In this editorial, the co-editors-in-chief outline the journal’s new direction.

We review the history in connection with the resolution formula of microlithography and argue that it was Abbe rather than Rayleigh who definitively stated the 0.5λNA resolution limit for the minimum pitch first, using an approach more relevant to projection imaging, and hence, this expression should be more appropriately referred to as the Abbe formula for the resolution of a projection imaging system.

Next-generation extreme ultraviolet (EUV) systems with numerical apertures of 0.55 have the potential to provide sub-8-nm half-pitch resolution. The increased importance of stochastic effects at smaller feature sizes places further demands on scanner and mask to provide high contrast images. We use rigorous mask diffraction and imaging simulation to understand the impact of the EUV mask absorber and to identify the most appropriate optical parameters for high NA EUV imaging. Simulations of various use cases and material options indicate two main types of solutions: high extinction materials, especially for lines spaces, and low refractive index materials that can provide phase shift mask solutions. EUV phase masks behave very different from phase shift masks for DUV. Carefully designed low refractive index materials and masks can open up a new path toward high contrast edge printing.

Background: To increase the resolution and depth of focus (DOF) of flat panel display (FPD) exposure systems, off-axis illumination (OAI) conditions are used extensively. OAI using narrowband wavelength illumination has been studied sufficiently. In contrast, new techniques that consider broadband wavelength illumination are needed because the effects of OAI differ between broadband and narrowband illumination.

Aim: This paper presents a divided spectrum illumination (DSI), a new design concept that achieves both high resolution and a large DOF.

Approach: The source wavelength is optimized according to the illumination angle.

Results: Experimental imaging results for line and space patterns with a line width of 1.0 and a pitch of 2.0  μm demonstrate that the DSI design provides improved resolution. Exposure results also indicate that resist profiles using DSI are sufficiently sharp to retain pattern fidelity at the top of the resist. The DOF with DSI is also improved by 21% compared to that obtained with traditional OAI.

Conclusions: DSI achieves both high resolution and a large DOF while maintaining high productivity.

Background: Conventional scanning electron microscopy (SEM) that is used for 2D top-view metrology, a classical line edge roughness (LER) measurement technique, is incapable of measuring 3D structures of a nanoscale line pattern. For LER measurements, SEM measurement generates a single line-edge profile for the 3D sidewall roughness, although the line-edge profile differs at each height in the 3D sidewall.

Aim: To develop an evaluation method of SEM-based LER measurement techniques and to verify how the 3D sidewall shape is reflected in the SEM’s 2D result.

Approach: Direct comparison by measuring an identical location of a line pattern by SEM and an atomic force microscopy (AFM) with the tip-tilting technique that is capable of measuring the 3D sidewall. The line pattern has vertical stripes on the sidewall due to its fabrication process. Measured line edge profiles were analyzed using power spectral density, height-height correlation function, and autocorrelation function.

Results: Line edge profiles measured by SEM and AFM were well matched except for noise level. Frequency and scaling analyses showed that SEM profile contained high noise and had lost a property of self-affine fractals in contrast to AFM.

Conclusions: In the case of the line pattern with vertical stripes on the sidewall, SEM profile is generally consistent with 3D sidewall shape. The AFM-based LER measurement technique is useful as LER reference metrology to evaluate other LER measurement techniques.

Background: Although the wet cleaning process has been widely used in semiconductor device manufacturing due to its convenience, it faces theoretical limits. That is, when the size of the objected particle is smaller than 100 nm, it is buried in the stagnant layer where there is substantially no fluid flow.

Aim: Only small particles below the stagnant layer (<100  nm) is removed without any damage to the fine patterns or substrate: pattern collapse, critical dimension shift, and optical property shift.

Approach: Utilizing unique characteristics of water: volume expansion when freezing, solid (ice) is lighter than liquid (water), and particles adhered the substrate is peeled off from the substrate and rise to the water surface along with the surrounding ice.

Results: By repeating the cycle of cooling, thawing, and rinsing, polystyrene sphere particle of 80 nm in diameter can be removed with high particle removal efficiency (PRE >90  %  ) and no negative influences on the pattern or substrate.

Conclusions: A new cleaning method for very small (<100  nm) particles is proposed with high PRE and low damage. This method is thought to be applied to every process if water can infiltrate into the gap between the particles and the substrate.