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Multi-level polysilicon surface-micromachining technology: Applications and issues

Description: Polysilicon surface micromachining is a technology for manufacturing Micro-Electro-Mechanical Systems (MEMS) which has, as its basis, the manufacturing methods and tool sets used to manufacture the integrated electronic circuit. This paper describes a three-level mechanical-polysilicon surface-micromachining technology and includes a discussion of the advantages of this level of process complexity along with issues which affect device fabrication and performance. Historically, the primary obstacles to multi-level polysilicon fabrication were related to the severe wafer topography generated by the repetition of film depositions and etching. The introduction of Chemical Mechanical Polishing (CMP) to surface micromachining has largely removed these issues and opened significant avenues for device complexity. Several examples of three-level devices with the benefits of CMP are presented. Of primary hindrance to the widespread use of polysilicon surface micromachining, and in particular microactuation mechanisms, are issues related to the device surfaces. The closing discussion examines the potential of several latter and post-fabrication processes to circumvent or to directly alleviate the surface problems.
Date: August 1996
Creator: Sniegowski, J. J.
Partner: UNT Libraries Government Documents Department

Chemical-mechanical polishing: Enhancing the manufacturability of MEMS

Description: The planarization technology of Chemical-Mechanical-Polishing (CMP), used for the manufacturing of multi-level metal interconnects for high-density Integrated Circuits (IC), is also readily adaptable as an enabling technology in Micro Electro Mechanical Systems (MEMS) fabrication, particularly polysilicon surface micromachining. CMP not only eases the design and manufacturability of MEMS devices by eliminating several photolithographic and film issues generated by severe topography, but also enables far greater flexibility with process complexity and associated designs. Thus, the CMP planarization technique alleviates processing problems associated with fabrication of multi-level polysilicon structures, eliminates design constraints linked with non-planar topography, and provides an avenue for integrating different process technologies. Examples of these enhancements include: an simpler extension of surface micromachining fabrication to multiple mechanical layers, a novel method of monolithic integration of electronics and MEMS, and a novel combination of bulk and surface micromachining.
Date: October 1, 1996
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

MEMS: A new approach to micro-optics

Description: MicroElectroMechanical Systems (MEMS) and their fabrication technologies provide great opportunities for application to micro-optical systems (MOEMS). Implementing MOEMS technology ranges from simple, passive components to complicated, active systems. Here, an overview of polysilicon surface micromachining MEMS combined with optics is presented. Recent advancements to the technology, which may enhance its appeal for micro-optics applications are emphasized. Of all the MEMS fabrication technologies, polysilicon surface micromachining technology has the greatest basis in and leverages the most the infrastructure for silicon integrated circuit fabrication. In that respect, it provides the potential for very large volume, inexpensive production of MOEMS. This paper highlights polysilicon surface micromachining technology in regards to its capability to provide both passive and active mechanical elements with quality optical elements.
Date: December 31, 1997
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Tribological issues of polysilicon surface-micromachining

Description: Polysilicon surface-micromachining is a Micro-Electro-Mechanical Systems (MEMS) manufacturing technology where the infrastructure for manufacturing silicon integrated circuits is used to fabricate micro-miniature mechanical devices. This presentation describes a multi-level mechanical polysilicon surface-micromachining technology and includes a discussion of the issues which affect device manufacture and performance. The multi-level technology was developed and is employed primarily to fabricate microactuated mechanisms. The intricate and complex motion offered by these devices is naturally accompanied by various forms of fraction and wear in addition to the classical stiction phenomena associated with micromechanical device fabrication and usage.
Date: December 1, 1997
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Micromachining technology for advanced weapon systems

Description: An overview of planned uses for polysilicon surface-micromachining technology in advanced weapon systems is presented. Specifically, this technology may allow consideration of fundamentally new architectures for realization of surety component functions.
Date: December 31, 1996
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Chemical mechanical polishing: An enabling fabrication process for surface micromachining technologies

Description: Chemical-mechanical polishing (CMP), once it is set-up and developed in a fabrication line can be readily adapted as a planarization technique for use in polysilicon surface micromachining technology. Although the planarization is a conceptually simple step, the benefit of its inclusion in the overall fabrication process is immense. Manufacturing impediments are removed while novel, expanded processes and designs become possible. The authors anticipate that CMP planarization, in the near future, will become a standard within the MEMS community for polysilicon surface micromachining. In addition, other MEMS fabrication technologies such as bulk micromachining and LIGA can potentially benefit from CMP.
Date: August 1, 1998
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Chemical mechanical polishing: An enabling fabrication process for surface micromachining technologies

Description: Chemical-Mechanical-Polishing (CMP), first used as a planarization technology in the manufacture of multi-level metal interconnects for high-density Integrated Circuits (IC), is readily adapted as an enabling technology in MicroElectroMechanical Systems (MEMS) fabrication, particularly polysilicon surface micromachining. The authors have demonstrated that CMP enhances the design and manufacturability of MEMS devices by eliminating several photolithographic definition and film etch issues generated by severe topography. In addition, CMP planarization readily allows multi-level polysilicon structures comprised of 4- or more levels of polysilicon, eliminates design compromise generated by non-planar topography, and provides an avenue for integrating different process technologies. A recent investigation has also shown that CMP is a valuable tool for assuring acceptable optical flatness of micro-optical components such as micromirrors. Examples of these enhancements include: an extension of polysilicon surface-micromachining fabrication to a 5-level technology, a method of monolithic integration of electronics and MEMS, and optically flat micromirrors.
Date: August 1, 1998
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Surface micromachined sensors and actuators

Description: A description of a three-level mechanical polysilicon surface-micromachining technology including a discussion of the advantages of this level of process complexity is presented. This technology is capable of forming mechanical elements ranging from simple cantilevered beams to complex, interconnected, interactive, microactuated micromechanisms. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Additional features of the Sandia three-level process include the use of Chemical-Mechanical Polishing (CMP) for planarization, and the integration of micromechanics with the Sandia CMOS circuit process. The latter effort includes a CMOS-first, tungsten metallization process to allow the CMOS electronics to withstand high-temperature micromechanical processing. Alternatively, a novel micromechanics-first approach wherein the micromechanical devices are processed first in a well below the surface of the CMOS starting material followed by the standard, aluminum metallization CMOS process is also being pursued. Following the description of the polysilicon surface micromachining are examples of the major sensor and actuator projects based on this technology at the Microelectronics Development Laboratory (MDL) at Sandia National Laboratories. Efforts at the MDL are concentrated in the technology of surface micromachining due to the availability of and compatibility with standard CMOS processes. The primary sensors discussed are a silicon nitride membrane pressure sensor, hot polysilicon filaments for calorimetric gas sensing, and a smart hydrogen sensor. Examples of actuation mechanisms coupled to external devices are also presented. These actuators utilize the three-level process (plus an additional passive level) and employ either surface tension or electrostatic forces.
Date: August 1, 1995
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Microfabricated actuators and their application to optics

Description: Several authors have given overviews of microelectromechanical systems, including microactuators. In our presentation we will review some of these results, and provide a brief description of the basic principles of operation, fabrication, and application, of a few selected microactuators (electrostatic and surface tension driven). We present a description of a three-level mechanical polysilicon surface-micromachining technology with a discussion of the advantages of this level of process complexity. This technology, is capable of forming complex, batch-fabricated, interconnected, and interactive, microactuated micromechanisms which include optical elements. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Two examples of microactuators fabricated using this process are provided to illustrate the capabilities and usefulness of the technology. The first actuator is an example of a novel actuation mechanism based on the effect of surface tension at these micro-scale dimensions and of a microstructure within a microstructure. The second is a comb-drive-based microengine which has direct application as a drive and power source for micro optical elements, specifically, micro mirrors and micro shutters. This design converts linear oscillatory motion from electrostatic comb drive actuators into rotational motion via a direct linkage connection. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism.
Date: December 31, 1994
Creator: Sniegowski, J.J. & Garcia, E.J.
Partner: UNT Libraries Government Documents Department

Microfabricated microengine for use as a mechanical drive and power source in the microdomain and fabrication process

Description: A microengine uses two synchronized linear actuators as a power source and converts oscillatory motion from the actuators into rotational motion via direct linkage connection to an output gear or wheel. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism. The microengine can be operated at varying speeds and its motion can be reversed. Linear actuators are synchronized in order to provide linear oscillatory motion to the linkage means in the X and Y directions according to a desired position, rotational direction and speed of said mechanical output means. The output gear has gear teeth on its outer perimeter for directly contacting a micromechanism requiring mechanical power. The gear is retained by a retaining means which allows said gear to rotate freely. The microengine is microfabricated of polysilicon on one wafer using surface micromachining batch fabrication.
Date: December 31, 1994
Creator: Garcia, E.J. & Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Multi-layer enhancement to polysilicon surface-micromachining technology

Description: A multi-level polysilicon surface-micromachining technology consisting of 5 layers of polysilicon is presented. Surface topography and film mechanical stress are the major impediments encountered in the development of a multilayer surface-micromachining process. However, excellent mechanical film characteristics have been obtained through the use of chemical-mechanical polishing for planarization of topography and by proper sequencing of film deposition with thermal anneals. Examples of operating microactuators, geared power-transfer mechanisms, and optical elements demonstrate the mechanical advantages of construction with 5 polysilicon layers.
Date: October 1, 1997
Creator: Sniegowski, J.J. & Rodgers, M.S.
Partner: UNT Libraries Government Documents Department

A manufacturing method for multi-layer polysilicon surface-micromachining technology

Description: An advanced manufacturing technology which provides multi-layered polysilicon surface micromachining technology for advanced weapon systems is presented. Specifically, the addition of another design layer to a 4 levels process to create a 5 levels process allows consideration of fundamentally new architecture in designs for weapon advanced surety components.
Date: January 1, 1998
Creator: Sniegowski, J.J. & Rodgers, M.S.
Partner: UNT Libraries Government Documents Department

IC-Compatible Technologies for Optical MEMS

Description: Optical Micro Electro Mechanical Systems (Optical MEMS) Technology holds the promise of one-day producing highly integrated optical systems on a common, monolithic substrate. The choice of fabrication technology used to manufacture Optical MEMS will play a pivotal role in the size, functionality and ultimately the cost of optical Microsystems. By leveraging the technology base developed for silicon integrated circuits, large batches of routers, emitters, detectors and amplifiers will soon be fabricated for literally pennies per part. In this article we review the current status of technologies used for Optical MEMS, as well as fabrication technologies of the future, emphasizing manufacturable surface micromachining approaches to producing reliable, low-cost devices for optical communications applications.
Date: April 30, 1999
Creator: Krygowski, T.W. & Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Surface micromachined microengine as the driver for micromechanical gears

Description: The transmission of mechanical power is often accomplished through the use of gearing. The recently developed surface micromachined microengine provides us with an actuator which is suitable for driving surface micromachined geared systems. In this paper we will present aspects of the microengine as they relate to the driving of geared mechanisms, issues relating to the design of micro gear mechanisms, and details of a design of a microengine-driven geared shutter mechanism.
Date: May 1, 1995
Creator: Garcia, E.J. & Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

An application of mechanical leverage to microactuation

Description: Preliminary results on the use of mechanical advantage to convert a short-displacement, high-force actuation mechanism into a long-displacement, medium-force actuator are presented. This micromechanical, mechanically-advantaged actuator is capable of relatively large displacement and force values. The target design values are lever ration of 17.5:1 leading to a {plus_minus}17.5 {mu}N of force throughout providing no less than 2.25 {mu}N of force throughout actuator`s range of motion for an applied voltage of less tan 50 volts. The basis for the mechanical advantage is simple levers with fulcrums.
Date: December 31, 1994
Creator: Sniegowski, J.J. & Smith, C.
Partner: UNT Libraries Government Documents Department

Characterization of the embedded micromechanical device approach to the monolithic integration of MEMS with CMOS

Description: Recently, a great deal of interest has developed in manufacturing processes that allow the monolithic integration of MicroElectroMechanical Systems (MEMS) with driving, controlling, and signal processing electronics. This integration promises to improve the performance of micromechanical devices as well as lower the cost of manufacturing, packaging, and instrumenting these devices by combining the micromechanical devices with a electronic devices in the same manufacturing and packaging process. In order to maintain modularity and overcome some of the manufacturing challenges of the CMOS-first approach to integration, we have developed a MEMS-first process. This process places the micromechanical devices in a shallow trench, planarizes the wafer, and seals the micromechanical devices in the trench. Then, a high-temperature anneal is performed after the devices are embedded in the trench prior to microelectronics processing. This anneal stress-relieves the micromechanical polysilicon and ensures that the subsequent thermal processing associated with fabrication of the microelectronic processing does not adversely affect the mechanical properties of the polysilicon structures. These wafers with the completed, planarized micromechanical devices are then used as starting material for conventional CMOS processes. The circuit yield for the process has exceeded 98%. A description of the integration technology, the refinements to the technology, and wafer-scale parametric measurements of device characteristics is presented. Additionally, the performance of integrated sensing devices built using this technology is presented.
Date: October 1, 1996
Creator: Smith, J.H.; Montague, S.; Sniegowski, J.J. & Murray, J.R.
Partner: UNT Libraries Government Documents Department

Performance tradeoffs for a surface micromachined microengine

Description: An electromechanical model of Sandia`s microengine is developed and applied to quantify critical performance tradeoffs. This is done by determining how forces impact the mechanical response of the engine to different electrical drive signals. To validate the theoretical results, model-based drive signals are used to operate actual engines, where controlled operation is achieved for the following cases: (1) spring forces are dominant, (2) frictional forces are dominant, (3) linear inertial forces are dominant, (4) viscous damping forces are dominant, and (5) inertial load forces are dominant. Significant improvements in engine performance are experimentally demonstrated in the following areas: positional control, start/stop endurance, constant speed endurance, friction load reduction, and rapid actuation of inertial loads.
Date: October 1, 1996
Creator: Miller, S.L.; Sniegowski, J.J.; LaVigne, G. & McWhorter, P.J.
Partner: UNT Libraries Government Documents Department

A novel method to characterize the elastic/plastic deformation response of thin films

Description: A novel experimental/numerical test method has been developed which allows accurate characterization of the elastic and large-strain plastic mechanical response of thin films. Silicon micromachining techniques have been used to fabricate isolated film features which are mechanically tested using our ultralow-load indentation test system. Macro-scale laboratory testing and finite element analysis were employed to optimize the design of the geometric feature used and to benchmark our analysis capabilities. A simple rigid-plastic geometric analysis of our test structure is developed and applied to the observed force-displacement response, allowing us to extract the uniaxial inelastic stress-strain response of micrometer-scale thin film structures. To our knowledge, this is the first time that the inelastic deformation behavior of metal alloy features of this size scale has been quantitatively determined.
Date: July 1, 1996
Creator: Bourcier, R.J.; Sniegowski, J.J. & Porter, V.L.
Partner: UNT Libraries Government Documents Department

Thin teflon-like films for eliminating adhesion in released polysilicon microstructures

Description: This paper presents a method for depositing thin Teflon-like films using a commercial plasma reactor to eliminate adhesion or stiction in released polysilicon microstructures. A Lam 384T oxide etch system is used in a remote plasma mode with commercially available trifluoromethane (CHF{sub 3}) to deposit thin hydrophobic films around and under released microstructures. Hard, uniform, Teflon-like films which penetrate into undercuts beneath structures have been produced. Thus far, surfaces beneath gears as large as 1600 micron diameter with a gap of 2.0 microns are hydrophobic after being exposed to plasma treatment. These Teflon-like coatings have been shown to reduce the coefficient of friction from 1.0 to 0.07.
Date: December 31, 1996
Creator: Smith, B.K.; Sniegowski, J.J. & LaVigne, G.
Partner: UNT Libraries Government Documents Department

Macrodesign for microdevices: Polysilicon surface-micromachining technology, applications and issues

Description: The intent of this tutorial is to overview the technology of multi-level polysilicon surface micromachining, to present examples of devices which fully utilize this level of complexity, and to discuss what they believe to be significant issues which are not fully resolved. Following this intent, the tutorial consists of four sections. The first is an introduction and description of multi-level polysilicon surface micromachining and its potential benefits. Specifically, the inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. The second section introduces wafer planarization by CMP as a process tool for surface micromachining. The third section presents examples of actuated geared micromechanisms which require the multi-level fabrication process. Demonstration of actuation mechanisms coupled to external devices are illustrated. Finally, polysilicon surface micromachining fabrication technology has reached a level where many device designs, for the most part, can be embodied in the technology to produce a mechanical construct which provides the desired function. When designed properly, the fabricated mechanical element, if free to operate, will produce the desired function. However, one set of issues which can hinder or prevent operation are related to the post-fabricated device surfaces. These surface issues; namely, stiction, friction, and wear, are emphasized in the final section as a major hindrance to realizing the full potential of surface micromachined devices.
Date: May 1, 1997
Creator: Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

Properties of low residual stress silicon oxynitrides used as a sacrificial layer

Description: Low residual stress silicon oxynitride thin films are investigated for use as a replacement for silicon dioxide (SiO{sub 2}) as sacrificial layer in surface micromachined microelectrical-mechanical systems (MEMS). It is observed that the level of residual stress in oxynitrides is a function of the nitrogen content in the film. MEMS film stacks are prepared using both SiO{sub 2} and oxynitride sacrificial layers. Wafer bow measurements indicate that wafers processed with oxynitride release layers are significantly flatter. Polycrystalline Si (poly-Si) cantilevers fabricated under the same conditions are observed to be flatter when processed with oxynitride rather than SiO{sub 2} sacrificial layers. These results are attributed to the lower post-processing residual stress of oxynitride compared to SiO{sub 2} and reduced thermal mismatch to poly-Si.
Date: January 4, 2000
Creator: Habermehl, S. D.; Glenzinski, A. K.; Halliburton, W. M. & Sniegowski, J. J.
Partner: UNT Libraries Government Documents Department

Designing microelectromechanical systems-on-a-chip in a 5-level surface micromachine technology

Description: A new 5-level polysilicon surface micromachine process has been developed that offers significantly increased system complexity, while further promoting the manufacturability and reliability of microscopic mechanical systems. In general, as complexity increases, reliability suffers. This is not necessarily the case, however, with MicroElectroMechanical Systems (MEMS). In fact, utilizing additional levels of polysilicon in structures can greatly increase yield, reliability, and robustness. Surface micromachine devices are built thousands at a time using the infrastructure developed to support the incredibly reliable microelectronics industry, and the batch fabrication process utilized in the 5-level technology further increases reliability and reduces cost by totally eliminating post assembly.
Date: May 1, 1998
Creator: Rodgers, M.S. & Sniegowski, J.J.
Partner: UNT Libraries Government Documents Department

5-level polysilicon surface micromachine technology: Application to complex mechanical systems

Description: The authors recently reported on the development of a 5-level poly-ilicon surface micromachine fabrication process consisting of four levels of mechanical poly plus an electrical interconnect layer. They are now reporting on the first components designed for and fabricated in this process. These are demonstration systems, which definitively show that five levels of polysilicon provide greater performance, reliability, and significantly increased functionality. This new technology makes it possible to realize levels of system complexity that have so far only existed on paper, while simultaneously adding to the robustness of many of the individual subassemblies.
Date: June 1, 1998
Creator: Rodgers, M. S. & Sniegowski, J. J.
Partner: UNT Libraries Government Documents Department

Thin teflon-like films for MEMS: Film properties and reliability studies

Description: This work presents film properties and initial reliability studies for thin Teflon-like films applied to a unique test vehicle, the Sandia-designed and fabricated microengine. Results on microengines coated with the film show a factor of three improvement in their lifetime and an order of magnitude reduction in the coefficient of friction when compared to uncoated samples. Coefficients Of Friction (COF) of 0.07 for the Teflon-like film and 1.0 for uncoated samples are extracted from models which match the measured behavior of working microengines. These films, deposited form a plasma source, exhibit the ability to penetrate into very narrow, deep channels common to many MEMS devices. For as-deposited film, both the refractive index at 1.4 and the contact angle with water at 108{degree} show the film to be very similar to bulk Teflon PTFE. Film stability as a function of temperature has been examined using Fourier Transformation Infrared (FTIR) spectroscopy. The film structure as observed by the fluorine-carbon (F-C) peak is stable up to 200 C, but starts decomposing above 250 C. Film composition has been examined using X-ray photoelectron spectroscopy (XPS) and is quite different for directly exposed surfaces compared with deep, narrow channels where the deposition process is diffusion limited.
Date: July 1, 1998
Creator: Smith, B.K.; LaVigne, G.; Sniegowski, J.J. & Brown, C.D.
Partner: UNT Libraries Government Documents Department