Application of Laser Heterodyne Interference Technology in Lithography

Zhiping Zhang; Xiaofeng Yang

doi:10.3788/LOP202259.0922017

Journals >Laser & Optoelectronics Progress >Volume 59 >Issue 9 >Page 0922017 > Article

Laser & Optoelectronics Progress
Vol. 59, Issue 9, 0922017 (2022)

Application of Laser Heterodyne Interference Technology in Lithography

Zhiping Zhang^* and Xiaofeng Yang

Author Affiliations

Shanghai Engineering Research Center of Ultra-Precision Motion Control and Measurement, Academy for Engineering and Technology, Fudan University, Shanghai , 201203, China

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DOI: 10.3788/LOP202259.0922017 Cite this Article Set citation alerts

Zhiping Zhang, Xiaofeng Yang. Application of Laser Heterodyne Interference Technology in Lithography[J]. Laser & Optoelectronics Progress, 2022, 59(9): 0922017 Copy Citation Text

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Fig. 1. Beat frequency diagram

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Fig. 2. Schematic diagram of dual frequency laser interferometer

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Fig. 3. Principle of grating measurement based on heterodyne interference

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Fig. 4. Multi-axis dual frequency laser interferometer in lithography machine^[10]

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Fig. 5. Plane grating measurement scheme of ASML lithography machine^[2,5,9]

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Fig. 6. Hybrid measurement scheme of Nikon lithography machine ^[9]

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Parameter	Homodyne interferometry	Heterodyne interferometry
Fundamental frequency	$f_{r} - f_{m} = 0$	$f_{r} - f_{m} = Δ f$
Amplifier type	DC amplifier	AC amplifier
Disturbed by environment	More	Less
Disturbed by low frequency	Yes	No
Optics nonlinearity	No	Yes，1-2 nm

Table 1. Comparison between homodyne interferometry and heterodyne interferometry

Item		Describe
Instrument error	Laser wavelength	The wavelength stability error of the laser is about 0.002×10^-6
	Electronics	It mainly comes from the subdivision and counting errors of the signal processing card，usually in 1-2 resolutions
	Optics nonlinearity	It is mainly caused by the aliasing of two frequencies，usually within 2 nm
Installation error	Abbe error	It is caused by the rotation or yaw angle of the measured object when the measured point does not coincide with the target point
	Cosine error	The error is caused by the included angle（cosine angle）between the measured optical axis and the motion axis. It is directly proportional to the measurement range
	Mirror map	The measurement error is caused by the uneven surface morphology of the measured mirror. It can be compensated by the measurement and calibration algorithm
Environmental error	Atmospheric compensation	The change of environmental parameters（temperature，pressure，humidity，etc.）leads to the change of wavelength on the measurement optical path，which leads to the measurement error
	Optics thermal drift	The error is caused by the volume change of optical components in the interferometer caused by temperature change. It can usually be controlled at 40 nm·℃^-1
	Material thermal expansion	The error is caused by the thermal expansion and cold contraction of mechanical parts between the interferometer and the measured object due to temperature change

Table 2. System error of dual frequency laser interferometer

Item	Dual frequency laser interferometer	Grating measurement system based on heterodyne interference
Common	Both are based on Doppler frequency shift and heterodyne interferometry
Difference
	The measured object is mirror	The measured object is grating
	The moving direction of the measured object is parallel to the optical axis	The moving direction of the measured object is perpendicular to the optical axis
	The displacement measurement reference is the laser wavelength	The displacement measurement reference is the grating spacing
	Large range measurement is greatly affected by the environment	The distance is fixed，the optical path is symmetrical，and is less affected by the environment
	Low cost at large range measurement	High cost at large range measurement

Table 3. Dual frequency laser interferometer versus gratingmeasurement system

Zhiping Zhang, Xiaofeng Yang. Application of Laser Heterodyne Interference Technology in Lithography[J]. Laser & Optoelectronics Progress, 2022, 59(9): 0922017

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