David A. Koester

MEMS infrastructure: the multiuser MEMS processes (MUMPs)

In order to help provide access to advanced MEMS technologies, and lower the barriers for both industry and academia, MCNC, and ARPA have developed a program which works to provide users with access to both MEMS processes and advanced integration techniques. The two distinct aspects of this program, the MUMPs and Smart MEMS, will be described in this paper. The multi-user MEMS processes (MUMPs) is an ARPA-supported program created to provide inexpensive access to MEMS technology in a multi-user environment. MUMPs is a proof-of-concept and educational tool to aid the developemnt of MEMS in the domestic community. MUMPs technologies currently include a 3-layer polysilicon surface micromachining process and LIGA processes that provide reasonable design flexibility within set guidelines. Smart MEMS is the development of advanced electronics integration techniques for MEMS through the application of flip chip technology.

Modeling of stress-induced curvature in surface-micromachined devices

This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.

MEMS: small machines for the microelectronics age

In the past few years, the micro-electromechanical systems (MEMS) industry has exceeded the

A design-based approach to planarization in multilayer surface micromachining

1-billion-a-year mark. Some economic forecasters estimate that the industry will surpass

Enhancement of deep-UV patterning integrity and process control using antireflective coating

14 billion by the year 2000. The reason for this tremendous growth is the enabling nature of MEMS, which give engineers and researchers the tools to build things that have been impossible or prohibitively expensive with other techniques. MEMS are micron- to millimeter-scale devices that can be fabricated as discrete devices or in large arrays. MEMS borrow much of their technology from integrated circuit (IC) manufacturing, providing three-fold benefits: miniaturization, multiplicity and microelectronics. First, miniaturization of the devices is inherent in the processing techniques. Modern microelectronics fabrication techniques are designed to build submicron-scale devices. By using the same techniques, engineers can easily leverage this technology to produce MEMS that are orders of magnitude smaller than their macroworld counterparts. Second, the use of photolithography techniques makes producing thousands or even millions of copies of a single device easy. Thus, single devices can be arrayed into systems to produce an effect impossible with discrete devices. Finally, because MEMS technology is so similar to IC fabrication technology, MEMS are integrable with microelectronics.

Thin-film thermoelectric energy harvesting for security and sensing applications

This paper describes a design-based planarization strategy that can control topography to within submicron levels. The design concept takes advantage of the inherent conformability of the film deposition processes to achieve planar topography, without the need for an additional planarization step. It is based on a universally regulating line spacing in patterned layers to within a predefined amount, thus allowing subsequent layers to fill in as they grow, conforming to the previous layer. Test structures were fabricated to study the effect of different feature sizes in underlying layers on the topography of subsequent layers. Predictions based on numerical and geometric models for topography generation are compared to fabricated devices. An example of successful application to a micromachined adaptive mirror is presented.

MEMS Foundry for High Volume Manufacturing and Product Reliance

In this paper, we describe the results of experiments performed using wafers having either phosphorous (POCl3) doped polysilicon, LPCVD silicon nitride, LPCVD silicon dioxide, LPCVD silicon dioxide over POCl3 doped polysilicon, evaporated aluminum, or CVD tungsten thin films, patterned with and without the use of deep UV anti-reflective coatings. The parameters of reflectance control, critical dimension control, focus/exposure latitude, and resist profiles were studied for line/space gratings and contacts. Incorporation of anti-reflective coatings was shown to be very beneficial for reducing the impact of highly reflective substrates, grainy surfaces, and topographical features encountered during deep UV imaging. The ARC process is independent of the substrates reflectivity, allowing the same exposure dose for all substrates studied. Without ARC the optimum exposure dose for the same substrates varied over a 35% range. ARC also provides slightly increased exposure and focus windows for some substrates, and was shown to significantly improve linewidth control on rough substrates such as POCl3 doped polysilicon and tungsten. The grainy surface of the tungsten wafers was nearly impossible to pattern without the use of an anti-reflective coating; without ARC, there was virtually no process window (approximately 2 mJ/cm2) for retention of 0.50 micrometers features.

Microelectromechanical devices including rotating plates and related methods

The past decade has seen significant advances in distributed sensors and sensor networks. Many of these advances have been driven by programs that support national intelligence and security interests. With these advances have come an increased interest in energy harvesting to provide continuous power sources to replace or augment existing power storage systems. The use of waste heat is an attractive source of energy for many applications where μW-mW power is required. The implementation of a thermoelectric power conversion system requires several basic elements in addition to an assumed heat source. These elements are: 1) a thermoelectric device, 2) a heat sink, 3) voltage regulation, 4) an energy storage device and 5) load management. The design and optimization of the system (and each element within the system) is highly dependent on the thermal boundary conditions and the power load. This presentation will review the key performance factors and considerations required to optimize each element of the system to achieve the required I-V characteristics for output power.

Reflective mems actuator with a laser

The establishment of standard processes has become increasingly important in the growth of MEMS technology. Standard processes enable developers to leverage stable process platforms without the risk, time and costs associated with extensive process development. JDS Uniphase has established multi-user programs in three different process technologies—polysilicon, SOI and metal—that provide easy, cost-effective vehicles for early stage development. These processes also provide low-risk pathways to manufacturing in high volume. This paper discusses these processes and provides additional background on the importance of a quality system in the management of foundry product development. Product reliability testing is discussed in the context of a customer/foundry model.© 2002 ASME