Effect of different pulse modes during Cl2/Ar inductively coupled plasma etching on the characteristics of nanoscale silicon trench formation

[Display omitted] •The silicon etch rates by Cl2/Ar plasmas are decreased in the sequence of CW, synchronously pulsed, asynchronously pulsed plasma conditions.•The etch selectivity of Si/SiO2 is increased in the sequence of CW, synchronously pulsed, asynchronously pulsed plasma conditions.•The aspect ratio dependent etching (ARDE) and etch profiles are also improved in the sequence of CW, synchronously pulsed, asynchronously pulsed plasma conditions.•The improvement of etch characteristics such as etch selectivity, ARDE, etc. by synchronously pulsed plasmas is related to the enhanced conduction and transport of radicals and byproducts to the etch trench bottoms during the plasma-off period.•The further improvement of those etch characteristics by asynchronously pulsed plasmas is related to the separation of etching cycle into a chemical adsorption period and an etch product removal period. The etch characteristics of silicon trenches masked with various SiO2/Si3N4pattern distances were investigated using synchronously and asynchronously pulse modes in addition to the continuous wave (CW) mode for Ar/Cl2inductively coupled plasmas. By using synchronously and asynchronously pulse modes instead of CW mode, the selectivity between Si and the mask layer was increased by 2 and 10 times, respectively. Also,the etch rate differences between wide and narrow pattern distance patterns (aspect ratio dependent etching, ARDE) was decreased from 35% to 21 and to 8%,respectively. The increased etch selectivity andreduction of ARDE for the synchronously pulsed mode were related to the increased conduction of Cl radicals/byproductsthrough the high aspect ratio trench, therefore, increased chemisorption/byproduct removal on the silicon trench surface during the pulse-off period. For the asynchronously pulsed mode, the further improved etch selectivity and reduced ARDE were believed to be related to the time separated etch cycle composed of Cl chemical adsorption on the silicon trench surface and the removal of the chemisorbed species by ion bombardment. It is believed that, the asynchronously pulsed plasma etching method can be applicable to various next generation deep nanoscale device fabrication requiring high etch selectivity and low ARDE.