Ali Zojaji

A study of low energy phosphorus implantation and annealing in Si:C epitaxial films

The effect of phosphorus implantation and thermal annealing on properties of Si:C epitaxial films was investigated. High resolution x-ray diffraction analysis and secondary ion mass spectroscopy indicated that spike annealing only causes slight loss of substitutional carbon. Phosphorus implantation, even with low energy, could cause surface damages and loss of substitutional carbon. Although spike annealing effectively activates implanted phosphorus, it also results in significant substitutional carbon loss (from 1.2% to less than 0.5%) within the phosphorus diffused layer. The interaction of carbon and phosphorus resulted in a junction profile as abrupt as with 3 nm/decade.

Heavily Phosphorus Doped Silicon Junctions for nMOS Applications

Epitaxially grown Silicon Carbon (Si:C) in recessed junction regions has been shown to induce tensile stress in the nMOS channel and thereby enhance the transistor performance. In addition to the stress induced in the channel, this technology also needs to achieve low resistivity junctions for widespread use. This work discusses epitaxially grown heavily doped Si/ Si:C layers which can be used in nMOS junctions and can address both these requirements. Si:C epitaxial layers are shown to have phosphorus concentrations as high as 1.25 X 10^21 cm^-3 with resistivities as low as 0.3 mOhm.cm. Applications of these layers can range from Si:P cap layers for low series resistance to Si:PC layers for inducing stress in the nMOS channel.

Application of Selective Si:C Epitaxy For Recessed Source/Drain Technology

INTRODUCTION It is understood that a uniaxial tensile stress along a channel of transistor enhances electron mobility and drive current of NMOS transistors. Typically, a tensile stress-enhanced silicon nitride layer is used to strain the channel [1]. For even further enhancement of transistor drive current, a use of silicon carbon alloy (Si:C) in recessed source/drain (S/D) area has been considered. Alloying Si with C decreases lattice parameters when carbon atoms occupy substitutional sites of Si lattices. Very recently, it has been reported that a use of Si:C epitaxy in recessed S/D generates tensile strain in the channel of NMOS transistor and consequently increases transistor drive current [2]. The Si:C recessed S/D technology has two major challenges in preparing an epitaxy solution: One is how to incorporate carbon atoms into substitutional sites. As the solid solubility of substitutional carbon in silicon is only ~10 cm, carbon atoms at concentrations higher than this easily incorporate into interstitial sites or precipitate as β-SiC, resulting in no strain in the epilayer. Therefore, in order to achieve high substitutional carbon concentration (≥ 1%) with minimizing interstitial carbon concentration, non-equilibrium epitaxial growth conditions such as low temperature (≤ 600 C) are required [3]. The other is to obtain selectivity and reasonable growth rate of selective Si:C epitaxy process with maintaining high substitutional carbons. We have developed selective Si:C epitaxy processes with 1% or higher substitutional carbon concentration and will discuss characteristics of the epitaxy grown on recessed area of patterned wafers.

The formation of ultrathin silicon oxide films using H2/N2O mixtures

This paper describes a process called N 2 O in situ steam generation, which uses a combustion-like reaction of lean hydrogen in N 2 O to form ultrathin (≈10 ) silicon oxide films on silicon. An important application is the formation of high-integrity gate dielectrics for integrated circuits. The atomic oxygen created through homogeneous reaction plays an important role in growing high-quality oxide films. This paper presents measured oxide-thickness profiles on 200 mm wafers under several processing conditions. Stirred-reactor and boundary-layer models are used to explain and interpret the data. An elementary chemical-reaction mechanism, which is drawn from the combustion literature, provides an excellent representation of this advanced materials process.

A Study of Low Energy Phosphorus Implantation and Annealing in Si:C Epitaxial Films

We investigated the effect of dopant implantation and thermal annealing on substitution carbon concentration of Si:C epitaxial film. While spike annealing at T=1050 degC results in slight loss of substitution carbon (0.6%) but maintains high crystalline, phosphorus implantation induces significant loss of substitution carbon and a change of carbon depth profile. It is also observed that very abrupt junction can be formed in a Si:C epitaxial film