Humidity- tunable liquefaction of Cr thin-film and its application to patterning

Abstract

Electric field induced liquefaction of chromium (Cr) thin-films, being a surface-based process, is affected by the moisture content in the surroundings. The said process is an electrochemical reaction, which takes place on an electrically stressed Cr thin-film. The reaction results in a liquid region, which flows out radially from the tip of the cathode. A proper understanding of the phenomenon is warranted as it is applied for performing a nanolithography process, electrolithography (ELG). In this study we have focused on the effect of relative humidity (RH) on the material formation and transport on electrically stressed Cr thin-film. Varying the RH over a wide range, the phenomenon is studied using different levels of DC stress. The effect of the applied DC stress coupled with varying levels of RH showed trends which are explained qualitatively and quantitatively. The results indicate that RH could be a pivotal parameter affecting the above-mentioned phenomenon on electrically stressed Cr thin-films and could significantly alter the minimum feature size attainable by ELG. To demonstrate the effect of RH on ELG, lines were drawn at various humidity levels resulting in greater than 100% increase in the attainable line width when RH was increased by about 40%.

Decrypting the thermal effects on the electric field-induced material formation process on Cr thin films

“…When we plot the corresponding radius of the formed liquid region versus the calculated RH local , for RH bulk = 84%, we obtain the graph shown in figure 4(b). A previous study on the effect of RH on the said liquid material formation process put forward a complex dependence of RH on the radius, r, of the liquid domain [20], and is given as:…”

“…Hence the local decrease in RH due to the rising temperature of the sample is again one of the reasons why increasing temperature helps to reduce the extent of liquid material formation on electrically stressed Cr thin films. This is because, a decrease in RH results in the reduction of the number of hydroxyl ions available to take part in the chemical reaction, equation (1) [20].…”

“…Since the basic anatomy of the chemical equation is quite similar to that of LAO, it is thereby majorly affected by similar parameters as that of o-SPL. The entire phenomenon is composed of several smaller sub-processes that take place before the oxidation reaction [20]: absorption of water molecules into the oxide domain; splitting up of water molecules into constituent ions; transport of the oxyanions to the perimeter of the liquid region to take part in the oxidation reaction. While investigating the effect of the applied alternating electric field modulation, it was revealed that the oxyanion transport process is the major controlling factor in the entire phenomenon [18].…”

“…The core phenomenon under discussion, i.e., electric field-induced liquid material formation on Cr thin films, is affected by various ambient parameters like relative humidity [20]. Other factors affecting the process include the thickness of the Cr film [14].…”