Length effect on creep of silicon cantilever microbeams

Creep behavior is very important to reliability of micromechanical components. Therefore, there are some emerging research efforts that focus on creep of silicon. However, few have focused on interaction among microscale dimension effect, temperature, and applied stress, which are more crucial to microelectrical mechanical system components compared with regular size components. This paper presents investigation of creep of single crystal silicon cantilever microbeams with a specific focus on the length effect. Results are presented characterizing the creep behavior in the length range of 300–700 µm, the temperature range of 600–700℃, and the stress range of 235–501 MPa. As the temperature or stress increases, the creep rate of silicon increases and duration of the steady-state creep decreases. Creep rate decreases with the increase of microbeam length. At 600℃, creep rupture lifetime approximately increases with the increase of microbeam length. At 700℃, maximum lifetime shifts to medium length of 400 µm. Factors that influence rupture lifetime include short beam effect, defect distribution, stress, temperature, and brittleness caused by oxidation. To summarize, creep failure modes for short beam and long beam are, respectively, dislocation motion by multiple slip systems and single slip system.