Browse Prior Art Database

OPTICAL MICROMILLING

IP.com Disclosure Number: IPCOM000026383D
Original Publication Date: 1991-Aug-31
Included in the Prior Art Database: 2004-Apr-05
Document File: 2 page(s) / 131K

Publishing Venue

Xerox Disclosure Journal

Abstract

A method is disclosed to controllably produce surface topographic structures on semiconductor substrates with micron feature sizes over wafer scales. The process consists of photoinduced etching of a substrate surface while exposed to a liquid etchant. The reaction is mediated by photo-excited free carriers, most likely holes, in the substrate which diffuse to the semiconductor surface and allow the reaction to occur. Various semiconductor/etchant systems are known for which the dissolution rate in the dark is essentially zero, whereas the rate under illumination is high. The lateral extent of etching should be limited by the carrier diffusion length. For strongly absorbed light and a high reaction probability at the surface, the minimum feature size should be approximately equal to the optical absorption length (-10Onm).

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XEROX DISCLOSURE JOURNAL

OPTICAL MICROMILLING

Classification Proposed David K. Biegelsen U.S. C1.437/249

Int. C1. HOll21/461

II ///CoverGIass k

Fig.

Lateral Dark Undercuting

\ rlrndanted Laver

Substrate

Light Scattering

Implanted Layer

Substrate

~ long Absorption Length

-1molanted Laver ,

Substrate

Transmission

,,, I \ , f /Transparent Layer

Substrate

Fig.2

Fig.2

Fig.2

Fig.2

XEROX DISCLOSURE JOURNAL - Vol. 16, No. 4 July/August 1991 271

I

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OPTICAL MICROMILLING(Cont'd)

A method is disclosed to controllably produce surface topographic structures on semiconductor substrates with micron feature sizes over wafer scales. The process consists of photoinduced etching of a substrate surface while exposed to a liquid etchant. The reaction is mediated by photo-excited free carriers, most likely holes, in the substrate which diffuse to the semiconductor surface and allow the reaction to occur. Various semiconductor/etchant systems are known for which the dissolution rate in the dark is essentially zero, whereas the rate under illumination is high. The lateral extent of etching should be limited by the carrier diffusion length. For strongly absorbed light and a high reaction probability at the surface, the minimum feature size should be approximately equal to the optical absorption length (-10Onm).

One embodiment of the optical micromill of this disclosure is shown in Fig. 1. A laser is focused on the surface...