Process Window Optimization for Mask Aligner Lithography · half-pitch, was illuminated with different illumination settings. Only one opening of the mask is shown in Figure 3. The

SPIE Advanced Lithography 2014, 9052-15 Opt. Microlithography XXVII, Voelkel et. al., February 25, 2014

Lithographic process window optimization for mask aligner proximity

lithography

Reinhard Voelkel*a, Uwe Voglera, Arianna Bramatia, Andreas Erdmannb, Nezih Ünalc,

Ulrich Hofmannc, Marc Hennemeyerd, Ralph Zoberbierd, David Nguyene, Juergen Bruggere

aSUSS MicroOptics SA, Rouges-Terres 61, CH-2068 Hauterive, Switzerland bFraunhofer Institut IISB, Schottkystr. 10, D-91058 Erlangen, Germany

GenISys GmbH, Eschenstr. 66, D-82024 Taufkirchen, Germany dSÜSS MicroTec Lithography GmbH, Schleissheimerstrasse 90, D-85748 Garching, Germany

École Polytechnique Fédérale de Lausanne, EPFL STI IMT, CH-1015 Lausanne, Switzerland

ABSTRACT

We introduce a complete methodology for process window optimization in proximity mask aligner lithography. The

commercially available lithography simulation software LAB from GenISys GmbH was used for simulation of light

propagation and 3D resist development. The methodology was tested for the practical example of lines & spaces, 5

micron half-pitch, printed in a 1 micron thick layer of AZ® 1512HS1 positive photoresist on a silicon wafer. A SUSS

MicroTec MA8 mask aligner, equipped with MO Exposure Optics® was used in simulation and experiment. MO

Exposure Optics® is the latest generation of illumination systems for mask aligners. MO Exposure Optics® provides

telecentric illumination and excellent light uniformity over the full mask field. MO Exposure Optics® allows the

lithography engineer to freely shape the angular spectrum of the illumination light (customized illumination), which is a

mandatory requirement for process window optimization. Three different illumination settings have been tested for 0 to

100 micron proximity gap. The results obtained prove, that the introduced process window methodology is a major step

forward to obtain more robust processes in mask aligner lithography. The most remarkable outcome of the presented

study is that a smaller exposure gap does not automatically lead to better print results in proximity lithography - what the

“good instinct” of a lithographer would expect. With more than 5'000 mask aligners installed in research and industry

worldwide, the proposed process window methodology might have significant impact on yield improvement and cost

saving in industry.

Keywords: mask aligner, proximity lithography, customized illumination, source-mask optimization, process window

optimization, lithography simulation, advanced mask aligner lithography, AMALITH

1. INTRODUCTION

The concept of lithographic process window optimization2,3 goes back to the late 80s. A process window is a collection

of values of process parameters that allow manufacturing within desired specifications. The lithographic process window

in projection lithography is typically defined as the set of values for focus and exposure to control critical dimension

(CD). The maximal inscribed rectangle or ellipses in this plot then represent the process window. The overall process

window for a specific lithography task is obtained from intersection or overlap of process windows for all different

layout patterns existing in a mask design. Process window analysis was developed for projection lithography, where it is

well established today4. Process window optimization has helped much to reduce the minimum feature size and to

improve the yield in production by giving a qualitative representation of the processes stability.

To the best knowledge of the authors, process window analysis and optimization has never been investigated in a

systematic way for mask aligner lithography. The reasons were manifold: no suitable lithography and resist simulation

tools, the immutable exposure light settings in most mask aligners, and the significant variance of uniformity and angular

spectrum over the mask field in standard mask aligner tools. The situation changed during the last decade. Projection

* [email protected], +41-32-5664444, www.suss.ch, www.suss.com


lithography software tools like Dr.LiTHO5 from Fraunhofer IISB (www.drlitho.com) have been adapted for the

simulation of mask aligner lithography. GenISys GmbH (www.genisys-gmbh.com) released LAB6, a lithography

simulation software with special focus on proximity lithography and 3D resist development modeling. Research

teams7,8,9,10 profited from these simulation tools to further investigate simulation and lithography enhancement

techniques for mask aligner lithography.

On the hardware side, the introduction of MO Exposure Optics® fundamentally changed the illumination system11,12 of

mask aligners. MO Exposure Optics® is based on a relay system of two microlens-based Köhler integrators and ensures

excellent light uniformity and identical angular spectrum over the full mask field. Telecentric illumination and full

control of the illumination settings (customized illumination) now enable simulation and optimization of mask aligner

lithography from the light source to the resist pattern (source-mask optimization). Lithography enhancement methods

from projection lithography can now be applied to mask aligner lithography.

Targets for mask aligner lithography optimization8 are manifold: compensating for errors and irregularities like corner

rounding, line width narrowing and edge shortening, elimination of remaining diffraction effects, increasing the gap

range of operation (minimum to maximum gap) and a larger free working distance (proximity gap), as well as resolution

enhancement.

Despite this encouraging progress in simulation, it remains difficult to assess proximity lithography enhancement

measures in practice. The interpretation of resist prints remains difficult. Sidewall angle measurements are laborious and

no suitable CD uniformity measurement tool is available for thick photoresists. Slight variations of the process

parameters might adulterate the results in exposure series. The presented methodology for process window optimization

is a first step to better compare the impact of lithography enhancement techniques in mask aligners. Process related

factors, like temperature, humidity and uncertainties in the wet process might still influence the individual exposure, but

the exposure latitude of the process window now allows the lithography engineer to rate process robustness and to

choose sweet spots.

2. DEFINITIONS AND TERMINOLOGY

For this study13 a 1 micron thick layer of AZ® 1512HS1 positive photoresist on silicon wafer was examined. Resist

simulation was based on the Mack 4 model3 with a development time of 30 seconds and a diffusion length of 25 nm. The

Mack 4 model parameters were set to Rmin = 0.61 nm·s-1, Rmax = 74.05 nm·s-1, Slope = 10, Mth = 0.473233. A photomask

with lines & spaces, 5 micron half-pitch, was used for exposure. The effects of dark erosion were not taken into account.

The raw data from LAB simulation was transferred to Matlab for data analysis and visualization13.

Figure 1. (Left) photograph (SEM) of 1 micron thick layer of AZ® 1512HS1 resist on silicon wafer after development, for

lines & spaces, 5 micron half-pitch, (right) scheme of photoresist structure with definitions. The sidewall angle is derived

from 20% and 80% of the resist height. CD is derived from the line width at 200 nm height to exclude any influence of resist

bottom effects and artifacts. Due to secondary diffraction orders unwanted side lobes and corresponding pits in the resist

might appear.

resist

he

igh

tga

p

Θ

wafer

photomask

20%

80%

sidewallangle

resist pit

200nmCD

half-pitch

http://www.drlitho.com/

http://www.genisys-gmbh.com/


Figure 1 shows (left) a photograph (SEM) and (right) a scheme of photoresist after development for a regular lines &

spaces pattern as described above. For this report the critical dimension CD was defined as line width at 200nm height of

the resist layer remaining after development. 200nm height instead of bottom CD was chosen to exclude any influence of

resist bottom effects. In some cases, e.g. for very thick photoresist layers, it might make more sense to use top CD at

80% or 100%. The sidewall angle Θ is derived from 20% and 80% width as shown in Figure 1. Secondary diffraction

orders might generate unwanted resist pits in-between two lines, as shown in the SEM picture Figure 1 (left).

3. SIMULATION OF SHADOW PRINTING LITHOGRAPHY IN A MASK ALIGNER

Lithography simulation for projection is typically based on far-field (Fraunhofer) diffraction theory7. Proximity

lithography is described by near-field (Fresnel-Kirchhoff) diffraction14, which represents a more difficult problem for

theoretical analysis. In the general case, near-field diffraction can be investigated by using so-called rigorous numerical

methods solving the Maxwell equations. For mask feature sizes significantly larger than the wavelength of the

illuminating light and for sufficiently large proximity gaps, approximate methods such as scalar diffraction theory yield

satisfactory results7. The achievable resolution for lines and spaces, half-pitch, for proximity lithography is deduced from

the Fresnel integral formula and given by the following expression7

𝑙𝑖𝑛𝑒 𝑤𝑖𝑑𝑡ℎ (ℎ𝑎𝑙𝑓 − 𝑝𝑖𝑡𝑐ℎ) =3

2√𝜆 (𝑔 +

𝑑

2) ≈ √𝜆𝑔. (1)

Here λ is the wavelength, 𝑔 the proximity gap and 𝑑 the resist thickness15. The resolution degrades with the square root

of the proximity gap. For this study13, the lithography simulation software LAB6 v4.1.0 from GenISys GmbH was used

for simulation. LAB provides full 3D simulation of shadow printing lithography in mask aligners for multiple

wavelengths and different illumination settings. The calculation of the aerial image is based on Kirchhoff scalar

diffraction theory solving the Rayleigh-Sommerfeld integral. Propagation in the resist is simulated by transfer matrix

model (thin film algorithm) including bleaching effects7. The light-induced modification and the development of the

photoresist material are described by the Dill parameters (extinction in the unbleached/bleached state and

photosensitivity of resist) and by the Mack 4 (development rate) parameters. The bulk image intensities are transferred

into inhibitor concentrations which define the dissolution rate and the resulting resist profile after development. The

resist data is transferred to Matlab® for systematic analysis and visualization13.

The angular spectrum of the mask illumination light in a mask aligner is product- and application-specific. An angular

divergence of typically ±3° to ±4° is preferred for contact, and ±1° to ±2° for proximity lithography. For SUSS MicroTec

mask aligners, the illumination optics for contact and small proximity gaps is referred as HR Optics (HR: high

resolution) and LGO Optics (LGO: large gap) for proximity.

HR(±3°) Optics LGO(±1.4°) Optics LGO(±0.7°) Optics

Figure 2. Different illumination settings for SUSS mask aligners: (left) HR(±3°) Optics, (center) LGO(±1.4°) Optics and

(right) LGO(±0.7°) Optics.

Figure 2 shows the three different illumination settings examined within this study.

±0.7°


4. DIFFRACTION EFFECTS FOR LINES & SPACES, 5 MICRON HALF-PITCH

As discussed above, proximity lithography in mask aligners is dominated by diffraction effects at the photomask pattern.

Figure 3 shows the intensity profiles obtained by simulation in LAB6. A regular pattern with lines & spaces, 5 micron

half-pitch, was illuminated with different illumination settings. Only one opening of the mask is shown in Figure 3. The

contour lines represent the intensity threshold levels obtained from simulation. The intensity coefficient is normalized to

1.0 for the dose-to-clear exposure dose.

HR(±3°) Optics (contact lithography settings)

LGO (±1.4°) Optics (proximity lithography settings)

Figure 3. Intensity profiles in air obtained by simulation in LAB lithography software for a photomask with lines & spaces,

5 micron half-pitch, illuminated with 365nm wavelength. Two different angular spectra are shown: (left) HR(±3°)

illumination and (right) LGO(±1.4°). The contour plot isobars correspond to equal exposure for the same exposure time. The

value 1.0 is equivalent to the dose-to-clear for a 1 micron thick layer of AZ® 1512HS positive photoresist on silicon.

4.1 Illumination coefficient contour plots

In both plots a central “red” spot with more light for 25 to 40 micron exposure gap is observed. This spot is generated by

diffraction at the edges of the 5 micron wide window in the mask layer. The intensity distribution behind the 5 micron

wide window looks very similar to the intensity distribution observed behind a 5 micron microlens with low optical

power16. As light is funneled towards the center, the light intensity is getting lower in outer regions. As result, the

contour lines show a remarkable narrowing at 30 micron gap. At 50 to 60 micron gap, the green area in Figure 3 is back

to 5 microns width, however, unwanted intensity peaks from secondary diffraction orders appear left and right.

Simulation was performed for an extended lines & spaces pattern, thus light from adjacent mask apertures overlap. As

shown in Figure 1, these peaks might lead to an unwanted resist structure (pits).


Figure 4 shows the contour plot of Figure 3 (right), corresponding to LGO(±1.4°) illumination, in more detail. A

coefficient of 0.2 corresponds to an exposure dose five times higher than the dose-to-clear for a 1 micron thick layer of

AZ® 1512HS positive photoresist on silicon. The contour plots indicate, that it is almost impossible to obtain a 5 micron

line width at a proximity gap of 30 microns by using 5 micron line width on mask level. For a value of 0.2 the contour

line width is 7 microns, for coefficient values > 0.4 the contour line is always < 3 microns. The process latitude for 30

micron gap is rather narrow. At a larger proximity distance > 40 micron a much larger exposure latitude is observed.

Figure 4. Intensity profiles from Figure 3 (right), corresponding to LGO (±1.4°), as contour plot. The contour lines

correspond to the equal dose levels for similar exposure time. The value 1.0 is equivalent to the dose-to-clear. (Left)

intensity coefficients indicated by different colors. (Right) Separate plots for intensity coefficients of 0.2, 0.4, 0.6, 0.8, 1.0

and 1.2 from (left). A coefficient of 0.2 corresponds to a dose of five times the dose-to-clear for a 1 micron thick layer of

AZ® 1512HS positive photoresist on silicon. A coefficient of 2.0 corresponds to a dose of 50% of dose-to-clear.

5. PROCESS WINDOW FOR LGO(±1.4°) ILLUMINATION SETTINGS

5.1 Process window for CD of 5 ±1 micron

As discussed, the process windows is application-specific. For some applications it is mandatory to achieve sidewall

angles Θ > 85°, but the actual dimensions of the resist structure are less relevant. For other applications, it is mandatory

to print resist structures with very small tolerances for CD, but the sidewall angles are not critical.

Figure 5: Process windows for critical dimension, 5 micron CD with ±1 micron tolerance, for LGO(±1.4°) illumination at

365nm wavelength, referring to an illumination light intensity distribution shown in Figure 3 (right) and Figure 4. The dark

0.2 0.4 0.6

0.8 1.0 1.2

B

A C


areas show combinations of proximity gaps and dose values, which produce CD values in the range of 5 ±1 micron. The

exposure latitude is indicated by rectangles fitted into the process window.

Figure 5 shows the obtained process windows for critical dimension 5 micron CD with ±1 micron tolerance. Illumination

using LGO(±1.4°) and 365nm wavelength referring to the intensity profiles shown in Figure 3 (right) and Figure 4.

Simulation was performed with LAB software from GenISys for a 1 micron thick layer of AZ® 1512HS positive

photoresist on silicon. The process windows shown in Figure 5 confirm the prediction made in the previous chapter, that

it is impossible to print a 5 micron line width at a proximity gap of 30 micron with a mask pattern of 5 micron width

using current illumination settings. The exposure latitude is indicated by rectangles fitted into the process window. From

contact to 25 microns (A) an exposure latitude of ±25mJ/cm2 is obtained. For proximity lithography there are two

options (B) and (C). For a proximity gap of 50 micron and a dose of 130 mJ/cm2 (B) the exposure latitude is ±25mJ/cm2

for a gap latitude of ±12 microns. In production environment a process window (C) with less critical gap latitude is

preferred. Exposure dose and development is usually very well controlled, whereas the gap latitude comprises different

factors like gap setting accuracy, mask bending, wafer flatness and all resist related surface defects like resist bubbles

and resist edge bead. In case (C) an exposure latitude of ±10 mJ/cm2 corresponds to a gap latitude of ±20 microns.

5.2 Process window for sidewall angle

In the process window shown in Figure 5 the CD was derived from 200nm resist height value as defined in Figure 1 with

no restriction to sidewall angle. This is not very realistic for most practical applications and in production.

Figure 6. Process window for sidewall angle and no restriction to critical dimension for lines & spaces, 5 micron half-pitch,

printed with LGO(±1.4°) illumination. (Left) sidewall angle requirement set Θ > 60° and (right) Θ > 80°. The green areas

show combinations of proximity gaps and dose values, which produce sidewall angles in the specified ranges.

Figure 6 shows the process windows for different sidewall angle requirements, but no restrictions to CD. For a sidewall

angle requirement of Θ > 80° it is very difficult to find a sweet spot for a robust lithography process. This is not

surprising. The used photoresist AZ® 1512HS works best as thin photoresist for higher resolution, but is not optimized

for obtaining steep sidewall angles.

5.3 Process window for side lobe printing

In Figure 4 (left), at (x, gap) positions (-5, 30) and (+5, 30), light from secondary diffraction orders is found. This light

might create unwanted pits in the resist as observed in Figure 1 (left). This effect is monitored by the side lobe printing

process window shown in Figure 7 for the exposure conditions described in previous chapters. The lower borderline

corresponds to the dose-to-clear exposure condition. Below this line the resist is not fully dissolved. Opaque areas inside

the window and above the higher borderline are – unwantedly – cleared. For an exposure gap of 50 microns the

secondary diffraction orders, viewable as “islands” Figure 1 (left), fully expose the resist and produce unwanted pits in

the resist. Similar effects are observable for a 30 micron proximity gap.


Figure 7. Side lobe printing process window for a 1 micron thick layer of AZ® 1512HS positive photoresist on silicon

exposed as described in the previous chapters. The lower borderline corresponds to the dose-to-clear exposure condition.

Below this line the resist is not fully dissolved. Above the higher borderline also opaque areas are – unwantedly – cleared.

The development time was set to 30 seconds.

5.4 Overlapped process window for all parameters

Assuming a tolerance of ±1 micron for 5 micron CD, a sidewall angle Θ > 60° is probably the best compromise for

proximity lithography using 1 micron thick layer of AZ® 1512HS positive photoresist on silicon. For a complete

assessment of a process all relevant process windows are combined.

Figure 8. Process window for proximity lithography using LGO(±1.4°) illumination settings as described in Figure 2

(center). A tolerance of ±1 micron for 5 micron CD and (left) a sidewall angle Θ > 60° and (right) a sidewall angle Θ > 70°

was set for the process window. The red areas show combinations of proximity gaps and dose values, which produce CD

values in the range of 5 ±1 micron and sidewall angles in the specified ranges. The exposure latitude is indicated by

rectangles fitted into the process window.


Figure 8 shows the resulting process windows from overlapping Figure 5, Figure 6 and Figure 7 and plotting the

intersections only, thus fulfilling all three conditions. For relaxed requirements regarding the sidewall angle, shown in

Figure 8 (left), the usable process windows range from 0 to 10 microns and 40 to 60 microns proximity gap

corresponding to an exposure dose of 85 to 160 mJ/cm2.

This result is quite surprising, contrary to the “good instinct” of experienced lithography experts and contrary to the

widely accepted equation (1) for proximity lithography. The common expectation is that the robustness of the proximity

process improves with decreasing proximity gap. An experienced lithography expert will always opt to reduce the

proximity gap to a minimum tolerable value dictated by mask and wafer bending, resist height deviation and gap setting

accuracy. The process window in Figure 8 clearly shows that printing lines & spaces, 5 micron half-pitch, at a 30 micron

proximity gap leads to a very unstable process. Whereas for a 50 micron gap and 120 mJ/cm2 exposure dose a latitude of

±20% is tolerable. The process window for harsher requirements to the sidewall angle of Θ > 70°, shown in Figure 8

(right), indicates that AZ® 1512HS is not the right choice of photoresist for steep sidewall angles.

The improvement of the lithography results for 50 micron proximity gap compared to 30 micron proximity gap can be

expected from the simulated intensity distributions on the right of Figure 3. However, the specific values of the

achievable dose latitude and range of favorable proximity gaps depend strongly on the photoresist parameters and

processing conditions. A careful process window optimization is required for different photoresists and processes.

6. PROCESS WINDOW FOR LGO(±0.7°) ILLUMINATION SETTINGS

In the previous chapter we observed, that printing lines & spaces, 5 micron half-pitch, by using proximity lithography

will typically lead to smaller resist structures. This unwanted effect might have its positive side in the case that a target

CD of 4 micron half-pitch is required. The process window for this case is shown in Figure 9 for illumination with

LGO(±0.7°) Optics, shown in Figure 2 (right). In the case of no criteria for sidewall angles, a stable process window,

shown in Figure 9 (left), could be found. For a sidewall condition of Θ > 60°, shown in Figure 9 (right), the exposure

latitude looks quite similar to the latitude for 5 micron CD with ±1 micron tolerance, shown in Figure 8 (right). Printing

4 micron structures with a 5 micron mask, i.e. compensating diffraction effects by adapting the mask pattern, is a very

useful strategy, also referred as optical proximity correction (OPC).

Figure 9: Process window for target critical dimension CD of 4 microns with ±1 micron tolerance. (Left) no restrictions to

sidewall angle and (right) a sidewall angle Θ > 60° as additional criteria. Exposure latitude is indicated by rectangles fitted

into the process window, mask CD of 5 microns.


7. PROCESS WINDOW FOR HR(±3°) ILLUMINATION SETTINGS

As discussed in chapter 3, the illumination settings for mask aligners are preset for contact or proximity lithography.

Mask aligners for contact lithography are typically equipped with an illumination optics providing a larger angular

spectrum of ±3° to ±4°. For proximity lithography, better collimated light with typically ±1° to ±2° angular spectrum is

preferred. For SUSS mask aligners, the illumination optics for contact and small proximity gaps is referred to as HR

Optics (HR: high resolution). For proximity lithography at large gaps, the illumination optics is referred to as LGO

Optics (LGO: large gap). For mask aligners equipped with MO Exposure Optics® the illumination settings are defined by

illumination filter plates (IFP) and can easily be changed11,12. In the following we examine the process window for a

mask aligner configured for contact lithography, i.e. equipped with HR (±3°) Optics shown in Figure 2 (left), but used

for proximity lithography.

Figure 10: Process window for critical dimension CD 5 micron with ±1 micron tolerance using HR(±3°) illumination optics,

designed for contact or small gap proximity lithography. (Left) process window with no restrictions to sidewall angle and

(right) a sidewall angle Θ > 60° as additional criteria. Exposure latitude is indicated by rectangles fitted into process

window.

Figure 11: Process window for critical dimension CD 5 micron with ±1 micron tolerance using HR(±3°) illumination optics,

designed for contact lithography. (Left) process window for side lobe printing and (right) the intersection of all three process

windows.


Figure 10 and Figure 11 show the corresponding process windows for using HR(±3°) illumination optics, designed for

contact and small proximity gap lithography. The comparison of Figure 11 for HR(±3°) illumination optics and Figure 8

for LGO(±1.4°) illumination optics demonstrates the significant influence of the illumination settings on proximity

lithography.

In practice, the choice if a mask aligner is equipped with HR or LGO illumination optics is made when the mask aligner

is purchased. Typically, a changeover from HR to LGO or vice versa requires the investment in new optical parts and a

fine adjustment of the illumination optics after each exchange. MO Exposure Optics®, the latest generation of

illumination optics for SUSS MicroTec mask aligners allows a changeover of the illumination settings within less than a

minute by changing an illumination filter plate (IFP). Lithography simulation software LAB6 allows lithography

engineers to evaluate any kind of illumination settings, including ring, dipole, quadrupole, multipole and even more

sophisticated angular spectra. The introduced process window methodology is a valuable method to assess the impact of

different illumination settings on the robustness of the overall lithographic process.

8. CONCLUSION AND OUTLOOK

The purpose of this report was the introduction of a complete methodology for process window optimization to

proximity mask aligner lithography. Recently, MO Exposure Optics®, a new type of illumination system was introduced

for SUSS MicroTec mask aligners. MO Exposure Optics® provides telecentric illumination, excellent light uniformity

over the full mask field and allows the lithographic engineer to change and optimize the illumination settings in

proximity lithography (customized illumination). Diffraction effects in proximity lithography could now be reduced by

using optical proximity correction (OPC) and source-mask optimization (SMO). It was demonstrated recently, that these

well-known lithography enhancement methods can be applied successfully to mask aligner lithography. However, it

remained difficult for the lithographic engineer to visualize and assess their impact on process robustness. The proposed

process window methodology now closes the gap. Process window optimization proved to be a valuable method to

obtain more robust lithography processes in mask aligner lithography. The most important outcome of this first report is,

that in proximity lithography a smaller exposure gap does not automatically lead to better print results. This is contrary to

what the “good instinct” of a lithography engineer would expect. Although some engineers might know about this, the

majority of the engineers working with mask aligners will not be aware. Regarding an installed base of more than 5’000

SUSS MicroTec mask aligners, the introduced process window methodology might have a significant impact on yield

improvement and cost saving in industry worldwide.

Some of the typical characteristics of the process window, such as achievable resolution, most appropriate ranges of

proximity gaps and qualitative impact of illumination settings can be already derived from computed intensity

distributions in the Fresnel region of the mask. However, the specific values of the achievable dose latitude and range of

favorable proximity gaps depend strongly on the photoresist parameters and processing conditions. A careful process

window optimization is required for different photoresists and processes. The presented results, obtained from

simulation, were verified by exposure tests using a 1 micron thick layer of AZ® 1512HS positive photoresist on a silicon

wafer in a SUSS MA8 mask aligner equipped with the described illumination settings13. The experimental results

corresponded largely to the simulation results and proved the applied methodology.


References

[1] AZ Electronic Materials, http://www.microchemicals.com/products/photoresists/az_1512hs.html

[2] C. P. Ausschnitt, “Rapid optimization of the lithographic process window,” Proceedings of SPIE 1088: Optical/Laser

Microlithography II, 115 (1989).

[3] C. A. Mack, “Fundamental Principles of Optical Lithography: The Science of Microfabrication,” John Wiley & Sons, London

(2007).

[4] J. Word, K. Sakajiri, “OPC to improve lithographic process window,” Proceedings of SPIE 6156: 61561I-2 (2006).

[5] Dr. LiTHO Software, Fraunhofer IISB Erlangen, www.drlitho.com.

[6] GenISys GmbH, LAB V4.1.0, 3D Proximity Lithography Simulation, www.genisys-gmbh.com.

[7] Péter Bálint Meliorisz, “Simulation of Proximity Printing”, PhD Thesis, Friedrich-Alexander University, Faculty of Engineering

(2010).

[8] R. Voelkel, U. Vogler, A. Bramati, T. Weichelt, L. Stuerzebecher, U.D. Zeitner, K. Motzek, A. Erdmann, M. Hornung, R.

Zoberbier; „Advanced mask aligner lithography“, Proc. SPIE 8326, Optical Microlithography XXV, 83261Y (Feb. 21, 2012).

[9] Bavarian Research Foundation Project “MALS: Mask Aligner Lithography Simulation”, 2008-2011.

[10] Subproject “FISMA: Flexible Illumination System in Mask Aligners”, within the frame of EU-FP7 “SEAL – Semiconductor

Equipment Assessment Leveraging Innovation”, www.seal-project.eu, 2010 – 2013.

[11] R. Voelkel, U. Vogler, A. Bich, K. J. Weible, M. Eisner, M. Hornung, P. Kaiser, R. Zoberbier, E. Cullmann, „Illumination system

for a microlithographic contact and proximity exposure apparatus“, EP 09169158.4, (2009).

[12] R. Voelkel, U. Vogler, A. Bich, P. Pernet, K.J. Weible, M. Hornung, R. Zoberbier, E. Cullmann, L. Stuerzebecher, T.

Harzendorf, U.D. Zeitner, "Advanced mask aligner lithography: New illumination system", Optics Express 18, 20968-20978 (2010).

[13] David Nyuyen, “Lithographic Process Window Optimization for Mask Aligner”, semester work, Ecole Polytechnique Fédérale de

Lausanne (EPFL), Section of Microengineering, Lausanne, Switzerland (2014).

[14] J. I. García-Sucerquia, R. Castaneda, F. F. Medina, G. Matteucci, “Distinguishing between Fraunhofer and Fresnel diffraction by

the Young experiment”, Optics Communications, 200, 15-22 (2001)

[15] P. Rai-Choudhury, ed., Handbook of Microlithography, Micromachining, and Microfabrication, SPIE Press, 1997

[16] Patrick Ruffieux, Toralf Scharf, Hans Peter Herzig, Reinhard Voelkel, Kenneth J. Weible, „On the chromatic aberration of

microlenses“, Optics Express, Vol. 14, No. 11, p. 4687 – 4694 (2006)

http://www.seal-project.eu/

Documents

Process Window Optimization for Mask Aligner Lithography · half-pitch, was illuminated with different illumination settings. Only one opening of the mask is shown in Figure 3. The