Part I: Background and Fundamentals Introduction, Mohamed Gad-el-Hak, University of Notre Dame Scaling of Micromechanical Devices, William Trimmer, Standard MEMS, Inc., and Robert H. Stroud, Aerospace Corporation Mechanical Properties of MEMS Materials, William N. Sharpe, Jr., Johns Hopkins University Flow Physics, Mohamed Gad-el-Hak, University of Notre Dame Integrated Simulation for MEMS: Coupling Flow-Structure-Thermal-Electrical Domains, Robert M. Kirby and George Em Karniadakis, Brown University, and Oleg Mikulchenko and Kartikeya Mayaram, Oregon State University Liquid Flows in Microchannels, Kendra V. Sharp and Ronald J. Adrian, University of Illinois at Urbana-Champaign, Juan G. Santiago and Joshua I. Molho, Stanford University Burnett Simulations of Flows in Microdevices, Ramesh K. Agarwal and Keon-Young Yun, Wichita State University Molecular-Based Microfluidic Simulation Models, Ali Beskok, Texas A&M University Lubrication in MEMS, Kenneth S. Breuer, Brown University Physics of Thin Liquid Films, Alexander Oron, Technion, Israel Bubble/Drop Transport in Microchannels, Hsueh-Chia Chang, University of Notre Dame Fundamentals of Control Theory, Bill Goodwine, University of Notre Dame Model-Based Flow Control for Distributed Architectures, Thomas R. Bewley, University of California, San Diego Soft Computing in Control, Mihir Sen and Bill Goodwine, University of Notre Dame Part II: Design and Fabrication Materials for Microelectromechanical Systems Christian A. Zorman and Mehran Mehregany, Case Western Reserve University MEMS Fabrication, Marc J. Madou, Nanogen, Inc. LIGA and Other Replication Techniques, Marc J. Madou, Nanogen, Inc. X-Ray-Based Fabrication, Todd Christenson, Sandia National Laboratories Electrochemical Fabrication (EFAB), Adam L. Cohen, MEMGen Corporation Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS, Robert S. Okojie, NASA Glenn Research Center Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide, Glenn M. Beheim, NASA Glenn Research Center Microfabricated Chemical Sensors for Aerospace Applications, Gary W. Hunter, NASA Glenn Research Center, Chung-Chiun Liu, Case Western Reserve University, and Darby B. Makel, Makel Engineering, Inc. Packaging of Harsh-Environment MEMS Devices, Liang-Yu Chen and Jih-Fen Lei, NASA Glenn Research Center Part III: Applications of MEMS Inertial Sensors, Paul L. Bergstrom, Michigan Technological University, and Gary G. Li, OMM, Inc. Micromachined Pressure Sensors, Jae-Sung Park, Chester Wilson, and Yogesh B. Gianchandani, University of Wisconsin-Madison Sensors and Actuators for Turbulent Flows. Lennart Loefdahl, Chalmers University of Technology, and Mohamed Gad-el-Hak, University of Notre Dame Surface-Micromachined Mechanisms, Andrew D. Oliver and David W. Plummer, Sandia National Laboratories Microrobotics Thorbjoern Ebefors and Goeran Stemme, Royal Institute of Technology, Sweden Microscale Vacuum Pumps, E. Phillip Muntz, University of Southern California, and Stephen E. Vargo, SiWave, Inc. Microdroplet Generators. Fan-Gang Tseng, National Tsing Hua University, Taiwan Micro Heat Pipes and Micro Heat Spreaders, G. P. "Bud" Peterson, Rensselaer Polytechnic Institute Microchannel Heat Sinks, Yitshak Zohar, Hong Kong University of Science and Technology Flow Control, Mohamed Gad-el-Hak, University of Notre Dame) Part IV: The Future Reactive Control for Skin-Friction Reduction, Haecheon Choi, Seoul National University Towards MEMS Autonomous Control of Free-Shear Flows, Ahmed Naguib, Michigan State University Fabrication Technologies for Nanoelectromechanical Systems, Gary H. Bernstein, Holly V. Goodson, and Gregory L. Snider, University of Notre Dame Index

The MEMS Handbook

This paper provides an overview on the current understanding of electromigration in metals. The discussion is first focused on studies in bulk metals and alloys. This part includes a thermodynamic formulation of electromigration, a kinetic analysis of the atomic processes and a review of the theory. In addition, experimental results in interstitial and substitutional systems are summarised. The second part of the paper reviews the studies in metallic thin films. This emerged as an important area of electromigration studies since the late 1960s when electromigration damage was found to cause failure of conductor lines in integrated circuits. The discussion will review first the basic nature of electromigration in thin films with emphasis on the role of grain boundaries in mass transport and damage formation. Then the materials issues of electromigration will be explored according to the scaling trends in VLSI technology. Finally, the recent results of electromigration in fine lines and device contacts of dimensions in the micrometre range are discussed.

https://iopscience.iop.org/article/10.1088/0034-4885/52/3/002/pdf

Electromigration in metals

Vaporizable material is supported within a vessel to promote contact of an introduced gas with the vaporizable material, and produce a product gas including vaporized material. A heating element supplies heat to a wall of the vessel to heat vaporizable material disposed therein. The vessel may comprise an ampoule having a removable top. Multiple containers defining multiple material support surfaces may be stacked disposed within a vessel in thermal communication with the vessel. A tube may be disposed within the vessel and coupled to a gas inlet. Filters, flow meters, and level sensors may be further provided. Product gas resulting from contact of introduced gas with vaporized material may be delivered to atomic layer deposition (ALD) or similar process equipment. At least a portion of source material including a solid may be dissolved in a solvent, followed by removal of solvent to yield source material (e.g., a metal complex) disposed within the vaporizer.

Method and apparatus to help promote contact of gas with vaporized material

Apparatus and method for volatilizing a source reagent susceptible to particle generation or presence of particles in the corresponding source reagent vapor, in which such particle generation or presence is suppressed by structural or processing features of the vapor generation system. Such apparatus and method are applicable to liquid and solid source reagents, particularly solid source reagents such as metal halides, e.g., hafnium chloride. The source reagent in one specific implementation is constituted by a porous monolithic bulk form of the source reagent material. The apparatus and method of the invention are usefully employed to provide source reagent vapor for applications such as atomic layer deposition (ALD) and ion implantation.

Solid precursor-based delivery of fluid utilizing controlled solids morphology

SiC materials are currently metamorphosing from research and development into a market driven manufacturing product. SiC substrates are currently used as the base for a large fraction of the world production of green, blue, and ultraviolet light-emitting diodes (LEDs). Emerging markets for SiC homoepitaxy include high-power switching devices and microwave devices for S and X band. Applications for heteroepitaxial GaN-based structures on SiC substrates include LEDs and microwave devices. In this paper we review the properties of SiC, assess the current status of substrate and epitaxial growth, and outline our expectations for SiC in the future.

SiC materials-progress, status, and potential roadblocks

The room‐temperature electrical resistivity, grain size, and impurity content of tungsten films deposited at low pressure on silicon wafers from tungsten hexafluoride and hydrogen reactants were determined These properties were examined as functions of deposition temperature and film thickness The resistivity is independent of thickness at a value of approximately 135 μΩ cm for films deposited at 300 °C For films deposited at 400 °C, the resistivity decreases from 24 to 85 μΩ cm as thickness increases from 0075 to 1 μm The resistivity behavior is interpreted in terms of grain‐boundary scattering with a zero reflection coefficient for the 300 °C films For the 400 °C films, a reflection coefficient that decreases from 067 to 038 over the above thickness range and a linear dependence of grain size on thickness are utilized For both deposition temperatures, the grain size exhibits a rapid initial growth to 30 nm followed by growth at a slope of 032 with respect to thickness The rapid initial growth is associated with the rapid, self‐limiting tungsten hexafluoride/silicon reaction The oxygen content of the films tracks the trend of the reflection coefficient in that it increases with increased deposition temperature or decreased film thickness Evidence suggests that the oxygen is located predominantly at grain boundaries and may be the primary determinant of boundary scattering Fluorine is found in films at concentrations (003–005 at %) similar to those of oxygen but does not vary with thickness and decreases with increased deposition temperature No evidence is found for surface scattering of carriers suggesting that all are specularly scattered Grain‐boundary scattering, with a constant reflection coefficient, adequately interprets previously published data Utilizing such results, together with the present ones, leads to the conclusions that the grain size is relatively independent of deposition temperature while the intragrain resistivity decreases with temperature and approaches the bulk value for 600 °C deposition

Resistivity, grain size, and impurity effects in chemically vapor‐deposited tungsten films

The effect of barrier and porous anodizations, either singly or sequentially, on the electromigration resistance of aluminum films was characterized. Samples were tested for current densities in the 4×105−2×106‐A/cm2 range and temperatures between 150 and 280°C with the median failure time being used as a basis for comparison of lifetimes. An initial barrier anodization was found to be necessary in order to consistently enhance lifetime. The addition of a porous layer as well led to the best result—an increase in lifetime by a factor of 23 at 227°C. All lifetime increases were attributable to increased activation energy for the electromigration‐failure process. An increase of 0.14 eV was obtained for the double anodic structure. Results for structures having a barrier layer adjacent to aluminum were considered in terms of surface sealing of the aluminum and/or response to mechanical constraints of the overlayer. Direct porous anodization resulted in preferential oxidation at grain boundaries, thereby wide...

Effect of structure and processing on electromigration‐induced failure in anodized aluminum

The low‐pressure chemical vapor deposition of phosphorus‐doped silicon films on oxidized silicon wafers was investigated as a function of phosphine/silane mole ratio, silane partial pressure, temperature, and wafer spacing. The deposition rate decreases, concomitant with increased phosphorus incorporation, as the mole ratio increases. The deposition rate tends to saturate or vary linearly with silane partial pressure for undoped and heavily doped films, respectively. This, together with differing deposition‐rate activation energies of 1.5 and 2.0 eV for undoped and doped films, respectively, is indicative of different reaction mechanisms in the two regimes. As the mole ratio increases, the deposition rate becomes increasingly dependent on the wafer spacing and the radial position on a wafer. Because phosphorus incorporation varies inversely with deposition rate, it develops similar dependencies on wafer spacing and radial position. The majority of these observations are interpretable in terms of a model that has been defined for the growth of oxide from the silane‐oxygen reaction where the phosphorus and oxygen play analogous roles. The resistivity of annealed films decreases with increased phosphorus incorporation (mole ratio) and for 0.5‐μm‐thick films reaches a minimum value of approximately 440 μΩ cm at about 1021 phosphorus atoms cm−3. The resistivity decreases with increasing deposition temperature which may be attributable to one or a combination of the decreased phosphorus incorporation at higher temperature or deposition rate, or decreased grain size at higher temperature. The decrease in resistivity with increased thickness is attributed to increased grain size with increasing thickness. At least for thicknesses less than 0.5 μm, lower resistivity is achieved by in situ doping than by doping of films subsequent to deposition.

Deposition and electrical properties of in situ phosphorus‐doped silicon films formed by low‐pressure chemical vapor deposition

Epitaxial beta SiC film formation on SiC by reactive evaporation or sputtering at low temperature

LOW‐TEMPERATURE EPITAXY OF β‐SiC BY REACTIVE DEPOSITION

The growth of silicon films by low pressure chemical vapor deposition in an unique vertical‐flow reactor and in a conventional tube reactor is studied, with emphasis on the vertical‐flow reactor. For a hydrogen‐carried silane process in the vertical‐flow reactor, the growth rate depends on both the partial pressure and the flow rate of silane. A growth rate expression incorporating both of these parameters is derived which accounts for a nearly linear dependence on either parameter for small values and saturation at large values. No dependence on hydrogen partial pressure is observed. An Arrhenius‐type dependence of growth rate on temperature is observed for both type of reactors, with an activation energy of 1.5 eV. Thickness uniformity of the films deposited in the vertical‐flow reactor is compared to that found in the conventional reactor. For high temperatures (above 650 °C) depletion effects degrade the thickness uniformity of the deposited films. Such effects are more pronounced in the conventional reactor than in the vertical‐flow reactor. These effects can be attributed to the shorter gas flow path in the vertical‐flow reactor. The vertical‐flow reactor can be operated without a temperature gradient along the deposition chamber so that uniform film properties can be obtained over the entire load.

Arthur J. Learn

Papers

Resistivity, grain size, and impurity effects in chemically vapor‐deposited tungsten films

Effect of structure and processing on electromigration‐induced failure in anodized aluminum

Deposition and electrical properties of in situ phosphorus‐doped silicon films formed by low‐pressure chemical vapor deposition

LOW‐TEMPERATURE EPITAXY OF β‐SiC BY REACTIVE DEPOSITION

Deposition properties of silicon films formed from silane in a vertical‐flow reactor