G. Dorda

Hot-electron and hole-emission effects in short n-channel MOSFET's

This paper presents a comparison of hot-carrier degradation experiments with simulations of hot electron and hole emission into the oxide. It is shown that both the emission of holes and of electrons are essential to explain the dominant generation of negative charge by a new degradation mechanism. Moreover, a peak of positive-charge generation at a gate voltage close to threshold was found in our experiments which is due to hole trapping. A simple degradation model based on the calculated electron and hole emission is presented which gives a very good description of the observed behavior of degradation effects.

Generation of interface states by hot hole injection in MOSFET's

The emission of hot electrons and hot holes from n-channel MOSFETs into the gate oxide is investigated as a function of the gate bias for a given lateral electric field. The resulting electron gate current as well as the substrate current are analyzed for both the saturation and the linear regime of the transistor. In the saturation regime, a remarkable increase of interface states occurs which can be correlated with the hole generation due to avalanche multiplication in the high-field region. In this case, the electric field normal to the Si-SiO2interface near the drain aids in the injection of hot holes along the channel which initiates acceptor-type interface states. In the linear operation regime, however, no pronounced generation of interface states can be detected.

Hot-electron effects on short-channel MOSFETs determined by the piezoresistance effect

The piezoresistance effect of n-inversion layers in the hot-electron regime is discussed. The measurements were performed on short-channel n-MOSFETs at both 77 and 300 K. From the data at 77 K, clear evidence is obtained for different saturation velocities of electrons in Si depending on the occupation of the subbands. By application of this effect to 300 K, good agreement between theory and experiment is achieved. Furthermore, the mechanical prestress inside the transistor has been estimated to reach values of up to 150 N-mm/sup -2/. >

Hot carrier degradation mechanism in n-MOSFETS

Hot carrier degradation experiments are compared to the results of a two-dimensional simulation of hot electron and hole emission into the oxide, taking into account carrier emission which does not lead to gate currents. A new degradation mechanism, due to trapping of electrons on trapped holes, is shown to be the dominant generator of negative effective charge. Hole trapping produces a sharp peak of positive effective charge close to threshold. A simple transistor degradation model based on the calculated carrier emissions gives a very good description of the experimental degradation behavior

Evidence for mobility domains in (100) silicon inversion layers

Abstract In proof of the existence of domains with different mobilities measurements of Shubnikov-de Haas oscillations, piezoresistance, and transverse “Hall” field due to mobility anisotropy are provided. The energy splitting between the ground state subbands of different valleys has been determined.

Effective masses in (100) silicon inversion layers

Abstract Shubnikov-de Haas oscillations at low electron concentrations have been studied under mechanical stress. The effective cyclotron mass of the anisotropic valleys has been determined to be m c m 0 = 0.43 . Additional piezo-resistance and anisotropic conductivity measurements proved a complete transfer of electrons from isotropic into anisotropic valleys. The existence of domains is necessary for the explanation of the experimental results.

Surface quantum oscillations in (100) inversion layers under uniaxial stress

Abstract Surface quantum oscillations have been measured with uniaxially stressed (100) n-type inversion layers. A relation between mechanical stress and cyclotron mass mc has been observed. In the quantum limit the two-fold valley degeneracy is lifted by about 1 meV with compression.

Valley degeneracy and mobility anisotropy under mechanical stress on (111) silicon inversion layers

Abstract Shubnikov-de Haas oscillations, piezoresistance, Hall mobility, and transverse “Hall” field due to mobility anisotropy have been studied on n-channel (111) Si inversion layers. The valley degeneracy was found to be 2 between 1.7 and 300 K. Under uniaxial mechanical stress the initially isotropic conductivity became strongly anisotropic. All results can be described by the existence of domains in the inversion layer.

Comments on the hole mass in silicon inversion layers

Abstract Published experimental data for hole masses mc in silicon inversion layers on (110), (111) and (100) surfaces are critically discussed. New results are presented for the (100) orientation. It is shown that self-consistent calculations of mc agree with those experimental data, which are compatible with cyclotron resonance results. It is demonstrated that a theoretical treatment by Falicov and Garcia, which predicts too large hole masses, is not tenable.

Mechanical stress at the (111) Si surface covered by SiO2 and AlSiO2 layers

The mechanical stress σSi at the (111) Si surface was studied on SiO2Si and AlSiO2Si sandwich structures as a function of temperature and layer thickness. The surface warp was measured with a Michelson interferometer in the temperature range between 4.2 and 370 K. For the SiO2Si structure an isotropic tension was observed at the Si surface. The tension is a function of oxide thickness and is of the order of 1 Nmm2 for a 120 nm thick SiO2 layer at room temperature. It remains unchanged while varying the temperature from 4.2 to 370 K. In contrast AlSiO2Si structures show an isotropic compression at the Si surface. For a sandwich with a thin oxide (3 nm) interface film and a 300 nm thick Al layer it amounts to (5.8 ± 0.6) Nmm2 at room temperature. This compression increases with decreasing temperature and saturates after a stress variation of 28 Nmm2 at about 100 K. By heating the structure the stress decreases and becomes zero at 90°C.