Browse Prior Art Database

Laser Etching Uniformity and End-Point Detector

IP.com Disclosure Number: IPCOM000061815D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 62K

Publishing Venue

IBM

Related People

Ritsko, JJ: AUTHOR [+2]

Abstract

An important aspect of the laser-assisted chemical etching process for metals is the uniformity of the etching over the large area of the projected image on the part to be etched. A related problem is the requirement of end-point detection. For example, in removing the top Cr layer from a Cr/Cu/Cr sandwich, a detector is needed to determine when the Cr layer has been etched through. Disclosed herein is a very simple inexpensive technique which not only provides end-point detection for the top Cr layer and the thick Cu layer of metallurgy but also can detect and monitor etching uniformity. The laser etching process, as currently practiced, involves exposure of blanket metal films (sandwiches of Cr/Cu/Cr, for example) to halogen gas (usually chlorine).

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Laser Etching Uniformity and End-Point Detector

An important aspect of the laser-assisted chemical etching process for metals is the uniformity of the etching over the large area of the projected image on the part to be etched. A related problem is the requirement of end-point detection. For example, in removing the top Cr layer from a Cr/Cu/Cr sandwich, a detector is needed to determine when the Cr layer has been etched through. Disclosed herein is a very simple inexpensive technique which not only provides end-point detection for the top Cr layer and the thick Cu layer of metallurgy but also can detect and monitor etching uniformity. The laser etching process, as currently practiced, involves exposure of blanket metal films (sandwiches of Cr/Cu/Cr, for example) to halogen gas (usually chlorine). The thin metal chloride which forms on the surface is successively and selectively removed by excimer laser pulses, resulting in a patterned metal structure in unirradiated areas. Accompanying the laser ablation of the copper chloride is intense characteristic optical emission from excited CuCl molecules and Cu atoms which have been formed by dissociation. The emission spectrum shown in Fig. 1 depends on the laser fluence (energy/unit area). However, at all fluences of practical interest (>0.2 Joules/cm2), an emission line appears at 510.4 nm, indicating the presence of Cu atoms. This is indicated in Fig. 1 as "Cu" and clearly shows that Cu is being removed. The presence of this emission is easily detected and separated from all other emission lines, which would be due (for example) to Cr or polymers, with a narrow band interference filter and a photomultiplier tube. Such a simple arrangement could detect the end-point of top Cr etching in Cr/Cu/Cr sandwiches by determining the onset of Cu etching. Similarly it could determine when the Cu is etched through. If operating at the lower fluences, it may be more sensitive to use the molecular CuCl emission at 437 nm in an identical fashion. Either emission at 510.4 nm or 437 nm could also be used to monitor the etching uniformity over the proje...