Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2001-09-21
2004-04-06
Meeks, Timothy (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S579000, C427S163200, C427S167000, C427S255380, C427S376200, C427S397700
Reexamination Certificate
active
06716476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the manufacture of high quality optical films, and in particular to a method of depositing an optical quality silica film by PECVD. The invention can be applied to the manufacture of photonic devices, for example, Mux/Demux devices for use fiber optic communications.
2. Description of Related Art
The manufacture of integrated optical devices, such as optical Multiplexers (Mux) and Demultiplexers (Dmux) requires the fabrication of optical quality elements, such as waveguides and gratings highly transparent in the 1.30 &mgr;m and 1.55 &mgr;m optical bands. These silica-based optical elements are basically composed of three layers: buffer, core and cladding. For reasons of simplicity, the buffer and cladding layers are typically of the same composition and refractive index. In order to confine the 1.55 &mgr;m (and/or 1.30 &mgr;m) wavelength laser beam, the core must have a higher refractive index than the buffer and cladding layers. The required refractive index difference is referred to as the ‘delta-n’ and is one of the most important characteristics of these silica-based optical elements.
It is very difficult to fabricate transparent silica-based optical elements in the 1.55 &mgr;m wavelength (and/or 1.30 wavelength) optical region while maintaining a suitable difference delta-n and preventing stress-induced mechanical and problems. Our co-pending U.S. patent application Ser. No. 09/799,491 filed on Mar. 7, 2000 entitled ‘Method of Making a Functional Device with Deposited Layers subject to High Temperature Anneal” describes an improved Plasma Enhanced Chemical Vapour Deposition technique for these silica-based elements which allows the attainment of the required ‘delta-n’ while eliminating the undesirable residual Si:N—H oscillators (observed as a FTIR peak centered at 3380 cm
−1
whose 2
nd
harmonics could cause an optical absorption between 1.445 and 1.515 &mgr;m), SiN—H oscillators (centered at 3420 cm
−1
whose 2
nd
harmonics could cause an optical absorption between 1.445 and 1.479 &mgr;m) and SiO—H oscillators (centered at 3510 cm
−1
and whose 2
nd
harmonics could cause an optical absorption between 1.408 and 1.441 &mgr;m) after a high temperature thermal treatment in a nitrogen ambient, typically at 800° C.
With such a high temperature thermal treatment are associated some residual stress-induced mechanical problems of deep-etched optical elements (mechanical movement of the side-walls) and some residual stress-induced mechanical problems at the buffer/core interface or at the core/cladding interface (micro-structural defects, micro-voiding and separation).
Recently published literature reveals various PECVD approaches to obtain these high performance optically transparent silica-based optical elements: Valette S., New integrated optical multiplexer-demultiplexer realized on silicon substrate, ECIO '87, 145, 1987; Grand G., Low-loss PECVD silica channel waveguides for optical communications, Electron. Lett., 26 (25), 2135, 1990; Bruno F., Plasma-enhanced chemical vapor deposition of low-loss SiON optical waveguides at 1.5-&mgr;m wavelength, Applied Optics, 30 (31), 4560, 1991; Kapser K., Rapid deposition of high-quality silicon-oxinitride waveguides, IEEE Trans. Photonics Tech. Lett., 5 (12), 1991; Lai Q., Simple technologies for fabrication of low-loss silica waveguides, Elec. Lett., 28 (11), 1000, 1992; Lai Q., Formation of optical slab waveguides using thermal oxidation of SiOx, Elec. Lett., 29 (8), 714, 1993; Liu K., Hybrid optoelectronic digitally tunable receiver, SPIE, Vol 2402, 104, 1995; Tu Y., Single-mode SiON/SiO2/Si optical waveguides prepared by plasma-enhanced Chemical vapor deposition, Fiber and integrated optics, 14, 133, 1995; Hoffmann M., Low temperature, nitrogen doped waveguides on silicon with small core dimensions fabricated by PECVD/RIE, ECIO'95, 299, 1995; Bazylenko M., Pure and fluorine-doped silica films deposited in a hollow cathode reactor for integrated optic applications, J. Vac. Sci. Technol. A 14 (2), 336, 1996; Poenar D., Optical properties of thin film silicon-compatible materials, Appl. Opt. 36 (21), 5112, 1997; Hoffmann M., Low-loss fiber-matched low-temperature PECVD waveguides with small-core dimensions for optical communication systems, IEEE Photonics Tech. Lett., 9 (9), 1238, 1997; Pereyra I., High quality low temperature DPECVD silicon dioxide, J. Non-Crystalline Solids, 212, 225, 1997; Kenyon T., A luminescence study of silicon-rich silica and rare-earth doped silicon-rich silica, Fourth Int. Symp. Quantum Confinement Electrochemical Society, 97-11, 304, 1997; Alayo M., Thick SiOxNy and SiO2 films obtained by PECVD technique at low temperatures, Thin Solid Films, 332, 40, 1998; Bulla D., Deposition of thick TEOS PECVD silicon oxide layers for integrated optical waveguide applications, Thin Solid Films, 334, 60, 1998; Valette S., State of the art of integrated optics technology at LETI for achieving passive optical components, J. of Modern Optics, 35 (6), 993, 1988; Ojha S., Simple method of fabricating polarization-insensitive and very low crosstalk AWG grating devices, Electron. Lett., 34 (1), 78, 1998; Johnson C., Thermal annealing of waveguides formed by ion implantation of silica-on-Si, Nuclear Instruments and Methods in Physics Research, B141, 670, 1998; Ridder R., Silicon oxynitride planar waveguiding structures for application in optical communication, IEEE J. of Sel. Top. In Quantum Electron., 4 (6), 930, 1998; Germann R., Silicon-oxynitride layers for optical waveguide applications, 195
th
meeting of the Electrochemical Society, 99-1, May 1999, Abstract 137, 1999; Worhoff K., Plasma enhanced cyhemical vapor deposition silicon oxynitride optimized for application in integrated optics, Sensors and Actuators, 74, 9, 1999; and Offrein B., Wavelength tunable optical add-after-drop filter with flat passband for WDM networks, IEEE Photonics Tech. Lett., 11 (2), 239, 1999.
A comparison of these various PECVD techniques is summarised in
FIG. 1
which shows the approaches and methods used to modify the ‘delta-n’ between buffer (clad) and core with post-deposition thermal treatment.
The various techniques can be grouped into main categories: PECVD using unknown chemicals, unknown chemical reactions and unknown boron (B) and/or phosphorus (P) chemicals and unknown chemical reactions to adjust the ‘delta-n’ (When specified, the post-deposition thermal treatments range from 400 to 1000° C.); PECVD using TEOS and unknown means of adjusting the ‘delta-n’ (The post-deposition thermal treatments are not specified); PECVD using oxidation of SiH
4
with O
2
coupled with silicon ion implantation or adjustment of silicon oxide stoichiometry as means of adjusting the ‘delta-n’ (The post-deposition thermal treatments range from 400 to 1000° C.); PECVD using oxidation of SiH
4
with O
2
coupled with the incorporation of CF
4
(SiH
4
/O
2
/CF
4
flow ratio) as means of adjusting the ‘delta-n’ (When specified, the post-deposition thermal treatments range from 100 to 1000° C.); PECVD using oxidation of SiH
4
with N
2
O coupled with variations of N
2
O concentration (SiH
4
/N
2
O flow ratio) as means of adjusting the silicon oxide stoechiometry and the ‘delta-n’ (The post-deposition thermal treatments range from 400 to 1100° C.); PECVD using oxidation of SiH
4
with N
2
O coupled with variations of N
2
O concentration and with the incorporation of Ar (SiH
4
/N
2
O/Ar flow ratio) as means of adjusting the silicon oxide stoechiometry and the ‘delta-n’ (The post-deposition thermal treatments is 1000° C.); PECVD using oxidation of SiH
4
with N
2
O coupled with the incorporation of NH
3
(SiH
4
/N
2
O/NH
3
flow ratio) to form silicon oxynitrides with various ‘delta-n’ (When specified, the post-deposition thermal treatments range from 700 to 1100° C.); PECVD using oxidation of SiH
4
with N
2
O coupled with the incorporation of NH
3
and Ar (SiH
4
/N
2
O/NH
3
/Ar flow ratio) as to form silicon oxynitrides with various ‘delta-n’ (The po
Lachance Jonathan
Ouellet Luc
(Marks & Clerk)
Dalsa Semiconductor Inc.
Meeks Timothy
LandOfFree
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