Formation Mechanism of Unique Voids in Cu Interconnects for ULSI

在Si-ULSI（超大规模集成电路）产业中，向Cu互连的发展是积极的需求。铜互连线和硅器件的性能和可靠性下降是目前发展面临的一个严重问题。到目前为止，Cu的空化机制主要是由于退火过程中的热应力和蠕变现象。本研究的目的是研究与以往完全不同的独特微孔，并阐明Cu薄膜中微孔的形成机制。近年来，采用电镀和溅射沉积的方法制备了铜互连。在这两种沉积方法中，杂质或沉淀物如有机添加剂和Cu氧化物（Cu0）通常在Cu薄膜生长过程中被引入。Cu薄膜中的这些杂质可能对孔隙的形成有很大的影响。事实上，在H_2/N_2气氛中退火后，溅射沉积的Cu/Cu0/Cu多层膜中出现了空洞。很明显，这种空化是由Cu0中的0与大气中的H_2发生化学反应而产生的H_20气泡造成的。对于电镀Cu薄膜，退火后在薄膜与衬底的界面处形成了大量的空隙。有机添加剂极有可能引起镀层中的空穴现象。因此，了解和控制这些杂质的数量对于防止孔隙的形成是非常重要的。在本研究中，我们对Cu薄膜中的空化现象有了宝贵的认识。从形成机制的角度来看，观察到的微孔是独特的。为了开发高性能、可靠的铜互连，对这些独特空隙的理解将是非常必要的。

Development to Cu interconnect is positively required in Si-ULSI(Ultra-Large-Scale Integrate) industries. The serious problem for the development is void formation, resulted in degradation of the performances and reliabilities in the Cu interconnects and Si devices. So far, mechanism of voiding in the Cu has been considered due to thermal stress and creep phenomena during annealing. The purpose in the present study is to investigate unique microvoid, which is completely different from the previous one, and to elucidate the mechanisms of the void formation in the Cu films.Recently, the Cu interconnects are fabricated using electroplating and sputtering depositions. In both depsitin methods, impurities or precipitates such as organic additives and Cu oxide(Cu0) are commonly introduced in the Cu films during growth. These impurities in the Cu films may have strong influence on the void formation. In fact, the formation of voids in the Cu/Cu0/Cu multilayers deposited by sputtering was observed after annealing in H_2/N_2 atmosphere. It is clear that this voiding is resulted from the formation of H_20 bubbles produced by chemical reaction between 0 in Cu0 and H_2 in the atmosphere. In case of the electroplated Cu films, a lot of voids were formed at the interface between the film and the substrate after annealing. There is much possibility that the organic additives trigger off the voiding in the electroplating depositions. As a consequence, it is quite essential to understand and control the amount of these impurities for prevention of the void formation.In the present study, we got precious knowledge of the voiding phenomena in the Cu films. The microvoids observed are unique from the point of view of the formation mechanism. Understandings of these unique voids will be strongly required fox the developments of high-performance and -reliable Cu interconnects.