# US 8,772,902 B2 · Fabrication of a localized thick box with planar oxide/SOI interface on bulk silicon substrate for silicon photonics integration

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- Number: US 8,772,902 B2
- Document ID: US8772902B2
- Status: Granted
- Kind: B2
- Application number: 13/451,141
- Filed: 2012-04-19
- Published: 2013-10-24
- Granted: 2014-07-08
- Earliest claimed: 2012-04-19
- Assignees: International Business Machines Corporation
- Applicants: Solomon Assefa; William M. J. Green; Marwan H. Khater; Yurii A. Vlasov
- Inventors: Solomon Assefa; William M. J. Green; Marwan H. Khater; Yurii A. Vlasov
- Web page: https://patentgrep.com/patent/US8772902B2

## CPC

- G02B 6/13: Integrated optical circuits characterised by the manufacturing method
- H10P 90/1906: {Preparing SOI wafers}
- H10W 10/0145: {of trenches having shapes other than rectangular or V-shape (H10W10/0143 takes precedence)}
- H10W 10/021: {of air gaps}
- H10W 10/061: {using SOI processes together with lateral isolation, e.g. combinations of SOI and shallow trench isolations}
- H10W 10/17: formed using trench refilling with dielectric materials, e.g. shallow trench isolations
- H10W 10/181: {Semiconductor-on-insulator [SOI] isolation regions, e.g. buried oxide regions of SOI wafers}
- H10W 10/20: Air gaps
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- 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

Line trenches are formed in a stack of a bulk semiconductor substrate and an oxygen-impermeable layer such that the depth of the trenches in the bulk semiconductor substrate is greater than the lateral spacing between a pair of adjacently located line trenches. Oxygen-impermeable spacers are formed on sidewalls of the line trenches. An isotropic etch, either alone or in combination with oxidation, removes a semiconductor material from below the oxygen-impermeable spacers to expand the lateral extent of expanded-bottom portions of the line trenches, and to reduce the lateral spacing between adjacent expanded-bottom portions. The semiconductor material around the bottom portions is oxidized to form a semiconductor oxide portion that underlies multiple oxygen-impermeable spacers. Semiconductor-on-insulator (SOI) portions are formed above the semiconductor oxide portion and within the bulk semiconductor substrate.

## Claims

### Claim 1

A semiconductor structure comprising:
a semiconductor oxide portion embedded within a semiconductor substrate, wherein said semiconductor substrate contiguously extends from a first portion underlying said semiconductor oxide portion to a second portion overlying a peripheral portion of said semiconductor oxide portion;
a semiconductor material portion having a planar bottom surface that is in contact with a planar top surface of said semiconductor oxide portion and comprising a same semiconductor material as said second portion;
a first line trench located on one side of said semiconductor material portion and extending into said semiconductor oxide portion; and
a second line trench located on an opposite side of said semiconductor material portion and extending into said semiconductor oxide portion, wherein said semiconductor material portion laterally extends between a first sidewall of said first line trench and a second sidewall of said second line trench, and is laterally spaced from said second portion by one of said first line trench and said second line trench, and wherein each bottom surface of said first and second line trenches comprises a non-planar convex surface of said semiconductor oxide portion or a pair of grooves between which a portion said semiconductor oxide portion protrudes above bottommost surfaces of said grooves.

### Claim 2 (depends on 1)

The semiconductor structure of claim 1, wherein said first sidewall includes a first semiconductor sidewall of said semiconductor material portion and a first semiconductor oxide sidewall of said semiconductor material portion, and said second sidewall includes a second semiconductor sidewall of said semiconductor material portion and a second semiconductor oxide sidewall of said semiconductor material portion.

### Claim 3 (depends on 2)

The semiconductor structure of claim 2, wherein said first semiconductor sidewall is parallel to said second semiconductor sidewall.

### Claim 4 (depends on 3)

The semiconductor structure of claim 3, wherein said first semiconductor sidewall and said second semiconductor sidewall are parallel to a sidewall of said second portion.

### Claim 5 (depends on 1)

The semiconductor structure of claim 1, wherein a bottom surface of said semiconductor material portion is substantially planar.

### Claim 6 (depends on 1)

The semiconductor structure of claim 1, further comprising at least one semiconductor device located on, or in, said second portion.

### Claim 7 (depends on 1)

The semiconductor structure of claim 1, wherein said first line trench, said second line trench, and at least another line trench contiguously surrounds said semiconductor material portion laterally as a set of contiguous line trenches.

### Claim 8 (depends on 1)

The semiconductor structure of claim 1, further comprising at least one shallow trench isolation structure comprising a dielectric material and filling said first line trench and said second line trench.

### Claim 9 (depends on 1)

The semiconductor structure of claim 1, wherein said semiconductor material portion and said semiconductor substrate include a same single crystalline semiconductor material.

### Claim 10 (depends on 9)

The semiconductor structure of claim 9, wherein semiconductor oxide portion comprises a thermal oxide of said same semiconductor material.

### Claim 11 (depends on 1)

The semiconductor structure of claim 1, further comprising:
a first pair of oxygen-impermeable material portions located at a bottom of said first line trench and embedded in said semiconductor oxide portion; and
a second pair of oxygen-impermeable material portions located at a bottom of said second line trench and embedded in said semiconductor oxide portion.

### Claim 12 (depends on 11)

The semiconductor structure of claim 11, wherein a sidewall of one of said first pair of oxygen-impermeable material portions is vertically coincident with said first sidewall of said first line trench, and a sidewall of one of said second pair of oxygen-impermeable material portions is vertically coincident with said second sidewall of said second line trench.