Il-Yong Jang

Control of the sidewall angle of an absorber stack using the Faraday cage system for the change of pattern printability in EUVL

A patterned TaN substrate, which is candidate for a mask absorber in extreme ultra-violet lithography (EUVL), was etched to have inclined sidewalls by using a Faraday cage system under the condition of a 2-step process that allowed the high etch selectivity of TaN over the resist. The sidewall angle (SWA) of the patterned substrate, which was in the shape of a parallelogram after etching, could be controlled by changing the slope of a substrate holder that was placed in the Faraday cage. The performance of an EUV mask, which contained the TaN absorber of an oblique pattern over the molybdenum/silicon multi-layer, was simulated for different cases of SWA. The results indicated that the optical properties, such as the critical dimension (CD), an offset in the CD bias between horizontal and vertical patterns (H-V bias), and a shift in the image position on the wafer, could be controlled by changing the SWA of the absorber stack. The simulation result showed that the effect of the SWA on the optical properties became more significant at larger thicknesses of the absorber and smaller sizes of the target CD. Nevertheless, the contrast of the aerial images was not significantly decreased because the shadow effect caused by either sidewall of the patterned substrate cancelled with each other.

A study of Cr to Mosi in situ dry etching process to reduce plasma induced defect

Dry etching process is widely used in semiconductor field and in photomask manufacturing. Even though dry etching technique can be much better in obtaining straight profile and better CD (Critical Dimension) uniformity than wet etching technique, it has a severe problem in terms of defect issue. Especially, very tough controllability of defects is essential for the photomask dry etching process because defect can be printed on the wafer over. Therefore, we studied defect free photomask etching techniques and found out the possibility of particle evasion. With In-situ etching method, defect generation by MoSiON etching could be reduced compared to when standard etching process is used while the process result is almost same as that of the standard process. In this paper, we will present the experimental result of in-situ. dry etching process technique for Cr and MoSiON, which reduces the defect level significantly.

Durability of Ru-based EUV masks and the improvement

In EUV Lithography, an absence of promising candidate of EUV pellicle demands new requirements of EUV mask cleaning which satisfy the cleaning durability and removal efficiency of the various contaminations from accumulated EUV exposure. It is known that the cleaning with UV radiation is effective method of variety of contaminants from surface, while it reduces durability of Ru capping layer. To meet the expectation of EUV mask lifetime, it is essential to understand the mechanism of Ru damage. In this paper, we investigate dominant source of Ru damage using cleaning method with UV radiation. Based on the mechanism, we investigate several candidates of capping to increase the tolerance from the cycled UV cleaning. In addition, we study durability difference depending on the deposition method of Ru capping. From these studies, it enables to suggest proper capping material, stack and cleaning process.

Develpment of etch rate uniformity adjustment technology for photomask quartz etch in manufacturing the 100% attenuated PSM

As the feature size of integrated circuits decreases, it is difficult to have a good resolution with an ordinary lithography technology. Resolution enhancement technologies (RETs), therefore, become prominent way to achieve better resolution. Among various RETs, Phase Shift Mask (PSM) can be one of the most useful technologies in these days and especially Chrome-Less Mask (CLM) or Phase Edge PSM (PE-PSM) is used for utilizing strong effect of PSM technology. In manufacturing the CLM or PE-PSM, the quartz layer of the photomask should be etched to 2480 in depth which is the equivalent value in phase, 180°. But quartz etch is one of the difficult processes in photomask manufacturing due to the absence of stopper layer. Moreover, the depth uniformity should be controlled within the tolerance of 5°. But there are etch rate variations from center to edge positions within the 6-inch mask area which originates from the deficit of plasma uniformity. As a result, phase deviation in those area occurs after quartz etch up to several degrees in phases and this problem makes the manufacturing of CLM or PE-PSM difficult. We thought there would be some relations between etch rate uniformity and hardware, such as focus ring which is used for confinement of plasma species. Various experiments, therefore, were executed with regard to the type of focus ring (shape, and height). As a result, the outstanding tendencies which show the relations, can be obtained. On this paper, the detailed descriptions of the experiments and their results will be presented.

Improvement of photomask CD uniformity using spatially resolved optical emission spectroscopy

According to the design rule shrinkage, more precise control of mask CD, including mean to target and uniformity, is required in lithography process. Since dry etching is one of the most critical processes to determine CD qualities in photomask, optical emission spectroscopy (OES) to monitor plasma status during dry etching process could be useful. However, it is not possible to obtain distributional information of plasma with a conventional OES tool because the OES acquires totally integrated signals of light from the chamber. To overcome the limit of OES, we set up a spatially resolved (SR)-OES tool and measure the distribution of radicals in plasma during dry etch process. The SR-OES consists of a series of lenses, apertures, and a pinhole as a spatial filter which enable us to focus on certain area in the chamber, to extract the emitted light from plasma, and to perform the spectroscopic analysis. The Argon based actinometry combined with SR-OES shows spatially distinguished peaks related to the etch rate of Chromium on photomask. In this paper, we present experimental results of SR-OES installed on a commercial photomask dry etcher and discuss its practical effectiveness by correlation of the results with chamber etch rate.

Evaluating Printability of Buried Native EUV Mask Phase Defects through a Modeling and Simulation Approach

The availability of defect-free masks is considered to be a critical issue for enabling extreme ultraviolet lithography (EUVL) as the next generation technology. Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of the native EUV mask defects. In this work, we performed a systematic study of native mask defects to understand the defect printability caused by them. The multilayer growth over native substrate mask blank defects was correlated to the multilayer growth over regular-shaped defects having similar profiles in terms of their width and height. To model the multilayer growth over the defects, a novel level-set multilayer growth model was used that took into account the tool deposition conditions of the Veeco Nexus ion beam deposition tool. The same tool was used for performing the actual deposition of the multilayer stack over the characterized native defects, thus ensuring a fair comparison between the actual multilayer growth over native defects, and modeled multilayer growth over regular-shaped defects. Further, the printability of the characterized native defects was studied with the SEMATECH-Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory (LBNL). Printability of the modeled regular-shaped defects, which were propagated up the multilayer stack using level-set growth model was studied using defect printability simulations implementing the waveguide algorithm. Good comparison was observed between AIT and the simulation results, thus demonstrating that multilayer growth over a defect is primarily a function of a defect’s width and height, irrespective of its shape. This would allow us to predict printability of the arbitrarily-shaped native EUV mask defects in a systematic and robust manner.

Evaluating printability of buried native extreme ultraviolet mask phase defects through a modeling and simulation approach

Abstract. Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of the native extreme ultraviolet (EUV) mask defects. In this work, we performed a systematic study of native mask defects to understand the defect printability they cause. The multilayer growth over native substrate mask blank defects was correlated to the multilayer growth over regular-shaped defects having similar profiles in terms of their width and height. To model the multilayer growth over the defects, a multilayer growth model based on a level-set technique was used that took into account the tool deposition conditions of the Veeco Nexus ion beam deposition tool. Further, the printability of the characterized native defects was studied at the SEMATECH-Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory. Printability of the modeled regular-shaped defects, which were propagated up the multilayer stack using level-set growth model, was studied using defect printability simulations implementing the waveguide algorithm. Good comparison was observed between AIT and the simulation results, thus demonstrating that multilayer growth over a defect is primarily a function of a defect’s width and height, irrespective of its shape.

30nm full field quartz template replicated from Si master for FLASH active layer NIL

38nm half pitch pattern was replicated from Si master pattern to quartz blank template. It is a novel approach different from typical quartz to quartz replication. This replication concept is expected to alleviate the burden not only in cost but also resolution for NIL template fabrication. In this study, full field Si master fabricated by ArF immersion lithography, UV-transparent hard mask for quartz blank template and core-out quartz blank template were applied to prove the concept. And the replica template was evaluated with NIL and subsequent etching.

New approach for quartz dry etching using hardmask for sub-90-nm photomask technology

Quartz dry etching is critical to realize the resolution enhancement technology (RET) mask, such as chromeless phase lithography (CPL) mask, alternating phase shift mask, and RIM type phase shift mask. Quartz etching is one of challenging processes in photomask manufacturing due to the absence of etch stopper. The requirements of quartz etching are sidewall angle, phase uniformity, depth linearity, and micro/macro loading effect in wide range of feature sizes. In this paper, we will discuss the improvement of quartz dry etching using Cr hardmask without any hardware modifications. We can control the tendency of phase uniformity across mask surface in convex or concave curvature with nearly vertical sidewall angle. Two-step quartz etching recipe, which consists of two kinds of sub-etching recipe, is introduced to meet the phase uniformity and quartz profile at the same time. We have optimized quartz dry etching with vertical sidewall angle, low depth uniformity, and low micro/macro loading effect.

New method for approaching the loading-free process for photomask Cr etching

In photomask manufacturing, etch loading effect is one of the most serious problems. The equal size of isolated clear patterns, each of which is surrounded by different pattern density, can show different CD (critical dimension) results after Cr etching process. Furthermore, as the feature size decreases and pattern density increase, the burden of Cr loading effect in mask fabrication is more enlarged than ever. In this paper, we will present the new method for approaching to the loading free process in photomask Cr dry etch.