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CN-117007286-B - Focal plane measuring device

CN117007286BCN 117007286 BCN117007286 BCN 117007286BCN-117007286-B

Abstract

The invention provides a focal plane measuring device, which comprises an objective lens, a reflection module, a modulator, a photoelectric detector, a mixer, a low-pass filter, a signal processor and a signal processor, wherein the objective lens images an illumination light beam to the surface of an object to be measured and transmits a reflection light beam generated by reflecting the illumination light beam by the object to be measured, the reflection module receives and transmits the reflection light beam and focuses the reflection light beam, the modulator modulates the reflection module to form a modulated reflection light beam and outputs a signal of which a modulation source is subjected to phase shift, the photoelectric detector receives the modulated reflection light beam and outputs a light intensity signal, the mixer mixes the light intensity signal and the signal of which the modulation source is subjected to phase shift and outputs a mixing signal, the low-pass filter filters the mixing signal and outputs a demodulation signal, and the signal processor detects the demodulation signal and determines the defocus amount of the object to be measured according to the intensity of the demodulation signal. The focal plane measuring device can measure the defocus amount of the object to be measured by only using a single photoelectric detector, and can reduce the installation difficulty and reduce the influence of dark current on a measuring result.

Inventors

  • Ouyang Xinchuan

Assignees

  • 上海微电子装备（集团）股份有限公司

Dates

Publication Date
20260508
Application Date
20220427

Claims (10)

  1. 1. A focal plane measuring device, comprising: An illumination source for providing an illumination beam; the objective lens is used for imaging the illumination beam to the surface of the object to be detected and transmitting a reflected beam generated by reflecting the illumination beam by the object to be detected; the reflection module is used for receiving and transmitting the reflected light beam and focusing the reflected light beam; A modulator for applying modulation to the reflection module to change an optical path length of an optical path so that a reflected light beam passing through becomes a modulated reflected light beam, and outputting a signal of a modulated source after phase shift; The photoelectric detector is used for receiving the modulated reflected light beam output by the reflecting module and outputting a light intensity signal; the frequency mixer is used for receiving the light intensity signal and the signal of the modulation source after phase shifting, mixing the light intensity signal and the signal of the modulation source after phase shifting and outputting a mixed signal; A low-pass filter for filtering the mixed signal and outputting a demodulation signal, and And the signal processor is used for detecting the demodulation signal and determining the defocus amount of the object to be detected according to the intensity of the demodulation signal.
  2. 2. The focal plane measuring device of claim 1, wherein the reflection module comprises a focusing lens, a first aperture diaphragm and a second aperture diaphragm, wherein the reflected light beam is focused between the first aperture diaphragm and the second aperture diaphragm after being processed by the focusing lens, and the reflected light beam irradiates the photodetector after passing through the first aperture diaphragm and the second aperture diaphragm.
  3. 3. The focal plane measurement device of claim 2, wherein the modulator applies modulation to the focusing lens or the modulator applies modulation to the first aperture stop and the second aperture stop simultaneously.
  4. 4. The focal plane measuring device of claim 2, wherein the reflecting module comprises a second beam splitter prism and a first reflecting mirror, wherein the reflected light beam passes through the second beam splitter prism after passing through the focusing lens, irradiates the first reflecting mirror, is reflected by the first reflecting mirror, then is reflected by the second beam splitter prism, and then is reflected by the second beam splitter prism to the first aperture stop.
  5. 5. The focal plane measurement device of claim 4, wherein the modulator applies modulation to the first mirror.
  6. 6. The focal plane measurement device of claim 2, wherein the reflection module includes a second mirror, the reflected light beam is reflected by the second mirror and impinges on the focusing lens, and the modulator applies modulation to the second mirror.
  7. 7. The focal plane measuring device of claim 1, wherein the demodulation signal satisfies a formula Wherein S is a demodulation signal, x 0 is the defocus of an object to be measured at any position, I (x 0 ) is the intensity of a reflected light beam generated by reflection of the object to be measured at any position, x m is the modulation depth of the reflected light beam, A is the modulation depth of a signal after phase shifting of a modulation source, phi 0 is the initial phase of the modulated reflected light beam, and phi is the initial phase of the signal after phase shifting of the modulation source.
  8. 8. The focal plane measurement device of claim 7, wherein the modulator includes a phase shifter for adjusting an initial phase of the modulated reflected beam such that the demodulated signal satisfies a formula 。
  9. 9. The focal plane measuring apparatus according to claim 1, wherein the focal plane measuring apparatus includes a work stage, and the signal processor has a focal plane feedback loop for adjusting a position of the work stage according to a focal plane compensation amount and a defocus amount of the object to be measured which is tested by the signal processor.
  10. 10. The focal plane measuring apparatus according to claim 1, wherein the objective lens is provided with a piezoelectric driver, and the signal processor has a focal plane feedback loop that controls the piezoelectric driver according to a focal plane compensation amount and a defocus amount of the object to be measured obtained by the signal processor to adjust a focal length of the objective lens.

Description

Focal plane measuring device Technical Field The invention relates to the technical field of focal plane measurement, in particular to a focal plane measurement device. Background A lithographic apparatus is a machine that transfers a target pattern onto a substrate that is coated with a radiation-sensitive material, such as a photoresist. In integrated circuit fabrication, it is necessary to transfer different patterns onto different layers of a substrate to achieve a particular function. The overlapping of the different layers of the substrate is called overlay, and the quality of the overlay can affect the performance of the chip. There is therefore a need to use a metrology device to manage overlay in a lithographic process. In order to enable the measuring device to accurately measure the overlay of the object to be measured, the area to be measured of the object to be measured needs to be located on the focal plane of the objective lens, and focal plane locking of the object to be measured is achieved by adjusting the relative position of the objective lens or the object to be measured, and the focal plane locking precision of the object to be measured depends on the measurement precision of the defocus amount of the object to be measured. FIG. 1 is a schematic diagram of a focal plane measuring device. As shown in fig. 1, in the focal plane measuring apparatus, an illumination spot is imaged on the surface of an object to be measured 525 through a lens 510, a beam splitter 515 and an objective lens 520, and the spot reflected by the object to be measured 525 is split by a beam splitter 530 and transferred to an aperture 535 and an aperture 540 after passing through the objective lens 520 and the beam splitter 515, and photodetectors 545 and 550 measure optical signals passing through the aperture 535 and the aperture 540, respectively. Fig. 2 is a schematic diagram of confocal differential signals obtained by testing by the focal plane measuring device of fig. 1. As shown in fig. 2, confocal differential signal 580 is generated using signal 560 from the combination of aperture 535 and photodetector 545 and signal 570 from the combination of aperture 540 and photodetector 550, and confocal differential signal 580 is used to obtain the defocus of the test object (defocus). However, when the focal plane measuring device measures the defocus amount of the object to be measured, two photodetectors are required to be symmetrically installed, and the confocal differential signal is generated by relying on the optical signals measured by the two photodetectors, so that the requirement on the installation precision of the two photodetectors is high, and the influence of dark current on the measurement precision of the defocus amount of the object to be measured can be increased by the two photodetectors. Disclosure of Invention The invention provides a focal plane measuring device which can measure the defocus amount of an object to be measured by using a single photoelectric detector, can reduce the installation difficulty and the influence of dark current of the photoelectric detector on a measuring result, and is beneficial to improving the measuring precision of the defocus amount of the object to be measured. In order to achieve the above object, a focal plane measuring apparatus of the present invention includes: An illumination source for providing an illumination beam; the objective lens is used for imaging the illumination beam to the surface of the object to be detected and transmitting a reflected beam generated by reflecting the illumination beam by the object to be detected; the reflection module is used for receiving and transmitting the reflected light beam and focusing the reflected light beam; A modulator for applying modulation to the reflection module to change an optical path length of an optical path so that a reflected light beam passing through becomes a modulated reflected light beam, and outputting a signal of a modulated source after phase shift; The photoelectric detector is used for receiving the modulated reflected light beam output by the reflecting module and outputting a light intensity signal; the frequency mixer is used for receiving the light intensity signal and the signal of the modulation source after phase shifting, mixing the light intensity signal and the signal of the modulation source after phase shifting and outputting a mixed signal; A low-pass filter for filtering the mixed signal and outputting a demodulation signal, and And the signal processor is used for detecting the demodulation signal and determining the defocus amount of the object to be detected according to the intensity of the demodulation signal. Optionally, the reflection module comprises a focusing lens, a first aperture diaphragm and a second aperture diaphragm, the reflection light beam is focused between the first aperture diaphragm and the second aperture diaphragm after being processed by the fo