BEOL Reliability Enhancement by Applying New Capping Materials

Abstract

With the increasing miniaturization of devices, back-end-of-line (BEOL) reliability has become a prime concern. Electromigration (EM) is usually improved using cap materials, such as atomic layer deposition tungsten (ALD-W) and cobalt tungsten phosphide (CoWP). This study investigates the efficacy of EM and the time-dependent dielectric breakdown enhancement models (TDDB) based on cap materials. The selectivity of low-resistivity ALD-W using WF6 is improved when the reducing agent SiH4 is replaced with B2H6. The modified ALD-W also exhibits a higher dissociation rate for W nucleation. The chosen precursor plays an important role in the selective deposition of dielectric or Cu materials. Relative to Cu, the EM failure time of SiH4 treatment with CoWP, untreated CoWP and ALD-W was improved more than tenfold, tenfold, and threefold, respectively. The higher EM enhancement in CoWP than in ALD-W may be attributed to the thicker cap attainable by CoWP without selectivity loss. When CoWP is used as the cap material, the appearance of an etching stop layer (ESL) confirms that there is no benefit to the time-dependent dielectric breakdown performance because of the relatively low breakdown voltage. Finally, we demonstrate the feasibility of using different cap materials for improving BEOL reliability, EM, and TDDB.