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  Using deuterated source gasses to fabricate low loss gesion sion waveguidesUSPTO Application #: 20060003484Title: Using deuterated source gasses to fabricate low loss gesion sion waveguides Abstract: The present invention provides a method of manufacturing optical devices which includes the steps of providing a substrate and forming at least one optical layer on the substrate. The optical layer is formed by a chemical vapor deposition (CVD) process which includes a deuterated source gas. The present invention also provides an optical device which includes a substrate and an optical layer including deuterium. (end of abstract)
Agent: Foley And Lardner LLP Suite 500 - Washington, DC, US Inventors: Robert Bellman, Ikerionwu A. Akwani, Paul A. Sachenik, Thomas P. Grandi USPTO Applicaton #: 20060003484 - Class: 438069000 (USPTO) Related Patent Categories: Semiconductor Device Manufacturing: Process, Making Device Or Circuit Responsive To Nonelectrical Signal, Responsive To Electromagnetic Radiation, Including Integrally Formed Optical Element (e.g., Reflective Layer, Luminescent Layer, Etc.) The Patent Description & Claims data below is from USPTO Patent Application 20060003484. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention is directed generally to the manufacture of optical waveguides and more particularly to the use of deuterated source gasses to manufacture optical waveguides. BACKGROUND OF THE INVENTION [0002] Practical optical devices must be fabricated so as to direct the light energy. Commonly, this is achieved by creating a waveguide. In the waveguide, a cladding layer of lower refractive index (typically 1.44) directs light by internal reflectance to an optical core of higher refractive index (typically 1.45-1.5). Both the core and cladding layer can be made from many different materials. Common materials include glasses of SiO.sub.2-GeO.sub.2, SiO.sub.2-B.sub.2O.sub.3-P.sub.2O.sub.5, SiO.sub.2-GeO.sub.2-B.sub.2O.sub.3-P.sub.2O.sub.5, SiO.sub.2 and SiON. Silicon dioxide, silicon nitride and silicon oxynitride are materials which are particularly valued for their optical properties, in particular their high optical transparency and wide range of refractive indices (1.45-2.5). These materials are used in a host of optical devices. The devices include, for example, planar waveguides, arrayed waveguides (AWG), wavelength demultiplexers., power splitters, optical couplers, phasers, and variable optical attenuators (VOA). [0003] Typically, chemical vapor deposition (CVD) is used to deposit layers of silicon dioxide, silicon nitride or silicon oxynitride. In the CVD process, the substrate is placed on a heated susceptor in a quartz reaction chamber and then the reactant gases are introduced into the chamber. Typically, the gasses react on the surface of the substrate and form a deposited layer. However, some reactions may also occur as the gasses flow into the chamber. The most common gasses for the deposition of silicon dioxide, silicon nitride and silicon oxynitride are silane (SiH.sub.4), chlorinated silane (SiH.sub.xCl.sub.4-x), nitrous oxide (N.sub.2O), ammonia (NH.sub.3) and nitrogen (N.sub.2). These gases are inexpensive and can be purchased in great abundance. [0004] Although the CVD process is the preferred process for depositing many of the materials used to manufacture optical devices, it is not without problems. The use of ammonia and silane in the production of silicon nitride and silicon oxynitride results in the incorporation of large amounts of hydrogen (up to 20 at % for silicon nitride) in the optical film. [0005] The incorporated hydrogen generates significant optical losses at the 1550 nm optical communication band due to a strong overtone of the N--H bond. FIG. 1 illustrates the loss spectrum of conventionally processed silicon oxynitride, i.e., the loss over a range of wavelengths. The peak in loss is due to N--H absorption. In conventional manufacturing processes, the silicon oxynitride contains a significant amount of hydrogen. The figure clearly illustrates the deleterious effect of the overtone of the N--H bond. The center of the loss peak occurs at a wavelength of approximately 1510 nm. This is just 40 nm from 1550 nm, a preferred optical communications wavelength. [0006] It is possible to remove much of the entrapped hydrogen with high temperature thermal annealing. However, the optical SiON film can blister and crack at the high temperature, rendering the device useless. [0007] Therefore, it would be desirable to develop a method to manufacture optical devices which did not result in the incorporation of hydrogen in the optical SiON film and high losses at 1550 nm. Furthermore, it would be desirable to develop a process having the benefits of the speed and control of the conventional CVD process without resorting to a high temperature anneal to drive out the hydrogen. SUMMARY OF THE INVENTION [0008] The present invention provides a method of manufacturing optical devices comprising providing a substrate and forming at least one optical layer on the substrate by a CVD process including at least one deuterated source gas. [0009] The present invention also provides an optical device comprising a substrate and an optical layer including deuterium. BRIEF DESCRIPTION OF THE DRAWINGS [0010] The foregoing and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims and the exemplary embodiments shown in the drawings, which are briefly described below. It should be noted that unless otherwise specified like elements have the same reference numbers. [0011] FIG. 1 is a plot of the loss spectrum of silicon oxynitride in the vicinity of the N--H absorption peak. [0012] FIG. 2 is a plot of the FTIR spectra of GeSiON films deposited with ND.sub.3 and with NH.sub.3. [0013] FIG. 3 is a cross section of an embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0014] The present invention is directed to reducing the optical transmission loss in a waveguide by reducing the hydrogen content in the waveguide. FIG. 3 shows the cross section of a planar waveguide manufactured according to a preferred embodiment of the present invention. In this embodiment, an insulating buffer layer 102 is deposited on a substrate 101. A waveguide core 103 including deuterium is then deposited on the buffer layer 102 and the entire structure is coated with a cladding layer 104. As demonstrated below, the use of deuterated source gasses is effective in reducing the hydrogen content of the waveguide. [0015] Silicon is the preferred material for the substrate 101. However, the substrate 101 may be made out of any material suitable for supporting the waveguide core 103. Example substrate materials include, but are not limited to, GaAs, InP, SiO.sub.2, Si.sub.3N.sub.4, ceramics and plastics. [0016] The preferred material for the buffer layer 102 is silicon oxynitride (SiON) or germanium doped silicon oxynitride (GeSiON). More preferably, the material for the buffer layer 102 is deuterated silicon oxynitride (SiON) or deuterated germanium doped silicon oxynitride (GeSiON). Additional materials suitable for the buffer layer include fluorine doped silica (FSG), phosphorous doped silica (PSG) and boron and phosphorous doped silica (BPSG). However, any suitable material can be used. For optimum results, the buffer layer 102 should have an index of refraction less than the index of refraction of the waveguide core 103. The buffer layer 102 may be omitted if the substrate is formed from a suitable material with a lower index of refraction than the core. [0017] The preferred material for the cladding layer 104 is SiON or GeSiON. More preferably, the preferred material for the cladding layer 104 is deuterated SiON or deuterated GeSiON. However, any suitable material, such as plastics for example, can be used. For optimum results, the cladding layer 104 should have an index of refraction less than the index of refraction of the waveguide core 103. [0018] The core 103 of the optical waveguide preferably comprises deuterated germanium doped silicon oxynitride (Ge.sub.wSi.sub.zO.sub.xN.s- ub.y), where the sum of w, x, y and z is equal to 1. More preferably, the core 103 comprises deuterated silicon oxynitride (Si.sub.zO.sub.xN.sub.y)- , where the sum of x, y and z is equal to 1. The deuterium replaces hydrogen and thereby reduces the hydrogen content in the waveguide. The index of refraction of the core is preferably between 1.44 and 2.2. More preferably, the index of refraction of the core is between 1.6 and 1.8. Furthermore, transmission losses due to attenuation are preferably less than 4.0 dB/cm in multimode slab waveguides and less than 2.0 dB/cm in single mode slab waveguides. More preferably, the transmission losses due to attenuation are less than 1.5 dB/cm in multimode slab waveguides and less than 0.2 dB/cm in single mode slab waveguides at 1550 nm. [0019] By using deuterium source gasses in manufacturing the core 103, the hydrogen content of the core 103 is reduced and consequently the optical loss is reduced. This is shown, for example, by the Fourier transform infrared (FTIR) spectra of germanium doped silicon oxynitride (GeSiON) films are illustrated in FIG. 2. Continue reading... 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