Plasma etching of copper using ultraviolet irradiation

Abstract

Copper etching is one of the most difficult processes to overcome in order to realize copper metallization for the next generation semiconductor technology. Cooper chloride formed during etching is not so volatile as reaction product in coventional etching. In this dissertation, we proposed a new plasma etching method using ultraviolet(UV) irradiation in order to etch, that is, desorb the copper choloride effectively. Chlorine plasma reacts rapidly with copper to be etched and form copper chloride ($CuCl_x$) thick and nonvolatile. Therefore, in order to analyze the etch characteristics, it should be necessary to understand how the copper chloride is formed in the plasma. So, we suggested a growth model of copper chloride that is able to anticipate the thickness exactly with practical process parameters, such as, plasma current, and bias voltage. From the model, we could extract criteria suggesting how fast UV should desorb the copper chloride (about 2100nm/min). Surely, experimental results showed that UV should enhance the desorption of $CuCl_x$. Unfortunately, our UV system did not have enough capability to catch up the formation rate of $CuCl_x$. Compared etch data with the temperature simulation and with the measured temperature, what is worse, the dominant effect of UV is found out to be heating up the sample then yielding desorption of $CuCl_x$. QMS analysis of the emitted chloride species shows a possibility that photons above 3eV could desorb the $CuCl_x$ at lower temperature. A new concept using plasma together with light (UV) was proposed and applied to etch copper. Although the first trial does not yield good results, this concept could be applied to any semiconductor process using plasma and might give a chance to improve the process.