Achieving micron-scale plasticity and theoretical strength in Silicon

Ming Chen,Laszlo Pethö,Ralph Spolenak,Alla S Sologubenko,Jeffrey M Wheeler,Huan Ma,Johann Michler

doi:10.1038/s41467-020-16384-5

Abstract

As the backbone material of the information age, silicon is extensively used as a functional semiconductor and structural material in microelectronics and microsystems. At ambient temperature, the brittleness of Si limits its mechanical application in devices. Here, we demonstrate that Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength ~4 GPa) and plastic deformation at the micron-scale, one order of magnitude larger than samples made using focused ion beams, due to superior surface quality. This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Further, the micron-scale plasticity of Si allows the investigation of the intrinsic size effects and dislocation behavior in diamond-structured materials. This reveals a transition in deformation mechanisms from full to partial dislocations upon increasing specimen size at ambient temperature. This study demonstrates a surface engineering pathway for fabrication of more robust Si-based structures.

Highlights

As the backbone material of the information age, silicon is extensively used as a functional semiconductor and structural material in microelectronics and microsystems
No plasticity is seen in Si pillars with diameters of 10 and 5 μm, but lithographic pillars display higher strengths compared to their focused ion beam (FIB)-milled counterparts
FIBmilled pillars acquired an amorphized layer at the surface (Fig. 5a, b) with a thickness of ~40 nm (Supplementary Fig. 4c)

Summary

Introduction

As the backbone material of the information age, silicon is extensively used as a functional semiconductor and structural material in microelectronics and microsystems. We demonstrate that Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength ~4 GPa) and plastic deformation at the micron-scale, one order of magnitude larger than samples made using focused ion beams, due to superior surface quality This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Studies employing conventional lithography techniques in semiconductors[20] indicated an improvement in strength over FIB-milled specimens but induced a fluorosilicate layer and/ or oxide shell[21] These additional layers significantly affect the mechanical properties and dislocation nucleation and dissipation at the surface[17]. Both FIB machining and lithography etching are routinely used in semiconductor industry and nanofabrication[22]

Methods

Results

Conclusion