A formation of nanostructured anodic oxide on the silicon surface

Background. In modern microelectronics, silicon remains the main material in the production of semiconductor devices and integrated microcircuits. This is largely due to the physicochemical properties of silicon oxide - $SiO_{2}$, which determines a wide range of its application as an universal dielectric. Due to the possibility of forming porous layers, silicon is also a promising material for the creation of lithium-ion batteries, supercapacitors, solar cells, etc. One of the main methods for preparing silicon for such purposes is the method of electrochemical anodic etching. The patterns of coatings formation by this method are largely determined by the modes of anodic treatment and the microstructure of the treated surface. Materials and methods. To analyze the growth features of anodic oxide films, we used n-type Si single crystal samples. Distilled water was used as an electrolyte. To obtain a higher concentration of defects in the surface layer of silicon, some of the samples were subjected to isothermal annealing at a temperature of 900$^{\circ}$C for 90 min under 4 reference loads of 4.8 N. The analysis of the surface topology of oxide films was carried out by atomic force microscopy (AFM). Results. It is shown that as a result of anodic treatment, the silicon surface is covered with a nanostructured oxide film. The surface of the film is presented in the form of islands, with a base size of 180-600 nm and a height of 25-80 nm. The nonplanar nature of the oxide layer is associated with the formation of oxide islands at electrical active sites, namely, the emergence of dislocations on the surface. The similar nature of the growth of the passivating layer on silicon opens up the possibility of a simple controlled growth of structured thin films both by changing the defectiveness of the substrate and the composition of the electrolyte used for anodizing. Conclusions. Thus, we have investigated the morphology of silicon oxide formed by electrochemical anodic oxidation. It was shown by AFM that the film is not planar and is covered with many oxide islands. Moreover, the formation of islands occurs in the places where dislocations emerge on the surface, which is confirmed by the data of analysis of samples with different dislocation densities. The observed kinetics of silicon oxide growth opens up the possibility of forming nanostructured layers with controlled morphology. The defect-selective dissolution of the Si substrate discovered in this work upon changing the working solution (for example, based on HF) can also lead to the formation of macroporous silicon, which remains a promising and actively studied material for electrodes of lithium-ion batteries.