Sascha Perlitz

Actinic review of EUV masks: first results from the AIMS EUV system integration

The EUV mask infrastructure is of key importance for a successful introduction of EUV lithography into volume production. In particular, for the production of defect free masks, actinic review of potential defect sites is required. To realize such an actinic review tool, Zeiss and the SEMATECH EUVL Mask Infrastructure consortium started a development programme for an EUV aerial image metrology system (AIMS™ EUV). In this paper, we discuss the status of the on-going system integration and show first results from the first light tests of the prototype tool.

Concept and feasibility of aerial imaging measurements on EUV masks

On the road to and beyond the 22nm half-pitch on chip patterning technology, 13.5nm EUVL is widely considered the best next technology generation following deep ultraviolet lithography. The availability of an actinic measurement system for the printability analysis of mask defects to ensure defect-free mask manufacturing and cost-effective high-volume EUV production is an infrastructural prerequisite for the EUVL roadmap and represents a significant step toward readiness for commercialization of EUV for high-volume-manufacturing . Carl Zeiss and SEMATECHs EUVL Mask Infrastructure (EMI) program started a concept study and feasibility plan for a tool that emulates the aerial image formed by a EUV lithography scanner supporting the 22 nm half-pitch node requirements with extendibility to the 16nm half-pitch node. The study is targeting a feasible concept for the AIMSTM EUV platform, bridging a significant gap for EUV mask metrology.

Novel solution for in-die phase control under scanner equivalent optical settings for 45nm node and below

As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever. Both attenuated and alternating Phase Shifting Masks (PSM) need precise control of phase as a function of both pitch and target sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets and require custom designed patterns in order to function properly, which limits phase measurement Zeiss is currently developing an optical phase measurement tool (PhameTM), providing the capability of extending process control from large CD test features to in-die phase shifting features with high spatial resolution. The necessity of designing this optical metrology tool according to the optical setup of a lithographic exposure tool (scanner) has been researched to be fundamental for the acquisition of phase information generated from features close to the size of the used wavelength. It was found by simulation that the image phase of a scanner depends on polarization and the angle of incidence of the illumination light due to rigorous effects. Additionally, for small features the phase value is strongly influenced by the imaging NA of the scanner due to the loss of phase information in the imaging pupil. Simulations show that the resulting scanner phase in the image plane only coincides with the etch-depth equivalent phase for large test features, exceeding the size of the in-die feature by an order of magnitude. In this paper we introduce the PhameTM phase metrology tool, which enables the industry to perform in-die phase control for Alternating PSM, Attenuated PSM and CPL masks. The PhameTM uses a 193nm light source with the optical capability of phase measurement at scanner NA up to the equivalent of a NA1.6 immersion scanner, under varying, scanner relevant angle of incidence for Attenuated PSMs and CPLs, and with the possibility of polarizing the illuminating light. New options for phase shifting mask process control on in-die features will be outlined with first phase measurement results for varying states of polarization.

Actinic review of EUV masks: Status and recent results of the AIMS EUV system

The EUV mask infrastructure is of key importance for the successful introduction of EUV lithography into volume production. In particular, for the production of defect free masks an actinic review of potential defect sites is required. To realize such an actinic review tool, Carl Zeiss and the SEMATECH EUVL Mask Infrastructure consortium started a development program for an EUV aerial image metrology system, the AIMS™ EUV. In this paper, we discuss the current status of the prototype integration and show recent results.

AIMS EUV first light imaging performance

Overcoming the challenges associated with photomask defectivity is one of the key aspects associated with EUV mask infrastructure. In addition to establishing specific EUV mask repair approaches, the ability to identify printable mask defects that require repair as well as to verify if a repair was successful are absolutely necessary. Such verification can only be performed by studying the repaired region using actinic light at an exact emulation of the scanner illumination conditions of the mask as can be done by the AIMSTM EUV. ZEISS, in collaboration with the SEMATECH EUVL Mask Infrastructure (EMI) consortium are currently developing the AIMSTM EUV system and have recently achieved First Light on the prototype system, a major achievement. First light results will be presented in addition to the current development status of the system.

Development status and infrastructure progress update of aerial imaging measurements on EUV masks

The high volume device manufacturing infrastructure for the 22nm node and below based on EUVL technology requires defect-free EUV mask manufacturing as one of its foundations. The EUV Mask Infrastructure program (EMI) initiated by SEMATECH has identified an actinic measurement system for the printability analysis of EUV mask defects to ensure defect free mask manufacturing and cost-effective high-volume EUV production as an infrastructural prerequisite for the EUVL roadmap ([1], [2]). The Concept and Feasibility study for the AIMSTM EUV resulted in a feasible tool concept for 16nm defect printability review. The main development program for the AIMSTM EUV has been started at Carl Zeiss leading to a commercialized tool available in 2014. In this paper we will present the status of the progress of the design phase of this development and an infrastructure progress update of the EUV Mask defect printability review.

Laterally resolved off-axis phase measurements on 45-nm node production features using Phame

As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever. To ensure an accurate printing both attenuated and alternating PSMs (Phase Shift Masks) need precise control of phase as a function of both pitch and target sizes. However critical target CDs fall much below conventional phase metrology tools capabilities. Interferometer-based phase shift measurements are limited to large CD targets and require custom designed features in order to function properly, which limits phase measurement. AFM (Atomic Force Microscopy) methods are able to capture small feature sizes but do not consider any diffraction effects which are caused by the topography of the features itself when getting close to the used wavelength. Imaging simulations, both, in a rigorous and a Kirchhoff regime, show the dependency of the phase in the image plane of a microlithography exposure tool on numerical aperture and pitch due to the loss of phase information in the imaging pupil. Additionally, for small features the phase is strongly impacted by polarization and 3D mask effects. For these feature sizes, the image phase does not coincide with the etch depth equivalent phase calculated from the nominal depth and optical constants of the shifter material. Deviations up to 20° have been observed leading to strong variations in the imaging quality and process window variations during scanner printing. Considerations of CD variation between 0 and pi features by simulation show lowest 0/pi CD variation and therefore largest process window if the scanner relevant phase is at 180°. The simulation results illustrate the importance to measure the scanner relevant phase, effective in the image plane of the scanner. Consequently Zeiss, in collaboration with Intel, has developed a laterally resolving Phase Metrology Tool - Phame® - for in-die phase measurements. The optical metrology tool is able to perform in-die phase measurement on alternating PSM, attenuated PSM and CPL masks down to 120nm half pitch at mask. On-axis measurement results have already been published. In this paper we elaborate on off-axis phase measurement theory and procedure. Furthermore we present first off-axis measurement results over varying features sizes using different illumination conditions.

Actinic review of EUV masks: performance data and status of the AIMS EUV System

The EUV mask infrastructure is of key importance for the successful introduction of EUV lithography into volume production. In particular, for the production of defect free masks an actinic review of potential defect sites is required. ZEISS and the SUNY POLY SEMATECH EUVL Mask Infrastructure consortium started a development program for such an EUV aerial image metrology system, the AIMS EUV. In this paper, we provide measurement data on the system’s key specifications and discuss its performance and capability status.

Phase behavior through pitch and duty cycle and its impact on process window

Immersion lithography has moved into 45nm node and will soon go into 32nm node. Alternating Phase Shifting Masks (alt. PSMs) are one of the most effective methods to enhance resolution and process window. . However there are two major challenges: intensity balancing and quartz dry etch process. The dry etch process requires not only an uniform quartz etch but also a good linearity over a wide range of feature sizes to ensure a 180° phase shift through pitch and duty cycle. Phase errors lead to an image placement error during printing becoming even worse through focus. As feature sizes shrink imaging effects and 3D mask effects impact the phase shift and accurate phase shift measurement becomes extremely important. In this paper we report on phase shift measurements through pitch and duty cycle on alt. PSM taken on the newly developed phase metrology system Phame® and compare them to rigorous 3D simulations. Furthermore we correlate the phase shift measurements to process window data such as maximum exposure latitude. Through pitch investigations on alt. PSM show that for print pitches below 200nm (wafer level) the phase shift drops significantly below 180° which will lead to an image placement error during printing and a shrinking process window. Furthermore a strong correlation between phase shift and maximum exposure latitude is shown. Largest maximum exposure latitude is achieved for phase shift close to 180°. Phame® enables optical phase shift measurement in critical production features down to 120nm half pitch providing the opportunity to optimize the quartz dry etch process in terms of signature and linearity. This will help to optimize the phase shift of critical features on alt. PSM for largest process window and hence increase end of line yields for reducing overall chip manufacturing costs.

Investigation of phase distribution using Phame in-die phase measurements

As lithography mask processes move toward 45nm and 32nm node, mask complexity increases steadily, mask specifications tighten and process control becomes extremely important. Driven by this fact the requirements for metrology tools increase as well. Efforts in metrology have been focused on accurately measuring CD linearity and uniformity across the mask, and accurately measuring phase variation on Alternating/Attenuated PSM and transmission for Attenuated PSM. CD control on photo masks is usually done through the following processes: exposure dose/focus change, resist develop and dry etch. The key requirement is to maintain correct CD linearity and uniformity across the mask. For PSM specifically, the effect of CD uniformity for both Alternating PSM and Attenuated PSM and etch depth for Alternating PSM becomes also important. So far phase measurement has been limited to either measuring large-feature phase using interferometer-based metrology tools or measuring etch depth using AFM and converting etch depth into phase under the assumption that trench profile and optical properties of the layers remain constant. However recent investigations show that the trench profile and optical property of layers impact the phase. This effect is getting larger for smaller CDs. The currently used phase measurement methods run into limitations because they are not able to capture 3D mask effects, diffraction limitations or polarization effects. The new phase metrology system - Phame(R) developed by Carl Zeiss SMS overcomes those limitations and enables laterally resolved phase measurement in any kind of production feature on the mask. The resolution of the system goes down to 120nm half pitch at mask level. We will report on tool performance data with respect to static and dynamic phase repeatability focusing on Alternating PSM. Furthermore the phase metrology system was used to investigate mask process signatures on Alternating PSM in order to further improve the overall PSM process performance. Especially global loading effects caused by the pattern density and micro loading effects caused by the feature size itself have been evaluated using the capability of measuring phase in the small production features. The results of this study will be reported in this paper.