저온 Cu-Cu본딩을 위한 12nm 티타늄 박막 특성 분석
Evaluation of 12nm Ti Layer for Low Temperature Cu-Cu Bonding
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초록
최근 반도체 소자의 소형화는 물리적 한계에 봉착했으며, 이를 극복하기 위한 방법 중 하나로 반도체 소자를수직으로 쌓는 3D 패키징이 활발하게 개발되었다. 3D 패키징은 TSV, 웨이퍼 연삭, 본딩의 단위공정이 필요하며, 성능향상과 미세피치를 위해서 구리 본딩이 매우 중요하게 대두되고 있다. 본 연구에서는 대기중에서의 구리 표면의 산화방지와 저온 구리 본딩에 티타늄 나노 박막이 미치는 영향을 조사하였다. 상온과 200oC 사이의 낮은 온도 범위에서 티타늄이구리로 확산되는 속도가 구리가 티타늄으로 확산되는 속도보다 빠르게 나타났고, 이는 티타늄 나노 박막이 저온 구리 본딩에 효과적임을 보여준다. 12 nm 티타늄 박막은 구리 표면 위에 균일하게 증착되었고, 표면거칠기(Rq)를 4.1 nm에서3.2 nm로 낮추었다. 티타늄 나노 박막을 이용한 구리 본딩은 200oC에서 1 시간 동안 진행하였고, 이후 동일한 온도와 시간 동안 열처리를 하였다. 본딩 이후 측정된 평균 전단강도는 13.2 MPa이었다.
Abstract
Miniaturization of semiconductor devices has recently faced a physical limitation. To overcome this, 3D packaging in which semiconductor devices are vertically stacked has been actively developed. 3D packaging requires three unit processes of TSV, wafer grinding, and bonding, and among these, copper bonding is becoming very important for high performance and fine-pitch in 3D packaging. In this study, the effects of Ti nanolayer on the antioxidation of copper surface and low-temperature Cu bonding was investigated. The diffusion rate of Ti into Cu is faster than Cu into Ti in the temperature ranging from room temperature to 200oC, which shows that the titanium nanolayer can be effective for low-temperature copper bonding. The 12nm-thick titanium layer was uniformly deposited on the copper surface, and the surface roughness (Rq) was lowered from 4.1 nm to 3.2 nm. Cu bonding using Ti nanolayer was carried out at 200oC for 1 hour, and then annealing at the same temperature and time. The average shear strength measured after bonding was 13.2 MPa.
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