Transition from a punched-out dislocation to a slip dislocation revealed by electron tomography
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Grace S. Liu Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801
Tomonobu Kishidab) and Kenji Higashida Department of Materials Science and Engineering, Kyushu University Nishi-ku, Fukuoka 819-0395, Japan
Ian M. Robertsonc) Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801 (Received 29 July 2010; accepted 7 September 2010)
Punched-out dislocations emitted from an octahedral oxide precipitate in single-crystal silicon were investigated using high-voltage electron microscopy and tomography (HVEM-tomography) to understand the mechanism of softening caused by the oxide precipitates. In the present paper, direct evidence of the transition of a punched-out prismatic dislocation loop to a slip dislocation is presented. The punched-out dislocation grows into a large matrix dislocation loop by absorption of interstitial atoms, which were produced during oxide precipitation. I. INTRODUCTION
Oxide precipitates are included in some silicon wafers to increase the purity of the active device area, with the concomitant enhancement of the electrical properties.1 Either octahedral or platelet precipitates can be grown by performing the appropriate heat treatments.2 Metallic ions are trapped at lattice defects produced around the precipitates. These defects may take the form of punched-out prismatic dislocation loops or stacking faults. It has been reported that the precipitates affect not only the optical properties but also the mechanical properties.3–9 For example, the yield stress of silicon with precipitates can be up to 33% lower than that of silicon with no precipitates.5 The magnitude of the decrease is dependent on the precipitate size. One of the proposed mechanisms to explain the decrease in yield stress involves the punchedout dislocations transitioning to Frank–Read sources.4 However, punched-out dislocations cannot themselves be Frank–Read sources as the segment length of punched-out dislocations is usually less than a few hundred nanometers a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Mitsubishi Heavy Industries, Ltd., 10 Ooe-cho, Minato-ku, Nagoya, 455-8515 Japan. c) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2010.0308 2292
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J. Mater. Res., Vol. 25, No. 12, Dec 2010 Downloaded: 29 Mar 2015
so that the resolved shear stress to bow out the segment is too large. In the present paper, direct evidence of the transition from a punched-out dislocation to a slip dislocation is presented; electron tomography10–12 was used to reveal the dislocation distribution around a precipitate three-dimensionally. II. EXPERIMENTAL
A (001) P-type Czochralski silicon wafer containing octahedral precipitates with an average size of 300 nm and a density of 4 1010 cm3 were
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