Through-glass copper via using the glass reflow and seedless electroplating processes for wafer-level RF MEMS packaging

Abstract

We present a novel method for the fabrication of void-free copper-filled through-glass-vias (TGVs), and their application to the wafer-level radio frequency microelectromechanical systems (RF MEMS) packaging scheme. By using the glass reflow process with a patterned silicon mold, a vertical TGV with smooth sidewall and fine pitch could be achieved. Bottom-up void-free filling of the TGV is successfully demonstrated through the seedless copper electroplating process. In addition, the proposed process allows wafer-level packaging with glass cap encapsulation using the anodic bonding process, since the reflowed glass interposer is only formed in the device area surrounded with silicon substrate. A simple coplanar waveguide (CPW) line was employed as the packaged device to evaluate the electrical characteristics and thermo-mechanical reliability of the proposed packaging structure. The fabricated packaging structure showed a low insertion loss of 0.116 dB and a high return loss of 35.537 dB at 20 GHz, which were measured through the whole electrical path, including the CPW line, TGVs and contact pads. An insertion loss lower than 0.1 dB and a return loss higher than 30 dB could be achieved at frequencies of up to 15 GHz, and the resistance of the single copper via was measured to be 36 mΩ. Furthermore, the thermo-mechanical reliability of the proposed packaging structure was also verified through thermal shock and pressure cooker test.

Advanced MEMS Process for Wafer Level Hermetic Encapsulation of MEMS Devices Using SOI Cap Wafers With Vertical Feedthroughs

“…Moreover, the step coverage of metal-based alloys is not as good as the glass-frit, since the thickness of these alloys is typically limited to few micrometers, mostly due to their high stress. There are also examples of verticallytransferred sensor leads in the literature [12]- [18]. These approaches typically require the drilling of the silicon or glass substrates by using a laser [12], DRIE [13]- [15], or wet etching [16], [17] and then hermetic filling of these trenches with thermal oxidation [15], metal bumps/patterning [16], [17], glass reflow [13], [14], or metal electroplating [12], [18].…”

“…These approaches typically require the drilling of the silicon or glass substrates by using a laser [12], DRIE [13]- [15], or wet etching [16], [17] and then hermetic filling of these trenches with thermal oxidation [15], metal bumps/patterning [16], [17], glass reflow [13], [14], or metal electroplating [12], [18]. Therefore, they either suffer complex process steps such as void-free hermetic-filling of the feedthrough openings [12], [15] or trench-refill processes [13], [16], [18]. Another challenge with the vertical feedthrough processes is to ensure precise control of the thicknesses and the relative offsets of the sealing material, sensor leads, sealing regions, and vertical feedthroughs [18], in order to achieve the sealing and the lead transfer simultaneously.…”

“…Therefore, they either suffer complex process steps such as void-free hermetic-filling of the feedthrough openings [12], [15] or trench-refill processes [13], [16], [18]. Another challenge with the vertical feedthrough processes is to ensure precise control of the thicknesses and the relative offsets of the sealing material, sensor leads, sealing regions, and vertical feedthroughs [18], in order to achieve the sealing and the lead transfer simultaneously.…”

3-D Integration and Through-Silicon Vias in MEMS and Microsensors

“…A similar technique has also been developed by using reflow of Pyrex 7740 at 750°C to surround silicon conductive pillars [243]. Cu TSVs in glass, specifically for RF applications, have also been developed using a similar glass reflow process [244], [245], as shown in Fig. 28.…”

Die size reduction by optimizing the dimensions of the vertical feedthrough pitch and sealing area in the advanced MEMS (aMEMS) process

“…The use of vertical feedthroughs can overcome all of these problems by transferring the sensor leads vertically to the substrate. However, it is difficult to fabricate such vertical feedthroughs as they typically need complex via/trench-refill process steps [4,5]. METU-MEMS Center has already reported a new hermetic packaging method, called as the aMEMS process [6][7][8][9][10], which can eliminate all these challenges with a smart combination of simple and traditional MEMS processes without any need for complex via/trenchrefill process steps.…”