Aluminium-Scandium as bondpad chipmetallisation for copper wire bonding

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In this project it is intended to process and investigate an Aluminium-Scandium alloy as an alternative chip-metallisation for copper wire bonding. Aluminium alloys with a content of 0.1 to 0.3 % Scandium show an increased yield strength of up to 140-200 MPa compared to 20 MPa for pure aluminium at room temperature. Scandium is an alloying element which forms heat resisting spherical Al3Sc-precipitattions with particle sizes of less than 10 nm. Resulting from a lattice mismatch of 1.9% between Al-matrix and the Al3Sc-particles, the precipitations improve the strength and inhibit grain growth processes.It is known that in ultrasonic wire bonding process the used pure Aluminium, AlSi1 and AlSi1Cu0,5 alloys tend to undergo softening by dynamic recrystallization and dynamic recovery. These softening processes can be inhibited by the very fine Al3Sc-precipitations.It is planned to investigate the deformation- and softening behavior of 1-5 µm thick AlSc-layers during ultrasonic bonding with copper wire by varying bonding force and ultrasonic power. Additionally, a reduction of the Al-splashing when using AlSc as chipmetallisation is expected. The results will help to improve the copper wire bonding process by reducing cratering.