Unidirectional Growth of Microbumps on (111)-Oriented and Nanotwinned Copper

• Published in: Science (American Association for the Advancement of Science) Vol. 336; no. 6084; pp. 1007 - 1010
• Main Authors: Hsiao, Hsiang-Yao, Liu, Chien-Min, Lin, Han-wen, Liu, Tao-Chi, Lu, Chia-Ling, Huang, Yi-Sa, Chen, Chih, Tu, K. N.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 25.05.2012; The American Association for the Advancement of Science
• Subjects: Architecture; Arrays; Condensed matter: structure, mechanical and thermal properties; Copper; Cross-disciplinary physics: materials science; rheology; Defects and impurities: doping, implantation, distribution, concentration, etc; Direct current; Electrodeposition, electroplating; Electronic components; Electroplating; Exact sciences and technology; High density; Integrated circuits; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Microstructure; mixing; nanomaterials; Nanostructure; packaging; Physics; Soldering; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Three dimensional; Voids; Twin boundaries; Nanodefect; Vacancies; Directional solidification; Direct current; Lead free solder; Electrodeposition; Microstructure; Focused ion beam technology; Texture; EBSD
• DOI: 10.1126/science.1216511
• ISSN: 0036-8075; 1095-9203

One challenge in moving to three-dimensional integrated circuit architectures is the need for aligned interconnects to join neighboring layers. Hsiao et al. (p. 1007 ) applied rapid stirring to the direct current electroplating of copper to produce films with oriented copper grains that have a high density of nanotwin defects. The resulting material was an excellent platform for the growth of copper-tin intermetallic compounds in the form of arrays of microbumps potentially suitable for the soldering of electronic components. Oriented copper grains grown using direct-current electroplating serve as a template for intermetallic microbumps. Highly oriented [111] Cu grains with densely packed nanotwins have been fabricated by direct-current electroplating with a high stirring rate. The [111]-oriented and nanotwinned Cu (nt-Cu) allow for the unidirectional growth of Cu 6 Sn 5 intermetallics in the microbumps of three-dimensional integrated-circuit packaging; a uniform microstructure in a large number of microbumps of controlled orientation can be obtained. The high-density twin boundaries in the nt-Cu serve as vacancy sinks during the solid-state reaction between Pb-free solder and Cu and greatly reduce the formation of Kirkendall (or Frenkel) voids.