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Ô³çèêî-õ³ì³÷íà ìåõàí³êà ìàòåð³àë³â. – 2015. – ¹ 3. – Physicochemical Mechanics of Materials

EFFECT OF PROLONGED HOLDING UNDER CONTACT LOADING
ON THE PECULIARITIES OF PHASE CHANGES IN SILICON
1 1 2
O. SHIKIMAKA , A. PRISACARU , A. BURLACU
1
Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Moldova Republic;
2
Institute of Electronic Engineering and Nanotechnologies “D. Ghitu”, Academy of Sciences of Moldova,
Chisinau, Moldova Republic
It was shown that prolonged holding under the peak load during indentation of Si (100) led
to the creep of material even at room temperature that became possible due to the phase
transition into more plastic metallic b-Sn phase. The end structural phases in the indenta-
tion zone, studied by micro-Raman spectroscopy were found to be affected by the longer
holding under the load and demonstrated more intensive peaks for amorphous phase (a-Si)
in the depth of the indentation comparatively with those for short holding indentations.
It was suggested that this effect was caused by the activation of the dislocation mechanism
of a-Si formation, as a result of longer shear stresses action under prolonged holding. This
fact induced some changes in the kinetics of the unloading events, which demonstrated the
tendency to the “kink pop-out” formation instead of typical “pop-out” and “elbow”.
Keywords: indentation, silicon, phase transformation, amorphous phase, unloading
events, creep, holding time.
Although a lot of new materials for micro- and optoelectronics have been elabo-
rated within the last years, silicon remains the principal component of most semicon-
ductor devices and has many industrial uses. Along with electrical and optical proper-
ties, mechanical behaviour of Si, especially under local loading, obtained a special in-
terest due to its peculiarity for structural phase transformation in nano- or micro-volu-
mes of deformed material. High pressure created under nano/microindentation leads to
the phase transformation of initial diamond cubic structure (Si-I) into high conductive
b-Sn structure (Si-II) under loading. On pressure release Si-II transforms into body
centered cubic (Si-III), rhombohedral (Si-XII) and amorphous (a-Si) structures depen-
ding on the unloading rate [1, 2], load value, type of indenter [3–5] or deformation
temperature [6, 7].
Recently silicon has found a wide application in micro-electro-mechanical sys-
tems (MEMS), the reliability of which strongly depends on the mechanical durability
of material used. During exploitation the Si MEMS components can undergo the influ-
ence of long lasting constant load. The nanoindentation technique is the most suitable
one to investigate the time-dependent mechanical response of material in such condi-
tions and to study various aspects of creep process at nano- and microscale.
In spite of a lot of works concerning the mechanical behaviour of Si under nano/
microindentation at various loading conditions like cyclic loading [3, 8] or scratching
[5], apparently there is a gap in indentation creep investigations on Si. Mostly the data
regarding the silicon creep characterization were obtained using uniaxial compression
or bending tests for comparatively low stresses (from 2 to 150 MPa) and enhanced
temperatures (from 800 to 1300°C) [9, 10]. The main deformation mechanism during
creep was shown to be the dislocation movement that is obvious for the used range of

Corresponding author: O. SHIKIMAKA, e-mail: olshi@phys.asm.md

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