Selective wet etching of Si3N4/SiO2 in phosphoric acid with the addition of fluoride and silicic compounds

ACS Sustainable Chem. Eng.

Tikue

et al. 2021

Three-dimensional NAND flash memory featuring dozens of vertically stacked memory cells is the state-of-the-art technology for most storage platforms. To fabricate threedimensional (3D) NAND memory, lateral etching of the Si 3 N 4 layer over SiO 2 is an essential step that is conducted through a wet etching process using a phosphoric acid-based etchant. Silylphosphate or highly selective nitride serves as an etching solution additive to control the SiO 2 layer dissolution rate. However, silylphosphate is prepared with an expensive monomeric silica precursor and at high reaction temperatures and generates environmentally harmful byproduct gases, such as HCl, HF, and CH 3 OH. This study demonstrates that silyl-phosphate can be prepared using low-cost polymeric silica under a mild reaction temperature by changing the characteristic acidity of phosphoric acid. The possibility of tuning the phosphoric acid acidity was first studied by molecular dynamics simulations, and phosphoric acids with stronger acidity were prepared by the evaporation of water from H 3 PO 4 (85%). The concentrated phosphoric acid enabled a fast reaction of polymeric silica and phosphate at a low reaction temperature (80 °C). The obtained silyl-phosphate lowered the SiO 2 layer dissolution rate, thereby yielding a Si 3 N 4 /SiO 2 layer etching ratio of up to 940. The proposed method offers an environmentally friendly production process for special chemicals used in 3D NAND flash memory fabrication. KEYWORDS: 3D NAND, concentrated H 3 PO 4 , fumed silica, Si 3 N 4 layer, SiO 2 layer, wet etching

Section: ■ Results and Discussionmentioning

confidence: 94%

Section: ■ Introductionmentioning

confidence: 99%

Green Manufacturing of Silyl-Phosphate for Use in 3D NAND Flash Memory Fabrication

ACS Sustainable Chem. Eng.

Tikue

et al. 2021

Section: Introductionmentioning

confidence: 99%

Selective etching of silicon nitride over silicon oxide using ClF3/H2 remote plasma

et al. 2022

Sci Rep

Precise and selective removal of silicon nitride (SiNx) over silicon oxide (SiOy) in a oxide/nitride stack is crucial for a current three dimensional NOT-AND type flash memory fabrication process. In this study, fast and selective isotropic etching of SiNx over SiOy has been investigated using a ClF3/H2 remote plasma in an inductively coupled plasma system. The SiNx etch rate over 80 nm/min with the etch selectivity (SiNx over SiOy) of ~ 130 was observed under a ClF3 remote plasma at a room temperature. Furthermore, the addition of H2 to the ClF3 resulted in an increase of etching selectivity over 200 while lowering the etch rate of both oxide and nitride due to the reduction of F radicals in the plasma. The time dependent-etch characteristics of ClF3, ClF3 & H2 remote plasma showed little loading effect during the etching of silicon nitride on oxide/nitride stack wafer with similar etch rate with that of blank nitride wafer.

“…due to high insulating characteristics, high thermal and mechanical stability, etc. and selective etching of silicon nitride over silicon and/or silicon oxide is important for various microelectronic applications [2]. These days, in the three dimensional Not-AND (3D NAND) device fabrication, the number of silicon nitride/silicon oxide (SiN x /SiO y ) stack is increasing and the thickness of one SiN x /SiO y layer is decreasing continuously for higher memory density in the vertical direction.…”

Section: Introductionmentioning

confidence: 99%

Selective Etching of Silicon Nitride Over Silicon Oxide using ClF3/H2 Remote Plasma

et al. 2021

Preprint

Precise and selective removal of silicon nitride in a SiNx/SiOy stack is crucial for a current 3D-NAND (not and) fabrication process. In this study, fast and ultra-high selective isotropic etching of SiNx have been studied using a ClF3/H2 remote plasma in an inductively coupled plasma system and a mechanism of SiNx etching was investigated by focusing on the role of Cl, F, and H radicals in the plasma. The SiNx etch rate over 800 Å/min with the etch selectivity of ~130 could be observed under a ClF3 remote plasma at a room temperature. Furthermore, compromising the etch rate of SiNx by adding H2 to the ClF3 plasma, the etch selectivity of SiNx over SiOy close to ~ 200 could be obtained. The etch characteristics of SiNx and SiOy with increasing the process temperature demonstrated the higher activation energy of SiOy compared to that of SiNx with ClF3 plasma.