Research Of BeO Ceramic Substrate Planarization Modification

For its characteristics of high insulation, low dielectric constant, high chemicalstability and high thermal conductivity, BeO was widely used as the main ceramicmaterials in power semiconductor, microwave electric vacuum devices, nuclear industryet al. In order to reduce the surface roughness of BeO ceramic substrates and eliminatethe hole defects on the substrates surface for the advantage of the thin films growth onthe substrates and promoting of the BeO ceramic substrates in the thin films products,planarization modified method of coating glass glaze on BeO by screen printing wasdiscussed in this paper.According to the coefficient of thermal expansion of BeO ceramic, the matchingglass glaze formula was designed through theoretical calculation. The organic carrier forscreen printing glass glaze was concocted and the content of organic solvent andadditive was optimized. So the formula of organic carrier with good hierarchicalvolatilization, thixotropy, and uniformity was obtained and applied to screen printingglass paste.The effect of sintering temperature and holding time on the surface roughness ofglazed planarization substrate was studied. The Ra of the substrate surface roughnesswas reduced to100nm or less from356.7nm, and it achieved the requirements of thinfilm devices. The RMS of glazed planarized BeO substrate was reduced to24.9nmcomparing with141.9nm of the polished BeO ceramic substrate. The test results showedthat the glass layer of about20μm thickness had no significant effects on the thermalperformance of the BeO ceramic substrates. And the glazed planarization modificationmethod was suitable for the ceramic substrates of high thermal conductivity.In order to test the result of the glazed BeO ceramic substrate modification, theTaN thin films prepared by reactive RF magnetron sputtering was discussed in thisarticle. The TaN thin film was grown on the glazed BeO ceramic substrate to verify theglazed planarized modification was conducive to BeO ceramic substrate application infabricating the thin film devices.The of reactive RF magnetron sputtering TaN thin films were studied. By testing the effects of different nitrogen content, substrate temperature, sputtering power, heattreatment temperature on TaN thin films TCR and square resistance, optimumtechnological parameters of preparation of TaN thin films with low temperaturecoefficient of resistance were explored. Sputtering pressure:0.5Pa, nitrogen content:0.8%, substrate temperature:100℃, sputtering power:200W, heat treatmenttemperature:500℃, holding time of heat treatment:30min. The TCR and squareresistance of the TaN thin film prepared with these parameters were-69ppm/℃and4.3/□.TaN thin films and metal lines were fabricated on the glazed planarized modifiedBeO ceramic substrate, the result of substrate planarization was fine and the substratewas suitable for preparation of thin film devices.