Browse Prior Art Database

Etch Completion Indication

IP.com Disclosure Number: IPCOM000077388D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Chwalow, ML: AUTHOR

Abstract

The complete etching of contact and diffusion holes in the insulating layer formed on the surface of a semiconductor substrate can be determined by noting the change in acceptance angle of a light beam, which traverses an optical path confined between the oxide layers which are formed on both surfaces of the semiconductor. This technique is based on the principle that the optical path within a material, having a high index of refraction, will change if the medium surrounding the material is converted or replaced by another medium, which has a different refractive index than the first medium.

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Etch Completion Indication

The complete etching of contact and diffusion holes in the insulating layer formed on the surface of a semiconductor substrate can be determined by noting the change in acceptance angle of a light beam, which traverses an optical path confined between the oxide layers which are formed on both surfaces of the semiconductor. This technique is based on the principle that the optical path within a material, having a high index of refraction, will change if the medium surrounding the material is converted or replaced by another medium, which has a different refractive index than the first medium.

In the figure, silicon wafer 1 is initially coated on both sides by a silicon dioxide layer 2. The wafer is immersed in an etchant 3 which is disposed in container 4. A silicon wafer has an index of refraction of 3.5; the silicon dioxide has an index of 1.49 and the etchant has an index of refraction of 1.35. The etchant is typically buffered hydrofluoric acid. A beam from filament 6 is focused into wafer 11 by lens 7. The light will reflect off the sides of the wafer and emanate from the wafer at an exit angle of theta(i).

As the etching proceeds, some of the oxide dissolves, leaving some of the surfaces of the semiconductor exposed directly to the etchant. Because of the lower index of refraction of the etchant than the oxide, the final exit angle theta(f), is reduced. This difference in exit angles can be detected by a suitably placed photodetect...