Biosensing well array with protective layer

1. A method of making a BioFET device, comprising:

forming a plurality of FETs on a semiconductor substrate, wherein the plurality of FETs each includes a gate structure formed on a first surface of the semiconductor substrate and a channel region;

forming a gate contact on the gate structure in each of the plurality of FETs;

forming one or more metal interconnect layers over the plurality of FETs;

forming a plurality of top metal stacks having a protective layer on sidewalls of the top metal stacks;

forming a passivation layer over the plurality of top metal stacks;

etching microwells in the passivation layer to expose a subset of the plurality of top metal stacks, wherein a bottom surface area of the microwells is larger than respective top surfaces of respective ones of the subset of the plurality of top metal stacks;

depositing a sensing layer in the microwells and over a field portion between the microwells, wherein the sensing layer fills any openings between the subset of the plurality of top metal stacks and the passivation layer; and

removing at least the field portion of the sensing layer.

2. The method of claim 1 , further comprising:

forming respective openings over respective ones of a second subset of the plurality of top metal stacks;

removing a protective layer and an antireflective layer in the second subset of the plurality of top metal stacks; and

forming respective contacts between the top metal in the second subset of the plurality of top metal stacks and respective package terminals.

3. The method of claim 1 , wherein the forming a plurality of top metal stacks comprises:

depositing an underlayer on a planarized semiconductor substrate surface;

depositing a top metal on the underlayer;

depositing an antireflective layer on the top metal;

depositing and patterning a first photoresist layer over the antireflective layer;

etching a first pattern through the underlayer to form separate stacks of the underlayer, top metal, and antireflective layer;

depositing a protective layer covering sidewalls of the top metal; and

separating the protective layer according to the pattern;

wherein each top metal stacks is a stack comprising the underlayer, the top metal, the antireflective layer, and a protective layer over the antireflective layer and peripherally surrounding the top metal.

4. The method of claim 3 , wherein separating the protective layer comprises

anisotropically plasma etching the protective layer to remove a bottom portion of the protective layer, said bottom portion disposed between the top metal stacks.

5. The method of claim 3 , wherein separating the protective layer comprises

depositing a second photoresist layer;

patterning the second photoresist layer to expose a portion of the protective layer between the top metal stacks;

removing the exposed portions of the protective layer; and

removing the second photoresist.

6. The method of claim 5 , wherein the patterning the second photoresist layer comprises exposing the second photoresist to light generated from a photomask used to pattern the first photoresist layer at an intensity level different from an intensity level to pattern the first photoresist layer.

7. The method of claim 3 , wherein the depositing a protective layer comprises sputtering a titanium nitride target.

8. The method of claim 3 , wherein the depositing a protective layer comprises depositing a titanium nitride using atomic layer deposition.

9. The method of claim 1 , wherein the depositing a sensing layer comprises depositing a high-k dielectric layer.

10. The method of claim 1 , wherein the protective layer is titanium nitride.

11. A method of making a BioFET device, comprising:

forming on a planar surface of a substrate a top metal layer;

patterning the top metal layer to form a top metal stack having a top surface and a sidewall;

forming a protective layer having a protective layer top portion extending along the top surface of the top metal stack and having a protective layer sidewall portion extending along the sidewall of the top metal stack;

depositing a passivation layer on the protective layer;

patterning the passivation layer to form an opening, wherein the opening has a bottom formed by the protective layer top portion and the opening has a passivation layer sidewall; and

forming a sensing layer on the protective layer top portion and the protective layer sidewall portion and on the passivation layer sidewall.

12. The method of claim 11 , wherein the step of forming on a planar surface of a substrate a top metal layer comprises:

depositing on the planar surface a conductive underlayer; and

depositing on the conductive underlayer a conductive layer.

13. The method of claim 11 , wherein the step of forming a protective layer comprises:

blanket depositing the protective layer; and

patterning the protective layer using a dry etching process.

14. The method of claim 13 , further comprising patterning the protective layer using a first photomask pattern and further comprising patterning the top metal layer using the first photomask pattern.

15. The method of claim 11 , wherein the step of forming a sensing layer on the protective layer top portion and the protective layer sidewall portion and on the passivation layer sidewall comprises:

blanket depositing the protective layer on the protective layer top portion, the protective layer sidewall portion, the passivation sidewall, and atop the passivation layer; and

removing the sensing layer from atop the passivation layer.

16. A method of making a BioFET device, comprising:

forming a transistor on a semiconductor substrate;

forming at least one intermediate metallization layer above and electrically contacting the transistor;

forming a top metal stack above and electrically contacting the at least one intermediate metallization layer, wherein the top metal stack includes a conductive feature having a top surface and sidewalls;

forming over the top surface and sidewalls a patterned protective layer; and

forming on the patterned protective layer a sensing layer, wherein the sensing layer extends along the top surface and along the sidewalls.

17. The method of claim 16 , wherein the step of forming top metal stack includes:

blanket depositing an underlayer, a conductive layer, and an antireflective layer, and patterning the underlayer, the conductive layer, and the antireflective layer using a photomask pattern.

18. The method of claim 17 , further comprising forming a microwell above the top metal stack by:

depositing a passivation layer on the top metal stack; and

patterning the passivation layer to expose a top surface of the patterned protective layer.

19. The method of claim 17 , wherein the step of forming over the top surface and sidewalls a patterned protective layer includes:

blanket depositing a protective layer; and

patterning the protective layer using the photomask pattern.

20. The method of claim 16 , further comprising:

forming a second top metal stack above and electrically contacting the at least one intermediate metallization layer, wherein the top metal stack includes a conductive feature having a top surface and sidewalls;

removing the patterned protective layer from the top surface of the second top metal stack; and electrically connecting the second top metal stack to a package terminal.