Adaptive cavity thickness control for micromachined ultrasonic transducer devices

1. An ultrasonic transducer device, comprising:

a patterned film stack disposed on first regions of a substrate, the patterned film stack comprising a metal electrode layer and a bottom cavity layer formed on the metal electrode layer;

a planarized insulation layer disposed on second regions of the substrate layer;

a cavity formed in a membrane support layer and a CMP stop layer, the CMP stop layer comprising a top layer of the patterned film stack and the membrane support layer formed over the patterned film stack and the planarized insulation layer; and

a membrane bonded to the membrane support layer, wherein the CMP stop layer underlies portions of the membrane support layer but not the cavity.

2. The ultrasonic transducer device of claim 1 , wherein the CMP stop layer comprises a dielectric material.

3. The ultrasonic transducer device of claim 2 , wherein the CMP stop layer comprises SiN.

4. The ultrasonic transducer device of claim 1 , wherein the metal electrode layer comprises titanium (Ti).

5. The ultrasonic transducer device of claim 4 , wherein the metal electrode layer has a thickness of about 100 nm to about 300 nm.

6. The ultrasonic transducer device of claim 1 , wherein the insulation layer comprises SiO 2 .

7. The ultrasonic transducer device of claim 1 , wherein the bottom cavity layer comprises a chemical vapor deposition (CVD) SiO 2 layer and an atomic layer deposition (ALD) Al 2 O 3 layer formed on the SiO 2 layer.

8. The ultrasonic transducer device of claim 7 , wherein the CVD SiO 2 layer has a thickness of about 10 nm to about 30 nm and the ALD Al 2 O 3 layer has a thickness of about 20 nm to about 40 nm.

9. The ultrasonic transducer device of claim 1 , wherein the membrane support layer comprises SiO 2 and the membrane comprises doped silicon.

10. The ultrasonic transducer device of claim 1 , wherein the membrane support layer has a thickness of about 100 nm to about 300 nm, and the membrane has a thickness of about 2 microns (μm) to about 10 μm.

11. An ultrasonic transducer device comprising:

a substrate;

a film stack formed over the substrate and having a metal electrode layer and a chemical mechanical polishing (CMP) stop layer formed over the metal electrode layer; and

a membrane support layer formed over the film stack; wherein

the membrane support layer has a thickness dependent upon a measured thickness of the CMP stop layer, such that a combined thickness of the CMP stop layer and the membrane support layer corresponds to a particular transducer cavity depth.

12. The ultrasonic transducer device of claim 11 , wherein the CMP stop layer comprises a dielectric material.

13. The ultrasonic transducer device of claim 12 , wherein the CMP stop layer comprises SiN.

14. The ultrasonic transducer device of claim 11 , wherein the metal electrode layer comprises titanium (Ti).

15. The ultrasonic transducer device of claim 14 , wherein the metal electrode layer has a thickness of about 100 nm to about 300 nm.

16. The ultrasonic transducer device of claim 11 , wherein the film stack further comprises a bottom cavity layer disposed between the metal electrode layer and the CMP stop layer.

17. The ultrasonic transducer device of claim 16 , wherein the bottom cavity layer comprises a chemical vapor deposition (CVD) SiO2 layer and an atomic layer deposition (ALD) Al 2 O 3 layer formed on the SiO2 layer.

18. The ultrasonic transducer device of claim 17 , wherein the CVD SiO 2 layer has a thickness of about 10 nm to about 30 nm and the ALD Al 2 O 3 layer has a thickness of about 20 nm to about 40 nm.

19. The ultrasonic transducer device of claim 11 , wherein the membrane support layer comprises SiO 2 and the membrane comprises doped silicon.

20. The ultrasonic transducer device of claim 19 , wherein the membrane support layer has a thickness of about 100 nm to about 300 nm, and the membrane has a thickness of about 2 microns (μm) to about 10 μm.