Systems and methods for controlling release of transferable semiconductor structures
View Patent ↗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 0 0). 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.
1. An array of micro devices, the array comprising:
a source substrate comprising silicon (1 0 0) having a process side;
a sacrificial layer comprising silicon (1 0 0) sacrificial material having an anisotropic crystal structure on the process side of the source substrate;
a plurality of releasable micro objects formed at least in part on the sacrificial layer;
a plurality of anchor structures located on the process side of the source substrate, wherein the anchor structures remain rigidly attached to the source substrate in the absence of the sacrificial material; and
a plurality of tethers, wherein each tether of the plurality of tethers laterally connects a releasable micro object of the plurality of releasable micro objects to a portion of one of the anchor structures, each releasable micro object is connected to an anchor by a single tether, and the tethers are shaped to fracture in response to pressure.
2. 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.
3. The array of claim 1 , wherein the sacrificial material is a portion of the source substrate.
4. The array of claim 1 , 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.
5. 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.
6. 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.
7. The array of claim 1 , wherein the portion of the tether in contact with the anchor does not overlap the portion of the tether in contact with the releasable micro object in a direction parallel to the edge of the releasable micro object or the anchor to which the tether is attached.
8. The array of claim 1 , wherein the tether has opposing sides that are not attached to the anchor or the releasable micro object, wherein the opposing sides overlap in at least one of the x-direction and the y-direction.
9. The array of claim 1 , wherein the releasable micro object is separated from the anchor in the x-direction by a separation distance x, the tether is attached to the anchor or the releasable micro object at an acute angle theta, and the distance between the first edge and second edges at which the tether is attached to the anchor or releasable micro object is y, and y is less than or equal to x*tan(theta).
10. The array of claim 1 , wherein:
a first pair of first and second tethers are offset the y-direction and do not overlap in the offset direction and a second pair of first and second tethers are offset in the x-direction perpendicular to the edge of the anchor or releasable micro object and do not overlap in the offset direction; or
a pair of first and second tethers are offset in the y-direction and do not overlap in the offset direction and are offset in the x-direction and do not overlap in the offset direction.
11. An array of micro devices, the array comprising:
a source substrate having a process side;
a sacrificial layer comprising silicon (1 0 0) 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 plurality of anchor structures located on the process side of the source substrate, wherein the anchor structures remain rigidly attached to the source substrate in the absence of the sacrificial material; and
a plurality of tethers, wherein each tether of the plurality of tethers laterally connects a releasable micro object of the plurality of releasable micro objects to a portion of one of the anchor structures, the tethers are shaped to fracture in response to pressure, and 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, so that in the absence of the sacrificial material the releasable micro objects are capable of moving with respect to the anchor structures and the tethers deform when mechanically stressed.
12. The array of claim 11 , wherein the sacrificial material is a portion of the source substrate.
13. The array of claim 11 , wherein it is not possible to draw a rectangle covered by the anchors, tethers, and micro object with an edge parallel to the <0 1 1> directions that has an edge passing through the micro object.
14. The array of claim 11 , wherein any rectangle covered by the anchors, tethers, and printable structure with edges parallel to the <0 1 1> directions does not have an edge passing through the releasable micro object.
15. The array of claim 11 , wherein it is not possible to draw a rectangle covered by the anchors, tethers, and printable micro object with edges parallel to the <0 1 1> directions that has an edge passing through releasable micro object.
16. The array of claim 11 , wherein the tether is disconnected from the substrate surface in the area of a convex hull drawn around the exposed surface of the sacrificial layer.