CMOS Force Sensor with Scanning Signal Process Circuit for Vertical Probe Card

Abstract

The constant advancement of semiconductor technology has prompted a further reduction in size and an increase in the density of integrated circuits. In order to meet the various requirements of the industry, higher accuracy, longer fatigue life, and a greater capability to withstand temperature extremes have become important criteria in the design of probe cards (Iscoff, 1994; Gilg, 1997). After a certain period of use, probe cards must be calibrated by a professional machine; several properties need to be verified, such as the probe’s maximum current, resistivity (contact resistance), and reaction force. This verification procedure may influence the efficiency of production lines, since it is performed offline. One crucial step in this procedure is monitoring the reaction force exerted by the probes on each other, in order to compute the average reaction force and complete coplanarity to ensure the efficient operation of the probe cards. To expedite this procedure, we designed an arraytype CMOS force sensor that is capable of monitoring the status of vertical probe cards online in both die-level and wafer-level applications. In the past, the fabrication of pressure sensors typically involved an MEMS process with backside etching adopted for its post process (Ghalichechian, 2002; Malhair & Barbier, 2003). However, in recent years, more and more researchers have proposed to combining the standard CMOS process with the MEMS process to manufacture both microsensors and integrated circuits (Yang et al., 2005; Peng et al., 2005; Wang et al., 2006). The combined process also has additional advantages, such as a reduction in the noise and number of pads. Our design also adopted the combined CMOS-MEMS process to fabricate force sensors and their signal conditioning circuits. Moreover, as the conventional post process can barely handle the increasingly smaller pitch between the probes (Wilson, 1999), we etched a cavity on the silicon substrate to deform the membrane in the post process (RLS dry etching).