It has been reported that high-temperature (/spl sim/1100/spl deg/C) N/sub 2/O-annealed oxide can block boron penetration from poly-Si gates to the silicon substrate. However, this high-temperature step may be inappropriate for the low thermal budgets required of deep-submicron ULSI MOSFETs. Low-temperature (900/spl sim/950/spl deg/C) N/sub 2/O-annealed gate oxide is also a good barrier to boron penetration. For the first time, the change in channel doping profile due to compensation of arsenic and boron ionized impurities was resolved using MOS C-V measurement techniques. It was found that the higher the nitrogen concentration incorporated at Si/SiO/sub 2/ interface, the more effective is the suppression of boron penetration. The experimental results also suggest that, for 60/spl sim/110 /spl Aring/ gate oxides, a certain amount of nitrogen (/spl sim/2.2%) incorporated near the Si/SiO/sub 2/ interface is essential to effectively prevent boron diffusing into the underlying silicon substrate. >

Suppression of boron penetration in p/sup +/ polysilicon gate P-MOSFETs using low-temperature gate-oxide N/sub 2/O anneal

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. >

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

We report on a quantitative study of boron penetration from p/sup +/ polysilicon through 5- to 8-nm gate dielectrics prepared by rapid thermal oxidation in O/sub 2/ or N/sub 2/O. Using MOS capacitor measurements, we show that boron penetration exponentially increases with decreasing oxide thickness. We successfully describe this behavior with a simple physical model, and then use the model to predict the magnitude of boron penetration, N/sub B/, for thicknesses other than those measured. We find that the minimum t/sub ox/ required to inhibit boron penetration is always 2-4 nm less when N/sub 2/O-grown gate oxides are used in place of O/sub 2/- grown oxides. We also employ the boron penetration model to explore the conditions under which boron-induced threshold voltage variation can become significant in ULSI technologies. Because of the strong dependence of boron penetration on t/sub ox/, incremental variations in oxide thickness result in a large variation in N/sub B/, leading to increased threshold voltage spreading and degraded process control. While the sensitivity of threshold voltage to oxide thickness variation is normally determined by channel doping and the resultant depletion charge, we find that for a nominal thickness of 6 nm, threshold voltage control is further degraded by penetrated boron densities as low as 10/sup 11/ cm/sup -2/.

Thickness dependence of boron penetration through O/sub 2/- and N/sub 2/O-grown gate oxides and its impact on threshold voltage variation

MOSFET's with ultrathin (5 to 8.5 nm) silicon oxynitride gate film prepared by low-pressure rapid thermal chemical vapor deposition (RTCVD) using SiH/sub 4/, N/sub 2/O and NH/sub 3/ gases, are studied by low-frequency noise measurements (1 Hz up to 5 kHz). The analysis takes into account the correlated mobility fluctuations induced by those of the interfacial oxide charge. The nitrogen concentration, determined from SIMS analysis, varies from 0 to 11% atomic percentage. A comparison of the electrical properties between thermal and silicon oxynitride films is presented. The increasing LF noise signal with nitrogen atomic percentage indicates the presence of a higher density of slow interface traps with increasing nitrogen incorporation. Besides, a higher Coulomb scattering rate due to the nitridation induced interface charge explains reasonably well the degradation of the low field mobility after nitridation.

Low-frequency noise characterization of n- and p-MOSFET's with ultrathin oxynitride gate films

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.

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

The ability of thin reoxidized nitrided oxide (ONO) gate dielectrics formed by rapid thermal processing to act as a barrier to boron penetration resulting from p/sup +/ poly gate processing are investigated. Measurements comparing the threshold voltage instability of capacitors fabricated with BF/sub 2/ implanted poly gates subjected to various postgate thermal cycles have been performed. The ONO gate dielectrics are found to be an excellent impurity barrier to boron diffusion, even in the presence of fluorine. The extent of the nitridation is also found to affect the diffusion barrier properties, with the highest temperature nitridations forming the best barriers. Reoxidation of the nitrided films reduces the barrier properties somewhat, but improvement is still observed over SiO/sub 2/. >

Impurity barrier properties of reoxidized nitrided oxide films for use with P/sup +/-doped polysilicon gates

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Impurity barrier properties of reoxidized nitrided oxide films for use with P/sup +/-doped polysilicon gates