Tomiyuki Arakawa

Thin-gate SiO/sub 2/ films formed by in situ multiple rapid thermal processing

A reliable method of forming very thin SiO/sub 2/ films (<10 nm) has been developed by rapid thermal processing (RTP) in which in situ multiple RTP sequences have been employed. Sub-10-nm-thick SiO/sub 2/ films formed by single-step RTP oxidation (RTO) are superior to conventional furnace-grown SiO/sub 2/ on the SiO/sub 2//Si interface characteristics, dielectric strength, and time-dependent dielectric-breakdown (TDDB) characteristics. It has been confirmed that the reliability of SiO/sub 2/ film can be improved by pre-oxidation RTP cleaning (RTC) operated at 700-900 degrees C for 20-60 s in a 1%HCl/Ar or H/sub 2/ ambient. The authors discuss the dielectric reliability of the SiO/sub 2/ films formed by single-step RTO in comparison with conventional furnace-grown SiO/sub 2/ films. The effects and optimum conditions of RTC prior to RTO on the TDDB characteristics are demonstrated. The dielectric properties of nitrided SiO/sub 2/ films formed via the N/sub 2/O-oxynitridation process are described.

Relationship between Nitrogen Profile and Reliability of Heavily Oxynitrided Tunnel Oxide Films for Flash Electrically Erasable and Programmable ROMs

A larger charge-to-breakdown value and much less threshold-voltage narrowing in the endurance properties of flash electrically erasable and programmable ROMs were achieved by incorporating a greater amount of nitrogen (∼ 10 21 atoms/cm 3 ) into the bulk of thin oxide films, as well as near the oxide/Si interface. The charge to breakdown value of thin oxide films formed under an optimized heavy oxynitride condition (dry oxidation at 1100°C; NH 3 annealing at 1000 °C for 30 s; N 2 O annealing at 1100°C for 30 s) was four times as large as that of a conventional dry oxide film. These results were attributed to the suppression of stress-induced charge traps and the interface state, due to the introduction of nitrogen atoms in the oxide bulk, as well as at the oxide/Si interface

Effect of Nitrogen Profile on Tunnel Oxynitride Degradation with Charge Injection Polarity.

The relationship between nitrogen profiles and polarity dependence of wearout and breakdown in oxynitride films was investigated. With positive bias stress, higher concentration of nitrogen atoms near an oxynitride/Si interface (∼2 at.%) and in the oxynitride bulk (∼0.3 at.%) reduce charge trap and interface state generation, and produce greater charge-to-breakdown (Q bd ). In contrast, with negative bias stress, nitrogen atoms near an interface decrease the number of charge traps, but, cannot reduce interface state generation, and thus give smaller Q bd . Furthermore, nitrogen atoms near an oxynitride surface (over 1.5 at.%) cause undesirable results for both bias stresses. Optimum nitrogen profile in an oxynitride film is discussed the viewpoint of reliability for both bias stresses.

Impact of nitrogen concentration profile in silicon oxynitride films on stress-induced leakage current

Abstract Stress-induced leakage currents of silicon oxynitride films (9 nm thick) with different nitrogen concentration profiles have been investigated. We found that leakage current at a gate electric field of approximately 6 MV/cm after electron injection (0.1-1.0 C/cm 2 is reduced upon the incorporation of approximately 0.75 at% of nitrogen atoms near the oxynitride/Si interface. However, stress-induced leakage current increases with increasing nitrogen atom concentration at a depth of 1.5 nm in silicon oxynitride films. The optimum nitrogen atom concentration profile in silicon oxynitride films can decrease the number of tunneling sites and lead to small stress-induced leakage current at low electric field.

Impact of Tunnel Film Oxynitridation on Band-to-Band Tunneling Current and Electron Injection in Flash Memory

The impact of the use of oxynitride tunnel film on write, erase and read operations of flash memories was investigated. We found that during electron ejection from a floating gate into a drain, band-to-band tunneling currents of flash memory cells with tunnel films having a high degree of nitridation are two orders of magnitude smaller than that of flash memory cells with oxide tunnel films. Consequently, higher-nitridation tunnel films improve the endurance characteristics of flash memory. However, during electron injection from a channel into the floating gate, Fowler-Nordheim tunneling gate currents of flash memory cells with higher-nitridation tunnel films are two orders of magnitude smaller than that of flash memory cells with oxide tunnel films. Moreover, the threshold voltage of flash memory cells with oxynitride tunnel films is 0.24–0.48 V smaller than that of flash memory cells with oxide tunnel films in read operations. These results can be explained by the modification of the electric field under oxynitride tunnel films due to the formation of donor layers, which is induced by nitridation of tunnel oxide films.

Effect of synchrotron radiation on electrical characteristics of SiOxNy thin films formed by rapid thermal processing in a N2O ambient

The synchrotron radiation durability of SiOxNy films (about 10 nm) formed by rapid thermal processing in a N2O ambient was studied. No significant difference between the flat‐band voltage of SiOxNy‐metal‐oxide semiconductors (MOS) capacitors patterned by synchrotron radiation lithography (SR‐MOS) and that of capacitors patterned by conventional optical lithography (OP‐MOS) was observed. The midgap interface state density of the SR‐MOS was approximately one order of magnitude larger than that of the OP‐MOS. The differences between the SR‐MOS and the OP‐MOS were nearly independent of the SR dose in the range of 540–2700 mJ/cm2, and were eliminated by annealing in a hydrogen ambient at 400 °C for 30 min.

Optical waveguide fabrication by combination of spin-on-glass and plasma-enhanced chemical vapor deposition for optoelectronic integration

Low-loss optical waveguides for optoelectronic integration were realized by the combination of spin-on- glass (SOG) and plasma-enhanced chemical vapor deposi- tion (PECVD). Undercladdings of 20-mm thickness together with cores of 6-mm height and 8-mm width were formed on Si substrates by PECVD and reactive ion etching. Overclad- dings were formed by a combination of SOG and PECVD SiO2 films. This method successfully filled narrow gaps be- tween cores of optical circuits. The refractive index of over- claddings was adjusted by SOG curing and fluorine incorpo- ration in PECVD SiO2 films. A buried-type optical waveguide formed by the combination of SOG and PECVD showed single-mode propagation. Propagation losses and polariza- tion dependent losses at the 1.3-mm wavelength were mea- sured to be 0.3 dB/cm and below 0.15 dB, respectively.

Time-dependent dielectric breakbown evaluation for rapid-thermally grown SiO2 films formed on submicron-grooved Si surfaces

Abstract MOS capacitors formed on submicron-grooved (100)Si surfaces have been studied by time-dependent dielectric breakdown tests and transmission electron microscopy. Their time to breakdown depends on the number and profile of groove corners. Rounding off the convex upper corners of Si grooves by rapid thermal processing and rounding off the concave bottom corners by reactive ion etching successfully suppress electric field localization at groove corners and improve the reliability of MOS capacitors formed on grooves.

Improvement in radiation stability of SiN X-ray mask membranes

The synchrotron radiation (SR) stability of silicon nitride (SiN) X-ray mask membranes was successfully improved by low-pressure chemical vapor deposition at a growth temperature of 1000°C. The transmission of the SiN membrane formed at 1000°C exceeded 90% at about 633 nm even after SR absorption with a dose of about 100 MJ/cm3, although those of membranes formed at 800 and 900°C decreased to below 85% after the same SR absorption. In addition, SR-induced pattern displacements for the SiN membrane formed at 1000°C were suppressed to σx=11 nm and σy=10 nm with a dose of 20 MJ/cm3. The N/Si atomic ratio increased, and the H and O concentrations in the SiN decreased with the increase of the growth temperature. The increase ratio of the spin density before and after the SR absorption decreased with the increase of the growth temperature.

Synchrotron Radiation Damage Mechanism of X-Ray Mask Membranes Irradiated in Helium Environment

The mechanism of X-ray mask membrane displacement induced by synchrotron radiation (SR) has been discussed. Silicon nitride (SiN) and silicon carbide (SiC) membranes were irradiated by SR in a 1 atm helium ambient. SR-induced displacement for both membranes was 25-97 nm (σ). Oxygen concentration in both SiN and SiC was below 0.01 in O/Si atomic ratio. Although an increase in dangling bond density of SiN was observed, no remarkable increase in spin density was detected in SiC. Moreover, the most important finding was that thin oxides were grown on the membrane surface after SR irradiation. From these results, it is considered that the oxide growth on SiC membrane surfaces, and both the oxide growth and the increase of dangling bond density in SiN play an important role in the SR-induced displacement for the X-ray mask membranes.