Novel WLCSP technology solution for fusion device of CMOS integrated circuit with MEMS

Abstract

For the realization of the IoT (Internet of Things) society where the arrival is strongly predicted soon, the construction of an intelligent sensor network is important. For such a sensor network construction, the enormous numerical fusion devices that CMOS devices and MEMS sensors are integrated are essential. To develop WLCSP (Wafer Level Chip Size Packaging) technologies as high density packaging technology for mass production of the high reliability and low-cost devices, improving performance and downsizing of these devices, is important including novel process integration. Considering new integration of WLCSP in future, it is considered necessary to develop DRIE (Deep Reactive Ion Etching) technology for etching Si, mold, metal and insulator, or heterogeneous sacks of these materials. We have developed Non-Bosch “scallop-free” etching method for Si DRIE in our original high density NLD (magnetic Neutral Loop Discharge) plasma. [1] In this work, the first trial of Bosch etching was conducted using same plasma source of Non-Bosch. It is quietly important to control atmosphere of the sealed cavity with MEMS, there is a possibility that higher-quality controlling technology for atmosphere of sealed cavity is required with WLCSP evolution in future. Conventional MEMS etching method is Bosch etching. In Bosch method, Si is etched to anisotropic profile by using fluorine radical reaction to Si, and sidewall passivation of fluorocarbon polymer. [2] Due to such etch reaction mechanism, the residues of fluorine and fluorocarbon exist on etched surface, it is possible that these residual will have a negative impact to the cavity atmosphere after sealed. In this paper, as a part of the data acquisition to consider about the management standard of the sealed cavity atmosphere, we started comparison between Bosch and Non-Bosch to investigate whether influence of Si etching method influence to sealed cavity atmosphere or not. In this work, each sample of Bosch and Non-Bosch sample was prepared using by NLD plasma etcher, then, TDS (Thermal Desorption Spectroscopy) analyses were carried out to detect desorption species from etched surface of sample. TDS analyses were conducted each process step; after Si etched, after O2 plasma ashing, and after wet cleaning for fluorocarbon polymer.