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 this study, an isotropic etching process of SiO2 selective to Si3N4 using NF3/H2/methanol chemistry was investigated. HF was formed using a NF3/H2 remote plasma, and in order to remove the F radicals, which induces spontaneous etching of Si-base material, methanol was injected outside the plasma discharge region. Through this process, etch products were formed on the surface of SiO2, and then the (NH4)2SiF6 was removed by following heating process. When the H and F radicals were abundant, the highest SiO2 etch per cycle (EPC) was obtained. And, the increase of H2 and methanol percentage in the gas chemistry increased the etch selectivity by decreasing the F radicals. The etch products such as (NH4)2SiF6 were formed on the surfaces of SiO2 and Si3N4 during the reaction step and no noticeable spontaneous etching by formation of SiF4 was observed. By optimized conditions, the etch selectivity of SiO2 over Si3N4 and poly Si higher than 50 and 20, respectively, was obtained while having SiO2 EPC of ~ 13 nm/cycle. It is believed that the cyclic process using NF3/H2 remote plasma and methanol followed by heating can be applied to the selective isotropic SiO2 etching of next generation 3D device fabrication.

In this study, an isotropic etching process of SiO2 selective to Si3N4 using NF3/H2/methanol chemistry was investigated. HF was formed using a NF3/H2 remote plasma, and in order to remove the F radicals, which induces spontaneous etching of Si-base material, methanol was injected outside the plasma discharge region. Through this process, etch products were formed on the surface of SiO2, and then the (NH4)2SiF6 was removed by following heating process. When the H and F radicals were abundant, the highest SiO2 etch per cycle (EPC) was obtained. And, the increase of H2 and methanol percentage in the gas chemistry increased the etch selectivity by decreasing the F radicals. The etch products such as (NH4)2SiF6 were formed on the surfaces of SiO2 and Si3N4 during the reaction step and no noticeable spontaneous etching by formation of SiF4 was observed. By optimized conditions, the etch selectivity of SiO2 over Si3N4 and poly Si higher than 50 and 20, respectively, was obtained while having SiO2 EPC of ~ 13 nm/cycle. It is believed that the cyclic process using NF3/H2 remote plasma and methanol followed by heating can be applied to the selective isotropic SiO2 etching of next generation 3D device fabrication.

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Sn is the one of the materials that can be used for next generation extreme ultraviolet (EUV) mask material having a high absorption coefficient and, for the fabrication of the next generation EUV mask, a precise etching of Sn is required. In this study, the atomic layer etching (ALE) process was performed for the precise etch thickness control and low damage etching of Sn by the formation SnHxCly compounds on the Sn surface using with H and Cl radicals during the adsorption step and by the removal of the compound using Ar+ ions with a controlled energy during the desorption step. Through this process, optimized ALE conditions with different H/Cl radical combinations that can etch Sn at ~2.6 Å/cycle were identified with a high etch selectivity over Ru which can be used as the capping layer of the EUV mask. In addition, it was confirmed that not only the Sn but also Ru showed almost no physical and chemical damage during the Sn ALE process.