Integration of Atomic Layer Deposition-Grown Copper Seed Layers for Cu Electroplating Applications

Abstract

A plasma-enhanced atomic layer deposition ͑PEALD͒ copper process, using Cu͑II͒ acetylacetonate and atomic hydrogen, was developed for Cu seed applications in nanoscale semiconductor processing. In this paper, the integration characteristics of PEALD Cu with electroplated Cu for advanced interconnect applications were investigated. Superconformal electroplated ͓electrochemical deposition ͑ECD͔͒ copper was demonstrated on PEALD Cu-seeded high aspect ratio patterned structures. The filling characteristics of ECD/PEALD-grown Cu were compared with those of a conventional ECD/physical vapor deposition ͑PVD͒-grown Cu stack. Void-free electroplated Cu was demonstrated on 60 and 35 nm patterned via structures using both atomic layer deposition Ru/TaN and conventional PVD Ta/TaN liner/barrier structures coupled with PEALD Cu seed layers. The resulting integration characteristics suggest that electroplated/PEALD Cu is a promising integration approach for emerging complementary metal oxide semiconductor metallization applications.Cu electroplating, or electrochemical deposition ͑ECD͒, is the interconnect conductor deposition method of choice for leading edge nanoelectronics. 1 A thin Cu seed layer is required before the Cu electroplating step to provide a more conductive substrate and to facilitate the nucleation of the electroplated Cu. 2 This seed layer is deposited over a barrier/liner stack, often TaN/Ta. 1 The conformality and coverage of the Cu seed layer over via and trench patterns is critical in determining whether the subsequent Cu electroplating is void free. 1 With the downscaling of interconnect feature dimensions, each individual layer within the metallization stack must become thinner and more conformal to comply with the overarching geometric constraints. 1 The ionized physical vapor deposition ͑iPVD͒ process currently employed becomes increasingly challenged to meet the seed/barrier requirements with respect to sidewall coverage and uniformity. 3 The low sidewall coverage, asymmetry, and overhang of the iPVD barrier/seed can result in electroplated Cu filling voids, which compromise the reliability and electrical performance of the Cu interconnects. 4,5 Therefore, a more conformal Cu seed layer is desirable to allow void-free filling of subsequent Cu electroplating in sub-45 nm interconnect structures.Atomic layer deposition ͑ALD͒ is a self-limiting thin-film deposition method based on alternating saturated surface chemical reactions, which allows conformal deposition of materials on high aspect ratio ͑AR͒ trenches. 6 ALD is a promising alternative barrier/seed deposition method because of its excellent conformality and precise thickness control capability. 7 In particular, plasma-enhanced atomic layer deposition ͑PEALD͒ can deposit high density films at low processing temperatures, which is critical for the growth of thin continuous Cu films that are resistant to agglomeration. 8,9 The agglomeration of chemically deposited thin Cu layers is a major roadblock to extending Cu seed layer technology. 10 However...

ALD-grown seed layers for electrochemical copper deposition integrated with different diffusion barrier systems

“…In this respect, ALD-grown Cu seed layers appear even more advantageous compared to PVD Cu. These results are in line with a recent study by Wu and Eisenbraun [17]. The authors report that PEALD-grown Cu seed layers integrated with a PEALD Ru liner on a TaN diffusion barrier gave considerably better ECD results with respect to film roughness and void-free filling of interconnect features compared to samples without Ru.…”

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

“…A classic example is the ALD of metal oxides from b-diketonate precursors, such as those with acac (acetylacetonate), [97][98][99][100] hfac (1,1,1,5,5,5-hexafluoroacetylacetonate), 101,161,162 and thd (2,2,6,6,-tetramethyl-3,5-heptanedionato) 102,104,[275][276][277][278][279] ligands. Such precursors require more reactive co-reactants as they show no or low reactivity with H 2 O (in essence, they do not readily undergo hydrolysis reactions).…”

Conformality of Plasma-Assisted ALD: Physical Processes and Modeling

“…For instance, for ALD of metal oxides with O 2 plasmas, ϳ100% conformality has been reached for Al 2 O 3 in pores with AR = 8, 21 for TiO 2 deposition in trenches with AR = 9, 16,22 and for Ta 2 O 5 in trenches with AR = 11. 23 Regarding H 2 plasmas used for ALD of metals and metal nitrides, Ͼ95% step coverage for TiN in pores with AR = 10 has been reported; 24 ϳ100% for TaN in pores with AR = 10, 25 ϳ100% conformality for Cu in trenches with AR = 9, 26 as well as conformal growth for Ag in trenches with AR = 9 27 were also reported. For ALD of Ta with a H 2 plasma, ϳ100% conformality was found up to trenches with AR = 15, whereas the rest of the trench ͑AR = 40͒ had a conformality of 40%.…”