Isochronal annealing studies of carbon-related defects in irradiated Si

Abstract

We report infrared spectroscopy studies of defects in neutron-irradiated, carbon-doped, Cz-grown silicon. At room temperature irradiations, among the main defects formed are the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ complexes. A peak in the spectra at 544 cm⁻¹ was found to be the contribution of two bands at 543.5 and 545.5 cm⁻¹. From the corresponding annealing behavior of these bands, the 543.5 cm⁻¹ band was correlated with the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ defect although the 544.5 cm⁻¹ band with the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ defect. At high-irradiation doses, complexes as the ${\mathrm{C}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ $(953,960{\mathrm{cm}}^{-1})$, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})(934,1018{\mathrm{cm}}^{-1})$, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}({\mathrm{Si}}_{\mathrm{I}})(987,993{\mathrm{cm}}^{-1})$ and ${\mathrm{C}}_{\mathrm{s}}{\mathrm{C}}_{\mathrm{s}}(527{\mathrm{cm}}^{-1})$ form. Isochronal anneals performed in order to study the thermal evolution of these centers, showed that the ${\mathrm{C}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ begin to decay in the spectra around 150 °C. Their disappearance is not accompanied by the emergence of any signal. The ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ and the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}({\mathrm{Si}}_{\mathrm{I}})$ centers begin to decay around $\sim 250{}^{\circ }\mathrm{C}$. Their disappearance is accompanied by the emergence of two pairs of bands at $(918,1006{\mathrm{cm}}^{-1})$ and $(945,964{\mathrm{cm}}^{-1})$, respectively. The origin of the centers, giving rise to these bands is discussed.

Introduction

Carbon is, besides oxygen, the most important impurity in Si. It has been studied intensively during the last 50 years. However, in spite of the very large amount of work that has been done so far, some aspects of its behavior, especially those concerning the reaction processes that carbon participates in, are not known in detail. Upon irradiation of carbon-rich Cz-grown Si, carbon-substitutional atoms $({\mathrm{C}}_{\mathrm{s}})$ are ejected [1] at interstitial sites $({\mathrm{C}}_{\mathrm{i}})$, according to the Watkins-replacement mechanism $({\mathrm{C}}_{\mathrm{s}}+{\mathrm{Si}}_{\mathrm{I}}\to {\mathrm{C}}_{\mathrm{i}})$. ${\mathrm{C}}_{\mathrm{i}}$ is very mobile at room temperature and it readily reacts [2] with ${\mathrm{C}}_{\mathrm{s}}$ and ${\mathrm{O}}_{\mathrm{i}}$ defects forming the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ pairs, respectively. Most of the primary defects produced by the irradiation tend to annihilate between themselves $(\mathrm{V}+{\mathrm{Si}}_{\mathrm{I}}\to Ø)$, although some of them are captured by impurities present in the material $(\mathrm{V}+{\mathrm{O}}_{\mathrm{i}}\to \mathrm{VO},{\mathrm{Si}}_{\mathrm{I}}+{\mathrm{C}}_{\mathrm{s}}\to {\mathrm{C}}_{\mathrm{i}}$, etc.) and some other pair with each other $(\mathrm{V}+\mathrm{V}\to {\mathrm{V}}_2,{\mathrm{Si}}_{\mathrm{I}}+{\mathrm{Si}}_{\mathrm{I}}\to ({\mathrm{Si}}_{\mathrm{I}}\text{–}{\mathrm{Si}}_{\mathrm{I}}))$. Defect reaction modeling foresees and experiments verify [3], [4], [5] that a percentage of the ${\mathrm{Si}}_{\mathrm{I}}$'s is also captured by centers formed during the irradiation. Thus, the ${\mathrm{C}}_{\mathrm{i}}$, the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ defects act as neucleation sites for the ${\mathrm{Si}}_{\mathrm{I}}$'s and at high radiation doses, complexes as the ${\mathrm{C}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$, the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ and the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}({\mathrm{Si}}_{\mathrm{I}})$ form, as well. A pair of local vibrational mode (LVM) bands at $(953,966{\mathrm{cm}}^{-1})$ has been correlated [2] with the ${\mathrm{C}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$, another pair at $(940,1024{\mathrm{cm}}^{-1})$ has been correlated [2] with the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ complex and another one at $(987,993{\mathrm{cm}}^{-1})$ has been correlated [6] with the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}({\mathrm{Si}}_{\mathrm{I}})$ complex. On the other hand, vacancies are also trapped by the ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ complexes [7] leading to the formation of the ${\mathrm{C}}_{\mathrm{s}}{\mathrm{C}}_{\mathrm{s}}$ defect $(527.4,748.7{\mathrm{cm}}^{-1})$, through the reaction ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}+\mathrm{V}\to {\mathrm{C}}_{\mathrm{s}}{\mathrm{C}}_{\mathrm{s}}$.

In neutron-irradiated ${\mathrm{S}}_{\mathrm{i}}$, due to the spatial separation [8] of the produced vacancies and self-interstitials, complexes related to these defects form in larger concentrations. Therefore, weak signals in the spectra related to such complexes are expected to be detected more easily, facilitating their study. The purpose of this work is to study the production and evolution with temperature of the ${\mathrm{C}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}({\mathrm{Si}}_{\mathrm{I}})$, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}({\mathrm{Si}}_{\mathrm{I}})$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{s}}$ defects. It is a continuation of a previous work [6], aiming in particular at throwing new light on carbon-related defects and processes, where aggregations of primary defects are involved.