitridation are expected to have a lifetime three orders of magnitude longer than that of those fabricated using RTN.     

Effect of the nitrous oxide plasma treatment on the MIM capacitor

We report the demonstration of near zero voltage coefficient of capacitance (VCC) by exposing the silicon nitride dielectric of the metal-insulator-metal capacitor (MIM) to nitrous oxide (N₂O) plasma. Oxidization in the N₂O plasma enhanced the hard breakdown field, whereby an excess of 9 MV/cm was achieved. In addition, low-temperature coefficient of capacitance (TCC) of < 20 ppm/K and high dielectric constant ⩾ 6.5 were preserved     

Highly robust ultrathin silicon nitride films grown atlow-temperature by microwave-excitation high-density plasma for gigascale integration

This paper focuses attention on electrical properties of ultra-thin silicon nitride films grown by radial line slot antenna high-density plasma system at a temperature of 400°C as an advanced gate dielectric film. The results show low density of interface trap and bulk charge, lower leakage current than jet vapor deposition silicon nitride and thermally grown silicon oxide with same equivalent oxide thickness. Furthermore, they represent high breakdown field intensity, almost no stress-induced leakage current, very little trap generation even in high-field stress, and excellent resistance to boron penetration and oxidation     

Improved reliability of low-temperature polysilicon TFT by post-annealing gate oxide

We have investigated the electrical characteristics of gate oxide films deposited by plasma enhanced chemical vapor deposition (PECVD) with respect to gate oxide integrity (GOI) and its reliability. In the investigation, post-annealed gate oxide was compared with as-deposited oxide. It was shown that the characteristics of GOI strongly depended on the charge trapping characteristics and deep level interface states generation under FN stress, which was remarkably improved by post-annealing after gate oxide deposition. Improved FN stress and hot carrier stress reliability of CMOS devices implemented on the glass substrate are also discussed.     

Low temperature plasma enhanced chemical vapor deposition of silicon oxide films using disilane and nitrous oxide

Silicon oxide films have been deposited between room temperature and 300°C using disilane and nitrous oxide by plasma enhanced chemical vapor deposition. Film deposition was investigated as a function of the gas flow ratio of nitrous oxide to disilane, the substrate temperature, the total gas flow rate, the radio frequency discharge power, and the process pressure. The stoichiometric SiO₂ films were obtained when the gas ratio of nitrous oxide to disilane was in the range of 50-150. The deposition was found to be nearly temperature independent indicating the mass transport limited regime.     

High dielectric constant TiO2 film grown on polysilicon by liquid phase deposition

In this study, titanium dioxide (TiO₂) films were grown on polycrystalline silicon by liquid phase deposition (LPD) with ammonium hexafluoro-titanate and boric acid as sources. The film structure is amorphous as examined by X-ray diffraction (XRD). A uniform composition of LPD-TiO₂ was observed by SIMS examination. The leakage current density of an Al/LPD-TiO₂/poly-Si/p-type Si metal–oxide–semiconductor (MOS) structure is 1.9 A/cm² at the negative electric field of 0.7 MV/cm. The dielectric constant is 29.5 after O₂ annealing at 450 °C. The leakage current densities can be improved effectively with a thermal oxidized SiO₂ added at the interface of LPD-TiO₂/poly-Si. The leakage current density can reach 3.1×10⁻⁴ A/cm² at the negative electric field of 0.7 MV/cm and the dielectric constant is 9.8.     

High performance low temperature polysilicon thin film transistorusing ECR plasma thermal oxide as gate insulator

Electron cyclotron resonance (ECR) plasma thermal oxide has been investigated as a gate insulator for low temperature (⩽600°C) polysilicon thin-film transistors based on solid phase crystallization (SPC) method. The ECR plasma thermal oxide films grown on a polysilicon film has a relatively smooth interface with the polysilicon film when compared with the conventional thermal oxide and it shows good electrical characteristics. The fabricated poly-Si TFT's without plasma hydrogenation exhibit field-effect mobilities of 80 (60) cm²/V·s for n-channel and 69 (48) cm²/V·s for p-channel respectively when using Si₂ H₆(SiH₄) source gas for the deposition of active poly-Si films     

Highly reliable, high-C DRAM storage capacitors with CVD TA2O5 films on rugged polysilicon

The authors report on a highly reliable stacked storage capacitor with ultrahigh capacitance using rapid-thermal-annealed low-pressure chemical vapor deposited (LPCVD) Ta₂O₅ films (~100 Å) deposited on NH₃-nitrided rugged poly-Si electrodes. Capacitances as high as 20.4 fF/μ² (corresponding to the thinnest t_ox.eff (16.9 Å) ever reported using LPCVD-Ta₂O₅ and poly-Si technologies) have been achieved with excellent leakage current and time-dependent dielectric breakdown (TDDB) characteristics. Extensive electrical characterization over a wide temperature range (~25-300°C) shows that Ta₂O ₅ films on rugged poly-Si electrodes have a better temperature stability in dielectric leakage and breakdown compared to the films on smooth poly-Si electrodes     

Thin tunnel oxide grown on silicon substrate pretreated by CF4 plasma

High tunneling current and large resistance against stress were the main issue of tunnel oxide for scaling down the operation voltage of EEPROMs. In this letter, thin-tunnel oxides grown on a CF₄ pretreated silicon substrate were prepared and investigated for the first time. The fabricated oxide has about three orders of tunneling current higher than that of control one; furthermore, the stress induced anomalous and low electric field leakage currents were greatly suppressed. The improvement could be contributed to F-incorporation in oxide. This type of oxide is suitable for fabricating low-voltage EEPROMs and less process complexity was added     

Degradation of submicron N-channel MOSFET hot electron reliabilitydue to edge damage from polysilicon gate plasma etching

The impact of poly-Si gate plasma etching on the hot electron reliability of submicron NMOS transistors has been explored. The results show that the gate oxide and SiO₂-Si interface near the drain junction have a susceptibility to hot electron injection that increases with overetch time. We show for the first time that this degradation of hot electron reliability is attributable to the edge type of gate oxide damage resulting from direct plasma exposure during overetch processing. We demonstrate that this type of damage does not scale with channel length and becomes even more important in shorter channel transistors