Separation Of Thin Films From Transparent Substrates By Selective Optical

Tech ID: 16901 / UC Case 2000-026-0

Abstract

Compound semiconductors, such as III-V semiconductors, have interesting properties that make them very useful for high-speed and high temperature electronics and for optical emitters and detectors in particular optical wavelength bands; e.g., GaN in the blue region. Some of these semiconductor materials, GaN in particular, are difficult to grow as bulk material and for many applications must be grown as a thin film on a substrate such as sapphire, removed and reattached to another substrate. The removal step is currently accomplished by means such as etching away a sacrificial layer or physically abrading away the substrate, or by high temperature/high energy laser irradiation. All these techniques have significant drawbacks, foremost of which is the tendency to damage the film.

Researchers at the University of California at Berkeley have developed a process to transfer a crystalline film from a growth substrate to an acceptor substrate. The film of one composition is grown on a substrate of another composition having an absorption edge at a shorter wavelength than that of the grown film, then the film side is bonded to an acceptor substrate. The side of the structure having the growth substrate is irradiated with a short pulse optical beam of selected wavelength. The result of the irradiation is that the interfacial bond between the film and the growth substrate is weakened but the irradiated area does not separate. A separation step is performed after completion of the laser irradiation. Thus, this two-step separation process permits the separation of films from substrates that are larger than the area of the optical beam. The transfer may also be done by irradiating a sacrificial layer grown between the growth substrate and the thin film.

Researchers have demonstrated the process for various III-V semiconductors and perovskite oxides, including GaN and Pb(Zr,Ti)O3 ("PZT"). It has been used to successfully transfer thin films and device heterostructures, including light-emitting diodes, from donor to acceptor substrates and to produce free standing substrates by removal of a thick film without carrying out the bonding step.

Patent Status

Country	Type	Number	Dated	Case
United States Of America	Issued Patent	6,420,242	07/16/2002	2000-026
United States Of America	Issued Patent	6,335,263	01/01/2002	2000-026
United States Of America	Issued Patent	6,071,795	06/06/2000	2000-026