A Review of Microelectronic Manufacturing Applications Using DMSO-Based Chemistries

Dimethyl Sulfoxide (DMSO) is a proven solvent used for many applications in microelectronic manufacturing. Common processes where DMSO is used include casting, definition, and stripping applications. A unique high polarity as defined by a dielectric constant of 48.9 as compared to NMP (32.0) and DMAC (37.78) enables the solvent to provide excellent dissolution character for a wide range of salts or materials where solubility is typically limited to aqueous systems [1-2]. This property of high organic solvency makes DMSO a good casting and stripper choice for a wide range of photoresists representing g-line to DUV that comprise cresolformaldehyde (novolak), P-HOST (poly-hydroxystyrene), and acrylics. DMSO has become a key solvent choice for stripping novolak-based resists from FPD IC's (figure 1) [3]. The largest potential volume use of DMSO is represented as an ancillary for stripping resists and etch residues [4]. Next generation ancillaries will require improved performance to clean residues from cured polymers present in smaller geometries, a challenge that is likely to be achieved only by mixtures with strong acids and bases. DMSO is a good choice as a carrier solvent as it exhibits limited hydrolysis or chemical rearrangement as commonly exhibited by NMP [5] and DMAC [6]. This unique stability supports cleaning applications where cured polymers are stripped from sensitive metal features as in solder bumping for wafer level packing (figure 2) [79]. DMSO has been demonstrated as a base-chemistry to remove high dose ion-implanted resist, where its unique character facilitates delivery of a wide range of agents to help breakdown and remove tenacious polymer [10]. Safety classification as non-regulated is in accordance with the US EPA [11] and the European Union [12], a condition that is consistent with the ITRS challenge for next generation products used in the fab [13]. Figure 1. SEM photos of metal lines patterned by novolak resist (before left) and stripped (after-right) with DMSObased chemistries. Images shown are low (top) and high (bottom) magnification.