Post-Cu CMP cleaning for colloidal silica abrasive removal Po-Lin Chen a,b, * , Jyh-Herng Chen a , Ming-Shih Tsai c , Bau-Tong Dai c , Ching-Fa Yeh d a Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan b Department of Materials Science and Engineering, National Chiao Tung University, No. 1001, Ta-Hsueh Rd., Hsinchu 300, Taiwan c National Nano Device Laboratory, Hsinchu, Taiwan d Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan Received 7 May 2004; accepted 28 June 2004 Available online 9 August 2004 Abstract In this study, an efficient approach for the removal of colloidal silica abrasives from the polished copper surface was proposed and demonstrated. This post-chemical mechanical polishing (CMP) cleaning process combines a buffing proc- ess with dilute HNO 3 /benzotriazole (BTA) aqueous solution for copper surface passivation and a polyvinyl alcohol (PVA) brush scrubbing process with wetting surfactants, Triton X-100, for colloidal silica removal. Buffing with HNO 3 /BTA aqueous solution was able to remove copper oxide and form the Cu(I)–BTA hydrophobic passivation. Scrubbing with Triton X-100 surfactant is to enhance the wettability on Cu(I)–BTA surface for the removal of residual silica abrasives. The wetting ability of Triton X-100 was determined by a contact angle and surface tension measure- ments. It was demonstrated that silica abrasives could be removed efficiently without copper corrosion by this cleaning process. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Copper; Colloidal silica abrasive; Post-chemical mechanical polishing cleaning; Benzotriazole; Triton X-100 1. Introduction Copper has been accepted as the material for high performance interconnect technology, owing to its unique electrical properties such as low resis- tivity and high resistance to electromigration com- pared with aluminum [1,2]. Since copper is difficult to associate with reactive ion etching (RIE), a Damascene structure has been implemented to realize the copper on-chip interconnects. The Damascene processing utilizes chemical mechani- cal polishing (CMP) to define the copper intercon- nect structure. However, this process leaves a large 0167-9317/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2004.06.006 * Corresponding author. Tel.: +886 3 5731950; fax: +886 3 5724727. E-mail address: [email protected](Po-Lin Chen). Microelectronic Engineering 75 (2004) 352–360 www.elsevier.com/locate/mee
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Microelectronic Engineering 75 (2004) 352–360
www.elsevier.com/locate/mee
Post-Cu CMP cleaning for colloidal silica abrasive removal
Po-Lin Chen a,b,*, Jyh-Herng Chen a, Ming-Shih Tsai c, Bau-Tong Dai c,Ching-Fa Yeh d
a Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwanb Department of Materials Science and Engineering, National Chiao Tung University, No. 1001, Ta-Hsueh Rd., Hsinchu 300, Taiwan
c National Nano Device Laboratory, Hsinchu, Taiwand Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan
Received 7 May 2004; accepted 28 June 2004
Available online 9 August 2004
Abstract
In this study, an efficient approach for the removal of colloidal silica abrasives from the polished copper surface was
proposed and demonstrated. This post-chemical mechanical polishing (CMP) cleaning process combines a buffing proc-
ess with dilute HNO3/benzotriazole (BTA) aqueous solution for copper surface passivation and a polyvinyl alcohol
(PVA) brush scrubbing process with wetting surfactants, Triton X-100, for colloidal silica removal. Buffing with
HNO3/BTA aqueous solution was able to remove copper oxide and form the Cu(I)–BTA hydrophobic passivation.
Scrubbing with Triton X-100 surfactant is to enhance the wettability on Cu(I)–BTA surface for the removal of residual
silica abrasives. The wetting ability of Triton X-100 was determined by a contact angle and surface tension measure-
ments. It was demonstrated that silica abrasives could be removed efficiently without copper corrosion by this cleaning
sives from slurry, undesired metallic ions and other
chemical components [3]. Furthermore, the coppercorrosion phenomenon during the post-CMP
cleaning process must be prevented [4].
In the copper Damascene process, the CMP
procedure is reported to have several stages, i.e.,
removal of the overburdened copper (out of
trench) and Ta/TaN diffusion barrier [5]. During
the first stage, overburdened copper with 1–2 lmthickness must be polished at a high rate and stopsat the diffusion barrier layer. Sequentially, a non-
selective CMP process removes the residual metal
(Ta/TaN and Cu) and stops at the SiO2 dielectric
layer, resulting in a flat wafer surface. However,
tantalum always spontaneously forms a compact,
impervious, and continuous passive oxide
(Ta2O5) film, which is thermodynamically stable
in acidic and alkaline noncomplexing aqueoussolutions [6]. Therefore, during the polishing stage
of tantalum, a rather low polishing rate of tanta-
lum accompanying longer overpolishing time will
lead to a serious dishing and erosion of copper
lines. Many researches have been attempted to
accomplish a higher polishing rate of tantalum
[7–10]. Colloidal silica slurry has been suggested
to collocate with H2O2 to achieve a higher polish-ing rate of tantalum. The CMP of tantalum is usu-
ally performed using the alkaline aqueous
solutions. Babu et al. [8,9] reported that tantalum
forms soluble oxotantalate and hydroxotantalate
in the presence of H2O2 at a high pH value 12.
The effect of H2O2 in improving the polishing rate
of tantalum is mainly owing to enhanced dissocia-
tion of peroxide in the alkaline solution. Colloidalsilica abrasives with moderately high removal
rates, good uniformity values, low defectivity,
and excellent ability to remove the tantalum layer
are one of the most promising candidates for the
copper and tantalum CMP. However, as polishing
with colloidal silica based slurry, it shows a strong
tendency of the absorption of colloidal silica on
the copper surface, which seems to be related tothe corrosion of copper and copper oxides forma-
tion in the alkaline solution. If H2O2 exists, copper
tends to be oxidized to form cupric/cupreous oxi-
des (CuO or Cu2O) and copper hydroxides
(Cu(OH)2) passivation on surface, this may result
in the silica abrasives chemisorbed onto this oxide
layer by means of the oxygen bridging bonding, as
shown in Fig. 1. It is difficult to remove thuschemisorbed colloidal silica by conventional
post-CMP cleaning process [3].
In this study, an efficient process for the re-
moval of colloidal silica from the polished copper
surface was proposed and demonstrated. This
post-CMP cleaning process involves a buffing
process on polishing pad with a HNO3/benzotriaz-
ole (BTA) aqueous solution (abrasive free) forcopper surface passivation and a polyvinyl alcohol