Fabrication method of making silica-based optical devices and op

Details Fabrication method of making silica-based optical devices and op Fabrication method of making silica-based optical devices and op

1998-02-12

2000-11-28

Healy, Brian

Optical waveguides

Integrated optical circuit

385 15, 385 49, 385129, 385130, 385131, 385141, 437 51, 437130, 437131, 65385, 65391, 65413, G02B 612, H01L 2170, C03B 37023

Patent

active

061545821

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates generally to a method of fabricating an integrated opto-electronic device and devices fabricated by the method, to a method of fabricating an optical device by a plasma enhanced chemical vapour deposition process, and, to low temperature fabrication of integrated opto-electronic devices, utilising a plasma enhanced chemical vapour deposition process.


BACKGROUND OF THE INVENTION

Processes and devices which merge silica optical devices with advanced silicon electronics in integrated form are desirable. This will enable, for example, "super chips" to be provided which interface between optical and electronic technologies.
To achieve this integration it is desirable to be able to produce devices which combine thin film waveguides, and/or other optical components, usually silica based, married to a semiconductor substrate containing an electronic device or devices, usually silicon based.
One problem to be overcome in the fabrication of such devices is development of low temperature deposition processes which would allow deposition of thin film waveguides directly on top of electronic devices in a semiconductor substrate, without damaging the electronic devices. Plasma enhanced chemical vapour deposition (PECVD) is an attractive option for such low temperature deposition processes. Over the years of commercial use in conventional VLSI fabrication it has proven to be reliable, clean and well matched to modern automated IC production.
Some work has been done on the PECVD fabrication of waveguides. optical waveguide fabricated by low temperature processes", Electron. Lett., Vol. 29, 1993, pp. 1123-1124.] "Plasma enhanced chemical vapour deposition of low-loss SiON optical waveguides at 1.5-.mu.m wavelength", Appl. Opt., Vol. 30, 1991, pp. 4560-4564.] D. Obias, and T. Fitzgerald: "Fabrication of waveguides using low-temperature plasma processing techniques", J. Vac. Sci. Technol., Vol. A11, 1993, pp. 1268-1274.] technologies for fabrication of low-loss silica waveguides:, Electron. Lett. Vol., 28, 1992, pp. 1000-1001.] Crouillet: "Low-loss PECVD silica channel waveguides for optical communications", Electron. Lett., Vol. 26, 1990, pp. 2135-2137.] high-quality silicon-oxynitride waveguides", IEEE Trans. Phot. Techn. Lett., Vol 3, 1991, pp. 1096-1098.]
These prior art processes have utilised nitrogen as a refractive index increasing dopant and/or nitrous oxide as an oxidant for silane. Such waveguides suffer, however, from high (3 to 10 dB/cm) losses in the wavelength range 1.50 to 1.55 .mu.m due to a large absorption peak in this region. These losses can only be reduced by annealing the fabricated device at temperatures around 1000.degree. C., which would destroy any electronic circuits in an associated semiconductor substrate. These processes do not, therefore, allow production of practical integrated opto-electronic devices. Nitrous oxides has always been used in prior art processes as an oxidant for silane. This is because it gives better thickness uniformity and is able to be used under high pressures, so as to optimise productivity.


SUMMARY OF THE INVENTION

The present invention is, in part, based upon the belief that N--H bonds are mostly responsible for the large absorption in the 1.50 to 1.55 .mu.m range.
From a first aspect, the present invention provides a method of fabricating an integrated opto-electronic arrangement, comprising an optical component fabricated in silica and an electronic component fabricated in a semiconductor substrate, the method comprising the step of forming the optical component by plasma enhanced chemical vapour deposition (PECVD) onto the semiconductor substrate. Preferably the PECVD is carried out in the absence of nitrogen and nitrogen containing source materials.
Nobody has before proposed the use of an oxidant which does not contain nitrogen. Nobody before has made any suggestion that the absence of nitrogen, together with a PECVD process for forming an optical device, would result in an improvement in the losses suffe

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Syms, et al. "Reduction of propagation loss in silica-on-silicon channel waveguides formed by electron beam irradiation" Electronic Leters, Sep. 1, 1994, vol. 30, No. 18, (2pgs.).
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