Cyclic etching of silicon oxide using NF₃/H₂ remote plasma and NH₃ gas flow

Abstract

Selective isotropic cyclic dry etching of silicon oxide (SiO2) was investigated using a three‐step cyclic process composed of hydrogen fluoride (HF) adsorption by NF3/H2 remote plasma and reaction with NH3 gas flow to form ammonium fluorosilicate ((NH4)2SiF6), and desorption by heating. The variation of the ratio of NF3:H2 (2:1 to 1:3) and adsorption time (10–180 s) showed the highest etch selectivity of SiO2 over Si3N4 at 1:2 ratio of NF3:H2 and with the adsorption time of 20 s. The etch selectivity higher than 40 was observed with 20 s of adsorption time with a 1:2 ratio of NF3:H2 remote plasma and the total etch depth was linearly increased with the increase of cycles with the SiO2 EPC of ~7.5 nm/cycle.

In Situ Monitoring of Etching Characteristic and Surface Reactions in Atomic Layer Etching of SiN Using Cyclic CF4/H2 and H2 Plasmas

“…Figure b illustrates the absorbance band at around 2900 cm –1 , which corresponds to the C–H band resulting from the formation of the HFC layer deposited by the CF 4 /H 2 plasma during the deposition step, consistent with the results shown in Figure . As shown in Figure c, the presence of N–H 4 bending vibration indicates the formation of the AFS, (NH 4 ) 2 SiF 6 , compound. − This is also confirmed by the presence of the SiF 6 2– peak in the spectrum, which can be found in the Supporting Information (Figure S1). The negative peaks observed at approximately 3350, 2150, and 900 cm –1 correspond to the removal of bonding (etching), specifically the SiN–H, Si–H, and Si–N bonds originating from the SiN film.…”

Selective Isotropic Etching of SiO2 over Si3N4 using NF3/H2 Remote Plasma and Methanol Vapor

“…[22,23] Therefore, to avoid direct reaction between NH 3 and HF in gaseous or plasma state, alternate SiO 2 dry etching processes have been investigated through reaction with NF 3 gas after inducing NH 3 formation through N 2 /H 2 plasma [24] or through the formation of (NH 4 ) 2 SiF 6 on SiO 2 by sequential supply of NH 3 gas after adsorption of HF from HF vapor or from plasmas generated with SF 6 /H 2 or NF 3 /H 2 . [25,26] The above processes still use NH 3 gas or NH 3 formed through plasma which might generate particles, therefore, in this study, selective isotropic SiO 2 dry etching process not generating noticeable NH 3 , by using H 2 /NF 3 plasma as HF source and methanol (CH 3 OH) vapor as a solvent, has been investigated. In order to minimize the generation of F radical during dissociation of NF 3 in the plasma which induces spontaneous etching of Si-base material [27], H 2 /NF 3 gases were supplied to the remote plasma area and methanol were injected to the processing area located outside the plasma discharge region.…”

Topographically-selective atomic layer etching of SiO2 using radical fluorination of the surface followed by Ar ion bombardment

“…Area-selective ALE aims to achieve etch selectivity among different and increasingly unconventional materials used in patterning. 12,[18][19][20] On the other hand, topographicallyselective ALE is used to explore 3D substrates and the feasibility of modifying and etching the material anisotropically, or in other words, with a preferred orientation; for example, in a trenched patterned sample, preferentially etching the horizontal surfaces over the sidewalls of the material or vice versa. 5,10,21,22) The goal of the current study is to evaluate the feasibility of a topographically selective PE-ALE of SiO 2 using alternative co-reactants.…”