Thermodynamics of Processing Copper Thick Film Systems in a Reactive Atmosphere

Abstract

A major drawback of current copper thick‐film technology is the inefficient removal of the organic binder associated with the dielectric material in the low‐oxygen inert gas (N2) atmosphere of the furnace. In processing large area and/or multilayer substrates, the incomplete binder removal causes deleterious effects which have been well documented. Therefore, it is necessary to remove hydrocarbons and residual carbon from the films in the burn‐out section of the furnace before the films begin developing their characteristic microstructures. However, the atmosphere currently employed is not capable of removing all the carbon and hydrogen in the form of gaseous oxides. In literature, in addition to furnace modifications, several atmosphere modifications and manipulations have been proposed to achieve optimum properties for the fired films. With few exceptions, the scientific basis for such atmosphere modifications and manipulations has been left either unaddressed or obscure. With this background, this paper examines the feasibility of using a reactive gas mixture in the furnace to achieve efficient organic binder removal. Phase stability diagrams are presented to illustrate the stability of (i) carbon, (ii) thick film copper ingredients, (iii) active phases of resistors, and (iv) components of glassy and crystalline phases of dielectrics in selected reactive atmospheres. The stability of certain furnace belt constituents is also addressed. Mass balance calculations are shown to demonstrate the extent of carbon removal and copper oxidation in typical nitrogen atmospheres. Based on the interpretation of thermodynamic data and reaction mechanisms involved, a specific H2‐H2O mixture with nitrogen as the carrier gas is recommended. The approach presented here constitutes a general analytical scheme to understand materials‐atmosphere interactions occurring across a temperature range. Several issues in furnace design are also discussed from the standpoint of gas‐solid reaction kinetics. These deal with the design of gas‐flow systems that facilitate removal of organic binders.

Citation

Palanisamy, P. and Sarma, D.H.R. (1987), "Thermodynamics of Processing Copper Thick Film Systems in a Reactive Atmosphere", Microelectronics International, Vol. 4 No. 2, pp. 13-20. https://doi.org/10.1108/eb044270