Process for filling etched holes
A process for filling one or more etched holes defined in a frontside surface of a wafer substrate. The process includes the steps of: (i) depositing a layer of a thermoplastic first polymer onto the frontside surface and into each hole; (ii) reflowing the first polymer; (iii) exposing the wafer substrate to a controlled oxidative plasma; (iv) optionally repeating steps (i) to (iii); (v) depositing a layer of a photoimageable second polymer; (vi) selectively removing the second polymer from regions outside a periphery of the holes using exposure and development; and (vii) planarizing the frontside surface to provide holes filled with a plug comprising the first and second polymers, which are different than each other. Each plug has a respective upper surface coplanar with the frontside surface.
1. A process for filling one or more etched holes defined in a surface of a wafer substrate, said process comprising the steps of:
(i) depositing a layer of a thermoplastic first polymer onto the surface and into each hole;
(ii) reflowing the first polymer;
(iii) exposing the wafer substrate to a controlled oxidative plasma so as to reveal the surface;
(iv) optionally repeating steps (i) to (iii);
(v) depositing a layer of a photoimageable second polymer so as to overfill each hole with said second polymer;
(vi) selectively removing the second polymer from regions outside a periphery of the holes to provide overfilled holes, the selective removing comprising exposure and development of the second polymer; and
(vii) planarizing the surface to provide one or more holes filled with a plug comprising the first and second polymers, each plug having a respective upper surface coplanar with the surface of the wafer substrate, wherein the first and second polymers are different.
2. The process of claim 1 , wherein each hole has a depth of at least 10 microns.
3. The process of claim 1 , wherein each hole has an aspect ratio of >1:1.
4. The process of claim 1 , wherein the first polymer is less viscous than the second polymer.
5. The process of claim 1 , wherein, in step (iii), the controlled oxidative plasma exposure is timed so as to remove a predetermined thickness of the first polymer.
6. The process of claim 1 , wherein, in step (vii), the wafer is planarized by a chemical-mechanical planarization (CMP) process.
7. The process of claim 1 , wherein an extent of overfill of the hole immediately prior to step (vii) is less than 12 microns.
8. The process of claim 1 further comprising additional MEMS fabrication steps.
9. The process of claim 8 , wherein the additional MEMS fabrication steps construct inkjet nozzle devices on the planarized surface of the wafer substrate.
10. The process of claim 9 , wherein each nozzle device comprises a nozzle chamber in fluid communication with at least one hole.
11. The process of claim 10 , wherein a respective inlet for each nozzle chamber is defined by one of said holes.
12. The process of claim 11 , further comprising at least one of: wafer thinning and backside etching of ink supply channels.
13. The process of claim 12 , wherein each ink supply channel meets with one or more filled holes.
14. The process of claim 13 , wherein each ink supply channel is relatively wider said one or more holes.
15. The process of claim 14 , further comprising oxidative removal of the first and second polymers from the holes.