# US 7,608,909 B2 · Suspended transmission line structures in back end of line processing

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- Number: US 7,608,909 B2
- Document ID: US7608909B2
- Status: Granted
- Kind: B2
- Application number: 11/164,765
- Filed: 2005-12-05
- Published: 2006-09-07
- Granted: 2009-10-27
- Earliest claimed: 2004-04-29
- Assignees: International Business Machines Corporation
- Inventors: Anil K. Chinthakindi; Robert A. Groves; Youri V. Tretiakov; Kunal Vaed; Richard P. Volant
- Web page: https://patentgrep.com/patent/US7608909B2

## CPC

- H01P 11/003: {Manufacturing lines with conductors on a substrate, e.g. strip lines, slot lines}
- H10W 20/031: {of conductive parts of the interconnections}
- H10W 20/072: {of dielectric parts comprising air gaps}
- H10W 20/423: {Shielding layers}
- H10W 20/46: comprising air gaps
- H10W 20/495: {Capacitive arrangements or effects of, or between wiring layers}
- H10W 20/425: {Barrier, adhesion or liner layers}
- H10W 44/212: {Coaxial feed-throughs in substrates}
- H10W 44/216: {Waveguides, e.g. strip lines}
- H01P: WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE (operating at optical frequencies G02B)
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

A method for forming a transmission line structure for a semiconductor device includes forming an interlevel dielectric layer over a first metallization level, removing a portion of the interlevel dielectric layer and forming a sacrificial material within one or more voids created by the removal of the portion of the interlevel dielectric layer. A signal transmission line is formed in a second metallization level formed over the interlevel dielectric layer, the signal transmission line being disposed over the sacrificial material. A portion of dielectric material included within the second metallization level is removed so as to expose the sacrificial material, wherein a portion of the sacrificial material is exposed through a plurality of access holes formed through the signal transmission line. The sacrificial material is removed so as to create an air gap beneath the signal transmission line.

## Claims

### Claim 1

A back end of line microstrip transmission line structure, comprising:
a signal transmission line formed on one metallization level;
a ground plane formed on another metallization level;
an air gap disposed between said signal transmission line and said ground plane, said air gap formed within an interlevel dielectric layer;
one of said signal transmission line and said ground plane further comprising a plurality of access holes formed therethrough to provide removal access to a sacrificial material used to define said air gap, said plurality of access holes being arranged along a direction parallel to conductor edges of one of said signal transmission line and said ground plane; and
a support structure disposed directly beneath said one of said signal transmission line and said ground plane having a plurality of access holes, said support structure; consisting of material entirely from said interlevel dielectric layer, and wherein a bottom surface of said support structure is in contact with the other of said signal transmission line and said ground plane.

### Claim 2 (depends on 1)

The microstrip transmission line structure of claim 1, wherein said support structure further comprises a continuous rail.

### Claim 3 (depends on 2)

The microstrip transmission line structure of claim 2, wherein said support structure further comprises a plurality of individual posts.

### Claim 4 (depends on 3)

The microstrip transmission line structure of claim 3, wherein said signal transmission line and said ground plane further comprise a back end of line metallic material completely encapsulated within a liner material.

### Claim 5

A back end of line coplanar waveguide transmission line structure, comprising:
a signal transmission line formed on a first metallization level;
a pair of coplanar shielding lines adjacent said signal transmission line in said first metallization level;
an air gap disposed beneath signal transmission line, said air gap formed within a first interlevel dielectric layer;
said signal transmission line further comprising a plurality of access holes formed therethrough to provide removal access to a sacrificial material used to define said air gap, said plurality of access holes being arranged along a direction parallel to conductor edges of said signal transmission line; and
a support structure disposed directly beneath said signal transmission line, said support structure; consisting of material entirely from said first interlevel dielectric layer, and wherein a bottom surface of said support structure is in contact with a lower level interlevel dielectric layer with respect to said first interlevel dielectric layer.

### Claim 6 (depends on 5)

The coplanar waveguide transmission line structure of claim 5, further comprising a first ground plane formed on a second metallization level.

### Claim 7 (depends on 6)

The coplanar waveguide transmission line structure of claim 6, further comprising:
a second ground plane formed on a third metallization level;
said first metallization level disposed between said second metallization level and said third metallization level; and
both of said first and said second ground planes electrically connected to said pair of coplanar shielding lines.

### Claim 8 (depends on 5)

The coplanar waveguide transmission line structure of claim 5, wherein said support structure further comprises a continuous rail.

### Claim 9 (depends on 5)

The coplanar waveguide transmission line structure of claim 5, wherein said support structure further comprises a plurality of individual posts.