Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-11-14
2004-07-06
Stein, Stephen (Department: 1775)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S450000, C428S689000, C428S620000
Reexamination Certificate
active
06759132
ABSTRACT:
PRIORITY CLAIM
The present application claims priority from European patent Application No. 01830701.7, filed Nov. 14, 2001, which is incorporated by reference.
FIELD OF THE INVENTION
The present invention refers generally to methods for the manufacture of electromagnetic radiation reflecting devices. In particular, one embodiment of the invention refers to the fabrication of reflecting devices comprising silicon substrates provided with a wall having the function of a mirror and usable, for example, in the photonic field.
BACKGROUND OF THE INVENTION
As is known, reflecting devices, hereinafter called mirrors, are used to deflect a beam of incident radiation, or light, at an appropriate angle.
For example, in the field of telecommunications, mirrors are used as an interface between optical fibers and transmitting/receiving devices. According to a known fabrication method, the optical fiber is inserted into a silicon substrate and one end of the fiber, suitably cut and polished, is covered with a layer of reflecting aluminum inclined at 45° in relation to the fiber axis.
This mirror placed at the end of the fiber deflects the light beam by 90° which, after passing through a suitable glass covering element, reaches, for example, a photo-detector. Several optical fibers can be inserted into the substrate in U-grooves obtained by means of mechanical micro-machining of the substrate itself. Typically, the grooves have one side of 125 &mgr;m and a pitch of 250 &mgr;m.
In another application, the mirrors are used to deflect (typically by 90°) the light emitted by a laser source to hit an Optical Compact Disc (OCD) in a reading process.
A conventional method for manufacturing mirrors used for OCDs comprises the steps of micro-machining glass bars in order to form a mirror wall, followed by a welding operation of said bars on to silicon wafers used for the correct alignment of the devices.
The methods based on micro-machining of substrates or silicon bars are both complex and costly, so research into alternative methods is attractive.
In the article “Fabrication of 45° Optical Mirrors on <100> Silicon Using Surfactant-added TMAH Solution” M. Semikura and H. Naruse, Transducer '99; Jun. 7-10, 1999, Sendai Japan, a mirror fabrication method is described in which the silicon support is etched chemically by an anisotropic agent. According to this method, the silicon support has an orientation of <100> and is etched, through a suitable oxide mask formed on its external surface, with a solution (at a temperature of 90° C.) containing the anisotropic agent Tetramethylammonium Hydroxide (TMAH) to which a surfactant has been added. The TMAH agent cuts into the silicon substrate <100> giving rise to free parallel walls with crystalline planes {110}. According to the authors, this chemical etching makes it possible to obtain a wall parallel to the planes {110 and, therefore, inclined at 45° in relation to the external surface of the substrate <100>.
The authors of the article report that they obtained, with the above-mentioned method, walls at 45° having a root-mean-square of roughness equal to 50 nm and peak-to-valley values of around 200 nm.
It should be noted that these roughness values make the method proposed in the article unsuitable for the production of mirrors destined for photonic applications, such as those mentioned as an example above. In fact, this type of application necessitates a reflection quality higher than that obtainable with mirror walls having the roughness indicated in the article.
SUMMARY OF THE INVENTION
An embodiment of the present invention is to propose a method for manufacturing reflecting devices which overcomes the limits and disadvantages of the methods described above with reference to the known art.
Other embodiments of the invention include a device for the reflection of electromagnetic radiation and a system using a device for the reflection of electromagnetic radiation.
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Masayuki Sekimura, “Anisotropic Etching of Surfactant-Added Tmah Solution”, Micro Electo Mechanical Systems, 1999, Twelfth IEEE International Conference in Orlando, Florida, pp. 650-655.
Ernest Bassous “Fabrication of Novel Three-Dimensional Microstructures by the Anisotropic Etching of (100) and (110) Silicon”, IEEE Transactions on Electron Devices, vol. ED 25. No. 10 Oct. 1978, pp. 1178-1185.
Kyoung-Sun Seo et al. “Tunable Micromirror Switches Using (110) Silicon Wafer” Seventh International Symposium on Micro Machine and Human Science, pp. 73-77.
L. Smith et al. “Silicon Micromachined (2×2) Opto Coupler”, Optical Interconnections and Networks 1990, SPIE vol. 1281.
Carola Strandman et al. “Fabrication of 45° Mirrors Together with Well-Defined V-Grooves Using Wet Anisotropic Etching of Silicon” Journal of Microelectromechanical Systems, Dec. 1995, No. 4.
Yuji Uenishi et al. “Micro-opto-mechanical Devices Fabricated by Anisotropic Etching of (110) Silicon” Journal of Micromechanics & Micorengineering, vol. 5, 1995.
Ylva Backlund “New Shapes in (100) Si Using KOH and EDP Etches” Journal of Micromechanics & Microengineering, vol. 2, No. 2, Jun. 1992.
L. Rosengren et al. “Micromachined Optical Planes and Reflectors in Silicon” Sensors and Actuators, Apr. 1, 1994, Nos. 1/3.
Barlocchi Gabriele
Corona Pietro
Mastromatteo Ubaldo
Villa Flavio
Graybeal Jackson Haley LLP
Stein Stephen
STMicroelectronics S.R.L.
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