The demand for EUV mask qualification by inspection and metrology techniques continues with the technology node shrink. Smaller node products contain a higher number of masks that require EUV exposure. Semiconductor industries have developed a variety of inspection and metrology tools to accommodate these needs. The progress of these techniques provides well-qualified semiconductor devices. Blank manufacturing is the initial step of the mask-making process. Nanometer-scale bumps and pits on the substrate, uniformity of multilayer stack, and particle-induced wafer printing defects must be controlled during the blank-making process. Both optical mask inspection and actinic blank inspection (ABI) are widely used as effective qualification methods to detect a defect of interest. Patterned mask inspection is an essential process step for mask making. The optical pattern inspection operating at DUV wavelengths near 193nm, Actinic Patterned Mask Inspection (APMI) that uses EUV 13.5nm wavelength, and EB inspection are the presently used patterned mask inspection technologies. APMI plays a key role in EUV mask inspection due to its high-resolution imaging. The introduction of reliable database mode inspection capability added more usability for the latest single die configuration masks. To manage all the printing defects, actinic solutions have the capability to realize fast and reliable results. EUV pellicles are already in use with EUV masks. Thus, the actinic solution is considered a required inspection method for patterned mask qualification for pellicle mounted mask too. Multiple APMI systems have already been installed in mask industries for through-pellicle inspection purposes. We will report the current progress of patterned mask inspection technologies, applications, and the future roadmap for high NA EUV.
In 2019, Lasertec successfully developed ACTISTM, the world’s first actinic patterned mask inspection (APMI) system, and has since been providing it as a solution to customers for use in EUV lithography production processes. APMI, is a type of inspection that utilizes the same 13.5nm EUV light used in EUV lithography. ACTIS can perform high-resolution, high-throughput inspection of EUV photomasks and detect all types of printable defects, the mask defects that would be printed on wafers in the EUV lithography process. DUV inspection can detect some of the printable defects. However, DUV inspection cannot detect phase defects, whereas APMI can. A comparison between the inspection performance of DUV and APMI for several defects, including phase defects, is provided in this paper. High-NA lithography is expected to be used for the EUV process at the technology nodes of N3 and beyond. High-NA lithography will be achieved by utilizing anamorphic optics, where magnification scales of projection differ along the horizontal and vertical axes. ACTIS has the extendibility to meet the requirements of high-NA lithography as it can be modified to have the NA on the mask extended along a single axis. Lasertec will develop a new generation ACTIS for use in high NA EUV lithography with higher NA projection optics. Discussions on increasing the NA of projection optics give rise to questions about inspection resolution due to light being blocked by the absorber on the EUV photomask. This paper will discuss this question using the results of simulations at varying absorber heights and NA values.
EUV lithography enters the high-volume manufacturing stage, and the semiconductor industry considers a lithography-wavelength- matched actinic patterned mask inspection (APMI) tool to be a crucial infrastructure for EUV mask qualification. ACTISTM, the world’s first high-sensitivity actinic patterned mask inspection system, was released in 2019. ACTIS detects lithographic impact defects that cannot be seen with the existing DUV inspection tools. The actual results of production mask inspection show that only an actinic EUV inspection system can visualize small surface topography and phase changes that propagate through multilayer stacks. In this paper, we present the progress of ACTIS inspection technology, defect sensitivity, die-to-database inspection and through pellicle inspection. For technology nodes beyond N3, a high-NA EUV anamorphic lithography system will be used. The mask structure in the high-NA era will be different from the current configuration. For inspection tool design, it is necessary to adopt a different magnification of mask-to-wafer projection in the vertical and horizontal directions. ACTIS has the extendibility to a high-NA system since its projection NA area has room for extension in one direction. The high-NA EUV inspection tool will be discussed in this paper as well.
As extreme ultraviolet lithography (EUVL) enters high volume manufacturing (HVM), the integrated circuit (IC) industry considers actinic patterned mask inspection (APMI) to be the last major EUV mask infrastructure gap. For over 20 years, there have been calls for an APMI tool for both the final qualification of EUV masks in the mask shop and for the requalification of EUV masks in the wafer fab1. Actinic, in this context, is matching the 13.5 nm scanner wavelength to that of the inspection tool so that all types of EUV mask defects can be detected. In order to enable EUVL HVM, we have developed and introduced the world’s first commercially available APMI tool. Actinic inspection enables HVM EUVL by ensuring that the EUV mask going to the EUV scanner is free from EUVprintable defects that may have been overlooked during EUV blank manufacturing or occurred during EUV mask manufacturing, cleaning and use. In this paper we will review EUV mask defect requirements from the maskshop and fab perspective, as well as capabilities of different inspection methods available for HVM. Further, we will provide an overview of the history of APMI tool development and highlight challenges and successes made when designing major components for the tool. APMI enables reliable detection of all classes of EUV-printable mask defects: small absorber defects, phase and amplitude defects in the multi-layer, In this paper, inspection performance of the APMI tool will be reviewed using representative cases from programmed defect masks with designs resembling real production cases. Finally, we will provide an outlook for the next steps in tool development including Die-to-Database inspection, throughpellicle inspection and platform extendibility to high NA EUVL.
As extreme ultraviolet (EUV) lithography enters high volume manufacturing, the semiconductor industry has considered a lithography-wavelength-matched actinic patterned mask inspection (APMI) tool to be a major remaining EUV mask infrastructure gap. Now, an actinic patterned mask inspection system has been developed to fill this gap. Combining experience gained from developing and commercializing the 13.5nm wavelength actinic blank inspection (ABI) system with decades of deep ultraviolet (DUV) patterned mask defect inspection system manufacturing, we have introduced the world’s first high-sensitivity actinic patterned mask inspection and review system, the ACTIS A150 (ACTinic Inspection System). Producing this APMI system required developing and implementing new technologies including a high-intensity EUV source and high-numerical aperture EUV optics. The APMI system achieves extremely high sensitivity to defects because of its high-resolution, low noise imaging. It has demonstrated a capability to detect mask defects having an estimated lithographic impact of 10% CD deviation on the printed wafer.
Optical metrology tool, LX530, is designed for high throughput and dense sampling metrology in semiconductor manufacture. It can inspect the dose and focus variation in the process control based on the critical dimension (CD) and line edge roughness (LER) measurement. The working principle is shown with a finite-difference-time-domain (FDTD) CD simulation. Two optical post lithography wafers, including one focus-exposure-matrix (FEM) wafer and one nominal wafer, are inspected for CD, dose and focus analysis. It is demonstrated that dose and focus can be measured independently. A data output method based on global CD uniformity (CDU), inter CDU and intra CDU is proposed to avoid the data volume issue in dense sampling whole wafer inspection.
We have developed a sensor optical system for the Far Infrared Interferometric Telescope (FITE). The spatial
resolution of FITE is expected to be 2.5 arcseconds. In order to derive the spatial extent of target objects, the
visibility of interference fringes has to be measured precisely. For this purpose, we constructed the focal plane
assembly of the FITE interferometer with the sensor optics. The focal plane is the entrance focus of the sensor
optics. A far-infrared (FIR) array detector is installed on the final focal plane of the sensor optics. Its camera
optics has F/106 beam for each beam of the interferometer. The PSF is dominated by diffraction, and its size
corresponds approximately to the array size so that the fringe pattern can be measured by the array in real time.
This system employs of two IR detectors and an optical CCD. The FIR detector has a format of 1.5mm ×15
pixels. In addition to the FIR array detector, we have a mid-IR detector and an optical CCD. They are also
installed on the final focal plane of the sensor optics. These two detectors are used for the precise alignment of the
interferometer optics.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.