EUV (Extreme Ultraviolet) process is the technology that is currently drawing the most interests for microfabrication process of semiconductor. However, there are still many tasks that need to be resolved as EUV process is still in its initial phase. Samsung Electronics stated that it is conducting R&D on various solutions such as extreme low-temperature process and extreme low-pressure process to resolve possible challenges.
Master Park Jong-cheol of Samsung Electronics explained during ‘The Korean Society of Semiconductor & Display Technology Fall Conference’, which was held at Hanyang University on the 19th, that there are currently two obstacles for etching process that shaves off circuits as the semiconductor industry is starting to enter an EUV process era.
‘Micro bridge’ that occurs at the bottom of a circuit is the first obstacle. Also, it has also become more difficult to place a material deep inside in order to shave off circuits as the width of a circuit has become extremely narrow.
EUV process is a photolithography process that repeatedly prints circuits on a circular wafer with EUV light source (13.5nm). Because the wavelength is about 14 times smaller than the wavelength of ArF (Argon Fluoride, 193nm) light source, which is the most commonly used light source, EUV process can print circuits more elaborately and finely. This is the reason why Samsung Electronics and TSMS from Taiwan are focusing all of their abilities in order to gain leadership in this technology.
However, shorter wavelength causes new flaws such as micro bridge.
EUV photoresist is applied on a semiconductor wafer during photolithography process. Main problem is that the energy of the wavelength of EUV light source becomes 10 times greater as wavelength becomes shower. Because wavelength and energy are inversely proportional, wavelength hits the surface of a wafer harder as it becomes shorter. Light source with greater energy either causes the nucleus of an atom of a reactant that is included in an EUV photoresist to pop out or it causes brand new atoms to combine. As a result, foreign substances that semiconductor manufacturers do not want are formed. In addition, the width of a circuit has become thinner causing areas that are not supposed to be shaved off to be connected. This is called micro bridge.
“Although photolithography process can be lengthened in order to resolve micro bridge issue, we have to consider the fact that the productivity of an EUV photolithography system that costs about $171 million (200 billion KRW) can decline faster.” said Master Park.
He explained that Samsung Electronics has chosen a method that repeatedly shaves off micro bridges while protecting the upper part of a circuit with polymer.
“Because it may be difficult to maintain this method for next-generation processes, it is likely that we are going to need a brand new etching technology.” said Master Park.
Another problem is that it has become difficult to place materials that are needed for etching process deep inside of a circuit as the width of a circuit has become significantly narrower. Polymer covers the surface during etching process in order to prevent circuits from shaved off unevenly.
Problem is that circuits made through EUV are already thin and that polymer that is currently used makes entrance even narrower and causes ‘bottleneck phenomenon’. As a result, more time and cost are necessary in order to place etching materials and ions deep inside through a narrow entrance.
“Because etching process time becomes longer and there needs to be more power to place etching materials deep inside, there is a vicious cycle such as protecting the upper part of a circuit even more.” said Master Park. “Samsung’s executive team is already aware of this issue and is laboring over for a solution.”
Master Park suggested ‘extreme low-temperature’ etching process as a possible solution. By decreasing the temperature of the inside of a chamber where wafers go in, gaseous movements that are necessary for etching process are minimized even without polymer. His solution is based on a principle that materials that are active in room temperature move slowly in extreme low-temperature.
“Extreme low-temperature method to create effective etching materials and ‘high pumping’ etching technology that prevents bottleneck phenomenon by forcing gas inside of a chamber to move faster can be possible alternatives.” said Master Park. “Samsung Electronics is currently conducting R&D on these technologies to apply them to actual mass-production process.” He also added that more research on these issues by the academic industry will be a big help for the semiconductor industry.
Staff Reporter Kang, Hyeryung | firstname.lastname@example.org