The advent of extreme ultraviolet (EUV) technology enables much smaller patterns. In order to commercialize EUV technology, some mechanical problems should be studied. Especially, pellicle temperature rising due to EUV exposure is one of the critical problems. It affects on pellicle life expectancy. We can use gas flow to cool down EUV pellicle as well as to blow off the defects fallen between the pellicle and mask. The cooling behaviors of various EUV pellicle types are studied by finite element method. Figure 1 shows the cooling of 50 nm thick p-silicon monolayer pellicle and the cooling rate is increased with the hydrogen gas flow rate, while the cooling rate without H2 flow is very slow so that it might not reach to the room temperature. The same analysis is applied to other known multi-layer pellicles (Fig. 2). Well known ASML and Samsung pellicles are compared to a single p-silicon layer pellicle. As expected, the maximum temperatures of multi-layer pellicles are lower than single-layer pellicle and we can see that the cooling by gas flow for multi-layer is better than that for a single layer. This study might suggest that EUV pellicle cooling is efficient enough to use a single layer pellicle and we might not need to use the multi-layer pellicle which was originally adapted to cool down and extend the lifetime of the pellicle. The deformation and the stress dependency of the various pellicles on the gas flow rate and pressure difference will be also shown.
Extreme ultraviolet (EUV) lithography is the most promising candidate for sub-1x nm pattering. CO2 laser irradiates to a Sn droplet and then, EUV radiation can be emitted. In this process, infrared radiation (IR) is simultaneously emitted 3 to 5 times more than EUV radiation. In order to suppress IR, spectral purity filter (SPF) [8] at collector mirror and dynamic gas lock (DGL) [4] are used. Nevertheless, some amount of IR still reaches to the wafer and it can lead to wafer heating issue, so that we investigated temperature and deformation of the wafer by using finite element method (FEM) simulation. Two different silicon wafer types are compared. There is a difference in temperature and deformation between single layered wafer with and without the bottom chuck. We also found that the temperature increased more with added stacks like hard mask or photoresist on the top of the wafer.
Thermal and structural deformations of extreme ultraviolet lithography (EUVL) masks during the exposure process may become important issues as these masks are subject to rigorous image placement and flatness change. The reflective masks used for EUVL absorb energy during exposure, and the temperature of the mask rises as a result. This can cause thermomechanical deformation that can reduce the pattern quality. Therefore, it is necessary to predict and optimize the effect of energy transmitted from the extreme ultraviolet (EUV) light source and the resultant patterns of complex multilayer structured EUV masks. Our study shows that temperature accumulation and deformation of the EUV mask are dependent on the absorber structure.
The thermo-optical optimization of extreme-ultraviolet pellicles for 3 nm node or smaller is described. Various material and multilayer structure candidates for the optimized pellicles are simulated using a finite element method. The result shows that a silicon-cored pellicle has relatively high transmission, whereas a graphene-cored pellicle shows relatively low stress compared with its material tensile strength.
The analysis of the thermal stress and the extreme-ultraviolet (EUV) pellicle is important since the
pellicle could be easily damaged since the thickness of the pellicle is 50 nm thin due to 90% required
EUV transmission. One of the solution is using a high emissivity metallic material on the both sides of the
pellicle and it can lower the thermal stress. However, using a metallic coating on pellicle core which is
usually consist of silicon group can decrease the EUV transmission compared to using a single core layer
pellicle only. Therefore, we optimized thermal and optical properties of the pellicle and elect three types
of the pellicle. In this paper we simulated our optimized pellicles with 500W source power. The result
shows that the difference of the thermal stress is small for each case. Therefore, our result also shows that
using a high emissivity coating is necessary since the cooling of the pellicle strongly depends on
emissivity and it can lower the stress effectively even at high EUV source power.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.