In-Yong Kang

Novel absorber stack for minimizing shadow effect in extreme ultraviolet mask

Finding an optimized absorber stack is becoming a more critical issue in the fabrication of extreme ultraviolet (EUV) mask since it is directly related to the performance of lithography such as pattern fidelity and productivity. Optical simulation, deposition, and measurement have been conducted to establish an optimized absorber stack including antireflection coating (ARC), absorber layer, and capping (or buffer) layer, which satisfies major requirements for EUV mask applications. TaN and the other absorber candidates do not show acceptable reflectivity value (lower than 5%) in deep ultraviolet (DUV) wavelength region (199 or 257nm) for pattern inspection. DUV reflectivity can be lowered by applying C and Al2O3 layers as top ARCs for 199 and 257nm wavelengths, respectively, while keeping the EUV reflectivity at 13.5nm less than 1%. ARC-covered TaN absorber stacks result in a reduction of printed CD variation owing to the mitigation of the shadow effect. However, long-term stability and fabricability of t...

Combined absorber stack for optimization of the EUVL mask

Integration and optimization of the absorber stack has become a critical issue with the progress of the extreme ultraviolet lithography development because it influences many issues such as throughput, pattern fidelity, and mask yield. Simulation works to optimize an absorber stack were carried out and the results were empirically confirmed. TaN showed a great potential as an extreme ultraviolet absorber property but it did not meet the requirement for deep ultraviolet reflectivity for inspection. According to the simulation, Al2O3 was selected as an anti-reflection coating for DUV wavelength. Al2O3 ARC with optimum thickness reduces the DUV reflectivity from 42.5 to 4.4 % at 248 nm while maintaining the other properties. A novel absorber stack consisted of TaN absorber, Ru capping, and Al2O3 ARC is proposed, and the total thickness of the stack is only 47 nm and the EUV and DUV reflectivities are 0.97 % at 13.5 nm and 4.4 % at 248 nm, respectively.

Numerical modeling of absorber characteristics for EUVL

The characteristics of various potential absorbers, such as Cr, Ta, and TaN materials were quantitatively investigated by calculating the optical contrast and geometrical width variation of pattern image of 25-nm-width transferred through the exposure system. The intrinsic absorber performance was evaluated by the numerical modeling of the reflectivity on the mask and the aerial image intensity on the wafer. The reflectivity on the mask was calculated for various absorber thicknesses (40-70 nm) using Fresnel equation. For the calculation of the aerial image intensity of pattern features with various absorbers, SOLID-EUV, which is capable of rigorous electromagnetic field computation, was employed. It could be reasonably concluded that the TaN absorber model showed superior optical characteristics compared to other absorber systems, whereas the best performance on the geometrical characteristics was found in the Ta absorber system.

Angular dependency of off-axis illumination on 100-nm-width pattern printability for extreme ultraviolet lithography: Ru/Mo/Si reflector system

The pattern printability of the Ru/Mo/Si system was quantitatively investigated by two successive schemes, reflectivity of the mask, and aerial image intensity transferred through the system. The reflectivity of a Ru/Mo/Si reflector was calculated and compared with the value of Mo/Si reflector for various incident angles (0°–5°) using Fresnel equation. In order to verify angular dependency of aerial image intensity in a Ru/Mo/Si reflector, we employed SOLID-EUV, which is capable of rigorous electromagnetic field computation. In the calculation, 100 nm line and space pattern was generated by 2D mask geometry with perfect absorber of opaque material. Through the investigation of the angular dependency on the pattern printability of Ru/Mo/Si and Mo/Si reflectors, we could suggest the optimal reflector system for specific condition of incident angle, i.e., Ru/Mo/Si system for ≲3° and Mo/Si system for ≳4° for maximizing optical performance of the EUVL system.

Improving mask yield by implementing an advanced mask blank inspection system

As the semiconductor industry advances to ever-smaller nodes with finer feature sizes and more complex mask designs, reticle quality and reticle defects continue to be a top mask yield risk. The primary reticle defect quality requirement is defined as “no reticle defects causing 10% or larger CD error on wafer”. Beginning at around the 7 nm Logic node, EUV lithography will start pilot production in several leading fabs. EUV masks stress reticle defectivity requirements for mask shops even more than optical masks due to the larger printing impact from a similar size defect on the mask, and the greater cost and longer cycle time for EUV masks. In a mask shop, generally there are three use cases for a blank inspection system, which are used to monitor and improve mask defectivity; 1) Inspecting process monitor masks, which are used to partition the mask process and identify defect excursions, 2) inspecting ‘witness’ blanks, which are used to measure and control defectivity in each process tool / chamber and 3) inspecting incoming mask blanks to ensure defect-free starting materials for advanced optical and EUV reticles. Traditionally, mask shops have been using bright field confocal technology to perform these tasks. However, due to more stringent defect requirements and the flexibility necessary to support these varied use cases, the industry requires a new approach to drive yield improvements in mask manufacturing. In this paper, we report on the introduction of a new system that provides superior sensitivity, with very high throughput and the flexibility to adapt to many different use cases in a production environment.

Aerial Image Characteristics of a Modified Absorber Model for Extreme Ultraviolet Lithography (EUVL)

The extreme ultraviolet lithography (EUVL) is the most promising technique for manufacturing ultra-large-scale integration (ULSI) devices for the sub 50-nm technology node (Gwynn et al., 1998). The pattern image characteristics of EUVL mask has directly bearing on the lithographic performance and the accuracy of the resist imaging (Yan et al., 2000). For the oblique illumination on a EUVL mask in the exposure systems, the geometrical shadowing effect by the patterned absorber stack becomes critical issue in the pattern transfer process. Therefore, many research efforts have been focused on the absorber design to maximize the optical performance (Deng et al., 2003; Deng et al., 2004). In this work, the pattern printability of modified absorber models with various sidewall angles was quantitatively investigated by simulating aerial image intensity transferred through the system.

Aerial image characteristics of modified absorber model for extreme ultraviolet lithography (EUVL)

The extreme ultraviolet lithography (EUVL) is the most promising technique for manufacturing ultra-large-scale integration (ULSI) devices for the sub 50-nm technology node (Gwynn et al., 1998). The pattern image characteristics of EUVL mask has directly bearing on the lithographic performance and the accuracy of the resist imaging (Yan et al., 2000). For the oblique illumination on a EUVL mask in the exposure systems, the geometrical shadowing effect by the patterned absorber stack becomes critical issue in the pattern transfer process. Therefore, many research efforts have been focused on the absorber design to maximize the optical performance (Deng et al., 2003; Deng et al., 2004). In this work, the pattern printability of modified absorber models with various sidewall angles was quantitatively investigated by simulating aerial image intensity transferred through the system.

Characteristics of Mo/Ru/Si multilayer reflector structure

TaeGeun Kim, WooSam Kim, In-Yong Kang+, Yong-Chae Chung+, SeungYoon Lee, and Jinho Ahn Div. of Adv. Materials Science and Engineering, Hanyang University +Dept. of Ceramic Engineering, Hanyang University 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea Introduction The characteristics of multilayer reflector is important since it is the core optical component for EUV projection. The multilayer structure as an EUV mask application should satisfy the following properies like high EUV reflectivity, low defect, compatibility with defect correction process and cleaning efficiency. The practical reflectivity of multilayer is always lower than that of the theorical value, and its main causes are non-ideal properties at the interface (interfacial mixing) and inside the films (density variation).

Structural Characterization of a Mo/Ru/Si Extreme Ultraviolet (EUV) Reflector by Optical Modeling

The performance of a multilayer extreme ultraviolet (EUV) reflector has a direct bearing on process throughput and the cost of new technology. Using measured data from an experimentally manufactured reflector, we intend, in this work, to show that the reflectivity of the Bragg reflector can be characterized by using structural parameters such as the d-spacing, density, thicknesses of the interdiffusion layers and oxidation layer. This quantitative analysis of the reflectivity derived from the structural parameters can be utilized to optimize the optical properties of the existing Mo/Ru/Si system and to provide fundamental insights into the science involved in a Bragg EUV reflector.

Structural characterization of Mo/Ru/Si EUV reflector by optical modeling

The performance of multilayer extreme ultraviolet (EUV) reflector has direct bearing on the process throughput and cost of new technology. Using measured data from the experimentally manufactured reflector, we intended, in this work, to show that the reflectivity of the Bragg reflector can be characterized by structural parameters such as d-spacing, density, and the thickness of inter-diffusion layers and oxidation layer. This quantitative analysis of the reflectivity derived from the structural parameters can be utilized to optimize the optical properties of the existing Mo/Ru/Si system as well as to provide fundamental insights into the science involved in a Bragg EUV reflector.