[17p-E206-1~7] 13.4 Si wafer processing /Si based thin film /Interconnect technology/ MEMS/ Integration technology

△ [17p-E206-6] Printing deposition of thin group-IV films based on ballistic hot electron incidence

〇Ryutaro Suda¹, Mamiko Yagi¹, Akira Kojima¹, Jun-ichi Shirakashi¹, Nobuyoshi Koshida¹ (1.Tokyo Univ. of Agri. & Technol.)

Keywords:Nanocrystalline silicon diode, Ballistic hot electron, Printing deposition

Nanocrystalline silicon (nc-Si) diode acts as a supplier of highly reducing hot electrons. When the nc-Si emitter is driven in metal or semiconducting salt solutions, ballistic hot electrons induce reductive reaction leading to the deposition of thin their films. The reduction proceeds neither with counter electrodes nor gas evolutions contrary to the conventional electroplating. The usefulness of this process has been further enhanced by employing a printing scheme, in which a target substrate is separately located in close proximity to the emitter. It was demonstrated that under this scheme thin Cu, Si, and Ge films were deposited on the target substrates. We report here the results of the printing deposition of thin Si, Ge, and SiGe films. On Cu substrates coated with SiCl₄+solvent mixture solutions, we observed uniform deposition of thin Si films in the same way as metals. Similar thin film deposition was obtained from GeCl₄ solution. In accordance with XPS measurements, thin films are oxidized, though the thin Ge film is not fully oxidized. It is difficult from these results to suppose that thin films are deposited as continuous layers. Possibly the formation of very small nano-clusters occurs at the initial stage of electron incidence and subsequently fast oxidation proceeds in solutions associated with deposition, rather than natural oxidation, though the details of competitive process of nucleation and oxidation should be clarified. The model nano-clusters formation has been supported by Raman spectrum of thin Ge film. We estimated the free energy of a cluster formation, as a function of incident electron energy on a basis of thermodynamic nucleation analysis. The thermodynamic nucleation analyses showed that the electron incidence at energy of 10 eV is a critical factor for triggering the cluster formation. As a related experiment, thin film was deposited using a SiCl₄+GeCl₄ mixture (1:1 in volume ratio) solution, under incidence of electrons with a mean energy of 4 eV. In accordance with the result of EDX measurement, a significantly Ge-rich film (Si: Ge ~ 0.3:0.7) was deposited. Obviously Ge nano-clusters are preferentially formed at low electron energies. This is consistent with our model and the free energy behavior of Si and Ge. As being a clean, low-temperature, damage-less, and power-effective process, the unilateral reduction mode presented here provides alternative means of thin film deposition on versatile substrates.