CN-122029486-A - Laser diffraction optical microscopy for ultra-thin pattern wafers

CN122029486ACN 122029486 ACN122029486 ACN 122029486ACN-122029486-A

Abstract

An optical microscope is provided for inspecting patterns in an electron beam inspection system or performing wafer alignment in an ultra-thin photoresist layer on a semiconductor substrate. The optical microscope may include a laser configured to generate diffracted light in the microscope objective lens. The optical microscope may be capable of generating an optical image of the latent image pattern in the ultra-thin photoresist.

Inventors

YE NING
ZHANG JIAN
ZHANG YOUSHENG
KANG ZHIWEN

Assignees

ASML荷兰有限公司

Dates

Publication Date: 20260512
Application Date: 20240917
Priority Date: 20231017

Claims (15)

1. An optical microscope, comprising: An objective system comprising a first objective; Image sensor, and An off-axis illumination system comprising a first laser configured to radiate a pattern on a substrate with a first laser beam to produce a first diffracted light, wherein The objective lens is configured to collect the first diffracted light, and The optical microscope is configured to generate an image of the pattern on the image sensor using the first diffracted light.
2. The optical microscope of claim 1, further comprising: A coaxial illumination system comprising a light source configured to radiate the substrate with a beam from the objective lens system.
3. The optical microscope of claim 2, wherein: The objective system includes a second objective lens, the first objective lens having a first numerical aperture and the second lens having a second numerical aperture, and The first numerical aperture is smaller than the second numerical aperture.
4. The optical microscope of claim 2, wherein the coaxial illumination system is configured to radiate the substrate with the beam from the first objective lens of the objective lens system.
5. The optical microscope of claim 2, further comprising: An optical element configured to: Directing the light beam to the objective lens system; receiving the light beam from the objective system, and The first diffracted light is received from the objective lens system.
6. The optical microscope of claim 1, wherein the off-axis illumination system further comprises: a barrel mount configured to mount the first laser to a frame of the optical microscope, the barrel mount comprising an adjuster configured to adjust one of an axial height, an inclination angle, or an azimuth angle of the first laser.
7. The optical microscope of claim 6, wherein the off-axis illumination system further comprises: a second laser, wherein the barrel mount is configured to mount the second laser to the frame of the optical microscope.
8. The optical microscope of claim 1, wherein the first laser beam comprises wavelengths in the visible spectrum.
9. The optical microscope of claim 1, wherein the first laser is configured to generate the first diffracted light by irradiating a pattern in a latent image in a resist layer.
10. The optical microscope of claim 9, wherein the resist layer has a thickness of 20nm a or less.
11. The optical microscope of claim 9, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of between 800 nm and 10 μιη.
12. The optical microscope of claim 1, further comprising a controller configured to control the optical microscope to perform operations comprising: Emitting the first laser beam from a first azimuth angle to generate the first diffracted light; Collecting the first diffracted light by the first objective lens; Emitting a second laser beam from a second azimuth angle to generate a second diffracted light; collecting the second diffracted light by the first objective lens, and An optical microscope image is generated based on one of the first diffracted light and the second diffracted light.
13. The optical microscope of claim 12, further comprising: a second laser, wherein emitting the second laser beam at the second azimuth angle includes emitting the second laser beam from the second laser.
14. The optical microscope of claim 12, further comprising: An adjustable optical element, wherein emitting the second laser beam at the second azimuth angle includes emitting the second laser beam from the first laser and directing the second laser beam to the substrate via the adjustable optical element.
15. A non-transitory computer-readable medium storing a set of instructions executable by at least one processor of an apparatus to cause the apparatus to perform operations comprising: Emitting a first laser beam from a first laser of an off-axis illumination system from a first azimuthal angle toward the substrate to produce a first diffracted light; collecting the first diffracted light by a first objective lens of an optical microscope; Emitting a second laser beam from a second azimuth angle to generate a second diffracted light; collecting the second diffracted light by the first objective lens, and An optical microscope image is generated based on one of the first diffracted light and the second diffracted light.

Description

Laser diffraction optical microscopy for ultra-thin pattern wafers Cross Reference to Related Applications The present application claims priority from U.S. application 63/590,919 filed on 10/17 2023, which is incorporated herein by reference in its entirety. Technical Field The description herein relates to methods and apparatus for inspecting a surface of a substrate, and in particular to methods and apparatus for inspecting an ultra-thin resist layer on a substrate using an optical microscope. Background A photolithographic process is a process that applies a desired pattern onto a substrate, typically onto a target portion of the substrate. The lithographic apparatus may be used, for example, in the manufacture of Integrated Circuits (ICs). In this case, a patterning device (which is alternatively referred to as a mask or a reticle) may be used to generate a circuit pattern to be formed on an individual layer of the IC. The pattern may be transferred onto a target portion (e.g., a portion including one or more dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. A step or scan movement may be involved to repeat the pattern at successive target portions across the substrate. The pattern may also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate. To enhance the yield of semiconductor processes, defects must be identified as soon as possible to mitigate the effects of such defects. The optical microscope may be used in conventional optical inspection (including bright field inspection and dark field inspection). For example, an optical microscope may utilize a light beam to scan each die on a wafer, and an image of each die may be generated and stored. Inter-die (D2D), die-to-database (D2 DB), or other comparisons may be used to identify any anomalies or defects in the image. Optical microscopy can be used to image finished or intermediate structures on a wafer. For example, an optical microscope may scan the exposed resist layer to identify defects in the latent image prior to a development step or other post-exposure operation. Inspection systems using optical microscopy typically have resolutions as low as hundreds of nanometers, and the resolution is limited by the wavelength of the light. As the physical dimensions of IC components continue to decrease below 100 nanometers or even below sub-10 nanometers, inspection systems with higher resolution than systems utilizing optical microscopy are needed. For example, the inspection may be performed using a Scanning Electron Microscope (SEM) or other charged particle inspection device. Nevertheless, optical microscopy may be useful in photolithographic processes. For example, an optical microscope may be used to quickly locate a region of interest on a substrate using its relatively large field of view. A higher resolution examination apparatus such as an SEM may then examine the region of interest. Furthermore, the optical microscope may be used in, for example, an alignment operation. Disclosure of Invention Some embodiments of the present disclosure provide an optical microscope. The optical microscope may include an objective system including a first objective lens, an image sensor, and an off-axis illumination system including a first laser configured to radiate a pattern on a substrate with a first laser beam to produce a first diffracted light, wherein the objective lens is configured to collect the first diffracted light, and the optical microscope is configured to generate an image of the pattern on the image sensor using the first diffracted light. Some embodiments of the present disclosure provide methods. The method may include emitting a first laser beam from a first azimuth angle toward a substrate to generate a first diffracted light, collecting the first diffracted light by a first objective lens of an optical microscope, emitting a second laser beam from a second azimuth angle to generate a second diffracted light, collecting the second diffracted light by the first objective lens, and generating an optical microscope image based on one of the first diffracted light and the second diffracted light. Some embodiments of the present disclosure provide a non-transitory computer readable medium. The non-transitory computer readable medium may store a set of instructions executable by at least one processor of an apparatus to cause the apparatus to perform operations comprising the above-described method. Drawings The above aspects and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments given in connection with the accompanying drawings. FIG. 1 illustrates an example lithographic apparatus consistent with embodiments of the present disclosure. FIG. 2 illustrates an example lithography unit consistent with embodime