csmc 0.5um工艺里面的p plug层是什么作用？

各位，我有个问题要请教，csmc的0.5工艺，有两个option，一个是with p plug另一个是without p plug。mask层数一样，前者增加一层p plug photo layer。我查了很久没找到p plug是什么意思，这个差异在哪里?
两套pdk我比较过，只有design rule有一点点区别，with plug的，active area overlap contact的距离最小是0.15，without plug的，是0.3

active area overlap contact =0.15um=>need contact implant to avoid leakage

所以，contact implant叫plug ? p plug?

所以，contact implant叫plug ? p plug?

所以，contact implant叫plug ? p plug?

仔细研究了上华的工艺，孔注入有两种
1. Contact N+普注， Conact P+ with mask 注入。此时 N+/P+ active overlap contact:0.15/0.3.
2. Contact N+普注, No contact P+ 注入，此时 N+/P+ active overlap contact:0.3/0.3.