Silicon Wafer CMP Slurry Using a Hydrolysis Reaction Accelerator with an Amine Functional Group Remarkably Enhances Polishing Rate

Abstract

Recently, as an alternative solution for overcoming the scaling-down limitations of logic devices with design length of less than 3 nm and enhancing DRAM operation performance, 3D heterogeneous packaging technology has been intensively researched, essentially requiring Si wafer polishing at a very high Si polishing rate (500 nm/min) by accelerating the degree of the hydrolysis reaction (i.e., Si-O-H) on the polished Si wafer surface during CMP. Unlike conventional hydrolysis reaction accelerators (i.e., sodium hydroxide and potassium hydroxide), a novel hydrolysis reaction accelerator with amine functional groups (i.e., 552.8 nm/min for ethylenediamine) surprisingly presented an Si wafer polishing rate >3 times higher than that of conventional hydrolysis reaction accelerators (177.1 nm/min for sodium hydroxide). This remarkable enhancement of the Si wafer polishing rate for ethylenediamine was principally the result of (i) the increased hydrolysis reaction, (ii) the enhanced degree of adsorption of the CMP slurry on the polished Si wafer surface during CMP, and (iii) the decreased electrostatic repulsive force between colloidal silica abrasives and the Si wafer surface. A higher ethylenediamine concentration in the Si wafer CMP slurry led to a higher extent of hydrolysis reaction and degree of adsorption for the slurry and a lower electrostatic repulsive force; thus, a higher ethylenediamine concentration resulted in a higher Si wafer polishing rate. With the aim of achieving further improvements to the Si wafer polishing rates using Si wafer CMP slurry including ethylenediamine, the Si wafer polishing rate increased remarkably and root-squarely with the increasing ethylenediamine concentration.

Keywords: 3D heterogeneous packaging; chemical–mechanical planarization; colloidal silica; hydrolysis reaction accelerator; processing in memory (PIM); silicon wafer (Si wafer).

Figure 1

Dependencies of the Si wafer polishing rate on the chemical structure of a hydrolysis reaction accelerator and its concentration. (a) Effect of the hydrolysis reaction accelerator including amine functional group on the enhancement of Si wafer polishing rate and (b) correlation between the Si wafer polishing rate and OH⁻ concentration. The background Figure 1b is the SEM image of colloidal silica abrasives used in our study.

Figure 2

Dependency of the chemical compositions on the EDA concentration for the polished Si wafer surface after CMP, analyzed by XPS. (a) O 1s XPS spectra, (b) normalized XPS spectra percentage at O 1s XPS spectra depending on the EDA concentration, (c) Si 2p XPS spectra, and (d) normalized XPS spectra percentage at Si 2p XPS spectra depending on the EDA concentration.

Figure 3

Dependencies of the degree of adsorption (i.e., contact angle) on the chemical structure of the hydrolysis reaction accelerators and their concentration at the polished Si wafer surface. (a) Contact angles of the CMP slurries using NaOH, KOH, and EDA on the polished Si wafer surface, depending on concentration. (b) Dependencies of contact angle on the pH of the CMP slurry using NaOH, KOH, or EDA.

Figure 4

Influence of mechanical properties (i.e., relative electrostatic repulsive force between the colloidal silica abrasives and the polished Si wafer surface) on the Si wafer polishing rate. (a) Zeta-potentials of the colloidal silica abrasives in the Si wafer CMP slurries, (b) zeta-potentials of the polished Si wafer surface after CMP, (c) relative electrostatic repulsive force between the colloidal silica abrasives and the polished Si wafer surface, and (d) effect of the relative electrostatic repulsive force on the Si wafer polishing rate, depending on the chemical structure of the hydrolysis reaction accelerator (i.e., NaOH, KOH, and EDA) and their concentration.