Effect of Thermal Deformation on Imaging Performance for 16 nm Extreme Ultraviolet Lithography Objective

Yanqiu Li; Yan Liu; Lihui Liu

doi:10.3788/AOS201939.0122001

Acta Optica Sinica, Volume. 39, Issue 1, 0122001(2019)

Effect of Thermal Deformation on Imaging Performance for 16 nm Extreme Ultraviolet Lithography Objective

Yanqiu Li^1、*, Yan Liu², and Lihui Liu¹

¹ Key Laboratory of Photoelectronic Imaging Technology and System, Ministry of Education, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China

² Beijing Aerospace Institute for Metrology and Measurement Technology, Beijing 100076, China

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Figures & Tables(16)

Fig. 1. (a) Layout of EUVL objective; (b) modulation transfer function

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Fig. 2. Finite element model of M1 mirror

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Fig. 3. Heat loading steps-time plot of mirror

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Fig. 4. (a) Annular distribution of luminous intensity; (b) distribution of illuminance on mask

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Fig. 5. Curve of reflectivity of Mo/Si multilayer relative to incidence angle

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Fig. 6. (a) Temperature and (b) thermal deformation maps of M1 mirror at the end of last-heat-loading step

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Fig. 7. Curves of (a) temperature and (b) thermal deformation RMS value of each mirror relative to time

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Fig. 8. Image annular field of view

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Fig. 9. (a) WFE RMS and (b) distortion of objective system on the moments of maximum temperature and minimal temperature

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Fig. 10. (a) WFE RMS and (b) distortion of edge image field of view caused by thermal deformation of each mirror on maximum temperature moment

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Fig. 11. Curvature of each mirror, height of chief ray and incidence angle of chief ray

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Table 1. Characteristic parameters of mirrors and supporting mount materials

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Table 1. Characteristic parameters of mirrors and supporting mount materials

Parameter	ULE	Si	Mo	Invar
Density /(g·cm^-3)	2.205	2.33	10.3	8.12
Thermal conductivity /(mW·mm^-1·K^-1)	1.31	148	138	1.09
Specific heat /(J·kg^-1·K^-1)	0.766	0.712	0.255	-
Emissivity	0.735	0.122	0.122	0.28
Young's ratio /GPa	67.6	107	272	134
Poisson's ratio	0.17	0.25	0.25	0.3
Thermal expansion coefficient /(10^-6 K^-1)	0.02	2.50	5.35	1.06

Table 2. Model of 16 nm EUVL prototype productivity

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Table 2. Model of 16 nm EUVL prototype productivity

Item	Value
Throughout /(wafer·h^-1)	125
EUV power of intensity focus /W	250
Total time for one wafer /s	28.8
Exposure time /s	7.2
Wafer exchange time /s	721.6
Wafer diameter /mm	300
Resist sensitivity /(mJ·cm^-2)	15
Power at wafer /mW	689

Table 3. Relevant calculating data of the absorbed EUV power density for each mirror

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Table 3. Relevant calculating data of the absorbed EUV power density for each mirror

Mirror	M1	M2	M3	M4	M5	M6
Mean incidence angle /(°)	6.3	6.6	22.4	11.5	12.4	4.7
Mean reflectivity /%	67.5	67.7	67.3	67.6	67.7	67.5
Absorbed EUV power /mW	2402.19	1609.03	1102.80	735.38	495.58	337.59
Reflective area /mm²	17439	33338	4782	12508	5077.4	55102
Absorbed power density /(mW·mm^-2)	0.138	0.048	0.231	0.059	0.098	0.006

Table 4. Imaging performance demands for objective
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Table 4. Imaging performance demands for objective
Item Value
WFE RMS <0.03λ
Distortion <1.1 nm

Table 5. Analysis of thermal deformation for 16 nm and 22 nm EUVL objectives
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Table 5. Analysis of thermal deformation for 16 nm and 22 nm EUVL objectives
Item PO1 PO2
3D thermal deformation (M1-M6) /nm 8.3,3.8,6.2,1.1,4.2,0.5 1.6,4.1,4.8,0.4,2.5,0.2
WFE RMS /λ 0.1 0.006
Maximum distortion /nm 56 7

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Yanqiu Li, Yan Liu, Lihui Liu. Effect of Thermal Deformation on Imaging Performance for 16 nm Extreme Ultraviolet Lithography Objective[J]. Acta Optica Sinica, 2019, 39(1): 0122001

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