# US 12,119,258 B2 · Semiconductor structure comprising a buried porous layer for RF applications

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- Number: US 12,119,258 B2
- Document ID: US12119258B2
- Status: Granted
- Kind: B2
- Application number: 17/623,499
- Filed: 2020-03-25
- Published: 2022-11-10
- Granted: 2024-10-15
- Earliest claimed: 2019-07-02
- Assignees: Soitec; Commissariat A L'energie Atomique Et Aux Energies Alternatives
- Applicants: Commissariat à L'energie Atomique Et Aux éNergies Alternatives; Soitec
- Inventors: Emmanuel Augendre; Frédéric Gaillard; Thomas Lorne; Emmanuel Rolland; Christelle Veytizou; Isabelle Bertrand; Frédéric Allibert
- Web page: https://patentgrep.com/patent/US12119258B2

## CPC

- H10P 90/1916: {with separation or delamination along an ion implanted layer, e.g. Smart-cut}
- H10P 14/665: {Porous materials}
- H10P 14/69215: {the material being a silicon oxide, e.g. SiO2}
- H10W 10/181: {Semiconductor-on-insulator [SOI] isolation regions, e.g. buried oxide regions of SOI wafers}
- H10W 44/00: Electrical arrangements for controlling or matching impedance
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

A semiconductor structure for radio frequency applications includes a support substrate made of silicon and comprising a mesoporous layer, a dielectric layer arranged on the mesoporous layer and a superficial layer arranged on the dielectric layer. The mesoporous layer comprises hollow pores, the internal walls of which are mainly lined with oxide. The mesoporous layer has a thickness between 3 and 40 microns and a resistivity greater than 20 kohm·cm over its entire thickness. The support substrate has a resistivity between 0.5 and 4 ohm·cm. The invention also relates to a method for producing such a semiconductor structure.

## Claims

### Claim 1

A semiconductor structure for radiofrequency applications, comprising:
a carrier substrate comprising silicon and including a mesoporous layer, the mesoporous layer including hollow pores, internal walls of the hollow pores being coated with oxide, the hollow pores not being completely filled with a solid material a thickness of the mesoporous layer being between 3 μm and 40 μm, a resistivity of the mesoporous layer being higher than 20 kohm·cm throughout the entire thickness of the mesoporous layer, a resistivity of the carrier substrate being between 0.5 ohm·cm and 4 ohm·cm;
a dielectric layer on the mesoporous layer; and
a surface layer on the dielectric layer.

### Claim 2 (depends on 1)

The semiconductor structure of claim 1, wherein the thickness of the mesoporous layer is less than 20 μm.

### Claim 3 (depends on 2)

The semiconductor structure of claim 2, wherein the resistivity of the carrier substrate is between 1 ohm·cm and 2 ohm·cm.

### Claim 4 (depends on 3)

The semiconductor structure of claim 3, wherein the surface layer comprises at least one material chosen from among the group consisting of silicon, germanium, silicon carbide, IV-IV, III-V or II-VI semiconductor compounds, or piezoelectric materials.

### Claim 5 (depends on 4)

The semiconductor structure of claim 4, wherein the porosity of the mesoporous layer is between 40% and 60%.

### Claim 6 (depends on 5)

The semiconductor structure of claim 5, further comprising radiofrequency devices in and/or on the surface layer.

### Claim 7 (depends on 1)

The semiconductor structure of claim 1, wherein the resistivity of the carrier substrate is between 1 ohm·cm and 2 ohm·cm.

### Claim 8 (depends on 1)

The semiconductor structure of claim 1, wherein the surface layer comprises at least one material chosen from among the group consisting of silicon, germanium, silicon carbide, IV-IV, III-V or II-VI semiconductor compounds, or piezoelectric materials.

### Claim 9 (depends on 1)

The semiconductor structure of claim 1, wherein the porosity of the mesoporous layer is between 40% and 60%.

### Claim 10 (depends on 9)

The semiconductor structure of claim 9, wherein the porosity of the mesoporous layer is about 50%.

### Claim 11 (depends on 1)

The semiconductor structure of claim 1, further comprising radiofrequency devices in and/or on the surface layer.

### Claim 12

A method of fabricating a semiconductor structure for radiofrequency applications, the method comprising:
a step a) of providing a donor substrate including a buried weakened plane delimiting a surface layer with respect to a front face of the donor substrate;
a step b) of providing a carrier substrate comprising silicon, the carrier substrate exhibiting a resistivity of between 0.5 ohm·cm and 4 ohm·cm;
a step c) of porosifying the carrier substrate and forming a mesoporous layer in a front portion of the carrier substrate, the mesoporous layer exhibiting a resistivity higher than 20 kohm·cm, the mesoporous layer having a thickness between 3 μm and 40 μm;
a step d) of annealing the carrier substrate under an oxidizing atmosphere at a temperature of between 300° C. and 400° C. to stabilize the mesoporous layer with hollow pores, internal walls of the hollow pores being coated with oxide, the hollow pores not being completely filled with a solid material;
a step e) of depositing a dielectric layer on the mesoporous layer,
a step f) of attaching the donor substrate, via the front face thereof, to the dielectric layer; and
a step g) of separating the donor substrate along the buried weakened plane order to transfer the surface layer to the carrier substrate.

### Claim 13 (depends on 12)

The method of claim 12, wherein the carrier substrate provided in step b) exhibits a resistivity of between 1 ohm·cm and 2 ohm·cm.

### Claim 14 (depends on 12)

The method of claim 12, wherein the porosification in step c) is carried out electrochemically.

### Claim 15 (depends on 12)

The method of claim 12, wherein a duration of the anneal under an oxidizing atmosphere in step d) is between 5 min and 200 min.

### Claim 16 (depends on 15)

The method of claim 15, wherein step d) comprises, after the anneal under an oxidizing atmosphere, an anneal under a neutral atmosphere at a temperature of between 400° C. and 450° C.

### Claim 17 (depends on 16)

The method of claim 16, wherein the duration of the anneal under a neutral atmosphere in step d) is between two hours and 16 hours.

### Claim 18 (depends on 12)

The method of claim 12, wherein step g) comprises a separating heat treatment carried out at a temperature of between 200° C. and 500° C.

### Claim 19 (depends on 17)

The method of claim 17, wherein the duration of the anneal under the neutral atmosphere in step d) is 10 hours.

### Claim 20 (depends on 18)

The method of claim 18, wherein the separating heat treatment is carried out at a temperature of 400° C.