One of the major issues introduced by development of Extreme Ultra Violet Lithography (EUV) is high level of flare and shadowing introduced by the system. Effect of the high level flare degrades the aerial images and may introduce unbalanced Critical Dimension Uniformity (CDU) and so on. Also due to formation of the EUV tool, shadowing of the pattern is another concern added from EUVL. Shadowing of the pattern will cause CD variation for pattern directionality and position of the pattern along the slit. Therefore, in order to acquire high resolution wafer result, correction of the shadowing and flare effect is inevitable for EUV lithography.
In this study, we will analyze the effect of shadowing and flare effect of EUV alpha demo tool at IMEC. Simulation and wafer testing will be analyzed to characterize the effect of shadowing on angle and slit position of the pattern. Also, flare of EUV tool will be plotted using Kirk's disappearing pad method and flare to pattern density will also be analyzed. Additionally, initial investigation into actual sub 30nm Technology DRAM critical layer will be performed. Finally simulation to wafer result will be analyzed for both shadowing and flare effect of EUV tool.
As design rule of memory device is smaller and smaller, the CD uniformity of a photomask become the most
important factor to satisfy wafer exposure performance. Once the photomask is made, CD uniformity of the mask
can't be changed and if CD uniformity of the mask is not good to use for wafer exposure, we must reject it and
make another one again. But, after applying transmission control tool for CD uniformity, we have an extra chance
to control mask CD uniformity in one mask and this is very effective for wafer printing result.
In this paper, we are going to evaluate the behavior of wafer CD due to transmission control position change
within photomask substrate and find the optimum control position for better wafer result.
As design rule of memory device is shrinking, the various errors obtained by process, such as line edge roughness, local CD variation and electron beam shot placement error, are significant to CD measurement results on mask and wafer. Reliable CD measurement is needed to represent real feature size of mask and wafer results in high accurate CD target and uniformity by various CD correction techniques before mask fabrication and after. Recently light transmittance control technique on mask has been introduced, which reduce the field CD variation of wafer . To correct the wafer field CD uniformity by selective control of the light transmittance of mask, good correlation of mask CD and wafer field CD is important . AIMS (aerial image measurement and simulation) or light intensity uniformity of inspection tools or other light intensity measurement tools are generally used to measure mask CD uniformity on mask. In this study, mask CD uniformity measured by CD-SEM was used to compensate the field CD variation on wafer, by enhancing the correlation between wafer field CD uniformity and mask using spatial filtering of SEM image and area CD measurement concept. Expected residual error of wafer field CD error using correction of mask CD uniformity were compared to wafer CD variation by selective light correction using wafer CD uniformity map.
As the semiconductor industry requires lithography suitable for 32-nm node, extreme ultraviolet lithography (EUVL) has the potential to provide this capability for the mass fabrication of semiconductor devices. But because an extreme ultraviolet (EUV) lithography exposure system is operated in vacuum, during irradiation by EUV light, hydrocarbons are decomposed in vacuum1-3, for example, by the out-gassing from EUV mask, and contaminate the surface of imaging optics which is coated with Mo/Si multi-layers with carbon. Thus, this contamination not only reduces the reflectivity of the Mo/Si multi-layers of imaging optics and degrades the exposure uniformity, but also degrades the resolution of the imaging optics. In this study, as we examined the volume of the out-gassing and the species from EUV mask after every process for EUV mask production, we will control the carbon contamination of EUV mask.
Keywords: EUV, carbon contamination, reflectance, out-gassing
Haze formation on reticle continues to be a significant source of concern for the photolithography.
Possible sources and causes continue to be investigated. This paper provides a haze source evaluation result
under the sub-pellicle defect on the mask.
It is well known that there are several sources to produce the haze. One is inorganic molecules such as SOx, NH3,
H2O and CO2. The haze formation of inorganic sources is promoted for growing defect size by the exposure
energy in time. The other is organics that are prevalent Fab and storage environment.
In this paper, we deal with the haze that is immediately generating with a low energy exposure. Especially, this study
treats the haze source during the mask packaging method.
In order to realize the effect of pattern-specific off-axis illumination under the conventional circular illumination, the
illumination method using a mask grating formed on the top side of a photo mask was evaluated and improved. Contrary
to an off-axis illumination, it could provide the locally different off-axis illumination depending on the pattern shape
defined on the bottom side of a mask. The structure of the mask grating was determined from the feature characteristics
of the mask pattern and its performance was evaluated with the simulated Bossung curves.
A new inspection system with DUV laser beam and high NA optic for EUV mask has been developed to inspect defects
on EUV blank mask and defects by process and handling. The development of new reflective image and optics has
increased inspection speed on EUV mask before absorber etch and after absorber etch. Defect classification and
operation has increased the productivity of inspection and particle control on EUV mask process. With this new
inspection system, defects on blank mask, after resist develop and after etch processed mask were classified and
evaluated to install EUV mask process. And defect sensitivities according to various pattern size and process steps were
evaluated with required defect size of simulated printing effect on wafer. Designed defect pattern of 46nm node were
prepared. Blank masks from Hoya were used. Patterns were exposed using 50KeV electron beam writer. After resist
develop, patterns with program defect were inspected. After absorber etching, defects were inspected and evaluated.
According to sub film, inspection condition was optimized. Using simulation tool, defects printability were simulated
and compared with sensitivity of this inspection tool. Our results demonstrate that this inspection tool is very effective
to detect and identify defects and their sources on EUV mask process. In this paper, mask inspection performance of
high NA, DUV optic with short working distance was evaluated and described on programmed EUV mask.
As device pattern size is shrinking to below 65nm on wafer, the small amount of CD variation on wafer field determine the wafer yield. Most of the wafer field CD variations come from mask CD variations across mask field. By correction of dose and transmittance on mask using wafer field CD variation, wafer CD uniformity can be extremely enhanced. To get fine correction of wafer field CD uniformity, we have developed various methods to get close correlation of mask and wafer field CD uniformity by SEM, scatterometry and area CD methods. Especially, area CD from CD-SEM and optical CD measurement tools are developed to represent each area of masks. By optimizing measurement methods, repeatability and correlation of CD uniformity between masks and wafers are enhanced to get more than 0.7 of correlation between mask and wafer. And these give us the correction method to compensate field CD variation of maskCD on wafer. More than mask CD uniformity requirement on 65nm tech of DRAM memory device has been achieved.
Sensitivity of newly developed photo mask inspection tool with reflective optic was evaluated for 45nm DRAM device.
To get the required defect sensitivity of mask, printability of mask defect on wafer were simulated using in house
simulation tool. Simulation results were compared with inspection results. Characteristic and sensitivity comparison
between conventional transmissive and reflective optic tools were evaluated for several types of mask layer of 45nm and
55nm DRAM according to pixel size of detector of inspection tools. This reflective optic with short working distance
was equivalent in sensitivity to transmissive optic tool. Mask for 45nm DRAM can be qualified by current status of the
art inspection tools.
As pattern size is shrinking, required mask CD specification is tighter and its effect on wafer patterning is more severe.
To enhance the device performance, wafer CD uniformity should be enhanced and controlled by mask global CD
uniformity. Mask global CD uniformity usually can be enhanced by mask process and optimal fogging effect correction.
To enhance the mask global CD uniformity on mask, resist process and FEC (Fogging Effect Correction), reliable CD
measurement tool and methods are necessary. Recently, group CD using OCD(Spectroscopic Ellipsometer) or
AIMS(Aerial Image Measurement and Simulation) is used to represent global CD variation on mask. These methods are
removing local CD variation on mask. Because local CD variation on wafer is large compared with the effect of local
CD variation of mask, global CD uniformity can be measured with suppressed local CD variation . In this paper,
local CD variation of mask and wafer is evaluated, and area CD and smoothing methods are used to measure CD on
mask and wafer, and the correlation of global CD of mask and field CD of wafer are evaluated. By these methods, CD
measurement repeatability can be enhanced to get closer correlation of mask and wafer. Close correlation makes fine
CD correction on mask to get better field CD uniformity on wafer. And the repeatability of field to field CD uniformity
of wafer is evaluated according to measurement tool of CD-SEM and scatterometry.
As pattern size is shrinking, required mask CD specification is tighter and its effect on wafer patterning is more severe.
Recent study showed that the effect of mask local CD variation of mask on wafer is much smaller than that of global
CD variation. To enhance the device performance, wafer CD uniformity should be enhanced and controlled by mask
global CD uniformity. Mask global CD uniformity usually can be enhanced by mask process and optimal fogging effect
correction. To enhance the mask global CD uniformity on mask, resist process and FEC (Fogging Effect Correction),
reliable CD measurement tool and methods are necessary. Recently, group CD using OCD(Spectroscopic Ellipsometer)
or AIMS(Aerial Image Measurement and Simulation) or polynomial fitting method is introduced to represent global CD
variation on mask. These methods are removing local CD variation on mask. The local CD variation will be
remained as residual CD after approximation. In this paper, local CD variation of mask and wafer is evaluated and 2
kinds of methods are used to measure CD on mask and wafer, and the correlation of global CD of mask and field CD of
wafer are evaluated. And the repeatability of field to field CD uniformity of wafer is evaluated to correct the fields CD
uniformity of wafer by controlling the selective changing of transmittance of mask or to feed back to mask process.
Higher correlation between fields of wafer, more accurate correction can be possible.
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.
As feature size is shrinking and MEEF (Mask error enhancement factor) is increasing, CD measurement accuracy is more important, and CD SEM is widely used to replace optic tools because of their resolution. But CD-SEM is not representing the effect of Cr profile or transmittance of light which is transferred to wafer. Recently, new OCD (optic CD) tool which use scatterometry (Spectroscopic Ellipsometry) *1) is introduced to compensate the demerit of SEM of low through-put and reflected surface information of mask. This scatterometry tool can be used only on periodic pattern like DRAM. And this tool must be calibrated on each pattern type and shape. This calibration is the barrier to use this scatterometry method to mask process where all masks are processed one time.
In this work, new optical CD measurement method which use conventional optic microscope of transmitted and reflected light with high resolution lens of DUV on periodic patterns is introduced. To enhance the accuracy of measurement, interpolating method and FFT (Fast Fourier Transform) are used. CD measurement results of linearity by optic CD, SE and CD-SEM were compared on several patterns. And CD variations on full field of image were evaluated on L/S patterns and active layer of DRAM.
As required CD (critical dimension) measuring accuracy is tighter, it is necessary to enhance the repeatability of CD-SEM on photo-mask, by optimizing charge up, scan speed, beam size, acceleration, current and temperature control. CD-SEM shows sparkle noise which degrades the image of CD-SEM. And defocus is also getting the source of worse gauge R&R. We evaluated the effect of defocus and noise on CD repeatability by extracting CD from gradient value of image after anisotropic nonlinear diffusion filtering on SEM image. As SEM image is measured after averaging the intensity of image on range of interest (ROI) to remove scan noise, anisotropic nonlinear diffusion (AND) which has different diffusivity according to direction, is efficient tool to get smooth pattern without averaging. This smoothing technique is effective in measuring isolated pattern on mask which is difficult to measure around corner. Some simple CD measuring algorithms are available to get better CD repeatability. Using the maximum intensity and gradient of image, we were able to measure CD on various shaped patterns with enhanced repeatability.
As pattern size is shrinking, required mask specification is tighter and defect on mask is easily transferred to wafer. It is difficult to distinguish a defect what it is and where it is from, even though high NA optic lens is used. According to small pattern size and attenuated PSM material of ArF area, image quality of FIB (focused ion beam microscopy) to repair defect is getting worse. But, recently, SEM (Secondary Electron Microscopy) review tool is used to overcome the limited resolution of optic microscope such as review mode of inspection tool. To use this higher image quality of SEM compared to FIB process, we introduce image processing and replacement to enhance the accuracy of FIB repair on mask pattern. As the image of ion beam generally shows speckle noise, we adopted AND (anisotropic nonlinear diffusion) technology to remove noise without loss of pattern, by different diffusion along pattern edge. Using this AND technique, we enhanced the image quality of FIB and SEM, and productivity of FIB.
As current feature size on mask is under the wave length of inspection source, it is difficult to distinguish a defect where it is on or from, even though high NA optic lens is used. The disadvantage of this hi-res defect detection method require review step which spend much of inspection time. So this lack of resolution of optical inspection tool requires new review tools such as SEM (Second electron Beam Microscope) or FIB(Focused Ion Beam). As the image of ion beam generally shows speckle noise, we adapted anisotropic nonlinear diffusion technology to remove noise without loss of pattern, by different diffusion along pattern edge. And a fine defect image by image processing to repair was extracted to replace the pattern copy function of FIB.
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.
We investigated the defect printability of KrF attenuated PSM. To analyze the printability of PSM defects, the programmed defect mask was designed and fabricated. The programmed defect mask contains background pattern layer of 800nm contact holes. Various types and sizes of MoSi defects such as extensions, dots and holes were programmed on the background patterns. We used a KrF excimer step-and-scan exposure system for wafer printing test. Based on the experimental results, we defined the maximum non-printable defects size of MoSi defects and tested repair performance of current tools by comparing the printability of defect pattern between pre-repair and post-repair. In addition, we calculated CD of defected patterns by simulation and compared it with the print CD.
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.
CD control of FEP-171 is difficult due to abnormal CD variation in single puddle development. Fogging analysis patterns show that space CD in large open region is smaller than that in small open region. That is caused by develop loading effect, which is largely affected by developer dispensing condition in single puddle method. Double puddle development improves the abnormal CD trend and has a good CD uniformity (3sigma 5.4nm). Contrary to FEP-171, abnormal CD trend is not observed in UV-82(CAR). The low dissolution rate of FEP-171 is the cause of the abnormal CD trend. The yield of CD uniformity and MTT increases with applying double puddle method to FEP-171 process.
It is intended to evaluate the feasibility of 0.15μm generation mask fabrication with a KrF photomask repeater. Inter-field registration accuracy(3sigma) is 28nm in X direction and 45nm in Y direction on a daughter mask in the KrF photomask repeater process and that is out of the registration specification(3sigma 30nm) of 0.15μm generation mask. The intra-field registration accuracy(3sigma) within a 18.4mm × 23.0mm field on a daughter mask is about 9nm with compensation of mis-registration to a mother mask. Inter-field CD uniformity(3sigma) is 8nm on a daughter mask and intra-field CD uniformity(3sigma) can be improved into 15nm with the compensation of CD error to a mother mask. Pattern fidelity in the KrF photomask repeater is inferior to that of the e-beam process. Hence it is necessary to apply OPC pattern to a mother mask in order to fabricate the 0.15μm generation mask.
We have developed a new method to make cell projection aperture with high degree of accuracy which provides stable and accurate pattern fidelity on wafer and could be adaptable to mask process. As an electron beam mask, deep and vertical silicon pattern is made by MERIE poly etcher. Trench pattern profile can be optimized by etching chemistry. And to obtain fine pattern with cell projection exposure, various techniques are used such as pattern fracturing, modified cell aperture layout and shot shift. As a feasibility of cell projection EB exposure, 0.2μm feature were defined with VSB (variable shaped beam) and CPB (cell projection beam) on wafer and evaluated.
It is intended to clarify the feasibity of 0.15 μm generation mask fabrication with the photomask repeater that is based on a KrF stepper(step-and-repeat exposure system). In a photomask repeater patterning, a daughter mask is exposed to KrF light through a mother mask. Inter-field registration accuracy(3sigma) is 14 nm in X direction and 28nm in Y direction within a 80mm ×100mm area on a daughter mask and intra-field registration accuracy(3sigma) is 21nm in X direction and 26nm in Y direction within a 18.4mm ×23.0mm field on a daughter mask. Inter-field CD uniformity (3sigma) is 8nm in 100mm ×100mm area on a daughter mask and intra-field CD uniformity (3sigma) is 24nm within a 18.4mm ×23.0mm field on a daughter mask.
The errors of registration and CD within a field can be improved by compensating for these errors to a mother mask. With the compensation, the intra-field registration error can be reduced to about 13.5nm and the intra-field CD uniformity (3sigma) can be improved into 15nm. Pattern fidelity in the KrF photomask repeater is inferior to that in the e-beam process. So we need to apply OPC pattern to a mother mask in order to get an equivalent pattern fidelity to profiles in the e-beam process.
It is intended to clarify the feasibility of 0.15μm generation mask fabrication with the photomask repeater that is based on a KrF stepper(step-and-repeat exposure system). In a photomask repeater patterning, a daughter mask is exposed to KrF light through a mother mask. Inter-field registration accuracy(3sigma) is 14.9nm in X direction and 29.1nm in Y direction within a 100mm×100mm area on a daughter mask and intra-field registration accuracy(3sigma) is 21nm in X direction and 26nm in Y direction within a 18.4mm×23.0mm field on a daughter mask. The registration error within the field on a daughter mask can be reduced to about 13.5nm(range) by compensating for the registration error to a mother mask. Inter-field CD uniformity(3sigma) is 8nm in 100mm×100mm area on a daughter mask and intra-field CD uniformity (3sigma) is 24nm within a 18.4mm×23.0mm field on a daughter mask. The intra-field CD uniformity (3sigma) can be improved into 15nm by compensating for the CD error to a mother mask . In order to satisfy the 30nm registration and 15nm CD uniformity specification of a 0.15μm generation mask, we need to reduce the inter-field registration error with removing the backside defect of a daughter mask and improve the intra-field CD uniformity by changing the dose distribution of the photomask repeater.
To solve the very low throughput of an e-beam writer in mask fabrication, a new patterning method based on a step-and-repeat exposure system, that is a photomask repeater, has been developed. In this paper, we intended to clarify the feasibility of 0.15 micrometers generation mask fabrication with the KrF photomask repeater. Inter-field registration accuracy (3sigma) in the photomask repeater is 14.9 nm in X direction and 29.1 nm in Y direction and can meet the registration specification (30 nm) of a 0.15 micrometers generation mask. Intra-field mis-registration caused by stepper lens distortion is 14 nm (3sigma) in X direction and 12 nm in Y direction for a 12 mm X 12 mm field and gets larger with an increase of a field size. Inter-field CD uniformity (3sigma) is 15.7 nm in 122.5 mm X122.5 mm mask area and intra-field CD uniformity is 10.3 nm in 12 mm X 12 mm field area. The sum of inter-field and intra-field value in the KrF photomask repeater don't currently satisfy the 30 nm registration and 15 nm CD uniformity specification of a 0.15 micrometers generation mask. So we need to reduce the registration and CD errors with optimizing PR coating and development process, using a small field size and compensating the errors of intra-field factors to a mother mask.
To solve very low throughput of e-beam writer, a new patterning method based on stepper, photomask repeater has been developed. For the KrF photomask repeater development we have modified a wafer-exposing stepper to expose photomasks. In this paper, we intended to clarify the feasibility of 0.15 micrometers generation mask fabrication with KrF photomask repeater. Interfield registration almost satisfied the 28 micrometers specification. Intra-field mis- registration was 10 nm in 18 mm by 18 mm field area and so we have to use a small field size and basically improve this intra-field mis-registration. CD uniformity could not meet the 13 nm specification. Though the evaluated results of KrF photomask repeater process have not satisfied the specification of 0.15 micrometers generation mask, we have found the mask fabrication with KrF photomask repeater is feasible with optimization of field and process, we have found the mask fabrication with KrF photomask repeater is feasible with optimization of field and process.
It is required that CD uniformity in the mask fabrication process should be controlled much more tightly for manufacturing mask to meet below 0.13um design rule of photolithography. The first factors that affect CD uniformity on mask are resist thickness, range, and uniformity of coating temperature, etc. The second factors are fogging effect happening during E-beam writing and CD error caused by E-beam stitching in local area. So, It is on checking and evaluating new equipments as well as suitable process condition. The third is develop process factor that the space CD of mask center area is larger than that of edge area in spin type develop process. Various process recipes and chemical spraying methods is also on applying and evaluating to solve the problem like this. The forth is dry etch factors which are CD error resulted from the unstable plasma condition, inappropriate etch time, error factor from the poor resist selectivity, and CD difference caused by non-optimized exhaust condition in etcher. In this paper, the third factor is discussed, and the method to optimize develop process is studied and evaluated
We investigated KrF attenuated PSM defect printability for 120nm node actual DRAM lithography process. A programmed defect mask was fabricated for the experiment, which contains three different background pattern layers of isolation, bit lines, and bit line contact holes of the 120nm DRAM device. Various types and sizes of MoSi defects such as extensions, intrusions, dots, and holes were programmed on those background patterns. We used a high NA DUV scanner and high contrast resist for wafer printing test. Based on the experimental results, we defined the non-printable defect sizes of MoSi defects and evaluated the detection capabilities of i-line inspection tools for those printable defects. In addition, we tested repair performance of current tools by comparing the process windows of defect patterns between pre-repair and post-repair.
Cell projection e-Beam lithography is one of the technology to increase the throughput capability, which is the demerit of conventional e-Beam lithography. In cell projection e-Beam lithography, Stencil mask fabrication is one of the most essential issue. Particularly, in fabricating stencil mask, both dry etching technique for forming aperture pattern and backside wet etching technique for forming silicon membrane are the most important technologies. With improvements in the techniques, Stencil mask that has low electric resistance compared with that made of SOI (Silicon-on-Insulator) wafer and vertical cross sectional profile is fabricated by the use of a (100) oriented silicon wafer. In addition, A device pattern of 0.13 micrometer which is sufficient for fabricating a 1G DRAM was delineated on wafer using this stencil mask.
A new methodology using the admittance diagram is proposed for optimization of an antireflective layer (ARL) and the simple ARL optimizer with its own 2D and 3D dynamic graphic tools is developed. Under the methodology, the overall dependency of the reflectivity on optical properties of ARLs can be viewed from a single 2D graph, and the tolerance of process step for the optimally designed ARL can be evaluated geometrically. And also, the optimal condition of an ARL for DUV lithography process is determined by our optimizer and its performance is simulated from our own lithography simulator based on rigorous vector theory. Finally, the effect of ARLs are investigated experimentally, and their results are compared with simulation results.
This paper discusses a more stable algorithm of rigorous coupled wave analysis applicable to 2-D exposure simulation in an optical lithography. This algorithm can resolve a divergence problem inherently and can easily be implemented as a full vector model. 2-D exposure simulator based on this algorithm is developed and applied successfully to a very thick photoresist system. Intensity distributions inside the photoresist are simulated and compared with those of other vector models. The adaptive layering technique is introduced to the simulation of bleaching process in order to reduce the computation time. It is found that the technique can greatly reduce memeory size and computation time with reasonable accuracy.
The application of attenuated PSM to dense contact array is restricted by intense optical interference of sidelobe peaks around hole pattern which is called proximity effect. In order to reduce the effect of proximity, it is necessary to optimize the transmittance of mask field and the exposing energy which cause mask bias. The vast of data are required for doing above job. Using simulation, however, by sidelobe, E- D curves can not be used directly to find the depth of focus. The criterion for sidelobe was defined to find process window from E-D curve. To reduce sidelobe in dense contact hole array, the auxiliary patterns were placed between holes. By simulations and experiments, attenuated PSM with auxiliary pattern could be applied effectively to the dense contact hole of 64MDRAM.