# US 11,440,794 B2 · Process for manufacturing a microelectromechanical device with a mobile structure, in particular a micromirror

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- Number: US 11,440,794 B2
- Document ID: US11440794B2
- Status: Granted
- Kind: B2
- Application number: 16/565,803
- Filed: 2019-09-10
- Published: 2020-03-12
- Granted: 2022-09-13
- Earliest claimed: 2018-09-12
- Assignees: STMicroelectronics S.r.l.
- Applicants: STMicroelectronics S.r.l.
- Inventors: Sonia Costantini; Davide Assanelli; Aldo Luigi Bortolotti; Michele Vimercati; Igor Varisco
- Web page: https://patentgrep.com/patent/US11440794B2

## CPC

- B81C 1/00182: {Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer}
- B81B 7/008: {MEMS characterised by an electronic circuit specially adapted for controlling or driving the same (B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00)}
- B81B 7/02: containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] (B81B7/04 takes precedence)
- B81C 1/00666: {Treatments for controlling internal stress or strain in MEMS structures}
- G02B 26/0833: {the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B)}
- G02B 26/0841: {the reflecting element being moved or deformed by electrostatic means}
- H04N 9/3102: {using two-dimensional electronic spatial light modulators (micromechanical modulators as such G02B26/0833; liquid crystal modulators as such G02F1/13)}
- B81B 2201/042: Micromirrors, not used as optical switches
- B81B 2203/0315: Cavities
- G02B 26/101: {with both horizontal and vertical deflecting means, e.g. raster or XY scanners (colour television using laser beams scanning a display screen H04N9/3129)}
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A bottom semiconductor region is formed to include a main sub-region, extending through a bottom dielectric region that coats a semiconductor wafer, and a secondary sub-region which coats the bottom dielectric region and surrounds the main sub-region. First and second top cavities are formed through the wafer, delimiting a fixed body and a patterned structure that includes a central portion which contacts the main sub-region, and deformable portions in contact with the bottom dielectric region. A bottom cavity is formed through the bottom semiconductor region, as far as the bottom dielectric region, the bottom cavity laterally delimiting a stiffening region including the main sub-region and leaving exposed parts of the bottom dielectric region that contact the deformable portions and parts of the bottom dielectric region that delimit the first and second top cavities. The parts left exposed by the bottom cavity are selectively removed.

## Claims

### Claim 1

A method for manufacturing a microelectromechanical device, comprising:
delimiting a first semiconductor wafer by a front surface and a rear surface;
coating the rear surface with a bottom dielectric region;
forming a first bottom window through the bottom dielectric region;
forming a bottom semiconductor region that includes a first main sub-region which extends through the first bottom window and contacts the first semiconductor wafer, and a secondary sub-region which coats the bottom dielectric region and laterally surrounds the first main sub-region;
selectively removing portions of the first semiconductor wafer, starting from the front surface so as to form a first top cavity and a second top cavity that extend as far as the bottom dielectric region and laterally delimit a fixed supporting body and a patterned structure, the patterned structure including a central portion which contacts the first main sub-region of the bottom semiconductor region and a number of deformable portions, interposed between the central portion and the fixed supporting body, in contact with the bottom dielectric region;
selectively removing portions of the bottom semiconductor region so as to form a bottom cavity that extends through the bottom semiconductor region as far as the bottom dielectric region, and laterally delimits a stiffening region including the first main sub-region of the bottom semiconductor region, the bottom cavity also extending laterally so as to expose parts of the bottom dielectric region that contact the deformable portions and parts of the bottom dielectric region that delimit the first and second top cavities; and
selectively removing the parts of the bottom dielectric region left exposed by the bottom cavity, in such a way that the first and second top cavities and the bottom cavity form an overall cavity, suspended inside which is the patterned structure.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the first semiconductor wafer is comprised of monocrystalline semiconductor material; wherein the step of forming the bottom semiconductor region comprises performing an epitaxial growth such that the first main sub-region of the bottom semiconductor region forms a monolithic monocrystalline region with the first semiconductor wafer; and wherein the secondary sub-region of the bottom semiconductor region is comprised of polycrystalline semiconductor material.

### Claim 3 (depends on 2)

The method according to claim 2, wherein the stiffening region includes a portion of the secondary sub-region of the bottom semiconductor region that laterally surrounds the first main sub-region, the portion of the secondary sub-region coating a corresponding portion of the bottom dielectric region which is laterally staggered with respect to the parts of the bottom dielectric region that delimit the first and second top cavities; and further comprising the step of selectively removing sub-portions of the portion of the secondary sub-region, so as to expose a the corresponding portion of the bottom dielectric region, and subsequently carrying out the step of selectively removing the parts of the bottom dielectric region left exposed by the bottom cavity.

### Claim 4 (depends on 1)

The method according to claim 1, further comprising coating the front surface of the first semiconductor wafer with a top dielectric region, and forming a top window through the top dielectric region; and wherein the step of selectively removing portions of the first semiconductor wafer starting from the front surface comprises removing portions of the first semiconductor wafer that give out onto the top window.

### Claim 5 (depends on 4)

The method according to claim 4, further comprising:
subsequent to formation of the first and second top cavities and prior to the step of selectively removing portions of the bottom semiconductor region, fixing the first semiconductor wafer to a second semiconductor wafer via interposition of a bonding region that extends on the top dielectric region and within the first and second top cavities; and
subsequent to the step of selectively removing the parts of the bottom dielectric region left exposed by the bottom cavity, separating the first semiconductor wafer from the second semiconductor wafer.

### Claim 6 (depends on 1)

The method according to claim 1, further comprising forming a metal region on the central portion of the patterned structure.

### Claim 7 (depends on 1)

The method according to claim 1, wherein the central portion of the patterned structure is mobile with respect to the fixed supporting body, following deformation of the number of deformable portions.

### Claim 8 (depends on 1)

The method according to claim 1, wherein the first and second top cavities laterally delimit a number of peripheral portions, fixed with respect to the bottom dielectric region; wherein each deformable portion of the patterned structure is interposed between the central portion of the patterned structure and a corresponding peripheral portion; and further comprising manufacturing process further comprising forming a number of additional bottom windows through the bottom dielectric region, the step of forming a bottom semiconductor region further comprising forming a number of additional main sub-regions, each of which extends through a corresponding additional bottom window, is laterally staggered with respect to the first main sub-region, and contacts a corresponding peripheral portion.

### Claim 9

A microelectromechanical (MEMS) device, comprising:
a fixed supporting body of semiconductor material, delimited by a rear surface;
a bottom dielectric region fixed with respect to the fixed supporting body and extending underneath the rear surface;
a patterned region of semiconductor material and suspended in a cavity laterally delimited by the fixed supporting body, the patterned region comprising:
a central portion, which in resting conditions extends above the rear surface; and
a number of deformable portions, each of which is interposed between the central portion and the fixed supporting body; and
an additional semiconductor region forming, together with the central portion of the patterned region, a mobile structure, the additional semiconductor region contacting the central portion of the patterned region and extending, in resting conditions, underneath the rear surface, the mobile structure being mobile with respect to the fixed supporting body, following upon deformation of the number of deformable portions;
wherein the central portion of the patterned region and the additional semiconductor region form a monolithic monocrystalline region.

### Claim 10 (depends on 9)

The MEMS device according to claim 9, further comprising a metal region extending on the central portion of the patterned region.

### Claim 11

A microelectromechanical (MEMS) projector system comprising:
a MEMS device comprising:
a fixed supporting body of semiconductor material, delimited by a rear surface;
a bottom dielectric region fixed with respect to the fixed supporting body and extending underneath the rear surface;
a patterned region of semiconductor material and suspended in a cavity laterally delimited by the fixed supporting body, the patterned region comprising:
a central portion, which in resting conditions extends above the rear surface; and
a number of deformable portions, each of which is interposed between the central portion and the fixed supporting body; and
a metal region extending on the central portion of the patterned region;
an additional semiconductor region forming, together with the central portion of the patterned region, a mobile structure, the additional semiconductor region contacting the central portion of the patterned region and extending, in resting conditions, underneath the rear surface, the mobile structure being mobile with respect to the fixed supporting body, following upon deformation of the number of deformable portions; and
an optical source configured to generate an optical beam that impinges upon the metal region; wherein the central portion of the patterned region and the additional semiconductor region form a monolithic monocrystalline region.

### Claim 12 (depends on 11)

A portable electronic apparatus comprising a MEMS projector system according to claim 11.

### Claim 13 (depends on 12)

The portable electronic apparatus according to claim 12, wherein the MEMS projector system is a stand-alone accessory having a casing coupled in a releasable way to a respective casing of the portable electronic apparatus.

### Claim 14 (depends on 12)

The portable electronic apparatus according to claim 12, wherein the MEMS projector system is formed in an integrated way, within a casing of the portable electronic apparatus.

### Claim 15

A device, comprising:
a microelectromechanical (MEMS) device, comprising:
a fixed supporting body of semiconductor material;
a bottom dielectric region extending underneath a rear surface of the fixed supporting body;
a patterned region suspended in a cavity laterally delimited by the fixed supporting body, the patterned region comprising:
a central portion; and
a plurality of deformable portions, each deformable portion being interposed between the central portion and the fixed supporting body; and
an additional semiconductor region contacting the central portion of the patterned region and extending underneath the rear surface;
wherein the central portion of the patterned region and the additional semiconductor region form a monolithic monocrystalline region.

### Claim 16 (depends on 15)

The device according to claim 15, further comprising a metal region extending on the central portion of the patterned region.