Effects of materials characteristics on ultrasonic bonding for Cu/Cu microelectronic joints

• Main Authors: I-Yu Yu, 俞亦祐
• Other Authors: 宋振銘
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5159057%22.&searchmode=basic

碩士 === 國立中興大學 === 材料科學與工程學系所 === 107 === Due to the advantages of low electrical resistance and size miniaturization, Cu to Cu direct bonding has become one of the important trends in microelectric interconnect fabrication. However, strict processing requirements, e.g. high vacuum, long bonding time and excess coating, limit its industrial application. Robust Cu-to-Cu bonding with low temperature, ambient pressure (under N2 or air) and short processing time is strongly requested by advanced IC stacking, MEMS hermetic sealing, and flexible electronics assembly as well. To fulfill those requirements, ultrasonic technique has recently be adopted. Rather than ultrasonic parameters (e.g., loading and vibration amplitude), this study optimized the geometric design of copper bumps and also focused on the influences of surface physical features on direct bonding between two copper electro-deposits. Experimental results show that with a similar contact area, a bigger bump diameter as well as a shape change for bumps from round to square contributed to a stronger bonding. Increases in surface roughness and bonding temperature both gave rise to better bonding. Joints consisting of hard bumps bonded with soft pads exhibited superior bonding strength than soft bump on soft substrate, in turn higher than hard bump on hard substrate. Through alloying and dealloying with Zn, a more roughened faying surface further raised the bonding strength. However, the formation of porous sub-surface structure brought about a negative influence in mechanical support.