Method of forming a compliant bipolar micro device transfer head with silicon electrodes

1. A method of forming a compliant bipolar transfer head array comprising:

etching a top silicon layer of a silicon-on-insulator stack to form a first array of silicon electrodes electrically connected with a first silicon interconnect, and a second array of silicon electrodes aligned with the first array of silicon electrodes and electrically connected with a second silicon interconnect to form an array of bipolar silicon electrode pairs, each silicon electrode in the first and second arrays of silicon electrodes including an electrode lead and a mesa structure that protrudes above the first and second silicon interconnects;

forming a dielectric layer over the first and second arrays of silicon electrodes; and

etching one or more cavities in the base substrate directly underneath the first and second arrays of silicon electrodes such that each silicon electrode in the first and second arrays of silicon electrodes is deflectable into the one or more cavities.

2. The method of claim 1 , wherein etching one or more cavities in the base substrate comprises reactive ion etching with a fluorinated plasma selected from the group consisting of SF 6 and XeF 2 .

3. The method of claim 1 , wherein etching one or more cavities in the base substrate comprises etching a separate cavity in the base substrate directly underneath each bipolar silicon electrode pair.

4. The method of claim 1 , wherein etching one or more cavities in the base substrate comprises etching a single cavity in the base substrate directly underneath the array of bipolar silicon electrode pairs.

5. The method of claim 4 , further comprising etching the single cavity in the base substrate such that it wraps around an end of one of the first and second silicon interconnects.

6. The method of claim 1 , wherein etching the top silicon layer of the silicon-on-insulator stack exposes a buried oxide layer.

7. The method of claim 6 , further comprising forming a patterned layer over the buried oxide layer and the dielectric layer after forming the dielectric layer over the first and second arrays of silicon electrodes, and etching through the buried oxide layer to expose a portion of the base substrate.

8. The method of claim 7 , further comprising etching the one or more cavities in the base substrate directly underneath the first and second arrays of silicon electrodes using the dielectric layer as an etching mask.

9. The method of claim 6 , wherein forming the dielectric layer comprises thermal oxidation of the first and second arrays of silicon electrodes.

10. The method of claim 6 , further comprising etching an array of joint trenches between the mesa structures of the first and second arrays of silicon electrodes simultaneously with etching the top silicon layer of the silicon-on-insulator stack to form the first and second arrays of silicon electrodes, wherein etching the array of joint trenches exposes the buried oxide layer.

11. The method of claim 10 , further comprising forming the dielectric layer within the array of joint trenches and in direct contact with the buried oxide layer simultaneously with forming the dielectric layer over the first and second arrays of silicon electrodes.

12. The method of claim 11 , wherein forming the dielectric layer comprises thermal oxidation of the first and second arrays of silicon electrodes.

13. The method of claim 12 , further comprising completely filling the array of joint trenches with the dielectric layer to form an array of oxide joints between the first and second arrays of silicon electrodes.

14. The method of claim 6 , further comprising etching a first backside via opening through the base substrate directly underneath the first silicon interconnect, and etching a second backside via opening through the base substrate directly underneath the second silicon interconnect.

15. The method of claim 14 , further comprising, forming a passivation layer within the first and second backside via openings, wherein forming the passivation layer comprises simultaneously thermally oxidizing the first and second arrays of silicon electrodes and the base substrate within the first and second backside via openings.

16. The method of claim 15 , further comprising forming a patterned conductive layer within the first and second via openings to make electrical contact with the first and second silicon interconnects.

17. The method of claim 16 , wherein forming the patterned conductive layer comprises depositing the patterned conductive layer through a shadow mask.

18. The method of claim 7 , further comprising etching through the dielectric layer to expose a first portion of the first silicon interconnect and a second portion of the second silicon interconnect simultaneously with etching through the buried oxide layer to expose the portion of the base substrate.

19. The method of claim 18 , further comprising etching a first topside via opening through the exposed first portion of the first silicon interconnect and the buried oxide layer, etching a second topside via opening through the exposed second portion of the second silicon interconnect and the buried oxide layer, and forming a patterned conductive layer within the first and second topside via openings to make electrical contact with the first and second silicon interconnects.

20. The method of claim 7 , further comprising etching through the dielectric layer to expose each of the mesa structures simultaneously with etching through the buried oxide layer to expose the portion of the base substrate.

21. The method of claim 20 , further comprising forming a patterned second dielectric layer over each of the mesa structures.

22. The method of claim 21 , wherein forming the patterned second dielectric layer comprises blanket depositing the second dielectric layer, and removing a portion of the second dielectric layer.

23. The method of claim 22 , wherein blanket depositing the second dielectric layer comprises atomic layer deposition.

24. The method of claim 7 , further comprising etching through the dielectric layer to expose a first portion of the first silicon interconnect, a second portion of the second silicon interconnect, and each of the mesa structures simultaneously with etching through the buried oxide layer to expose the portion of the base substrate.

25. The method of claim 24 , further comprising etching a first topside via opening through the exposed first portion of the first silicon interconnect and the buried oxide layer, etching a second topside via opening through the exposed second portion of the second silicon interconnect and the buried oxide layer, and forming a patterned conductive layer within the first and second topside via openings to make electrical contact with the first and second silicon interconnects.

26. The method of claim 25 , wherein etching the one or more cavities further comprises using the second dielectric layer formed over each of the mesa structures and the conductive layer formed within the first and second topside via openings as an etching mask.