Investigation of the Physical Properties of Plasma Enhanced Atomic Layer Deposited Silicon Nitride as Etch Stopper

Harrison Sejoon Kim; Xin Meng; Si Joon Kim; Antonio T Lucero; Lanxia Cheng; Young-Chul Byun; Joy S Lee; Su Min Hwang; Aswin L N Kondusamy; Robert M Wallace; Gary Goodman; Alan S Wan; Michael Telgenhoff; Byung Keun Hwang; Jiyoung Kim

doi:10.1021/acsami.8b15291

Investigation of the Physical Properties of Plasma Enhanced Atomic Layer Deposited Silicon Nitride as Etch Stopper

ACS Appl Mater Interfaces. 2018 Dec 26;10(51):44825-44833. doi: 10.1021/acsami.8b15291. Epub 2018 Dec 11.

Authors

Affiliations

¹ Department of Materials Science and Engineering , The University of Texas at Dallas , 800 West Campbell Road , Richardson , Texas 75080 , United States.
² Department of Electrical Engineering , The University of Texas at Dallas , 800 West Campbell Road , Richardson , Texas 75080 , United States.
³ Department of Electrical and Electronics Engineering , Kangwon National University , 1 Gangwondaehakgil , Chuncheon-si , Gangwon-do 24341 , Republic of Korea.
⁴ Evans Analytical Group , 104 Windsor Center Drive , East Windsor , New Jersey 08520 , United States.
⁵ Dow Chemical , 2200 West Salzburg Road , Midland , Michigan 48686 , United States.

PMID: 30485061
DOI: 10.1021/acsami.8b15291

Abstract

Correlations between physical properties linking film quality with wet etch rate (WER), one of the leading figures of merit, in plasma-enhanced atomic layer deposition (PEALD) grown silicon nitride (SiN _x) films remain largely unresearched. Achieving a low WER of a SiN _x film is especially significant in its use as an etch stopper for technology beyond 7 nm node semiconductor processing. Herein, we explore the correlation between the hydrogen concentration, hydrogen bonding states, bulk film density, residual impurity concentration, and the WERs of PEALD SiN _x using Fourier transform infrared spectrometry, X-ray reflectivity, and spectroscopic ellipsometry, etc. PEALD SiN _x films for this study were deposited using hexachlorodisilane and hollow cathode plasma source under a range of process temperatures (270-360 °C) and plasma gas compositions (N₂/NH₃ or Ar/NH₃) to understand the influence of hydrogen concentration, hydrogen bonding states, bulk film density, and residual impurity concentration on the WER. Varying hydrogen concentration and differences in the hydrogen bonding states resulted in different bulk film densities and, accordingly, a variation in WER. We observe a linear relationship between hydrogen bonding concentration and WER as well as a reciprocal relationship between bulk film density and WER. Analogous to the PECVD SiN _x processes, a reduction in hydrogen bonding concentration arises from either (1) thermal activation or (2) plasma excited species. However, unlike the case with silane (SiH₄)-based PECVD SiN _x, PEALD SiN _x WERs are affected by residual impurities of Si precursors (i.e., chlorine impurity). Thus, possible wet etching mechanisms in HF in which the WER is affected by hydrogen bonding states or residual impurities are proposed. The shifts of amine basicity in SiN _x due to different hydrogen bonding states and the changes in Si electrophilicity due to Cl impurity content are suggested as the main mechanisms that influence WER in the PEALD processes.

Keywords: atomic layer deposition (ALD); bulk film density; hexachlorodisilane (HCDS); hydrogen bonding state; hydrogen/chlorine content; plasma-enhanced ALD (PEALD); silicon nitride; wet etch rate (WER).