An extreme ultraviolet (EUV) pellicle is needed for the protection of EUV masks from defects, contaminants, and particles during the exposure process. However, the EUV pellicle can be easily deformed during the exposure process because it has an extremely thin thickness for high transmission of EUV lights. Due to the very thin thickness and the weak structure of the pellicle, a pellicle is easily deformed; a wrinkled pellicle causes an image distortion, which leads to critical dimension (CD) variation. In addition, a particle defect on an EUV pellicle can result from scanner building materials. Added materials of the particle defect on an EUV pellicle can also cause image distortion and CD variation. We investigated the impact of wrinkles and particle defects on the transmission and CD variation for the 5- and 3-nm nodes of isomorphic and anamorphic numerical aperture (NA) systems. The variation in transmission and the critical size of the particle defect with a wrinkled EUV pellicle were calculated to obtain the requirement of a CD variation of 0.2 nm for a EUV pellicle. As a result, a change in transmission of 1.9% (after two pass) resulted in a 0.2-nm variation in the CD for the anamorphic NA system (3-nm node), whereas a transmission variation of 1.3% (after two pass) caused a 0.2-nm CD variation in the isomorphic NA system (5-nm node). From these results, an allowable local tilt angle can be calculated; the allowable local tilt angle of an isomorphic NA system is 0.31 rad and that of an anamorphic NA system is 0.41 rad. When the particle defect is added on a wrinkled EUV pellicle, the critical size of the particle defect is 1.2 μm for the 5-nm node and 2.2 μm for the 3-nm node.
Extreme ultraviolet (EUV) pellicle is required for protecting the EUV mask from defects, contaminations, and particles during exposure process. EUV pellicle should be very thin for high transmission of EUV wavelength. Therefore, EUV pellicle can be easily deformed during the exposure process, and the multi-stack pellicle is suggested to minimize this deformation of EUV pellicle. The EUV multi-stack pellicle is made of polysilicon-based core layer and capping layers for the durability during the exposure process. Nevertheless, there remains other manufacturing, thermal, and mechanical problems. In this study, we investigated the impact of wrinkles of EUV pellicle, which can be formed during pellicle manufacturing or exposure process, in terms of transmission non-uniformity and critical dimension (CD) variation for 5- nm and 3-nm nodes. To fabricate 3-nm node, we need a high numerical aperture (NA) system such as an anamorphic NA system with chief ray angle of 6-degree. The wrinkle can be uniform in height and period, but we assumed a realistic non-uniform wrinkle. This non-uniform wrinkle of multi-stack pellicle may cause different image distortion for 5-nm and 3-nm nodes with the isomorphic and anamorphic NA systems. The transmission non-uniformity is calculated with various heights and periods of non-uniform wrinkles of the pellicle. It is found that the transmission non-uniformity for wrinkled pellicle for the anamorphic NA system can be larger than that for the isomorphic NA system to obtain CD uniformity below 0.2 nm.
For protecting mask from debris, EUV pellicle is considered as a most effective solution. EUV pellicle can avoid
contamination on mask by covering mask. Usage of EUV pellicle can reduce mask damage caused by contamination but
the pellicle involves transmission loss due to absorption of EUV light. To get high transmission, pellicle made with thin
thickness but it can be deformed easily due to weak structure. Deformation of pellicle such as wrinkle leads transmission
non-uniformity and transmission non-uniformity will involve CD non-uniformity. For real-application at lithography
process, the optical study of deformed pellicle is required to avoid degradation of CD uniformity. In this paper, we
discuss transmission non-uniformity with various off-axis-illumination (OAI) conditions. Then we studied CD nonuniformity
caused by wrinkled pellicle with various patterns. By increasing spatial coherence, transmission nonuniformity
is decrease at small wrinkle region. However, transmission non-uniformity variation is independent with
illumination conditions at large wrinkle which has large period. Not only wrinkled pellicle imaging but also CD variation
caused by non-uniform transmission is also dependent on illumination conditions. In contrast with transmission nonuniformity,
CD non-uniformity with high coherent light is smaller than the result with low coherent light. With all of
results, we find that the allowable local tilt angle is varied with wrinkle size and illumination conditions and smallest size
of allowable local tilt angle is about 250 mrad for both illuminations.
We report on out-of-band (OoB) radiation that can cause degradation to the image quality in extreme-ultraviolet (EUV) lithography systems. We investigated the effect of OoB radiation with an EUV pellicle and found the maximum allowable reflectivity of OoB radiation from the EUV pellicle that can satisfy certain criteria (i.e., the image critical dimension error, contrast, and normalized image log slope). We suggested a multistack EUV pellicle that can obtain a high EUV transmission, minimal reflectivity of OoB radiation, and sufficient deep ultraviolet transmission for defect inspection and alignment without removing the EUV pellicle in an EUV lithography system.
We studied various particle defects such as Fe, Al, and SiO2 which are frequently generated during extreme ultraviolet lithography (EUVL). It is important to find the critical sizes of the defect that do not make 10% critical dimension (CD) error because the defect causes CD variation. We found that the critical size of a defect was dependent on the extinction coefficient of the defect material and the particle defect with larger extinction coefficient made smaller critical size that could make 10% CD error. In addition it is needed to study the critical size of the defect which is located on the side of the absorber because it is hard to clean the location. We investigated the defect, which was located on the left side of absorber, affect more on patterning. Also arbitrary shape of defect is studied. As a result, the aerial image is most sensitive with defect area over the length and the height of the defect.
The out-of-band (OoB) radiation that can cause serious aerial image deformation on the wafer is reported. In order to check the maximum allowable OoB radiation reflectivity at the extreme ultra-violet (EUV) pellicle, we simulated the effect of OoB radiation and found that the maximum allowable OoB radiation reflectivity at the pellicle should be smaller than 15 % which satisfy our criteria such as aerial image critical dimension (CD), contrast, and normalized image log slope (NILS). We suggested a new multi-stack EUV pellicle that can have high EUV transmission, minimal OoB radiation reflectivity, and enough deep ultra-violet transmission for inspection and alignment of the mask through the EUV pellicle.
The adaption of EUVL requires the development of new cleaning method for the removal of new contaminant without
surface damage. One of the harsh contaminants is the carbon contamination generated during EUV exposure. This highly
dense organic contaminant is hardly removed by conventional SPM solution on Ru capped Mo/Si multilayer. The
hopeful candidate for this removal is ozonated water (DIO3), which is not only well-known strong oxidizer but also
environmentally friendly solution. However, this solution might cause some damage to the Ru capping layer mostly
depending on its concentration. For these reasons, DIO3 cleaning solutions, which are generated with various additive
gases, were characterized to understand the correlation between DIO3 concentration and damages on 2.5 nm thick
ruthenium (Ru) surface. An optimized DIO3 generation method and cleaning condition were developed with reduced
surface damage. These phenomena were explained by electrochemical reaction.
A laser shock cleaning (LSC) technique as a new dry cleaning methodology has been applied to remove micro and nano-scale inorganic particulate contaminants. Shock wave is generated in the air just above the wafer surface by focusing intensive laser beam. The velocity of shock wave can be controlled to 10,000 m/sec. The sub-micron sized silica and alumina particles are attempted to remove from bare silicon wafer surfaces. More than 95% of removal efficiency of the both particles are carried out by the laser-induced airborne shock waves. In the final, a removal of nano-scale slurry particles from real patterned wafers are successfully demonstrated by LSC after chemical-mechanical polishing (CMP) process.
A new dry cleaning methodology named laser-induced shock cleaning has been applied to remove the chemical-mechanical polishing (CMP) slurries from silicon wafer surfaces. After CMP process using the slurries, the slurry particles should be removed from the surface in order to avoid the circuit failure and enhance the yield. The well-distributed remaining silica particles were attempted to remove from the surface by using laser-induced plasma shock waves. In order to evaluate the cleaning performance quantitatively, the number of particles on the wafer surfaces were measured by surface scanner before and after cleaning. It was found that most of the silica particles on the wafer surface were removed after the treatment of laser-induced shock waves. The average removal efficiency of the particles was 99% over. It was found that cleaning performance is strongly dependent on a gap distance between laser focus and the surface and a suitable control of the gap is crucial for the successful removal of the particles.