Studying electro‐physical material characteristics of vacuum‐deposited layers of aluminium (tantalum) when using aluminium sheet as a carrier for MCM, interconnections, vias and resistive groups

Abstract

Investigations of material parameters within the system Al, Al2O3, Ta, Ta2O5 and TaOxN1‐x are presented. This combination is characteristic when using Al sheet for production of substrates including electronic interconnections, vias and resistive groups. They can serve for MCMs due to the specific features of Al. The technological process includes first electrochemical oxidation of Al‐sheet as base isolation layer Al2O3 (50‐70μm). This process is followed by vacuum deposition of relatively thick layers of Al (2‐5μm). Each layer is then processed by lithographic methods followed by selective electro‐chemical oxidation as a help process for structuring. The development of this combined structuring method allows the simultaneous achievement of interconnections (Al) and isolation (Al2O3) levels with least size up to 50μm. The importance of the method consists of a vertical combination of several conductive layers of Al structured as described above, “burying” the interconnections in the insulating Al2O3 films. All necessary combinations and configurations of different kinds of microstrip lines are possible. The dielectric characteristics of Al2O3, achieved through the above mentioned method, can be changed in accordance with the parameters of the technological steps and filling of the porous structure. Thus some interesting high frequency features of microstrips are obtained. Extra advantage is the ability of combination of conductive Al layers with other types of such layers as tantalum (Ta). With Ta can be achieved other permittivity constants of the insulation layers and in combination with TaOxN1‐x intermediate planes of resistive groups are developed. The measurement of the stripline parameters is done by microwave technics, because the desired application of the substrates is for high‐speed digital signals in the GHz range.