A manufacturing method of a plug structure having low contact resistance includes
the following steps. First, a silicon substrate and a BPSG layer covering thereon
are provided. The silicon substrate has a dopant area. Next, the BPSG layer is
etched to form a contact window to be contiguous with the dopant area. If the dopant
area is doped with boron, a silicon-germanium layer is formed upon the dopant area
as a barrier layer. Then, a barrier layer is formed next to the contact window,
and a metal plug surrounded by the barrier layer is formed. After conductive interconnecting
lines are formed upon the BPSG layer, a rapid thermal annealing is adopted to reactivate
the dopant area. In the case that the boron is doped in the dopant area, the silicon-germanium
layer keeps the boron from migrating to the barrier layer to lower the contact
resistance of the plug structure.
