Infrared differential interference contrast microscopy for 3D interconnect overlay metrology.
One of the main challenges for 3D interconnect metrology of bonded wafers is measuring through opaque silicon wafers using conventional optical microscopy. We demonstrate here the use infrared microscopy, enhanced by implementing the differential interference contrast (DIC) technique, to measure the wafer bonding overlay. A pair of two dimensional symmetric overlay marks were processed at both the front and back sides of thinned wafers to evaluate the bonding overlay. A self-developed analysis algorithm and theoretical fitting model was used to map the overlay error between the bonded wafers and the interconnect structures. The measurement accuracy was found to be better than 1.0 micron.
Center for Measurement Standards, ITRI, Bldg. 12, 321 Sec. 2, Kuang Fu Rd., Hsinchu, Taiwan. yku@itri.org.tw
Yi-sha
YS
Ku
Deh-Ming
DM
Shyu
Yeou-Sung
YS
Lin
Chia-Hung
CH
Cho