Effects of plasma H2 pretreatment to Cu seed/TaN/BPSG on Cu electroplating

초록

Electroplating is an attractive deposition method for copper with the need for a conformal seed layer. The seed layer carries current along the contours of the patterned damascene structure, serving as a nucleation layer. In addition, the Cu seed layer should be highly pure so as not to compromise the effective resistivity of the filled copper interconnect structure. In this study, two types of copper seed layers deposited by MOCVD and magnetron sputtering onto a tantalum nitride barrier layer were used for electroplating copper in the forward pulsed mode and prior to electroplating a copper film, the Cu seed layer (by MOCVD or Sputtering) was cleaned by plasma H2. In the plasma H2 treatment substrate temperature was varied from room temperature to 200℃ and plasma power from 20 to 140W. MOCVD-Cu seed layers showed higher step coverage than sputtered Cu seed layers, but did not adhere well to the TaN barrier after the Cu electroplating. Effects of plasma H2 pretreatment to Cu seed/Tantalum nitride (TaN)/borophosphosilicate glass (BPSG) samples on electroplating of copper (Cu) films were studied. The pretreatment removes oxide and etch residues at the bottom of a via. Characteristics of copper films and via filling capability of electroplating were investigated. The Cu seed layer requires low electrical resistivity, smooth surface, good adhesion to the barrier metal for ensuring void-free fill. Our results show that Cu films electroplated on plasma pretreated copper seed layers offers better electrical resistivities, surface morphologies, adhesion and selective filling capability than those on copper seed layers without plasma pretreatment. The (111) preferred orientations of Cu films were as good as those without plasma pretreatment. Plasma H2 precleaning is more effective to the MOCVD-Cu seed layer than the sputtered one.