TRANSMISSION LASER BONDING FOR MEMS PACKAGING

MILLING OF 3D NANOSCALE MOLDS FOR NANOIMPRINTING AND MICROFORMING USING FOCUSED ION BEAMS

ELECTRON-BEAM LITHOGRAPHY OF NANOBOWTIE ARRAY FOR OPTICAL INSPECTION OF NANODEFECTS

NONLINEAR DYNAMICS STUDY AND DEVELOPMENT OF HIGH PERFORMANCE MEMS GYROSCOPES

FABRICATION OF MICRO- AND NANO-SCALE CHANNELS FOR MICROSYSTEMS

INTEGRATED SOLID FREEFORMING OF METAL PARTS

 

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TRANSMISSION LASER BONDING FOR MEMS PACKAGING

 

The objective of this research is to advance a wafer-bonding technique, called transmission laser bonding, to be reliable and applicable for packaging microelectromechanical (MEMS) devices. The approach is to use both experimental and numerical schemes to study the physical and chemical phenomena in the bonding region during and after bonding at micro- and nano-scale levels. Using characteristics of laser and the associated optical properties, the technique can efficiently bond a transparent wafer, such as glass, to an opaque substrate, such as silicon, by laser melting of a thin layer near the interface. The success of the proposed research will lead to significant cost savings and quality enhancement in microdevice packaging. Since packaging costs represent more than fifty percent of the total device cost, the proposed research should be extremely important to the associated industry. Currently, the applications of these microdevice products have been extended from the traditional automotive and aerospace sectors to many emerging markets, including consumer electronics, biomedical, and information systems. These products will have a major impact either directly or indirectly, on people's daily lives.

The micromechanical testing results disclose that the TLB bonded strength depends on not only the contact pressure applied, but also on the surface roughness and the thickness of the intermediate oxide layer. However, the bonding strength reaches a stable value of 10.5 MPa with the contact pressure higher than 0.5 MPa, oxide layer thinner than 100-nm, and surface roughness less than 1-nm. The strength of 10.5 MPa is equivalent to, if not better than those obtained by other major bonding processes, including anodic and fusion bonding, which are currently used by MEMS packaging. The results also reveal that the wafer roughness and flatness required by TLB can be less stringent than those specified in the current industrial standards, so that the typical wafers used by industry can be directly adopted for the present TLB. Indeed, TLB can provide high quality bonds that are as good as the other major wafer bonding techniques but without the long processing time, high processing temperature, and externally high electrical potentials, normally required by the other major techniques, including anodic and fusion bonding. The TLB technique can also be performed at room temperature without the need of an intermediate layer and clean room environment.

 

Collaborators: Dr. Jong-Seung Park, Dr. George Vakanas, Dr. Taewoo Lee, Dr. Kuan Chen

Sponsors: US National Science Foundation (DMI-0423457), Pacific Technology, and Freescale Semiconductor

Selected Publication:

1.    Park, J-S. and Tseng, A. A. (2004), Transmission laser bonding of glass with silicon wafer, in Proceedings of 2004 Japan-USA Symposium on Flexible Automation, Paper No. UL-073, ASME.

2. Park, J-S. and Tseng, A. A (2005), Development and characterization of transmission laser bonding technique in Proceedings of IMAPS Int. Conf. Exhibition Device Packaging, Paper No. TA15, Int. Microelectronics and Packaging Society.

3. Park, J-S. and Tseng, A. A. (2006), Line bonding using transmission laser bonding for microsystem packaging, in ITherm 2006 Proceedings, IEEE.

4. Park, J-S. (2006), Characterization of transmission laser bonding technique for microsystem packaging, presentation.

 

 

MILLING OF 3D NANOSCALE MOLDS FOR NANOIMPRINTING AND MICROFORMING USING FOCUSED ION BEAMS

 

A focused ion beam (FIB) milling technology will be developed for the fabrication of three-dimensional (3D) nanoscale molds for the mass production of micro- and nano-structures using nanoimprinting and microforming. Nanoimprinting is a major candidate for next generation lithography (NGL) in the semiconductor industry, as well as being a critical tool for nano/micro-electromechanical systems (N/MEMS). Microforming is the emerging technology for the large-scale production of MEMS and other miniature parts with various applications. The success and proliferation of nanoimprinting and microforming technologies are highly dependent on the ability to make the molds and tools required for these technologies.

The main challenges in making 3D nanomolds are controlling the milling rates at sub-nanometer scales and making nonlinear curved mold surfaces from the normal milling abilities, which include simple wedge or rectangular geometries. The proposed approaches involve both traditional manufacturing automation tasks and the study of nontraditional fabrication phenomena at atomic levels, especially the interaction between energetic ion particles and target materials at quantum scales. The tasks for automation include modeling development to enhance the ability of existing computer-aided manufacturing (CAM) systems to guide FIB milling operations, producing precisely predetermined geometric shapes. The study of fabrication phenomena involves the numerical modeling and experimental study of nanoscale phenomena, such as sputtering, redeposition and amorphization by FIBs. Both modeling and experimentation will be used to establish the relationship between the major operation parameters and the material-milling rate to provide the necessary information for the CAM system to guide FIB operations. Furthermore, the knowledge base gained from the proposed study can not only improve the fundamental knowledge of the interaction between the energetic ions and target materials that would help in understanding the basic science at nanoscales, but also enhance the nanofabrication capability, which would play an important role in building nanosystems of the same complexity found in nature.

 

Collaborators: Dr. Jong-Seung Park, Dr. Yajing Liu, Mr. I. A. Insua, and Mr. B. Leeladharan

Sponsors: Nanotron, Pacific Technology, Walsin Lihwa, and Oldcastle Glass

Selected Publication:

1.    Tseng, A. A., Leeladharan, B., Li, B., Insua, I. A. and Chen, C. D. (2003), Fabrication and modeling of microchannel milling using focused ion beam, Int. J. Nanoscience, Vol. 2, Nos. 4 & 5, pp. 375-379.

2. Tseng, A. A., Insua, I. A., Park, J. S., and Chen, C. D. (2005), "Submicron milling of two-layer substrates using focused ion beam," J. Micromech. Microeng, Vol. 15, No. 1, pp. 20-28.

3. Tseng, A. A. (2004), Recent developments in micromilling using focused ion beam technology, J. Micromech. Microeng., Vol. 14, No. 4, pp. R15-R34.

4. Tseng, A. A. (2005), Recent developments in nanofabrication using focused ion beams, Small, Vol. 1, No. 10, pp. 924-939.

 

 

ELECTRON-BEAM LITHOGRAPHY OF NANOBOWTIE ARRAY FOR OPTICAL INSPECTION OF NANODEFECTS

 

Defects in the micrometer or nanometer scales are the leading cause of failure in components and end products in widely diverse industries. The on-line inspection tools needed to identify such defects are also required to meet or exceed current inspection rates of thirty wafers per hour. Optical probes are the fastest inspection tools currently on the market. However, as the defects or objects approach the order of the wavelength of the optical probe, it becomes difficult to image them. After reaching the diffraction limit, the signal to noise ratio eventually becomes prohibitively low to support fast, reliable on-line inspection. In the standard optical scattering approach, the smallest objects that can be reliably examined are on the order of 200 nm. Therefore, a new method that can quickly and reliably detect defects significantly smaller than the diffraction limit is needed.

Near-field optics, which enable optical imaging with spatial resolution that is significantly better than the diffraction limit, has recently found application in microwave ranges. In this light, the goal of the present research is to examine the extension of the near-field concept from the microwave to the optical wave ranges. A bowtie array proposed by the investigators that implements the newly-invented concept of the Wave Interrogated Near-Field Array (WINFA) is designed and fabricated so that the new optical probe can overcome the diffraction limit by combining the sensitivity of near-field detection with the speed of optical scanning.

In the present research, a scaled-down nanobowtie array will be built to demonstrate that the WINFA concept can be extended to a much shorter wavelength for nanoscale inspection. The fabrication process featuring electron-beam lithography of nanoscale structures, especially the considerations specific to fabricating a nanobowtie array, will be studied. Different substrate materials and different lithographic conditions will be considered for pattern variation evaluations. A prototype WINFA system including the nanobowtie array, scanning stage, holographic filters, and pattern recognition software will be assembled and tested to optimize the system's efficiency.

 

Collaborators: Dr. Chii D. Chen, Dr. Rudy E. Diaz, Dr. T. P. Chen, Dr. A. Notargiacomo, and Mr. Bo Li.

Sponsors: US National Science Foundation, and ASU Consortium for Metrology of Semiconductor Nanodefects

Selected Publication:

1.    Tseng, A. A., Chen, C. D., Wu, C. S., Diaz, R. E., and Watts, M. E. (2002), Electron-beam lithography of microbowtie structures for next generation optical probe, J. Microlithography, Microfabrication, and Microsystems, Vol. 1, No. 2, pp. 123-135 (cover article).

2. Tseng, A. A., Chen, K., Chen, C. D., and Ma, K. J. (2003), Electron beam lithography in nanoscale fabrication: recent development," IEEE Trans. Electronics Packaging Manufacturing, Vol. 26, No. 2, pp. 141-149.

3. Tseng, A. A., Notargiacomo, A., and Chen, T. P. (2005), Nanofabrication by scanning probe microscope lithography: a review, J. Vac. Sci. Technol. B, Vol. 23, No. 3, pp. 877-894

4. Liu, Y., Chen, T. P., Ng, C. Y., Ding, L., Tse, M. S., Fung, S. and Tseng, A. A. (2006), Influence of Si-nanocrystal distribution in the oxide on the charging behavior of metal-oxide-semiconductor structures, IEEE Trans. Electron Devices, Vol. 53, No. 4, pp. 914-917.

 

 

NONLINEAR DYNAMICS STUDY AND DEVELOPMENT OF HIGH PERFORMANCE MEMS GYROSCOPES

 

Even though microelectromechanical gyroscopes, also known as MEMS gyros or microgyros, are about to be commercialized, the low technical performance of these microgyros limits their use in less demanding automotive applications. As such, high performance MEMS gyroscopes are in demand; a specific example of this is the navigation of vehicles and micro-spacecraft. It is believed that understanding the nonlinear dynamics of MEMS gyroscopes is essential to achieving improved gyro performance. The major task required to achieve this objective is to understand the instability reported by other investigators. The onset of instability in MEMS gyroscopes prevents the microgyros from operating at optimum conditions. Specifically, the mismatch between the resonance frequencies in the microgyro structure has not been minimized by existing designs. Since the microgyros have very low damping, operating at imperfect resonance greatly limits the performance of the gyro. To overcome this limitation, nonlinearity in the system must be considered since the system dynamics near resonance are well known to be greatly affected by nonlinear effects, even though these nonlinear effects are otherwise small.

The goal of the present effort is to develop better fabrication techniques for the thick structures of the microgyros. This is motivated by the simple fact that microgyros are inertia sensors and thicker structures will accentuate the Coriolis force, making the signal detection more immune to the noise associated with signal amplification. Despite the tremendous amount of research and development on MEMS inertia sensors, the crucial research results are not available in the literature. Much of the know-how on microgyro designs remains proprietary. Through the proposed research, it is our hope to provide the research community with findings on the design considerations and innovative fabrication techniques for microgyros.

 

Collaborators: Dr. Zaichun Feng, Dr. Gary X. Li, Mr. Bo Li, and Mr. Biswanath Dutta

Sponsors: National Science Foundation, University of Missouri, Freescale Semiconductor.

Selected Publication:

1. Tseng, A. A., Tang, W.C., Lee, Y.-C., and Allen, J. (2000), NSF 2000 workshop on manufacturing of micro-electro-mechanical systems, J. Mat. Processing & Manufacturing Science, Vol. 8, No. 4, pp. 292-305.

2. Li, G. X. and Tseng, A. A. (2000), Transient and impact dynamics of a micro-accelerometer, J. Mat. Processing & Manufacturing Science, Vol. 9, No. 2, pp. 143-155.

3. Li, G. X. and Tseng A. A., Low Stress Packaging of A Micro-Machined Accelerometer,IEEE Trans. Electronics Packaging Manufacturing, Vol. 24, No. 1, pp. 16-25, 2001.

4. Tseng, A. A., Chen, Y. T., and Ma, K. J. (2004), Fabrication of high-aspect-ratio microstructures using excimer lasers, Optics & Lasers Eng., Vol. 41, No. 6, pp. 827-847,

 

 

FABRICATION OF MICRO- AND NANO-SCALE CHANNELS FOR MICROSYSTEMS

 

It is understood that the majority of processes for MEMS fabrication, driven by the semiconductor industry, are mask-based, parallel in nature, and CMOS-compatible. As an alternative, the present research focuses on the development of direct-write technologies for MEMS fabrication. In principle, the direct-write technologies, including laser micromachining, are serial in nature and feature shorter lead-time, lower material removal rates, and lower speeds when compared to parallel processes. However, the emergence of MEMS has provided an impetus to direct-write laser-micromachining, turning some of the intrinsic disadvantages of the process when applied on the macroscale into advantages when it comes to the meso- and micro-scale. As a result, the purpose of the present research is to establish an agile direct-write laser-based fabrication system for MEMS and the processing of magnetically hard and soft materials.

Our laser-based research has identified two processes for engineering magnetic MEMS by laser-micromachining. The first technique is a derivative of the laser thermo-magnetic recording process in which the magnetic material is thermally- and magnetically-processed, but is not structurally changed or ablated. The second process includes mesoscopic material removal (ablation). Although most of the energy of the laser light beam is contributed by the electric field, with the magnetic field component being negligible (at least six orders of magnitude smaller), laser micromachining of magnetic materials remains a coupled electromagnetic and thermo-hydrodynamical problem when in comes to analyzing the melt pool in the case of ablating material through fusion. Several CAD geometries have been successfully constructed on 10 m thick films and 100 m thick sheets of a representative magnetic material, such as permalloy (Ni80Fe20), an integral part of magneto-thermo-fluidic (MTF) MEMS. Optical and atomic microscopes and statistical analysis have been used to quantify the dimensional accuracy of these patterned CAD geometries. A typical MTF MEMS device with applications in microscale fluid mixing and separating has been designed and analyzed and a fabrication schedule for realizing the device has been reported.

 

Collaborators: Dr. George Vakanas, Dr. J. Gu, Dr. F. Zenhausern and Mr. Ravi K. Gupta

Sponsors: Intel Corp., Walsin Lihwa, ROC National Science Council, ASU Seed Funding

Selected Publication:

1.    Vakanas, G. P, Tseng, A.A., and Winer, P. (2002), Laser-assisted chemical etching for embedded microchannels and overhanging microstructures on Si/SiO2 substrates, J. Laser Applications, Vol. 14, No. 3, pp. 185-190.

2. Tseng, A. A., Insua, I. A., Park, J. S., Li, B., and Vakanas, G. P. (2004), "Milling of submicron channels on gold layer using double charged arsenic ion beam," J. Vac. Sci. Technol. B, Vol. 22, No.1, pp. 82-89.

3. Chen, Y. T., Ma, K. J., Tseng, A. A., and Chen, P. H. (2005), "Projection ablation of glass-based single and arrayed microstructures using excimer laser," Optics & Laser Tech., Vol. 37, No. 4, pp. 271-280..

4. Gupta, R. K., (2005), Fabrication of integrated nanofluidic systems, MS Thesis, Mechanical Engineering, ASU (Advisor: A. A. Tseng).

 

 

INTEGRATED SOLID FREEFORMING OF METAL PARTS

 

Technological advancements in rapid freeforming have dramatically reduced the lead-time in parts manufacturing, resulting in an increase in overall process efficiency. However, due to the nature of layer manufacturing, dimensional accuracy and surface texture are still a major limitation of freeform product fabrication. Post-product finishing is estimated as adding significantly to the cost of the production of freeformed parts. This problem will persist despite the continuous evolution of freeforming technology; thus, a new conception of rapid freeforming techniques incorporating the need for increased dimensional accuracy and improved surface texture is presented.

The aim of this research is to develop an innovative solid freeforming technique that allows freeforming parts to be interactively fabricated by the layer deposition process and material removal process. Depending on the part geometry, several layers of the material will be deposited initially, and then the surface contour of the incomplete part will be processed to achieve the desired dimension and surface finish. Then, additional layers of the material will be deposited onto the still-incomplete part to build another segment of the envisioned product. These interactive processes will be reiterated until the part has been completed as designed. A post processor based on the concept of parallel kinematic structures with the capability of 5-axis motion will be built and integrated with an existing freeforming machine to form an integrated rapid fabrication cell. The post processor will be equipped with multiple tools to remove the excess material, which will effectively depend on feature size, dimension tolerance, and surface texture. The present research is motivated by the need to develop innovative and robust methods to advance the technology of freeform fabrication and parallel kinematic machines for agile and precision manufacturing. As such, if successful, this research will significantly impact the rapid precision manufacturing of freeform parts, which is an extremely important global niche for American industry.

 

Collaborators: Dr. J. H. Chun, Dr. Jong I. Mou, Dr. Munhee Lee, Dr. B. S. Zhao, Dr. J. G. Zhou, and Mr. Masahito Tanaka

Sponsors: US Department of Energy, US National Science Foundation, Phoenix Analysis and Design, and Advanced Ceramics Research

Selected Publication:

1. Tseng, A.A., Lee, M. H., and Zhao, B. (2001), Design and operation of a droplet deposition system for freeform fabrication of metal parts, ASME J. Eng. Mat. Tech, Vol. 123, No. 1, pp. 74-84.

2. Tseng, A. A., and Tanaka, M. (2001), Advanced deposition techniques for freeforming metal and ceramic parts, Rapid Prototyping J., Vol. 7, No. 1, pp. 6-17 (Received 2002 High Commended Award).

3. Zhou, J. G., Kokkengada, M., He, Z., Kim, Y. S., and Tseng, A. A. (2004), "Low temperature polymer infiltration for rapid tooling,"Materials and Design, Vol. 25, No. 2, pp. 145-154.

4. Tseng, A. A. (2000), Adaptable filament deposition system and method for freeform fabrication of three-dimensional objects, US Patent No. 6,030,199; US Patent No. 6,113,696; US Patent No. 6,149,072; US Patent No. 6,216,765; US Patent No. 6,251,340B1; US Patent No. 6,309,711; and US Patent No. 6, 372,178 B1; US Patent No. 6,851,587).