Manufacture of etched substrates such as infrared detectors

Details Manufacture of etched substrates such as infrared detectors Manufacture of etched substrates such as infrared detectors

1994-10-20

1997-07-15

Dang, Thi

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

15665911, 15666211, 216 41, 216 83, H01L 2100

Patent

active

056479549

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to methods of etch manufacturing elements such as infrared detector elements, in which at least one narrow aperture is etched in a substrate or body. The body may comprise an infrared-sensitive material, particularly but not exclusively, cadmium mercury telluride. However, it is also recognised by the applicants that such an etching process may be applied to other electronic devices, for example those comprising other semiconductor materials.
2. Description of the Prior Art
For many years it has been known to use buffered chemical (isotropic) etchants in the manufacture of electronic devices, including semiconductor devices and infrared detectors. Published United Kingdom patent specification GB-A-1 559 473 describes the manufacture of infrared detector elements of cadmium mercury telluride in which separate body portions are formed for each element by etching slot-shaped apertures through cadmium mercury telluride bodies mounted on a temporary support. On the bodies, an etchant resistant mask of photoresist is provided having windows where the slots are to be etched. In a particular embodiment, the width of the slots is 30 um (micrometers) as finally etched through bodies which themselves have a thickness of 8 um. It is noted that, even if the thickness of the bodies is reduced to 6 um, it is not readily possible to achieve a separation of less than 12 um using such an etchant treatment. For this reason, the separate detector elements defined by this etching treatment in the embodiment of GB-A-1 559 473 are formed on a temporary support from which they are subsequently removed and assembled, with a closer separation, on a substrate of the detector device.


SUMMARY OF THE INVENTION

The present invention is based on a recognition that, by using non-buffered etchants and by constraining the etchant flow in the window, narrow and deep apertures can be formed. Thus, the present invention employs a type of preferential (non-isotropic) etching whereby the etchant in a mask window etches at a faster rate adjacent to the side-walls of the mask.
According to the present invention, there is provided a method of etching a substrate to form a narrow trough of predetermined width therein, the method comprising the steps of masking said substrate with an etch resistant mask having a thickness, said mask including an aperture in register with a location whereat the trough is to be formed, said mask aperture being defined by facing side-walls of height equal to said mask thickness, etching said substrate through said aperture with a non-isotropic etchant providing, adjacent said side-walls, areas of faster etching, and further including the step of forming said mask aperture with said side-walls so spaced that said areas overlap.
The present invention also provides a method of manufacturing an infrared detector having at least one aperture etched in a body comprising infrared-sensitive material, which method includes the steps of (a) providing, on the body, an etchant resistant mask having a window where the aperture is to be etched, the mask having facing side=walls at the window, and (b) subjecting the infrared-sensitive material of the body, via the window, to an etchant which etches at a faster rate adjacent to the side-walls of the mask, wherein the facing side-walls are sufficiently close to each other that the flow of the etchant within the window is constrained by these side-walls of the mask and that the areas of faster etching at the facing side-walls overlap within the window to form a narrow and deep aperture in the body adjacent to the window.
It should be noted that, as described in published International (PCT) patent application WO 91/02270, known chemical etchants when not buffered typically exhibit a property known as preferential etching whereby the etch rates are faster at the side-walls of the etchant resistant mask than in areas further away from these side-walls. This preferential etching was considered an undesirable pr

REFERENCES:
patent: 3817799 (1974-06-01), Schutze et al.
patent: 4128467 (1978-12-01), Fischer
patent: 4521798 (1985-06-01), Baker
patent: 4720738 (1988-01-01), Simmons
patent: 4867842 (1989-09-01), Bohrer et al.
"Thin Film Prozess", by J.L. Vossen and W. Kern, Chemical Etching, Part III-B: Semiconductors, pp. 401, 427, 430-432, tables XII,XIII, Academic Press, 1978.

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