Impurity Gettering In Silicon Research Articles

Siにおける不純物のゲッタリング : III. プロセス誘起不純物偏析

Siにおける不純物のゲッタリング : III. プロセス誘起不純物偏析

Trans-projected-range effect in proximity gettering of impurities in silicon

Deep gettering layers have been formed in n-type Si wafers by high-energy ion implantation of Si +, P +, Ge + and As + and subsequent annealing. The samples have then been contaminated with Cu by implanting the impurity into the back face and performing an additional thermal treatment. The resulting copper depth profiles measured by secondary ion mass spectrometry show strong gettering of Cu well beyond the projected ion range R P and formation of a separate gettering band therein. We call this phenomenon the “trans- R P effect”. It has been observed for both the P and As implants, but not for the Si and Ge implants. This effect indicates the presence of a significant amount of defects much deeper than R P . The size of these defects is below the resolution limit of our transmission electron microscopy analysis and we suggest that they are small interstitial clusters. Their gettering ability is higher than that of the extended defects at R P as the amount of Cu atoms gettered beyond R P is much greater than that in the implanted gettering layer. A mechanism for the defect formation and clustering in the trans- R P region is proposed, and an explanation for the differences in the results for the P and As implants is given.

Simulation of metallic impurity gettering in silicon by MeV ion implantation

A simple model for metallic impurity gettering by buried layers created by MeV ion implantation in silicon is presented. For our experimental conditions, the precipitation of supersaturated Fe at dislocation loops in silicon is not diffusion limited. Furthermore, a non-zero silicide-matrix interfacial energy density was required to fit our experimental data. In samples containing dislocations and boron-implanted layers, the dislocations trap more Fe than the boron, but the latter is more effective at reducing the concentration of ungettered Fe. Although we were able to simulate impurity distributions fairly well in many cases, the model is not free from adjustable parameters due to a lack of knowledge of detailed impurity–defect interactions and the silicide-matrix interfacial energy density.

Impurity Gettering in Silicon by Thin Polycrystalline Films

ABSTRACTCapability of impurity gettering by thin polycrystalline films on the backside of silicon wafer was evaluated by minority-carrier diffusion length. Cu was gettered easily during usual cooling after high temperature annealing. On the other hand, intentional slow cooling or low temperature annealing was necessary for effective Fe gettering. The gettering efficiency for Fe increased with lowering the annealing temperature when Fe was diffused sufficiently. From the quantitative consideration of Fe gettering, we propose the model of impurity gettering based on the chemical equilibrium of impurity reaction in polysilicon films. It was also expected that gettering efficiency increased with the thickness of polysilicon film.

Relaxation-Induced Gettering of Metal Impurities in Silicon: Microscopic Properties of Effective Gettering Sites

ABSTRACTSome gettering processes like internal gettering or backside damage gettering base on heterogeneous precipitation of metal impurities at defects in pre-de ter mined parts of silicon wafers during cooling from high temperatures. We consider microscopic properties of effective heterogeneous nucleation sites for cobalt, nickel and copper impurities from the fundamental point of view of suicide precipitate formation. We follow the basic concept that such gettering sites are defects which allow fast precipitation, i.e. which remove kinetic limitations known from homogeneous precipitation of these impurities at small supersaturation. For Co and Ni it follows that distorted lattice sites in the core of dislocations may establish high incorporation rates of interstitial atoms into suicide particles, whereas for Cu sinks for silicon self-interstitials are suitable gettering sites.

Gettering of Impurities in Silicon

ABSTRACTDespite the apparent dissimilarities between different gettering methods, we show that many can be understood in terms of two basic mechanisms. The first involves the interaction of selfinterstitials (emitted, for example, by P in-diffusion and precipitation, 0 precipitation, or Ar implantation) with the impurities to be gettered. The second relies on a strain-field/point defect interaction (for example around a dislocation), which appears capable of enhancing the diffusivity of the impurities. In either case, gettering can be viewed as a particular and particularly useful instance of the wider class of defect/defect interactions.