Photolithography Overview 9/29/03 Brainerd/photoclass/ECE580/Overvie w/overview

Transcription

1 1

2 Moore s law only holds due to photolithography advancements in reducing linewidths 2

3 All processing to create electric components and circuits rely on photolithography 3

4 Typical MOS transistor NMOS = n-type carrier across gate 4

5 Transistor fabrication N-MOS P-MOS 5

6 Interconnect 6

7 Chapter 1 sections 1-7 : 7

8 8

9 Basic process flow 9

10 10

11 Wafer clean: removal of Organics and metalics 11

12 HMDS Hexamethyldisilazane Prime: Replaces surface adsorbed H 2 O and gives off Ammonia. This material produces a bond with the wafer surface creating a polar surface ( electrostatic). No surface wetting by Photoresist occurs on an un-treated SiO2 surface with these bonded hydroxyl groups. Basically the Photoresist is hydrophobic and will not adhere to a hydrophilic surface. The HMDS is a hydroxyl getter and creates a hydrophobic surface, which the Photoresist had good adhesion. BOTTOMLINE: Priming adjusts the surface energy of the wafer so that it is comparable to the surface energy of the Photoresist. 12

13 Photoresist 13

14 Spin Coat 14

15 Spin Coat: RPMs: Spread or cast, Ramp,and terminal 15

16 Spin Coat 16

17 Spin Coat 17

18 Softbake Removes solvent from film and stablizing coating: typical: 90C to 120C I-line DNQ 100C to 130C: DUV CAR 18

19 Alignment 19

20 Photoresist Exposure DNQ photoresist actinic radiation 20

21 DUV: Photoresist Exposure wavelengths below 200nm All use excimer lasers Note 248nm = KrF laser 21

22 Photoresist Exposure 22

23 Exposure and feature type 23

24 Positive and Negative Tone Photoresists 24

25 Contact/Proximity/Projection printing 25

26 Projection printing: Typical stepper 26

27 Projection printing: Numerical Aperture 27

28 Projection printing: High NA lens 28

29 Projection printing: Resolution 29

30 Projection printing: Depth of Focus 30

31 Projection printing: Depth of Focus 31

32 Optical lithography Performance: Resolution NA and wavelength coherent systems 32

33 Photoresist Standing waves: reflection/interference 33

34 Photoresist Post Exposure Bake Purposes: key idea DNQ/Novolak positive tone: diffusion bake : Diffusion of PAC to improve CD contact by removing standing waves. PAG/Novolak negative tone: (acid hardened resist: AHR) Diffusion of H+ ion to react with polymer causing polymer to become insoluble.( PAG: Triazine) DUV PAG/Blocking group/phs: Diffusion of H+ ion to react with blocking group causing PHS to become soluble 34

35 Photoresist exposure and dissolution Key ideas: DNQ and Novolak Resin I-line 365nm system 1. DNQ or Photo Active Compound PAC is an Inhibitor: It inhibits Development rate when present! There is very little dissolution in an OH solution. 2. Photolytic conversion of DNQ to ICA in by exposure to Near UV radiation ( Hg lamp) increases development rate PAG and Poly Hydroxystyrene PHS DUV CAR 248nm system 1. PAG Photo-Acid-Generator creates an Acid (H+) upon exposure to 248nm radiation. There is very little dissolution in an OH solution. 2. The addition of thermal energy using a PEB bake causes the H+ to diffuse and react with the blocking group, causing the exposed area to become soluble. 35

36 Photoresist Development Threshold dose Develop exposed photoresist in TMAH (2.38%) basic solution 36

37 Photoresist CDs Dose Vs linewidth Polysilicon Linewidth DUV photoresist 0 Focus offset. 0.7 Photoresist linewidth CD um y = x R 2 = ACEN ALL ALR AUL AUR ZCEN ZLL ZLR ZUL ZUR Linear (AUL) Exposure Dose 37

38 Photoresist CDs Dose Vs Spacewidth Contact CD Vs Exposure Dose Mj/cm2 IX405 i-line Photoresist Nominal 0.80u 0.95 Contact Photoresist CD microns CEN DI Linear (201CEN DI) y = x R 2 = ASML 5500/100C Exposure dose mj/cm2 38

39 I-line Positive tone Photoresist 365nm Line dense isolated line isolated space contact 39

40 I-line negative tone Photoresist 365nm 40

41 DUV Photoresist KrF 248nm 41

42 DUV Photoresist OH contamination issue 42

43 Photoresist Post-develop bake Hardbake Improve adhesion of photoresist for subsequent wet processing: Wet etches: BHF, Acetic acid, H 2 O 2 Plateup: Au or Cu Increasing hardbake temperature will cause photoresist patterns to flow. 43

44 Photoresist Etch 44

45 Photoresist Etch: RIE 45

46 Photoresist removal: Strip Post etch 46