Development of EUV wavefront metrology system (EWMS)

Transcription

1 Development of EUV wavefront metrology system (EWMS) October 18, 2006 Katsuhiko Murakami, Katsumi Sugisaki, Masashi Okada, Katsura Ohtaki, Zhu Yucong, Zhiqian Liu, Jun Saito, Chidane Ouchi, Seima Kato, Masanobu Hasegawa, Takayuki Hasegawa, Hideo Yokota EUVA Masahito Niibe University of Hyogo Mitsuo Takeda University of Electro-Communications 1

2 Outline Introduction EUV wavefront metrology methods EUV experimental interferometer (EEI) results Status of EUV wavefront metrology system (EWMS) Summary 2

3 Introduction EUV Wavefront System (EWMS) was developed by EUVA in NEDO project. Before the development of EWMS, EUV experimental interferometer (EEI) was developed and several wavefront metrology methods were tested using EEI. Non-EUV wavefront metrology systems installed in the factories will be used in the manufacturing of EUV lithography tools. EWMS will play an important role as a standard system of EUV wavefront metrology. 3

4 EUV wavefront metrology project outline Project name: Development of EUV Wavefront Metrology Technology NEDO funding project Period: Start: January, 2002, End: March, 2006 Continuous research now underway Objective: Development of EUV wavefront metrology system for high-na (0.25) full-field projection optics Target: accuracy of less than 0.1nmRMS Light source: Undulator beamline of New Subaru synchrotron radiation source at University of Hyogo (UH) 4

5 Concept of EUV wavefront metrology system (EWMS) Goal of the project Wavefront of high NA (0.25) full-field projection optics can be measured. vacuum chamber stage EUV light (provided from SR undulator) metrology frame PO-box holder grating CCD pinhole PO-box pinhole/window stage vibration isolator vacuum pump 5

6 Why we need EUV wavefront metrology? Generally reflection type optics have no chromatic aberration. However, phase change accompanies the reflection by multilayer mirrors. Therefore wavefront measured with non-euv radiation is not equal to that measured with EUV radiation. The difference is not negligible considering optical performance. Wavefront metrology using EUV radiation is required. Reflectivity Reflectivity [%] Phase Phase Incidence angle 6

7 Difficulties and solutions of EUV wavefront metrology No coherence light source Common path type interferometer Limitation of optical elements Simple interferometer design using pinholes and gratings Extremely high accuracy required No mechanical reference surface 7

8 EUV wavefront metrology methods Seven different type of EUV metrology methods were tested using EEI. Diffraction type interferometers Point Diffraction Interferometer (PDI) Line Diffraction Interferometer (LDI) Shearing type Interferometers Lateral Shearing Interferometer (LDI) Slit Lateral Shearing Interferometer (SLDI) Cross-grating Lateral Shearing Interferometer (CGLSI) Digital Talbot Interferometer (DTI) Double-grating Lateral Shearing Interferometer (DLSI) 8

9 Diffraction type interferometers 1st Pinhole Pinhole (or Slits) Grating Test optics Gratings Window and 2nd Pinhole CCD Window and Slit CCD (a) PDI (b) LDI 9

10 Shearing type Interferometers 1/2 1st Slits 1st Pinhole 1st Pinhole Grating Test optic Grating Grating Windows CCD CCD CCD Windows CCD (a) SLSI (b) LSI (c) CGLSI (d) DTI 10

11 Lateral shearing Interferometer 2/2 Grating DLSI Windows Grating Test optics Window CCD 11

12 Concept of EUV experimental interferometer (EEI) Folding Mirror Vacuum Chamber EUV light (From illumination system) 3 rd Grating Stage (for DLSI) 1 st Grating Stage (for PDI, LDI) Photo Diode O 2 Gas Supply 1 st Mask Stage Schwarzschild Optics (NA=0.2) Vibration Isolator 2 nd Grating Stage (for Shearing interferometer) O 2 Gas Supply 2 nd Mask Stage Photo Diode CCD Camera 12

13 EUV wavefront metrology beam line at New Subaru 実験干渉計 EEI Schwarzschild 照明用 illuminator Schwarzschild Differential 差動排気機構 pumping system BL-9a Pumping 排気チャンバ chamber Filter フィルタ部 chamber M5 M4 13

14 EUV experimental interferometer (EEI) at New Subaru Clean chamber EEI Illuminator(NA:0.01) EUV beamline EUV beam Test optics Entire view of EEI Inside of EEI 14

15 EUV interference fringes PDI LDI LSI SLSI DLSI CGLSI DTI EUV interference fringes were obtained for 7 different wavefront metrology methods. 15

16 Measured EUV wavefront using EEI Diffraction type interferometers Shearing type interferometers 1.29 nmrms 1.21 nmrms 1.26 nmrms 1.20 nmrms 1.52 nmrms 0.95 nmrms (a) PDI (b) LDI (c) CGLSI (d) DTI (e) LSI (f) DLSI EUV wavefront was measured using 6 different metrology methods. Good agreement between deferent metrology methods. 16

17 Comparison of metrology method Method Test result PDI LDI LSI SLSI DLSI CGLSI DTI High Accuracy, Small measurement range, Difficult operation (alignment of PH, contamination of PH) Higher fringe contrast than PDI, Two sets of measurement in X, Y direction Wide measurement range, Easy alignment, Two sets of measurement in X, Y direction, Difficult to measure astigmatism Improved LSI but no significant advantage, Two sets of measurement in X, Y direction Need the least photons, Two sets of measurement in X, Y direction, Difficult to measure astigmatism Wide measurement range, Easy alignment, Astigmatism can be measured, Moderate accuracy Wide measurement range, Easy alignment, Astigmatism can be measured CGLSI was selected as a main metrology method of EWMS. 17

18 Measurement of system error (criterion of accuracy) of EEI Measured wavefront Rotate test optic Remove Test wavefront System error derivation SYSTEM TEST SYSTEM SYSTEM - = SYSTEM TEST SYSTEM Measurement with rotating test optics can distinguish system error of interferometer from error of test optics. 18

19 Measured system error in PDI and CGLSI Zernike coefficients [nm] Zernike orders Measured system errors: 0.06nmRMS (PDI), 0.12nmRMS (CGLSI) Our target accuracy (0.1nmRMS) was achieved in PDI. CGLSI showed very good accuracy beyond our expectation. 19

20 EUV wavefront metrology system (EWMS) PO loading crane Optical element stage Metrology frame EUV light 3.8m PO loader Projection optics (PO) Illumination optics stage PO rotation stage Optical element stage 20

21 Installation of EWMS at New Subaru completed 21

22 EWMS is ready to start EUV wavefront metrology Optical elements for metrology (pinholes and gratings) for EWMS were completed. Thermal chamber was installed. Prototype EUV projection optics will be delivered at the end of October. 22

23 Summary 7 different EUV metrology method were tested using EEI. Measured system error were 0.06nmRMS for PDI and 0.12nmRMS for CGLSI. CGLSI was selected main metrology method of EWMS. EWMS was completed and ready to start EUV wavefront metrology. 23

24 Acknowledgment The authors would like to thank the operation staff of New Subaru synchrotron facility for their help. This work was supported by NEDO (New Energy and Technology Development Organization). 24