Facing the challenge of designing for Cu/low-k reliability

Die singulation technologies for advanced packaging: A critical review

“…Increasing interconnect density can be achieved by increasing the number of metal layers while shrinking interconnect dimensions. In fact, the poor adhesion induced thin film delamination and cracking issue has been identified as one of the key failure modes in chemical mechanical polishing (CMP) 14,[17][18][19][20] and packaging processes, including wafer dicing, die attach, wire bonding and molding. In addition, higher resistance also induces increased power consumption and heat generation, reduced metal line spacing causes more crosstalk.…”

“…However, smaller metal cross sections and reduced wire spacing lead to a significant increase in R and C, causing a higher RC delay. [19][20][21][22][23][24] Also, copper is more ductile than aluminum and will enhance the premature clogging of dicing blade, which adds additional loading to the blade to cause excessive chipping. 10,11 a) Electronic mail: wei-sheng_lei@amat.com As the interconnect structures transition from Al/SiO 2 ILD to Cu/low-k ILD, the RC delay can be effectively reduced due to the reduction of resistivity from aluminum (Al, 2.65-2.82 lX-cm) to copper (Cu, 1.6 lX-cm) and that of dielectric constant from SiO 2 ILD (k ¼ 4.1) to low-k ILD (k 3).…”

Low‐kMaterials: Recent Advances

“…It is then not surprising that critical reliability issues have been encountered during chip-package interaction (CPI) [56,57]. Indeed, the thermal deformation of the packaging structure is directly coupled into the BEOL interconnects, creating large stresses at the ultra-low-k levels that can induce materials fracture and/or delamination [58].…”

Wire bonding using copper wire

“…The bonding position significantly affects the local stress near the bond, and the wire should be bonded at the pad center Chen et al (2004) The stress is large if the pad size is close to the wire ball size Cu and Au bond wires have a work-hardening effect and higher forces are needed to form a Cu bond, leading to higher stresses in the pad structure Degryse et al (2004Degryse et al ( , 2005 Slip was the major mechanism involved in the overall deformation of polycrystalline copper Hong et al (2005) Higher bonding force and power are needed for the second bond than the first bond to have strong pull force Tian et al (2005Tian et al ( , 2008) Decreased hardness and strength of the HAZ led to breakage sites of the wires to be in the HAZ near Cu balls Hung et al (2006) Annealed Cu wires exhibited tensile strength and elongation characteristics comparable to those of Au wires Chen et al (2006a) With a TiW barrier layer adopted, Cu or Au diffusion to Si is decreased Zhang et al (2006Zhang et al ( , 2007 Cu-Al IMC is thinner than Au-Al IMC at the bonding interface, resulting better bond strength and smaller electrical resistance Pd-plated Cu wire demonstrated excellent reliability and bondability Kaimori et al (2006a, b) A new capillary with a new surface morphology leads to satisfactory results in ball shear and stitch pull tests Goh and Zhong (2007a) Increasing the temperature can enlarge the bondability window and less bonding force can be used England and Jiang (2007) Lower ultrasonic power and bonding force can help minimise pad cratering Plasma cleaning of lead-frames before bonding increases the tail breaking stability significantly Lee et al (2007) Asperity plastic deformation is the most significant factor for good bonding Murali et al (2007) Ultrasonic energy breaks the oxide film and deforms asperities, while the bonding force increases the asperity proximity To have shorter firing time during FAB formation, use a lower contact velocity and provide sufficient inert-gas coverage is recommended for a softer FAB and minimised stress induced during ball bond impact Zhong et al (2007b) Cu/Al IMCs are mainly Cu 9 Al 4 and CuAl 2 , with CuAl present in smaller amounts Hang et al (2008) increasing research on applying FEA to wire-bonded packages (Chen et al, 2006b;Ishiko et al, 2006;Saiki et al, 2006;Fiori et al, 2007a, b;van Driel, 2007;Viswanath et al, 2007;…”