One-Step Fabrication of Copper Thin Films on Insulators Using Supercritical Fluid Deposition

Abstract

A one-step fabrication method for direct supercritical fluid deposition (SCFD) of Cu on insulators was developed. This overcomes the limitation of conventional SCFD, which cannot directly deposit Cu on insulators. In our one-step method, a relatively small amount of an Mn precursor was mixed with a Cu precursor to deposit a CuMn x O y composite layer on an insulative underlayer. This underlayer then acted as a buffer layer, allowing subsequent Cu deposition. This method successfully achieved Cu deposition on insulators, including SiO 2 , boron phosphorus silicon glass (BPSG), and Parylene. The superior conformal deposition ability of conventional SCFD was also demonstrated using our one-step method, where Cu was deposited uniformly on an overhung test structure. Detailed analysis revealed that our one-step method was initiated by deposition of MnO x , which could include Cu, resulting in CuMn x O y film formation, followed by Cu deposition. The amount of the MnO x deposited during Cu deposition was negligible due to the much lower growth rate of MnO x compared with Cu. This process is useful for the fabrication of electronic devices having complex features and comprising various materials. . This paper is part of the JES Focus Issue on Electrochemical Processing for Interconnects.Microfabrication technologies, such as deep reactive ion etching (DRIE), 1-4 have enabled the fabrication of three-dimensional (3D) complex structures with extremely high aspect ratios (HAR), above 50 for instance, on the surface of silicon wafers. Thin-film technologies that enable conformal coatings on these features have been applied to a variety of electronic devices, including microelectromechanical systems (MEMS), 5-7 dynamic random access memory (DRAM), 8-10 and through silicon via (TSV), 11,12 to exploit the large surface area and to functionalize the devices. Chemical vapor deposition (CVD), which is a technology having good step coverage, cannot meet these demands. Electroless deposition (ELD) is another candidate, which conventionally requires catalytic underlayer, and recently becomes possible on the insulating underlayers using Au nanoparticle catalyst. 13-15 ELD is a wet process, and thus advantageous in simplicity of equipment, while supercritical fluid deposition (SCFD), which is a focus of this paper, requires incidental facilities including a high pressure pump and a pressure control system to realize deposition under high pressure environment. Nevertheless, SCFD seems to have more possibility to achieve conformal deposition on extremely high-aspect-ratio features. Because step coverage is determined by the balance between the transportation of the precursor by diffusion within the trenches and consumption of the precursor on the side walls by deposition reactions, higher diffusivity in SCFD (10 −7 -10 −8 m 2 /s) compared with that in liquid solution of ELD (10 −10 m 2 /s) leads to higher step coverage.SCFD is a novel approach that achieves conformal deposition onto HAR features. This method uses the oxidation/reduction...

Influence of Pretreatment on Adhesion Quality of Supercritical-fluid-deposited Cu Film on Si

“…(12) Cabañas et al presented that a high reaction temperature was required for direct SCFD on an insulator. They also demonstrated Au SCFD on SiO 2 , (15) and CuMn x O y SCFD on SiO 2 was reported by Uejima et al (16) Although direct Cu SCFD on SiO 2 was also demonstrated, (17) a Cu film on SiO 2 has very poor adhesivity. (18) Inserting an adhesion layer can contribute to the improvement of adhesion on a SiO 2 surface.…”