Xing Sheng, 微纳光电子材料与器件工艺原理. Doping 掺杂. Xing Sheng 盛兴. Department of Electronic Engineering Tsinghua University

Transcription

1 微纳光电子材料与器件工艺原理 Doping 掺杂 Xing Sheng 盛兴 Department of Electronic Engineering Tsinghua University 1

2 Semiconductor PN Junctions Xing Sheng, LEDs lasers detectors solar cells 5

3 CMOS Transistors 6

4 CMOS Transistors 7

5 Doping ingots and wafers 8

6 For silicon: p dopant: B, Al, Ga,... n dopant: P, As, Sb,... germanium is similar to Si. Doping in Silicon 9

7 For silicon: p dopant: B, Al, Ga,... n dopant: P, As, Sb,... Doping in Silicon 10

8 Doping in GaAs For GaAs: p dopant: replace Ga: Mg, Zn, Be replace As: C... n dopant: replace As: Se replace Ga: Si, Ge... 11

9 Doping Methods Thermal diffusion Ion implantation In situ growth 12

10 Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Sources Phosphorus (P) Liquid - POCl 3 Gas - PH 3 Boron (B) Liquid - BBr 3 Solid - B 2 O 3 Gas - B 2 H 6 Arsenic (As) Solid - As 2 O 3 Gas - AsH 3 13

11 Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Gas Source Diffusion 14

12 Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Liquid Source Diffusion 15

13 Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Solid Source Diffusion 16

14 Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Spin-on doping 17

15 Thermal Diffusion Process Parameters Time Temperature Gas pressure Gas flow rate Control Parameters Junction depth Doping concentration Doping profile 18

16 Diffusion Law Liquid Solid C concentration (mol/m 3 ) J D diffusion flux (mol/m 2 /s) diffusivity (m 2 /s) 19

17 Diffusion Law Fick's first law 1D J D C x 3D J DC Fick's second law C t D 2 C 2 x t C 2 1D 3D D C J: mol/m 2 /s D: m 2 /s C: mol/m 3 20

18 Dopant Diffusivity in Silicon Diffusivity ( 扩散系数 ) D rate of spread unit: cm 2 /s fast D D 0 exp( E A kt ) Diffusion length L slow L Dt diffusivity of defects in Si 21

19 Dopant Diffusivity in Silicon Xing Sheng, B, P, As, Sb, Si,... Cu, Fe, Li, H, Au,... 22

20 Dopant Solubility in Silicon maximum dopant amount in silicon Xing Sheng, 23

21 Dopant Diffusion in Silicon when the source is semi-infinite, and the surface is at the solubility limit C ss Xing Sheng, EE@Tsinghua C D t C( x 0, t C( x, t C( x 0, t 2 C 2 x 0) 0) 0) 0 0 C ss C( x, t) source Si C ss erfc x 2 Dt Error Function x 24

22 Dopant Diffusion in Silicon when the source is semi-infinite, and the surface is at the solubility limit C ss Xing Sheng, EE@Tsinghua source Si x C( x, t) C ss erfc 2 x Dt 25

23 Dopant Diffusion in Silicon when the source is limited, Xing Sheng, C( x C( x C D t 0, t 0, t C( x, t 2 C 2 x 0) 0) 0) Q 0 0 C( x, t) Si Q Dt exp Gaussian Function 2 x 4Dt x 26

24 Dopant Diffusion in Silicon when the source is limited, Xing Sheng, Si x C( x, t) Q Dt exp 2 x 4Dt Gaussian Function 27

25 Diffusion Masks Q: why not photoresist? 28

26 Laser Assisted Annealing Xing Sheng, local heating 29

27 Doping Methods Thermal diffusion Ion implantation In situ growth 30

28 Ion Implantation ( 离子注入 ) Xing Sheng, EE@Tsinghua 31

29 Ion Implantation - Advantages Xing Sheng, EE@Tsinghua Precise control of dose, depth and profile Low temperature process Tailor lateral distribution Wide selection of dopants 32

30 Ion Implantation - Advantages Xing Sheng, EE@Tsinghua Precise control of dose, depth and profile vs. Thermal diffusion Ion implantation 33

31 Ion Implantation - Advantages Low temperature process implantation at room temperature mask materials: photoresist, SiO 2, metal,... Lateral distribution Thermal diffusion Ion implantation 34

32 Ion Implantation - Advantages Low temperature process implantation at room temperature mask materials: photoresist, SiO 2, metal,... Lateral distribution shadow effect 35

33 Self Alignment n dopant n-si n-si p-si n-si 36

34 Dopant Distribution Process Parameters dopant type (B, P, As, Sb,...) implantation dose (# /cm 2 ) energy (ev) substrate orientation anneal time, temperature Control Parameters Junction depth Doping concentration Doping profile 37

35 Simulation Software - SRIM Xing Sheng, EE@Tsinghua 38

36 Dopant Distribution dopant type 39

37 Dopant Distribution dose 40

38 Dopant Distribution energy 41

39 Dopant Distribution Ideal case: Gaussian profile 42

40 Dopant Distribution Light atoms (e.g. B): back scattering Heavy atoms (e.g. Sb): forward scattering 43

41 Dopant Distribution ( 沟道效应 ) 44

42 Dopant Distribution ion channeling 45

43 Reduce Channeling Effects Xing Sheng, tilt the crystal form a thin oxide layer damage the surface by implantation 46

44 Video: Bullet in gel Implantation Damage Xing Sheng, amorphous 47

45 Implantation Damage Xing Sheng, anneal & activation 48

46 Effect of Annealing x C D t C 0 0), ( ) ( 0), ( 0 t x C x C t x C Dt x x C t x C 4 exp ) ( ), ( 2 0

47 Make Silicon-on-Insulator (SOI) oxygen ion implant 'SIMOX' Separation by IMplanted OXygen 50

48 Make Silicon-on-Insulator (SOI) 'Smart-Cut' 51

49 Doping Methods Thermal diffusion Ion implantation In situ growth 52

50 Doping of Gallium Arsenide (GaAs) GaAs growth MOCVD: Ga(CH 3 ) 3 + AsH 3 GaAs + 3CH 4 add dopant gas: SiH 4, Mg, Zn,... vertical structures with high quality thin-films Example: GaAs solar cell 53

51 GaAs VCSEL Vertical Cavity Surface Emitting Laser growth with in situ doping isolation by ion implantation ion implanted (H +, O -,...) region for isolation highly damaged and resistive region 54

52 Doping of Gallium Nitride (GaN) n-gan is easy use Si to replace Ga p-gan is very difficult use Mg to replace Ga, but... Mg deep level acceptor H. Amano, et al., Jpn. J. Appl. Phys. 28, L2112 (1989) S. Nakamura, et al., Appl. Phys. Lett. 64, 1687 (1994) I. Akasaki H. Amano S. Nakamura 2014 Nobel Prize in Physics hydrogen reduces distortion 55

53 Doping Measurement Xing Sheng, 56

54 Resistivity Four Point Probe Measurement conductivity ( x) e C( x) 1 ( x) sheet resistance 1 R s x t 0 ( x) dx 57

55 SIMS SIMS: Secondary Ion Mass Spectroscopy equipment similar with ion implantation 58

56 Thank you for your attention 60