Oxynitride Gate Dielectrics Research Articles

The removal of nitrogen during boron indiffusion in silicon gate oxynitrides

The effect which nitrogen has upon boron diffusion through oxynitride gate dielectrics has been studied with secondary ion mass spectroscopy of polycrystalline silicon–oxynitride–silicon structures, and with x-ray photoelectron spectroscopy of silicon–boron–oxynitride–silicon structures. These studies show that the indiffusion of boron results in removal of nitrogen from the oxynitride. This indicates that the role of nitrogen in suppressing boron penetration is chemical in nature rather than diffusive.

Highly reliable chemical vapor deposited stacked oxynitride gate dielectrics fabricated by in situ rapid thermal multiprocessing

High-quality chemical vapor deposited (CVD) stacked oxynitride gate dielectrics have been fabricated by in situ rapid thermal multiprocessing. Bottom thin oxynitrides were formed by rapid thermal processing (RTP) of Si in nitric oxide (NO) or nitrous oxide (N2O) ambient, followed by rapid thermal chemical vapor deposition (RTCVD) of SiO2 films using SiH4 and N2O. The stacked dielectrics were then subjected to in situ rapid thermal annealing in an O2 ambient. Results show that CVD stacked oxynitride gate dielectrics have improved endurance to interface state degradation, higher charge to breakdown values, and significantly reduced defect densities compared to control thermal gate oxide.

Mobility behaviour of n-channel and p-channel MOSFETs with oxynitride gate dielectrics formed by low-pressure rapid thermal chemical vapor deposition

The electric field dependence of electron and hole mobility was investigated in n-channel and p-channel metal-oxide-semiconductor field-effect transistors with oxynitride gate dielectrics formed using low-pressure rapid thermal chemical vapor deposition with SiH/sub 4/, N/sub 2/O and NH/sub 3/ as the reactive gases. The peak electron mobility was observed to decrease with increasing nitrogen and hydrogen concentration whereas the high-field mobility degradation was improved. The hole mobility was observed to decrease for all electric fields. A self-consistent physical explanation for the observed electron and hole mobility behaviour is suggested based on the electrical results. We attribute the observed mobility characteristics mainly to the trapping behaviour of these films.

Degradation of oxynitride gate dielectric reliability due to boron diffusion

In this letter, we report on the impact of the suppression of boron diffusion via nitridation of SiO2 on gate oxide integrity and device reliability. SiO2 subjected to rapid thermal nitridation in pure nitric oxide (NO) is used to fabricate thin oxynitride gate dielectrics. Both n+ polycrystalline silicon (polysilicon) gated n-MOS (metal–oxide semiconductor) and p+-polysilicon gated p-MOS devices were subjected to anneals of different times to study the effect of dopant diffusion on gate oxide integrity. As expected, an advanced oxynitride gate dielectric will effectively alleviate the boron-penetration-induced flatband voltage instability in p+-polysilicon gated p-MOS capacitors due to the superior diffusion barrier properties. However, such improvements are observed in conjunction with some degradation of the oxide reliability due to the boron-blocking/accumulation inside the gate dielectric. Results show that even though the oxide quality is slightly degraded for NO-nitrided SiO2 with p+-polysilicon gates, p-MOSFETs (metal–oxide semiconductor field effect transistors) with these dielectrics still show improved interface stability as compared to conventional SiO2 due to the reduced boron penetration into the Si/SiO2 interface and underlying channel region.

Structure and Growth of N2O Gate Oxynitrides

AbstractA series of investigations have been conducted into the properties of N2O silicon oxynitride gate dielectrics, and the various methods of their growth. One of the principle advantages of these oxides is their resistance to interface state generation. This is linked to the presense of nitrogen near the substrate interface, where it is triply bonded to silicon. It is also demonstrated that during N2O-based furnace growth, the total concentration of NOx species varies strongly with the flow rate of N2O. This has been correlated to the temperature profile of the furnace, which can be affected by the exothermic decomposition of N2O. This property has been exploited to controllably adjust the rate of nitrogen incorporation by up to a factor of three. Although nitrogen incorporation during furnace processing is generally stable, it is shown that atomic oxygen is capable of removing previously incorporated nitrogen. Sources of atomic oxygen include the decomposition of N2O during RTP treatment, N2O processing in a high flow rate furnace, or from ozone annealing.

Low-pressure rapid thermal chemical vapor deposition of oxynitride gate dielectrics for n-channel and p-channel MOSFETs

The properties of oxynitride gate dielectrics formed using a low-pressure, rapid thermal chemical vapor deposition (RTCVD) process with SiH/sub 4/, NH/sub 3/, and N/sub 2/O as the reactive gases are presented. Material analyses show an increase of uniform nitrogen and interfacial hydrogen content with increasing NH/sub 3//N/sub 2/O flow rate ratio. MOS capacitors with both n-type and p-type substrates and both n-channel and p-channel MOSFETs were analyzed electrically. The results show increasing fixed oxide charge and interface state density with increasing nitrogen and hydrogen content in the film. A decrease in peak transconductance and improved high-field transconductance was observed for n-channel MOSFETs. Improved resistance to hot-carrier interface state generation was also observed with increasing nitrogen concentration in the films. The results suggest that an optimal nitrogen concentration of approximately 3 at.% can be considered for further development of this technology.

N-channel and p-channel MOSFETs with oxynitride gate dielectrics formed using low pressure rapid thermal chemical vapor deposition

Silicon oxynitride has become an interesting alternative to silicon dioxide for use as a gate dielectric. Typically, these oxynitride films are formed by thermally growing the dielectric with a N 2O gas source or by performing a post-oxidation anneal in ammonia [1,2]. Both of these techniques increase the thermal budget requirement because of the slower growth rate in N 2O and the extra high temperature process step required for the thermal nitridation. In this work, the properties of both n-channel and p-channel transistors with oxynitride gate dielectrics formed using a low pressure, rapid thermal chemical vapor deposition (RTCVD) process is presented.

Recent developments in Ultra thin oxynitride gate dielectrics

This paper reviews recent developments in N 2O- and NO-based oxynitride gate dielectrics for CMOS ULSI applications. These dielectrics are extremely attractive due to their process simplicity, thickness controllability, and excellent electrical characteristics. In this paper, several issues like thickness scaling, growth kinetics, chemical composition, electrical properties, hot-carrier reliability, and EEPROM applications of these dielectrics are discussed.

Electrical properties and reliability of MOSFET's with rapid thermal NO-nitrided SiO/sub 2/ gate dielectrics

This paper reports on the performance and hot carrier reliability of N- and P-channel MOSFET's with oxynitride gate dielectrics fabricated by rapid thermal nitridation (RTN) of thermally grown SiO/sub 2/ in pure nitric oxide (NO) ambient. It is found that current drivability of N-channel MOSFET's increases with NO-nitridation of SiO/sub 2/. A significant enhancement in high field electron mobility is also observed with increasing NO-nitridation. P-channel MOSFET's with NO-nitrided SiO/sub 2/ gates show somewhat lower current drivability and hole mobility compared to SiO/sub 2/ for both low- and high-V/sub g/. Both N- and P-channel MOSFET's with NO-nitrided oxides show excellent immunity to channel hot carrier degradation. The improvement in hot-carrier reliability is attributed to the efficient incorporation of nitrogen in the dielectric through NO-nitridation. A 1000/spl deg/C, short 10-second NO-anneal was found to be the optimum nitridation condition since, compared to control oxide devices, these devices showed comparable electron and hole mobility but significantly enhanced hot-carrier immunity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High Quality Ultrathin Gate Dielectrics Prepared by In-Situ RTP

AbstractThis paper reports on the formation of high quality ultrathin oxynitride gate dielectric by in-situ rapid thermal multiprocessing. Four such gate dielectrics are discussed here; (i) in-situ NO-annealed SiO2, (ii) N2O- or NO- or O2-grown bottom oxide/RTCVD SiO2/thermal oxide, (iii) N2O-grown bottom oxide/Si3N4/N2O-oxide (ONO) and (iv) N2O-grown bottom oxide/RTCVD SiO2/N2O-oxide. Results show that capacitors with NO-based oxynitride gate dielectrics, stacked oxynitride gate dielectrics with varying quality of bottom oxide (O2/N2O/NO), and the ONO structures show high endurance to interface degradation, low defect-density and high charge-to-breakdown compared to thermal oxide. The N2O-last reoxidation step used in the stacked dielectrics and ONO structures is seen to suppress charge trapping and interface state generation under Fowler-Nordheim injection. The stacked oxynitride gate dielectrics also show excellent MOSFET performance in terms of transconductance and mobility. While the current drivability and mobilities are found to be comparable to thermal oxide for N-channel MOSFET's, the hot-carrier immunity of N-channel MOSFET's with the N2O-oxide/CVD-SiO2/N2O-oxide gate dielectrics is found to be significantly enhanced over that of conventional thermal oxide.

High quality oxynitride gate dielectrics prepared by reoxidation of NH3-nitrided SiO2 in N2O ambient

The significant advantages of reoxidation of NH3-nitrided SiO2 using N2O, as opposed to O2, in a rapid thermal system have been demonstrated. MOS capacitors with N2O-reoxidised NH3-nitrided SiO2 show improved charge-to-breakdown characteristics and suppressed interface state generation under both injection polarities compared to those with pure SiO2 and O2-reoxidised NH3-nitrided SiO2. Significant reduction of nitridation-induced traps by N2O reoxidation is mainly responsible for these improvements.

Effects of AC hot carrier stress on n- and p-MOSFET's with oxynitride gate dielectrics

Effects of AC hot carrier stress on n- and p-MOSFET's with pure, NH/sub 3/-nitrided (RTN) and reoxidized nitrided (RTN/RTO) gate oxides are studied. Irrespective of the gate dielectric used, n-MOSFET's show enhanced degradation but p-MOSFET's show suppressed degradation under AC stress as compared to DC stress for the same duration. Dependence of degradation on frequency and duty cycle of gate pulse is studied. Results show that the degradation under AC stress in n-MOSFET's is suppressed whereas it is increased slightly in p-MOSFET's with the use of RTN/RTO gate oxides instead of conventional gate oxides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hot carrier effects on analog performance of N- and P-MOSFET's with oxynitride gate dielectrics

In this paper we report the impact of hot-carrier stress on analog performance of n- and p-MOSFET's with conventional oxide, NH/sub 3/-nitrided oxide (RTN) and reoxidized nitrided oxide (RTN/RTO) as gate dielectrics. Changes due to hot-carrier stress in crucial analog parameters viz., drain output resistance, voltage gain, and input offset voltage of a source coupled differential MOSFET pair are investigated. Results show that RTN/RTO gate dielectrics suppress degradation of analog parameters in n-MOSFET's but increase it slightly in p-MOSFET's, as compared to conventional oxide MOSFET's.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparing the Structure and Behavior of Point Defects in Silicon Oxynitride Gate Dielectrics formed by NH3-Nitridation and N2O-Growth/Nitridation

ABSTRACTIn this work, an electron spin resonance study of NH3-nitrided, N2O-nitrided, and N2O-grown oxides yields information relating the process history, point defect structure, and electrical behavior. NH3-nitridation is responsible for the introduction of bridging nitrogen centers, high capture cross section neutral electron traps, while N2O-processed dielectrics never exhibit these defects. In addition, structural changes at the interface due to nitridation result in observable differences in the interfacial defects.

Oxynitride gate dielectrics for p/sup +/-polysilicon gate MOS devices

Different oxynitride gate dielectrics (NH/sub 3/-nitrided, reoxidized NH/sub 3/-nitrided, N/sub 2/-annealed NH/sub 3/-nitrided, and N/sub 2/O grown oxides) are investigated for use in p/sup +/-polysilicon gate MOS devices. The comparison is based on flatband voltage shift as well as decrease in inversion capacitance. Results show that NH/sub 3/-nitrided and N/sub 2/-annealed NH/sub 3/-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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reliability issues in submicron MOSFETs with oxynitride gate dielectrics

A review of critical reliability issues in submicron MOSFETs with oxynitride gate dielectrics is presented. We have focussed our attention on: substrate and gate currents in short channel MOSFETs, hot carrier induced MOSFET degradation under DC and AC stress, gate-induced drain leakage current and its enhancement due to stress, neutral trap generation due to electrical stress and degradation of analog MOSFET parameters. We have also discussed the problems of radiation induced neutral trap generation and boron penetration through the gate dielectric, which arise due to the advanced processing techniques utilized in submicron MOSFET processing. It is concluded that the use of oxynitride gate dielectrics can effectively solve several reliability issues encountered in scaling down MOSFETs to submicron dimensions.

Comparison of neutral electron trap generation by hot-carrier stress in n-MOSFET's with oxide and oxynitride gate dielectrics

A comparative study of neutral electron-trap generation due to hot-carrier stress in n-MOSFETs with pure oxide, NH/sub 3/-nitrided oxide (RTN), and reoxidized nitrided oxide (RTN/RTO) as gate dielectrics is reported. Results show that neutral electron trap generation is considerably suppressed by nitridation and reoxidation. The nature of neutral traps is described based on the kinetics of trap filling by electron injection into the gate dielectrics immediately after channel hot-electron stress (CHES). Improved endurance of the RTN and RTN/RTO oxides is explained using physical models related to interfacial strain relaxation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Charge trapping properties in thin oxynitride gate dielectrics prepared by rapid thermal processing

In this letter, effects of post-nitridation anneals on charge trapping properties and charge-to-breakdown (Qbd) of thin (∼8.6 nm) rapidly thermal nitrided (RTN) gate SiO2 have been studied. Post-nitridation anneals consist of either rapid thermal reoxidation (RTO) in pure O2 or rapid thermal anneal (RTA) in pure N2 ambient. Both the gate voltage shift (ΔVg) and flatband voltage shift (ΔVfb) have been used to characterize the charge trapping properties under Fowler–Nordheim electron injection. It is found that both RTO and RTA reduce ΔVfb and/or ΔVg resulting from the reduction of trapped electrons as well as high-field stress-induced positive charge generation. Positive charge generation resulting from either donor-type interface state generation or trapped holes is discussed. Qbd of RTN SiO2 has been improved after RTO, and can be even larger than that of the thermal SiO2. RTA of RTN SiO2 in N2 also improves Qbd; however, the charge trapping behavior is different from that of RTO/RTN SiO2. The physical mechanism is discussed to account for the observation.

Transconductance degradation and interface state generation in metal-oxide-semiconductor field-effect transistors with oxynitride gate dielectrics under hot-carrier stress

The hot-carrier immunity of submicrometer (0.8 μm) n-channel metal-oxide-semiconductor field-effect transistors with thin (∼8.6 nm) oxynitride gate dielectrics prepared by rapid thermal reoxidation (RTO) of rapidly thermal nitrided (RTN) SiO2 has been studied. The hot-carrier immunity was evaluated in terms of hot-carrier-induced transconductance degradation (ΔGm/Gm0) and interface state generation (ΔDit/Dit0) which was measured by using charge pumping current (Icp) measurement. It is found that for improved device performance and reliability, there exists an optimum RTO condition for a given RTN SiO2. In addition, a strong correlation between ΔDit/Dit0 and ΔGm/Gm0 has been observed.

Polarity dependence of charge to breakdown and interface state generation of oxynitride gate dielectrics prepared by rapid thermal processing

MOS devices were fabricated with dry thermal oxides, nitrided oxides and annealed nitrided oxides. The anneals were performed in O2 or N2 ambients using rapid thermal processing. Charge to breakdown, Qbd, and interface state generation, ΔDit for these devices were studied using Fowler–Nordheim electron injection. The gate bias polarity dependence of Qbd and ΔDit was investigated. A model is proposed to explain the observed dependence of these quantities on the polarity of injection and process parameters.