J. O. Olowolafe

Electrical conduction and dielectric breakdown in aluminum oxide insulators on silicon

Leakage currents and dielectric breakdown were studied in MIS capacitors of metal-aluminum oxide-silicon. The aluminum oxide was produced by thermally oxidizing AlN at 800-1160/spl deg/C under dry O/sub 2/ conditions. The AlN films were deposited by RF magnetron sputtering on p-type Si (100) substrates. Thermal oxidation produced Al/sub 2/O/sub 3/ with a thickness and structure that depended on the process time and temperature. The MIS capacitors exhibited the charge regimes of accumulation, depletion, and inversion on the Si semiconductor surface. The best electrical properties were obtained when all of the AlN was fully oxidized to Al/sub 2/O/sub 3/ with no residual AlN. The MIS flatband voltage was near 0 V, the net oxide trapped charge density, Q/sub 0x/, was less than 10/sup 11/ cm/sup -2/, and the interface trap density, D/sub it/, was less than 10/sup 11/ cm/sup -2/ eV/sup -1/, At an oxide electric field of 0.3 MV/cm, the leakage current density was less than 10/sup -7/ A cm/sup -2/, with a resistivity greater than 10/sup 12/ /spl Omega/-cm. The critical field for dielectric breakdown ranged from 4 to 5 MV/cm. The temperature dependence of the current versus electric field indicated that the conduction mechanism was Frenkel-Poole emission, which has the property that higher temperatures reduce the current. This may be important for the reliability of circuits operating under extreme conditions. The dielectric constant ranged from 3 to 9. The excellent electronic quality of aluminum oxide may be attractive for field effect transistor applications.

Effect of composition on thermal stability and electrical resistivity of Ta-Si-N films

The role of composition on the resistivity and thermal stability of sputtered Ta–Si–N films have been studied using X-ray diffraction, Rutherford backscattering spectrometry, and sheet resistance measurement. Films with higher silicon to tantalum ratio were found to be more thermally stable and have higher sheet resistance than films with lower Si to Ta ratio. While Ta0.28Si0.07N0.65 starts to crystallize at about 900°C, Ta0.24Si0.10N0.66 and Ta0.24Si0.12N0.64 were thermal for heat treatment below 1100°C. In-situ sheet resistance measurement also showed that the sheet resistance for the alloys varies with composition and decreases with temperature. Our results indicate that Ta–Si–N films would find other applications in semiconductor devices, beside being used as a diffusion barrier.

The effects of oxidation temperature on the capacitance–voltage characteristics of oxidized AlN films on Si

The thermal oxidation of AlN thin films produces a high quality insulator which exhibits the gate voltage-controlled charge regimes of accumulation, depletion, and inversion on Si surfaces. The temperature dependence of oxidation is important for device processing. We report on the composition, structure, and electrical properties of the AlN versus the oxidization temperature. AlN layers 500 nm thick were deposited by rf sputtering on p-type Si (100) substrates, followed by oxidation in a furnace at temperatures from 800 to 1100 °C with O2 flow. An oxidation time of 1 h produced layers of Al2O3 with small amounts of N having a thickness of 33 nm at 800 °C, and 524 nm at 1000 °C. Electrical measurements of metal-oxide-semiconductor capacitors indicated that the dielectric constant of the oxidized AlN was near 12. The best layer had a flatband voltage near zero with a net oxide trapped charge density less than 1011 cm−2. These results show that oxidized AlN has device-grade characteristics for the gate regi...

THERMALLY OXIDIZED ALN THIN FILMS FOR DEVICE INSULATORS

The structural, optical, and electronic properties of an insulating material prepared by the thermal oxidation of AlN thin films on Si have been studied by a number of different experimental techniques. The thermal oxidation at 1100 °C of reactively sputtered AlN films on Si wafers was found to result in the formation of an oxide with a relative Al to O concentration near Al2O3 with small amounts of incorporated N. The structure of the AlO:N oxide could be varied between amorphous and polycrystalline, depending on the preparation conditions, and the oxide surface was found to be approximately three time smoother than the as-sputtered AlN films. Metal–oxide–silicon capacitors had an oxide charge density of about 1011 cm−2, capacitance–voltage characteristics similar to pure SiO2, and a dielectric constant of 12.4. Infrared measurements yielded a refractive index of 3.9. These results indicate that thermally oxidized AlN films show promise as insulating structures for many integrated circuit applications, p...

Band gap of Ge rich Si1−x−yGexCy alloys

Si1−x−yGexCy films ( x≊0.90, y⩽0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x‐ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C‐resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions.

Analysis of high-temperature materials for application to electric weapon technology

High-power and temperature pulsed-power electronics can be exploited by future military combat systems using advanced electric weapon concepts such as electrothermal-chemical (ETC) and electromagnetic (EM) gun technologies. The results of experiments conducted demonstrate the electrical behavior of SiC and metal ohmic-contact layers as a function of thermal stress. It has been determined from these experiments that both titanium (Ti) and tantalum (Ta) metalization structures will provide a stable electrical ohmic-contact with n-type SiC at elevated temperatures for short bursts that are considered relevant for pulsed-powered electric weapon technologies. The Ti-SiC structure exhibited a stable current-voltage (I-V) characteristic to as much as 800/spl deg/C for a 10-min burst, while Ta metalizations provided a stable I-V characteristic on SiC even after a temperature burst of 1000/spl deg/C for as long as a 3-min interval. For samples of n-type, 4H SiC, metalized with (Ti), the standard deviation in resistance (resistivity) of the measured samples is less than 0.17 ohms for a sample having an average resistance of 4.45 ohms. The Ti-SiC sample was exposed to an elevated temperature range of 300-1,120/spl deg/C. For the Ta contact on SiC, the standard deviation in resistance is 0.05 ohms for a sample having an average resistance of 4.25 ohms over a temperature range of 600-1120/spl deg/ C. The experiments showed that for both Ti and Ta metalized SiC samples, the change in resistivity of annealed samples is between 3.8% and 1.2% compared to the average values of sample resistance based upon the I-V measurement technique used.

Analysis of metalized 4H-SiC for high-temperature electric weapon applications

While silicon (Si) based electronic materials and devices continue to play a dominant role in much of the electrical power industry, novel high-power and high-temperature materials are of great interest to the electric combat systems community. The technical interest in silicon carbide (SiC) is mainly due to its ability to operate at greatly elevated power and temperature (>300/spl deg/C) levels compared to its Si-based counterpart. High-power and temperature pulsed-power electronics can be exploited by future military combat systems, which could potentially provide significantly improved combat vehicle performance including increased lethality through extending the maximum obtainable gun performance using advanced electric weapon concepts such as electrothermal-chemical (ETC) and electromagnetic (EM) gun technologies.

C–V Profiles

The sections in this article are 1 Capacitance and Semiconductor Devices 2 Capacitance of Semiconductor Devices 3 Doping Profiles 4 Surface States 5 Response Time 6 C–V Profiling on Wide Band-GAP Semiconductor Substrates

Structural, electronic and optical properties of AlN-based oxides on Si and GaN substrates

The properties of novel high-quality AlN-based oxides suitable for device applications are presented in this paper. The process steps employed in this investigation are similar to these of SiO/sub 2/, providing new technology for group III-nitride based electronic devices. The oxides were prepared by thermal oxidation of AlN films or direct deposition of ultra-pure aluminum in a O/sub 2/-N/sub 2/ ambient on Si or GaN substrates. The structure of the films depends on deposition conditions for oxidized AlN and on composition for the Al films deposited in the N/sub 2/-O/sub 2/ ambient. The dielectric constant was evaluated to be 12.74 while the effective charge density is about 10/sup 11/ cm/sup -2/ for fully oxidized AlN. The refractive index of the oxide was about 3.9 using infrared techniques. Our results indicate that the AlN-based oxides provide a wide choice of high-quality insulators for electronic and optoelectronic applications.