I. Bhattacharyya, J. Tseng, D. Acquard, R. Manley, P. Mazumder
Keywords: ultrathin glass, flexible substrates, temporary bonding, debonding, aqueous solution, high throughput manufacturing
Summary:Recent demand in flexible display for smart phone, tablet and television market has led manufacturers to address challenges in handling flexible substrates in innovative ways. For that, temporary bonding methods has been developed by which a flexible substrate can undergo all necessary process steps for manufacturing microelectronics while it is reliably bonded to a rigid carrier. The rigid carrier provides structural support by preventing bowing and bending but doesn’t chemically bond to the flexible substrate. Thus, the flexible substrate with functional devices can be debonded from the carrier afterwards. Several approaches for temporary bonding-debonding have been investigated over the past few years including adhesive films, plasma-polymerized fluorocarbon layer and laser-releasable polymers etc. The interlayer between flexible substrate and rigid carrier is generally chosen based on the peak processing temperature requirement for the microelectronics device. In this work, we present an aqueous surface functionalization process using surfactant molecules which provides high enough adhesion between flexible glass (WillowTM) and a rigid glass carrier via secondary forces while allows mechanical debonding even after heating to 400C (relevant for thin film transistor processing). Through optimization of processing and surface chemistry we achieve following key attributes – (i) control of hydrophilicity/hydrophobicity of glass through surface density of surfactants (ii) self-bonding of glass pairs via strong secondary forces leading to spontaneous bond-wave propagation (ii) mechanical debonding after thermal treatment that does not require expensive laser lift-off and (iii) minimal defect formation related to potential degradation of surface treatment molecules. Additionally, we show feasibility of high-throughput manufacturing-friendly processability of this technology.