Evolution of photoluminescent defect clusters in proton- and copper-implanted silicon crystals during annealing

Abstract

Evolution of intrinsic defects (interstitials or vacancies) formed by implanting with protons and copper ions in silicon crystals and then annealing the crystals at temperatures from 100 to 800 °C was investigated by photoluminescence (PL) measurements. For samples annealed below 400 °C, only the well known W and I3 center peaks were observed for both proton and copper implantations. Several no-phonon PL peaks (at least six), that were inferred to be due to interstitial clusters, were newly evolved between 1.2 to 1.4 μm for samples heavily implanted with both protons and copper ions after annealing between 500 and 600 °C, indicating the existence of several self-interstitial clusters having a stability between that of the W center and the {311} defects. From the dependences of the PL intensities of these new peaks on the densities of the displaced atoms formed by implantations and on the annealing temperatures, these clusters were thought to be composed of larger numbers of self-interstitials than the W center. In addition to these peaks (the W, I3, and new centers), several broad peaks seemingly due to plural origins were observed after annealing the heavily implanted samples from room temperature to 600 °C, however, they completely vanished after annealing at 700 °C. Evolution of the PL peak located at 1.376 μm and known to be due to the {311} defects was not observed after the annihilation of the preceding peaks that are presumed to be the precursors of the {311} peak.

Structure and stability of small compact self-interstitial clusters in crystalline silicon

“…26,27 The earlier inverse model studies suggested that there would be a structural transition from compact to elongated forms when the cluster size ͑n͒ is around 10 atoms, and also the differential formation energies of small clusters ͑n Ͻ 10͒ exhibit two strong minima at n = 4 and n = 8. The predictions were also advocated by recent low temperature photoluminescence studies [22][23][24] which demonstrated possible existence of small and compact interstitial clusters of various sizes. The minimum-energy configurations of a few small clusters ͑n =1-5͒ have recently been determined using extensive firstprinciples-based atomistic simulations.…”

“…20 Hence, most interstitials are likely to remain in the form of clusters in bulk Si. 3,4 While extended ͕311͖ defects have been well characterized by transmission electron microscopy, earlier spectroscopy measurements based on deep level transition, 21,22 photoluminescence, [22][23][24] and electron spin resonance 25 have also evidenced the formation of small interstitial clusters ͑Ͻ50 Å in equivalent diameter͒ at low doses ͑10 12 -10 14 Si/ cm 2 ͒ and moderate annealing temperatures ͑ഛ600°C͒ before they evolve into larger extended defects with increased ion fluence ͑ജ5 ϫ 10 13 Si/ cm 2 ͒ and elevated annealing temperatures ͑ജ700°C͒. In fact, in ultrashallow junction formation with low-energy implanted dopants, small self-interstitial clusters are thought to be a main source for free interstitials responsible for dopant TED and clustering during postimplantation annealing.…”

Growth and shape transition of small silicon self-interstitial clusters

“…This prediction has been supported by a series of low-temperature photoluminescence ͑PL͒ studies 7,9,10 which show the signatures of small compact clusters of various sizes in ion-implanted Si upon short annealing. In addition, the PL measurements demonstrate changes in the spectra from multiple sharp peaks to broad but distinct signatures during prolonged annealing, ascribed to the shape evolution of self-interstitial clusters from compact to extended forms.…”

“…The formation and structure of rodlike ͕311͖ defects have been well characterized by high-resolution transmission electron microscopy ͑HRTEM͒. [3][4][5] In addition, a series of recent spectroscopy measurements [6][7][8][9][10][11] have evidenced existence of small compact self-interstitial clusters before they evolve into larger extended defects. In ultrashallow junction formation with low-energy implanted dopants, such small interstitial clusters are thought to be a main source for free interstitials responsible for dopant transient enhanced diffusion and agglomeration during postimplantation thermal treatment.…”

Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon

“…1 We report here on the interstitial/vacancy nature of luminescence centers created when silicon is implanted at room temperature with MeV Si + ions and subsequently annealed. 2 Some PL centers have recently been associated with interstitial clusters, 3 on the basis of their stability at 600°C, well above the annealing temperature of vacancy defects measured by deep level transient spectroscopy ͑DLTS͒ on lowdose implanted samples. 1͒, PL can unambiguously monitor each specific defect.…”