Filling the voids in silicon single crystals by precipitation of Cu₃Si

Abstract

This article presents a method to decorate all open volume defects in a silicon single crystal by Cu 3 Si precipitation. Si single crystals are being used for the determination of Avogadro's number with sufficient accuracy (1 part in 10 8 ) to allow the establishment of a physical standard for the kilogram. The method described here can be used to certify that the open volume in such crystals is sufficiently small. The voids in this work were formed artificially by annealing Heimplanted silicon wafers. Annealing after application of a copper nitrate solution to the surface followed by slow cooling produced Cu 3 Si precipitates in the 0 phase in the voids. To fill all the voids completely it proved necessary to coat the surfaces, after application of the nitrate, with a pure Cu layer as well. Slow cooling keeps the supersaturation of Cu small but sufficient to precipitate Cu into the voids. Formation of dislocation loops and stacking faults, often seen during Cu silicide precipitation in silicon after fast cooling, can be minimized. Other transition metals, such as Au, Ni, and Fe, were found to be less suitable than Cu for filling voids.

Position Controlled Growth of Single Crystal Cu3Si Nanostructures

“…2,15 The HRTEM image of the grown nanostructure in Figure 3 η″ pattern with a 0.35 nm d spacing, which is in good agreement with previously reported measurements. 24 Based on the HRTEM (Figure 3(b)) and EDX data (see see Fig. S2(d) of SI), the structural composition of this nanostructure is unambiguously identified as Cu3Si.…”

“…These voids facilitate the direction reaction between Cu and Si to form Cu3Si nanostructures. 9 This void reaction mechanism was further emphasized by Wen et al 24 using artificially created voids less than 100 nm in size by He-implantation in silicon. In that study, a copper nitrate solution was used to decorate all the open-volume defects in the single crystal resulting in local Cu3Si precipitation.…”

Quantification of the Void Volume in Single-Crystal Silicon

“…The coated sample was annealed in vacuum at 740 °C using an electrical oven. The temperature was slowly increased starting from room temperature; the transient between 700 °C and 740 °C took about 3 h. At 740 °C, the oven was switched off and the sample left in it to ensure the Cu 3 Si precipitation into the voids without formation of dislocation loops and stacking faults due to fast cooling; the cooling rate reached a maximum of 3 °C min –1 , immediately after the oven was switched off, and gradually decreased to 1 °C min –1 in 10 h. Finally, the external Cu layer was removed by etching it with a 10:1 solution of nitric acid, HNO 3 , and hydrofluoric acid, HF, for 40 min. The mass removed by etching, 485 mg, corresponds to a surface Si layer about 100 μm thick.…”

New investigation of phase equilibria in the system Al–Cu–Si

“…At 600 °C, the additional three phase field {(Cu) + (Al,Cu)-β + (Al,Cu)-γ 1 } appears, where (Al,Cu)-β shows a solubility of about 4 at.% Si. Both at 500 and 600 °C, He et al allocate the binary phase Cu 3 Si to Cu 3 Si-η, which is contradicting to the binary Cu–Si system [23,29,39] .…”