Yokichi Itoh

Thermal oxidation of silicon in various oxygen partial pressures diluted by nitrogen

Oxide growth kinetics of SiO2 films grown on silicon at 950 to 1100 °C in an O2/N2 mixture is empirically studied. It is found that a linear‐parabolic law is in excellent agreement with the oxidation data under the oxygen partial pressure PO2 of 1 or 10−1 atm. However, a parabolic law is obtained at 10−2 atm, and an inverse‐logarithmic law at 10−3 atm. The Mott‐Cabrera oxidation rate equation is adapted to the thermal oxidation of silicon in the case of PO2≲10−2 atm. Finally, 43.9 kcal/mole is derived as the activation energy value of silicon atoms entering into the oxide.

Stress and Thermal‐Expansion Coefficient of Chemical‐Vapor‐Deposited Glass Films

The stress in thin films of chemical‐vapor‐deposited (CVD) glass on Si substrates was measured by the Newton‐ring method. The CVD films studied were Silane‐oxidized SiO2, phosphosilicate glass and borosilicate glass deposited at 400°–450°C. Stress reduction due to moisture absorption was observed in the CVD films, but it was not observed in the sputtered SiO2 and the thermally grown SiO2 films. The initial tensile stress in the CVD films changed into compressive stress after heat treatments at 600°–900°C. By measuring the stress at elevated temperatures, the intrinsic stress was reduced from the total stress. From the thermal stress measurement, the thermal‐expansion coefficient and the elastic constant of the CVD glass films were estimated.

n-channel Si-gate MNOS Device for High Speed EAROM

New technologies for high speed and high performance electrically alterable read-only memories are developed. The memory cell consists of an n-channel silicon gate MNOS device and a switching transistor (two devices per bit). This cell configuration and advanced processing technologies realize high speed, no read-cycle limitations, long data retention and high packing density for n-channel EAROMs when compared to conventional p-channel aluminum gate EAROMs. The features of the new MNOS transistors are investigated and capability of ten year unpowered data storage at 125°C is confirmed. Write and erase times are 100 µs and several ms at 25 V, respectively. A single 5 V 2 k-bit EAROM with complete peripheral circuits is also fabricated. The measured access time is about 100 ns, which is more than five times faster than conventional EAROMs.

Analysis and Experimentation on FIMOS (n-channel FAMOS) Devices

Non-volatile nature of FIMOS (Floating gate Ionization-injection MOS) memory is based on the storage of electrons in the floating gate. This paper analyzes the electron injection efficiency in terms of the impact ionization rate and the peak electric field in the channel. The latter is related to the device parameters such as the acceptor concentration in the channel and the oxide thicknesses. Threshold voltage shifts due to the electron injection were measured on experimental units with varied device parameters under various programming conditions. Qualitative agreements were obtained between the theoretical prediction and experimental results. Thus, the injection model should prove useful in the design of better memory devices.