A Combined Process of Formic Acid Pretreatment for Low-Temperature Bonding of Copper Electrodes

A new combined process of formic acid pretreatment for low temperature Cu direct bonding was proposed. Cu film and Cu micro-electrodes samples were treated by formic acid and successfully bonded together at 200°C. Cu surface oxide was reduced at 200°C using formic acid treatment without/with Pt catalyst. Particularly, the treatment with heated Pt catalyst is more effective for Cu surface reduction than that without Pt catalyst or with room temperature Pt catalyst. After formic acid treatment under various conditions, Cu film and Cu micro-electrodes samples were bonded together at 200°C in N2. Among them, the bonded samples treated by formic acid using heated Pt catalyst showed the strongest bonding strength. Very few oxide and carbon was remained at the bonding interface. It also proves that the treatment can reduce surface oxide resulting in strong bonding at low temperature.

[1]  T. Suga,et al.  Low temperature Cu-Cu direct bonding using formic acid vapor pretreatment , 2011, 2011 IEEE 61st Electronic Components and Technology Conference (ECTC).

[2]  Jian-Qiang Lu,et al.  Low Temperature Wafer Bonding by Copper Nanorod Array , 2009 .

[3]  Preparation of Pt-Pd catalysts for direct formic acid fuel cell and their characteristics , 2007 .

[4]  T. Itoh,et al.  Bumpless interconnect through ultrafine Cu electrodes by means of surface-activated bonding (SAB) method , 2006, IEEE Transactions on Advanced Packaging.

[5]  A. Shigetou,et al.  Direct bonding of CMP-Cu films by surface activated bonding (SAB) method , 2005 .

[6]  M. Bowker,et al.  An STM, TPD and XPS investigation of formic acid adsorption on the oxygen-precovered c(6×2) surface of Cu(110) , 1998 .

[7]  M. Bowker,et al.  Temperature-programmed desorption studies of methanol and formic acid decomposition on copper oxide surfaces , 1998 .

[8]  Kuan-Neng Chen,et al.  Microstructure examination of copper wafer bonding , 2001 .

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

[10]  M. Bowker,et al.  Formic acid adsorption and oxidation on Cu(110) , 2008 .

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

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

[13]  Sari Johanna Kaipio,et al.  Reduction of Copper Oxide Film to Elemental Copper , 2005 .

[14]  A. Shigetou,et al.  Bumpless Interconnect of 6- $\mu$m-Pitch Cu Electrodes at Room Temperature , 2008, IEEE Transactions on Advanced Packaging.