Method for forming a suspended lithium-based membrane semiconductor structure
View Patent ↗In one aspect, a microelectronic device comprises: a suspended lithium-based thin film; and one or more electrodes disposed on the suspended lithium-based thin film, wherein the one or more electrodes comprises one or more fingers, and a width of at least one outer finger of the one or more fingers is smaller than a width of at least one inner finger of the one or more fingers.
1. A method for forming a suspended lithium-based membrane semiconductor structure, the method comprising:
depositing a bonding agent on a surface of a lithium-based carrier substrate;
implanting ions into a surface of a lithium-based donor substrate;
forming, based on implanting, an ion-implanted surface of the lithium-based donor substrate;
bonding the ion-implanted surface of the lithium-based donor substrate to the bonding agent;
removing the lithium-based donor substrate from the ion-implanted surface that is bonded to the bonding agent, with at least a portion of the ion-implanted surface remaining bonded to the bonding agent following removal;
forming, based on removing, a lithium-based membrane on the bonding agent, with the lithium-based membrane comprising the at least a portion of the ion-implanted surface that remains bonded to the bonding agent;
forming one or more electrodes on the lithium-based membrane;
etching at least one release window extending through the lithium-based membrane to the bonding agent; and
removing, using the at least one release window, the bonding agent to suspend a portion of the lithium-based membrane with respect to the lithium-based carrier substrate.
2. The method of claim 1 , wherein the bonding agent comprises one or more of an adhesive agent or an oxide.
3. The method of claim 2 , wherein the adhesive agent comprises one or more of benzocyclobutene or polyimide.
4. The method of claim 1 , wherein the lithium-based carrier substrate and the lithium-based donor substrate each comprise one or more of lithium niobate or lithium tantalate.
5. The method of claim 1 , wherein a thickness of the ion-implanted surface of the lithium-based donor substrate is based on an amount of ions that are implanted and is further based on an energy of the ions that are implanted.
6. The method of claim 5 , wherein the average thickness of the ion-implanted surface of the lithium-based donor substrate is between 100 nm and 30 nm.
7. The method of claim 1 , further comprising:
prior to bonding the ion-implanted surface of the lithium-based donor substrate to the bonding agent, forming one or more additional electrodes on the ion-implanted surface of the lithium-based donor substrate.
8. The method of claim 1 , wherein removing the lithium-based donor substrate from the ion-implanted surface that is bonded to the bonding agent comprises:
heating the lithium-based donor substrate at a temperature based on an amount and energy of the ions implanted on the lithium-based donor substrate; and
removing, based on heating, the lithium-based donor substrate from the ion-implanted surface that is bonded to the bonding agent.
9. The method of claim 8 , wherein the temperature is an average temperature between 200 degrees Celsius and 350 degrees Celsius.
10. The method of claim 8 , wherein the lithium-based donor substrate is heated between two hours and twelve hours.
11. The method of claim 1 , wherein the lithium-based donor substrate comprises an X-cut substrate.
12. The method of claim 1 , further comprising:
after removal of the lithium-based donor substrate, polishing an exposed surface of the lithium-based membrane to reduce roughness of the exposed surface of the lithium-based membrane.
13. The method of claim 12 , wherein the roughness of the exposed surface of the lithium-based membrane is less than 5 nm.
14. The method of claim 1 , wherein forming the one or more electrodes on the lithium-based membrane comprises:
forming the one or more electrodes using one or more of physical sputtering, electron-beam evaporation, and thermal evaporation.
15. The method of claim 1 , wherein the one or more electrodes comprise one or more of aluminum, gold, platinum, molybdenum, or copper.
16. The method of claim 1 , wherein each of the one or more electrodes comprise one or more fingers.
17. The method of claim 16 , wherein at least one of the one or more fingers has an average thickness between 5 nm and 150 nm.
18. The method of claim 16 , wherein the one or more fingers of the one or more electrodes comprise a plurality of inter-digital fingers.
19. The method of claim 18 , wherein a width of at least one outer inter-digital finger of the plurality of inter-digital fingers is smaller than a width of at least one inner inter-digital finger of the plurality of inter-digital fingers.
20. The method of claim 1 , wherein etching the at least one release window extending through the lithium-based membrane to the bonding agent comprises:
depositing an etch mask layer over the lithium-based membrane and the one or more electrodes;
depositing a photo-resist layer on the etch mask layer;
etching a pattern in the photo-resist layer;
transferring the pattern of the photo-resist layer to the etch mask layer; and
stripping away the photo-resist layer.
21. The method of claim 20 , wherein the etch mask layer comprises one or more of an oxide or a nitride.
22. The method of claim 20 , wherein depositing an etch mask layer over the lithium-based membrane and the one or more electrodes comprises:
depositing an etch mask layer over the lithium-based membrane and the one or more electrodes using plasma-enhanced chemical vapor deposition or physical sputtering.
23. The method of claim 20 , wherein transferring the pattern of the photo-resist layer to the etch mask layer comprises:
transferring the pattern of the photo-resist layer to the etch mask layer using reactive ion etching with a fluorine-based etching recipe.
24. The method of claim 20 , further comprising:
after removing the bonding agent, removing the etch mask layer.
25. The method of claim 24 , wherein removing the etch mask layer comprises:
removing the etch mask layer using reactive ion etching with a fluorine-based etching recipe.
26. The method of claim 1 , wherein etching the at least one release window extending through the lithium-based membrane to the bonding agent comprises:
etching the at least one release window using reactive ion etching or inductively-coupled plasma etching with a chlorine-based solvent.
27. The method of claim 1 , wherein removing the bonding agent comprises:
releasing an etchant in the at least one release window using a liquid chemical etch or a vapor etch.
28. The method of claim 27 , wherein the etchant comprises one or more of a sulfuric acid based etchant or a hydrofluoric acid based etchant.
29. The method of claim 1 , further comprising:
performing drying after removing the bonding agent.
30. The method of claim 29 , wherein performing drying comprises:
performing point drying after removing the bonding agent.
31. A micro-electro-mechanical system (MEMS) comprising a suspended lithium-based membrane semiconductor structure formed according to the method of claim 1 .
32. A moving structure comprising a suspended lithium-based membrane semiconductor structure formed according to the method of claim 1 .