A light-shieldable film (12) is formed on one principal plane of an optically transparent substrate (11), and the light-shieldable film (12) has a first light-shieldable film (13) and a second light-shieldable film (14) overlying the first light-shieldablefilm (13). The first light-shieldable film (13) is a film that is not substantially etched by fluorine-based(F-based)dry etching and is primarily composed of chromium oxide, chromium nitride, chromium oxynitride or the like. The second light-shieldable film (14) is a film that is primarily composed of a silicon-containing compound that can be etched by F-based dry etching, such as silicon oxide, silicon nitride, silicon oxynitride, silicon/transition-metal oxide, silicon/transition-metal nitride or silicon/transition-metal oxynitride.

Photomask blank, photomask and fabrication method thereof

Optical immersion lithography utilizes liquids with refractive indices >1 (the index of air) below the last lens element to enhance numerical aperture and resolution, enabling sub-40-nm feature patterning. This shift from conventional dry optical lithography introduces numerous challenges requiring innovations in materials at all imaging stack levels. In this article, we highlight the recent materials advances in photomasks, immersion fluids, topcoats, and photoresists. Some of the challenges encountered include the fluids’ and photomask materials’ UV durability, the high-index liquids’ compatibility with topcoats and photoresists, and overall immersion imaging and defectivity performance. In addition, we include a section on novel materials and methods for double-patterning lithography—a technique that may further extend immersion technology by effectively doubling a less dense pattern’s line density.

/pdf/immersion-lithography-photomask-and-wafer-level-materials-29k58rswaw.pdf

Immersion Lithography: Photomask and Wafer-Level Materials

PROBLEM TO BE SOLVED: To provide a photomask having a fine photomask pattern formed thereon with high precision, and also to provide a photomask blank for the photomask. SOLUTION: A light-shieldable film 12 is formed on one principal plane of an optically transparent substrate 11, wherein the light-shieldable film 12 comprises a first light-shieldable film 13 and a second light-shieldable film 14 successively layered. The first light-shieldable film 13 is a film that is not substantially etched by fluorine-based (F-based) dry etching and is primarily composed of chromium oxide, chromium nitride, chromium oxynitride or the like. The second light-shieldale film 14 is the film that is primarily composed of a silicon-containing compound that can be etched by F-based dry etching, such as silicon oxide, silicon nitride, silicon oxynitride, silicon/transition-metal oxide, silicon/transition metal nitride or silicon/transition metal oxynitride. The silicon-containing compound has a composition of 10 to 95 at% silicon, 0 to 60 at% oxygen, 0 to 57 at% nitrogen, and 0 to 35 at% transition metal, and the transition metal is, for example, molybdenum (Mo). COPYRIGHT: (C)2006,JPO&NCIPI

Photomask blank, photomask and method for manufacturing the same

Thermal scanning probe lithography is used for creating lithographic patterns with 27.5 nm half-pitch line density in a 50 nm thick high carbon content organic resist on a Si substrate. The as-written patterns in the poly phthaladehyde thermal resist layer have a depth of 8 nm, and they are transformed into high-aspect ratio binary patterns in the high carbon content resist using a SiO2 hard-mask layer with a thickness of merely 4 nm and a sequence of selective reactive ion etching steps. Using this process, a line-edge roughness after transfer of 2.7 nm (3σ) has been achieved. The patterns have also been transferred into 50 nm deep structures in the Si substrate with excellent conformal accuracy. The demonstrated process capabilities in terms of feature density and line-edge roughness are in accordance with today’s requirements for maskless lithography, for example for the fabrication of extreme ultraviolet (EUV) masks.

Thermal Probe Maskless Lithography for 27.5 nm Half-Pitch Si Technology

PROBLEM TO BE SOLVED: To provide a halftone type phase shift mask on which a fine photomask pattern is formed with high accuracy, and to provide a mask blank for producing the above mask. SOLUTION: A semitransparent film 15 having a predetermined phase shift and transmittance to exposure light and a light shielding film 12 placed on the semitransparent film 15 are disposed on one principal face of a transparent substrate 11 such as quartz as a photomask substrate. The light shielding film 12 is surely a so-called "light shielding film" but it can also act as an antireflection film. The semitransparent film 15 is a halftone phase shift layer comprising a halftone material containing both of silicon (Si) and molybdenum (Mo) as an absorbent material. In order to use the halftone phase shift mask blank for producing a mask for ArF exposure, the film thickness and composition of the light shielding film 12 are selected to obtain the optical density OD of the film in the range of 1.2 to 2.3 with respect to light at 193 or 248 nm wavelength. COPYRIGHT: (C)2007,JPO&INPIT

Phase shift mask blank, phase shift mask, and method for manufacturing the same

PROBLEM TO BE SOLVED: To provide a halftone phase shift mask blank in which the transmittance can be easily controlled without varying phase difference by controlling the refractive index of the transmittance controlling layer to a desired value in a shifter layer comprising a phase difference controlling layer and the transmittance controlling layer, and a halftone phase shift mask. SOLUTION: The halftone phase shift mask blank 10 has the shifter layer 4 comprising the transmittance controlling layer having the refractive index n satisfying 0.9≤n≤1.1 and the extinction coefficient k satisfying 1.0<k and the phase difference controlling layer 3 having the phase difference controlled to 180, on a transparent substrate 1. A resist pattern 5 is formed on the halftone phase shift mask blank 10, the shifter layer 4 is patterned by dry etching or the like, and the resist pattern 5 is removed to obtain the halftone phase shift mask 100 having the shift pattern 4a comprising a transmittance controlling pattern 2a and a phase difference controlling pattern 3a. COPYRIGHT: (C)2004,JPO&NCIPI

Halftone phase shift mask blank, and halftone phase shift mask

Extreme Ultraviolet Lithography (EUVL) is the leading candidate for next generation lithography. EUVL has good
resolution because of the shorter wavelength (13.5nm). EUVL also requires a new and complicating mask structure. The
blank complexity and substrate polishing requirements result in defects that are difficult to eliminate or repair. Due to
these challenges, shifting the pattern so that absorber covers the multilayer defects is one option for mitigating the
multilayer defect problem. We investigated the capability and effectiveness of pattern shifting using authentic layouts.
The rough indication of, “how many of what size defects are allowable”, is shown in this paper based on the margin for
the 11nm HP pattern. Only the twenty 300nm-sized defects are allowable for current location accuracy of the blank
inspection and writing tools. On the other hand, sixty70nm-sized defects are allowable for the improved location
inaccuracy. Furthermore we exercised the full process for pattern shift using a leading-edge 50 keV e-beam writer to
confirm feasibility and it was successfully performed.

Using pattern shift to avoid blank defects during EUVL mask fabrication

The line-edge roughness (LER) of a photomask image has a measurable impact on the corresponding printed wafer LER. This impact increases as wafer exposures move from 193nm DUV to 13.5nm EUV wavelengths since the imaging tool is a low-pass filter with EUV passing more spatial frequencies. Even the high frequency mask LER may impact the wafer image by lowering its image log-slope (ILS). Studying the magnitude and frequency content of mask LER is a first step to reducing the wafer LER. The next step is to determine which components of mask line roughness actually contribute to the wafer line roughness. Order is imposed on this study by fabricating programmed LER patterns on an EUV mask to introduce controlled variations in LER spatial frequency and magnitude. More specifically, line-width roughness (LWR), LER and power spectral density (PSD) are extracted from 64nm and 90nm (1X) pitch lines on a programmed LER EUV photomask. The same mask is then exposed on the ASML EUV Alpha Demo Tool (ADT) at best focus and dose. Three chemically amplified EUV photoresists are evaluated using the programmed LER photomask through PSD and LWR comparisons and the highest performance resist is used for a comprehensive LER transfer analysis. Wafer LWR is extracted from 64nm and 90nm pitch lines and correlated back to the base mask patterns revealing an empirical LWR transfer function (LTF). Finally, the study is extended to 45nm (1X) pitch lines by deploying a pupil filter on the ADT to explore the effect on LWR as the feature sizes shrink.

https://www.sas.upenn.edu/~zjq/SPIE_8522-96.pdf

Impact of EUV photomask line-edge roughness on wafer prints

Alternating Aperture Phase Shift Mask (AAPSM) is one of the most effective approaches to improve the resolution of 
logic gate structures for ArF lithography of the 65nm half-pitch node and beyond because AAPSM shows good 
performance due to the high image contrast and the small mask error enhancement factor (MEEF). 
For AAPSM, the issue of intensity imbalance between pi-space and zero-space is well known. In order to solve this 
issue, several kinds of AAPSM, such as single trench with undercut, single trench with bias are used in production 
application. 
The fabrication of single trench with bias AAPSM requires that the quartz dry etch satisfies many conditions. The 
etched quartz features must not only show excellent depth uniformity but also good etch depth linearity across a wide 
range of feature sizes. However, in defocus conditions, the through-pitch image placement error becomes worse even 
with good quartz etch depth linearity. The reason is that the phase error caused by mask topography is different 
depending on the pitch. 
In this work, we minimize the phase error through-pitch and through-focus by rigorous 3D mask simulations. Based 
on the results, we have fabricated two masks with opposite quartz depth linearity signatures to estimate the imaging 
impact of phase errors and used them for exposures on an ASML XT:1250Di immersion scanner. We discuss the 
feasibility of this method by comparison of through-focus and through-pitch image placement errors between wafer 
printing, AIMS, and simulation.

Through-pitch and through-focus characterization of AAPSM for ArF immersion lithography

PROBLEM TO BE SOLVED: To provide a phase shift mask having a simple structure which requires neither recessed part on a substrate surface nor multilayer film structure and manufacturing steps of which are not increased, in the phase shift mask which inverts a phase difference between transmission light passing through a recessed part formed on a substrate surface and transmission light adjacent to it, and to provide a method for manufacturing the phase shift mask and a method for transferring a pattern. SOLUTION: The phase shift mask has a refractive index varied portion in a transparent substrate, which generates 180° phase difference between transmission light passing through in the refractive index varied portion and transmission light passing through the transparent substrate. By the method for manufacturing a phase shift mask, the refractive index varied portion in the transparent substrate is formed by converging laser light into the position in the transparent substrate to induce laser ablation to produce a high-density portion or a hole. COPYRIGHT: (C)2006,JPO&NCIPI

Toshio Konishi

Papers

Halftone phase shift mask blank, and halftone phase shift mask

Using pattern shift to avoid blank defects during EUVL mask fabrication

Impact of EUV photomask line-edge roughness on wafer prints

Through-pitch and through-focus characterization of AAPSM for ArF immersion lithography

Phase shift mask, its manufacturing method, and method for transferring pattern