Plasma processes have been used for many years in the manufacturing of semiconductors. They have been so far the only technological solution to address the critical dimension control at the nanometer range imposed by the continuous downscaling of the CMOS devices dimensions.

However, the current etch processes are reaching their limits of controlling the etch selectivity and the critical dimensions at the atomic scale. In this study we investigate the potential of pulsed plasmas to further improve dry etching processes.

The experiments are carried out in a commercially available 300 mm AdvantEdgeTM tool from Applied Materials Inc. The inductively coupled plasma is sustained by two RF generators operating at 13.56 MHz, one to generate the plasma and the other mainly to polarize the wafer. These generators have been modified using the PulsyncTM system to allow pulsing at frequencies between 10 Hz and 20 kHz and duty cycles between 10 and 90 %. Even though a delay can be applied between the generators only the synchronous case is studied here. Several modifications of the plasma chamber were carried out in order to use advanced plasma diagnostics like in situ ellipsometry, UV absorption spectroscopy and mass spectroscopy. Furthermore an angle resolved XPS system is connected to the plasma chamber under vacuum allowing quasi in-situ analysis of the wafer surface after etching.

This article focuses on HBr/O2 plasmas dedicated to STI (Shallow Trench Isolation) etch processes. We demonstrate the ability of synchronously pulsed etch plasmas at different frequencies and duty cycles to modify the etched profiles strongly compared to the standard continuous case. Especially experiments carried out at a frequency of 1 kHz and a duty cycle of 20 % show a very distinct alteration. In this case, ellipsometry measurements indicate a sharp increase in time compensated etch rate (etch rate relative to the actual plasma ON time of the etch process). Additionally, the etched profiles show a strongly enhanced quality, in particular a high selectivity, uniformity and a minimization of the aspect ratio dependent etching phenomena. We demonstrate that these improvements are linked to the balance between plasma dissociation and recombination during the ON and OFF time of the pulsed plasma which can directly influence the composition of neutral and ion flux. This balance is controlled by the duty cycle rather than the pulsing frequency.