Metallization of nanostructures by High Power Impulse Magnetron Sputtering

In this contribution, we present the use of High Power Impulse Magnetron Sputtering (HiPIMS) for metallization of nanostructures for microelectronics. This work is motivated by meeting the increasing demands on deposition processes due to the increasing density of integration. Shrinking lateral dimensions of the structures more rapidly than vertical dimensions means increasing aspect ratios. There is also a need for deposition of new materials. Traditionally, ionized PVD (I-PVD) has been used for metallization of nanostructures. Unlike most other I-PVD techniques, HiPIMS is compatible with standard magnetron sputtering systems. It may therefore be an attractive alternative to the techniques with additional ionization of the sputtered metal flux. With two examples, we will show the great flexibility of HiPIMS in making conformal deposition vs. directed via filling.First, we show conformal formation of ultrathin Ni films in a modified self-aligned silicide process, thanks to the Ni ionization in HiPIMS. After appropriate annealing, the thickness of the resulting Ni-silicide films could be readily adjusted in the range from 4.7 to 8.6 nm by proper substrate biasing [1]. Good sidewall coverage was also achieved [2].Second, we discuss filling of via holes for vertical stacking at device level. Here, narrow (sub 100 nm) trenches and holes need to be filled with a highly conductive metal. We explore the potential of HiPIMS and determine the maximum aspect ratio that can be filled. In our experiment with Cu, the ionized metal flux fraction is estimated to be about 70% from the substrate from the substrate ion current. A significant improvement over DC sputtering has been achieved, as shown in Fig. 1, with success in filling vias of aspect ratio 1.5. We analyze the influence of ion energy and discuss approaches to further improving the filling process.