Application of imaging ellipsometry: graphene - pinpointing and ellipsometric characterization ULRICH WURSTBAUER CHRISTIAN RÖLING PETER H.

Transcription

1 Application of imaging ellipsometry: graphene - pinpointing and ellipsometric characterization ULRICH WURSTBAUER CHRISTIAN RÖLING PETER H. THIESEN

2 Introduction to imaging ellipsometry

3 Ellipsometry in general makes use of the fact that the polarization state of light may change when the light beam is reflected from a surface. p E p E s s ( Paul Drude, Lehrbuch der Optik, Leipzig, 1906 )

4 ( Paul Drude, Lehrbuch der Optik, Leipzig, 1906 )

5 Reflections at optical interfaces & coherent superposition of the partial beams # 1 # 2 # 3 N ~ 0 Change of amplitudes and phases of the p- and s-polarised components of the reflected beam: N ~ 1 N ~ 2 d tan e i R R p s E reflected ( p) E incident ( p) E reflected ( s) E incident ( s) pp ss tan R R p s pp ss p p out in s s out in Measurement precision for d: ca. 0.01nm!

6 Ellipsometry is a method based on models Fit Measurement Model Result Measurands, y Layer thickness d Optical properties n, k Searched variables d, n, k, (for all layers + substrate)

7 How does it work? ( Paul Drude, Lehrbuch der Optik, Leipzig, 1906 ) nanofilm_ep3se, 2009

8 illumination detection AOI

9 illumination detection

10 illumination detection

11 illumination detection detector polarizer compensator analyser sample

12 illumination Light source detection detector polarizer compensator analyser sample

13 Method: Nulling Ellipsometry

14 P s p polarizer

15 P s p compensator

16 P s p sample

17 P A s p analyser angles P, C, A, Nulling Ellipsometry advantage 1: high sensitivity for ultra-thin films ideal instrument, C=45 : 2P 90 A

18 Nulling Ellipsometry Imaging Ellipsometry Light source CCD camera polarizer compensator sample Objective analyser Nulling Ellipsometry advantage 2: real time ellipsometric contrast, good for imaging image

19 polarizer analyser

20 polarizer analyser

21 polarizer analyser

22 polarizer analyser

23 polarizer analyser

24 polarizer analyser

25 polarizer analyser

26 polarizer analyser

27 grayscale nulling condition polarizer angle

28 grayscale polarizer angle

29 regions of interest localized measurements of, model localized film thickness or optical properties

30 analyzer: map Evaluating all pixels : map

31 , maps

32 , maps Optical model Result: thickness maps or maps of n, volume fraction etc.

33 The depth-of-focus problem caused by the oblique imaging angle with conventional optics, focus is achieved only in a narrow stripe. Solution: mechanical focus scanning + image processing focus

34 focus scanning CCD (detector) polarizer compensator Objective sample analyser

35 focus scanning CCD (detector) polarizer compensator sample Objective analyser

36 focus scanning CCD (detector) polarizer compensator sample Objective analyser

37 focus scanning CCD (detector) polarizer compensator sample Objective analyser

38 focus scanning + image processing:

39 Pinpointing and identification

40 Pinpointing and identification Ellipsometric contrast micrographs

41 Pinpointing and identification Ellipsometric contrast micrographs

42 Pinpointing and identification Ellipsometric contrast micrographs Graphene monolayer

43 Pinpointing and identification Ellipsometric contrast micrographs Graphene monolayer

44 Pinpointing and identification Psi-map

45 Pinpointing and identification Psi-map

46 Pinpointing and identification Psi-map

47 ellipsometric characterization Variable angle imaging spectroscopic ellipsometry

48 ellipsometric characterization Variable angle imaging spectroscopic ellipsometry

49 ROI 1

50 ROI 6

51 ROI 4

52 ROI 3

53 ROI 5

54 ROI 7

55 ROI 0

56 ROI 2

57 ROI 8

58 ellipsometric characterization data evaluation The spectra of graphene and of the substrate seem to be very similar. The differences between substrate ROIs and a refence ROI and between graphene ROIs the reference ROI are significantly unlike each user.

59 AOI = 43 substrate = RoI 6 - Reference RoI 4 3,5 3 2,5 2 1,5 1 0,5 0-0,5-1

60 AOI = 43 graphene = RoI 5 - Reference RoI 4 3,5 3 2,5 2 1,5 1 0,5 0-0,5-1

61 AOI = 43 graphene = RoI 3 - Reference RoI 4 3,5 3 2,5 2 1,5 1 0,5 0-0,5-1

62 AOI = 43 graphene = RoI 4 - Reference RoI 4 3,5 3 2,5 2 1,5 1 0,5 0-0,5-1

63 AOI = 43 graphene = RoI 7 - Reference RoI 4 3,5 3 2,5 2 1,5 1 0,5 0-0,5-1

64 AOI = 43 graphite = RoI 0 - Reference RoI

65 AOI = 43 graphite = RoI 2 - Reference RoI

66 AOI = 43 graphite = RoI 8 - Reference RoI

67 ellipsometric characterization Optical model

68 Modeling 1. step: calculation of the SiO 2 thickness SiO 2 (predefined) Si (predefined)

69 Modeling 1. step: calculation of the SiO 2 thickness SiO 2 (predefined) ROI Thickness / nm RMSE Si (predefined)

70 Modeling 1. step: calculation of the SiO 2 thickness SiO 2 (predefined) Si (predefined) ROI Thickness / nm RMSE

71 Modeling 2. step: n and k for graphene from Wang et al. at 532 and 633 nm -- linear interpolation graphene 300 nm SiO 2 Si (predefined)

72 Modeling 2. step: n and k for graphene from Wang et al. at 532 and 633 nm linear interpolation graphene nm SiO 2 Si (predefined)

73 Modeling 2. step: n and k for graphene from Wang et al. at 532 and 633 nm linear interpolation graphene nm SiO 2 Si (predefined) ROI Thickness / nm RMSE

74 Modeling Drude function Drude nm SiO 2 Si (predefined)

75 Modeling Drude function

76 Modeling Drude function Best fit ROI 3 Drude nm SiO 2 Si (predefined)

77 Modeling Drude function Best fit ROI 4 Drude nm SiO 2 Si (predefined)

78 Modeling Drude function Best fit ROI 5 Drude nm SiO 2 Si (predefined)

79 Modeling Drude function Best fit ROI 7 Drude nm SiO 2 Si (predefined)

80 Modeling Drude function Best fit ROI 7 High correlation between thickness Drude and (n/meff) nm SiO 2 with additional information concerning the thickness, the dispersion Si (predefined) function is available.