Hydrogen silsesquioxane explained

200px|thumbnail|right| Hydrogen silsesquioxane (R = H).

Hydrogen silsesquioxane(s) (HSQ, H-SiO_x, T^H_n, H-resin) are inorganic compounds with the empirical formula [HSiO_3/2]_n. The cubic H₈Si₈O₁₂ (T^H₈) is used as the visual representation for HSQ. T^H₈, T^H₁₀, T^H₁₂, and T^H₁₄ have been characterized by elemental analysis, gas chromatography–mass spectroscopy (GC-MS), IR spectroscopy, and NMR spectroscopy.^[1]

High purity semiconductor-grade HSQ has been investigated as a negative resist in photolithography and electron-beam (e-beam) lithography.^[2] HSQ is commonly delivered in methyl isobutyl ketone (MIBK) and can be used to form 0.01–2 μm films on substrates/wafers. When exposed to electrons or extreme ultraviolet radiation (EUV), HSQ cross-links via hydrogen evolution concomitant with Si-O bond crosslinking. Recently, the possibility of crosslinking HSQ using ultrashort laser pulses through multiphoton absorption and its application to 3D printing of silica glass have been demonstrated.^{[3] [4]} Sufficiently dosed and exposed regions form a low dielectric constant (low-k) Si rich oxide that is chemically resistant/insoluble towards developers, such as tetramethylammonium hydroxide (TMAH). Sub-10 nm patterning is achievable with HSQ. The nanoscale patterning capabilities and low-k of the Si rich oxide produced is potentially of broad scope of nano applications and devices.^[5]

HSQ has been available as 1 and 6% (wt%) MIBK solutions from Dow Inc. (Formally Dow Corning), called XR-1541-001 and XR-1541-006, respectively. HSQ in MIBK has a short shelf life. Alternatively, Applied Quantum Materials Inc. (AQM) produces HSQ with a longer shelf life.^{[6] [7]} AQM HSQ solutions are available in the United States from DisChem, Inc.

Further reading

• Chen. Huiping. Tecklenburg. Ron E.. October 2006. Characterization of low and intermediate molecular weight hydrogen silsesquioxanes by mass spectrometry. Journal of the American Society for Mass Spectrometry. 17. 10. 1438–1441. 10.1016/j.jasms.2006.06.010. 1044-0305. 16872839. 3674845 . free. 2006JASMS..17.1438C .
• Frye. Cecil L.. Collins. Ward T.. 1970-09-01. Oligomeric silsesquioxanes, (HSiO3/2)n. Journal of the American Chemical Society. 92. 19. 5586–5588. 10.1021/ja00722a009. 0002-7863.

Notes and References

1. Agaskar. P. A.. Day. V. W.. Walter G. Klemperer. Klemperer. W. G.. 1987-09-01. A new route to trimethylsilylated spherosilicates. Synthesis and structure of [Si12O18](OSiMe3)12, D3h-[Si14O21](OSiMe3)14, and C2v-[Si14O21](OSiMe3)14]. Journal of the American Chemical Society. 109. 18. 5554–5556. 10.1021/ja00252a058. 0002-7863.
2. Namatsu. H.. Yamaguchi. T.. Nagase. M.. Yamazaki. K.. Kurihara. K.. 1998-03-01. Nano-patterning of a hydrogen silsesquioxane resist with reduced linewidth fluctuations. Microelectronic Engineering. International Conference on Micro- and Nanofarbication. en. 41-42. 331–334. 10.1016/S0167-9317(98)00076-8. 0167-9317.
3. Jin . Feng . Liu . Jie . Zhao . Yuan-Yuan . Dong . Xian-Zi . Zheng . Mei-Ling . Duan . Xuan-Ming . 2022-03-15 . λ/30 inorganic features achieved by multi-photon 3D lithography . Nature Communications . en . 13 . 1 . 1357 . 10.1038/s41467-022-29036-7 . 2041-1723 . 8924217 . 35292637. 2022NatCo..13.1357J .
4. Huang . Po-Han . Laakso . Miku . Edinger . Pierre . Hartwig . Oliver . Duesberg . Georg S. . Lai . Lee-Lun . Mayer . Joachim . Nyman . Johan . Errando-Herranz . Carlos . Stemme . Göran . Gylfason . Kristinn B. . Niklaus . Frank . 2023-06-07 . Three-dimensional printing of silica glass with sub-micrometer resolution . Nature Communications . en . 14 . 1 . 3305 . 10.1038/s41467-023-38996-3 . 2041-1723 . 10244462 . 37280208. 2023NatCo..14.3305H .
5. Chen. Yifang. 2015-03-05. Nanofabrication by electron beam lithography and its applications: A review. Microelectronic Engineering. en. 135. 57–72. 10.1016/j.mee.2015.02.042. 0167-9317.
6. Shen. Jiashi. Aydinoglu. Ferhat. Soltani. Mohammad. Cui. Bo. 2019-03-01. E-beam lithography using dry powder resist of hydrogen silsesquioxane having long shelf life. Journal of Vacuum Science & Technology B. 37. 2. 021601. 10.1116/1.5079657. 2019JVSTB..37b1601S . 104333826 . 2166-2746.
7. Jiashi. Shen. 2018-09-28. E-beam Lithography using Dry Powder HSQ Resist Having Long Shelf Life and Nanogap Electrode Fabrication. en.