The oxide electrochemistry of ruthenium and its relevance to trench liner applications in damascene copper plating

Abstract

There is considerable interest in the use of ruthenium as an ultrathin trench liner in damascene copper plating used to fabricate on-chip interconnects. The problem is that when freshly deposited ruthenium films are exposed to air, their surfaces tend to undergo spontaneous oxidation, and such deposits (as demonstrated here) are reluctant to undergo reduction. Copper deposition in an acid plating bath occurs readily on the oxidized ruthenium, but the presence of oxide is known to have a detrimental effect both on the copper superfilling process and copper adhesion at the Ru/Cu interface.

Effect of additives and pulse plating on copper nucleation onto Ru

“…Burke et al have also studied oxide Table 1 The surface coverage of deposited copper for the examples (per cent of the surface that is covered with copper islands) given in Fig. 2 (a) Pretreatment applied 80.4% (b) 1 min air exposed after pretreatment 77.6% (c) 15 min air exposed after pretreatment 63.6% (d) No pretreatment applied 20.1% removal for copper electrodeposition and discussed the effect of potential on the reduction of surface oxyruthenium species [36].…”

Copper underpotential deposition on Ru quasi-single-crystal films

“…In addition, Cu-UPD on Ru is not only of fundamental interest, but electrochemically deposited Cu films on Ru substrates recently also gained interest because of their important role in the damascene process, where Ru is used to avoid segregation of Cu on electrical circuits in microcontroller devices [14][15][16][17][18]. Another important question addressed in this paper concerns the possibility to deposit Cu solely at the steps.…”

Direct-on-barrier copper electroplating on ruthenium from the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

“…For both applications, large aspect ratios (AR [ 10) are required, often combined with features' dimensions as small as a few tens of nanometers. In a typical interconnect process scheme, a thin layer of copper is deposited by physical vapor deposition (PVD) on a patterned insulator covered by a metal barrier, typically Ta/TaN.…”

“…The complex oxide electrochemistry of ruthenium was thoroughly investigated by Burke et al [10]. These authors mention that the spontaneous oxidation of a freshly deposited layer of ruthenium to anhydrous and hydrated ruthenium oxides is enhanced by the existence of metastable forms.…”