Laser Machining of Thin Films and Integrated Circuits

The feasibility of using the YAG laser as a tool to thermally machine integrated circuits has been studied. Results suggest that defining the resistor geometry, trimming the resistors to value, fabricating gap capacitors, and defining interconnecting circuitry might be performed by such a laser. Pattern generation by laser machining has been demonstrated on various thin and electroplated films. Vaporized lines (gaps) are readily attainable as fine as 0.25 mil in thin films and 0.4 mil in plated films. Much thinner lines may be obtained under particularly well-controlled conditions. These films may be removed with minimum effect to the substrate surface. The heat-affected region of the substrate may be confined to less than one film thickness. Better laser output control and shorter pulse widths will diminish this thickness. Gap capacitors have been made on sapphire substrates with capacitance approaching 20 pf in 0.04 square inches, and experiments suggest improvements. Tantalum films may be shaped to resistor geometries and trimmed to tolerance by removing metal or by oxidizing the resistive film with the laser. Resistors usually can be trimmed to tolerances of less than ±0.1 per cent. With further development it might be possible to combine these laser machining processes into a single-step, automated fabricating procedure for certain types of integrated circuits. We review some of the technical aspects of this and discuss using Q-spoiled YAG lasers to directly machine masks for photoetching.