Photoresist dissolution into a CO 2 compatible salt and CO 2 solution: investigation of processing conditions

Abstract

New lithographic techniques are being implemented to help further reduce feature sizes in microelectronics. A technique for the development of standard extreme ultraviolet (EUV) photoresists in a carbon dioxide compatible salt (CCS) and supercritical carbon dioxide (scCO 2 ) solution is being investigated to reduce line edge roughness and image collapse of high aspect ratio features. 1, 2 To understand the kinetics and overall mechanism of photoresist dissolution into the high pressure CCS/scCO 2 solution, a quartz crystal microbalance (QCM) was previously used to measure the effects of temperature, pressure, and density on the photoresist removal rate. 3,4 In this paper, the effects of a CO 2 drying step before development and an adhesive coating on the photoresist removal rate and the formation of residual photoresist droplets were studied at 50°C and 5000 psi. The results implied that neither the CO 2 drying step nor the HMDS coating had an effect on the bulk photoresist removal rate. It was also found that using an HMDS adhesive coating reduces residual photoresist droplet size on the substrate due to the lower substrate / photoresist surface energy.

Mechanism of Extreme Ultraviolet Photoresist Development with a Supercritical CO2 Compatible Salt

“…At the end of the experiment at ambient pressure, the mass fraction photoresist removed is nearly 100%. The discrepancy is due to remaining photoresist droplets on the rough SiO 2 surface, whose presence was verified using atomic force microscopy in previous work …”

“…At this point the mass dependence on time is no longer linear due to the differing mechanism of photoresist droplet removal from the SiO 2 surface. The droplets are reduced in size and amount in experiments with wafer coupons using a hexamethyldisilazane (HMDS) adhesive coating as discussed in previous work . The bulk photoresist removal rate and not the droplet removal rate was the concentration of this paper.…”

Fluorinated Quaternary Ammonium Salts as Dissolution Aids for Polar Polymers in Environmentally Benign Supercritical Carbon Dioxide

“…Recently, several researchers have reported the ability to develop conventional polymeric resists in scCO 2 using cosolvents or tailored soluble additives. Mao et al have shown that the addition of selected cosolvents such as acetone or alcohols allows for the development of fluorinated and nonfluorinated photoresists in scCO 2 . , In addition, other researchers have shown that the inclusion of certain surfactants into scCO 2 imparts solubility to otherwise insoluble polymers …”