Laser formed connections for integrated circuit chip personalization

The use of lasers for thermal processing of materials has been studied extensively [1,2]. Their use in integrated circuit processing has been limited mainly to material removal (resistor trimming, metal delineation, etc.) [3]. This paper describes a recently discovered process in which nanosecond dye laser pulses are used to form reliable low resistance ohmic contacts between conductors on integrated circuit chips. In particular, connections have been formed between the aluminum and diffused silicon layers of a conventional MOS structure (Fig. 1). The key to the connection process is the use of short laser pulses (2-6 ns) which are capable of redistributing materials in a microscopic region without damaging heat sensitive structures surrounding that region. This process of connecting initially isolated structures makes it possible to personalize integrated circuit chips after fabrication without the use of high voltages, high currents or decoding circuitry. Moreover the process allows isolation of propagating faults such as short circuits. The rapid turnaround time of this approach is attractive for ROS and PLA personalization [4] and makes chip repair and the interconnecting of good working parts at the chip or wafer level possible. The purpose of this paper is to describe experimental studies of these laser formed connections with an emphasis on the mechanism, reliability and reproducibility of the process.