Phase Imaging of Extreme-Ultraviolet Mask Using Coherent Extreme-Ultraviolet Scatterometry Microscope

Abstract

Phase-shifting masks were developed for extreme ultraviolet (EUV) lithography to enlarge the process window, and some researchers developed mask phase defect compensation methods adopting absorber pattern modification. To evaluate these small phase structures, a phase-imaging microscope is required. For actinic phase imaging, we have developed a coherent EUV scatterometry microscope (CSM) based on a coherent diffraction imaging method. The image-forming optics are replaced by an inverse computation, where the frequency space phase data are retrieved. Therefore, the aerial image phase data are also reconstructed. The CSM thus observes the intensity and phase image. We improved the reconstruction algorithm by which the illumination probe was simultaneously reconstructed; phase images of a crossed line pattern, an 88 nm line-and-space pattern, and a phase defect were reconstructed quantitatively. The CSM will be helpful for phase-shift mask development and phase defect compensation.

Tabletop nanometer extreme ultraviolet imaging in an extended reflection mode using coherent Fresnel ptychography

“…A few successful demonstrations have applied CDI to reflection-mode imaging. However, work to date has either been limited to highly reflective EUV lithography masks in a normal incidence geometry [8], restricted to low numerical aperture through the use of a transmissive mask [9], or restricted to isolated objects [10,11].…”

Quantitative Chemically Specific Coherent Diffractive Imaging of Reactions at Buried Interfaces with Few Nanometer Precision

“…In particular, by combining coherent, short-wavelength beams from either high harmonic generation (HHG) [10] or X-ray free electron lasers (XFELs) [11] with coherent diffractive imaging (CDI) [12][13][14][15], it is now possible to reach near-wavelength resolution imaging in the EUV and X-ray regions for the first time [16,17]. Accordingly, CDI has found a range of applications in transmission and reflection geometries [18][19][20] to investigate nanoscale strain [21,22], semiconductor structures [18], and for biological imaging [23][24][25]. EUV/X-ray CDI can be non-destructive and suffers no charging effects or resolution loss with depth.…”

Phase defect characterization on an extreme-ultraviolet blank mask using microcoherent extreme-ultraviolet scatterometry microscope

“…[16][17][18][19][20] The sample phase defect was exposed using coherent EUV light, and the diffracted light was recorded using a CCD camera. To reconstruct the pattern image, the phase information of the diffraction image is required, but this information is not recorded.…”

“…17 In addition to the conventional intensity images, the phase images were also acquired by the coherent EUV scatterometry microscope (CSM). 20 The EUV-phase shift value of an absorber structure and the phase difference in the L/S pattern with shadowing effects were evaluated, because they could cause actinic critical-dimension changes. The phase distribution of a 1 lm square-sized phase defect was also reconstructed, from which the phase value was quantitatively evaluated.…”

“…The phase distribution of a 1 lm square-sized phase defect was also reconstructed, from which the phase value was quantitatively evaluated. 20 This EUV-phase distribution is the basic information required to predict defect printability at the EUV exposure tools. Because the defect shape on a glass substrate is different to the defect shape on a multilayer surface, the conventional atomic force microscope (AFM) tool cannot be used to evaluate the printability.…”