The controlled etching of micro/nano structures is essential for a variety of technological applications, including microelectromechanical systems (MEMS) fabrication. XeF2 is an isotropic and highly selective etching gas used to remove semiconductors (such as Si, Ge) and metals (such as Mo, W) in the fabrication of MEMS and other devices. While the kinetics of XeF2 etching of Si has been widely documented, XeF2 etching of metals is not widely understood. For better process control and device quality, it is important to understand the etching mechanism at the molecular level. In this work, we explore the surface and gas phase chemistry of XeF2 etching of metallic films, focusing on Mo. Studies of the general characteristics of XeF2 etching of Mo blanket films at different sample temperatures and etchant pressures were carried on 1000ÅMo/475ÅSiO2/100ÅNi/glass samples in a standalone etching chamber, then they were analyzed ex-situ by multiple surface sensitive tools. Atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) were used for chemical and morphological analysis of the etched surfaces. Rutherford back scattering (RBS) and medium energy ion scattering (MEIS) were used to measure the thickness of the films and the depth profile of near-surface species after etching. Mo is etched by XeF2 rapidly and selectively. XPS, AFM, and RBS data on the morphology and composition of surfaces after etching at different temperatures and pressures is presented. Data showing how the condition of the surface prior to etching (initial surface) affects the initiation and progress of etching is also discussed. The composition and chemical state of the etched surface (reaction layer) is further investigated by in-vacuo etching and XPS analysis experiments using 3750ÅMo/quartz samples in an integrated etching/analysis system. The XPS studies have clarified issues on the thickness and chemical composition of the reaction layer during etching. The effects of the surface native oxides and adventitious hydrocarbons on etching and re-deposition of etched products were also examined by in-vacuo etching and XPS. Post etching thermal processing and XPS analysis studies were performed to investigate the chemical composition of residues left after etching. These studies have indicated that after etching there are physisorbed and chemisorbed fluorine species that desorb at different temperatures. Downstream mass spectrometry was used to identify the gas phase by-products of the etching process. Since etching is non-uniform and the initial condition of the surface affects the etching process, using time dependencies vs. etched thicknesses is shown to be an unreliable method to measure the rate of etching. Thus, alternative methods, including the total pressure change and a quartz crystal micro balance (QCM), were used to calculate the rate of etching of blanket Mo films. Under the conditions reported here, the rates of etching of blanket films were determined to be 60-75 nm/sec at 25- 90° C. The order of reaction is close to one. The rate of undercut etching, measured on patterned samples, changes significantly (0.5-2.5 æ/min) under different conditions, depending on the etching method, temperature, and pattern size. Mask deformation is observed on certain shapes. Different gas delivery methods were tested and their efficiency is discussed. Both on etching of patterned and blanket films, pulsing of the etchant gas is shown to be a more efficient method for etching than static etching.

Reactions which lead to the solution or volatilization of molybdenum and which are suitable for high-precision etching of patterns in thin films of molybdenum are not well known. In a search for a process for etching cavities in films 1mu thick it has been found that the formation and simultaneous removal of molybdenum trioxide can be achieved by exposure of heated molybdenum films to a mixture of oxygen and hydrogen chloride gases. Etch rates of 1000 to 10,000 A/min have been obtained with specimen temperatures of 400 to 600C and with gas pressures between 0.1 and 1 torr. An etch factor of about 2 has been typical, and the final etched surface has been as smooth if not smoother than the original surface. Aluminum oxide of about 0.1mu thickness has been used as a resist. It is hoped than an electron-exposed organic resist can eventually be adapted for use with this process. Discussion and speculation on the mechanism of formation of the oxide and its removal have been included, as well as discussion of some of the factors which are important in predicting the optimum conditions for etching. A residue of a very thin, adherent layer of MoO2 on partially etched molybdenum surfaces has been a problem, and means for removing this film are discussed. The process appears to have promise for etching with dimensional control accurate to better than 0.1mu in films 1mu thick. Greater precision may be possible in films thinner than 1mu.

Pulsed Laser Deposition (PLD) technique, with its vast tunability in terms of thin film fabrication has been the center of this study. By changing the temporal component of the laser source used for deposition into the femtosecond (fs) regime, interesting structural, morphological changes can be achieved which may prove to be beneficial for photocatalytic applications. In particular, molybdenum oxide thin films, which are the less well-studied and potentially newer candidates for photocatalysis applications have been chosen for investigation. Hence, a detailed characterization study of molybdenum oxide thin films synthesized using femtosecond-based (f-PLD) and nanosecond-based (n-PLD) techniques, was carried out in terms of their structural, morphological, surface chemical/ electronic states and vibrational properties using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The f-PLD technique was found to produce more favorable molybdenum oxide thin films deposited on glass for surface-related applications, in terms of having a higher surface to volume ratio, than the n-PLD technique. A related simultaneous study of substrate-based effect on the thin films produced using n-PLD system, also revealed both variation among the morphological, structural, and electronic (in terms of Mo oxidation state) properties depending upon the nature of the substrate used to synthesize the molybdenum oxide thin films. Special cases of thin films on epitaxial substrates (Si, sapphire) have been characterized to determine the parameters necessary for fabricating highly-textured thin films with large surface-area to volume ratio, which is key to efficient photo-catalysts.

This sequel to the 1978 classic, Thin Film Processes, gives a clear, practical exposition of important thin film deposition and etching processes that have not yet been adequately reviewed. It discusses selected processes in tutorial overviews with implementation guide lines and an introduction to the literature. Though edited to stand alone, when taken together, Thin Film Processes II and its predecessor present a thorough grounding in modern thin film techniques. Provides an all-new sequel to the 1978 classic, Thin Film Processes Introduces new topics, and several key topics presented in the original volume are updated Emphasizes practical applications of major thin film deposition and etching processes Helps readers find the appropriate technology for a particular application

Physics of Thin Films: Advances in Research and Development primarily deals with the influence of ions or optical energy on the deposition, properties, and etching on thin films. The book is a collection of five articles, with one article per chapter. Chapter 1 covers ionized cluster beam deposition; epitaxy; and film-formation mechanism. Chapter 2 discusses the activated reactive evaporation process; the deposition of refractory compounds; the role of plasma in the process; and its applications. Chapter 3 focuses on ion-beam processing of optical thin films; ion sources and ion-surface interactions; and the different kinds of bombardment involved. Chapter 4 deals with laser induced etching - its mechanisms, methods, and applications. Chapter 5 talks about contacts to GaAs devices; Fermi-level pinning; and heterojunction contacts. The book is recommended for physicists and engineers in the field of electronics who would like to know more about thin films and the progresses in the field.