Ultrathin Gate Dielectrics Research Articles

Gate Oxynitride Grown in N2O and Annealed in NO Using Rapid Thermal Processing

AbstractIn this paper a new technique for the formation of high quality ultrathin gate dielectrics is proposed. Gate oxynitride was first grown in N2O and then annealed by in-situ rapid thermal NO-nitridation. This approach has the advantage of providing a tighter nitrogen distribution and a higher nitrogen accumulation at or near the Si-SiO2 interface than either N2O oxynitride or nitridation of SiO2 in the NO ambient. It is applicable to a wide range of oxide thickness because the initial rapid thermal N2O oxidation rate is slow but not as self-limited as NO oxidation. The resulting gate dielectrics have reduced charge trapping, lower stress-induced leakage current and significant resistance to interface state generation under electrical stress

Integration of Plasma-Assisted and Rapid Thermal Processing for Low-Thermal Budget Preparation of Ultra-Thin Dielectrics for Stacked-Gate Device Structures

This paper discusses a new approach to the formation of ultra-thin gate dielectrics for Si-ULSI applications in which separately controlled plasma-assisted and/or rapid thermal processing steps are combined to fix the chemical bonding and minimize the defect structure at the Si–SiO2 interface, and within the dielectric layers. One example of this approach combines (i) low-temperature (300° C) plasma-assisted processing to control the initial bonding chemistries at (a) the Si–SiO2 interface, and (b) in homogeneous oxide, or composite dielectrics with nitride or oxynitride layers, with (ii) higher temperature (900° C), but low-thermal budget, rapid thermal annealing to promote physical and/or chemical relaxations that minimize both interfacial and bulk dielectric defects, thereby improving device performance.

Improvement of the SiO2/Si interface of metal-oxide-semiconductor devices using gate dielectrics formed by NF3-aided oxidation and N2O post-annealing

With the increasing requirement for ultrathin gate dielectrics in advanced metal-oxide-semiconductor structures, a low thermal budget process to grow thin dielectric film is vital, while at the same time maintaining the good interface quality and thin film reliability. In this article, thermal nitridation of fluorinated oxide in N2O ambient was investigated. While fluorinated oxides provide a lower thin film stress and better interface than conventional oxides, an excess amount of fluorine in the starting oxide has an adverse effect on the high field stability. For N2O-nitrided oxide, high temperature and prolonged nitridation time reduce the interface state generation ΔDit resulting from avalanche electron injection at the expense of increasing the flatband voltage shift ΔVfb. The electrical properties are strongly process dependent. The best operating window of N2O nitridation of fluorinated oxide (F-ox), grown at 900 °C with a 100 ppm NF3 additive, lies between 30 and 120 min at 950 °C. With careful control of fluorinated oxide growth parameters and N2O annealing, we have demonstrated an excellent way to fabricate dielectric thin films for future applications.

Electrical and Structural Properties of Ultrathin SiO2 Gate Dielectrics Prepared Under Various Conditions

We have fabricated ultrathin layers between 5 and 10 nm. Conventional thermal and rapid thermal oxide forming processes were applied, as well as a low temperature chemical vapor deposition (CVD) process. With these dielectrics, single layers have been produced for structural investigations by infrared (IR) absorbance spectroscopy. The IR‐spectra of the thermal oxides and the postannealed CVD‐oxide revealed nearly the same vibrational properties. Metal oxide semi‐conductor devices such as capacitors and field effect transistors (FETs) have been fabricated with these dielectrics. Breakdown measurements revealed a reduced high field breakdown voltage with a broadened distribution for CVD layers as compared to the results obtained for thermal oxides. This effect was reduced with decreasing thickness. From transfer characteristics and charge pumping measurements on FETs, no considerable difference in the number of fixed oxide charge and interface trapped charge density was observed for all oxides. The device properties appear to be more strongly effected by substrate dopant concentrations and the oxide thickness than by the intrinsic properties of the oxide.

P-channel MOSFET's with ultrathin N/sub 2/O gate oxides

The performance and reliability of p-channel MOSFETs utilizing ultrathin ( approximately 62 AA) gate dielectrics grown in pure N/sub 2/O ambient are reported. Unlike (reoxidized) NH/sub 3/-nitrided oxide devices, p-MOSFETs with N/sub 2/O-grown oxides show improved performance in both linear and saturation regions compared to control devices with gate oxides grown in O/sub 2/. Because both electron and hole trapping are suppressed in N/sub 2/O-grown oxides, the resulting p-MOSFETs show considerably enhanced immunity to channel hot-electron and -hole-induced degradation (e.g., hot-electron-induced punchthrough).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Highly Reliable Stacked Thermal/LPCVD Oxides for Ultrathin Gate Dielectric Applications

Highly Reliable Stacked Thermal/LPCVD Oxides for Ultrathin Gate Dielectric Applications

ChemInform Abstract: High Quality Ultrathin Gate Dielectrics Formation by Thermal Oxidation of Si in N2O.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

High Quality Ultrathin Gate Dielectrics Formation by Thermal Oxidation of Si in N 2 O

Ultrathin metal‐oxide‐semiconductor (MOS) gate dielectrics have been fabricated by conventional thermal oxidation of Si in pure ambient. Electrical results show that gate dielectrics prepared by this method exhibit comparable fixed charge density compared to control , but significantly reduced interface state generation and charge trapping under constant current stressing. A nitrogen incorporation at the interface is observed and suggested to be responsible for the improved characteristics.

Comparison of performance and reliability between MOSFETs with LPCVD gate oxide and thermal gate oxide

Summary form only given. The time-dependent dielectric breakdown (TDDB) characteristics and MOS properties and reliability of ultrathin (65-AA) LPCVD silicon oxides annealed in N/sub 2/ ambient have been studied and compared with those of thermal oxide of identical thickness. It is shown that the devices with CVD oxide have much lower defect densities and are less susceptible to interface state generation, charge trapping, and transconductance degradation than those with thermal oxide. The results indicate that CVD oxide is a promising candidate for future ULSI technology, for which reliable ultrathin gate dielectrics are required. >

Electrical characteristics of ultrathin oxynitride gate dielectric prepared by rapid thermal oxidation of Si in N2O

This letter presents a unique process to grow high quality ultrathin (∼60 Å) gate dielectrics using N2O (nitrous oxide) gas. Compared with conventional rapid thermally grown oxide in the O2, the new oxynitride dielectrics show very large charge-to-breakdown (at +50 mA/cm2, 850 C/cm2 for oxynitride compared to 95 C/cm2 for the control thermal oxide) and less charge trapping under constant current stress. Significantly reduced interface state generation was also observed under constant current stress and x-ray radiation. A secondary-ion mass spectroscopy depth profile indicates a nitrogen-rich layer at the Si/SiO2 interface, which can explain the improved integrity of oxynitride dielectric.

Study of inversion layer mobility in metal-oxide-semiconductor field-effect transistors with reoxidized nitrided oxides

The carrier effective mobility μeff in the inversion layer for both n- and p-channel metal-oxide-semiconductor field-effect transistors with ultrathin gate dielectrics prepared by rapid thermal reoxidation (RTO) of rapid thermal nitrided (RTN) SiO2 has been studied. It is found that although RTN/RTO degraded the low-field μeff, it improved significantly the electron μeff under high normal field compared to control SiO2. The effect of RTN/RTO on the hole effective mobility has also been examined and found to be quite different than on the electron effective mobility. A physical mechanism is discussed to account for the observation.

Submicron P-Channel Mos Devices with Boron Doped Polysilicon Gates Fabricated by Rapid Thermal Processing

AbstractA low thermal budget process is demonstrated for the fabrication of submicron Boron doped polysilicon gate p-channel MOS devices with ultra thin gate insulators. All critical processing steps with temperatures above 700 °C, including gate oxide growth and shallow source/drain junction formation, were performed by Rapid Thermal Processing (RTP). In situ doped polysilicon was used to eliminate the need for a high temperature drive-in step. Surface channel p-channel enhancement mode devices with excellent characteristics were fabricated to demonstrate the feasibility of this process.

Nitridation and post-nitridation anneals of SiO/sub 2/ for ultrathin dielectrics

A technique of post-oxidation annealing to improve the properties and long-term reliability of ultrathin (<100 AA) MOS gate dielectrics is discussed. In this technique, after oxidation, nitridation is done in NH/sub 3/, followed by a light reoxidation in O/sub 2/, and then an inert anneal in Ar or N/sub 2/. Using this technique, both optimum performance and reliability can be obtained without sacrificing either. NH/sub 3/ anneal of SiO/sub 2/ improved the hot-electron immunity, but degraded the interface quality. Good properties could be obtained by a strong reoxidation of the nitrided films, at the expense, however, of a substantial increase in the film thickness. Nitrogen and argon ambients were found to be equally effective at improving film properties. By annealing the film in an inert ambient following reoxidation of the nitroxide, fixed charge can be further decreased with little oxide grown, electron mobility in NMOS FETs increases further, and the hot-electron lifetime is much longer than that of the starting oxide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improved radiation hardness of MOS devices with ultrathin nitrided oxide gate dielectrics prepared by rapid thermal processing

The radiation hardness of MOS devices with ultrathin nitrided oxides ( approximately 100 AA) prepared by rapid thermal nitridation (RTD) of thin oxides has been studied. The radiation was performed by exposing devices under X-rays of 50 keV to a dose of 0.5 Mrad(Si). Compared with conventional thermal oxides, the RTN oxide devices exhibit a much smaller increase in both the fixed charge N/sub f/ and the interface state D/sub it/ densities. In addition, it is found that higher RTN temperature and/or longer durations produce smaller Delta N/sub f/ and Delta D/sub it/. >

Performance and Reliability of Ultrathin Oxynitride Gate Dielectrics Prepared using In-Situ Multiple Rapid Thermal Processing

ABSTRACTThe electrical characteristics of ultrathin oxynitride gate dielectrics prepared by in-situ multiple rapid thermal processing in reactive ambients (O2 and NH3) have been studied. Specifically, the conduction mechanism, charge trapping properties, time-dependent breakdown, and interface hardness in oxynitride films have been characterized as a function of both RTO and RTN processing parameters. In addition, N-channel MOSFET's have been fabricated using oxynitrides as gate dielectrics and their hot carier immunity has been examined and compared with devices with pure thermal oxides. Devices with superior electrical characteristics and reliability have been produced by optimizing RTO/RTN parameters.

The Effect of Post-Growth Anneals on Nitroxide Films

ABSTRACTA new technique of post-oxidation annealing has been introduced to improve the properties and long term reliability of ultrathin (&lt;100 Å) MOS gate dielectrics. In this technique, after oxidation, nitridation is done in NH3 followed by a light reoxidation in O2 and then an inert anneal in Ar or N2. Using this technique both optimum performance as well as reliability can be obtained without sacrificing either. NH3 anneal of SiO2 improved the hot electron immunity, but degraded the interface quality. Good properties could be obtained by a strong reoxidation of the nitrided films, however, at the expense of a substantial increase in the film thickness. Nitrogen and argon ambients were found to be equally effective at improving film properties. By annealing the film in an inert ambient following reoxidation of the nitroxide, fixed charge can be further decreased with little oxide grown, electron mobility in NMOS FETs increases further, and the hot electron lifetime is much longer than that of the starting oxide.

Electrical characteristics and irradiation sensitivity of IGFETs with rapidly grown ultrathin gate dielectrics

Results are reported on n-channel insulated-gate field effect transistors (IGFETs) with gate insulators (50-60 AA) formed by rapid thermal processing (RTP) in O/sub 2/ and NH/sub 3/ ambients. Two types of gate dielectrics were grown: rapid thermal oxides grown in O/sub 2/ and nitroxides formed by multicycle processing in NH/sub 3/ and O/sub 2/. RTP was also used for annealing AS/sup +/-implanted source-drain junctions at 1050 degrees C for 30 s. The transistors were characterized by measuring mu /sub eff/, V/sub T/, subthreshold slope, Q/sub f/, D/sub if/, D/sub bd/, and hot-electron immunity. The observed trends are discussed. The results demonstrate excellent device characteristics, including, in particular, increased hot-electron immunity and resistance against high-energy electron irradiation. >

Low-temperature direct nitridation of silicon in nitrogen plasma generated by microwave discharge

Plasma nitridation of silicon has been performed at low temperatures (at ≊500 °C and also lower temperatures) in nitrogen plasma generated by microwave discharge. The effects of various growth parameters such as microwave power, nitrogen gas pressure, anodization current and polarity, growth time and substrate temperature on the thickness, surface morphology, uniformity, composition and stoichiometry, and electrical and physical characteristics of the grown films have been studied. The thickness of the grown films varied between 30 and more than 100 Å depending on the growth conditions. Based on the grazing-angle Rutherford-backscattering data, the grown films were silicon nitride with some oxygen and carbon contamination. A typical breakdown field of ≊10 MV/cm was measured for these films. The preliminary results obtained indicate that these nitride films can be considered as potential candidates for ultrathin gate, tunnel, and dram memory insulators for very large scale integration devices.