Development of an integrated organic film removal and surface conditioning process using low molecular weight alcohols for advanced integrated circuit (IC) fabrication

Higher yield in semiconductor device fabrication hinge critically upon the cleanliness of the semiconductor surfaces. About fifty percent of the yield loss is due to surface contaminants that decrease device reliability. Due to decreasing feature sizes, the conventional methods of removing contaminants especially photoresist residues are no longer sufficient to obtain the desired device properties and yield. In this work, we investigate new solvents and methods for surface cleaning, in particular removal of organic films and drying. A two-chamber reactor was designed and used to remove organic contaminants especially unexposed photoresist from semiconductor surfaces. Relatively benign solvents such as low molecular weight alcohols (in particular isopropanol) were investigated both a stripping agent and as surface drying agent. A method was developed to consolidate stripping, rinsing and drying of the semiconductor surfaces in a single step process. Both high-dose ion-implanted and post bake photoresist removal was studied. Effectiveness of different additives, mainly, ammonium hydroxide and water to IPA for removal of the adhesion promoter (HMDS) layer was investigated. In-situ x-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to study the surface compositions and surface bonding configurations as function of additive concentrations, process temperature and pressure. Infrared spectroscopy (IR) along with XPS was used to gain insight on the photoresist removal mechanism. In-situ visual monitoring system was used in order to study the effect of flow and pressure on photoresist stripping. Integration of the process with organic low-k materials were also investigated using Benzocyclobutene (BCB). The change in thickness, chemical structure and dielectric constants of BCB films were studied as function ammonium hydroxide concentrations in IPA, stripping times and process temperatures. Current-voltage (I-V) studies indicated the effect of IPA-based resist stripping process electrical characteristics of SiO₂. Low surface carbon concentrations of 2.5 atomic percent in XPS was achieved using IPA/ammonium hydroxide based stripping solvents. Atomic force microscopy studies indicated the IPA/ammonium hydroxide based stripping process did not roughen silicon, silicon dioxide and aluminum films. Activation energy measurements XPS and IR suggests that resist removal mechanism was primarily diffusion controlled dissolution.