Integrated circuit waveguide

Details Integrated circuit waveguide Integrated circuit waveguide

2001-12-17

2003-09-23

Powell, William A. (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Combined with the removal of material by nonchemical means

C216S024000, C216S038000, C216S033000, C216S039000, C385S129000, C385S131000, C438S745000, C438S735000, C438S737000

Reexamination Certificate

active

06624077

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of the invention generally relate to integrated circuit optical waveguides.
2. Description of the Related Art
As the demand for more powerful microprocessors increases, the interconnection technology within integrated circuits (ICs) must also advance in order to support the next generation of faster and more powerful microprocessors. Conventional ICs utilize electrical signals for data transmission. However, since an optical signal propagates at a velocity that is faster than the propagation velocity of an electrical signal, optical transmission mediums and interconnect devices have an inherent ability to transmit data at higher speeds. Therefore, optical signals offer great potential for increasing the signal transmission rate within ICs. Furthermore, several optical signals may share a single common optical transmission medium without interfering with each other. Alternatively, when more than one electrical signal occupies a transmission medium, interference often occurs. This interference, generally termed crosstalk, is defined as a disturbance caused by the electric and/or magnetic fields of a first signal affecting the electric and/or magnetic fields of a second signal in the same or an adjacent transmission medium. As a result of crosstalk, the signal transmission density is substantially greater for optical signal based systems than for electrical based systems. As a result of these differences, along with other advantages of optical based systems, optical signal transmission methods and processes are an attractive option for supporting the next generation of faster and more powerful ICs and microprocessors.
Current technology generally supports optical signal transmission through, for example, optical fiber networks. These optical fiber networks are generally supported by an infrastructure of individual optical fibers, fiber bundles, or other optically conductive transmission mediums. Optical fibers, which are the most common transmission medium for optical signals, generally include an outer shell or body portion that supports an inner optically conductive core portion. The optically conductive core generally has a diameter of approximately 8 micrometers. The terminating ends of the individual optical fibers are received by various optical devices, such as an optical waveguide, for example. An optical waveguide may include at least one optical signal input, an inner optical core portion that is conductive for optical signals and in optical communication with the optical signal input, and at least one optical signal output that is in optical communication with the optical core. These waveguides operate to receive an optical signal from a first optical signal source at an optical input, transmit the optical signal through the core portion of the waveguide, and disseminate the optical signal to another optical device or another optical transmission medium at an output of the waveguide. This process is ideally conducted with minimal loss or distortion to the optical signal as it travels through the waveguide.
Optical waveguides exist at multiple levels. For example, an optical waveguide may be used in larger devices, such as a router for an optical network. Optical waveguides may also be used in devices as small as ICs. Optical waveguides are used at the IC level to communicate optical signals between various IC components. U.S. Pat. No. 5,464,860 to Fujimoto describes a conventional IC waveguide and a method for manufacturing such, as illustrated in FIG.
1
. The waveguide of Fujimoto is formed by depositing a cladding layer
101
on a substrate
100
, and then depositing a metal layer
102
over the cladding layer
101
. A trench
106
having a rectangular shape is then anisotropically etched into the middle of the cladding layer
101
through the metal layer
102
. The trench
106
is then filled with an active waveguide polymer
103
. The polymer layer
103
in the rectangular trench
106
is then etched back to a level below the metal layer
102
and the trench
106
is backfilled with an optically non-conductive buffer layer
104
, which operates to optically isolate the polymer layer
103
in the rectangular trench
106
.
However, conventional optical fiber cores are circular, and therefore, an inherent mismatch exists between the circular fiber core and the rectangular core of conventional IC waveguides. This mismatch represents a potential loss and/or degradation region for optical signals traveling from a fiber into a waveguide. Another problem with conventional IC optical waveguides is that the core is generally sized to approximate the core dimension of standard optical fibers, which is generally 8 micrometers. This poses a substantial problem, as the current trend is to manufacture high refractive index devices having substantially smaller core dimensions, in the range of between about 8 micrometers and about 2 micrometers. High refractive index cores allow the design of OIC's to be smaller as well as enable low-loss integration of silicon and class III/IV-based devices, such as lasers, amplifiers, detectors, and other devices into hybrid circuits. This presents a problem, as it is difficult to couple a standard 8 micrometer optical fiber to a device core that has a smaller dimension, for example ¼ that of the optical fiber size, or about 2 micrometers, without incurring substantial signal loss or degradation.
Therefore, there exists a need for a method for manufacturing an IC optical waveguide that eliminates coupling mismatch loss and/or signal degradation. Further, there exists a need for an IC optical waveguide capable of coupling to optical sources having a core dimension that is substantially larger than the core dimension of the optical waveguide.
SUMMARY OF THE INVENTION
Embodiments of the invention generally provide a method for manufacturing an IC optical waveguide. The method includes depositing a cladding material on a first substrate, forming a trench in the cladding material on the first substrate, and filling the trench with a optically conductive core material. The upper surface of the cladding material and the optically conductive core material are then planarized to produce a substantially planar surface. The method further includes depositing a cladding material on a second substrate, forming a mirror image trench into the cladding material on the second substrate, and filling the mirror image trench with the optically conductive core material. The upper surface of the second cladding layer and the core material therein is then planarized. Thereafter, the first substrate is affixed to the second substrate such that the trench and the mirror image trench are in abutment and form a substantially circular optical core.
Embodiments of the invention also provide a method for forming a substantially circular optical channel in a waveguide. The method includes depositing a cladding layer on a substrate, etching a first trench in the cladding layer, the first trench having a substantially semi-circular cross section, and etching a mirror trench in the cladding layer, the mirror trench also having a substantially semi-circular cross section. The first trench and the mirror trench are filled with an optically conductive core material, and the upper surface of the cladding layer and an area over the first trench and the mirror trench is planarized. Thereafter, the mirror trench is folded onto the first trench and affixed thereto to form a substantially circular optical core surrounded by a continuous cladding layer.
Embodiments of the invention further provide an optical waveguide having a circular optical core. The waveguide includes a bottom portion and a top portion that are affixed together to form the waveguide. The bottom portion includes a bottom substrate, a first dielectric cladding layer is deposited on the bottom substrate and has a substantially planar first outer surface, a semi-circular trench is formed in the first cladding layer, and an optically conductive

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