Study Of The Character Of Aluminum Nitride Co-fire Metalization And Multilayer Thin Film Metalization

With the development of VLSI, there are increasing demands for 1C interconnection. The high-density package technology becomes mainstream in advanced systems. Multichip module (MCM) is high-level mode in electronic package. MCM is that bare dice and microelements are assembled on a high-density interconnection (HDI) substrate. MCM can meet the demands of compact packaging and high density. It's a method to realize system integration. The HDI substrate is critical to MCM.Aluminum nitride (A1N) has been considered as a material for ceramic packaging in view of the recent trends in the semiconductor industry toward higher speed, power dissipation and packaging density. This is because of its natural properties. These properties include a high thermal conductivity (200W/m K), a high mechanical strength and a thermal expansion coefficient close to that of silicon. Other electrical characteristics of A1N, such as insulation resistance, dielectric constant and dielectric loss are very close to those of Al2O3. These characteristics are suitable for semiconductor packaging that is required to have particularly high reliability. Thus, A1N substrate is useful for multi-chip module and for MEMS as packaging material.Low sheet resistance and good matching between substrate and paste are the principal requirements for conductor paste in multi-layer cofire substrate. We need to start their sintering at same temperature and to ensure conductor paste and green-sheet ceramic bodies have the same shrinkage rate.In this sense, SiO2 is a good additive. SiO2 is used as a component in many kinds of pastes. The softening point of pure SiO2 glass is at about 1600, the same temperature at which A1N green-sheet ceramic bodies start shrinkage. SiO2 can react with A1N and form sialon glass. In this paper, a tungsten paste is proposed with SiO2 glass as the only additive.CaO and Y2O3 are additives in A1N green sheet. YA1O and CaAlO complex oxides have low melting point compare to the soaking temperature of A1N sintering. YA10 and CaAlO complex oxides become liquid phase in the process of sintering. SiO2reacts with CaO, A12O3 and Y2O3, producing CaSiAlO and YSiO phases which are detected at the interface between conductor paste and A1N substrate. Ysialon and casialon glasses also form at the interface.If 0.45%wt SiO2 is added in the paste, the tungsten paste has low sheet resistance and matching shrinkage of A1N green-sheet bodies. At this concentration of SiO2 in the paste, A1N substrate is little porous at interface. A1N grains at interface are no different from those in the bulk. The sintering stress is decreased to the degree that cannot influence the substrate shrinkage. The A1N substrate contains nine levels with size of 50 50mm2. The sheet resistance is 10m/, substrate bending is smaller than 50 u m/50mm and adhesion strength is greater than 30MPa.Polyimide (PI) is a thermally stable insulator and is used in multi layer thin-film interconnection (MCM-D). PI is made from precursors after heat treat. These precursors polymerize to form polyamic acid (PAA). The PAA reacts with metal film such as copper. Thus its character become worse and circuit resistance increases. Having reacted with copper, PAA becomes complex. The complex decomposes after heat treating and cause the increase in dielectric constant and reduction in dielectric breakdown strength. Otherwise Cu2O and CuO emerge from the complex, too. These defects can be overcome by a film structure of Pl/Cr/Cu/Cr.Cr/Cu/Cr film has been widely used in MCM-D. Having been treated at variable temperature in atmosphere, we can get the conclusions: (1) Treated at 300, there are little diffusion coefficients between Cu and Cr; (2) Treated over 500, Cr and Cu diffuse into each other evidently. Cu film oxidizes and there are cracks in Cr film. Cr and Cu cannot form alloy and compound at any temperature.