James P. McVittie

Two-dimensional thermal oxidation of silicon. II. Modeling stress effects in wet oxides

For pt.I see ibid., vol.ED-34, p.1008-17 (May 1987). The authors propose that the stress from two-dimensional oxide deformation affects the kinetic parameter in the Deal-Grove model (1965). In particular, the viscous stress associated with the nonuniform deformation of the oxide is identified as the fundamental force of retardation. In this model, the stress normal to the Si-SiO/sub 2/ interface reduces the surface reaction rate in both convex and concave surfaces, whereas the stress in the bulk of the oxide (compressive for concave and tensile for convex surfaces) is responsible for the thinner oxides on the concave structures. The model is described by a simplified mathematical formulation made possible by the symmetry in cylindrical structures. Comparisons with experimental data, possible applications, and limitations of the model are also discussed. >

Technology and reliability constrained future copper interconnects. I. Resistance modeling

A realistic assessment of future interconnect performance is addressed, specifically, by modeling copper (Cu) wire effective resistivity in the light of technological and reliability constraints. The scaling-induced rise in resistance in the future may be significantly exacerbated due to an increase in Cu resistivity itself, through both electron surface scattering and the diffusion barrier effect. The impact of these effects on resistivity is modeled under various technological conditions and constraints. These constraints include the interconnect operation temperature, the effect of copper-diffusion barrier thickness and its deposition technology, and the quality of the interconnect/barrier interface. Reliable effective resistivity trends are established at various tiers of interconnects, namely, at the local, semiglobal, and global levels. Detailed implications of the effect of resistivity trends on performance are addressed in the second part of this work.

Ge-Interface Engineering With Ozone Oxidation for Low Interface-State Density

Passivation of Ge has been a critical issue for Ge MOS applications in future technology nodes. In this letter, we introduce ozone oxidation to engineer Ge/insulator interface. Density of interface states (D_it) across the bandgap and close to the conduction band edge was extracted using conductance technique at low temperatures. D_it dependence on growth conditions was studied. Minimum D_it of 3 times 10¹¹ cm^-2V^-1 was demonstrated. Physical quality of the interface was investigated through Ge 3d spectra measurements. We found that the interface and D_it are strongly affected by the distribution of oxidation states and the quality of the suboxide.

Electrical properties of heavily doped polycrystalline silicon-germanium films

The electrical properties of polycrystalline silicon-germanium (poly-Si/sub 1/spl minus/x/Ge/sub x/) films with germanium mole fractions up to 0.56 doped by high-dose ion implantation are presented. The resistivity of heavily doped p-type (P/sup +/) poly-Si/sub 1/spl minus/x/Ge/sub x/ is much lower than that of comparably doped poly-Si, because higher levels of boron activation and higher hole mobilities are achieved in poly-Si/sub 1/spl minus/x/Ge/sub x/. The resistivity of heavily doped n-type (N/sup +/) poly-S/sub 1/spl minus/x/Ge/sub x/ is similar to that of comparably doped poly-Si for x >

A tuned Langmuir probe for measurements in rf glow discharges

Measurements of charged‐particle concentrations and the electron energy distribution function (EEDF) have been made in Ar and SF6 glow discharges using a tuned Langmuir probe technique. A simple passive circuit connected to the probe when properly tuned increases the impedance between the probe and ground, thereby forcing the probe to follow the instantaneous plasma potential. In this manner, rf‐induced distortion of the probe characteristic is mitigated. At 13.56 MHz the electron collection characteristic of a detuned probe is distorted by rf interference; the ion collection characteristic is unaffected. The EEDF is highly non‐Maxwellian in argon discharges, but quite Maxwellian in SF6 discharges. The mean electron energy increases with decreasing pressure and increasing power in argon discharges, but is independent of pressure and power in SF6 discharges. The measured distribution functions and charged particle concentrations are in good agreement with calculations.

Notching as an example of charging in uniform high density plasmas

Numerical simulation was used to study both surface charging and ion trajectory distortion during submicron patterning in high density plasma etching. The plasma was assumed uniform and the cause for the surface charging was the directionality difference between ions and electrons. The role of ion transit time effects on the ion energy distribution function was also considered, while the effect of discharging currents such as through insulators was not included. Using a Monte Carlo sheath simulator, a Poisson equation solver, and an ion/electron trajectory simulator, the steady state potential distribution and ion trajectories were calculated for various line‐and‐space structures and plasma conditions where notching, which is a local sidewall etching, has been observed after the overetching part of polysilicon etching processes. The results show significant positive charging at the bottom of high aspect ratio spaces which depends on the ion energy distribution function. Notching at the bottom of an outerm...

New test structure to identify step coverage mechanisms in chemical vapor deposition of silicon dioxide

A new test structure has been developed to identify unambiguously the main mechanism which determines the profiles of thin films deposited by low‐pressure chemical vapor deposition (LPCVD) in structures such as steps, trenches, and via‐holes. The two mechanisms considered are reemission due to a low surface reaction probability and surface diffusion. Experimental results using silane, diethylsilane (DES), tetraethoxysilane (TEOS), and tetramethylcyclotetrasiloxane (TMCTS) as the silicon sources for oxide deposition by LPCVD show that indirect deposition from reemission is the major contributing factor in determining the step coverage.

Simulation of profile evolution in silicon reactive ion etching with re-emission and surface diffusion

This article describes a model that simulates etching profiles in reactive ion etching. In particular, models are developed to explain the significant lateral etch rate that is observed in many etch profiles. The total etch rate is considered to consist of two superimposed components: an ion‐assisted rate and a purely ‘‘chemical’’ etch rate, the latter rate being due to etching by radicals in the absence of ion bombardment. The transport of radicals to the evolving interface is studied for two different transport mechanisms: re‐emission from the surface and diffusion along the surface. For the case of transport by surface re‐emission, a reactive sticking coefficient is defined for the radicals, and a formulation is developed to simulate etching for any value (between zero and unity) that this sticking coefficient may assume. When the sticking coefficient approaches either zero or unity, the method of characteristics is shown to be useful for profile simulation. Transport of radicals by surface diffusion i...

Technology and reliability constrained future copper interconnects. II. Performance implications

For pt. I see ibid., vol.49, no.4, pp.590-7 (2002). This work extends the realistic resistance modeling of on-chip copper interconnects to assess its impact on key interconnect performance metrics. As quantified in part I of this work, the effective resistivity of copper is not only significantly larger than its ideal, bulk value but also highly dependent on technology and reliability constraints. Performance is quantified under various technological conditions in the future. In particular, wire delay is extensively addressed. Further, the impact of optimal repeater insertion to improve these parameters is also studied using realistic resistance trends. The impact of technologically constrained resistance on power penalty arising from repeater insertion is briefly addressed. Where relevant, aforementioned results are contrasted with those obtained using ideal copper resistivity.

Experimental study of biaxial and uniaxial strain effects on carrier mobility in bulk and ultrathin-body SOI MOSFETs

Biaxial and uniaxial strained silicon technologies are promising for enhancement of CMOS performance. However, the advantage of uniaxial/biaxial strain over biaxial/uniaxial strain in terms of carrier mobility is not clear, since biaxial and uniaxial strain effects on carrier mobility have not till date been directly compared. Furthermore, the carrier mobility under uniaxial strain has not been fully studied in terms of strain directions. On the other hand, in spite of the importance of ultrathin-body (UTB) SOI MOSFETs to suppress the short channel effects in sub-20-nm regime, strain effects in UTB MOSFETs with SOI thickness, T/sub SOI/, of less than 5nm have not be explored yet. In this report, biaxial and uniaxial strain effects on carrier mobility are systematically studied, for the fist time, utilizing externally applied mechanical stress. The biaxial and uniaxial strain effects in UTB MOSFETs with T/sub SOI/ of less than 5nm are also investigated, for the first time.