Paper PS2-WeM10
Production-Worthy Pulsed ICP Plasma Processes

Wednesday, October 22, 2008, 11:00 am, Room 306

The transition to 45nm and smaller technologies has triggered intensive research effort among academic and industrial communities in search of wider range of plasma operating conditions aiming to improve etch processes for finer features. Pulsed radio frequency (PRF) plasmas are promising to achieve such a goal. It has been demonstrated through numerical modeling and basic experimental studies that PRF plasma might exhibit higher selectivity, improved uniformity, and minimal charge damage in many etch processes. However, due to the lack of efficient RF power delivery, PRF has only been utilized in a limited number of large-scale commercial applications. Particularly, two main PRF regimes were utilized in inductively coupled plasma (ICP) reactors. In the first, the source operates in the continuous wave (CW) RF mode while the bias operates in the PRF mode. In the second, the source power is pulsed while having the bias operating in the CW mode. The main challenge has been to minimize the amount of reflected power. Specifically, high bias reflected power was observed for low-pressure processes with source pulsing, in which time-modulation of the source power is highly coupled to the bias. The high reflected power is mainly due to the mechanical nature of conventional dynamic matching networks used to reduce the reflected power. The response time of the mechanical adjustment is of the order of hundreds of milliseconds. Hence, the match cannot track the changes in the time-modulated power as the pulse frequencies of interest are greater than 1kHz. There is a vital need for new capability to reduce the reflected power in sub-millisecond time scale. Recently, we have developed production-worthy, reliable and robust PRF plasma operation in a commercial ICP reactor that provides an expanded window of operation by establishing multiple techniques for optimizing RF power delivery in PRF mode. By so doing the matching response time is reduced to as low as a few microseconds. Accordingly, larger number of etch processes operating at pulsed plasma mode are feasible. The robustness of the system is manifested by its ability to provide a variety of RF modes of operation, furnishing more flexibility in etch processes design. By utilizing these modes in ICP reactor, it was demonstrated that one can improve uniformity, enhance selectivity and eliminate micro-trenching in real production etch processes. Supporting plasma modeling and diagnostics will be discussed.