## 1 Introduction
Opposite to the approach used in Reference [3], we assume the possibility of waveguides crossings and, unlike the NAVOLCHI project, we focus on well-de  
Figure 1: Optical interconnects schemes: (**a**) The scheme without multiplexing (like the NAVOLCHI project [7]), (**b**) The proposed scheme with plasmonic interconnects without multiplexing using vertical cavity surface-emitting lasers (VCSELs) to excite waveguide modes. suitable for mass production--vertical cavity surface-emitting lasers (VCSELs). It is worth noticing, that commercially available VCSELs are already supporting data transmission rates up to 25 Gbit/s in a wide temperature range from 25 to 85 \({}^{\circ}\)C [13]. The proposed interconnects scheme is shown in Figure 1b. The basis for the proposed interconnects is the plasmonic data transmission line-plasmonic waveguide combined with in- and out-coupling structures (input/output diffraction gratings). We outline that such waveguides must support propagation of a plasmonic guided mode over sufficiently large distances and have low scattering loss at waveguides intersections. We demonstrated in the paper below (see Section 3), that the waveguides with numerically optimized parameters meet both the requirements simultaneously. We consider plasmonic waveguides due to its ability to support sufficiently long mode propagation distances, possibility to integrate plasmonic waveguides with electrical contacts of active photonic devices in a natural way [14]. In addition, plasmonic waveguides have the potential of using elements of optical chemical, bio and other sensors due to strong field enhancement near metal waveguide elements [15; 16]. The typical chip-to-chip interconnect length for a system in housing is about 1 mm. In the case of plasmonic waveguides, such a propagation length is achievable only for the so-called LR-DLSPPWs (long-range dielectric-loaded surface plasmon-polariton waveguides), which we consider in this paper. The long-range plasmonic mode propagates along a thin metal film (about 10-20 nm thick) [17; 18; 19; 20], with materials of the same dielectric permittivity on both sides of the film. Since for practical use the plasmonic waveguide must be fabricated on a rigid optically transparent substrate, quartz is usually chosen as such a substrate. To match the dielectric permittivity, the thin metal film can be coated from its upper side with liquid saline solution [21]. By changing the salt concentration, the solution dielectric permittivity can be precisely matched to the substrate's one. An alternative approach is to fabricate an intermediate layer (between the substrate and the metal film) with low dielectric permittivity and deposit a high-dielectric-permittivity layer atop the metal film. Both approaches are not easy-to-use in term of interconnects fabrication, as they require specific materials which are not used in the electronics industry. In our paper, we propose plasmonic long-range waveguides with the widely used material, Al\({}_{2}\)O\({}_{3}\), as a high-index dielectric. To fabricate multilayer Al\({}_{2}\)O\({}_{3}\)-metal structures, a technological process was developed that includes the following basic operations: deposition of thin-film functional layers, e-beam lithography and dry plasma-chemical etching. One of the most critical technology issues of the dielectric-metal-dielectric long-range nanoplasmonic waveguides fabrication is low-damage plasma-chemical etching. The fact is, that the defined stack materials (Al\({}_{2}\)O\({}_{3}\)/Au(Ag)/Al\({}_{2}\)O\({}_{3}\)) require both contradicting etch recipe parameters and gas mixtures, which lead to degradation of ultrathin metal films. The optical and plasmonic properties of thin noble metal films and the mechanisms of their degradation are well studied [22; 23; 24; 25]. In our paper, a multistage and precise process of dry plasma-chemical etching is proposed, which ensures reproducible etching of the multilayer waveguide nanostructures and eliminates the degradation of their optical (plasmonic) properties.