In this paper we investigate an in situ measurement of polymer and lithographic resist film mechanical properties on a silicon substrate, with a Dynamical Mechanical Analysis tool (DMA).
This technique allows the measure of the glass transition temperature (Tg) of the resist film (thickness range: several μm to few nm) and its elastic and viscous modulus variations with a high
precision and reproducibility. Indeed, DMA appears to be more sensitive than other thermal analysis methods like Differential Scanning Calorimetry (DSC), to monitor Tg variations induced by film
First we will discuss the performance of the tool and present the variations of the glass transition
temperature of a PMMA (PolyMethylMethAcrylate) layer as a function of its thickness: we observe a shift towards higher temperatures up to 30°C when the film thickness decreases from one
micrometer to 10nm. This behavior highlights the importance of surface properties versus bulk. We will also discuss the interest of the DMA technique applied to more complex chemistries, as it is the
case for lithographic resist formulations, i.e. a blend of polymer with grafted functionalities, photoactive compounds and various additives. We successfully applied this technique to
characterize different resist film thicknesses and we observed the effect of the thickness on the thermal events. Such kind of change is important to take into account in the optimization of material
performance for thin film applications. This material understanding allows to better define the process conditions and can be applied to different microelectronic topics such as: thermal flow
treatment of positive tone photo resists, hot-embossing nanoimprint, cross linking reactions with negative tone resists or so called "hardening" processes.
In this paper, we investigate the capabilities to form small contact holes with various 193nm
resists applying a thermal flow process. We first compare the material properties (glass
transition temperature Tg and thermal deprotection T<sub>D</sub>) of different 193nm resists to our
reference process for thermal reflow, namely the 248nm reference resist (RoR). The main
difficulty related to 193nm acrylate backbone is the high Tg value, which implies some flow
bake temperature closed to or superior to the deprotection temperature. Depending on the
resist chemistry, different behaviours have been observed such as acceleration of the flow
rate, formation of bubble defects linked to gaseous by-products or even contact hole diameter
increase. These results are strongly dependent on the chemical reactions occurring in the resist
film at the same time as the film softening. In order to better select the most promising 193nm
resist candidates for contact hole reflow technique, we also develop a polymer flow
measurement with Dynamic Mechanical Analysis (DMA). By measuring the creep
compliance of the resist film spin-coated onto a silicon wafer under various bake
temperatures, we are able to define the optimal temperature range for resist flow.