Elucidating the physiochemical and lithographic behavior of ultra-thin photoresist films

Abstract

As resist feature sizes and film thicknesses continue to shrink in dimension, a number of resist feature size and film thickness dependent effects are being observed in the lithographic performance of high resolution photoresists. In order to understand these phenomena, a better understanding of the physiochemical behavior of complex multi-component organic resist thin films is needed. As a first step in that direction, a series of model photoresists were studied in an effort to begin to understand the thermophysical properties of such multi-component thin films. The influence of photoacid generator (PAG) loading and PAG chemistry on the glass transition behavior using the model photoresists was studied. A thermal flow experiment was used to characterize an "apparent glass transition temperature" of the resist thin films as a function of PAG type and loading. These results were compared to traditional glass transition measurements made on the same resist compositions using differential scanning calorimetry (DSC). The two methods, namely DSC and the thermal flow measurement, yielded very different results depending on the type of PAG used. Further studies using ToF SIMS to profile the distribution of PAG in the resist thin films revealed that the two PAGs focused on in this work, a triphenylsulfonium triflate (TPS.OTF) and a triphenylsulfonium nonaflate (TPS.ONF), exhibited very different distribution behavior in resist thin films. In the case of TPS.OTF, the PAG was observed to show a depletion region near the resistsubstrate interface while the TPS.ONF PAG was relatively homogeneously distributed in the resist thin films. In the case of TPS.ONF, it was also the resist system which showed very different thermophysical behavior when comparing the glass transition temperature measured using DSC to the thermal flow temperature measurement. This work points out the fact that component distribution and thin film effects must be carefully considered in interpreting and analyzing the behavior of multi-component thin films.