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Laser Ablation Tool for Clean Products

IP.com Disclosure Number: IPCOM000038441D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Donelon, JJ: AUTHOR [+4]

Abstract

Ablation debris can be kept away from substrates by laser ablation in a reduced atmosphere or below the claimed threshold pressure. Threshold pressure for laser ablation of polyimide is 20 mTorr of air or 100 mTorr of He. The laser beam entrance window can be kept free from ablation products with a window gas curtain with pressure higher than 1 Torr. This laser etch tool concept keeps both the beam window and substrate free from ablation product contamination. Recently, there has been great interest and development of using laser ablation for etching polymers and metal compounds. In such processes, the ablation etch products are ejected from the irradiated area with translational speed in the order of 105 cm/sec.

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Laser Ablation Tool for Clean Products

Ablation debris can be kept away from substrates by laser ablation in a reduced atmosphere or below the claimed threshold pressure. Threshold pressure for laser ablation of polyimide is 20 mTorr of air or 100 mTorr of He. The laser beam entrance window can be kept free from ablation products with a window gas curtain with pressure higher than 1 Torr. This laser etch tool concept keeps both the beam window and substrate free from ablation product contamination. Recently, there has been great interest and development of using laser ablation for etching polymers and metal compounds. In such processes, the ablation etch products are ejected from the irradiated area with translational speed in the order of 105 cm/sec. If the laser ablation process is carried out in air, the ablated etch product can make multiple collisions with the air molecules and can be backscattered on the parts. This is normally called debris. The debris can obviously affect the adhesion of the material subsequently deposited on the parts. In laser etching of polymers, the debris cannot be removed in water or acetone-like solvents. Thin layers of debris from laser etching of polyimide can easily be etched in a plasma. On the other hand, if the area of polymer to be etched is large, then debris piles up requiring extensive clean up work. A way to avoid debris accumulation is to etch parts in a vacuum. Without the scattering media, the ablated products eject from the parts and will not return. However, it implies that the ablation product will deposit onto the optical window through which the laser beam enters the chamber. Such etch product deposition on the window substantially attenuates the laser beam energy and transmitted through the window is thus not acceptable. It is especially true for etching fine patterns with an optical projection system that no debris should be in the optical path after the imaging lenses. This laser etching system avoids the ablation product deposition on parts and the chamber laser windows. Depending on the size and momentum of the ablation product, the etch product can be kept away from the window by implementing a gas curtain near the optical window. With proper flow and pressure, the product is swept away by the laminar flow near the window. The typical pressure should be around 1 Torr or higher to ensure short mean free paths. To keep a substrate free from debris contamination, the ambient pressure at the sample surface where ablation is occurring should be low (long mean free paths) so the ejected abla...