Gold metallizations for eutectic bonding of silicon wafers

Gold eutectic bonding of silicon wafers is a good candidate for wafer level vacuum packaging of vibrating MEMS: in this paper we investigated several e-beam evaporated metallizations stacks including a titanium adhesion layer, an optional diffusion barrier (Ni or Pt) and a gold film for eutectic bonding on Si and SiO₂/Si wafers. Interdiffusion in the multilayers for annealing temperatures (380–430°C) larger than the Au–Si eutectic temperature (363°C) and times corresponding to a bonding process was characterized by RBS, roughness and resistivity measurements. Au/Pt/Ti and Au/Ti/SiO₂ were found to have the best characteristics for bonding. This was confirmed by bonding experiments.     

Vacuum measurement in wafer level encapsulations by interference microscopy

Vacuum encapsulation is required for various microsensors to improve their performances. In the case of wafer level vacuum encapsulation, dedicated techniques must be developed to measure the background pressure in the bonded cavities. In this paper we investigated ex situ measurement techniques based on the measurement by interference microscopy of the deformation and vibrations of the caps as function of an external pressure. Because these techniques detect the equality between external and internal pressure, they do not require any modelling nor prior calibration. Application to wafer level encapsulations fabricated by gold-silicon eutectic wafer bonding demonstrates that a detection limit in the 10⁻²–10⁻¹ mbar range can be reached for millimetre size caps.

     

Low temperature solid–liquid interdiffusion wafer and die bonding based on PVD thin Sn/Cu films

Microsystem Technologies - Cu–Sn intermetallic diffusion has been studied with thin Sn and Cu films deposited by physical vapor deposition. It was found that annealing time is critical to the...     

X-ray multilayer monochromator with enhanced performance

An x-ray multilayer monochromator with improved resolution and a low specular background is presented. The monochromator consists of a lamellar multilayer amplitude grating with appropriate parameters used at the zeroth diffraction order. The device is fabricated by means of combining deposition of thin films on a nanometer scale, UV lithography, and reactive ion etching. The performance of this new monochromator at photon energies near 1500 eV is shown.     

MEMS packaging process by film transfer using an anti-adhesive layer

A low cost and low temperature thin film packaging process based on the transfer of an electroplated Nickel 3D cap is proposed. This process is based on adhesion control of a thick molded cap Ni film on the carrier wafer by using a plasma deposited fluorocarbon film, on mechanical debonding and on adhesive bonding of the microcaps on the host wafer with BCB sealing rings. Mechanical characterizations show that the transferred microcaps have a high stiffness, a low stress and a high adhesion. Because this process is simple and only involves a low temperature (250°C) heating of the host wafer, it is highly versatile and suitable for the encapsulation of micro and nano devices, circuits and systems elaborated on a large range of substrate materials.     

High current densities in copper microcoils: influence of substrate on failure mode

Copper planar microcoils were processed by U.V. lithography on SiO₂/Si and Kapton^®. They were packaged on different types of support in order to study the influence of thermal exchange conditions on device functioning. An electric current was injected in the coil and step by step increased until the electric connection broke, while the temperature of the microcoils remained free. This latter was estimated from the copper resistivity. It allowed demonstrating that the thermal exchange mode of the wire-bonded microcoils is conductive. The current density was calculated taking into account the deterioration of the coils by oxidation. Its maximum value is linearly decreasing with the thermal exchange ability of the support. The failure modes of the microcoils are related to track melting and oxidation, the current density remaining one order too weak to induce electromigration.     

Growth and characterization of shape memory alloy thin films for Si microactuator technologies

NiTi thin film alloys have been grown on Si (1 0 0) substrates by sequential multilayer deposition of Ni and Ti layers followed by metal interdiffusion via annealing. Short-time (5 min) annealing of the deposited layers at 500 °C leads to alloying of Ni and Ti, provided that preferential oxidation of Ti is avoided. This has been achieved by capping the layers with AlN, which constitutes a very efficient barrier preventing oxygen contamination of the film. For uncapped films, annealing has to be performed under high vacuum conditions. The structure of the processed films strongly depends on the temperature and time of the thermal process, obtaining Ni- and Ti-rich phases when the films are annealed at higher temperatures and/or during longer times. As-grown and processed films are analyzed by X-ray diffraction, in-depth Auger electron spectroscopy and X-ray photoelectron spectroscopy techniques. Finally, resistivity measurements show the existence of a phase transition in the films annealed at 600 °C without the capping layers (vacuum furnace). This contrasts with the behavior observed for AlN capped films, where cracking of the film occurs during cooling, which has been attributed to generation of stress in the buried film during the phase transition.     

Experimental measurements and behavioral modeling of an electrostatically actuated bi-axial micromirror

Recent developments in micro-electro-mechanical systems and micromachining technologies have made possible the development and integration of micromirrors that can be employed for a number of consumer applications such as free space optical switching (Syms in J Lightwave Technol 20(7):1084–1094, 2002; Pan in Micromech Microeng 14(1):129–137, 2004), 2D scanning or image projection (Texas Instruments DLP ). This high level of integration provides many advantages such as reproductivity and improved performance. Obviously, these increased levels of miniaturization raise new characterization and modeling concerns. We present in this paper the design, the fabrication process, the characterization and the behavioral modeling approach of a novel electrostatically actuated bi-axial micromirror. This micro-opto-electro-mechanical system is a result of a joint development between our partners Colibrys and Coventor companies (Colibrys ; Coventor ). In the field of this work, two HDL multi-physics models using Verilog-A language and Matlab have been developed and validated by different experimental measurements.     

Vacuum measurement in wafer level encapsulations by interference microscopy

Vacuum encapsulation is required for various microsensors to improve their performances. In the case of wafer level vacuum encapsulation, dedicated techniques must be developed to measure the background pressure in the bonded cavities. In this paper we investigated ex situ measurement techniques based on the measurement by interference microscopy of the deformation and vibrations of the caps as function of an external pressure. Because these techniques detect the equality between external and internal pressure, they do not require any modelling nor prior calibration. Application to wafer level encapsulations fabricated by gold-silicon eutectic wafer bonding demonstrates that a detection limit in the 10^?2–10^?1 mbar range can be reached for millimetre size caps.