Poly doped with phosphor and WSix are generally used as the gate-stack for deep trench DRAM product. These two films are critical ones that influence CP yield. In manufacturing, yield can gain much after solving Isb (I-standby) failure caused by gate WSix extrusion. Researches presented tungsten rich during WSix deposition or O2 leak during gate anneal process could lead to WSix extrusion (1), (2). Our study reveals that the concentration of phosphor, [P] in gate poly is another critical parameter to cause WSix extrusion after polycide pull-back process. In this paper, the mechanism of WSix extrusion is described and an optimized poly deposition process is proposed to solve Isb failure.