This paper describes the development and evolution of the critical architecture for a laser-produced-plasma (LPP) extreme-ultraviolet (EUV) source for advanced lithography applications in high volume manufacturing (HVM). In this paper we discuss the most recent results from high power sources in the field and testing on our laboratory based development systems, and describe the requirements and technical challenges related to successful implementation of those technologies on production sources. System performance is shown, focusing on pre-pulse operation with high conversion efficiency (CE) and with dose control to ensure high die yield. Finally, experimental results evaluating technologies for generating stable EUV power output for a high volume manufacturing (HVM) LPP source will be reviewed.
Multiple NXE:3300 are operational at customer sites. These systems, equipped with a Numerical Aperture (NA) of 0.33, are being used by semiconductor manufacturers to support device development. Full Wafer Critical Dimension Uniformity (CDU) of 1.0 nm for 16nm dense lines and 1.1 nm for 20nm isolated space and stable matched overlay performance with ArF immersion scanner of less than 4nm provide the required lithographic performance for these device development activities. Steady progresses in source power have been achieved in the last 12 months, with 100Watts (W) EUV power capability demonstrated on multiple machines. Power levels up to 90W have been achieved on a customer machine, while 110W capability has been demonstrated in the ASML factory. Most NXE:3300 installed at customers have demonstrated the capability to expose 500 wafers per day, and one field system upgraded to the 80W configuration has proven capable of exposing 1,000 wafers per day. Scanner defectivity keeps being reduced by a 10x factor each year, while the first exposures obtained with full size EUV pellicles show no appreciable difference in CDU when compared to exposures done without pellicle. The 4th generation EUV system, the NXE: 3350, is being qualified in the ASML factory.
The first NXE3300B systems have been qualified and shipped to customers. The NXE:3300B is ASML’s third generation EUV system and has an NA of 0.33. It succeeds the NXE:3100 system (NA of 0.25), which has allowed customers to gain valuable EUV experience. Good overlay and imaging performance has been shown on the NXE:3300B system in line with 22nm device requirements. Full wafer CDU performance of <1.5nm for 22nm dense and iso lines at a dose of ~16mJ/cm2 has been achieved. Matched machine overlay (NXE to immersion) of around 3.5nm has been demonstrated on multiple systems. Dense lines have been exposed down to 13nm half pitch, and contact holes down to 17nm half pitch. 10nm node Metal-1 layers have been exposed with a DOF of 120nm, and using single spacer assisted double patterning flow a resolution of 9nm has been achieved.
Source power is the major challenge to overcome in order to achieve cost-effectiveness in EUV and enable introduction into High Volume Manufacturing. With the development of the MOPA+prepulse operation of the source, steps in power have been made, and with automated control the sources have been prepared to be used in a preproduction fab environment.
Flexible pupil formation is under development for the NXE:3300B which will extend the usage of the system in HVM, and the resolution for the full system performance can be extended to 16nm. Further improvements in defectivity performance have been made, while in parallel full-scale pellicles are being developed.
In this paper we will discuss the current NXE:3300B performance, its future enhancements and the recent progress in EUV source performance.
This paper describes the development of a laser-produced-plasma (LPP) extreme-ultraviolet
(EUV) source for advanced lithography applications in high volume manufacturing. EUV
lithography is expected to succeed 193nm immersion double patterning technology for sub-
20nm critical layer patterning. In this paper we discuss the most recent results from high
power testing on our development systems targeted at the 250W configuration, and describe
the requirements and technical challenges related to successful implementation of these
technologies. Subsystem performance will be shown including Conversion Efficiency (CE),
dose control, collector protection and out-of-band (OOB) radiation measurements. This
presentation reviews the experimental results obtained on systems with a focus on the topics
most critical for a 250W HVM LPP source.
Laser produced plasma (LPP) light sources have been developed as the primary approach for EUV scanner imaging of circuit features in sub-20nm devices in high volume manufacturing (HVM). This paper provides a review of development progress and readiness status for the LPP extreme-ultra-violet (EUV) source. We present the latest performance results from second generation sources, including Prepulse operation for high power, collector protection for long lifetime and low cost of ownership, and dose stability for high yield. Increased EUV power is provided by a more powerful drive laser and the use of Prepulse operation for higher conversion efficiciency. Advanced automation and controls have been developed to provide the power and energy stability performance required during production fab operation. We will also discuss lifetesting of the collector in Prepulse mode and show the ability of the debris mitigation systems to keep the collector multi-layer coating free from damage and maintain high reflectivity.
The image border is a pattern free dark area around the die on the photomask serving as transition area between
the parts of the mask that is shielded from the exposure light by the Reticle Masking (ReMa) blades and the die.
When printing a die at dense spacing on an EUV scanner, the reflection from its image border overlaps with the
edges of neighboring dies affecting CD and contrast in this area. This is related to the fact that EUV absorber
stack has 1-3% reflectance for actinic light. For a 55nm thick absorber the induced CD drop at the edges is
found to be 4-5 nm for 27 nm dense lines. In this work we will show an overview of the absorber reflection
impact on CD at the edge of the field across EUV scanner generations, for several imaging nodes and multiple
Increasing spacing between dies on the wafer would prevent the unwanted exposure but results in an
unacceptable loss of valuable wafer real estate thereby reducing the yield per wafer and is thus not a viable
manufacturing solution. In order to mitigate the reflection from the image border one needs to create a so called
black border. The most promising approach is removal of the absorber and the underlying multilayer down to
the low reflective LTEM substrate by multilayer etching. It was shown in the previous study that the impact
on CD was reduced essentially for 27 nm dense lines exposed on ASML NXE:3100.
In this work we will continue the study of a multilayer etched black border impact on imaging. In particular, 22
nm lines/spaces imaging on ASML NXE:3300 EUV scanner will be investigated in the areas close to the black
border as well as die to die effects. We will look closer into the CD uniformity impact by DUV Out-of-Band
light reflected from black border and its mitigation. A possible OPC approach will also be evaluated.
All six NXE:3100, 0.25 NA EUV exposure systems are in use at customer sites enabling device development and cycles
of learning for early production work in all lithographic segments; Logic, DRAM, MPU, and FLASH memory. NXE
EUV lithography has demonstrated imaging and overlay performance both at ASML and end-users that supports sub-
27nm device work. Dedicated chuck overlay performance of <2nm has been shown on all six NXE:3100 systems.
The key remaining challenge is productivity, which translates to a cost-effective introduction of EUVL in high-volume
manufacturing (HVM). High volume manufacturing of the devices and processes in development is expected to be done
with the third generation EUV scanners - the NXE:3300B. The NXE:3300B utilizes an NA of 0.33 and is positioned at a
resolution of 22nm which can be extended to 18nm with off-axis illumination. The subsystem performance is improved
to support these imaging resolutions and overall productivity enhancements are integrated into the NXE platform
consistent with 125 wph. Since EUV reticles currently do not use a pellicle, special attention is given to reticle-addeddefects
performance in terms of system design and machine build including maintenance procedures.
In this paper we will summarize key lithographic performance of the NXE:3100 and the NXE:3300B, the NXE platform
improvements made from learning on NXE:3100 and the Alpha Demo Tool, current status of EUV sources and
development for the high-power sources needed for HVM.
Finally, the possibilities for EUV roadmap extension will be reviewed.
There are multiple mask parameters that can be tuned to optimize the lithographic performance of the EUV
photo mask. One of them is the absorber height. A reduction of the absorber height allows, for example, a
higher resolution patterning on mask and reduces the OPC needed for shadowing correction. Downside of
a thinner absorber is the increased reflectivity which manifests itself not only in the image field (contrast loss)
but also in the so called light shield area or image border.
The image border is a pattern free (absorber covered) area around the die on the photo mask forming the
transition area between the part on the mask that is completely shielded from the exposure light by the Reticle
Masking (REMA) blades and the die. The image border accommodates the finite REMA placement accuracy
and the half shadow of the REMA blades allowing close spaced die printing on the wafer.
When printing a die at dense spacing, which is common practice in a production environment, the image border
will overlap part of the neighboring die. This causes actinic EUV and DUV out of band light reflection from the
image border exposing the overlapped die area and affecting CD and contrast at the edges of the dies. For a 44
nm thick absorber we found a CD impact of 8 nm for 32 nm dense lines whereas for a 55 nm thick absorber
the effect was 4 nm for 27 nm dense lines. Increasing the die spacing would prevent this unwanted exposure
but results in an unacceptable loss of valuable wafer real estate thereby reducing the yield per wafer and is thus
not a viable manufacturing solution.
Optical Proximity Correction (OPC) using ASML Brion’s Tachyon NXE model at the edges of the die was
proposed as possible solution to this problem. An alternative is to create a so called Black Border: the
reflectivity in the image border is reduced to a sufficiently low level by for example increasing the absorber
thickness, add a special coating or replace the absorber with a low reflective material. The most radical
solution is removal of the absorber and the underlying multilayer down to the low reflective substrate, so-called
In this paper we will present the effects of such a Black Border created by a multilayer etch on features and
their placement on the reticle and the impact on CD of 27 nm dense lines on the wafer. By comparing the wafer
CDU printed with and without Black Border we will determine how well the image border effect is mitigated by
the multilayer etching.
EUV lithography requires an exposure system with complex reflective optics and an equally complex EUV dedicated
reflective mask. The required high level of reflectivity is obtained by using multilayers. The multilayer of the system
optics and the mask are tuned to each other. The mask is equipped with an additional patterned absorber layer.
The EUV mask is an optical element with many parameters that contribute to the final image and overlay quality on the
wafer and the productivity of the system. Several of these parameters can be tuned for optimal overlay, imaging and
productivity results. This should be done with care because of possible interaction between parameters.
We will present an overview of the EUV mask contributors to the imaging, overlay and productivity performance for
the 27 nm node and below, such as multilayer and absorber stack composition, reflectivity and reflectivity uniformity.
These parameters will be reviewed in the context of real-life scanner parameters for the ASML NXE:3100 and
NXE:3300 system configurations. The predictions will be compared to actual exposure results on NXE:3100 systems
(NA=0.25) for various masks and extrapolated to the NXE:3300 (NA=0.33).
In particular, we will present extensive multilayer and absorber actinic spectral reflectance measurements of a state-ofthe
art EUV mask over a range of incidence angles corresponding to an NA of 0.33 at multiple positions within the
image field. The ML measurements allow calibrating ML stack for imaging simulations. It allows also the estimation of
mask-induced apodization effects having impact on overlay.
In general, the reflectivity measurements will give detailed variations over the image field of mask parameters such as
ML centroid wavelength and absorber reflectivity which contribute to CD uniformity. Such a relation will be
established by means of rigorous full stack imaging simulations taking into account optical properties of the coming
Based on this investigation we will propose optimal EUV mask parameters for the 22 nm node EUV lithography and
below, to provide guidance for mask manufacturers to support the introduction of EUV High Volume Manufacturing.
ASML's NXE platform is a multi-generation TWINSCAN™ platform using an exposure wavelength of 13.5nm,
featuring a plasma source, all-reflective optics, and dual stages operating in vacuum. The NXE:3100 is the first product
of this NXE platform. With a 0.25 NA projection optics, a planned throughput of 60 wafers/hr and dedicated chuck
overlay of 4 nm, the NXE:3100 is targeted for extreme ultraviolet lithography (EUVL) implementation at 27nm halfpitch
(hp) and below. The next generation NXE tools utilize a 0.33NA lens and include off-axis illumination for high
volume manufacturing at a resolution down to 16nm hp and a targeted throughput of >100 wafers/hr. We share details
of the performance of the 0.25NA lithography products in terms of imaging, overlay, throughput, and defectivity. We
will show that we have met the required imaging performance associated with the 27nm hp node. We will also include a
summary of the EUV source development, which is a key enabler for cost-effective introduction of EUVL into highvolume
manufacturing. Finally, we will highlight some of the technical changes we introduced to enable the transition
from 27 to 22nm lithographic performance while introducing our 0.33NA Step & Scan system, the NXE:3300B.
EUVL requires the use of reflective optics including a reflective mask. The mask consists of an absorber layer pattern on
top of a reflecting multilayer, tuned for 13.53 nm. The EUVL mask is a complex optical element with many parameters
contributing the final wafer image quality. Specifically, the oblique incidence of light, in combination with the small
ratio of wavelength to mask topography, causes a number of effects which are unique to EUV, such as an HV CD offset.
These so-called shadowing effects can be corrected by means of OPC, but also need to be considered in the mask stack
In this paper we will present an overview of the mask contributors to imaging performance at the 27 nm node and below,
such as CD uniformity, multilayer and absorber stack composition, thickness and reflectivity. We will consider basic
OPC and resulting MEEF and contrast. These parameters will be reviewed in the context of real-life scanner parameters
both for the NXE:3100 and NXE:3300 system configurations.
The predictions will be compared to exposure results on NXE:3100 tools, with NA=0.25 for different masks. Using this
comparison we will extrapolate the predictions to NXE:3300, with NA=0.33.
Based on the lithographic investigation, expected requirements for EUV mask parameters will be proposed for 22 nm
node EUV lithography, to provide guidance for mask manufacturers to support the introduction of EUV High Volume
With the 1st NXE:3100 being operational at a Semiconductor Manufacturer and a 2nd system being shipped at the time of
writing this paper, we enter the next phase in the implementation of EUV Lithography. Since 2006 process and early
device verification has been done using the two Alpha Demo Tools (ADT's) located at IMEC in Leuven, Belgium and at
the CSNE in Albany, New York, USA. Now process integration has started at actual Chipmakers sites. This is a major
step for the development and implementation of EUVL. The focus is now on the integration of exposure tools into a
manufacturing flow, preparing high volume manufacturing expected to start in 2013.
While last year's NXE:3100 paper focused on module performance including optics, leveling and stages, this years
update will, in detail, assess imaging, overlay and productivity performance. Based on data obtained during the
integration phase of the NXE:3100 we will assess the readiness of the system for process integration at 27nm hp and
below. Imaging performance with both conventional and off-axis illumination will be evaluated. Although single
exposure processes offer some relief, overlay requirements continue to be challenging for exposure tools. We will share
the status of the overlay performance of the NXE:3100. Source power is a key element in reaching the productivity of
the NXE:3100 - its status will be discussed as well.
Looking forward to high volume manufacturing with EUV we will update on the design status of the NXE:3300B being
introduced in 2012 with a productivity target of 125wph. Featuring a 0.33NA lens and off-axis illumination at full
transmission, a half pitch resolution from 22nm to 16nm can be supported. In order to ensure a solid volume ramp-up the
NXE:3300B will be built on as many building blocks from the NXE:3100 as possible making optimum use of the NXE
Before being used in an extreme-ultraviolet (EUV) scanner, photoresists must be qualified to
ensure that they will not excessively contaminate the scanner optics or other parts of the vacuum
environment of the scanner. At the National Institute of Standards and Technology we have
designed and constructed a high-throughput beamline on the Synchrotron Ultraviolet Radiation
Facility (SURF III) in order to provide data on the contamination potential of the outgas products
of a candidate resist by simultaneously irradiating a witness substrate and a nearby resist-coated
wafer with EUV radiation, the so called witness sample test that is currently the resist
qualification method required by ASML. We will present results from four sample resists that
were subjected to the test.
Although the witness-sample test based on irradiating the resist with EUV radiation at 13.5 nm
most closely reproduces conditions in a scanner, the limited availability of suitable EUV sources
to conduct such tests has led to development of an alternative method which uses e-beam
irradiation in place of EUV radiation. We will also present the results of a comparison of these
The NXE platform is a multi-generation EUV production platform that builds the technology, design and experience of
both TWINSCAN™ and the two 0.25NA EUV tools (Alpha Demo Tools or ADT's) in use at two research centers for
EUV process development. This paper reviews the EUV Industry status, presents recent imaging and device work carried
out on the two 0.25NA ADT EUV tools and the status of the 1st production tool. Shipping in 2010, the NXE:3100 will be
the 1st generation of the EUV exposure platform. With an NA of 0.25 and a productivity of 60wph this tool is targeted
for EUV process implementation and early volume production at the 27nm node. We will highlight the key features of
the NXE:3100. On our way towards shipment we describe the manufacturing status and performance data of optics,
source and stages. The 0.32NA 2nd generation tool is designed as a lithography solution for high volume manufacturing
with EUV at the 22nm node and below. With a productivity >125wph the NXE:3300 will be a cost effective solution for
Lithography at the 22nm node and below. A 3rd generation with off-axis illumination at full transmission ensures
extendibility of the NXE:3300 for resolutions down to 16nm.
Cost, cost, cost: that is what it is - ultimately - all about. Single exposure lithography is the most cost effective means of
achieving critical level exposures, and extreme ultraviolet lithography (EUVL) is the only technology that will enable
this for ≤ 27nm production. ASML is actively engaged in the development of a multi-generation production EUVL
system platform that builds on TWINSCANTM technology and the designs and experience gained from the Alpha Demo
Tools (ADTs). The ADTs are full field step-and-scan exposure systems for EUVL and are being used at two research centers for EUVL process development by more than 10 of the major semiconductor chip makers, along with all major suppliers of masks and resist. Recently, successful implementation of EUVL for the contact hole and metal layer was demonstrated in the world's smallest (0.099 μm2) electrically functional 22nm CMOS SRAM device .
We will highlight the key features of the system description for the production platform, including the manufacturing
status of projection lens, illuminator optics, and source. Experimental results from ADT showing the progress in imaging
and resist work will be covered as well - a snapshot of imaging data can be seen in the figure below.
We will share our vision on the extendability of EUVL by discussing our system implementation roadmap. We will
explain our approach for multiple tool generations on a single platform, highlighting the ways to support the technology
nodes from 27nm half-pitch with a 0.25NA lens going down to below 16nm with a 0.32NA lens.
As part of its role in providing radiometric standards in support of industry, NIST has been active in advancing extreme ultraviolet dosimetry on various fronts. Recently, we undertook a major effort in accurately measuring the sensitivity of three extreme ultraviolet photoresists. It has been common practice to use photoresists as a transfer "standards" to determine the intensity and uniformity of the radiation transmitted by extreme ultraviolet steppers. In response to preliminary results from Lawrence Berkeley National Laboratory that showed that two "standard" photoresists were almost twice as sensitive as had been previously believed, NIST carried out similar measurements and confirmed the Berkeley results. However, we have found that the assumed sensitivities are more a question of system calibration than of absolute resist dose sensitivity. We will describe the facility we used to make these measurements.
Photoresists make less than perfect radiometers. They are very non-linear, sensitive to atmosphere, and difficult to calibrate. All of these characteristics led to the disparate results in assumed sensitivity values. We have developed an alternate wafer-plane dosimeter based on image plates. The dosimeter is linear over several orders of magnitude, comparatively insensitive to atmosphere, and can be re-calibrated as necessary. Moreover it can pass through a stepper as any other wafer. We will describe this dosimeter in detail
Single exposure lithography is the most cost effective means of achieving critical level exposures, and extreme
ultraviolet lithography (EUVL) is the technology that will enable this for 27nm production and below. ASML is actively
engaged in the development of a multi generation production EUVL system platform that builds on TWINSCANTM
technology and the designs and experience gained from the build, maintenance, and use of the Alpha Demo Tools
(ADTs). The ADTs are full field step-and-scan exposure systems for EUVL and are being used at two research centers
for EUVL process development by more than 10 of the major semiconductor chip makers, along with all major suppliers
of masks and resist. In this paper, we will present our EUVL roadmap, and the manufacturing status of the projection
lens for our first production system. Included will also be some test data on the new reticle pods. Experimental results
from ADT showing the progress in imaging (28 nm half pitch 1:1 lines/spaces CDU ~10%), single machine overlay
down to 3 nm, and resist complete the paper.
The ASML extreme ultraviolet lithography (EUV) alpha demo tool is a 0.25NA fully functional lithography tool with a
field size of 26×33 mm2, enabling process development for sub-40-nm technology. Two exposure tools are installed at
customer facilities, and are equipped with a Sn discharge source. In this paper we present data measured at intermediate
focus of the Sn source-collector module. We also present performance data from both exposure tools, show the latest
results of resist exposures including excellent 32-nm half pitch dense staggered and aligned contact hole images, and
present the highlights of the first demonstration of an electrically functional full field device with one of the layers made
using EUVL in ASML's alpha demo tool.
ASML has built and shipped to The College of Nanoscale Science and Engineering of the University at Albany (CNSE)
and IMEC two full field step-and-scan exposure tools for extreme ultraviolet lithography. These tools, known as Alpha
Demo Tools (ADT), will be used for process development and to set the foundation for the commercialization of this
technology. In this paper we will present results from the set-up and integration of both ADT systems, status of resist
and reticles for EUV, and the plans for using these tools at the two research centers. We will also present the first resist
images from one of the tools at the customer site, and demonstrate 32nm half-pitch dense lines/spaces printing as well as
32nm dense contact hole printing.
The ASML EUV alpha demo tool is operational! The alpha demo tool is a 0.25NA fully functional lithography tool with a field size of 26×33 mm2, enabling process development at the 40-nm technology node. In this paper we describe the tool performance, show that vacuum is achieved in a few hours, and demonstrate that our optics contamination strategy mitigates degradation of the optics. Additional data shows the Sn source cost-of-ownership to be comparable to state-of-the-art ArF source systems, by implementing a collector contamination mitigation strategy that includes cleaning. And, we present our first 35-nm dense lines and spaces (half pitch) resist images.
As the predecessor for Extreme Ultraviolet Lithography (EUVL) production tools, ASML is realizing a development exposure tool, the alpha demo tool. The main objectives for undertaking this effort are to minimize the risks of changing to a new lithographic technology in production and to support the development of the global infrastructure of masks, sources, and resist. For this, initial imaging of the alpha demo tool is aimed at features consistent with teh 45-nm technology node. In this paper we will present the status of the realization of the alpha demo tool. Several modules of the system have been integrated in the main body, and results of the system (vacuum) performance. We will summarize the current status of EUV sources including the recent work on alternatives to using Xe, report on our in-house source research, and provide an update on the fabrication of EUV optics. Polishing data of the projection optics mirrors shows that not only have we realized the requirements for 45-nm imaging, but also are we well underway in meeting the imagin requirements for production EUVL at the 32-nm node and beyond. Finally, since key to the commercial success of EUVL will be the availability of the infrastructure for reticles and resist, we will summarize the general status of EUV masks and resist.
ASML has continued to make significant investments in the development of extreme ultraviolet lithography (EUVL), addressing the critical challenges, including defect-free mask handling, reflective optics technology, environmental control, and source. We present updates in these key areas and in the realization of our process development exposure tool. This tool is used to minimize the risk of EUVL for the 45-nm technology node and below, and to support the development of the global infrastructure of masks, sources, and resist. Realization of the process development tool is well underway; most of the modules are in vacuum qualification and functional testing. From arial image simulations, we conclude that EUVL tools are particularly suited for contact printing, due to the use of dark-field masks, and hence, limited influence of flare.
With the realization of the α-tool, ASML is progressing with the pre-commercialization phase of its EUVL development. We report on the progress in the development of several key modules of the α-tool, including the source, wafer stage and reticle stage, wafer handling, baseframe, and optics modules. We demonstrate that the focus sensor meets its vacuum requirements, and that both stages after limited servo optimization approach the required scanning performance. A particle detection system has been built for the qualification of the reticle handling module, and preliminary results show that 50nm particles can be detected. The optics lifetime program showed substantial progress by utilizing caplayers to MoSi samples in order to suppress oxidation caused by H2O molecules under EUV illumination: a suppression ≥ 100x is achieved, compared to uncapped MoSi.
Within the recently initiated EXTATIC project a complete full-field lithography exposure tool for he 50-nm technology node is being developed. The goal is to demonstrate the feasibility of extreme UV lithography (EUVL) for 50-nm imaging and to reduce technological risks in the development of EUVL production tools. We describe the EUV MEDEA+) framework in which EXTATIC is executed, and give an update on the status of the (alpha) -tool development. A brief summary of our in-house source-collector module development is given, as well as the general vacuum architecture of the (alpha) -tool is discussed. We discuss defect-free reticle handling, and investigated the uses of V-grooved brackets glued to the side of the reticle to reduce particle generation during takeovers. These takeovers do not only occur in the exposure tool, but also in multilayer deposition equipment, e-beam pattern writers, inspection tools, etc., where similar requirements on particle contamination are present. Finally, we present an update of mirror fabrication technology and show improved mirror figuring and finishing results.
The ever-increasing demand on circuit performance necessitates rapid deployment of optical lithographic as well as early production next generation lithographic tools. Successful execution of the multitude of development programs involved requires careful consideration and implementation of system architecture with special emphasis on program synergy and modularity. This paper presents performance data and system budgeting and allocation for current generation lithographic tools, and building from that basis, discusses evolutionary approaches for critical performance areas and modules. Supporting analytical results regarding performance of these modules are also discussed.
As minimum feature size has decreased, and design rules have tightened, successful deep UV 0.35 micron technology has required a photolithography cluster. Linkage of the lithography exposure tool with the critical apply and develop process is driven by the need to improve cycle time, minimize defects, and optimize image tolerances. This paper summarizes results from Micrascan II photo clusters, and discusses the directions in which photo clusters must continue to evolve in order to satisfy the needs for 0.35 micron, and succeeding generations, of imaging technology.