Etching of molybdenum was demonstrated in two steps. Mo was first oxidized in an ozone gas ambient to form molybdenum oxide. It is shown that comparable oxide thicknesses can be obtained in ozone and oxygen but at lower temperatures for the former. Initial oxide growth is fast but then considerably slows down due to its diffusion-limited character. The metal-oxide thickness can be controlled by temperature and defines the amount of metal etch per cycle (EPC). XPS analysis showed that the thermally grown oxide is MoO3. In the second, wet-chemical step, MoO3 was dissolved selectively toward the Mo metal using an aqueous solution. The dissolution rate of amorphous MoO3 formed in O3 at temperatures below ∼230 °C is fast, but the dissolution of MoO3 formed at Tox > 230 °C was shown to be incomplete. Cross-section TEM showed a matrix of amorphous oxide with crystallized MoO3 islands, the latter more difficult to dissolve. However, the crystalline phase could be completely and selectively removed using a more concentrated NH4OH solution at an elevated temperature (70 °C). The EPC was determined for temperatures between 150 and 290 °C. The etch rates increased with temperature from 1–2 nm/cycle at 150 °C to 5–6 nm/cycle at 290 °C. This hybrid thermal-wet etching sequence is well suited for vertical and lateral recess etching as it shows a controlled and isotropic dissolution of polycrystalline Mo at the nanoscale. Furthermore, the process shows a progressive surface smoothening upon increasing the number of etching cycles.
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Research Article|
March 29 2023
Etching of molybdenum via a combination of low-temperature ozone oxidation and wet-chemical oxide dissolution
Special Collection:
Atomic Layer Etching (ALE)
Antoine Pacco
;
Antoine Pacco
a)
(Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing)
1
imec
, Kapeldreef 75,
Leuven 3001, Belgium
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Teppei Nakano;
Teppei Nakano
(Investigation, Methodology)
2
SCREEN SPE Germany
GmbH
, Fraunhoferstraße 7, Ismaning D-85737, Germany
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Shota Iwahata;
Shota Iwahata
(Investigation)
3
SCREEN Semiconductor Solutions Co.,
Ltd.
, 480-1, Takamiya-cho, Hikone, Shiga 522-0292, Japan
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Akihisa Iwasaki
;
Akihisa Iwasaki
(Supervision)
3
SCREEN Semiconductor Solutions Co.,
Ltd.
, 480-1, Takamiya-cho, Hikone, Shiga 522-0292, Japan
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Efrain Altamirano Sanchez
Efrain Altamirano Sanchez
(Resources, Supervision)
1
imec
, Kapeldreef 75,
Leuven 3001, Belgium
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Antoine Pacco
1,a)
Teppei Nakano
2
Shota Iwahata
3
Akihisa Iwasaki
3
Efrain Altamirano Sanchez
1
1
imec
, Kapeldreef 75,
Leuven 3001, Belgium
2
SCREEN SPE Germany
GmbH
, Fraunhoferstraße 7, Ismaning D-85737, Germany
3
SCREEN Semiconductor Solutions Co.,
Ltd.
, 480-1, Takamiya-cho, Hikone, Shiga 522-0292, Japan
a)
E-mail: [email protected]
Note: This paper is part of the 2023 Special Topic Collection on Atomic Layer Etching (ALE).
J. Vac. Sci. Technol. A 41, 032601 (2023)
Article history
Received:
December 07 2022
Accepted:
March 01 2023
Citation
Antoine Pacco, Teppei Nakano, Shota Iwahata, Akihisa Iwasaki, Efrain Altamirano Sanchez; Etching of molybdenum via a combination of low-temperature ozone oxidation and wet-chemical oxide dissolution. J. Vac. Sci. Technol. A 12 May 2023; 41 (3): 032601. https://doi.org/10.1116/6.0002404
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