Laser Machining of Thin Films and Integrated Circuits

The steps to fabricate thin film passive elements and interconnecting circuitry on hard substrates are well documented. 1 - 2 These procedures, defining resistor geometry and interconnecting circuitry, resistor trim385 386 T H E HELL SYSTEM TECHNICAL JOURNAL, MARCH 10(18 ming to value, and capacitor fabrication, are the essential steps for producing precise integrated circuits. It is our intention to show t h a t a laser can be used to vaporize, in a controlled manner, thin film structures, and t h a t it therefore might be capable of supplementing or performing these four processes; or it might be used to supplement photolithography by directly machining thin film masks for making circuits by photochemical methods. We studied methods for performing these steps with a continuous neodymium doped yttrium-aluminum-garnet (YA^G:Nd or YAG) laser. Laboratory work has demonstrated the feasibility of fabricating circuit building blocks and eliminating m a n y steps for film structures which are common to tantalum integrated circuits; t h a t is, circuits in which the resistive films are compounds of tantalum. Similar techniques will be applicable to other types of circuits. T a n t a l u m thin film resistors have been shaped and trimmed to value with a laser beam. A controlled laser has removed various combinations of thin films from substrates without adverse effects to the substrates. T a n t a l u m films have been thermally oxidized with the YAG laser as the heat source. Controlled parasitic or gap capacitors have been made with specific capacitance up to 4.5 Xl0~ 4 pf per square mil by laser machining narrow lines across thin films.