Study of thin film metallization adhesion in ceramic multichip module

The concept of Multichip module (MCM) packaging is popularized for evaluating prototypes of novel devices and materials in extreme environmental conditions. The packaging for these types of electronics must be mechanically well-built and the metallization must be low in thermal conductivity in order to prevent the heat transfer from the external environment to the protected device. Strong bonding between metal and ceramic has been an issue of concern for many years due to delamination tendencies at the interfaces. This paper evaluates the adhesion characteristics of sputtered Copper (Cu) thin films to alumina (Al₂O₃) substrates. The relationship between the surface roughness of the Al₂O₃ substrate with appropriate surface treatment and the adhesion with Cu thin film is established experimentally. An adhesion layer with lower thermal conductivity and smaller coefficient of thermal expansion (CTE) mismatch such as Titanium (Ti) or Chromium (Cr) was also inserted in between to investigate the adhesion improvement of the metal-substrate. We have seen that Ti is essentially used as an adhesion layer between the bonding of Cu and Al₂O₃ for electronic applications. With higher adhesion strength, and smaller CTE mismatch with Cu and Al₂O₃, insertion of Ti adhesion layer with optimum substrate surface roughness could lead to a more reliable packaging solution.