Renzo Capelli

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.

Defect mitigation considerations for EUV photomasks

Abstract. 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.

Scanner arc illumination and impact on EUV photomasks and scanner imaging

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.

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.

AIMS™ EUV tool platform: aerial-image based qualification of EUV masks (Conference Presentation)

With the EUV high volume manufacturing becoming reality and the closing gap of EUV mask infrastructure, EUV lithography is seeing or will shortly see the first production chips being fabricated with EUV. Pilot production in EUV HVM is most likely realized in a mix-and-match process with 193nm techniques. The degree of complexity introduced by the EUV lithographic process is transferred in parallel also to EUV mask: the combination of process sensitive 3D effects and material dependent EUV reflectivity make even the simplest EUV mask what the community is recognizing to be a very complex phase object. The qualification of such a complex piece of Infrastructure as the EUV mask is being addressed from many directions: defect review application is always more backed up by ancillary applications which aim at qualifying the printing behavior of the mask with the fundamental precondition of a full scanner emulation. ZEISS and the SUNY POLY SEMATECH EUVL Mask Infrastructure consortium have developed and commercialized the EUV aerial image metrology platform, the AIMS™ EUV platform, which fully addresses the industry requirements for EUV defectivity review. Additionally, this tool platform allows for mask qualification applications based on the employment of aerial image proven technology. In this paper, the status and recent achievements of the AIMSTM EUV platform will be presented. Promoting the detailed exploration of the aerial image content potential for EUV process understanding and mask qualification, we will present recent results on a printability study of embedded EUV multilayer defects, along with providing further insights into the relevance of mask 3D effects.

Aerial image based metrology of EUV masks: recent achievements, status, and outlook for the AIMS EUV platform

For upcoming EUV high volume manufacturing, the EUV mask infrastructure plays a central role for its successful introduction. One of the key items in the EUV mask infrastructure is the need of manufacturing defect free photomasks for which an actinic mask review capability is a critical success factor. ZEISS and the SUNY POLY SEMATECH EUVL Mask Infrastructure consortium have developed and commercialized the EUV aerial image metrology system, the AIMS™ EUV. In this paper we present the latest achievements of this AIMS™ EUV platform together with data and analysis of LER/LWR measurements in the aerial image. We provide an overall project overview and discuss possible future extensions options based on this actinic metrology platform.

Evaluation of EUV mask impacts on wafer line-edge roughness using aerial and SEM image analyses (Conference Presentation)

As more aggressive EUV imaging techniques and resists with lower intrinsic roughness are developed for patterning at 7nm and 5nm technology nodes, EUV mask roughness will contribute an increasing portion of the total printed linewidth roughness (LWR). In this study, we perform a comprehensive characterization of the EUV mask impacts on wafer LWR using actinic aerial images and wafer SEM images. Analytical methods are developed to properly separate and compare the LWR effects from EUV masks, photon shot noise, and resist stochastics. The use of EUV AIMSTM to emulate and measure incident photon shot noise effects is explored and demonstrated. A sub-10nm EUV mask is qualified using EUV AIMSTM with scanner equivalent dose settings that are required for patterning 16nm and 18nm half-pitch L/S features with low- and high-dose CAR resists. The variance and spectral components contributing to wafer LWR are quantified and compared.

Printability and actinic AIMS review of programmed mask blank defects

We report on the printability, mitigation and actinic mask level review of programmed substrate blank pit and bump defects in a EUV lithography test mask. We show the wafer printing behavior of these defects exposed with an NXE:3300 EUV lithography scanner and the corresponding mask level actinic review using the AIMSTM tool. We will show which categories of these blank substrate defects print on wafer and how they can be mitigated by hiding these defects under absorber lines. Furthermore we show that actinic AIMSTM mask review images of these defects, in combination with a simple thresholded resist transfer model, can accurately predict their wafer printing profiles. We also compare mask level actinic AIMSTM to top down mask SEM review in their ability to detect these defects.

Actinic review of EUV masks: challenges and achievements in delivering the perfect mask for EUV production

Actinic review of potential defect sites and verification of their repair is a key step in producing defect free masks. The AIMSTM systems are the industry proven standard for this task and the AIMSTM EUV has been developed to provide this functionality for EUV masks. Thereby it closes an important gap in the EUV mask infrastructure for volume production. In this paper, we show the readiness of the AIMSTM EUV for defect review and verification, and discuss the use of actinic aerial image metrology beyond this core application. In particular, we show measurements on mask 3D effects and the contribution of photon stochastics on wafer local CDU.