Photoinduced deposition of thin films

Abstract

A new thin film deposition technique has emerged, which is based on various photoinduced effects. It turned out that light can be used in a variety of ways as a unique energy source required to induce reactions leading to deposition. In this article, I describe the present status of the photoinduced deposition technique with emphasis on so-called photochemical vapor deposition (photo-CVD), which has attracted the greatest attention among various photoinduced methods. In this scheme, ultraviolet light is often used to photolyze source gases either in the gas phase or on substrate surfaces. In this case films can be deposited at low temperatures. If lasers are used in photo-CVD, a high degree of area selectivity can be obtained. In this case, pyrolytic reactions induced by substrate heating can be utilized, in addition to photolysis. Low-temperature deposition is possible with plasma processes, but photoexcited processes are characterized by selective excitation with monochromatic light. There are other related methods in photo-CVD, such as Hg photosensitization or vibrational excitation. As a completely different method pulsed-laser evaporation or laser sputtering of solid targets is available. In addition to deposition, the photoinduced effects are utilized to modify solid surfaces. These topics are briefly covered in this article, but photoinduced etching is not mentioned. Semiconductor, metal, and dielectric thin films deposited by various photoinduced methods are explained. This technique has been applied also to device fabrications. The choice of a proper light source is crucially important for successful deposition, and both traditional lamps and modem lasers have been used. In particular, lasers can be used to study reaction processes through spectroscopies, such as laser-induced fluorescence (LIF) or coherent anti-Stokes Raman spectroscopy (CARS).