Axiomatic Design of a Chemical Mechanical Polishing (CMP) Wafer Carrier With Zoned Pressure Control

Axiomatic Design was used to develop a complete platform for chemical mechanical polishing (CMP) of silicon wafers. A functional requirement of the machine emerging from the axiomatic design process is the control of the wafer-scale polishing uniformity. Mechanisms to maintain control of the uniformity were designed, and integrated into a wafer carrier, which holds the wafer during polishing and applies normal pressure to the polishing interface. The wafer carrier is capable of controlling the pressure in four annular zones on a 200 mm wafer, as well as the pressure of the surrounding retaining ring. Initial testing of the wafer carrier indicates a successful design, offering removal non-uniformity of 1.7% after polishing 5,700 Å of SiO2 from the surface of a silicon wafer.

A Novel Piezoelectrically Actuated Microvalve for Flow Control in a PEM Fuel Cell

A novel axial-flow piezoelectric microvalve for fuel cell applications has been designed and analyzed. Microvalves offer to improve flow maldistribution problems that have been identified in fuel cells. This paper will outline the design of an embeddable microvalve that has many novel features, including an axial flow characteristic, piezoelectric trimorph actuation mechanism, unlimited scalability, thermally-insensitive activation, and relative simplicity. Detailed electro-mechanical, thermal, and fluidic analyses of the design are conducted using ANSYS and MATLAB simulation packages. The valve geometry is heuristically optimized based upon the results of the analyses. Fabrication and testing of the valve is currently underway.

Computing Micro Synthetic Jet in Slip Regime With Moving Membrane

A Navier-Stokes (NS) solver for moving and deforming meshes has been modified to investigate numerically the diaphragm-driven flow in and out of two synthetic jet cavity geometries. The piezoelectric-driven diaphragm of the cavity is modeled in a realistic manner as a moving boundary to accurately compute the flow inside the jet cavity. The primary focus of the present paper is to describe the effect of cavity geometry and the wall slip, resulting from the relatively larger Kn number flows associated with micro sized geometries, on the exit jet velocity magnitude. Compressible flow simulations are required for rarefied flows to accurately predict the pressure field. The present computations for the quiescent external flow condition reveal that cavity geometry and the wall slip has an increasing effect on the magnitude of the average jet exit velocity as well as vortex shedding from the orifice.

A Demonstration of EFAB™ as a Fundamental Shift in the Way Microdevices Are Manufactured

The authors introduce the EFAB™ manufacturing process originally invented at the University of Southern California and currently being commercialized by MEMGen Corporation. They discuss its significant recent evolution as an alternative to conventional microdevice manufacturing technologies, suggest a range of geometries and applications that are enabled by this process, and develop the case that EFAB represents a fundamental shift in the way the microdevices are manufactured.

Chaotic Electroosmotic Flow

Two dimensional, time-independent and time-dependent electroosmotic flows driven by a uniform electric field in rectangular cavities with uniform and non-uniform zeta potential distributions along the cavities’ walls are investigated theoretically. The time-independent flow fields are computed with the aid of Fourier series. The series’ convergence is accelerated so that highly accurate solutions are obtained with just a few (<10) terms in the series. The analytic solution is used to compute flow patterns for various distributions of the zeta potential along the cavities’ boundaries. It is demonstrated that by time-wise periodic modulation of the zeta potentials, one can induce chaotic advection in the cavities. Such chaotic flows may be used to stir and mix fluids in microfluidic devices.

Three Dimensional PDMA Assembly: Design, Process, and Applications

This paper discusses a recent three-dimensional assembly process called the Plastic Deformation Magnetic Assembly (PDMA) method. The PDMA method allows three dimensional micromechanical structures to be realized efficiently using surface micromachining and wafer-scale, post-sacrificial-release assembly. We will discuss the principle of the PDMA method, along with the design methodology. The PDMA process has been used for a number of applications, including vertical micro RF inductors, micromachined hot wire anemometers, artificial lateral line sensors, and two dimensional neuron probes. The process for these applications will be discussed to illustrate the usefulness of the PDMA process.

Experimental Investigation on Wafer Polishing of Oxide and Copper Layers

Polishing, in particular chemical-mechanical polishing (CMP), is a critical technology for the planarization of wafers. This paper investigates, via experiments, and compares the performance of CMP process with different process parameters for wafers with silicon-dioxide (SiO2) layer and for wafers with copper (Cu) layer. Polishing pressure (P), speed (V), and back pressure (BP) are used as process parameters in this study. Different pads and slurries are also experimented for copper layer as its properties are different from that of conventional oxide layer. Material removal rate (RR) and non-uniformity (NU) are used as indices to measure the performance. Experimental data on oxide layers show RR increases as P and V increase but NU gets worse at the same time. This condition can be improved, for both oxide and copper layers, with suitable BP. Experiments on copper CMP using slurry with abrasives show that RR increases with higher P and V. While NU gets worse with higher P, it can be reduced as V increases using a soft pad. Better NU can be obtained using soft pad though RR is lower in this case. For abrasive-free polishing of copper layer, RR, though relatively lower compared to CMP with regular slurry, is unstable using hard pad despite that NU becomes better at higher P. NU of polished wafer is best at certain pressure but becomes worse at low pressure for hard pad and at high P for soft pad. It is also observed that NU of AFP can be improved with BP and softer pad. Soft pad gives better polishing quality and performance though RR is lower than that using slurry with abrasives.

Wafer Scale Modeling and Control for Yield Improvement in Wafer Planarization

Chemical mechanical polishing (CMP) is a planarization process that produces high quality surfaces both locally and globally. It is one of the key process steps during the fabrication of very large scale integrated (VLSI) chips in integrated circuit (IC) manufacturing. CMP consists of a chemical process and a mechanical process being performed together to reduce height variation across a wafer. High and reliable wafer yield, which is dependent upon uniformity of the material removal rate across the entire wafer, is of critical importance in the CMP process. In this paper, the variations in material removal rate (MRR) variation across the wafer are analytically modeled assumimg a rigid wafer and a flexible polishing pad. The wafer pad contact is modeled as the indentation of a rigid indenter on an elastic half-space. Load and curvature control strategies are investigated for improving the wafer yield. The notion of curvature control is entirely new and has not been addressed in the literature. The control strategy is based on minimizing a moment function that represents the wafer curvature and the height of the oxide layer left for material removal. Simulation results indicate that curvature control can improve wafer yield significantly, and is more effective than just the load control.

An Evaluation of Two Methods for Producing Intermetallic Microchannels

Microtechnology-based Energy and Chemical Systems (MECS) offer opportunities for portable power generation, distributed heat pumps, hydrogen separation for automotive fuel cells, on-site waste remediation and point-of-use chemical synthesis. In order to realize many of these applications, it is recognized that new techniques must be developed for producing microchannels within refractory materials. Material requirements include high-temperature resistance, chemical inertness and low-cost microfabrication. Advances in multilayer ceramics have allowed the microlamination of microreactor structures from ceramic tape. The tapes are formed in the green state and subsequently bonded through a sintering process. Problems include sagging, porosity, and volumetric shrinkage which can lead to dimensional instability. Intermetallics are another class of refractory materials which may hold some promise for high-temperature microchannel development. In this paper, several proposed methods of forming microchannel arrays in aluminide intermetallics are evaluated. These methods have the advantage of eliminating volumetric shrinkage due to binder removal. Results show that some NiAl systems may be suitable for microchannel designs. Issues to be addressed include cost, volumetric shrinkage due to phase changes or other creep-related phenomena incurred during phase changes.

Transport Enhancement in Tunable Laser Cavity Sensor

Dielectrophoresis and Electrothermal Flow are two physical processes investigated for enhancing transport of antigen to a region of immobilized conjugate antibodies on an immunosensor surface. Computational fluid dynamics (CFD) modeling is employed to understand these phenomena in detail to aid in the design optimization of the device.