Reflectivity control through angle is challenging at hyper NA, especially for Logic devices which have various
pitches in the same layer. When patterning critical layers, a multilayer antireflectant system is required in order
to control complex reflectivity resulting from various incident angles. Multilayer antireflectants typically consist
of an organic and inorganic (TiN and SiON) layers. Fewer or thinner layers are desired for etch pattern transfer.
However, it would make the reflectivity control through angle more difficult. We have investigated several
antireflectants for a simplified multilayer stack. The organic films differ in terms of n, k, thickness and etch rate.
The n, k, and thickness span the ranges of 1.60-1.85, 0.15-0.30, and 30-130nm, respectively. The overall
patterning performance including profiles, line width roughness (LWR), overlap depth of focus margin (ODOF)
and critical dimension uniformity (CDU) has been evaluated. An immersion tool at 1.35NA was used to perform
lithography. Simulation was performed using ProlithTM software.
In situ spectroscopic ellipsometry, deep UV ellipsometry, and imaging ellipsometry were employed to study the
absorption of liquid by photoresist(PR) used for 193 nm immersion lithography. When 140 nm thick PR was soaked in
water over a period of >70 minutes, ~7% increase in thickness was observed. From the analysis of ellipsometric spectra
covering from near infrared to deep UV, we could estimates less than 2 vol. % uptake of water by PR after completion of
soaking. This resulted in very small decrease in refractive index of PR (~0.4%). When imaging ellipsometry was used,
the absorption of water by PR in much shorter periods could be detectible. In imaging ellipsometry, the microscopic
images of (Δ,Ψ ) in small area are obtained thanks to two dimensional multi-channel detection systems such as CCD.
Using imaging ellipsometry, we could observe the interaction of PR with water even upon 1 s of contact. Also, we found
that the water absorption or interaction was not uniform over surface. More studies are required for the implication of
this observation. Obviously, imaging ellipsometry is a good technique to inspect water mark in immersion lithography.
We also repeated similar experiments for high reflective index liquid (JSR HIL-001) but to find negligible change by
Virtual OPC concept is suggested for soothing the problem that the roadmap of semiconductor devices proceeds the rate of development of exposure tools. Virtual OPC uses the simulated CD data for an OPC modeling instead of the measured CD data. For successful virtual OPC, the extreme accuracy of the simulation is required for obtaining the simulated CD data close to the actual CD values. In this paper, our efforts to enhance the simulation accuracy are presented and the accuracy of simulated sample data for OPC is verified. The applicability of virtual OPC to the production of devices was verified by performing the virtual OPC using the simulated sample data at 1.2 NA lithography and the result also is presented.
In order to perform an optical proximity correction of memory device nodes below half-pitch 50nm, so called 3D mask
effects need to be included in a model based OPC. As the mask pitch approaches wavelength of an optical system, and
the angle of off-axis illumination becomes increasingly greater than normal incident beam, combined effects of
transmission loss and mask induced polarization induces deviations from Kirchhoff thin mask approximation. Presently,
just a handful of methods are being developed for commercial use in full-chip scale optical proximity correction: edge
domain decomposition method (DDM), rim-type boundary layer and more recently, M3D model [1-6]. However, these
methods currently require extensive modeling and proximity correction runtime although its methods are being
continously improved for accuracy and speed. In this work, some results on an alternative approach to 3D mask
modeling that is suitable for OPC are presented. Using modeling test pattern experimental data and FDTD rigorous
simulation results, a thin mask approximation and alternative 3D mask approximate approaches are compared. And the
results indicate improved model accuracy in terms of root mean square of 30% for a cross-pole and a dipole illumination
conditions, respectively, while the OPC run-time remained similar. Furthermore, a flash memory gate-poly OPC results
using the 3D mask approximate model indicates improved correlation to experimental results than a thin mask model at
minimum resolution dense feature and narrow space regions.
Thin mask and proposed approximate 3D mask models were calibrated for three differing illumination conditions: two
X-dipole illuminations with Y-linear polarization and cross-pole quasar illumination with X&Y-linear polarization
states. For each of the extreme off-axis illumination conditions, 3D mask approximate model developed for OPC
indicated improved calibration results to both test pattern wafer images and rigorous simulation results. In addition,
OPC layout image contours of 3D mask approximate model correlated better to wafer image than the thin mask
approximation at nominal and defocus conditions.
We present simplified symmetric boundary layer model (BLM) for Optical Proximity Correction (OPC) in order to account for thick (or 3D or topographic) mask effect. In this approach, near-field mask image which is quite different from original mask pattern due to mask topography is approximated as the original pattern and boundary layer around it. In this work, the boundary layer is determined as such that residual critical dimension (CD) error between measured CD and modeled CD from the BLM is minimized for various types of features. In case of sub-50 nm memory patterning, this BLM shows sufficient accuracy that root mean square of the residual CD is as small as 4.3 nm. Also, OPC speed with BLM is reasonably fast as the OPC time with BLM increases as only around twice as the conventional OPC time without BLM, which is acceptable in practice.
The minimum feature size of the semiconductor device will be smaller and smaller because of the increasing demand for the high integration of the device. According to recently proposed roadmap, ArF immersion lithography will be used for 65 nm to 45 nm technology nodes. Polarization effect becomes a more important factor due to the increasing demand for high NA optical system and the use of immersion lithography. It is important to know that the polarization effect is induced by mask in small size patterning. The unpolarized plane waves leaving the illumination system are diffracted by the mask. So the light beam going through the mask will experience induced polarization by the mask. In this paper, we considered the change of polarization state as a function of mask properties. We calculated vector diffraction of 193 nm incident light. The masks considered are the chromeless mask, a binary chrome mask and 6 % attenuated phase shifting mask. We use the finite-difference time-domain method to solve the Maxwell equation. The aerial image depends on the polarization states induced by the mask properties such as materials, thickness, and pitch.
Most of simulation tools and OPC engines use Kirchhoff (thin mask) approximation for imaging calculation. Some commercial simulation tools have implemented the rigorous algorithm to solve the Maxwell's equations for the electric and magnetic fields. Currently, a rigorous algorithm is being used for the case of high topographical mask such as CPL and alternating PSM. However, the mask topographical effect of binary mask and attenuated PSM is not negligible in the case of hyper NA lithography. Implementing the rigorous algorithm on full chip OPC is impractical due to its OPC runtime limitation. Thin mask and rigorous simulation modeling are compared to check whether the current algorithms of OPC tools can sufficiently reflect the mask topography effect of hyper NA lithography and whether a combination of currently usable algorithms can cover the mask topography effect. OPC modeling is generally executed based on measured CD data. However we do not have usable hyper NA scanners, so the OPC modeling is executed based on full physical simulation data to the resist image, which we will define as a "Virtual OPC modeling".
For a lithography process, process windows are conventionally determined based on the amount of CD variation in a focus-exposure matrix (FEM). In a low-k1 region, however, a real process window can be smaller than is determined by the CD variation of FEM, due to a large mask error enhancement factor (MEEF). And the real process window cannot be determined by simply narrowing the process window obtained from a FEM, since MEEF itself is not a constant but a function of various process parameters. All the parameters which can affect MEEF should be considered carefully both in evaluation and in optimization of a real process window. Aerial-image base simulation was avoided in calculation of a process window because aerial-image based simulation cannot properly predict a process window even for simple 1-dimensional line-and-space patterns without introducing a fictitious variable like iso-focal bias, which cannot be extended to general 2-dimensional cases. In this study, a modified procedure for evaluation of process windows of critical layers has been proposed, and the process window was compared to the process window obtained by a conventional procedure. The proposed procedure has been implemented in our in-house lithography simulator to automatically process the evaluation of real process windows. Since the proposed procedure heavily relies on the accuracy of the lithography simulator, consideration of mask corner rounding effect and careful tuning of the physical properties of photoresists among others have also been included to guarantee the overall simulation accuracy.
Due to the polarization effect of high NA lithography, the consideration of resist effect in lithography simulation becomes increasingly important. In spite of the importance of resist simulation, many process engineers are reluctant to consider resist effect in lithography simulation due to time-consuming procedure to extract required resist parameters and the uncertainty of measurement of some parameters. Weiss suggested simplified development model, and this model does not require the complex kinetic parameters. For the device fabrication engineers, there is a simple and accurate parameter extraction and optimizing method using Weiss model. This method needs refractive index, Dill’s parameters and development rate monitoring (DRM) data in parameter extraction. The parameters extracted using referred sequence is not accurate, so that we have to optimize the parameters to fit the critical dimension scanning electron microscopy (CD SEM) data of line and space patterns. Hence, the FiRM of Sigma-C is utilized as a resist parameter-optimizing program. According to our study, the illumination shape, the aberration and the pupil mesh point have a large effect on the accuracy of resist parameter in optimization. To obtain the optimum parameters, we need to find the saturated mesh points in terms of normalized intensity log slope (NILS) prior to an optimization. The simulation results using the optimized parameters by this method shows good agreement with experiments for iso-dense bias, Focus-Exposure Matrix data and sub 80nm device pattern simulation.
It is expected that ArF lithography will be introduced for device manufacturing for sub-100 nm nodes, as high NA ArF step and scan systems (NA=0.75) become available. We previously reported on a platform, based on a vinyl ether- maleic anhydride (VEMA) alternating polymer system. This platform demonstrated both good resolution and high dry etch resistance in comparison to other platforms based on acrylate and cyclic-olefin-maleic anhydride (COMA) polymer systems. The VEMA platform has been continuously improved to meet the increasing requirements, such as resolution, depth of focus (DOF) iso-dense bias, and post-etch roughness for real device manufacturing. This VEMA system is being implemented for sub-100 nm device with high NA (NA=0.75) ArF exposure systems. In this paper, recent experimental results are reviewed.
ArF lithography, in combination with chemically amplified resists, has been investigated as one of the most promising technologies for producing patterns below 100 nm. In considering the polymer matrix for 193 nm photoresist applications, factors such as sensitivity, transparency to 193 nm radiation, adhesion to substrate, dry etch resistance, ease of synthesis, and availability of monomers are very critical. In these respects, remarkable progress has been made in development of ArF resist material. Polymers of acrylic and methacrylic esters show good imaging performance at 193 nm, but have insufficient dry-etch resistance under oxide or nitride etch condition. On the other hand, cyclic olefin-maleic anhydride (COMA) alternating copolymers exhibit good dry etch resistance, but have poor resolution capability. We previously reported a new platform, based on a vinyl ether-maleic anhydride (VEMA) alternating polymer system, that demonstrated both good resolution and high dry etch resistance. In this paper, VEMA systems with improved lithographic performance are presented. The new platform (VEMA) showed good performance in resolution, depth of focus (DOF), iso-dense bias, and post-etch roughness. With conventional illumination (NA=0.6, sigma=0.7), 120 nm dense line/space patterns with 0.4 (mu) M DOF were resolved. And 90 nm L/S patterns 0.6 (mu) M DOF were resolved with off-axis illumination (NA=0.63). Another important factor to be considered for the dry-etch process is post-etch roughness. In the case of VEMA system a clean surface was observed after etch under oxide, nitride, and poly conditions. The VEMA resist system is regarded as one of the most production-worthy material for real device manufacture.
In this paper we review the design and performance of ArF resists developed from various polymer platforms. Inadequate etch performance of early ArF acrylate platforms necessitated the development of new etch resistant platforms, in terms of both etch rate and etch uniformity. Two resist platforms were developed to address etch resistance: 1) alternating copolymers of cyclic olefins and maleic anhydride (COMA); and 2) polycycloolefin polymers (CO). Improvements have been made in the imaging performance of these resists, such that they now approach the lithographic performance of acrylate based resists. Recently, a third platform based on polymerization of vinyl ethers with maleic anhydride (VEMA), which has excellent etch performance, was developed by Samsung. Here we will focus our discussion on acrylate, COMA and VEMA based resists.
In this work we have studied new types of olefin-containing alicyclic lactones such as (alpha) -angelicalactone(AGL), (gamma) -methylene- (gamma) -butyrolactone((gamma) -MBL), (alpha) -methylene- (gamma) -butyrolactone((alpha) -MBL) and their derivatives. Particular attention was given to (alpha) -BML derivatives, which are readily synthesized. The relative monomer reactivities of the various lactones were found to be quite different. However in the case of (alpha) -MBL and its derivatives they have good radical reactivities with methacrylates and maleic anhydride. Methacrylate derivatives with acid-labile protecting groups were introduced for dissolution contrast. To further promote adhesion the relative ratios of maleic anhydride and norbornylene derivatives was optimized. These novel resists resolve 120nm L/S with conventional illumination (NA=0.6, (sigma) =0.7) and 0.6micrometers DOF with annular illumination (NA=0.6, (sigma) $=0.6/0.8). And also 100nm L/S resolution was achieved using strong off-axis illumination. Oxide etch resistance was found to be equivalent to acetal based KrF resists. Post exposure delay (PED) stability of more than 1 hour was achieved.
A series of new cycloaliphatic olefin monomers protected by alicyclic hydrocarbon groups were synthesized. New polymers of cycloaliphatic olefins and cycloolefin-maleic anhydride (COMA) systems were also designed and prepared using the new monomers for 193 nm resist applications. These polymers were synthesized by free radical polymerization technique, utilizing azobisisobutyronitrile (AIBN) or di-t-butyl peroxide initiators. The cycloolefin polymers synthesized by free radical polymerization method were not good for ArF lithography because of their poor transparency at 193 nm, although they showed a good dry etch resistance. However, the new COMA polymers had good transparency at 193 nm and had an etch rate in CF4 mixture plasma of approximate 1.0 times that of DUV resists. Using ArF exposure tools (NA equals 0.6, (sigma) equals 0.7), 130 nm line/space patterns were resolved. Using Off-Axis illumination, 100 nm line/space patterns were resolved.