The Comparison of the Reliability Performance of Different Top Metal Materials in MEMS Applications

The combination of analog/mixed-signal, high-voltage and embedded non-volatile memory options with sensor and actuator integration is still common in automotive, industrial, communication and medical applications. MEMS with or without integrated CMOS, 3D integration micro transfer printing and integrated microfluid systems are in use to realize such applications. The established top metal interconnect materials for analog/mixed-signal CMOS applications are thick Aluminum (AlCu with Titan and Titanium Nitride) and thick Copper. Integrated noble metal electrodes are necessary for MEMS applications like microfluidics. The reliability requirements of a CMOS/ MEMS process differs from a long storage shelf life at room temperature, long life time for medical (in-body) or space applications up to high operating conditions for automotive and industrial applications like oil drilling. Applications, like functional surfaces, combine integrated circuits for example for next generation DNA sequencing. The noble metals for electrodes on top are thinner for such applications. An additional reliability challenge for such a lab on a chip is corrosion. Automotive applications have often mission profiles which need high currents, high temperature and a growing mechanical stability. The reliability of noble top metals is more and more under investigation because MEMS are more common in automotive products. The knowledge about reliability especially about mechanical properties is an interesting topic in addition to the results from standard tests like electro migration and stress migration tests because of the advanced mechanical stress in the applications and the danger of corrosion. The comparison of the electromigration performance and mechanical stability of AlCu, Copper, Gold and Platinum as thick and/ or top metal tracks is necessary to evaluate and assess the suitability of the materials for the different applications. The possibilities to generate test results for thick and or noble metals are limited because of the necessary long test times for thick metals and materials like Gold or Platinum. The interaction of different failure mechanisms and the different material and stack combinations of the CMOS part make an assessment difficult. Simulations can support the choice of materials by values for mechanical stress and stress divergences as well as they can deliver basic knowledge about the main failure mechanisms. Only a smaller number of varying interconnect stacks will be realized in a development of a new process. The basic knowledge from simulation results will help to decide about the type of reliability test and test effort for the process qualification.