Fabrication of micro-probe beam using MEMS technology for new vertical silicon probe card

Abstract

As very large scale integration (VLSI) technology progresses toward higher levels of integration and higher operating speeds, semiconductor device dimensions shrink and complexity increases because of decreasing pad size and increasing numbers of pads [ 11. The traditional probe card, which is commonly used in testing IC chips, is composed of needles. However, although high density and high pin count probing are required in wafer level testing, traditional probe cards with needledwire have limitations due to the difficulty of manufacturing probe cards and the parasitic capacitance and inductance that is induced between needles in high operating speed tests[2]. This paper presents the new wafer probe card technology with 40 pm pitch and 605 pads by MEMS technology. We have fabricated a micro-probe beams using porous silicon micromachining, RIE (reactive ion etching), and electroplating process. In order to form electroplating mold, we used a thick negative SU-8 photoresist. To use probe beams as tip of probe card, their thermal and mechanical properties was investigated. Probe beams are curled up as a result of surface tension and difference in the thermal expansion coefficients between the thin films on the beams [ 3 ] .To achieve an effective probing action, the micro-probe beam was designed to provide a suficient deflection to contact the chip pads and endure a large force when making an ohmic contact. Fig. 1 shows a schematic of the mcro-probe beams. The basic structure was a multiplayer structure composed of AW"i-CriSi3Ndn-epi layers. The width and length of the micro-probe beam were 40 pm and 600 pm, respectively. The oxidized surface of the IC chip pads was broken down electrically using the mechanical scrubbing motion of the micro-probe beam. The mechanical characteristics of the micro-probe beam were analyzed using a finite element ANSYS simulation of the micro-probe beam before and after the annealing process. To find the optimal structure for mechanical stress, the ANSYS simulation was conducted using the results of the fabrication process. Fig. 2 shows a good correlation between the theoretical and experimental results for the probe beam without a radius curvature. Plus, the deflection height increased linearly with an increase in the input force.We have fabricated a micro-probe beam using porous silicon etching and electroplating technique. The starting material is the n-epi/n'/nin* layer. First, Si3N4 was deposited by LPCVD on both sides of the wafer. The Au(50O~)Mi-Cr(2,000&.), as seed layer and adhesion layer, was deposited on the Si3N4. After formation of the metal lines using thick photoresist (SU-X), the structure was fabricated by Au electroplating. Second, micro-probe beams were patterned and a dry etching was then performed. A porous silicon layer (PSL) was formed on a 20 pm-thick n+ difised layer by anodization. The anodic reaction was performed in 43 wt.% aqueous HF solution for 25 min at room temperature by applying a constant current density of 10 mA/cm2. The PSL was removed in a 5 wt.% N...