Silicon MOS Devices Research Articles

Invited: X-Ray Lithography

X-ray lithography has been used in the fabrication of surface-acoustic-wave, bubble-domain, and silicon MOS devices and is well suited for replicating sub-micrometer linewidth patterns. In order to be applied in the commercial exposure of silicon IC devices, however, high power sources, sensitive resists, distortion free masks, multiple mask alignment, and repeatability of local mask-to-wafer gap will be required. These items are discussed from the point-of-view of developing design criteria for an X-ray lithography system optimized for 1/2 µm linewidths, 1/10 µm superposition, and exposure times under 200. For linewidths below 1/2 µm, copper (λ=13.3 Å) or carbon (λ=44.7 Å) sources are preferred. Recent progress in using the copper radiation to replicate grating patterns with linewidths of the order of 1000 Å with sharp vertical sidewall profiles are described.

An observation by photoconductivity of strain splitting of shallow bulk donors located near to the surface in silicon mos devices

Photoconductivity is observed in n-channel inversion Si MOSFETS at 4.2 K at infrared frequencies up to 700 cm −1. Two groups of sharp lines of opposite sign are observed in the regions of 300 and 650 cm −1 together with a continuum of transitions starting at ∼ 350 cm −1. The sharp lines are interpreted as bound transitions from shallow neutral phosphorous donors and boron acceptors on either side of the depletion layer. The angular dependence of the Zeeman splitting of the sharp lines demonstrates that the normal 90° symmetry of the 100 surface is lifted for devices with thin metal gates due to the presence of a strong unixial stress component.

Self-consistent numerical solutions of p-type inversion layers in silicon mos devices

We present a self-consistent numerical calculation to study the energy of the subbands of holes on p-type inversion layers in silicon MOS devices. The variation of the masses with the concentration of carriers is considered self-consistently, taking into account the non-parabolicity and anisotropy of the valence band. These properties are mandatory on the behaviour of the excited states giving opposite trends for p-type and n-type channels.

An observation by photoconductivity of strain splitting of shallow bulk donors located near to the surface in silicon MOS devices : R. J. Nicholas, K. von Klitzing and R. A Stradling, Solid-State Commun.20, (1976)

An observation by photoconductivity of strain splitting of shallow bulk donors located near to the surface in silicon MOS devices : R. J. Nicholas, K. von Klitzing and R. A Stradling, Solid-State Commun.20, (1976)

Peaked structure appearing in the field effect mobility of silicon mos devices at temperatures above 20 K

Peaked structure appearing in the field effect mobility of silicon mos devices at temperatures above 20 K

Hole cyclotron masses in silicon MOS devices

Anistropy and non-parabolicity of the hole band structure in silicon, together with bound-state effects, can explain satisfactorily the observed hole cyclotron masses in MOS devices. The calculations presented here show a large increase (of about a factor of 2) in the masses as the carrier concentration varies from 0 to 5 × 10 12 holes cm 2 . In approximate terms it can be stated that 40% of the increase is due to pure band-structure effects and the remaining 60% is caused by combined effects of bound-state corrections and band structure.

Fabrication of silicon MOS devices using X-ray lithography

This paper reports on the high-yield fabrication of silicon MOS transistors using X-ray lithography, measurements and annealing of fast surface states and oxide charges created by X-ray irradiation, and design considerations for submicrometer linewidth X-ray lithography on 7.5-cm diameter silicon wafers.

Peaked structure appearing in the field effect mobility of silicon MOS devices at temperatures above 20K

Peaked structure is reported in the variation of field effect mobility with gate voltage of high-quality silicon MOS devices close to the switch-on voltage. The positions of the peaks are approximately independent of temperature but the amplitudes grow with increasing temperature in relative order to their proximity to the threshold voltage. These features can be explained on the assumption of a number of discrete trap states located approximately 10 meV below the band edge if the binding energy to the states increases as the gate voltage is raised because of the increasing energy of the size-quantized sub-bands within the inversion layer. The existence of these traps close to the band edge implies that the field effect mobility is not simply related to the true mobility in the threshold region of the device.

Effects of Ionizing Radiation on Thin-Film Semiconductor Devices

Results of an investigation of the transient and permanent effects of ionizing radiation on Al2O3-CdSe thin-film transistors and microcircuits are reported. The total-gamma-dose response of the devices did not differ significantly from that of conventional silicon MOS devices, and the observed shift in threshold voltage is consistent with a positive charge buildup in the gate oxide. In transient response studies, it was found that the thin-film devices will perform without failure up to peak dose rates of ~1010 rads(Si)/s (~30 ns pulsewidth).