Optimizing Middle of Line (MoL) Contact Cleaning to Preserve Tungsten (W) Integrity in Advanced Technology Nodes

Most of the advanced technology node semiconductor device manufacturing has adopted the gate-last approach which utilizes a RMG (Replacement Metal-Gate) process. The gate last method prevents unnecessary thermal loading on the high-k gate material and the metal layers; typically induced due to high-temperature activation of the doping regions. In gate-last process, junctions are salicidized after RMG requiring a different patterning approach for the active regions, i.e. an additional TS (Trench Silicide) mask is used. Thus the contact to the active regions is split into two levels. First the TS is formed and filled with tungsten which is followed by conventional contact patterning. With the increased complexity of contact architecture, contact cleaning becomes more critical in preventing contact opens as well as in maintaining the structural integrity to eliminate risks of contact to gate shorts and trench fill (tungsten) erosion. In this work, an advanced cleaning process is developed based on the electrochemical compatibility and interactions between the chosen chemistry and exposed layers as well as contaminants to be removed. The cleaning efficacy in the trenches is verified by measuring contact resistance as well as particle/flake inspections. Tungsten integrity is verified with bright field microscopy and damage to inter layer dielectrics is monitored by measuring trench and contact critical dimensions. Other structural interactions were studied with TEM imaging. The new cleaning process yielded substantially higher number of functional die as compared to POR (Process of Record). This paper will detail and discuss the above mentioned mechanism and performance data.