Reoxidized Nitrided Oxide Research Articles

Process dependency of radiation hardness of rapid thermal reoxidized nitrided gate oxides

The radiation hardness of MOS capacitors with various reoxidized nitrided oxide (RNO) structures was studied by changing the duration of rapid thermal processes during sample preparation and by applying irradiation-then-anneal (ITA) treatments on samples after preparation. It was found that the initial flatband voltage and midgap interface trap density of MOS capacitors exhibit turnaround dependency on the total time of nitridation and reoxidation processes. For samples with nitrided oxide (NO) structures, the radiation-induced variations of the above parameters are also turnaround-dependent on nitridation time. However, when the reoxidation process is performed, the radiation hardness for all samples is gradually improved with increasing reoxidation time no matter when the nitridation time. The most radiation-hard process for RNO structures is suggested. Finally, it was found that when ITA treatments are applied on samples after preparation, their radiation hardness is much improved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improvement in radiation hardness of reoxidized nitrided oxide (RNO) in the absence of post-oxidation anneal

A simple radiation-hard process for rapid thermal reoxidized nitrided oxide (RNO) structures is proposed. This process involves fast pulling (FP) of samples out of the furnace in a mixture of oxygen and nitrogen immediately after the oxidation has been completed. Samples with starting oxides prepared by conventional postoxidation annealing (POA) are also compared. It is found from CV curves that the initial interface property of an RNO structure with a fast pulled starting oxide (RNO/sub FP/) is almost the same as that with a postoxidation annealed starting oxide (RNO/sub POA/); however, after being exposed to Co-60 irradiation, the former becomes superior to the latter. Excess oxygen left at interface in the starting oxide during the fast pulling procedure might be the origin of the radiation-hard property for RNO/sub FP/ structures. >

Simplified closed-form trap-assisted tunneling model applied to nitrided oxide dielectric capacitors

Conduction has been studied in ultrathin nitrided oxide, re-oxidized nitrided oxide, and nitrogen-annealed nitrided oxide film capacitors in which the nitridation step was performed by a low-partial-pressure nitridation technique. Results indicate that, as well as some degree of barrier lowering due to the build-up of nitrogen at the injecting interface, a trap-assisted mechanism could be responsible for the enhanced conduction exhibited by the nitrided oxide devices. A simplified closed-form trap-assisted tunneling model is employed that produces a fit to the data with a trap depth of 2.1 eV. The difference between this trap model and a model requiring numerical integration was negligibly small (∼2%).

Interface-state generation under radiation and high-field stressing in reoxidized nitrided oxide MOS capacitors

The time evolution of interface-state (D/sub it/) buildup following radiation and high-field stressing in MOS capacitors was compared for 45-nm-thick conventional 'dry' oxide (SiO/sub 2/) and reoxidized nitrided oxide (RNO). While the oxide shows the expected postirradiation increase of D/sub it/ with time under positive bias, the RNO shows no time-dependent buildup. This indicates that hydrogen transport, widely held responsible for the slow evolution of D/sub it/ after radiation, does not play a role in D/sub it/ generation in RNO. It is suggested that this is due to a blocking effect of the nitrogen-rich oxynitride layer which is known to exist in RNO near the silicon/silicon-dioxide interface, and which inhibits the drift of hydrogen ions to the interface. Exposure of the capacitors to a hydrogen ambient after irradiation confirms that for RNO, unlike the case of oxide, there is no increase of D/sub it/ due to hydrogen effects. Postirradiation electron injection in RNO suggests that trapped-hole recombination may be responsible for the small D/sub it/ generation seen in RNO.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of radiative processing steps on inversion layer mobility and channel hot carrier damage in reoxidized nitrided oxide mosfets

The effects of x-ray irradiation and a subsequent low temperature anneal on the properties of reoxidized nitrided oxide (RNO) MOSFET's were examined. Irradiation was found to degrade conventional SiO2 MOSFET lifetime under channel hot carrier stress far more strongly than RNO lifetime, particularly for p-channel devices. This is attributed to reduced bulk neutral electron trap generation in RNO. The inversion layer mobility of RNOn-MOSFET's (and, to a lesser degree,p-MOSFET's) was found toincrease after irradiation and anneal. 1/f noise measurements indicate that this change in mobility is due to a reduction in the density of near-interface electron traps.

Hot-carrier-induced degradation in reoxidized-nitrided-oxide n-MOSFETs under mixed AC-DC stressing

Reduced degradation rate can be observed for reoxidized-nitrided-oxide (RNO) n-MOSFETs under dynamic stressing versus the corresponding static stressing. A new degradation mechanism is proposed in which trapped holes in gate oxide are neutralized by the hot-electron injection, with no significant generation of interface states because of the hardening on the Si-SiO/sub 2/ interface by nitridation/reoxidation steps. The RNO device degradation during AC stressing arises mainly from the charge trapping in the gate oxide rather than the generation of interface states. Moreover, the AC-stressed RNO devices are significantly inferior to the fresh RNO devices in terms of DC stressing, possibly due to lots of neutral electron traps in the gate oxide resulting from the AC stressing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-temperature furnace-grown reoxidized nitrided oxide gate dielectrics as a barrier to boron penetration

Reoxidized nitrided oxide (ROXNOX) gate dielectrics can be used to block the diffusion of boron into the MOS channel region. However, fixed oxide charge annealing can mask the effects of boron in the channel, a particularly important consideration for low-temperature gate oxides. The authors separate the effect of fixed charge annealing from the effect of boron diffusion and demonstrate that a low-temperature furnace-grown reoxidized nitrided oxide has a substantial advantage over conventional gate oxides in protecting the channel from boron over a wide range of annealing times and temperatures. They also address the issue of fixed charge annealing in low-temperature reoxidized nitrided oxides and present an approach to maintain acceptable gate dielectric quality while preserving a low D-t product for integration into a scaled dual-gate CMOS process. >

Radiation-induced increase in the inversion layer mobility of reoxidized nitrided oxide MOSFETs

The inversion layer mobility of reoxidized nitrided oxide (RNO) n-MOSFETs (and, to a lesser degree, p-MOSFETs) is found to increase after irradiation and subsequent low-temperature anneal, a process sequence which occurs in X-ray or electron-beam lithography fabrication of CMOS circuits. 1/f noise measurements indicate that the irradiation and anneal reduce the density of near-interface electron traps. Thus the findings support the model which invokes nitridation-induced near-interface electron traps as part of the explanation for reduced low-field electron mobility in RNO versus conventional oxide MOSFETs. The data for p-channel devices suggest that the near-interface trap is amphoteric in nature, but much less efficient at trapping holes. >

Temperature and field dependence of carrier mobility in MOSFETs with reoxidized nitrided oxide gate dielectrics

The vertical field ( E eff) dependence of electron and hole mobility ( μ n, p ) in MOSFETs with reoxidized nitrided oxide (RONO) gate dielectrics is characterized and compared with that of MOSFETs with thermal oxide (SiO 2) gate dielectrics over temperatures ranging from 100 to 350 K. In the devices studied it is found that, at 300 K, μ n (RONO)/ μ n (SiO 2) is less than 1 for E eff < 0.75 MV cm −1 and is 1.12 at E eff = 1 MV cm −1. As temperature is decreased to 100 K, μ n (RONO)/ μ n (SiO 2) at E eff = 1 MV cm −1 increases to 1.3. Furthermore, the E eff range over which μ n (RONO) > μ n (SiO 2) widens with decreasing temperature. However, μ p (RONO)/ μ p (SiO 2) is found to be consistently less than 1 at 300 K, and is degraded severely with decreasing temperature. A laser scanning technique was applied to measure the stress in thin N-rich Si layers that are on the surface of Si substrates and significant tensile stress was found. A model based on the nitridation-induced donor layer and tensile stress in the N-rich surface Si layer of RONO devices is proposed to qualitatively explain the field and temperature dependence of both μ n (RONO) and μ p (RONO). In addition, the saturation velocity of electrons ( ν sat) in RONO MOSFETs, important to the performance of short channel devices, is also determined. Implications of μ n, p (RONO) and ν sat on the performance of the RONO technology are discussed.

Thermal instability in p-channel transistors with reoxidized nitrided oxide gate dielectrics

The authors report p-channel transistor degradation at elevated temperatures due to negative bias temperature instability (NBTI) combined with high-temperature hot-carrier degradation in devices with reoxidized nitrided oxide (RNO) gate dielectrics. It is shown that the degradation is considerably more severe than in devices with oxide gate dielectrics. At temperatures below 150 degrees C and voltages below 6 V, the RNO degradation under NBTI and combined NBTI/hot-carrier stress conditions is roughly an order of magnitude worse than the oxide degradation. Compared to the NBTI stress alone, the combined effect of hot-carrier and NBTI stress is to increase the degradation of both RNO and oxide devices by an additional two orders of magnitude. The results obtained are particularly significant for the determination of appropriate burn-in conditions for integrated circuits.

Recovery of hot-carrier damage in reoxidized nitrided oxide MOSFET's

Recovery of channel hot-carrier damage in reoxidized nitrided oxide (RNO) n- and p-MOSFETs is examined. It is found that recovery is substantially greater in RNO versus conventional oxide (CO) devices, particularly for p-MOSFETs. The authors believe this recovery is due to the detrapping of electrons trapped in the nitridation-induced traps near the substrate interface. The more rapid recovery of the hot-carrier damage in RNO devices will produce greater circuit lifetime improvements over conventional oxides than predicted by accelerated static high-voltage tests.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field and temperature acceleration of time-dependent dielectric breakdown for reoxidized-nitrided and fluorinated oxides

The effects of injection current density and temperature on time-dependent dielectric breakdown (TDDB) of low-pressure thermally reoxidized-nitrided oxides (RNOs) and fluorinated oxides (FOs) with equivalent oxide thicknesses of 100 AA were examined. Time to breakdown for RNO was found to be improved over that for thermal oxide while both the impact ionization coefficient and the activation energy of lifetime are comparable to those of control oxide. On the other hand, no obvious TDDB improvement was observed for FO. This observation, in conjunction with the results for charge trapping measurements at different temperatures, indicates that the lifetime improvement for RNOs might be due to the reduced charge traps in these films. I-V ramp tests have shown that RNO has a comparable density to that of control oxide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Positive-charge trapping in nitrided oxide and reoxidized nitrided oxide gate dielectrics

The charge-trapping characteristics of nitrided oxide and reoxidized nitrided oxide (ROXNOX) gate dielectrics following constant-current stressing are studied, with an emphasis on the behavior of positive trapped charge. The positive charge is attributed to slow donor states, which are created and ionized during electrical stress. Slow donor states are shown to be responsible for a reversible, bias- and temperature-dependent charge relaxation that is observed following electrical stress. The number of slow donor states created during stress is found to be a function of the nitridation and reoxidation conditions. Using optimized process conditions, ROXNOX dielectrics can be grown with essentially no slow donor states and, hence, with little relaxation.

Trapping and trap creation studies on nitrided and reoxidized-nitrided silicon dioxide films on silicon

Alternative gate insulators for silicon-based technologies involving nitridation or reoxidation-nitridation of silicon dioxide layers are shown to be inferior to as-grown oxide in terms of charge trapping over a wide range of fields under uniform electron-injection conditions. Although nitrided layers seem to suppress trap generation more effectively than does silicon dioxide, background trapping in the as-fabricated oxynitride layers formed near their interfaces is greatly increased. The apparent reduction in trapped charges universally reported in reoxidized-nitrided oxides under high-field injection conditions is shown to be due to a decrease in occupation of these sites at fields exceeding 8 MV/cm.

Channel hot-carrier stressing of reoxidized nitrided oxide p-MOSFETs

Channel hot carrier reliability of reoxidized nitrided oxide (RNO) and conventional oxide p-MOSFETs was studied. RNO p-MOSFET degradation is shown to be due to electron trapping, as in oxide devices. Since nitridation introduces electron traps, device lifetimes determined by static stress were found to be lower by 2-3 orders of magnitude in the RNO than in the oxide p-MOSFETs. However, circuit life is determined by the shortest-lived device type. For conventional oxide, circuit lifetime is determined by n-MOSFET lifetime. The authors demonstrate that both RNO n- and p-channel lifetimes are many orders of magnitude longer than oxide n-channel lifetimes; therefore, for submicrometer CMOS, use of RNO is predicted to increase circuit lifetime significantly. X-ray irradiations were found to degrade oxide p-channel hot carrier reliability far more strongly than RNO reliability. >

Reoxidized nitrided oxides (RNO) for latent ESD-resistant MOSFET dielectrics

n-channel MOSFETs with reoxidized nitrided oxides (RNOs) are compared to conventional oxides with respect to their susceptibility to latent damage from electrostatic discharge (ESD) and ESD-like events. It is shown, using both ESD events and simulated ESD events by snapback, that the RNO devices have substantially better resistance to latent damage from such events. The increased resistance is explained by the robustness of the nitrided oxides both to interface state generation and to oxide trap creation by hot-hole injection. It is concluded that, along with hot-carrier resistance, the RNO robustness to latent ESD damage is another advantage of this technology. >

Dynamic hot-carrier stressing of reoxidized nitrided oxide

Dynamic channel hot-carrier stress measurements were performed on reoxidized nitrided oxide (RNO) nMOSFETs in order to determine the importance of the high-gate-voltage electron trapping that occurs during static stress. RNO transistors stressed under circuit operation conditions were found to exhibit extrapolated lifetime 10/sup 7/ times greater than the lifetime determined from static stress measurements at the worst-case condition V/sub g/ approximately V/sub d/. Comparing RNO with conventional oxide under high-voltage dynamic stress conditions predicts a lifetime gain of 10/sup 10/ for the RNO. This finding makes RNO an extremely attractive gate dielectric candidate for scaled CMOS devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of synchrotron X-ray radiation on the channel hot-carrier reliability of reoxidized nitrided silicon dioxide

Channel hot-carrier-induced degradation was studied in reoxidized nitrided oxide n-channel MOSFETs which were exposed to 1-2-keV X-rays from a synchrotron source. It is found that transconductance degradation under high gate bias stress (Vg=1.3 V/sub d/) is enhanced by the X-ray exposure to a lesser degree in reoxidized nitrided oxide (RNO) devices than in conventional oxide devices. This indicates that radiation generates fewer electron traps in RNO than in a conventional oxide. >

An optimized 850 degrees C low-pressure-furnace reoxidized nitrided oxide (ROXNOX) process

The electrical characteristics of thin (10 nm) MOS gate dielectrics formed at 850 degrees C by low-pressure furnace nitridation of SiO/sub 2/ followed by an oxygen anneal (reoxidation) are described. The ROXNOX process is demonstrated to be readily scalable from 950 degrees C to 850 degrees C through the use of higher partial pressures in the nitridation and reoxidation steps, resulting in the same quality dielectric formed with a lower D/sub t/ product. Electrical characterization results of capacitors and transistors with the 850 degrees C ROXNOX dielectric are presented. Reliability of the 850 degrees C ROXNOX dielectric is demonstrated through Fowler-Nordheim and channel hot-electron stressing results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Circuit performance of CMOS technologies with silicon dioxide and reoxidized nitrided oxide gate dielectrics

The circuit performance of CMOS technologies with silicon dioxide (SiO/sub 2/) and reoxidized nitrided oxide (RONO) gate dielectrics over the normal regime of digital circuit operation, i.e. V/sub GS/<or=5 V and B/sub DS/<or=5 V, is discussed. The simulation of a simple CMOS inverter has shown that the SiO/sub 2/ inverter consistently outperforms the RONO inverter over temperatures ranging from 300 to 100 K. This can be attributed mainly to the significantly lower mu /sub p/ (hole mobility) of RONO p-channel devices. At 300 K, mu /sub p/(RONO) is 14-8% smaller than mu /sub p/(SiO/sub 2/) over the entire range of gate biases, while mu /sub n/(RONO) (electron mobility of n-channel RONO devices) is also smaller than mu /sub n/(SiO/sub 2/) and reaches only 96% of mu /sub n/(SiO/sub 2/) at V/sub GS/=5 V. At 100 K, mu /sub n/(RONO)/ mu /sub n/(SiO/sub 2/) at V/sub GS/=5 V is increased to 1.10, however, mu /sub p/(RONO)/ mu /sub p/(SiO/sub 2/) at V/sub GS/=5 V is degraded to 0.59. The dependence of circuit performance on the supply voltage has also been evaluated for the RONO and SiO/sub 2/ inverters.<<ETX>>