Publication: Evaluation of sputtering process parameters on microstructural properties and silicon precipitate of aluminium-silicon-copper films
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Date
2025-09-01
Authors
Devah S/O Kalai Selvam
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Abstract
Silicon (Si) precipitates in Aluminium-Silicon-Copper (AlSiCu) bond pad metallization can cause interlayer dielectric (ILD) cracking during Copper (Cu) wire bonding, reducing device reliability. This study investigated the influence of sputtering process parameters such as deposition temperature, degas cooling, and post-deposition cooling rate on Si precipitate behaviour and film integrity. The Design of Experiments was performed using three factors: Deposition Temperature (60 °C, 120 °C, 180 °C, and 240 °C), Degas Cooling (with and without), and Cooling Rate (rapid and slow). Eight experimental conditions (Samples A–H) were evaluated for surface defect inspection, wafer stress, surface roughness, grain size, Si precipitate size and count, and electrical yield. Statistical analysis confirmed that deposition temperature is the dominant factor, significantly affecting Si precipitate size and count, grain growth, surface roughness, and wafer stress. Elevated deposition temperatures (240 °C) enhanced atomic mobility, resulting in larger grains and partial stress relaxation but also rougher surfaces and pronounced Si segregation. Cooling rate was identified as a secondary parameter, with slow cooling reducing wafer stress and producing smoother surfaces, while degas cooling showed only minor contributions, limited to surface roughness. Among the tested conditions, low deposition temperature (60 °C) combined with degas cooling and rapid post-deposition cooling produced the most favourable outcome, yielding fine grains (~6 μm), smooth morphology (~25–28 nm RMS), minimal Si precipitate (~950 nm average size, ~8 counts/region), and low wafer stress (~120 MPa). Despite microstructural variations, electrical yield remained consistently high (>98%), indicating that Si precipitate primarily impacts mechanical reliability rather than electrical performance. Overall, this study demonstrates a clear correlation between sputtering parameters and AlSiCu film properties, showing that precise control of deposition temperature combined with optimized cooling strategies is essential to suppress Si precipitate and improve bond pad stability. These findings provide a practical basis for tailoring sputtering conditions to achieve reliable metallization with reduced bonding failures.