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Novel Contact Hole Reticle Design for Enhanced Lithography Process

Window in IC ManufacturingChung-Hsing Chang

Remarkable Ltd.

7, Dai Shun St., Tai Po Industrial Estate Ctr., Tai Po, N.T., Hong Kong

ABSTRACT

For 90nm node generation, 65nm, and beyond, dark field mask types such as contact-hole, via, and trench patterns that all are verychallenging to print with satisfactory process windows for day-to-day lithography manufacturing. Resolution enhancementtechnology (RET) masks together with ArF high numerical aperture (NA) scanners have been recognized as the inevitable choice ofmethod for 65nm node manufacturing. Among RET mask types, the alternating phase shifting mask (AltPSM) is one of the well-known strong enhancement techniques. However, AltPSM can have a very strong optical proximity effect that comes with the use ofsmall on-axis illumination sigma setting. For very dense contact features, it may be possible for AltPSM to overcome the phaseconflict by limiting the mask design rules. But it is not feasible to resolve the inherent phase conflict for the semi-dense, semi-isolatedand isolated contact areas. Hence the adoption of this strong enhancement technique for dark filed mask types in todays ICmanufacturing has been very limited. In this paper, we present a novel yet a very powerful design method to achieve contact and viamasks printing for 90nm, 65nm, and beyond. We name our new mask design as: Novel Improved Contact-hole pattern Exposure

PSM (NICE PSM) with off-axis illumination, such as QUASAR. This RET masks design can enhance the process window ofisolated, semi-isolated contact hole and via hole patterns. The main concepts of NICE PSM with QUASAR off-axis illumination areanalogous to the Super-FLEX pupil filter technology.

Key Words: RET (Resolution Enhancement Technology), NICE PSM (Novel Improved Contact-hole pattern Exposure) PSM,

Contact Mask, Alternating PSM, Alt-PSM, Attenuated PSM, AttPSM, off-axis illumination, OAI, QUASAR

1. INTRODUCTION

For 90nm node generation, 65nm, and beyond, dark field mask types such as contact-hole and trench patterns that all are very

challenging to print with satisfactory process windows for day-to-day lithography manufacturing. To continue extending optical

lithography for printing feature with critical dimension (CD) under sub-half exposure wavelength, contact-hole patterning is the most

demanding one of all. Resolution enhancement technology (RET) masks together with ArF high numerical aperture (NA) scanners

have become the preferred method for 65nm node lithography manufacturing. So far several RETs have been introduced to improve

the printing resolution with adequate depth of focus (DOF), such as attenuated phase-shifting mask (AttPSM) and alternative phase-shifting masks (AltPSM), optical proximity effect correction (OPC), off-axis illumination (OAI), focus latitude enhancement

exposure (FLEX), and lens pupil filter technology (Super-FLEX).

Among the RET mask types, AltPSM is a strong enhancement technique. However, it suffers from strong optical proximity effect

(OPE) that comes with the use of small illumination sigma () setting. It can be very difficult to achieve 2D pattern fidelity. As for theinherent phase conflict, it might be feasible to apply design rule limitation to overcome for dense contact areas. But it still may be

very difficult for resolving the phase conflict in the semi-dense, semi-isolated, and isolated contact-hole areas. AttPSM with OAI

enhances the printing resolution and DOF for dense contact holes. For isolated and semi-isolated contact-hole printing, we can apply

symmetrical assist features, or anti-scattering bars (ASB) to enhance the printing. However, the DOF for certain pitch range of

contact-hole features may never be optimum due to compromised ASB placement in the limited feature spacing. Moreover, it is of

particularly complicated to optimize exposure settings for AttPSM to achieve a maximum common process window that includes the

full-pitch range, random contact-hole features. This is mainly due to mutually exclusive illumination settings as required by isolated,

semi-isolated, and dense contact holes. Small on-axis illumination setting is best for printing isolated contact hole to achieve a goodprinting resolution and DOF. While for dense contact holes, OAI is needed to get comparable printing resolution and DOF.

Multiple focal planes exposure, such as FLEX, can potentially increase DOF and image quality of contact holes pattern. One major

concern for FLEX is degraded image contrast due to excessively unwanted scattered light (flare) introduced by multiple exposure

passes. The flare issue is particularly severe for ArF; as a result, it can negate the benefit of FLEX. Lens pupil filtering technology,

also known as Super-FLEX, as compared to other techniques, is rather effective for enhancing the printing resolution and DOF.

However, this RET is generally difficult to implement in practice. This is because of the pupil design must take into account the

individual lens aberration signature, thermal expansion of the pupil filter, and light reflection characteristics from each of the

lens surface in the projection system. Those serious considerations make it very challenging before wanting to insert a pupil-filtering

Advanced Microlithography Technologies, edited by Yangyuan Wang,

Jun-en Yao, Christopher J. Progler, Proceedings of SPIE Vol. 5645(SPIE, Bellingham, WA, 2005) 0277-786X/05/$15 doi: 10.1117/12.576519

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lens located in the pupil plane of the optical projection lens system.

Therefore there is a need to develop a new style of PSM that works well with OAI to get good image contrast, improved printing

resolution, and greater DOF for better lithographic performance of both dense and isolated contact holes. The goal is to achieve the

same effectiveness similar to Super-FLEX but without the negative concerns. In this paper, we present a new mask design to achieve

those. This new mask design, which we call Novel Improved Contact-hole pattern Exposure PSM (NICE PSM) is shown in Figure 1.

Unlike the rim or outrigger type, the NICE PSM design contains symmetrical ASB in both 0- and -phases. Here we combine the 0and phase ASB with the use of OAI to design an optimum phase-shifting mask pattern for contact holes pattern printing. Usingthe NICE PSM with a QUASAR type of OAI, we observe improved image contrast, printing resolution, and DOF for sub-half through pitch contact holes patterning. The key concept for NICE PSM design is as follows. The novel mask design is to form an

apodized diffraction distribution pattern (Fourier transform pattern produced by passing light through the mask). When this is

projected onto the lens pupil plane, it becomes a natural pupil filter that is functionally similar to Super-FLEX. Then with an

optimized OAI, the DOF of the process window for both isolated and semi-isolated pitch contact-hole pattern can be simultaneously

enhanced.

2. PRINCIPLE OF NICE PSM DESIGN

The main concept of the NICE PSM combines the use of optimally placed phase-shifting ASB, and with an optimum OAI to generate

a phase apodizing distribution over the pupil plane. This is analogous to a naturally apodizing phase and amplitude pupil filter instead

of using a real pupil filtering lens. As explained by Hiroshi Fukuda [1,2,3,4], the NICE PSM design is based on the principle of

approximating the inverse Fourier transform of an apodizing pupil function. Here is an attempt to describe the principles under bothcoherent and partially coherent illuminations.

2.1 Coherent IlluminationThe configuration of an optical lithography projection system used for the modeling and analysis is depicted in Figure 2. In Fourier

optics, the calculation of electric field amplitude distribution in the ideal image planeE(x,y) starts with a Fourier transform of thecomplex amplitude transmittance of the mask function m(x,y), proceeds with calculating the propagation of the Fourier componentsin the optical system, and ends with an inverse Fourier transform. Based on Fourier optics [5,6], the amplitude distribution formed on

the image plane is calculated by:

(1)),(),(),(,),( )(21~~~

yx

yfxfi

yxyxyx dfdfeffPffOffPyxmFFyxEyx

),(

~

yx ffP

Where fx and fy represent the pattern spatial frequency normalized by NA/. F and F-1 denote Fourier transform and an inverse

Fourier transform respectively. The pupil function in eq. (1) represents the transmission function in the pupil plane of the projection system.(fx , fy) is the Fourier transform of the mask function m(x,y). Then, according to the Abbe theory of image

formation, the unity intensity distribution on the image plane is:

(2))(2~~

),(),(),(),(

2

2

yx

yyfxxfi

yxyx dfdfeffPffOyxEyxI

WhereI(x,y) is the intensity at the image coordinate (x,y). Here we assume that the projection lens has unit magnification with nolens aberrations. For a circularly symmetric optical projection system typically found in an exposure system,

~

(3).0

1122

x),(~

otherwise

ffif yyx ffP

),( yx ffPSubstitution of this expression for into eq. (2) results in

(4))(2~

),(),(

2

yxyyfxxfi

yx dfdfeffOyxI

The final image intensity distribution is formed from the interference of low-pass spatial frequency components ( 122x

yff ) of

the mask spectrum.

Figure 3 shows three isolated phase shifting mask designs with coherent illumination, 0.75NA and ArF wavelength light source for

contact hole patterning: rim, outrigger and NICE. The Fourier transform images of these PSMs on the pupil plane can be calculated in

an analytical form by the operation of phase shifting and addition properties of Fourier transform. For the outrigger design, its Fourier

Proc. of SPIE Vol. 5645 33


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transform, apart from a constant factor for energy conservation, is calculated by [7]:

(5))cos())sinc(sinc(2

)cos())sinc(sinc(2))sinc(sinc(),(2

~

yyoxo

xyxooyxoutriggeryx

dffhwfwh

dfwffhwhafafaffO

Here a is the width of main feature size; w, ho, and dare geometrical parameters of outrigger phase shifter related to the phase width,phase length, and pitch between the outrigger phase shifter and the main contact feature, respectively. And sinc() is sinc function.

Similarly, the Fourier transform of a rim-type contact is calculated by:

(6)])]sinc[()sinc[()(

))sinc(sinc(2))sinc(sinc(),(

2

r

2~

yrxrr

yxrryxrimyx

fwhfwhwh

fhfhhafafaffO

And for the new design, its Fourier transform distribution can also calculated by:

(7))cos()(sin)(sin2)cos()(sin)(sin2

)cos()cos(41)(sin)(sin),( 2~

O

dffhcwfcwhdfwfcfhcwh

dfdfafcafcaff

yynxnxyxnn

yxyxNICEyx

Figure 3(a) compares the Fourier transform distributions on the pupil plane for the three types of mask design rim, outrigger, and

NICE PSMs. Both of the rim and outrigger type of masks can generate axially-centered and phase-apodizing pupil filtering effect.

The (fx , fy) images formed on the pupil plane is effectively analogous to the spatial pupil filter by Super-FLEX, with cos(2r2-/2)

phase and amplitude transmission distribution [1,2] at the lens pupil. Better resolution and enhanced DOF are to be expected whenwith Super-FLEX effect during exposure. For the NICE PSM, on the other hand, the (fx , fy)NICE is not axial but a quadrupole shapeof apodized phase distribution on the pupil plane under coherent illumination. See Figure 3(b).

By analyzing the (fx , fy)rim distribution for the rim-type and outrigger-type masks versus the (fx , fy)NICEdistribution of NICE PSM,we observe that for rim-type and outrigger-type of PSMs, to achieve the best printing performance is to use small (i.e., morecoherent) illumination setting. With such an illumination, it is possible to better maintain axially-centered and phase-apodizing pupil

filter effect. In other words, for the rim and outrigger masks to behave as if with Super-FLEX effect during exposure, it is only

possible to combine with the use of applicable illumination. As shown in Figure 4, the Super-Flex effect is substantially diminished

when is larger than 0.3. One can expect that the corresponded aerial image quality for the contact hole is to become unusable. Interms of the NICE PSM, however, the smaller produces a non-axial but a quadrupole-type of phase-apodizing distribution on thepupil plane. This does not match to the Super-FLEX effect as described for the circular lens pupil. Hence, it is impossible to enhance

image resolution and DOF when we combine NICE PSM with a small illumination for contact holes exposure.

2.2 Partially Coherent IlluminationFor coherent illumination, the diffraction distribution on pupil plane is obtained by the Fourier transform of mask pattern. For

partially coherent illumination, the diffraction distribution on pupil plane is obtained by superposing Fourier transform of mask

pattern with various off-axis source illumination points. Figure 5 shows a conceptual view of an optical projection system with

partially coherent illumination used for this analysis. Each of the illumination source point can be associated with a coordinated pair

(fSx , fSy) that is corresponding to a specific location of diffraction distribution on the lens pupil plane. In the discussion of coherentillumination in Section 2.1, the point source is assumed to be on-axis such that (fSx , fSy)=(0, 0). For a partially coherent source pointwhere (fSx , fSy)(0, 0), we can make the approximation that the optical projection system has a center shift such that the Fouriertransform images of the mask due to the illumination source point, s, is described by a shifted function () in eq.(2): (fx- fSx , fy- fSy).According to Abbe method of imaging, the intensity distribution on the image plane can therefore be described mathematically by

slightly modified eq.(2):

(8))(2~~

),(),(),(

2

yx

yy

fxx

fi

yxSyySxx dfdfeffPffffOyxI

In Figure 6 (a), the (fx - fSx , fy - fSy) diffraction distributions are obtained along the pupil diameter for three isolated PSMs that aredesigned with a partially coherent illumination. This is a symmetrical illumination with four source points, or a quadrupole-type of

point source, with 0.75NA and ArF. Similarly, for the Fourier transform distribution of rim-type design, this is calculated by:

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(9)}))((sinc))((sinc)(

)(sinc)(sinc2)(sinc)(sinc{

),(

2

1 1r

2

~

SyyrSxxrr

m

i

n

jSyySxxrrSyySxx

rimSyySxx

ffwhffwhwh

ffhffhhffaffaa

ffffO

Here hr is the phase shifter width of rim-type PSM. The i,j are the numbers of illumination source points refer to the quadrupoleillumination source points. And for the Fourier transform distribution of NICE PSM, this is calculated by:

(10)})(cos)(sin)(sin2

)(cos)(sin)(sin2

)(cos)(cos41)(sin)(sin{

),(

2

1 1

~

dffffhcffwcwh

dffffwcffhcwh

ffdffdffacffaca

ffffO

SyySyynSxxn

SxxSyySxxnn

SxxSxxSyySxx

m

i

n

j

NICESyySxx

Figure 6(b) shows when the mask is illuminated by an off-axis point source, the diffraction distributions are shifted away from the

optical axis by a shifted function (fx- fSx , fy- fSy). From the pupil diagrams of Figure 6(b), we observe that the NICE PSM canproduce axially-centered and phase-apodizing pupil filter effect. This Super-FLEX effect is generated when with the quadrupole-type

of illumination point sources superposition-ed on the central region of pupil plane. But for the rim-type PSM, it instead generates a

non-axial and a quadrupole-type phase-apodizing distribution. It cannot form the intended Super-FLEX effect with the quadrupole-type of point sources. As explained in Section 2.1, we expect the NICE PSM with quadrupole illumination to have enhanced

resolution and DOF very similar to the ones achievable by combining rim-type (or outrigger-type) PSM with small illumination.Both are benefited by the Super-FLEX effect. Therefore, we conclude that the use of NICE PSM together with quadrupole-type of

OAI, we can expect excellent aerial image quality for enhanced resolution and larger DOF for contact holes pattern printing.

For the NICE PSM, when the center of OAI is smaller than 0.6, it begins to lose the Super-FLEX effect on the central region ofpupil plane, as shown in Figure 7. Figure 8 shows the summary and comparison of(fx- fSx, fy- fSy) image distributions of rim-typeand NICE PSM with respect to on-axis and off-axis (quadrupole-type) illumination point sources. Based on the comparison, we

observe: (1) For rim-type or outrigger-type PSM, superposing the distribution profiles of Fourier transform of mask with small illumination forms Super-FLEX effect on the lens pupil plane. Therefore, these type PSMs are basically applicable only under

coherent illumination. (2) For the NICE PSM, however, superposing the distribution profiles of Fourier transform of mask with

quadrupole-type of OAI point sources forms Super-FLEX effect on the circular pupil plane. Therefore, this NICE PSM is effective

or contact-hoe patterning when under OAI type of partially coherent illumination.f

3. RESULTS OF LITHOGRAPHY SIMULATION

The lithography performance analysis for aerial images and process windows is based on simulation using a non-paraxial vector

imaging model assumed the exposure settings of ArF (=193nm) and NA=0.75. We have also used electromagnetic field (EMF)simulation to verify the printing performance by considering the 3D topographical mask effect. The EMF simulation is based on the

finite difference time domain (FDTD) algorithm.

3.1 Aerial image simulation and process window analysis

The process window results of both rim-type and NICE PSMs for 100nm isolated contact hole printing are summarized in Figure 9.

For the illumination used, the QUASAR illumination setting is (0.93/0.7/20-degree) for (-out/-in/angle) and the conventional oneis with of 0.3. When with QUASAR, the NICE PSM has a rather large process window (DOF=0.65 m, exposure latitude orEL=7%) but the rim-type PSM produced no process window. When change to 0.3 conventional illumination, the rim-type PSM produces a decent process window (DOF=0.58m, EL=7%) but not the NICE PSM. From this result we have confirmed ourobservation in Section 2. That is, by forming a Super-FLEX effect with properly designed mask pattern and optimized illumination,we can enhance the printing resolution and process window for the isolated contact hole features.

Figure 10(a) plots the 1D aerial image intensity profiles of NICE PSM corresponding to different defocus settings (from 0m to -0.6m) under the same QUASAR illumination for the 100nm contact hole pattern. We observe that the center peak intensity profilesare able to be kept for the same ratio to the side-lobe intensity level for the entire defocus range investigated. Figure 10(b) shows 2D

intensity distribution of the NICE PSM on the focal plane. Figure 11 shows the process window results of NICE PSM with the

QUASAR illumination for 100nm and 80nm isolated contact hole. For 100nm isolated contact hole, the maximum DOF is

0.65m with 7% of EL. And for 80nm isolated contact hole, the maximum DOF is approximately 0.5m with 6% EL. This is a very



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reasonable process window for lithography manufacturing for 80nm contact hole CD target. Figure 12 shows simulation results of

common process window for the contact hole printing for both 200nm 1:1 pitch binary mask and isolated NICE PSM. Using the

QUASAR OAI, we can simultaneously enhance printing performance of both dense with binary mask and isolated contact holes with

NICE PSM. Under the same exposure conditions, the maximum overlapping common process window of 1:1 dense array and isolated

contact hole is 0.58m DOF at 10% EL for rectangular window. It is slightly bigger for elliptical window, the maximum DOF is0.64m at 12.8% EL.

Figure 13 shows the simulation results of aerial images and process windows for semi-isolated pitch contact hole printing. For semi-

isolated pitch NICE PSM, this pitch causes a degraded diffraction distribution profile under the same OUASAR OAI (0.93/0.7/20-

degree). This means that the Super-FLEX effect for this pitch range has become decreased due to more complex diffracted orders

entered into the lens pupil. To optimize, we decrease the inner radius of to compensate for this effect. The QUASAR illumination of(0.93/0.45/20-degree) is used for printing the semi-isolated pitch contact hole using NICE PSM design as shown. For 550nm pitch

contact hole with NICE PSM, the maximum DOF is 0.59m at 7% EL; while for 600nm pitch NICE contact hope pattern, themaximum DOF is 0.64m at 7% EL. Although the process windows are good for the semi-isolated pitch range using NICE PSMdesign, the use of smaller inner setting for semi-isolated pitch contact hole printing will impact negatively on the image quality andDOF of dense contact holes. But as shown, the larger inner setting is not preferable for more isolated pitch contact hole NICE PSM.To achieve a best overlapping process window for through-pitch contact holes printing, it is necessary to simultaneously optimize the

QUASAR illumination for both inner and outer settings.

3.2 Three dimensional mask simulationTo look into 3D topography effects [8,9,10] of the NICE PSM, we use EMF with high NA vector simulation. The intensity

distribution along the cross-sectional direction of the mask plane (near field) and image plane (far field) are both calculated.

Figure 14 shows the near field image profiles of two types of NICE PSM structure under a QUASAR illumination: one is the un-

etched main contact hole feature with un-etched ASB (or assist feature) structure in Figure 14(a) and another one is the etched main

contact hole feature with etched ASB structure in Figure 14(b). In the Kirchhoff (2D thin mask) approximation, the simulation results

of etched and un-etched ones are all corresponding to their respective 2D size. There is of little difference can be observed for the two

types. When with a rigorous 3D EMF simulation analysis for the near field intensity distribution, the etched main contact hole feature

with the etched ASB structure shows a stronger electromagnetic wave scattering effect due to the etched side-walls. This is likely to

negatively affect their imaging formation characteristics in the far field. More in-depth investigation is still needed for an overall

understanding of 3D mask topography impacts on the image formation quality.

Figure 15 shows the corresponded far field aerial image intensity profiles for the two types of NICE PSM as derived from the 3DEMF simulations. The comparison of the aerial images for etched and un-etched structures are shown in Figure 15(a) and 15(b).

Similar to near filed simulation results, the un-etched structure shows a better contour image quality than the etched one. Figure 15(c)

and 15(d) show the comparison of 0o with 45o cut-line of 1D aerial image intensity profiles. Again, the un-etched structure

outperforms with a better peak intensity.

4. CONCLUSIONS

In this paper, we present a new contact hole PSM design, named NICE PSM. When it is applied together with QUASAR OAI, we can

enhance the printing resolution to achieve an excellent overall process window for printing contact feature CD below sub-half

exposure wavelength. The imaging quality enhancement mechanism for NICE PSM is to use it together with QUASAR illumination

to form a natural pupil filter that is functionally behaved like the previously presented Super-FLEX effect. Using NICE PSM with

OAI is a much more elegant and flexible approach than to insert an actual pupil filer to the lens to form Super-FLEX. Although we

have demonstrated excellent printing perform for isolated contact hole, we show that this method call for additional illuminationoptimization in order to achieve optimized results for printing through-pitch, random array of contact hole patterns. We have also

investigated 3D mask topography effect for the NICE PSM, it seems that the un-etched main contact hole features with un-etched

ASB structures are the better imaging performer.

5. ACKNOWLEDGEMENT

The author has received help and support from ASML Masktools. Thanks to both J. Fung Chen and Stephen Hsu for their suggestions

in this work. The authors also wish to acknowledge the simulation software support from Sigma-C, GmbH.



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REFERENCES

1. Hiroshi Fukuda Axial imaging Superposing (Super-FLEX) Effect Using the Mask Modulation Method for in High-Numerical

Aperture I-Line Lens, Jpn. J. Appl. Phys. 30, 3037 (1991)

2. Hiroshi Fukuda, T. Terasawa, and S. Okazaki, Spatial filtering for depth of focus and resolution enhancement in optical

lithography, J.Vac. Sci. Technol. B, vol. 9, no. 6. (1991)3. Hiroshi Fukuda, Y. Kobayashi, K. Hama, T. Tawa, and S. Okazaki, Evaluation of Pupil Filtering stepper-lens system, Jpn. J.

Appl. Phys. 32, 5845 (1993)

4. Hiroshi Fukuda, Y. Kobayashi, T. Tawa, and S. Okazaki, Performance of pupil filtering stepper-lens system, Microelectric

Engineering 27, 213 (1995)

5. M. Born and E. Wolf, Principles of optics, sixth ed. (1980)

6. Alfred Wong, Resolution Enhancement Techniques in Optical lithography, chapter 2 and chapter 8. (2001)

7. Shuo-Yen Choua, Jen-Chung Loua, "Evaluating the Impact of Spherical Aberration on Sub-0.2-micron Contact/Via Hole

Patterning", Proc. SPIE 4346, 1318(2001)

8. C. Pierrat, A. Wong, and S. Vaidya, Phase-shifting Mask Topography effect on Lithographic Image Quality, IEDM, (1992)

9. A. Wong and A. Neureuther, Mask Topography Effects in Projection Printing of Phase-shifting masks, IEEE Transactions on

Electron Devices, vol. 41, no6, (1994)

10. Tsuneo TERASAWA, Norio HASEGAWA, Akira IMAI and Shinji OKAZAKI, Analysis of Nonplanar Topography effects of

Phase Shift Masks on Image Characteristics, Jpn. J. Appl. Phys. 34, 6578 (1995)

(b)(a)

0 deg

180 deg

Figure 1: NICE PSM design for contact hole patterning. (a) shows the 2D NICE mask structure including 3-D mask top-view and

cross-sectional profiles. In 3D mask cross-sectional profile, the zero degree cut-line means X-Z plane cross-sectional profile and the

45o cut-line refers to XY-Z plane cross-sectional profile. (b) shows diffraction distributions profile including 2D diffraction

distributions, 3D top view view, and cross-sectional profile of diffraction distributions on the lens pupil plane. The optical conditions

for diffraction calculations are ArF (193nm), 0.75NA, quadrupole-type of four illumination source points with ( =0.93).



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Figure 2: Modeling and anal sis of on-axis illumination projection system. Mask pattern m(x,y) on the object plane received a nearlyvertical incidence by coherent illumination creating an diffraction distribution (fx,fy) on the lens pupil plane. An intensitydistribution Ix, yis created on the image plane through the projection lens with NA= sin.

(a) (b)

0o

180o

Figure 3: Three isolated PSM designs under coherent illumination (0.75NA and ArF) for contact hole patterning: (a) shows rim andoutrigger types. By properly arranging the dimension and location of the phase assist features, (or anti-scattering bars, ASB) the

phase-apodizing, pupil-filtering effect at the center of the pupil can be generated. (b) is the new design PSM, or the NICE PSM. The(fx , fy)NICE is a non-axial but a quadrupole-type of phase-apodizing distribution on the pupil plane.

Figure 4: The Fourier transform distributions of rim-type PSM for settings range from 0 to 0.5. The Super-FLEX effect isdecreased when > 0.4. Here >0 refers to the use of quadrupole-type of four illumination source points.



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S

Figure 5: Modeling and analysis of off-axis illumination projection system. Mask pattern m(x,y) on the object plane received obliqueincidence by partially coherent illumination (where oblique incidence angle is S) creating an diffraction distribution (fx- fSx, fy- fSy)n the pupil plane.o

(a)

0o

180o

(b)

NICEPSM

Rim-typePSM

Figure 6: (a) shows the (fx- fSx, fy- fSy) distributions of three isolated PSMs design with partially coherent illumination (again refers to the useof quadrupole-type of four symmetrical illumination point sources), 0.75NA, and ArF wavelength. (b) shows when the mask is illuminated

by an off-axis point source, the diffraction distributions are shifted away from the optical axis. From the pupil diagrams on the right side of

(b), we observe that NICE PSM generates axially-centered, phase-apodizing pupil filter effect when with the quadrupole-type illumination

point sources that are superposition-ed on the central region of lens pupil plane.



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Figure 7: The Fourier transform distributions of NICE PSM with different settings (from 1.0 to 0.5) of quadrupole-type fourillumination source points. The Super-FLEX effect starts to become diminished when settings is smaller than 0.6.

(a) (b)

Figure 8: The summary of(fx- fSx, fy- fSy) image distributions for rim-type and NICE PSMs under on-axis and off-axis (quadrupole-

type) illumination point source. (a) shows non-axial quadrupole-type distribution from NICE PSM with on-axis coherent source pointand rim PSM from quadrupole-type of partially coherent illumination respectively. (b) shows axially-centered, phase-apodizing pupil

filter profile from rim PSM with on-axis coherent source point and NICE PSM with

quadrupole-type of partially coherent illumination.



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Figure 9: The summary of process window results of rim-type and NICE PSMs for printing 100nm isolated contact hole. Thesimulation conditions are 0.75NA, ArF, conventional illumination with =0.30 conventional and with QUASAR of(out/in=0.93/0.70 with opening of 20

o). The simulation results from the top two rows with QUASAR OAI: NICE PSM has a largeprocess window (DOF=0.65m, EL=7%) but no process window for the rim-type PSM as shown in the 2nd row. The bottom two rowsuse 0.30 conventional illumination, for rim-type PSM in the 3rd row, it can obtain large process window (DOF=0.58m, EL=7%)but not NICE PSM as shown in the 4th row.

(a) (b)

Figure 10: (a) shows the 1D aerial image intensity profiles of 100nm contact hole NICE PSM with the QUASAR illumination underdifferent defocus settings (from 0 to -0.6m). Using the NICE PSM with QUASAR OAI, the center peak intensity profiles are able to be kept for the same ratio to the side-lobe intensity level for the entire defocus range investigated. (b) shows the two dimensionintensity contour distribution of NICE PSM at the best focus.



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(a) (b)

Figure 11: The process window results of NICE PSM (QUASAR, 0.75NA, and ArF) for isolated contact hole printing. (a) shows100nm isolated contact hole printing with maximum DOF of 0.65m with EL of 7%. (b) is the result from the printing of 80nmisolated contact hole, the maximum DOF is approximately 0.5m with 6% of EL.

Figure 12: The common process window simulation results of 200nm pitch, 1:1, dense contact hole with binary mask and isolatedcontact hole by NICE PSM. With the same printing conditions in Figure 11, the maximum overlapping common process window of1:1 dense array and isolated contact hole is 0.58m DOF at 10% EL for rectangular window. And for elliptical process window, it isslightly bigger with the maximum DOF of 0.64m at 12.8% EL.

Figure 13: The simulation results of aerial images and process windows for semi-isolated pitch contact hole printing. For 550nm pitchcontact hole with NICE PSM, the maximum DOF is 0.59m at 7% EL; while for 600nm pitch NICE contact hope pattern, the maximumDOF is 0.64m at 7% EL. The printing conditions are: QUASAR 20o, out/in=0.93/0.45, 0.75NA, ArF.



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(a) (b)

EtchedUn-etched

Figure 14: The near field image profiles of two types of NICE PSM structure under a QUASAR illumination. (a) is the un-etchedmain contact hole feature with un-etched ASB structure. (b) is the etched main contact hole feature with etched ASB structure. The3D EMF simulations show that (b) has a stronger electromagnetic wave scattering effect due to the etched side-walls. This is likely tonegatively affect their imaging formation characteristics in the far field.

(b)(a)

(c) (d)

Figure 15: (a) & (b) show 2D contour image distributions for un-etched and etched types of NICE PSM structures. (c) & (d) show thecomparison between 0o with 45o cut-line of 1D aerial image intensity profiles. From simulation results, the un-etched main patternstructure has better peak intensity than the one from etched structure.


Date post:	07-Apr-2018
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