Dimethyl sulfoxide (DMSO) is an enabling process solvent in two high-technology industries. It is the dominant solvent for spinning polyacrylonitrile (PAN) carbon-fiber precursor, the route behind more than 90% of the world’s high-performance carbon fiber, and it forms the high-solvency backbone of copper-compatible post-etch residue removers in semiconductor fabrication. The two uses sit at opposite ends of the purity scale yet share the same behavior: DMSO dissolves polymers and organic residues while being fully miscible with water.
PAN Precursor Spinning
Over 90% of commercial carbon fiber is PAN-based. A typical dope holds 10–20% w/w PAN in DMSO at 50–80 °C, filtered and degassed before extrusion into a water/DMSO coagulation bath. Because DMSO and water are fully miscible, the rate of solvent exchange — and therefore the skin density and porosity of the nascent fiber — is tuned through bath temperature and DMSO concentration. DMSO is recovered from the dilute wash streams by multi-effect vacuum distillation and recycled within the spinning loop.
Although DMSO is washed out before high-temperature treatment, residual metal ions can catalyze oxidative degradation of PAN during the 200–300 °C stabilization step, weakening the final fiber. For aerospace-grade precursors, low-metal DMSO is therefore preferred even at this industrial end of the purity scale.
Post-Etch Residue Removal
At 90 nm nodes and below, copper replaced aluminum as the interconnect metal, and conventional alkaline amine strippers attack copper. DMSO forms the organic backbone of the copper-compatible strippers developed for this shift, removing photoresist and the fluoropolymer post-etch residue left after plasma etching of copper and low-k dielectrics.
A typical formulation combines DMSO with hydroxylamine or amine chemistry, a benzotriazole (BTA) corrosion inhibitor, and water, processed at 60–80 °C. DMSO’s 189 °C boiling point allows this elevated temperature without excessive volatility. Here individual metal ions must sit below 10 ppb, and below 1 ppb at advanced nodes, with particles tightly controlled to SEMI standards.
| Industry | DMSO Application | Grade Required |
|---|---|---|
| Carbon fiber | PAN dope solvent & coagulation | Industrial (low-metal for aerospace) |
| Semiconductor | Post-etch residue & photoresist stripper | Electronic (metals < 10 ppb, < 1 ppb at advanced nodes) |
Table 1: Two high-technology DMSO applications and their purity requirements
Why DMSO Rather Than DMF or DMAc
In carbon fiber, DMSO has largely replaced DMF and DMAc because its water miscibility gives sharper, more controllable coagulation and its lower toxicity simplifies plant operations. In semiconductor stripping, its strong dissolution of organic polymers removes fluoropolymer residues that weaker solvents leave behind, and unlike NMP-based strippers, DMSO formulations avoid REACH reproductive-toxin restrictions. The two applications differ only in purity: spinning tolerates industrial-grade DMSO, while wafer processing demands electronic-grade material made under cleanroom conditions.
References
- Frank, E.; et al. Carbon fibers: precursor systems, processing, structure, and properties. Angew. Chem. Int. Ed. 2014, 53(21), 5262–5298.
- SEMI Standard C33: Specification for pure dimethyl sulfoxide (DMSO) for semiconductor processing.