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Si 기판의 캐비티 형성이 불필요한 웨이퍼-레벨 MEMS capping 공정을 연구하였다. 4인치 Si 웨이퍼에 Ni 캡 을 전기도금으로 형성하고 Ni 캡 rim을 Si 하부기판의 Cu rim에 에폭시 본딩한 후, SnBi debonding 층을 이용하여 상부 기판을 Ni 캡 구조물로부터 debonding 하였다. 진공증착법으로 형성한 SnBi debonding 층은 Bi와 Sn 사이의 심한 증기 압 차이에 의해 Bi/Sn의 2층 구조로 이루어져 있었다. SnBi 증착 층을 150oC에서 15초 이상 유지시에는 Sn과 Bi 사이의 상호 확산에 의해 eutectic 상과 Bi-rich β상으로 이루어진 SnBi 합금이 형성되었다. 150℃에서 유지시 SnBi의 용융에 의 해 Si 기판과 Ni 캡 구조물 사이의 debonding이 가능하였다.


We investigated the wafer-level MEMS capping process for which cavity formation in Si wafer was not required. Ni caps were formed by electrodeposition on 4" Si wafer and Ni rims of the Ni caps were bonded to the Cu rims of bottom Si wafer by using epoxy. Then, top Si wafer was debonded from the Ni cap structures by using SnBi layer of low melting temperature. As-evaporated SnBi layer was composed of double layers of Bi and Sn due to the large difference in vapor pressures of Bi and Sn. With keeping the as-evaporated SnBi layer at 150oC for more than 15 sec, SnBi alloy composed of eutectic phase and Bi-rich β phase was formed by interdiffusion of Sn and Bi. Debonding between top Si wafer and Ni cap structures was accomplished by melting of the SnBi layer at 150℃.


We investigated the wafer-level MEMS capping process for which cavity formation in Si wafer was not required. Ni caps were formed by electrodeposition on 4" Si wafer and Ni rims of the Ni caps were bonded to the Cu rims of bottom Si wafer by using epoxy. Then, top Si wafer was debonded from the Ni cap structures by using SnBi layer of low melting temperature. As-evaporated SnBi layer was composed of double layers of Bi and Sn due to the large difference in vapor pressures of Bi and Sn. With keeping the as-evaporated SnBi layer at 150oC for more than 15 sec, SnBi alloy composed of eutectic phase and Bi-rich β phase was formed by interdiffusion of Sn and Bi. Debonding between top Si wafer and Ni cap structures was accomplished by melting of the SnBi layer at 150℃.