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Combined Acoustic and Pyroelectric Laser (or E Beam) Drilling Monitor

IP.com Disclosure Number: IPCOM000045361D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Arbach, GV: AUTHOR [+3]

Abstract

Both electromagnetic and acoustic energy arising from a drill site will be sensed by a pyroelectric piezoelectric detector, such as a detector composed of PZT (lead zirconate titanate). During a laser-drilling process, such a detector provides both a reflected light signal and an acoustic signal, which are spaced from each other (delayed) in time. The light signal from the detector can be used to time gate an acoustic signal from the same detector during drilling and/or provide optical alignment information prior to or during drilling. The acoustic signal from the detector may be used to monitor the drilling process for control of drilling variables and/or determination of a drilling endpoint.

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Combined Acoustic and Pyroelectric Laser (or E Beam) Drilling Monitor

Both electromagnetic and acoustic energy arising from a drill site will be sensed by a pyroelectric piezoelectric detector, such as a detector composed of PZT (lead zirconate titanate). During a laser-drilling process, such a detector provides both a reflected light signal and an acoustic signal, which are spaced from each other (delayed) in time. The light signal from the detector can be used to time gate an acoustic signal from the same detector during drilling and/or provide optical alignment information prior to or during drilling. The acoustic signal from the detector may be used to monitor the drilling process for control of drilling variables and/or determination of a drilling endpoint.

Fig. 1 illustrates an embodiment for monitoring laser drilling.

A hollow cylinder 10 of PZT pyroelectric piezoelectric ceramic, radially poled, is suspended above a workpiece 12 at a drill site 11.

Incident light pulses 13 from a laser are focused onto drill site 11 by lens 15. The workpiece 12, illustrated in Fig. 1, comprises a top reflecting layer 17 with an etched hole 19 through which drilling is to be done. Under layer 17 is a material layer 21 to be ablated (drilled). The ole to be drilled should extend to conductor 23 so that subsequent electrical connection can be made to conductor 23 through the drilled hole (sometimes called a via).

A single ring 14 of vertical contact between cylinder 10 and holder 16, the contacting direction being perpendicular to the poling direction 18, helps discriminate against vertical vibrations from the drilling assembly and improves photoacoustic signal discrimination. PZT is used because of its low frequency response and because the response pulse is unipolar, which allows an integration algorithm. PZT is also used because it has pyroelectric behavior. The pyroelectric signal from this same sensor may be used to measure the amount of light scattered into the sensor. The amount of light scattered into She sensor as well as the integrated acoustic signal simultaneously give: (1) the degree of misalignment of an optical drilling pulse and (2) the amount of material ablated. When the drilling is badly off-center so that most of the light is reflected by the surface metallization, the pyroele...