Strain Determination Around Vickers Indentation on Silicon Surface by Raman Spectroscopy
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Paulo Sergio Pizani Departamento de Fisica, Universidade Federal de São Carlos, C.P.676, 13560-970 São Carlos, SP, Brazil (Received 25 November 2003; accepted 29 January 2004)
We used Raman spectroscopy to characterize indentations on silicon. We focused our attention on the strain field around several indentations made on an (001) oriented silicon wafer with loads ranging from 100 mN to 10 N. Micro-Raman spectroscopy was used for the analysis of the indentation strain field. By multiplying the frequency shift of the optical phonon of silicon by the distance from the center of the fingerprint to the point under investigation, we were able to determine the strained zone extension accurately with the boundary between the strained area and the unperturbed area, which becomes clearly visible. This method allowed us to propose an equation valid over a large range of loads (0.1–10 N), which allowed us to estimate the size of the strained zone. We show that even in the absence of visible defects, the strain field extended to a region relatively far from the imprint in between cracks. The analysis of the radial and lateral cracks gives information where the proposed equations are valid.
I. INTRODUCTION
Indentation is a technique widely used to test the material hardness and has been used for several decades.1–3 In the beginning of the twentieth century, this technique was used to gain information on metal alloys and subsequently has been extended to semi-conducting and ceramic materials. The information deduced from indentation experiments is useful to study the relaxation processes, for testing continuum mechanics simulations, and understanding micro-machining processes. Nanoindentation obtained with loads in the range of 10–100 mN can be used for studying the first stage of crack generation and the identification of new phases. Microindentation typically with 1–100 N loads is usually characterized by hardness and is used to understand the crack system by considering the morphology, the load– unload sequence, and the size of the imprint as a function of the load. The analysis of the core of the indentation and the characteristics of the cracks is widely documented in literature.1–4 For silicon, by varying the temperature, we can switch from a system with radial cracks at low temperature to a system with lateral cracks at high temperature.4 The
Address all correspondence to this author. a) e-mail: [email protected] DOI: 10.1557/JMR.2004.0165 J. Mater. Res., Vol. 19, No. 4, Apr 2004
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load–unload sequence allows to generate in the core of the indentation the formation of amorphous silicon or metastable phases of silicon by varying the speed. The surrounding of the plastic core has not been widely analyzed due to the lack of experimental techniques. The use of silicon in solar cells and the reduction in the size for making miniature machines for micro-electromechanical systems attracts much research attention.5–7 Modeling the contact loading is quite compli
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