Fabrication of capacitive micromachined ultrasonic transducers by local oxidation
First Claim
1. A method of fabricating a capacitive micromachined ultrasonic transducer (CMUT), said method comprising:
- (a) depositing an oxidation-blocking layer onto a substrate, wherein said substrate comprises an oxidation-enable material;
(b) patterning said oxidation-blocking layer, wherein said patterning forms a post region and a cavity region of a surface of said substrate, and wherein said patterning removes said oxidation-blocking layer from said substrate at said post region;
(c) thermally oxidizing said substrate, wherein said thermally oxidizing grows one or more oxide posts from said post region, and wherein said post defines a vertical dimension of said CMUT; and
(d) bonding a membrane layer onto said post, wherein said membrane layer forms a membrane of said CMUT.
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Abstract
The current invention provides methods of fabricating a capacitive micromachined ultrasonic transducer (CMUT) that includes oxidizing a substrate to form an oxide layer on a surface of the substrate having an oxidation-enabling material, depositing and patterning an oxidation-blocking layer to form a post region and a cavity region on the substrate surface and remove the oxidation-blocking layer and oxide layer at the post region. The invention further includes thermally oxidizing the substrate to grow one or more oxide posts from the post region, where the post defines the vertical critical dimension of the device, and bonding a membrane layer onto the post to form a membrane of the device. A maximum allowed second oxidation thickness t2 can be determined, that is partially based on a desired step height and a device size, and a first oxidation thickness t1 can be determined that is partially based on the determined thickness t2.
83 Citations
23 Claims
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1. A method of fabricating a capacitive micromachined ultrasonic transducer (CMUT), said method comprising:
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(a) depositing an oxidation-blocking layer onto a substrate, wherein said substrate comprises an oxidation-enable material; (b) patterning said oxidation-blocking layer, wherein said patterning forms a post region and a cavity region of a surface of said substrate, and wherein said patterning removes said oxidation-blocking layer from said substrate at said post region; (c) thermally oxidizing said substrate, wherein said thermally oxidizing grows one or more oxide posts from said post region, and wherein said post defines a vertical dimension of said CMUT; and (d) bonding a membrane layer onto said post, wherein said membrane layer forms a membrane of said CMUT. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method of fabricating a step on a substrate of a device, wherein said substrate comprises an oxidation-enable material, said method comprising:
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(a) determining a maximum allowed second oxidation thickness t2, wherein said determining is at least partially based on a desired height of said step and a size of said device; (b) calculating a first oxidation thickness t1, wherein said calculating is at least partially based on said determined maximum allowed t2; (c) thermally oxidizing said substrate to form an oxide layer on a surface of said substrate, wherein the thickness of said oxide layer is based on said calculated t1; (d) patterning said oxide layer to form an open region and a step region, wherein said patterning removes said oxide layer from said substrate at said open region; (e) thermally oxidizing said substrate and said patterned oxide layer based on said maximum allowed t2; and (f) removing approximately all of said oxide, whereby said substrate remaining has a step. - View Dependent Claims (20, 21, 22)
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23. A method of fabricating a device having a vertical critical dimension, said method comprising:
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(a) oxidizing a substrate to form an oxide layer on a surface of said substrate, wherein said substrate comprises an oxidation-enable material; (b) depositing an oxidation-blocking layer on said oxide layer; (c) patterning said oxidation-blocking layer and said oxide layer, wherein said patterning forms a post region and a cavity region of said surface of said substrate, and wherein said patterning removes said oxidation-blocking layer and said oxide layer from said substrate at said post region; (d) thermally oxidizing said substrate, wherein said thermally oxidizing grows one or more oxide posts from said post region, and wherein said post defines said vertical critical dimension of said device; and (e) bonding a membrane layer onto said post, wherein said membrane layer forms a membrane of said device.
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Specification