Supercritical CO2-based solvents in next generation microelectronics processing

Abstract

Large amount of chemicals and highly purified-water are needed in microelectronic manufacture. The ability of solutions to penetrate tiny spaces will become significantly more challenging as the feature size of semiconductor devices decreases to nanoscale dimensions and the functional complexity of integrated circuitries (ICs) ever increases. Supercritical fluids (SCFs) possess a unique combination of properties (no surface tension and gas-like viscosity) that can potentially be exploited for application in microelectronics manufacturing and processing in response to needs for material-compatible cleaning systems, small-dimension developing solvents, and low chemical-use processes. Recent microelectronics processes for cleaning and rinsing of patterned porous low-k dielectrics and drying of photoresist in CO 2 -based solvents are the main focus of this review. Additional topics in supercritical fluid processing include spin coating of photoresists, development with nanoscale dimensions, metal deposition and silylation.supercritical carbon dioxide, low-k dielectrics cleaning, photoresist drying A manufacture method for semiconductor devices includes many steps: coating, photolithography, etching and ashing, cleaning, drying, etc. Incorporating new low-dielectric isolation materials and low-resistance metals (Cu replacing Al as interconnects) will be required in next generation microelectronic processing. As the features in semiconductor devices shrink to nanoscale dimensions, a major hurdle will emerge in processing steps involving lithography coating, development, metal deposition, cleaning, and drying. In addition, encouraged by increased regulations on the release of toxic chemicals and costs of water and solvent use, the semiconductor industry is eager to abate chemical and water usage in main production processes. Therefore, new concepts in semiconductor manufacture are required to challenge this complexity.Supercritical CO 2 (Sc CO 2 )-based technologies accept a number of such challenges. The solvation properties of CO 2 are unique. The high compressibility of near-critical CO 2 and the dependence of solubility, transport and other properties on density allow the solvent quality to widely vary via simple pressure control without introducing a new component. Compared with liquid solvents, supercritical fluids are less viscous due to the greater free volume. Consequently, solutes diffuse more quickly. The surface tension of liquid CO 2 is only 1.5 mN/m at 25℃ and reaches to zero at the critical point, where liquid droplets are no longer formed. The low interfacial tension will allow CO 2 -based solvents to penetrate and wet nearly all features, no matter whether hydrophilic or hydrophobic. CO 2 can be evaporated at room temperature without remaining trapped liquid inside the pore structures, which could potentially affect the final product. Sc CO 2 is environmentally benign, nonflammable, nontoxic, leaves no liquid wastes, and is

Supercritical Fluids for the Fabrication of Semiconductor Devices: Emerging or Missed Opportunities?

“…Although supercritical carbon dioxide processing can be viewed as a “greener” alternative to other techniques, we do not place primary focus on this point. − Should SCF technology be implemented in industry, it is a welcome benefit that will follow. What is clear is that interest in the field, particularly in the area of cleaning and photoresist stripping, led to the development of full wafer process cluster tools that can be integrated into production lines. , These applications are among the most difficult for SCF carbon dioxide relative to its intrinsic physicochemical properties.…”

“…Applications development for SCF cleaning and photoresist stripping has been widely reviewed and is not the primary focus of this article. − ,− Instead, we concentrate on areas that are particularly well-positioned to take advantage of the unique properties of SCFs to deliver significant performance improvements and in at least one case, lower cost. These processes include conformal metal and metal oxide deposition, the preparation of ultra low k dielectrics, directly patterned dielectrics, and nanostructured metal oxide films, and the design and implementation of materials and processes for high resolution lithography.…”

Cleaning Using CO2‐Based Solvents

“…A small hysteresis is observed upon depressurization but the films shrink to the original values after the pressure goes back to ambient pressure, indicating that the pMSQ pores did not collapse in the pressurization and depressurization cycle. For the 248 nm KrF and 193 nm ArF resists, the maximum swelling was 5 or 10%, respectively, upon depressurization, the thickness of all resists return to their original thickness, indicating that CO2-based cleaning is a feasible technique for these photoresists [47,48].…”

Numerical Simulation Study on Flow Characteristics of Supercritical Carbon Dioxide in a New Cleaning Chamber

“…In recent years, the traditional cleaning technology has been developing rapidly, but the microelectronics and other high-tech cleaning industry still faces many problems. As the features shrink to nano-scale, the cleaning solution contained in the acid and alkali and strong oxidizing agents can cause surface microroughness and structural deformation, aqueous cleaning is unfeasible due to surface tension and capillary forces increase [2][3][4]. Nanoporous silica (NPS) is a hotspot in ultra-low dielectric constant material domain, but highly corrosive chemical cleaning will destroy the material, the capillary force of water can also cause structural collapse [5]; The traditional cleaning has consumed a great deal of pure water and organic solvent, which inevitably caused serious environmental pollution, physical hazards and water waste.…”