A Study on Reduced/Absent Adhesion/Cap Layers for Optimized BEOL RC Performance

Dewei Xu, Zhiguo Sun, Haojun Zhang, S. Pozder, P. Justison, Seungho Kook, R. Augur, R. Fox
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Abstract

Lower RC delay is vital to achieve optimal and competitive circuit performance and hence drives the endlessly pursued BEOL integration scheme advancement. To date low-k dielectric materials, i.e., fluorine-doped oxides, carbon-doped oxide (SiCOH), to porous carbon-doped oxides (p-SiCOH) have been implemented. However, due to the process integration challenges with inherently weak low-k materials, the trend to pursue lower k dielectrics has come to a plateau as technology nodes scale down past 20/14nm. On the other hand, the trend of geometry layer thickness shrinking down, such as trench CD and height, via CD and height, etc., still continues for each advanced technology node. In the BEOL stack adhesion layers (oxide + gradient layers) (ALs) with higher k value were introduced to enhance interface adhesion strength between SiCOH/p-SiCOH and dielectric cap film (SiCN), which offset the intrinsic RC benefit from low-k dielectric material. At more advanced nodes and beyond, the combined ALs and cap film could be up to via or trench height, which poses a huge challenge to meet desired RC performance and technology node scaling. Therefore, the thickness reduction of ALs and cap film becomes necessary for further technology node scaling. In this study, samples with interfacial full ALs, reduced ALs and bulk only (no ALs) for p-SiCOH (k=2.75) on various cap films were prepared, such as SiCN, SiCN/ODC, SiCN/AlONx, etc. TOF-SIMS analyses was used to confirm the composition of the dielectric stacks and later check the debonded surface morphology. Four-point bend adhesion tests were conducted to evaluate interfacial adhesion strength. Results show the interfacial adhesion strength on samples with reduced Als and bulk only (no ALs) is dropped by ~20% and ~30%, respectively. Additional ODC layer on top of SiCN would increase the interfacial adhesion strength by ~10%. It is suggested that reduced ALs may be adequate to satisfy overall CPI requirement for the BEOL integration scheme of p-SiCOH on advanced dielectric cap films (AlN + ODC). The coupling capacitance reduction for a combined reduced ALs and advanced dielectric cap can be up to 16% at M0 level and 10% at Mx level for a 40nm metal pitch.
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减少/无粘附/帽层对优化BEOL RC性能的研究
较低的RC延迟对于实现最佳和有竞争力的电路性能至关重要,因此推动了不断追求的BEOL集成方案的发展。迄今为止,低k介电材料,即氟掺杂氧化物,碳掺杂氧化物(SiCOH),多孔碳掺杂氧化物(p-SiCOH)已经实施。然而,由于固有的弱低k材料的工艺集成挑战,随着技术节点缩小到20/14nm以上,追求低k介电体的趋势已经进入平台期。另一方面,对于每个先进技术节点,几何层厚度的收缩趋势仍在继续,如沟槽CD和高度,通过CD和高度等。在BEOL叠层中引入高k值的附着层(氧化物+梯度层)(ALs)来增强SiCOH/p-SiCOH与介质帽膜(SiCN)之间的界面附着强度,抵消了低k介电材料的固有RC效应。在更先进的节点或更先进的节点上,ALs和cap膜的结合高度可能达到孔道或沟槽高度,这对满足期望的RC性能和技术节点规模提出了巨大挑战。因此,降低铝酸盐和帽膜的厚度成为进一步技术节点缩放的必要条件。本研究分别制备了SiCN、SiCN/ODC、SiCN/AlONx等不同帽膜上的界面full al、还原al和p-SiCOH (k=2.75)本体(no al)样品。使用TOF-SIMS分析来确定介电堆的组成,然后检查剥离的表面形貌。采用四点弯曲黏附试验评价界面黏附强度。结果表明,al还原后的试样界面粘附强度下降了约20%,未添加al的试样界面粘附强度下降了约30%。在SiCN表面增加ODC层可使界面粘接强度提高约10%。结果表明,还原后的al足以满足p-SiCOH在先进介质帽膜(AlN + ODC)上BEOL集成方案的总体CPI要求。对于40nm的金属间距,al和高级介电帽的耦合电容降低在M0级可达16%,在Mx级可达10%。
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