Photolithography 光刻 Part II: Photoresists

Save this PDF as:
 WORD  PNG  TXT  JPG

Size: px
Start display at page:

Download "Photolithography 光刻 Part II: Photoresists"

Transcription

1 微纳光电子材料与器件工艺原理 Photolithography 光刻 Part II: Photoresists Xing Sheng 盛兴 Department of Electronic Engineering Tsinghua University 1

2 Photolithography 光刻胶 负胶 正胶 4

3 Photolithography Dark room Yellow zone photography avoid UV exposure! 5

4 Photolithography Sample clean Surface treatment Photoresist coating Prebake Exposure Postexposure bake Development 6

5 Photoresist Adhesion: Issues Xing Sheng, Hydrophobic ( 疏水 ) clean Si, some polymers,... Hydrophilic ( 亲水 ) SiO 2, metals (Ag, Au), some polymers,... Most photoresists are hydrophobic ( 疏水 ) adhesion problems on glass, Ag, Au,... 7

6 Photoresist Adhesion: Solutions Surface clean wet clean SiO 2 for Si, use HF to remove SiO 2 plasma treatment Dehydration bake remove water from sample surface Si Si, before HF Si, after HF Q: Why? 8

7 Photoresist Adhesion: Solutions Adhesion promoter self-assembled monolayer (SAM) 9

8 Spin Coating Video thickness h t thickness viscosity time speed 10

9 Spin Coating Film Thickness thickness vs. speed and viscosity 11

10 Spin Coating Film Thickness thickness vs. spin time 12

11 Spin Coating - Troubleshooting - bubbles in resist - sample not clean - N 2 generation - accelerate too fast - sample off center - time too short - evaporate too fast - improper chuck - sample off center - accelerate too fast - sample off center - sample not clean - fluid too little - sample dewet - sample not clean - sample not clean - resist not clean 13

12 Other Coating Methods When spin coating is difficult... too thick, sample is not uniform,... save resists dip coating spray coating 14

13 Dry Resist Thick film, for PCB making 15

14 Exposure 16

15 Lambert Beer's law Optical Absorption I I exp( L) 0 thicker films require larger exposure dose example: SU-8 resist 17

16 Positive Resist: Example Xing Sheng, Base resin novolac Photoactive compound (PAC) diazoquinone (DQ) photosensitive novolac Solvent n-butyl acetate, xylene,... volatile control viscosity, film thickness,... DQ 18

17 Positive Resist: Example Xing Sheng, DQ UV exposure acid dissolves in base solution (developer) 19

18 Positive Resist: Example Xing Sheng, Process for SPR220-v3.0 clean sample (glass or silicon) acetone / isopropanol / DI water, N 2 gas blow dehydration bake at 110 C, 10 mins remove moisture spin coat SPR220-v3.0, 3000 rpm, 40 sec soft bake at 110 C, 90 sec evaporate solvent UV expose (i-line), 300 mj/cm 2 post-exposure bake at 110 C, 90 sec stabilize the resist (optional) develop in MIF300 (alkali developer), 1 min hard bake make resist robust during etching 20

19 Positive Resist: Example film thickness depend on solvent concentration, spin speed, etc 21

20 Negative Resist: Example Xing Sheng, soluble in organic developer UV exposure Negative resists are long-chain polymers heating only used for features > 2 m insoluble in organic developer 22

21 Negative Resist: Example Xing Sheng, Process for AZ nlof 2070 clean sample (glass or silicon) acetone / isopropanol / DI water, N 2 gas blow dehydration bake at 110 C, 10 mins remove moisture spin coat AZ nlof 2070, 3000 rpm, 40 sec soft bake at 110 C, 90 sec evaporate solvent UV expose (i-line), 50 mj/cm 2 post-exposure bake at 110 C, 90 sec cross link resist (required) develop in MIF300 (alkali developer), 1 min 23

22 Positive vs. Negative Xing Sheng, 24

23 Positive vs. Negative Xing Sheng, 25

24 Lithography - Troubleshooting positive resist Q: what will happen, if: 1. under-exposed 2. over-exposed 3. under-developed 4. over-developed how about negative resist? 26

25 Standing Waves 27

26 Proximity Scattering Xing Sheng, 28

27 Reducing Substrate Effects Xing Sheng, Add absorptive dyes in photoresists Apply anti-reflective coatings (ARC) ARC with ARC without ARC 29

28 Reducing Substrate Effects Xing Sheng, Apply multilayer resists 30

29 Pattern Transfer positive resist - etching negative resist - liftoff 31

30 Photoresist Reflow photoresists are soft polymers flow at high temperature 32

31 Photoresist Reflow Microlens array by reflow CMOS image sensor 33

32 Photoresist Removal Organic solvents acetone / isopropanol / DI water NMP, DMSO,... Highly cross-linked resist cannot be removed by solvents Oxygen plasma polymer (C, H, O,...) + O 2 = CO 2 + H 2 O

33 References for Photoresists Xing Sheng, Useful notes for photolithography Always read manuals before experiments 35

34 Advanced Lithography Xing Sheng, Interference / holographic lithography 3D lithography Plasmonic lithography Nanoimprint lithography Directed self-assembly lithography Inorganic materials based lithography 36

35 Interference / Holographic Lithography resolution ~ /2 easy to form periodic patterns 37

36 3D Lithography direct laser writing two photon absorption 38

37 3D Lithography J. R. Tumbleston, et al., Science 347, 1349 (2015) Video 39

38 Plasmonic Lithography Xing Sheng, subwavelength resolution field enhancement at metal surfaces 40

39 Nanoimprint Lithography Nanoscale mold fabricated by advanced lithography silicon, etc. reusable S. Y. Chou, et al., Science 272, 5258 (1996) 41

40 Direct Self-assembly Xing Sheng, Phase separation by block copolymers B A C. Tang, et al., Science 322, 429 (2008) 42

41 Lithography of Inorganic Materials Y. Wang, et al., Science 357, 385 (2017) 43

42 Metrology Optical microscope Profilometer (non-contact) Profilometer (contact) Atomic force microscope (AFM) Electron microscopy (SEM, TEM, cryo-em) Scanning tunneling microscope (STM) 44

43 Metrology Optical microscope use yellow filter to prevent resist exposure resolution determined by optics 45

44 Metrology Profilometer (non-contact) optical scanning measure 3D profile spatial resolution - wavelength not suitable for absorptive materials 46

45 Metrology Profilometer (contact) stylus measure film thickness 2D or 3D profile spatial resolution - stylus 47

46 Metrology Atomic force microscope (AFM) better horizontal and vertical resolution 48

47 Metrology Scanning electron microscope (SEM) vacuum required surface charging can combine with Ebeam lithography 49

48 Metrology transmission electron microscope (TEM) higher resolution than SEM thin samples A. Klug 1982 Nobel Prize in Chemistry E. Ruska 1986 Nobel Prize in Physics 50

49 Metrology cryo electron microscope (cryo-em) image biological samples! 2017 Nobel Prize in Chemistry 51

50 Metrology Scanning tunneling microscope (STM) atomic resolution ultrahigh vaccum image and manipulate atoms G. Binnig, H. Rohrer 1986 Nobel Prize in Physics 52

51 Thank you for your attention 54