This paper reports a thin-film encapsulation technology for wafer level micro-electro-mechanical systems (MEMS) package, using poly-benzo-oxazole (PBO) sacrificial material and plasma enhanced chemical vapor deposited silicon oxide (PECVD SiO) cap layer. This technique, which is applicable for MEMS technologies, saves die size and enables conventional package processes such as dicing, picking, mounting and bonding. Besides the fabrication processes of the thin-film encapsulation, this paper also presents the results of finite element models (FEMs) for the deflection and the mechanical stress of the thin-film caps.Moreover, in order to mount a MEMS chip with the thinfilm capsulations and another integrated circuit (IC) chip that controls a MEMS chip in the same package, we have also developed an epoxy reinforcement technique for protecting the thin-film encapsulations and a topography wafer thinning technique for the MEMS chip. And then the system in package (SiP) for the MEMS and IC chips is fabricated successfully based on the mechanical analysis of the SiP process. IntroductionSince MEMS, such as various sensors and radio frequency (RF) actuators [1], [2], consist of movable parts and need to be operated in vacuum or controlled atmosphere, the conventional package techniques for large-scale integrated circuits (LSIs) cannot be applied [3]. In many cases, as a MEMS chip, which needs to be controlled by another IC chip, is packaged using silicon or glass cap [4]-[6], it has been difficult to reduce the footprint on the printed circuit board (PCB) and assembly cost. To address these issues, we have developed the hermetic thin-film encapsulation structure fabricated by conventional back end of the line (BEOL) technologies of LSIs as a wafer-level packaging (WLP). In this work, the fabrication processes and mechanical modeling results for thin-film encapsulations and the SiP [7] for MEMS and IC chips are shown for the fabrication of the multi-chip package (MCP).

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In silicon capacitors, it is most important to increase the surface area of the surface forming the capacitor. In conventional silicon capacitors, trenches are generally formed in silicon wafer using reactive ion etching (RIE) method to expand their surface area. However, with this method, the depth of trenches that can be formed was limited. Furthermore, since RIE method processes silicon wafer only one by one, productivity is low. In this paper, Metal-assisted Chemical Etching (MacEtch) is proposed as a novel method of fabricating high-density silicon capacitors to solve the problems. We used gold formed by electroless plating as a catalyst and controlled them by forming conditions. As a result, vertical trenches greater than 100 μm depth and less than 1 μm width could be formed on a silicon wafer. The silicon wafer on which these trenches are formed has a surface area 100 times or more as compared with the case where there is no trench. We formed a dielectric film and electrodes on these trench surfaces. Consequently, we have realized a silicon capacitors with a capacitance density as high as 200 nF / mm2 or more.

In this paper, we describe optical characteristics and reliability of a novel wafer level white LED (light-emitting diode) package. In this package, re-distribution wiring layer and phosphor layer could be formed in a lump by wafer level process. As a result, ultrasmall size package that is almost same size as the chip could be attained. This approach results in drastic reduction in material and process cost. We determined the package structure from the results of the numerical analysis on the thermal cycle resistance of the package after reflow soldering. The sapphire substrate is removed by laser process and the GaN layer exists between phosphor layer and encapsulation resin. Applicative light extraction was achieved by control of GaN surface roughness. In addition, it was confirmed that the package had sufficient reliability in the thermal cycle test (TCT). Consequently, this low cost package could be applicable to LED components and also the cost of them is considered to drastically decrease.