Systems and methods for controlling release of transferable semiconductor structures

• US 10,347,535 B2
• Filed: 03/02/2018
• Issued: 07/09/2019
• Est. Priority Date: 06/18/2014
• Status: Active Grant

• Current Assignee: X Display Company Technology Limited (Sensinnovat BVBA)
• Original Assignee: X-Celeprint Limited
• Inventors: Bower, Christopher, Meitl, Matthew
• Primary Examiner(s): Toledo, Fernando L
• Assistant Examiner(s): Newton, Valerie N
• Application Number:
  US15/910,809
• Publication Number:
  US 20180204772A1
• Time in Patent Office: 494 Days
• CPC Class Codes: B81C 99/008 separating the processed structure from a mother substrate
• CPC Class Codes: H01L 21/561 Batch processing
• CPC Class Codes: H01L 21/568 Temporary substrate used as encapsulation process aid H01L21/4832 and H01L21/566 take precedence
• CPC Class Codes: H01L 21/6835 using temporarily an auxiliary support
• CPC Class Codes: H01L 21/6836 Wafer tapes, e.g. grinding or dicing support tapes adhesive tapes in general C09J7/20
• CPC Class Codes: H01L 21/7813 leaving a reusable substrate, e.g. epitaxial lift off
• CPC Class Codes: H01L 2221/68368 used in a transfer process involving at least two transfer steps, i.e. including an intermediate handle substrate
• CPC Class Codes: H01L 24/83 using a layer connector

Abstract

The disclosed technology relates generally to methods and systems for controlling the release of micro devices. Prior to transferring micro devices to a destination substrate, a native substrate is formed with micro devices thereon. The micro devices can be distributed over the native substrate and spatially separated from each other by an anchor structure. The anchors are physically connected/secured to the native substrate. Tethers physically secure each micro device to one or more anchors, thereby suspending the micro device above the native substrate. In certain embodiments, single tether designs are used to control the relaxation of built-in stress in releasable structures on a substrate, such as Si (1 1 1). Single tether designs offer, among other things, the added benefit of easier break upon retrieval from native substrate in micro assembly processes. In certain embodiments, narrow tether designs are used to avoid pinning of the undercut etch front.

Claims

1. A method of fabricating a plurality of transferable micro objects, comprising:

forming a sacrificial layer comprising sacrificial material on a process side of a source substrate;

forming a plurality of releasable micro objects at least in part on the sacrificial layer, so that the sacrificial material is disposed between the releasable micro objects and the source substrate;

applying a polymer layer over the plurality of releasable micro objects and at least a portion of the source substrate, wherein the polymer layer encapsulates the plurality of releasable micro objects;

treating the polymer layer to form;

(i) a plurality of anchor structures on the source substrate for the plurality of releasable micro objects,

(ii) at least one tether between each releasable micro object and a pre-determined anchor structure of the plurality of anchor structures, and

(iii) for each of the releasable micro objects, a port of ingress in the polymer layer to a portion of the sacrificial layer underneath a respective releasable micro object; and

removing at least a portion of the sacrificial layer between the plurality of releasable micro objects and the source substrate, to at least partially release the releasable micro objects from the source substrate.

2. The method of claim 1, wherein the one or more anchor structures remains rigidly attached to the substrate when the releasable micro object is moved.

3. The method of claim 1, wherein at least a portion of the sacrificial layer underneath the plurality of releasable micro objects causes each of the plurality of releasable micro objects to move and apply stress on a respective subset of the plurality of tethers.

4. The method of claim 3, wherein the respective subset of the plurality of tethers comprises a single tether.

5. The method of claim 1, comprising transferring the releasable micro objects and removing at least a portion of the polymer layer from the micro objects.

6. The method of claim 5, wherein removing at least a portion of the polymer from the micro objects comprises at least one of dissolution, etching, and ashing of the polymer layer.

7. The method of claim 1, comprising transferring the releasable micro objects by contacting at least a portion of a printing stamp to a corresponding portion of the polymer.

8. A source substrate and plurality of releasable micro objects, comprising:

a source substrate having a process side;

a sacrificial layer comprising sacrificial material on the process side of the source substrate;

a plurality of releasable micro objects formed at least in part on the sacrificial layer, so that the sacrificial material is disposed between the releasable micro objects and the source substrate;

a polymer layer applied over the plurality of releasable micro objects and at least a portion of the source substrate, wherein the polymer layer encapsulates the plurality of releasable micro objects,

wherein the polymer layer has been treated such that the polymer layer comprises;

(i) a plurality of anchor structures on the source substrate for the plurality of releasable micro objects,

(ii) at least one tether between each releasable micro object and a pre-determined anchor structure of the plurality of anchor structures, and

(iii) for each of the releasable micro objects, a port of ingress in the polymer layer to a portion of the sacrificial layer underneath a respective releasable micro object.

9. The source substrate and plurality of releasable micro objects of claim 8, wherein the sacrificial layer underneath the plurality of releasable micro objects defines a gap between the source substrate and each of the plurality of releasable micro objects.

10. The source substrate and plurality of releasable micro objects of claim 9, wherein the one or more anchor structures remains rigidly attached to the source substrate when the releasable micro object is moved.

11. The source substrate and plurality of releasable micro objects of claim 8, wherein at least a portion of the sacrificial layer underneath the plurality of releasable micro objects causes each of the plurality of releasable micro objects to move and apply stress on a respective subset of the plurality of tethers.

12. The source substrate and plurality of releasable micro objects of claim 11, wherein the respective subset of the plurality of tethers comprises a single tether.

13. The source substrate and plurality of releasable micro objects of claim 8, wherein the at least one tether has a narrow shape with a width of 10 μ

m to 40 μ

m, thereby inhibiting the formation of locally-concave or internal corners.

14. The source substrate and plurality of releasable micro objects of claim 8, wherein each tether of the plurality of tethers comprises one or more notches, the notch providing a point of fracture for a releasable micro object when the releasable micro object is moved.

15. The source substrate and plurality of releasable micro objects of claim 8, wherein the source substrate is a material selected from the group consisting of Silicon (1 1 1), silicon, indium phosphide, gallium arsenide, and sapphire.

16. The source substrate and plurality of releasable micro objects of claim 8, wherein the each of the plurality of tethers has an aspect ratio of less than 1.732.

17. The source substrate and plurality of releasable micro objects of claim 8, wherein the tether is sized and shaped to break when a corresponding micro object is contacted by an elastomer stamp for micro transfer printing from the source substrate to a target substrate, different from the source substrate.

18. The source substrate and plurality of releasable micro objects of claim 8, wherein the sacrificial material is a portion of the source substrate or wherein the sacrificial material comprises a material selected from the group consisting of Silicon (1 1 1), InAlP, InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb, InSb, InGaAlSbAs, InAlSb, and InGaP.

19. The source substrate and plurality of releasable micro objects of claim 8, wherein the anchor structure forms a continuous structure, spanning more than one releasable micro object of the plurality of releasable micro objects in at least one dimension or wherein each of the plurality of anchors are characterized by locally concave or internal corners and each of the plurality of releasable micro objects is locally characterized by convex or external corners.

20. The source substrate and plurality of releasable micro objects of claim 8, wherein each of the tethers has an aspect ratio of greater than 1.732.

21. A source substrate and plurality of releasable micro objects, comprising:

a source substrate having a process side;

a sacrificial layer comprising sacrificial material on the process side of the source substrate;

a plurality of releasable micro objects formed at least in part on the sacrificial layer;

a polymer layer applied over the plurality of releasable micro objects and at least a portion of the source substrate, wherein the polymer layer encapsulates the plurality of releasable micro objects,

wherein the polymer layer has been treated such that the polymer layer comprises;

(i) a plurality of anchor structures on the source substrate for the plurality of releasable micro objects,

(ii) at least one tether between each releasable micro object and a pre-determined anchor structure of the plurality of anchor structures, and

(iii) for each of the releasable micro objects, a port of ingress in the polymer layer to a portion of the sacrificial layer underneath a respective releasable micro object,

wherein the sacrificial layer has an anisotropic crystal structure.