On the mechanism of {113} defect formation in Si: a study by in situ HREM irradiation

Type {113} defects in Si are crucially important for device manufacture because they strongly influence the diffusion of dopant atoms at elevated temperatures during the technological process. The equilibrium hexagonal structure of interstitial type {113} defect has already been established [1], however, its initial formation stages are still unclear. There are two main questions: what is the mechanism for interstitial chains formation and why the structure of the defect is so complex? Ab initio calculations propose only compact configurations of the initial cluster [2]. Recently, a new four-fold-coordinated point defect (FFCD) corresponding to the close-bonded interstitial-vacancy pair was proposed as a building block for more extended defects [3, 4]. However, this FFCD has not been detected experimentally yet. In fact, we have already shown by using in situ HREM irradiation experiments that self-interstitials and vacancies in Si tend to aggregate together at {113} habit planes [5]. In the very initial stages, both <110>-split interstitials and vacancies are arranged within [110] atomic chains located on {113}. Due to the energy barrier (~1.3eV) for recombination of self-interstitials with the aggregates of vacancies, different intermediate defect configurations are formed at {113} and {111} habit planes depending on the local supersaturation of point defects at low temperature [6]. Here we present the experimental evidence of the existence of {113} defects consisting of FFCDs. The in situ HREM irradiation experiments were carried out on a JEOL-4000EX at 400 keV at room temperature. Electron irradiation at energies higher than the threshold of 200 keV in Si at room temperature has the advantage of creating only Frenkel pairs and allows a very detailed investigation of point defect clustering even at the strained Si/SiGe interface [7]. TEM specimens were prepared by chemical etching of high pure n-type FZ-(110)Si wafers with 4000 Ωcm resistivity. Thin specimens were then covered with a 5 nm thick Si 3 N 4 film to reduce point defect sink to the surface. Structural atomic models were optimized by the MM+ force field. Simulated HREM images of thus optimized models were calculated with the multislice program Musli. Figure 1a presents the experimental HREM image of the intermediate structure of a {113} defect preceding the final hexagonal structure formation. A schematic model superimposed on the image at Fig. 1(b) shows that the defect consists of eight-fold rings surrounded by five-fold rings. At the right side of the {113} defect an interstitial hexagonal structure starts to appear. …