ALD Platinum Substrate Preparation and Electrodeposition of Copper into Extremely Deep through-Silicon-Vias
Authors: Menk Lyle Alexander , Arrington Christian L. , Bauer Todd , Blain Matthew , Dominguez Jason , Goeke Ronald S. , Heller Edwin , Hollowell Andrew E , Jarecki Robert , Loviza Rebecca , McClain Jaime , Pillars Jamin Ryan , Resnick Paul , Timon Robert 
Published: February 2020

Copper electrodeposition into through-silicon-vias (TSV) is a rapidly developing and instrumental technique required for efficient high-density 3-D integration of complex semiconductor devices. The ubiquity of the electrodeposition of copper (Cu) in damascene interconnects has led to natural development towards Cu electrodeposition in TSVs. Many processes currently rely on either electroless plating or sputter deposition as a seed layer prior to the electrolytic deposition of Cu. However, these techniques are not capable of achieving a conformal seed layer throughout the full depth of the vias due to the geometric complexity of these devices. This work investigates via filling of electroplated Cu on substrates that have undergone atomic layer deposition (ALD) of a conformal seed metal. The intent of this work is to achieve uniform and void-free Cu electrodeposition into extremely deep vias (625μm) at aspect ratios as high as 10:1. Platinum (Pt) as a seed layer presents unique challenges due to the high affinity of carbon for collecting on the Pt surface, which renders the surface hydrophobic. In order to adequately wet the entire depth of the vias, the carbon compounds must be removed from the Pt to ensure the surface is hydrophilic. This work will present the results of both wet chemical and dry plasma processes to achieve this full-depth Pt via wetting. Further substrate preparation examines the impact of incubation in the electroplating chemistry under vacuum with an increased concentration of an accelerator additive. This step aims to further facilitate conformal plating into the vias by removing gas pockets from the vias while saturating these areas with accelerator to increase the initial plating rate in the bottom of the vias.

In addition to these surface preparation techniques, development of an optimized electroplating bath chemistry and applied current regime will be presented. DC plating as well as various pulse regimes are investigated in order to tailor the filling profile of the vias. With regard to the bath chemistry, high Cu concentrations (80g/L) in methanesulfonic acid (MSA) electrolyte chemistries are compared to conventional Cu concentrations (40-60g/L) in sulfuric acid (H2SO4) electrolyte chemistries. The higher solubility of Cu in the MSA (80g/L) versus H2SO4 electrolyte (50g/L) reduces mass transport limited depletion of Cu ions through the vias 1. The particularly large concentration of Cu ions in this electroplating bath promotes a more rapid replenishment of these ions in the deep and high aspect ratio structures throughout the deposition period. In addition to the different chemistries and plating regimes studied herein, the effects of accelerator, suppressor, and leveler additives are examined through analysis of their affects on cyclic voltammetry curves as well as fill ratios throughout the vias. These fill ratios are examined after the vias are cross-sectioned and polished through the use of chemical mechanical planarization, and subsequent characterization of the vias is achieved using optical and scanning electron microscopy techniques.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

S. K. Cho, M. J. Kim, and J. J. Kim, “MSA as a Supporting Electrolyte in Copper Electroplating for Filling of Damascene Trenches and Through Silicon Vias.” Electrochemical and Solid-State Letters, 14 (5) D52-D56 (2011).