We directly extracted the phase-shift values of an EUV mask by measuring the reflectance of the mask. The mask had
gradient absorber thickness along vertical direction. We measured the reflectance of the open multilayer areas and the
absorber areas by using an EUV reflectometer at various absorber thicknesses. We also measured the diffracted 0th order
light intensities of grating patterns having several sizes of lines or holes. The phase-shift values were derived from these
data assuming a flat mask interference model of the diffracted lights. This model was corrected by including the
scattering amplitude from the pattern edges. We recalculated the phase-shift values which was free from the mask
topological effect. The extracted phase-shift value was close to 180 degrees at 67 nm and 71 nm absorber thicknesses.
The phase measurement error around 180 degree phase shift was 5 degrees (3σ).
Phase-shifting effect of EUV masks with various absorber thicknesses has been studied both by simulations and
experiments. In EUV lithography, masks with 180 phase shifting absorber work like embedded attenuated phase-shifting
masks. At 66nm thickness of TaN/TaON absorber, 180 degree phase shifting can be achieved in theory. Based on the
experiments, we observed that the true180 degree phase shifting can be achieved with absorber thickness between 66 and
76 nm. In this paper, phase shifting impact of the various thickness absorbers has been characterized. Imaging
performance of masks with 51 nm, 66 nm and 76 nm thick absorber has been experimentally compared. The process
window of various thickness absorber masks are rigorously studied.
Extreme ultraviolet lithography (EUVL) is a leading technology to succeed optical lithography for high volume
production of 22 nm node and beyond. One of the top risks for EUVL is the readiness of defect-free masks, especially
the availability of Mo/Si mask blanks with acceptable defect level. Fast, accurate and repeatable defect inspection of
substrate and multi-layer (ML) blank is critical for process development by both blank suppliers and mask makers. In
this paper we report the results of performance improvements on a latest generation mask blank inspection tool from
Lasertec Corporation; the MAGICS M7360 at Intel Corporation's EUV Mask Pilot Line. Inspection repeatability and
sensitivity for both quartz substrates (Qz) and ML blanks are measured and compared with the previous Phase I tool
M7360. Preliminary results of high speed scan correction mirror implementation are also presented
EUV blank non-flatness results in both out of plane distortion (OPD) and in-plane distortion (IPD) [3-5]. Even for extremely flat masks (~50 nm peak to valley (PV)), the overlay error is estimated to be greater than the allocation in the overlay budget. In addition, due to multilayer and other thin film induced stresses, EUV masks have severe bow (~1 um PV). Since there is no electrostatic chuck to flatten the mask during the e-beam write step, EUV masks are written in a bent state that can result in ~15 nm of overlay error. In this article we present the use of physically-based models of mask bending and non-flatness induced overlay errors, to compensate for pattern placement of EUV masks during the e-beam write step in a process we refer to as E-beam Writer based Overlay error Correction (EWOC). This work could result in less restrictive tolerances for the mask blank non-flatness specs which in turn would result in less blank defects.
Extreme Ultraviolet Lithography (EUVL) masks have residual stress induced by several thin films on low thermal
expansion material (LTEM) substrates. The stressed thin films finally result in convex out-of-plane displacement (OPD)
of several 100s of nm on the pattern side of the mask. Since EUVL masks are chucked on EUVL scanners differently
from on e-beam writer, the mask pattern placement errors (PPE) are necessary to be corrected for to reduce overlay
errors. In this paper, experimental results of pattern placement error correction using standard chrome on glass (COG)
plate will be discussed together with simulations. Excellent agreement with simple bending theory is obtained.
Suitability of the model to compensate for other EUVL-related PPEs due to mask non-flatness will be discussed.
Extreme ultraviolet lithography (EUVL) tool development achieved a big milestone last year as two full-field
Alpha Demo Tools (ADT) were shipped to customers by ASML. In the future horizon, a full field "EUV1" exposure
tool from Nikon will be available by the end of 20071 and the pre-production EUV exposure tools from ASML are
targeted for 20092. It is essential that high quality EUVL masks can be made and delivered to the EUVL tool users to
support the technology development. In the past year, we have demonstrated mask fabrication with low stress absorber
deposition and good etch process control yielding a vertical etch profile and a mask CD control of 5.7 nm for 32 nm (1x)
space and 7.4 nm for 32 nm (1x) lines. Mask pattern resolution of 15 nm (1x) dense lines was achieved. Full field
reflective mask die-to-die inspection at a 125nm pixel size was demonstrated after low defect multilayer blanks became
In this paper, we will present details of the Intel EUVL Mask Pilot Line progress in EUVL mask defect reduction,
pattern CD performance, program defect mask design and inspection, in-house absorber film development and its
performance, and EUVL metrology tool development. We will demonstrate an overall improvement in EUV mask
manufacturing readiness due to our Pilot Line activities.
Extreme ultraviolet lithography (EUVL) is one of the leading candidates for the next generation lithography. As the requirement on critical dimension (CD) and side wall profile control becomes ever stringent as minimum feature sizes keep shrinking following the Semiconductor Industry Association (SIA) roadmap, the patterning of the EUV mask absorber material, cost of ownership (COO) of mask, and the capability for defect free EUV masks become the crucial path in enabling the overall success of EUV lithography. The purpose of this study is to understand the etch characteristics in TaN-based EUV mask absorber etch, which will enable us to determine robust process condition in terms of CD performance and profile control. In this paper, CD bias performance in TaN-based EUV mask absorber etching is investigated within inductively coupled plasma (ICP) of fluorine-containing and chlorine-containing gas chemistries. The effects of etch parameters, such as plasma source power, bias power, and pressure, on the CD bias are evaluated through design of experiments (DOE). Some other etching characteristics like etch rate and selectivity are also correlated to the CD performance and etch profile to understand the basic etch mechanism in TaN etch. Latest etch results of the TaN-based absorber are also presented.
Mask defect specifications not only are needed to ensure quality masks for acceptable resist patterning on wafers, but also are utilized as a common goal for tool development, noticeably for mask inspection and repair. Defect specifications are generally determined by the allowable critical dimension (CD) changes from 'defect printability' experiments where a programmed defect mask (PDM) with intentionally placed defects is exposed in a stepper and the changes in resist CDs are measured. With the recent availability of extreme ultra-violet micro-exposure tools (EUV MET), a small field stepper with a numerical aperture (NA) of 0.3, 5X reduction and adjustable degrees of coherence, we are able for the first time to perform extensive studies of pattern defect printability for EUV masks with a high NA exposure tool. Such studies have investigated the defect impact to feature CDs for three different types of patterns: poly gate layer, contacts, and dense lines and spaces. This paper presents the experimental results and analysis of printability data collected under two illumination conditions, annular and dipole, on the MET with full focus and dose matrix (FEM). We have investigated as many as 10 types of defects designed on the PDM for each pattern layer. For each type of defect, a total of 15 sizes are coded on the PDM. With the consideration of limited resolution and line edge roughness of current EUV resists commonly used for EUV lithography development, the CDs under study were chosen in the range of about 40nm to 70nm. Extrapolations from these data are made to predict pattern defect specifications for smaller resist line features. Resist resolution is the main reason for the discrepancies between aerial image simulations and data presented in this paper.
It becomes increasingly important to have an integrated process for Extreme UltraViolet (EUV) mask fabrication in order to meet all the requirements for the 32 nm technology node and beyond. Intel Corporation established the EUV mask pilot line by introducing EUV-specific tool sets while capitalizing on the existing photomask technology and utilizing the standard photomask equipment and processes in 2004. Since then, significant progress has been made in
many areas including absorber film deposition, mask patterning optimization, mask blank and patterned mask defect inspection, pattern defect repair, and EUV mask reflectivity metrology. In this paper we will present the EUV mask process with the integrated solution and the results of the mask patterning process, Ta-based in-house absorber film deposition, absorber dry etch optimization, EUV mask pattern defect inspection, absorber defect repair, and mask reflectivity performance. The EUV resist wafer print using the test masks that are fabricated in the EUV mask pilot line will be discussed as well.