Slow crack growth in single-crystal silicon

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Time-dependent crack growth is a critical factor in the long-term reliability of materials and devices.
• Understanding crack propagation mechanisms in silicon is essential for microelectromechanical systems (MEMS) and semiconductor reliability.
• Previous studies have focused on macroscopic materials, with less data available for nanoscale silicon structures.

Purpose of the Study:

• To measure time-dependent crack growth in a single-crystal silicon cantilever beam at resonance.
• To correlate crack growth with changes in the beam's resonant frequency.
• To investigate the potential failure mechanisms and implications for silicon device reliability.

Main Methods:

• A precracked, single-crystal silicon cantilever beam (75 micrometers long) was excited at its resonant frequency.
• Crack length was monitored by observing changes in the beam's resonant frequency.
• Crack growth rates were measured using a high-sensitivity apparatus capable of detecting extremely slow crack propagation.

Main Results:

• Steady-state crack growth rates as low as 2.9 x 10(-13) m/s were measured.
• The experimental setup can detect crack growth rates down to 10(-15) m/s.
• Changes in resonant frequency directly correlated with the measured crack length, validating the measurement technique.

Conclusions:

• Static fatigue of the native surface silica layer is postulated as the primary mechanism for crack growth in silicon.
• These findings demonstrate rate-dependent failure in silicon devices and the applicability of linear elastic fracture mechanics to microscale devices.
• Slow crack growth must be considered in the reliability assessment of thin-film silicon structures and MEMS.