Academic Paper
Inductively coupled plasma etching of bulk tungsten for MEMS applications
Yanming Xia , Zetian Wang , Lu Song , Wei Wang , Jing Chen , Shenglin Ma
Abstract
As a promising material for bulk micromachining for MEMS applications, tungsten can be used as microneedles for medicine injection and tools for micro-inject molding, ultrasonic machining, and electrical discharge machining. However, it is difficult to fabricate microstructures with high aspect ratios and small feature sizes due to the excellent material of tungsten properties, such as chemical stability, high hardness, and high melting point. Here, an inductively coupled plasma (ICP) deep etching process is developed for bulk tungsten, and its process parameters are studied. After optimizing the process parameters, three recipes were developed for different MEMS applications. A patterned tungsten structure with a depth of more than 300 µm was etched by tungsten (W) ICP deep etching (WIDE) at an etch rate of 2.73 µm/min and etch selectivity of 35. The WIDE process produced a tungsten microstructure with a high aspect ratio (> 20), a small feature size (< 3 µm), and a surface roughness of Ra 30 nm. To demonstrate the potential application prospect of deep etching bulk of tungsten, tungsten microneedles with a positive sidewall angle and several non-silicon substrates for MEMS applications were achieved based on the WIDE process.
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A RF Redundant TSV Interconnection for High Resistance Si Interposer
Mengcheng Wang , Shenglin Ma , Yufeng Jin , Wei Wang , Jing Chen , Liulin Hu and Shuwei He
Abstract
Through Silicon Via (TSV) technology is capable meeting effective, compact, high density, high integration, and high-performance requirements. In high-frequency applications, with the rapid development of 5G and millimeter-wave radar, the TSV interposer will become a competitive choice for radio frequency system-in-package (RF SIP) substrates. This paper presents a redundant TSV interconnect design for high resistivity Si interposers for millimeter-wave applications. To verify its feasibility, a set of test structures capable of working at millimeter waves are designed, which are composed of three pieces of CPW (coplanar waveguide) lines connected by single TSV, dual redundant TSV, and quad redundant TSV interconnects. First, HFSS software is used for modeling and simulation, then, a modified equivalent circuit model is established to analysis the effect of the redundant TSVs on the high-frequency transmission performance to solidify the HFSS based simulation. At the same time, a failure simulation was carried out and results prove that redundant TSV can still work normally at 44 GHz frequency when failure occurs. Using the developed TSV process, the sample is then fabricated and tested. Using L-2L de-embedding method to extract S-parameters of the TSV interconnection. The insertion loss of dual and quad redundant TSVs are 0.19 dB and 0.46 dB at 40 GHz, respectively.