Technologies for pattern fabrication using Nanoimprint lithography (NIL) process are being developed for various devices. NIL is an attractive and promising candidate for its pattern fidelity toward 1z device fabrication without additional usage of double patterning process. Layout dependent hotspots become a significant issue for application in small pattern size device, and design for manufacturing (DFM) flow for imprint process becomes significantly important. In this paper, simulation of resist spread in fine pattern of various scales are demonstrated and the fluid models depending on the scale are proposed. DFM flow to prepare imprint friendly design, issues for sub-20 nm NIL are proposed.
Thermal aberration becomes a serious problem in the production of semiconductors for which low-k1 immersion lithography with a strong off-axis illumination, such as dipole setting, is used. The illumination setting localizes energy of the light in the projection lens, bringing about localized temperature rise. The temperature change varies lens refractive index and thus generates aberrations. The phenomenon is called thermal aberration. For realizing manufacturability of fine patterns with high productivity, thermal aberration control is important. Since heating areas in the projection lens are determined by source shape and distribution of diffracted light by a mask, the diffracted pupilgram convolving illumination source shape with diffraction distribution can be calculated using mask layout data for the thermal aberration prediction. Thermal aberration is calculated as a function of accumulated irradiation power. We have evaluated the thermal aberration computational prediction and control technology “Thermal Aberration Optimizer” (ThAO) on a Nikon immersion system. The thermal aberration prediction consists of two steps. The first step is prediction of the diffraction map on the projection pupil. The second step is computing thermal aberration from the diffraction map using a lens thermal model and an aberration correction function. We performed a verification test for ThAO using a mask of 1x-nm memory and strong off-axis illumination. We clarified the current performance of thermal aberration prediction, and also confirmed that the impacts of thermal aberration of NSR-S621D on CD and overlay for our 1x-nm memory pattern are very small. Accurate thermal aberration prediction with ThAO will enable thermal aberration risk-free lithography for semiconductor chip production.
The purpose of this work was to identify the specific effects of mask topography by analyzing in the Fourier domain.
Our focus patterns extend from a simple contact hole (CH) with a fixed pitch and bias to ones that have a variety of
different pitches and hole sizes. We also attempt to predict phases and amplitudes of diffraction on the pupil plane
without a rigorous mask topography approximated model. Intensities of CH patterns are simulated using three mask
models. We had determined that there are serious differences among the three mask models concerning the contrast of
the intensity and the qualitative interpretation of the trend of contrast varies according to pitch and hole sizes.
The mask topography effects can be classified into waveguide and shadowing effects simply by using the diffraction
decomposition diagram. We clarify how much and when the mask topography influences imaging under hyper-NA
lithography by the diagram. From 1D near-field phase distribution, it is clarified that phase distribution has also been
decided by the MoSi width between holes so that waveguide effects are not only from hole but also from MoSi area.
It has been determined that the influence of the real 3D structures of the mask under the hyper-NA condition cannot
be disregarded. However, use of the rigorous EMF calculation costs much more and requires more time than using a
non-EMF calculation. We have also clarified the mechanism of 3D mask effects based on the amplitude and the phase
of the diffraction light in the Fourier-domain diagram and examined whether the 3D mask effects can be predicted by
thin mask approximation (TMA) and found that once we have values of amplitude and phase of the 0th and the 1st
diffraction in TMA, it will be possible to predict the values of the other pitch and the other hole size.
A hyper-NA lithography tool is used in production of the latest devices. In the next generation immersion lithography,
issues that had so for neglected had to be considered because NA of illumination optics is larger than conventional tools.
Here, items were listed up for accurate prediction of imaging by optical simulation. These were transmittance of
illumination rays to the mask, mask induced effects such as polarization and aberration, and pellicle induced effect. These
were depending on incident angle. Therefore consideration of angle dependency of these effects was necessary for more
accurate imaging simulation. We presented the requirements for simulation to facilitate discussion of the imaging
performance of below 40 nm hp pattern node immersion lithography.
The purpose of this work was to find the specific effects of hole patterns in 32nm node logic by analyzing in the Fourier domain and to clarify the mechanism of mask topography effects. Our focus patterns extend from the lines and spaces (LS) to the contact hole (CH). We also attempt to perform factor analyses of mask topography effects.
Intensities of LS and CH patterns are simulated using three mask models. For each of the three models, the method of approximating the mask topography effect is different. As a result, a serious difference among the three mask models has been found with respect to the intensity profile for 32nm node and beyond, though the mask sizes for all models are the same.
As the accuracy of mask model improved, it was found that the image contrast tends to decrease on LS patterns while increasing on CH patterns. The qualitative interpretation of the trend of contrast variations can be described by analyzing in the Fourier domain.
The mask topography effects can be separated into waveguide and shadowing effects using scatter graphs.
It is concluded from the result that one of the major differences between LS and CH is attributable to phase differences between 0th order and 1st order diffractions, because the size of effects for CH have been larger than that for LS.
In recent low-k1 lithography, the size of a mask pattern is becoming close to the wavelength of the light source. In a sub-100-nm pattern at wafer scale of 4× masks, transverse electric (TE) polarization light had higher transmittance of the zeroth order than TM polarization for a Cr mask according to rigorous model simulation of a finite difference time domain method. On the other hand, transverse magnetic (TM) polarization light had higher transmittance than TE polarization light for a MoSi mask. From the results of lithography simulation for a 45-nm pattern on the MoSi mask, TE polarization was better for wide exposure latitude, but TM polarization was better for large depth of field. The performance of a current MoSi mask is inferior to that of a Cr mask. However, a lower transmittance MoSi mask has better performance in the exposure defocus window under the dipole illumination. Also, rigorous simulation showed transmittance dependency of the light incident angle to the MoSi mask. The dependency was larger for TM polarization than for TE polarization.
Mask topography effects arise important components of optical image formation at 45nm node and beyond for attenuated Phase Shift Mask (attPSM). Since calculation of mask topography effects based on rigorous model is very costly, it is unrealistic for Optical Proximity Correction (OPC) and lithography design. This paper investigates an approximation model that takes mask topography effects into consideration. We propose the concept of Effectively Equivalent Mask Patterns (EEMP) method to obtain approximated optical images which include mask topography effects. We found mask space width is the main factor among mask topography effects. For realizing the EEMP method, we introduce and evaluate two approximation methods for mask topography effects. One is the simple space model and the other is the Proximity Mask Opening (PMO) model, which is a model of waveguide effects.
EEMP with PMO model can improve prediction accuracy at both 1-dimensional and 2-dimensional patterns and increase in run time for EEMP with PMO model is 40 percent of that required for thin film simulations.
Recent progress of immersion lithography technique could realize to apply hyper NA condition for real IC device manufacturing. Under the hyper NA lithography, we have to face the paradigm shift from scalar treatment to vector consideration in the region of modeling everywhere. In the historical view points, vector lithographic imaging model was introduced in 19861, and the beginning of 90’s, various evaluation works were reported in the field. And the research or evaluation of topographical mask effects were also focused and concentrated the same era using rigorous electromagnetic simulations2-4. But as for the “oblique illumination effects” at a reticle side, much concerns had not been paid about them. It was because the relaxation of incident angle due to magnification factor (4X or 5X), using small σ for alternating phase-shifting mask, and higher NA seemed to work worse as for decreasing DOF. Since the immersion lithography technique would be considered as “effective reduction of exposure wavelength by factor of the refraction index of immersion material” and superior DOF characteristics to the dry case, development of increasing exposure tool’s NA beyond 1.0 have been accelerated. In such a hyper NA region, we have to consider about the “oblique illumination effects” once again for various fields, such as combining to the model-based OPC application and so on. In this paper, 1st order approximation model is suggested and evaluated how much degree of influence of the oblique illumination effects should be taken care of, and how large area could be covered using this model. The former results denoted that around 10% of target CD might be varied in the case of hyper NA condition. But from the latter results, we did not sufficient validity for this model, so some additional approximation should be considered to improve the prediction accuracy.
In recent low-k1 lithography, the size of a mask pattern is becoming close to wavelength of the light source. The light intensity through the mask pattern is depending on polarization. TM polarization light is higher transmission than TE polarization light for a MoSi mask. This effect influences not only the zeroth-order light but the first-order light. On the other hand, TE polarization imaging makes higher contrast than TM polarization in two beam interference. Effects of
polarization to resolution are not simple. Since an attenuated phase shift mask is used in order to obtain high contrast, it is necessary to take into consideration the influence of that. It is also taken into consideration that illumination light is not perpendicular incidence but oblique incidence for an ArF hyper-NA tool. We will perform a rigorous simulation in consideration of the above conditions. Hereby influence of the to the utmost resolution will be clarified by the rigorous simulation.