STRESS IMAGING OF DEFORMATION AND CRACK DEFECTS IN SILICON BY CONFOCAL RAMAN SPECTROSCOPY

 

Yvonne B. Gerbig, M.D. Vaudin, S. Stranick*, and Robert F. Cook

Affiliation: Ceramics Division, NIST Gaithersburg, MD 20899

* Surface and Microanalysis Science Division, NIST Gaithersburg, MD 20899.

 

 

Due to the brittle nature of most materials used in microelectronic and microelectromechanical devices, stress-induced fracture is the main factor determining device yield and reliability. On the other hand, the microelectronics industry is increasingly taking advantage of strain-engineered semiconductors in order to improve carrier mobility. As a consequence, research on stress at suitable length scales has become crucial to the proper reliability evaluation of devices, as well as the better understanding of stress related issues regarding device design, processing and performance.

In this paper we analyze the correlation between stress distribution, mechanical behavior and crystallographic orientation of silicon. For this purpose, spherical indentations were formed on Si(100) and Si(111) wafers, and the residual stress fields around the indentations mapped using a confocal Raman microscopy technique. Combined with appropriate peak fitting and super resolution methods, this technique allows stress measurement with a resolution of approximately 20 MPa at spatial resolution of approximately 100 nm. The effect of load and crystallographic orientation on the stress fields around plastic indentations is demonstrated. As long as the threshold for crack initiation is not reached, the “stress signature” does not change significantly with increasing load whereas the local stress value in the stress field does. The main difference between the two orientations lies in the symmetry of the stress field, threefold for Si(111) and fourfold for Si(100). On exceeding the threshold for crack initiation, the occurrence of cracks may alter the residual stress field significantly, dependent on the crack size. The interactions between the stress field around a crack tip and the superimposed stress field of the indentation are demonstrated for different stages of crack development.

 

 

 

 

CATEGORY: Materials

 

 

Mentors Name: Robert F. Cook

Ceramics Division, MSEL

Room A 253, Bldg. 223, Mail stop 8520

Tel: x3207

Fax: x5334

Email: robert.cook@nist.gov

 

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