Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-01-29
2001-03-20
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C216S042000
Reexamination Certificate
active
06204189
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fabrication of etched facets on semiconductor materials.
BACKGROUND OF THE INVENTION
Devices such as specialized semiconductor optical amplifiers require mirror quality sidewalls, and the success of these devices is strongly dependent on reflectivity of the mirror surface. With the combination of optimized mirror design and crystal growth, and the use of anisotropic ion etching, micron-sized optical microresonators have been fabricated. These capabilities are now also applied to electrically and optically pumped surface-emitting microlasers and other vertical-cavity devices. In order to define the deep structures needed for these applications, highly anisotropic and nonselective ion etching processes must be optimized. Furthermore, improved masking techniques must be devised to produce low-resistance contacts for electrically pumped structures. Chemically assisted ion beam etching (CAIBE), a technique in which the sample is simultaneously subjected to both an ion beam and a reactive gas flux, has been demonstrated to be an extremely anisotropic pattern transfer method. The capabilities of this technique are ideal for solving the problems associated with microfabrication of semiconductor devices, such as vertical-emitting semiconductor lasers, and has already replaced cleaving techniques for making high quality mirror finish sidewalls. For III-V materials, facets can be cleaved in two orthogonal directions along preferred crystal directions. Whereas CAIBE etching can be done anywhere and practically any shape structure can be made including mesas, ridges and wells.
However, new or modified fabrication techniques which are used to produce optically and electrically pumped laser and microresonator arrays are still being sought. A technique known as dry etching can make smooth mirror quality etched surfaces, as well as depth and verticality requirements to semiconductor devices.
SUMMARY OF THE INVENTION
The invention provides a CAIBE method for controlling the verticality of mirrored sidewalls in semiconductor-containing devices by etching the sidewalls of a substrate such as a molecular beam epitaxy (MBE) material. The method correlates such factors as beam collimation and beam energy, the reactive gas (e.g., chlorine) flux at the substrate, the elimination of oxygen-containing species present in a vacuum system and the quality of the masking edge produced during photolithography to provide a quality etch to the surface of the device. The chlorine flux and the ion beam, working in tandem, etch a high quality vertical facet. The mask material can be a positive photoresist and the mask to substrate etch selectivity is above about 15 to 1. Such etch selectivities allow vertical sidewalls of high mirror quality that are at least 5 microns in height.
In a preferred embodiment, a high resolution for vertical sidewalls is achieved by applying optics above UV300 (e.g. UV400 at 20 mW/cm
3
) with a positive photoresist (e.g., AZ 5214-E resist) of thickness from about 1.0 to 1.2 microns in an allowable oxygen-containing atmosphere (e.g., water) of less than about 1×10
−10
Torr. Thermal stability is maintained with a hard bake temperature at least as high or higher than that experienced by the substrate during CAIBE. A chlorine flow is preferred at about 8 to about 14 sccm (e.g., 10 sccm) with two or more chlorine gas jets being employed. Etching is accomplished at a suitable rate with an etch beam energy preferably less than about 500 eV. The finished mirrored vertical surface of the substrate is within about +or −5% from vertical and has a roughness of less than 10 nm, calculated as mean square roughness (Rms) determined by an atomic force microscopic measurement in a field view area of 10 micron×10 micron.
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Dijaili Sol P.
Goward William D.
Petersen Holly E.
Deo Duy-Vu
The Regents of the University of California
Thompson Alan H.
Utech Benjamin L.
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