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.
Key enabler of the successful introduction of EUV lithography into volume production is the EUV mask
infrastructure. For the production of defect free masks, actinic review of potential defect sites to decide on the need
for repair or compensation is required. Also, the repair or compensation with the ZEISS MERiT electron beam repair
tool needs actinic verification in a closed loop mask repair solution. For the realization of actinic mask review,
ZEISS and the SEMATECH EUVL Mask Infrastructure consortium started a development program for an EUV
aerial image metrology system, the AIMSTM EUV, with realization of a prototype tool.
The development and prototype realization of the AIMSTM EUV has entered the tool calibration and qualification
phase utilizing the achieved capabilities of EUV aerial image acquisition and EUV mask handling. In this paper, we
discuss the current status of the prototype qualification and show recent measurement results.
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.
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.
The introduction of extreme ultraviolet (EUV) lithography into manufacturing requires changes in all aspects of the infrastructure, including the photomask. EUV reflective masks consist of a sophisticated multilayer (ML) mirror, capping layer, absorber layer, and anti-reflective coating thereby dramatically increasing the complexity of the photomask. In addition to absorber type defects similar to those the industry was forced to contend with for deep ultraviolet lithography, the complexity of the mask leads to new classes of ML defects. Furthermore, these approaches are complicated not only by the mask itself but also by unique aspects associated with the exposure of the photomask by the EUV scanner. This paper focuses on the challenges for handling defects associated with inspection, review, and repair for EUV photomasks. Blank inspection and pattern shifting, two completely new steps within the mask manufacturing process that arise from these considerations, and their relationship to mask review and repair are discussed. The impact of shadowing effects on absorber defect repair height is taken into account. The effect of mask biasing and the chief ray angle rotation due to the scanner slit arc shape will be discussed along with the implications of obtaining die-to-die references for inspection and repair. The success criteria for compensational repair of ML defects will be reviewed.
The combination of a reflective photomask with the non-telecentric illumination and arc shaped slit of the EUV scanner introduces what are known as shadowing effects. The compensation of these effects requires proper biasing of the photomask to generate the intended image on the wafer. Thus, the physical pattern on the mask ends up being noticeably different from the desired pattern to be written on the wafer. This difference has a strong dependence on both the illumination settings and the features to be printed. In this work, the impact of shadowing effects from line and space patterns with a nominal CD of 16nm at wafer was investigated with particular focus on the influence of pattern orientation and pitch, illumination pupil shape and fill (coherence) and absorber height. CD, best focus shift and contrast at best focus are utilized in detail in order to study the impact of the shadowing effects. All the simulation cases presented employ a complete scanner arc emulation, i.e. describe the impact of the azimuthal angle component of the illumination arc as in the NXE:3300 scanner and as it can be emulated by the AIMSTM EUV.
KEYWORDS: Etching, Quartz, Photomasks, Atomic force microscopy, Metrology, Critical dimension metrology, Inspection, Time metrology, Manufacturing, Back end of line
The ZEISS AIMS™ measurement system has been established for many years as the industry standard for qualifying the
printability of mask features based on the aerial image. Typical parameters in determining the printability of a feature
are the critical dimension (CD) and intensity deviations of the feature or region of interest with respect to the nominal.
While this information is critical to determine if the feature will pass printability, it gives little insight into why the
feature failed. For instance, determining if the failure occurs due to the quartz level deviating from that of the nominal
height can be problematic.
Atomic force microscopy (AFM) is commonly used to determine such physical dimensions as the quartz etch depth or
height and sidewall roughness for verification purposes and to provide feedback to front end processes. In addition the
AFM is a useful tool in monitoring and providing feedback to the repair engineers as the depth of the repair is one of the
many critical parameters which must be controlled in order to have a robust repair process.
In collaboration with Photronics nanoFab, we have previously shown the Bossung plot obtained from the AIMS™ aerial
image of a feature can be used to determine if the quartz level of a repaired region is above or below the nominal value.
This technique can further be used to extract the etch time associated with the nominal quartz height in order to optimize
the repair process. The use of this method can be used in lieu of AFM, effectively eliminating the time and effort
associated with performing additional metrology steps in a separate system. In this paper we present experimental
results supporting the technique and its applicability.
The ZEISS AIMS™ platform is well established as the industry standard for qualifying the printability of mask features
based on the aerial image. Typically the critical dimension (CD) and intensity at a certain through-focus range are the
parameters which are monitored in order to verify printability or to ensure a successful repair. This information is
essential in determining if a feature will pass printability, but in the case that the feature does fail, other metrology is
often required in order to isolate the reason why the failure occurred, e.g., quartz level deviates from nominal.
Photronics-nanoFab, in collaboration with Carl Zeiss, demonstrate the ability to use AIMSTM to provide quantitative
feedback on a given repair process; beyond simple pass/fail of the repair. This technique is used in lieu of Atomic Force
Microscopy (AFM) to determine if failing post-repair regions are "under-repaired” (too little material removed) or
“over-repaired” (too much material removed).
Using the ZEISS MeRiT E-beam repair tool as the test platform, the AIMSTM technique is used to characterize a series
of opaque repairs with differing repair times for each. The AIMSTM technique provides a means to determine the etch depth based on through-focus response of the Bossung plot and further to predict the amount of MeRiT® recipe change required in order to bring out of spec repairs to a passing state.
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