The abnormal growing defect (we called this defect 'scum haze defect') in the photomask which is generated during the wafer lithography process is very important issue on semiconductor industry. Because wafer yield loss could be caused by the mask CD variation and the transmittance loss due to the growing defects on the photomask, many studies have been done about the mechanism and the solution of the general type growing defects such as haze and Cr migration so far, However we still need to clarify some abnormal types of the growing defects such as scum haze defect. In this paper, we investigated the generation mechanism and prevention techniques of the scum haze defect on the attenuated phase shift mask. This defect composed of CrOx is caused by the increase of the accumulated exposure energy on photomask. This phenomenon is remarkably similar to the Cr migration on binary mask. But, the apparent difference is that this scum type defect is observed on the attenuated phase shift mask which mainly consists of MoSiON film, and it is difficult to control this defect because of its irregular generation characteristic. Additionally, this defect is not generally removed through the conventional wet cleaning process but it only could be removed by a kind of plasma treatment. In this study, the difference of generation mechanism between the scum haze defect and the general haze was discussed, and the optimal process for controlling scum haze defect in the mask manufacturing was described.
During EUV exposure, more frequent mask cleaning is essential for removing not only particles from lack
of pellicle but also the carbon contamination due to accumulative EUV exposure. Because of this reason,
process improvement for minimize corrosion and etching of the Ru capping layer is urgently needed. In this
work, the influence of TaBN absorber etch condition on Ru integrity followed by repetitive cleaning was
evaluated and the effects on long-term durability of Ru are compared under various cleaning conditions.
Consequently, it was shown that Ru durability was strongly influenced by the gas contents and over etch time
of absorber dry etch, not only as a function of cleaning conditions.
Backside defects a few micrometers in size are serious concern in lithography because they can degrade the image
quality on a wafer. It was known that defects attached on the backside affected the printing images on a wafer by locally
altering the partial coherence (σ) and the transmitted intensity of the illumination. The ability to detect and to simulate
their impact of defects on the backside is one of the key components in ensuring quality of photomask.
The purpose of this study is to determine the minimum size of defects on the backside which would be affected
printability in 193nm photolithography. It was investigated to the influence of wafer critical dimension (CD) variation
according to illumination and NA, that of refraction according to defect size.
For this study, a reticle was designed to include line and space patterns, contact patterns and isolated patterns on the front
side. And the type of defects attached on the backside was made of chrome to investigate the relation between
transmittance of backside defects and its printability.
The correlation of measurements made with UV and DUV-based inspection system; simulation performed with a
193nm aerial image measurement system. Besides the allowable size of backside defects was determined using the
criterion of a maximum intensity variation of 10%.
In sub-60nm technology node, cleaning process becomes specialized to clear the defects without pattern damage as
decreasing critical particle size to control. While cleaning process has to meet the primary requisite, removal of particle
including organic residue and prevention of particle re-deposition, it should enable to suppress haze phenomena for a
long life of photomask. However, to solve the problem of haze, the chemical materials caused haze seed should be
hardly used and physical force becomes strengthen as the compensation for cleaning efficiency. Unfortunately it brings
about another problem, pattern damage seriously.
In this paper, adequate cleaning conditions which are applicable in sub-60nm technology node are evaluated to meet the
dilemma among three requirements, high cleaning efficiency, and prevention of pattern collapse, and prevention of haze
phenomenon. All cleaning steps in photomask process were set up using only 172nm UV irradiation for degradation of
organic contaminants and deionized water (DI) with acoustic power for particle lift-off. The effect of UV and DI
cleaning on cleaning efficiency and haze phenomena was derived from carrying out chemical and physical analysis
simultaneously. Also, we could quantify the statistical probability of pattern collapse in each of technology node and
layer shape as different condition of megasonic frequency and its power. As a result, it was known that this cleaning
process have various merits to make out dilemma mentioned above, if it satisfies optimized conditions.
As the design rule of the semiconductor circuit shrinks, the specification for photomask becomes tighter. So, more
precise control of CD MTT (Critical Dimension Mean to Target) is required. We investigated the CD MTT control of the
attenuated PSM (Phase Shift Mask) by additional Cr dry etch. In conventional process, it is difficult to control CD MTT
precisely because about 5 factors - Blank Mask, E-beam writing, Resist develop, Cr dry etch, MoSiN dry etch - affect
CD MTT error. We designed the new process to control CD MTT precisely. The basic concept of the new process is to
reduce the number of factors which affect the CD MTT error. To correct CD MTT error in the new process, we
measured CD before MoSiN dry etch, and then additional corrective Cr dry etch and MoSiN dry etch was performed. So,
the factors affecting CD MTT error are reduced to 2 steps, which is additional corrective Cr dry etch and MoSiN dry
etch. The reliability of CD measurement before MoSiN dry etch was evaluated. The generable side-effect of the
additional corrective Cr dry etch was analyzed. The relationship between 'CD shift' and 'additional corrective Cr dry
etch time' was found for various patterns. As a result, accurate CD MTT control and significant decrease of CD MTT
error for attenuated PSM is achieved.
As the specification for photomask becomes tighter, it is strongly demanded for achieving precise CD MTT (critical
dimension mean to target) and enhanced defect controllability in photomask fabrication. First of all, it is necessary that
reducing the factors of CD MTT error and introducing the reliable method to correct CD error for accurate CD
requirement of attenuated PSM (phase shift mask). From this point of view, one of CD correction methods which consist
of Cr CD measurement step after resist strip (strip inspection CD: SI CD) and additional corrective Cr dry etch step was
developed. Previous SI CD correction process resulted in accurate CD control within the range of CD MTT. However it
was not appropriate for defect control due to additional resist processes for selective protection of Cr pattern during CD
In this study, the method for achieving precise CD MTT by correcting CD error without any resist process is
investigated. It is not suitable for the CD correction process to control CD MTT precisely that Cr etched resist (etch
inspection CD: EI CD) is very vulnerable to E-beam scanning during CD measurement. Otherwise, photoresist after Cr
etch selectively shrinks via UV irradiation under ozone (O3) condition, which drives a reduction of CD MTT error as a
result of accurate CD measurement (UV-irradiation inspection CD: UI CD). Moreover, it is not necessary any resist
process for Cr protection due to UV irradiated resist as enough for a etch barrier. It is a strong advantage of novel CD
correction method. This strategy solves the problems such as both CD measurement error on the EI CD correction
method and defects originated from resist process on the SI CD correction method at once. For the successful
incorporation of UI CD correction method, several items related with CD should be evaluated: accuracy and repeatability
of CD measurement under UI CD, control of CD MTT and CD uniformity, additional corrective etch bias for UI CD,
independence of corrective Cr etch process from UV irradiated resist, isolated-dense CD difference,.. etc. In this paper,
strategy of design for the progressive CD correction method for defect-free photomask and process details will be
As mask feature size is shrinking, required accuracy and repeatability of mask CD measurement is more severe. CD-SEM which is usually used to measure below 0.5um pattern shows the degradation of repeatability by the sparkle noise. To reduce this, larger ROI (range of interest) is recommended on line and space patterns. But this wide ROI is difficult to use on Hole or isolated patterns. In this paper, anisotropic diffusion filtering method will be introduced to replace the ROI, and evaluated on various patterns such as holes and isolated patterns. It can also reduce the effects of defocus of CD-SEM and enhance the repeatability of CD-SEM. And multi-point CD measurement technique is described to reduce the local CD errors on CD uniformity of mask which is usual on one dimensional CD measurement conventionally. Using these methods, local CD uniformity and global CD uniformity of masks which is the key performance of mask quality can be measured more exactly compared to old CD measurement method. And we can give correct information of mask to reduce global CD uniformity by process tuning such as FEC (Fogging Effect Correction) or development process.
The ability to eliminate the critical source of haze contamination which can be derived from the cleaning chemistry residues and mass production environment has become a major challenge for 193 nm photolithography in semiconductor industry. Furthermore, as the specification for pattern generation on photomask becomes tighter, it is getting harder and harder to eliminate defects with both minimal structural damage and preservation of photophysical properties. We designed for the smart cleaning strategy to achieve the defect-free photomasks as a concern of above current issue with a combination of well-known cleaning technology, such as using the collective effects of ozonated water (DIO3) for the alternative to conventional clean (SPM/SC1) and UV/O3 treatment for the control of sulfate concentration. In addition to photomask clean, these strategies are also used for photoresist stripping.
As well as the final cleaning process, it is a rational strategy that judicious modification of inter-process clean. Specially, that kind of view is focused on the after-development clean (ADC) process which mainly eliminated the source of fatal defects on the mask, such as pattern bridge following dry etch process.
In this paper we will propose a novel cleaning strategy for the elimination of potential source of haze formation and fatal defects.
The critical source of haze contamination which mainly occurred on MoSiN surface and the interface of MoSiN and quartz is known as sulfuric ions remained after mask process. In this experiment, the UV treatment with oxygen gas was carried out before and after wet cleaning process for reducing residue ions from mask surface, and the effect with the sequence of UV treatment and wet cleaning was investigated. The composition of amorphous MoSiN layer was slightly modified by 172nm UV treatment with oxygen gas, and the amount of chemical residue ions after wet cleaning which use the piranha and SC-1 was reduced according to the transformation of surface composite. And also the relation of the surface transformation and the phase shift after SC-1 cleaning was evaluated.
In this study, Cr defects resulted from high voltage E-beam writing in high Cr load Logic Mask were investigated. The Cr defect, which is a damage of anti-reflection layer on Cr, is mainly found in isolated Cr patterns of high Cr load Logic Mask. This defect appears under high voltage E-beam writing with high dose and dry etch process. High accelerating voltage and dose of E-beam writing decrease the thickness of remaining E-beam resist after developing. These phenomena are more significant in high Cr load Logic Mask consisted of isolated Cr patterns. Because the resist thickness of isolated Cr pattern is not enough for enduring dry etch process-induced damage, Cr surface is damaged during etching. Consequently, the Cr surface damage of high Cr load Logic Mask is related with voltage and dose of E-beam and dry etch process time. To prevent these defects, low accelerating voltage and dose of E-beam and low thickness of Cr layer to increase dry etch process margin are necessary.
In this study we investigated the defect due to pellicle frame materials for repeating exposure in months. Defects were found in the sub-pellicle and the defect density was high in the 4 corners compared to the center of the mask. The defects grew on MoSiON or the interface Quartz and MoSiON film, and the defect size was below 0.5 um. By analyzing with Raman Spectroscopy, defects consist of Ammonium Sulfates, Melamine Formaldade Resin and KClO3. The evaluation method for cleaning process and pellicles was Ion Chromatography. According to Ion Chromatography analysis, the main composition of defect was substances of pellicle frame materials. Also we confirmed the pellicle frame effect with the exposure test.