Bifocal wave zone plate interference microscopic-inspection device based on phase grating light splitting

Abstract

The invention discloses a bifocal wave zone plate interference microscopic-inspection device based on phase grating light splitting. The bifocal wave zone plate interference microscopic-inspection device comprises a 13.5nm of n ultraviolet light source, a vacuum chamber, a vacuum air-extracting pump, an air floatation optical vibration isolation platform, an extreme ultraviolet CCD (Charge Coupled Device), a five-dimensional precision fine-adjustment platform, a five-dimensional precision fine-adjustment platform controller and a bifocal wave zone plate interference microscopic-optical assembly based on the phase grating light splitting. The bifocal wave zone plate interference microscopic-inspection device disclosed by the invention has the advantages of simple structure, good vibration resistance, high accuracy and low system cost.

Description

technical field [0001] The invention belongs to the field of optical interference detection, in particular to a bifocal zone plate interference microscopic detection device based on phase grating light splitting. Background technique [0002] Since the 1970s, the semiconductor industry has continuously reduced the size of the graphics in integrated circuits according to Moore's Law, making the number of transistors on the central processing unit (CPU) in the computer double every two years. . Extreme ultraviolet (EUV) lithography is aimed at the 15nm node as the next generation of advanced lithography technology, opening up a new way for the semiconductor industry to be faster, smaller and cheaper. However, through the difficult progress of EUV lithography technology, we can realize that the development of lithography technology is not just a lithography machine, but the cooperation and optimization of other links, such as the need for suitable photoresists and defect-free ...

AI Technical Summary

Problems solved by technology

The defects of extreme ultraviolet masks can be divided into two types: amplitude type defects and phase type defects. The amplitude type defects are generally located on the surface of the Mo / Si multilayer film, and the phase type defects are hidden deep inside the Mo / Si multilayer film. Therefore, the phase type defects Defects are more difficult to detect with traditional microscopy, which also poses challenges for EUV mask defect detection

The main problem of this solution is that only the structural lines of the wider defects buried under the multilayer film can be detected, while the narrower lines are imaged, and the resulting image is larger than the width of the actual defect lines

Francesco Cerrina and others proposed an indirect detection method in the invention patent "Defect inspection of extreme ultraviolet lithography masks and the like" (patent number: US7179568 B2), the main principle of which is: extreme ultraviolet light is irradiated to a blank mask On the surface, the extreme ultraviolet light reflected by the blank mask is incident on an auxiliary detection plate coated with photoresist. The photoresist coated on the auxiliary detection plate contains fluorescent dyes. If the detected mask contains phase type or For amplitude defects, due to the scattering of the detection light by the defects, the exposure of the photoresist at the position corresponding to the defect on the auxiliary detection plate is insufficient, and the underexposed photoresist cannot be removed in the next development, and the fluorescent excitation light source is used After irradiating the developed auxiliary detection plate, the fluorescence emitted by the underexposed photoresist can be observed with an ordinary microscope, so as to determine the number and location of defects. This method is complicated, time-consuming, and expensive to detect. Defect size and depth information

In the article "Microscopy of extreme ultraviolet lithography masks with 13.2nm tabletop laser illumination" (OPTICS LETTERS,34(3):271-273,2009), F.Brizuela et al. proposed a transmission-type zone plate micro-magnification scheme. The system uses a light source with a wavelength of 13.2nm, and a hollowed-out zone plate concentrating illumination mask. The converging light is incident at an incident angle of 6°, and the light beam reflected from the mask passes through an off-axis zone plate (0.0625NA) to illuminate the image. Projected directly into the extreme ultraviolet CCD, the magnification is 660 times. The disadvantage of this system is that the energy utilization rate of the transmission zone plate is low. It is still a traditional imaging method and is not sensitive to phase defects.

Tetsuo Harada et al proposed a mask for coherent scattering imaging in "Mask observation results using a coherent extreme ultraviolet scattering microscope at NewSUBARU" (Journal of Vacuum Science & Technology B, 27(6): 3203-3207, 2009) Defect detection system, which adopts the diffraction conduction theory of mirrorless imaging. By recording the pattern of scattered and diffracted beams, the far-field pattern can be used to reconstruct the amplitude and phase information of the electric field intensity and restore the surface morphology of the mask. This system eliminates all Reflectors reduce system cost, but this solution has complex algorithms and unreliable defect information

CHUANG et al. published a four- to eight-piece reflective spherical or Aspherical optical elements constitute a microscopic detection scheme for extreme ultraviolet mask defects. This scheme adds an electronic amplification system on the basis of optical microscopic amplification, so it has certain advantages in overall magnification and can detect small defects. , but this solution uses multi-reflective extreme ultraviolet optical spherical and aspheric surfaces, which is difficult to process and high in manufacturing costs. At the same time, this solution belongs to the traditional microscopic amplification method and is not sensitive to phase defects.

Gao Zhishan, Wang Shuai and others invented a bifocal zone plate-based interference in the invention patent "Double-focal oblique-incidence interference microscopy device for extreme ultraviolet lithography mask defect detection" (application number: 201310069314.2) The microscopic device, which works under the extreme ultraviolet light of 13.5nm, uses the oblique-incidence interference microscopic characteristics of the bifocal zone plate to transfer the phase-type defect information in the EUV mask to the interferogram, and at the same time transfer the amplitude-type defect information to the interferogram. The defect or the physical deformation caused by it is enlarged and imaged, and the defect in the EUV mask is detected by solving the interferogram and identifying the microscopic image. The device uses reflective and diffractive optical elements. Compared with the multi-chip reflective system, The number of extreme ultraviolet reflective elements is reduced, it is sensitive to EUV mask phase defects, the algorithm is simple, and the reliability is high. However, the system uses two double-curvature surface mirrors and two bifocal zone plate interference microscope objectives. The angle requirements between the four mirrors are high, and the installation and adjustment of the system is difficult, and the device adopts oblique incidence and defocused lighting, which is limited in defect positioning accuracy and resolution.

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