Laser Separation of Dissimilar Substrates Using Water Washable Materials

Laser separation of substrates has been in practice for many years in OLED manufacturing and is recently reported for semiconductors [1-2]. Using an adhesive and/or release material, the device substrate is bonded to a transparent glass carrier, processed, and separated by exposing the material with a low-temperature laser process. Successful cleaning is dependent on minimal interaction of the laser with the bulk adhesive with low temperature generation. Laser dynamics on polymers has been reported, suggesting bulk material preservation is preferred with laser-induced photochemical (bond breakage) over photothermal (heating and evaporation) [3]. Our work applies similar principles by choosing wavelengths matched to the material and aligning the laser process to achieve rapid separation while preserving water rinsing. Laser pulse-controlled modulation down to pico- and femto-seconds allows processing of sensitive materials and delicate substrates, maximizing electron interaction (excitation) without thermal buildup in the surrounding material. This “cold processing” enables laser lift-off (LLO) of sensitive OLED products [4]. Semiconductor substrates can vary from inorganic (i.e. Si wafers) to organic (e.g. FR4), exist thin at <;100μ (microns), and some packages may include large topography exceeding several hundred microns (e.g. solder bumps). Most temporary bonding processes separate the carrier leaving the device wafer affixed on tape for rotary saw dicing or other singulation method. Cleaning is desired with green products, preferably water, aqueous-based, or tape-friendly products. Thermal resistant and washable materials are desired. Phenyl-containing chemistries exhibit thermal resistance ≥300°C to allow high temperature processing while certain functional groups may be added to allow variable water resistance to support electroplating, etching, and simple aqueous-based rinsing [5]. These same water washable materials are ideal for plasma resistant processing and conventional laser patterning. Other topics as substrate variability, UV-curable planarizing solutions, and laser separation throughput will be presented.