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 xingsheng@tsinghua.edu.cn 1
Semiconductor PN Junctions Xing Sheng, EE@Tsinghua LEDs lasers detectors solar cells 5
CMOS Transistors 6
CMOS Transistors 7
Doping ingots and wafers 8
For silicon: p dopant: B, Al, Ga,... n dopant: P, As, Sb,... germanium is similar to Si. Doping in Silicon 9
For silicon: p dopant: B, Al, Ga,... n dopant: P, As, Sb,... Doping in Silicon 10
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
Doping Methods Thermal diffusion Ion implantation In situ growth 12
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
Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Gas Source Diffusion 14
Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Liquid Source Diffusion 15
Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Solid Source Diffusion 16
Thermal Diffusion - Silicon Xing Sheng, EE@Tsinghua Spin-on doping 17
Thermal Diffusion Process Parameters Time Temperature Gas pressure Gas flow rate Control Parameters Junction depth Doping concentration Doping profile 18
Diffusion Law Liquid Solid C concentration (mol/m 3 ) J D diffusion flux (mol/m 2 /s) diffusivity (m 2 /s) 19
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
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
Dopant Diffusivity in Silicon Xing Sheng, EE@Tsinghua B, P, As, Sb, Si,... Cu, Fe, Li, H, Au,... 22
Dopant Solubility in Silicon maximum dopant amount in silicon Xing Sheng, EE@Tsinghua 23
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
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
Dopant Diffusion in Silicon when the source is limited, Xing Sheng, EE@Tsinghua 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
Dopant Diffusion in Silicon when the source is limited, Xing Sheng, EE@Tsinghua Si x C( x, t) Q Dt exp 2 x 4Dt Gaussian Function 27
Diffusion Masks Q: why not photoresist? 28
Laser Assisted Annealing Xing Sheng, EE@Tsinghua local heating 29
Doping Methods Thermal diffusion Ion implantation In situ growth 30
Ion Implantation ( 离子注入 ) Xing Sheng, EE@Tsinghua 31
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
Ion Implantation - Advantages Xing Sheng, EE@Tsinghua Precise control of dose, depth and profile vs. Thermal diffusion Ion implantation 33
Ion Implantation - Advantages Low temperature process implantation at room temperature mask materials: photoresist, SiO 2, metal,... Lateral distribution Thermal diffusion Ion implantation 34
Ion Implantation - Advantages Low temperature process implantation at room temperature mask materials: photoresist, SiO 2, metal,... Lateral distribution shadow effect 35
Self Alignment n dopant n-si n-si p-si n-si 36
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
Simulation Software - SRIM http://www.srim.org Xing Sheng, EE@Tsinghua 38
Dopant Distribution dopant type 39
Dopant Distribution dose 40
Dopant Distribution energy 41
Dopant Distribution Ideal case: Gaussian profile 42
Dopant Distribution Light atoms (e.g. B): back scattering Heavy atoms (e.g. Sb): forward scattering 43
Dopant Distribution ( 沟道效应 ) 44
Dopant Distribution ion channeling 45
Reduce Channeling Effects Xing Sheng, EE@Tsinghua tilt the crystal form a thin oxide layer damage the surface by implantation 46
Video: Bullet in gel Implantation Damage Xing Sheng, EE@Tsinghua amorphous 47
Implantation Damage Xing Sheng, EE@Tsinghua anneal & activation 48
Effect of Annealing 49 2 2 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
Make Silicon-on-Insulator (SOI) oxygen ion implant 'SIMOX' Separation by IMplanted OXygen 50
Make Silicon-on-Insulator (SOI) 'Smart-Cut' 51
Doping Methods Thermal diffusion Ion implantation In situ growth 52
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
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
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
Doping Measurement Xing Sheng, EE@Tsinghua 56
Resistivity Four Point Probe Measurement conductivity ( x) e C( x) 1 ( x) sheet resistance 1 R s x t 0 ( x) dx 57
SIMS SIMS: Secondary Ion Mass Spectroscopy equipment similar with ion implantation 58
Thank you for your attention 60