Avid Kamgar

Linear Zone-Melt Recrystallized Si Films Using Incoherent Light

One of the options being considered for the disposal of radioactive waste is deep burial in crystalline rocks such as granite. It is generally recognised that in such rocks groundwater flows mainly through the fracture networks so that these will be the “highways” for the return of radionuclides to the biosphere. The main factors retarding the radionuclide transport have been considered to be the slow water movement in the fissures over the long distances involved together with sorption both in man-made barriers surrounding the waste, and onto rock surfaces and degradation products in the fissures.

High frequency conductivity in silicon inversion layers: Drude relaxation, 2D plasmons and minigaps in a surface superlattice

Abstract We review experiments that measure the inversion layer conductivity as a function of frequency in the far infrared. Drude relaxation is considered prototypic. 2D plasmons excited by a spatially modulated infrared field are discussed, and the direct observation of a minigap produced by a surface superlattice is presented.

High-temperature rapid thermal nitridation of silicon dioxide for future VLSI applications

The use of nitrided SiO2for very large scale integration (VLSI) applications is becoming increasingly attractive. Nitridation can convert a thin surface region of SiO2into a nitroxide film which is a diffusion barrier that allows the use of thin dielectrics in MOS structures and a variety of gate metals without contaminating the interfacial region. We propose a two-activation-energy model of nitridation and suggest a structure for MOS gate insulator applications. We achieved this structure using rapid thermal nitridation at 1300°C for 20 s in 1 atm. of ammonia.

Recrystallization of polysilicon films using incoherent light

Abstract A novel system has been designed and constructed for recrystallization of polysilicon films. This system utilizes tungsten light sources to heat, zone melt and subsequently crystallize polysilicon films on insulating substrates. The system has been successfully used to crystallize 0.5 μm polysilicon films deposited on 0.5 μm SiO 21 grown on three inch Si wafers. Initial results are presented.

Rapid thermal anneal induced effects in polycrystalline silicon gate structures

Effects of dynamic temperature nonuniformities during rapid thermal anneal (RTA) cycles of layered structures have been investigated. Silicon gate capacitors (4000 A, As doped, polycrystalline Si on 175 A thermal oxide) were subjected to temperatures 450–1200 °C using incoherent radiation from W lamps. Capacitance‐voltage measurements before and after RTA showed that due to RTA, interface traps were generated at temperatures as low as 600 °C, but that they were passivated by a standard post‐metallization anneal. High‐temperature RTA induced, in addition, a residual flatband voltage shift which was not removed by hydrogen anneal. The residual shift can be due to either a change in oxide fixed charges or changes in the characteristics of the polycrystalline Si gate. Faster temperature ramp rates increased the generation of interface traps confirming the dynamic nature of stress, but did not affect the residual shift.

Junction leakage studies in rapid thermal annealed diodes

A detailed and comprehensive study of As‐implanted Si annealed using incoherent tungsten radiation has been perfomed. The study emphasized the leakage currrent results, correlating them with the junction depths obtained from Rutherford backscattering measurements, and the residual damage observed in transmission electron microscopy (TEM). Sheet resistance measurements, as well as comparisons with wafers annealed in conventional furnaces, were also made. It was found that higher temperatures and shorter times resulted in lower leakage currents for given junction depths. We also found that the absence of residual dislocations in TE studies of annealed wafers was not a sufficient indication of low junction leakage.

Kinetics of arsenic activation and clustering in high dose implanted silicon

We have observed a metastable state in activation of high dose arsenic implants into silicon. This state is marked by a local minimum in the sheet resistance which increases to a local maximum as the anneal time increases. Detailed sheet resistance data as well as Rutherford backscattering and transmission electron microscopy indicate that the initial minimum in sheet resistance is due to activation of arsenic atoms by occupying substitutional sites as the amorphous silicon recrystallizes. The subsequent clustering of arsenic atoms is the cause for the increase in the sheet resistance while the final drop is associated with the lateral diffusion of arsenic. We have studied this effect in the 850–1100 °C temperature range, and have obtained an activation energy of 1.1 eV for the clustering of arsenic atoms.

Subthreshold behavior of silicon MOSFETs at 4.2 K

Abstract The subthreshold behavior of Si MOSFETs has been studied at 300, 77 and 4.2 K. At 300 and 77 K satisfactory agreement between theory and experiment was obtained, showing that the gate voltage swing needed to change the drain current by one decade reduces proportionally with temperature. At 4.2 K, however, the conventional subthreshold behavior was not observed down to drain current of 10−13 A. To achieve better circuit performance, there seems to be no advantage in lowering the temperature below 77 K.

Self‐aligned TiN barrier formation by rapid thermal nitridation of TiSi2 in ammonia

Partial or full nitridation of TiSi2 layers has been achieved by rapid thermal nitridation in pure ammonia. Several analytical techniques such as transmission electron microscopy, x‐ray photoemission spectroscopy, and Rutherford backscattering, have been used to study the nitridation process. It was found that a 60‐s anneal at 900 °C was sufficient to yield a 20–30 nm TiN layer on top of the TiSi2 layer, provided that the starting TiSi2 surface was free of Si or Ti oxides. Annealing at 1000 °C for 60 s, on the other hand, nitrided the entire 95‐nm TiSi2 layer. Detailed structural and chemical analysis of the samples before and after nitridation showed that the nitridation process takes place by nitrogen atoms bonding to Ti atoms and displacing the Si atoms. The dissociated Si atoms diffuse towards the TiSi2/Si interface forming an epitaxial layer of nonuniform thickness on the Si substrate. The resulting TiN layer is substantially thinner than the starting TiSi2 layer. It has a somewhat rough top surface ...

On the discrepancies between absorption and photoconductivity measurements in silicon inversion layers

Abstract We have observed the intersubband transitions in Si inversion layers through absorption and photoconductivity. The two experiments yield identical results. Time-resolved measurements show that the resonance position depends on the degree to which electrostatic equilibrium is established in the Si substrate. These results suggest that the absence of the depletion layer in early photoconductivity measurements can account for previously reported discrepancies.