Separation of thin films from transparent substrates by selective optical processing

• US 6,420,242 B1
• Filed: 01/06/2000
• Issued: 07/16/2002
• Est. Priority Date: 01/23/1998
• Status: Expired due to Term

• Current Assignee: Formosa Epitaxy Incorporated (Epistar Corporation)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Sands, Timothy D., Wong, William S., Cheung, Nathan W.
• Primary Examiner(s): MULPURI, SAVITRI
• Application Number:
  US09/478,915
• Time in Patent Office: 922 Days
• Field of Search: 438/463, 438/464, 438/459, 438/33, 438/470, 438/977, 438/798
• US Class Current: 438/458
• CPC Class Codes: H01L 21/2007 Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer H01L21/2011 takes precedence; bonding of semiconductor wafers to semiconductor wafers for junction formation H01L21/187
• CPC Class Codes: H01L 2221/68363 used in a transfer process involving transfer directly from an origin substrate to a target substrate without use of an intermediate handle substrate
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48145 the bodies being stacked
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate

Abstract

A method of separating a thin film of GaN epitaxially grown on a sapphire substrate. The thin film is bonded to an acceptor substrate, and the sapphire substrate is laser irradiated with a scanned beam at a wavelength at which sapphire is transparent but the GaN is strongly absorbing, e.g., 248 nm. After the laser irradiation, the sample is heated above the melting point of gallium, i.e., above 30° C., and the acceptor substrate and attached GaN thin film are removed from the sapphire growth substrate. If the acceptor substrate is flexible, the GaN thin film can be scribed along cleavage planes of the GaN, and, when the flexible substrate is bent, the GaN film cleaves on those planes. Thereby, GaN lasers and other electronic and opto-electronic devices can be formed.

Claims

1. A method of separating a thin film from a growth substrate, comprising the steps of:

providing a crystallographically oriented growth substrate with a growth surface and an irradiation surface;

growing a thin film on said growth surface of said crystallographically oriented growth substrate;

attaching an acceptor substrate to said thin film;

irradiating said irradiation surface of said crystallographically oriented growth substrate with light of a wavelength that is substantially more strongly absorbed in said thin film than in said crystallographically oriented growth substrate until an interfacial layer attaching said thin film and said crystallographically oriented growth substrate is formed;

after completion of said irradiating step, severing said interfacial layer to separate said thin film from said crystallographically oriented growth substrate.

2. The method of claim 1 wherein said severing step includes the step of liquefying said interfacial layer.

3. The method of claim 1 wherein said severing step includes the step of dissolving said interfacial layer with ultrasonic energy.

4. The method of claim 1 wherein said severing step includes the step of etching said interfacial layer.

5. The method of claim 1 wherein said severing step includes the step of heating said interfacial layer.

6. The method of claim 1 wherein said attaching step includes the step of applying a glue layer between said thin film and said acceptor substrate.

7. The method of claim 1 wherein said attaching step includes the step of applying a metal layer between said thin film and said acceptor substrate.

8. The method of claim 1 wherein said attaching step includes the step of fusing said thin film to said acceptor substrate.

9. The method of claim 1 further comprising the step of isolating said thin film from said acceptor substrate to form a free-standing thin film.