Selectively oxidized porous silicon (SOPS) substrate for packaging

Abstract

Silicon substrate is widely used in packaging areas because of its advantages of lower cost and good thermal conductivity to help remove heat and to maintain low IC junction temperatures. The semi-conducting nature of silicon substrate, however, has prohibited the fabrication of high performance passive elements in silicon substrate. A selectively oxidized porous silicon (SOPS) substrate was proposed to use the microwave power multi-chip packaging area. In this work, anodization of p-type silicon was carried out under the condition of 2, 6, 10, 30 and 50mA/㎠ in electrolyte solution of HF(48 w/o):$C_2H_5OH$=1:1. Firstly, PIPS (pulse injected porous silicon) layer was obtained by novel pulse modulation method. This new method has an advantage of higher growth rate of porous silicon. SEPS (selective porous silicon) layer is successfully implemented by patterning of Cr/photoresist and n-type silicon mask of phosphorus diffusion. And, the thick oxide film had to be obtained by a short-time-oxidation process of porous silicon, because the phenomenon of oxidation for porous silicon is the reaction of sidewall of trenches. The porosity of porous silicon is most important factor but the porosity measurement of silicon weight loss (the gravimetric method) is contained the high error rate. In the porosity calculation of porous silicon, new exact method(JRM method) of hole counting is proposed from the tetravalent dissolution reaction of porous silicon and the proposed reaction factor $M_{si}$. Using the OPS (oxidized porous silicon) substrate with thick silicon dioxide layer, high performance passive devices such as spiral planar inductors, coplanar waveguide (CPW) were fabricated and characterized. For GaAs MMIC chip interconnection, Au-wire bonding with 25μm-diameter is characterized. Thick oxide layer increases resonant frequency and maximum Q factor in planar inductor because of the low parasitic capacitance between inductor metal and the substrate. For 6.29nH in...