ADAPTIVE CAVITY THICKNESS CONTROL FOR MICROMACHINED ULTRASONIC TRANSDUCER DEVICES
A method of forming an ultrasonic transducer device includes forming and patterning a film stack over a substrate, the film stack comprising a metal electrode layer and a chemical mechanical polishing (CMP) stop layer formed over the metal electrode layer; forming an insulation layer over the patterned film stack; planarizing the insulation layer to the CMP stop layer; measuring a remaining thickness of the CMP stop layer; and forming a membrane support layer over the patterned film stack, wherein the membrane support layer is formed at thickness dependent upon the measured remaining thickness of the CMP stop layer, such that a combined thickness of the CMP stop layer and the membrane support layer corresponds to a desired transducer cavity depth.
1 - 26 . (canceled)
27 . An ultrasound imaging device wherein:
the ultrasound imaging device includes a plurality of micromachined ultrasonic transducers (MUTs) arranged into an array pattern and wherein at least one of the MUTs comprises:
a patterned film stack disposed on first regions of a substrate, the patterned film stack includes 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 chemical mechanical polishing (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 fil stack and the planarized insulation layer; and
a membrane bonded to the membrane support layer but not the cavity.
28 . The ultrasonic transducer device of claim 27 , wherein the CMP stop layer comprises a dielectric material.
29 . The ultrasonic transducer device of claim 28 , wherein the CMP stop layer comprises SiN.
30 . The ultrasonic transducer device of claim 27 , wherein the metal electrode layer comprises titanium (Ti).
31 . The ultrasonic transducer device of claim 30 , wherein the metal electrode layer has a thickness of about 100 nm to about 300 nm.
32 . The ultrasonic transducer device of claim 27 , wherein the insulation layer comprises SiO 2 .
33 . The ultrasonic transducer device of claim 27 , 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.
34 . The ultrasonic transducer device of claim 33 , 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.
35 . The ultrasonic transducer device of claim 27 , wherein the membrane support layer comprises SiO 2 and the membrane comprises doped silicon.
36 . The ultrasonic transducer device of claim 27 , 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.