As the device design rule shrinks, photomask manufacturers need to have advanced defect controllability during the
ARC (Anti-Reflection Coating) and ABS (Absorber) etch in an EUV (extreme ultraviolet) mask. Therefore we studied
etching techniques of EUV absorber film to find out the evasion method of particle generation. Usually, Particles are
generated by plasma ignition step in etching process. When we use the standard etching process, ARC and ABS films are
etched step by step. To reduce the particle generation, the number of ignition steps need to decrease. In this paper, we
present the experimental results of in-situ EUV dry etching process technique for ARC and ABS, which reduces the
defect level significantly. Analysis tools used for this study are as follows; TEM (for cross-sectional inspection) , SEM
(for in-line monitoring ) and OES (for checking optical emission spectrum)
Main Topics of a photomask have been CD(Critical Dimension), Overlay and Defects. In side of
defects, technique suppressing growing defects which are occurring on a mask surface becomes as
important as defect control method during mask manufacturing process. Conventional growing defects
arise out of combination of sulfuric ion on a mask surface and environmental facts such as pellicle
ingredient, humidity and etc. So Mask cleaning process was driven to reduce sulfuric acid on a mask
surface which source of growing defects. And actually various cleaning process has been developed
through the elimination of sulfuric acid such as DI, O3 cleaning. Normally Conventional growing defects
are removed using DI, SC1 or SPM cleaning according to incidence.
But recently irregular growing defects are occurred which are completely distinct from conventional
growing defects. Interestingly, irregular growing defects are distributed differently from conventional on a
mask. They spread in isolated space patterns and reduce the transmittance so that space pattern size
continuously decreased. It causes Wafer Yield loss. Furthermore, irregular growing defects are not fully
removed by cleaning which is traditional removal process. In this study, we provide difference between
conventional and irregular growing defects based on its characteristic and distributed formation.
In addition, we present and discuss removal and control technique about irregular growing defects. For
elemental analysis and study, diverse analysis tool was applied such as TEM for checking Cross-Section,
AFM for checking the roughness of surface, EDAX, AES, IC for analyzing remained ions and particles on
the mask and AIMS.
In this study, the method to achieve the precise CD MTT (critical dimension mean to target) correction in
manufacturing attenuated PSM (phase-shift mask) is investigated. There has been a growing demand for
more precise Mask CD MTT control in recent years. The CD correction method has been developed and
applied to meet the tighter CD MTT specification . However, the efficiency of the CD correction is greatly
affected by the repeatability of the CD measurement. The factors, which can have an influence on the CD
measurement, are the fluctuations of the pattern profile and the electron current of the SEM.
The conventional CD MTT correction method is basically to correct MoSi CD MTT by applying the
additional dry etch for MoSi based on Cr CD value. Therefore, the repeatability of the Cr CD MTT is the
crucial point for the accuracy of the final CD MTT correction. Although the Cr CD MTT is the crucial factor for
the successful CD MTT correction, it has the fluctuation due to the Cr pattern profile. If the Cr pattern profile
has low patterned angle after MoSi etch process, it can cause the focusing error in the CD measurement
using CD SEM. Therefore, a method to improve the reliability of the Cr CD MTT should be developed.
The IS and the normalized Delta CD concepts are adopted to obtain more reliable Cr CD MTT. The IS
refer the variation of the Cr CD MTT according to the difference in CD values with CD measuring thresholds.
The normalized Delta CD is obtained from the correlation of IS and Delta CD. Finally, the normalized Delta CD
is applied to correct the MoSi CD MTT by dry etch process.
The reduction of the Cr CD MTT fluctuation range is achieved by using the new CD correlation process
including IS and the normalized Delta CD. Consequently, the final MoSi CD MTT is improved 60% of range by
using the new CD correlation process.
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.
This is an experimental result for the inhibition of effects of the growing defect. Up to now, it has been considered and defined that the growing defect is an unexpected and unusual reaction by bonding impure ions existed on the mask each other. This study is not only to suppress the unexpected reaction when making the final mask but also to stabilize the surface of mask by controlling by-product occurred when stripping upper Cr layer and damaged layer from sputtering process. According to the analysis of the surface roughness stemming from each process (from wet etching to cleaning Process) of MoSi layer, the surface still comes to be rough when a mask is done through all process. So, heat treatment was performed and surface roughness was measured to figure out how much the surface condition would be improved and how many remaining SO4, NH4 Ions on the surface after cleaning process reduced. This study shows the major factor causing plasma damage is a dry etcher, a way to control the damaged layer of MoSi at PR strip process, the level of stabilization of mask surface through cleaning process and a clue to be able to prove the stabilization by adding specific process. Analysis tools for this study are as follows. AFM (for checking the roughness of surface), TEM (for checking cross-section) and IC (Ion chromatography)analysis equipment.
In this study, A new inspection system with Nd:YAG laser beam has been developed to detect defects on blank mask and particles from process and handling. The development of new reflective image and optic system increased inspection speed for advanced Cr, PSM and Quartz substrate. Through easy operation and defect classification, the productivity of inspection and particle control on mask process was increased.
With this new inspection system, defects on blank mask was classified and evaluated after patterning process.
As a process monitoring tool, defects from all mask process equipments have been evaluated and monitored with different microscopy and metrology tools to identify and characterize them on various steps. Our results demonstrate that this process monitoring is very effective to identify defects and their sources, and to prevent mask reject caused by defect of each process.