Systems and methods for controlling release of transferable semiconductor structures

• US 9,947,584 B2
• Filed: 02/10/2017
• Issued: 04/17/2018
• 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:
  US15/430,101
• Publication Number:
  US 20170154819A1
• Time in Patent Office: 431 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. An array of micro devices, the array comprising:

a silicon (111) source substrate having a plurality of anchor portions in the silicon (111) source substrate that are laterally separated by etched portions in the silicon (111) source substrate;

a plurality of releasable micro objects, each located over an etched portion; and

a plurality of tethers, wherein each tether of the plurality of tethers connects a releasable micro object to an anchor portion, wherein the anchor portion to which the tether connects laterally separates adjacent releasable micro objects,

wherein the releasable micro objects are formed at least in part on the source substrate.

2. The array of claim 1, wherein each releasable micro object is connected to an anchor portion by a single tether.

3. The array of claim 1, wherein the source substrate is a growth substrate made of a substrate material on or over which the micro objects are formed and the tethers are made of a tether material.

4. The array of claim 3, wherein either the tether material is the same material as the substrate material or the tether material is not disposed between the releasable micro objects and the source substrate.

5. The array of claim 1, wherein the tethers are shaped to fracture in response to pressure.

6. The array of claim 1, wherein each releasable micro object is connected to an anchor portion by a single tether.

7. The array of claim 1, wherein each of the plurality of tethers 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.

8. The array of claim 1, 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.

9. The array of claim 1, wherein each of the plurality of tethers is a tether with a narrow shape and a width of 1 μ

m to 5 μ

m, 5 μ

m to 10 μ

m, 10 μ

m to 15 μ

m, 15 μ

m to 20 μ

m, or 20 μ

m to 40 μ

m.

10. The array of claim 1, wherein each of the tethers comprises one or more notches that provide a point of fracture when a respective releasable micro object is moved with respect to the anchor structures.

11. The array of claim 1, wherein each of the tethers has an aspect ratio of greater than 1.732.

12. The array of claim 1, wherein the releasable micro objects include silicon, silicon (1 1 1), silicon (1 0 0), or a compound semiconductor.

13. A method of making thin and low-cost wafer-packaged micro-scale devices suitable for micro transfer printing using a (111) silicon system, the method comprising:

providing a plurality of micro-scale devices;

assembling the micro-scale devices onto a carrier wafer using micro-assembly techniques, wherein the carrier wafer comprises silicon (111) and a first dielectric layer;

embedding the assembled micro-scale devices within a second layer of dielectric;

patterning the first and second dielectric layers to define a perimeter of each of the micro-scale devices with anchors and tethers that preserve the spatial configuration of the micro-scale devices with respect to the carrier wafer when the micro-scale devices are moved with respect to the carrier wafer, thereby providing a wafer-level thin wafer package having micro-scale devices suitable for micro transfer printing to other substrates.

14. The method claim 13, comprising:

forming package-in-package devices of the micro-scale devices using a wafer-fed die-attach tool.

15. The method of claim 13, comprising:

forming wafer-level-packages from the micro-scale devices using a wafer-fed die-attach tool or a wafer-fed micro-transfer printer.

16. A method of fabricating a printable component array, the method comprising:

providing a source substrate having a sacrificial layer comprising sacrificial material;

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

forming an anchor structure on the source substrate that remains rigidly attached to the source substrate in the absence of the sacrificial material;

forming a plurality of tethers, wherein each tether of the plurality of tethers connects a releasable micro object of the plurality of releasable micro objects to one of the anchor structures, each tether of the plurality of tethers is located on an off-center, anchor-facing edge of the respective releasable micro object of the plurality of releasable micro objects, and each tether is shaped to fracture in response to movement of the releasable micro object, so that in the absence of the sacrificial material;

the releasable micro objects move with respect to the anchor structures;

the tethers deform and are mechanically stressed; and

each tether of the plurality of tethers remains rigidly attached to both a respective anchor and a respective releasable micro object of the plurality of micro objects, thereby preserving the spatial configuration of the plurality of releasable micro objects with respect to the source substrate; and

removing at least a portion of the sacrificial material underneath the plurality of releasable micro objects so that the releasable micro objects move with respect to the anchor structures and the tethers deform and are mechanically stressed, wherein;

the portion of the anchor to which the tether connects laterally separates adjacent releasable micro objects,

the source substrate is a growth substrate made of a substrate material on or over which the micro objects are formed and the tethers are made of a tether material,

either the tether material is the same material as the substrate material or the tether material is not disposed between the releasable micro objects and the source substrate, and

the tethers are shaped to fracture in response to pressure.

17. The method of claim 16, wherein the removal process progresses rapidly under the plurality of releasable micro objects relative to the rate at which the anchor structure is released.

18. The method of claim 16, wherein each tether of the plurality of tethers 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.

19. The method of claim 16, wherein the sacrificial layer has an anisotropic crystal structure for which the removal process progresses faster in some directions and slower in other directions.

20. The method of claim 16, 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.

21. The method of claim 16, wherein the removal process reaches completion at areas near a given tether.

22. The method of claim 16, wherein the source substrate is a material selected from the group consisting of silicon (1 1 1), silicon, indium phosphide, gallium arsenide, and sapphire.

23. The method of claim 16, wherein the source substrate is a silicon (1 1 1) substrate and each releasable micro object is connected to an anchor by a single tether.