Atul Joshi

Hot-carrier-stress effects on gate-induced drain leakage current in n-channel MOSFETs

The effects of hot-carrier stress on gate-induced drain leakage (GIDL) current in n-channel MOSFETs with thin gate oxides are studied. It is found that the effects of generated interface traps ( Delta D/sub it/) and oxide trapped charge on the GIDL current enhancement are very different. Specifically, it is shown that the oxide trapped charge only shifts the flat-band voltage, unlike Delta D/sub it/. Besides band-to-band (B-B) tunneling, Delta D/sub it/ introduces an additional trap-assisted leakage current component. Evidence for this extra component is provided by hole injection. While trapped-charge induced leakage current can be eliminated by a hole injection subsequent to stress, such injection does not suppress interface-trap-induced leakage current.<<ETX>>

MOS characteristics of NH/sub 3/-nitrided N/sub 2/O-grown oxides

The technique of NH/sub 3/ nitridation of N/sub 2/O oxides is proposed and demonstrated for increasing nitrogen concentration in N/sub 2/O oxides so as to improve the resistance to boron penetration, without any adverse effects on electrical and reliability properties. Results show that NH/sub 3/-nitrided N/sub 2/O oxides exhibit excellent electrical (low fixed charge) and reliability (smaller charge trapping and suppressed interface state generation) properties, with an additional advantage of significantly improved resistance to boron generation. This technique may have a great impact on deep-submicrometer dual-gate CMOS technology.<<ETX>>

High-field breakdown in thin oxides grown in N/sub 2/O ambient

A detailed study of time-dependent dielectric breakdown (TDDB) in N/sub 2/O-grown thin (47-120 AA) 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/SiO/sub 2/ 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 N/sub 2/O 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 N/sub 2/O oxides. A large reduction in time-to-breakdown is observed under bipolar stress when the thickness is scaled below 60 AA. A physical model is suggested to explain this behavior. Overall, N/sub 2/O oxides show improved breakdown properties compared with pure SiO/sub 2/. >

Effect of rapid thermal reoxidation on the electrical properties of rapid thermally nitrided thin-gate oxides

The authors report a systematic study of the impact of post-nitridation rapid thermal anneals in oxygen and nitrogen on the electrical properties of MOS devices with thin gate oxides. A comparative study of the two annealing ambients has led to the formulation of qualitative models to describe the charge trapping properties of the respective gate dielectrics. Roles of the post-nitridation anneals in altering the radiation and hot-electron sensitivity of the MOS devices are investigated and explained on the basis of structural changes in the gate oxides during nitridation and subsequent annealing. The performance and reliability of MOSFETs with reoxidized nitrided gate oxides are investigated. Overall, the results indicate that reoxidized nitrided oxides show improved charge trapping properties, better resistance to radiation and hot-carrier stress, and improved high-field electron mobility in MOSFETs. >

Time-dependent dielectric breakdown characteristics of N/sub 2/O oxide under dynamic stressing

Time-dependent dielectric breakdown (TDDB) characteristics of MOS capacitors with thin (120-AA) N/sub 2/O gate oxide under dynamic unipolar and bipolar stress have been studied and compared to those with control thermal gate oxide of identical thickness. Results show that N/sub 2/O oxide has significant improvement in t/sub BD/ (2*under-V/sub g/ unipolar stress, 20*under+V/sub g/ unipolar stress, and 10*under bipolar stress). The improvement of t/sub BD/ in N/sub 2/O oxide is attributed to the suppressed electron trapping and enhanced hole detrapping due to the nitrogen incorporation at the SiO/sub 2//Si interface.<<ETX>>

High-field-induced leakage in ultrathin N/sub 2/O oxides

Stress-induced leakage current (SILC) is studied in ultrathin ( approximately 50 AA) gate oxides grown in N/sub 2/O or O/sub 2/ ambient, using rapid thermal processing (N/sub 2/O oxide or control oxide, respectively). MOS capacitors with N/sub 2/O 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 N/sub 2/O oxide is attributed to suppressed interface state generation due to nitrogen incorporation at the Si/SUO/sub 2/ interface during N/sub 2/O oxidation.<<ETX>>

Teledyne Imaging Sensors: silicon CMOS imaging technologies for x-ray, UV, visible, and near infrared

Teledyne Imaging Sensors develops and produces high performance silicon-based CMOS image sensors, with associated electronics and packaging for astronomy and civil space. Teledynes silicon detector sensors use two technologies: monolithic CMOS, and silicon PIN hybrid CMOS. Teledynes monolithic CMOS sensors are large (up to 59 million pixels), low noise (2.8 e- readout noise demonstrated, 1-2 e- noise in development), low dark current (<10 pA/cm2 at 295K) and can provide in-pixel snapshot shuttering with >103 extinction and microsecond time resolution. The QE limitation of frontside-illuminated CMOS is being addressed with specialized microlenses and backside illumination. A monolithic CMOS imager is under development for laser guide star wavefront sensing. Teledynes hybrid silicon PIN CMOS sensors, called HyViSITM, provide high QE for the x-ray through near IR spectral range and large arrays (2K×2K, 4K×4K) are being produced with >99.9% operability. HyViSI dark current is 5-10 nA/cm2 (298K), and further reduction is expected from ongoing development. HyViSI presently achieves <10 e- readout noise, and new high speed HyViSI arrays being produced in 2008 should achieve <4 e- readout noise at 900 Hz frame rate. A Teledyne 640×480 pixel HyViSI array is operating in the Mars Reconnaissance Orbiter, a 1K×1K HyViSI array will be launched in 2008 in the Orbiting Carbon Observatory, and HyViSI arrays are under test at several astronomical observatories. The advantages of CMOS in comparison to CCD include programmable readout modes, faster readout, lower power, radiation hardness, and the ability to put specialized processing within each pixel. We present one example of in-pixel processing: event driven readout that is optimal for lightning detection and x-ray imaging.

Effects of growth temperature on TDDB characteristics of N/sub 2/O-grown oxides

Effects of oxide growth temperature on time-dependent dielectric breakdown (TDDB) characteristics of thin (115 AA) N/sub 2/O-grown oxides are investigated and compared with those for conventional O/sub 2/-grown SiO/sub 2/ films with identical thickness. Results show that TDDB characteristics of N/sub 2/O oxides are strongly dependent on the growth temperature and, unlike conventional SiO/sub 2/, TDDB properties are much degraded for N/sub 2/O oxides with an increase in growth temperature. Large undulations at the Si/SiO/sub 2/ interface, caused by locally retarded oxide growth due to interfacial nitrogen, are suggested as a likely cause of degradation of TDDB characteristics in N/sub 2/O oxides grown at higher temperatures.<<ETX>>

Radiation hardness of MOSFETs with N/sub 2/O-nitrided gate oxides

Radiation hardness of furnace N/sub 2/O-nitrided gate oxides was investigated for both n- and p-channel MOSFETs by exposing devices in an X-ray radiation system. An enhanced degradation was observed in both control and N/sub 2/O-nitrided MOSFETs with reduction in the channel length. Compared to MOSFETs with control oxides, N/sub 2/O-nitrided MOSFETs show an enhanced radiation hardness against positive charge buildup and interface state generation. The effects of channel hot carriers on the irradiated devices with subsequent low-temperature forming gas annealing were also studied. The results show that N/sub 2/O-nitrided oxides have a greatly enhanced resistance against radiation-induced neutral electron trap generation. >

Gate oxide thickness dependence of RIE-induced damages on n-channel MOSFET reliability

We have investigated the effect of gate oxide thickness scaling on RIE-induced damage in n-MOSFETs. Our results show that active damage to gate oxide increases as the thickness is scaled down. On the other hand, thinner gate oxide devices show smaller degradation under hot carrier as well as Fowler-Nordheim stress compared to thicker gate oxide devices for a given antenna type and ratio. Reduced degradation in thinner oxide MOSFETs is explained based on smaller mobility degradation as well as on higher amount of channel inversion charge.