Cu is used as interconnect material in ULSI technology and through-Si via process for System In Package due to its a lower electrical resistivity and a higher resistance to electromigration than Al and its a higher thermal conductivity and lower electrical resistivity than W.
However, Cu is known to be very mobile in Si. Deep trap levels caused by diffusion of Cu lead to reduce the reliability of device. Therefore, the development of diffusion barrier is necessary to prevent Cu diffusion.
Amorphous structure of diffusion barrier is desirable because grain boundaries act as Cu diffusion path. And diffusion barriers must have a high crystallization temperature and chemically stable with Cu. Amorphous Ta-Si-N films have been studied as good diffusion barriers in Cu interconnect. However, the property of diffusion barrier was not studied as Cu diffusion barrier over a wide range of composition. This study covered the microstructure and the property against Cu diffusion of diffusion barrier over a wide range of composition.
All diffusion barrier layers were deposited by DC magnetron reactive co-sputtering. Changing the DC target current density and $N_2/(Ar+N_2)$ flow rate ratio, diffusion barrier layers with various composition were deposited. The microstructure of as-deposited diffusion barrier layers was investigated by XRD (X-ray diffraction). Ta-Si-N films containing Si above 10 at.% have the amorphous structure. And diffusion barrier layers have strong tendency of amorphous structure with increasing N and Si content.
After heat treatment of Cu/Ta-Si-N film(30nm)/Si structure, Ta-Si-N films with various composition have been investigated as the Cu diffusion barrier by XRD analysis. At Si composition ranging 0 from 15 at.%, the Cu diffusion barrier property was the best when the composition ratio of N and Ta+Si was almost same. And the contour map of failure temperature for various compositions against Cu diffusion was described.
구리는 낮은 비저항, 높은 열전도도 및 우수한 electromigration 저항성을 가지고 있어 마이크로프로세서와 3-D 패키징에서 TSV(through Si-via)충전물질로 사용되고있다.
하지만 구리는 Si과 $SiO_2$ 내에서 확산이 매우 용이하며 Si내부에서 generation recombination center로 작용하여 소자 오작동의 원인이 된다. 따라서 구리의 확산을 막아주는 확산방지막이 필요하다.
확산방지막은 구리와 화학적으로 안정해야 하며, 높은온도에서도 안정성을 유지해야 한다. 비정질확산방지막은 구리의 확산경로인 입계를 줄여 우수한 특성을 보인다. 비정질 Ta-Si-N 박막은 가장 우수한 특성을 보이는 것으로 보고 되었다.
하지만 Ta-Si-N 박막의 광범위한 조성범위에서 조성에 변화에 따른 미세조직의 변화와 구리확산방지특성은 보고되지 않았다. 따라서 본 연구에서는 광범위한 조성범위에서 Si과 N의 조성변화에 따른 미세조직의 변화를 XRD분석을 통해조사하였고, 열처리 실험을 통해 Si과 N조성변화에 따른 구리확산방지파괴온도를 조사하여 확산방지파괴온도 contour map을 완성하였다. 그리고 확산방지막에서 Si과 N의 조성비가 증가할수록 Ta-Si-N박막은 비정질화되었고, 구리확산방지 특성은 Si의 조성비가 약 20 at.%이하일 때, Ta+Si과 N조성비가 1:1이되는 조성범위에서 가장 우수한 특성을 가졌다.
