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.^{[clarification needed]} 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.