Ultra-thin Ti passivation mediated breakthrough in high quality Cu-Cu bonding at low temperature and pressure

Abstract Deposition of Ultra-thin Titanium (Ti) layer (3 nm) on Copper (Cu) surface inhibits surface oxidation upon exposure to ambient air as well as reduces surface roughness from about 2.1 nm (Cu only) to about 0.4 nm resulting in Cu-Cu bonding at a temperature as low as 160 °C and operating pressure as low as 2.5 bar. This simple passivation mechanism enhanced diffusion of Cu across the boundary and resulted in grain growth across the entire bonding layers as revealed by several methodical characterizations. This practical breakthrough has immense potential to usher us into practical realization of 3D IC integration.

[1]  J. Wei,et al.  Low temperature Cu-Cu thermo-compression bonding with temporary passivation of self-assembled monolayer and its bond strength enhancement , 2012, Microelectron. Reliab..

[2]  A. Fan,et al.  Copper Wafer Bonding , 1999 .

[3]  Chuan Seng Tan,et al.  Cu-Cu diffusion bonding enhancement at low temperature by surface passivation using self-assembled monolayer of alkane-thiol , 2009 .

[4]  A. Dutta,et al.  Room temperature desorption of Self Assembled Monolayer from Copper surface for low temperature & low pressure thermocompression bonding , 2015, 2015 IEEE 65th Electronic Components and Technology Conference (ECTC).

[5]  Kuan-Neng Chen,et al.  Microstructure evolution and abnormal grain growth during copper wafer bonding , 2002 .

[6]  D. F. Lim,et al.  Cu passivation for enhanced low temperature (≤300°C) bonding in 3D integration , 2013 .

[7]  Ching-Te Chuang,et al.  Novel Cu-to-Cu Bonding With Ti Passivation at 180 $^{\circ}{\rm C}$ in 3-D Integration , 2013, IEEE Electron Device Letters.

[8]  J. Torres,et al.  Electromigration resistance of copper interconnects , 1997 .

[9]  R. Gutmann,et al.  Wafer Level 3-D ICs Process Technology , 2008 .

[10]  Tadatomo Suga,et al.  Room temperature Cu–Cu direct bonding using surface activated bonding method , 2003 .

[11]  Ching-Te Chuang,et al.  Novel Cu-to-Cu Bonding With Ti Passivation at 180 °C in 3-D Integration , 2013 .

[12]  Chuan Seng Tan,et al.  Silicon Multilayer Stacking Based on Copper Wafer Bonding , 2005 .

[13]  Börje Johansson,et al.  First-principles calculations of the vacancy formation energy in transition and noble metals , 1999 .