Mechanics of crack path selection in microtransfer printing: Challenges and opportunities for process control

Abstract

Microtransfer printing is a manufacturing technique that relies on controlled selective delamination between two interfaces to transfer thin solid films and chips. Stamps in these processes are often designed to leverage strategies that modify the interfacial stress distribution at the stamp interface to achieve a specific adhesion response, however the effect of a modified stress distribution at the stamp interface on crack path selection between the two interfaces in the system is unclear. This paper investigates how the stress distribution beneath the stamp can affect the delamination path between the two interfaces in a microtransfer printing process using mechanics modeling. In general, altering the stress distribution at the stamp/chip interface also alters the stress distribution at the chip/substrate interface. For a sufficiently thin chip with no or small initial defects at the interfaces, the common approach of tuning adhesion by reducing the strength of stress singularity near the edge of the stamp does not provide a robust route to control the delamination path. An alternative stamp design strategy, guided by the singularity order of the stress distribution, is proposed and analyzed. In the proposed stamp design, the delamination path can be controlled through the stamp thickness and the application of a shear displacement. This work provides a fundamental understanding of the mechanics of the microtransfer printing process as well as guidance for designing successful microtransfer printing processes.