Alkaline composition for copper electroplating comprising a defect reduction agent

A composition for depositing copper on a semiconductor substrate, the composition comprising

• (a) 0.3 to 20 g/l copper ions;
• (b) 10 to 1000 ppm of a defect reducing agent of formula S1
• (c) 0.01 to 2 mol/l of a complexing agent to keep the copper ions in solution and to avoid their precipitation;
• and
• (d) optionally a buffer or a base to adjust the pH to a pH of from 7 to 13;
• wherein
• RS1 is selected from the group consisting of XS—YS,
• RS2 is selected from the group consisting of RS1 and RS3,
• XS is selected from the group consisting of linear or branched C1 to C10 alkanediyl, linear or branched C2 to C10 alkenediyl, linear or branched C2 to C10 alkynediyl, and —XS6—(O—C2H3RS6)m;
• YS is selected from the group consisting of ORS3, NRS3RS4, N+RS3RS4RS5 and NH—(C═O)—RS3;
• RS3, RS4, RS5 are individually the same or different and are selected from the group consisting of (i) H, (ii) C5 to C20 aryl, (iii) C1 to C10 alkyl (iv) C6 to C20 arylalkyl, (v) C6 to C20 alkylaryl, which may be substituted by OH, SO3H, COOH or a combination thereof, and (vi) —(C2H3RS6—O)n—RS6, and wherein RS3 and RS4 may together form a ring system, which may be interrupted by O or NRS7;
• XS6 is C1 to C6 alkanediyl;
• m, n are integers independently selected from the group consisting of 1 to 30;
• RS6 is selected from the group consisting of H and C1 to C5 alkyl;
• RS7 is selected from the group consisting of RS6 and
• and
• wherein the pH of the composition is from 7 to 13 and wherein the composition is free of any cyanide ions.