纳米材料和纳米结构第七讲-new-2-PVD

Concerned Problems and Challenges
Contamination
at the interfaces or intermixing involved
Multi-material systems Cost
of equipment and maintenance operation
Bombarding:
accelerated positive ions strike the target surface and remove mainly neutral atoms
neutral atoms leave the target and condense on the substrate surface, and form into thin films
1-3 Preparing Multilayer Structures by Sputtering 1-4 Current Status of Sputtering
1-1 Principle of Sputtering
Ejection（喷射） of Atoms from the Target
Accomplished
by an energetic particle bombarding a target surface with sufficient energy (50 eV – 1 000 eV)
Target
Cathode Connected Composed
to a negative voltage supply
Transporting
the material from the source to the substrate Formation of film by nucleation and diffusion
Application
In
coatings of electronic materials
BaTiO3 Nanolayer Ferroelectric Thin Film Capacitors
Advantage:
higher relative dielectric constant
high leakage current strongly depending upon the properties


Substrate: Ru/SiO2/Si
Technique: rf magnetron sputtering, sputtering interruption (中断）between layers to change the substrate temperatures (680°C, 60 °C) Layer structure: n-cycle alternate layers of amorphous and polycrystalline BaTiO3 (microcrystalline be obtained by annealing amorphous layer) Results obtained
Disadvantage: Electrical
processing condition, microcrystal structure, and choice of bottom electrode Amorphous: low dielectric constant (16 at 105 V/cm), low leakage current Polycrystalline: high dielectric constant (400 at 105
Improvement
method
Use high gas pressure: to reduce the energy of the negative ions
Use off-axis sputtering: to avoid the substrate directly facing the cathode
纳米材料和纳米结构
Physical Vapor Deposition
物理气相沉积
第七讲
Physical Vapor Deposition (PVD)
Definition
Deposition of films by condensation from vapor phase is commonly called physical vapor deposition (PVD).
Insulator Semiconductor Conductor Superconductor
Nanometer
scale multilayer structures
Advanced electronic devices Abrasion resistant （抗磨） coatings
In
reactive sputtering: introduce reactive gases such as O2 or N2
few mTorr to several hundreds mTorr
Pressure: a
Procedure
Generation
of positive ions: ionizing the sputtering gas by glow discharge



Leakage current density be considerably reduced, and the effect becoming better with increasing cycle number Dielectric constant be two or three times higher than single amorphous layer but lower than a single polycrystalline layer
Disadvantage of off-axis sputtering:
low
deposition rate
deposition area
small
Deposition of magnetic materials: facing target sputtering
systems
溅射枪 溅射源
Three Steps of PVD
Generating a
vapor phase by evaporation or sublimation

Electron-beam evaporation（电子束蒸发） Molecular-beam epitaxy（分子束外延, MBE） Thermal evaporation（热蒸发） Sputtering（溅射） Cathodic arc plasma deposition（阴极电弧等离子体沉积） Pulsed laser deposition（脉冲激光沉积）
Complexion of
Systems Described in This Section
Sputtering Pulsed
laser deposition
1 Sputtering（溅射）
1-1 Principle of Sputtering
1-2 Sputtering System
衬底
质谱仪
靶1 低温泵 旋转衬底支架
靶2
用 于 制 备 TiN /VN 多 层 膜 的 磁 控 溅 射 系 统
Ways to reduce the damage and resputtering of growing film
Damage
caused by negative ion effect and radiation enhanced diffusion
Feasibility
of large cathode size High sputtering yield Less bombardment to the substrate
氩气 锁定装置 低表
流量控制阀1 流量控制阀2
流量控制阀
阀门
压力传感器
冷却水
1-3 Preparing Multilayer Structures by Sputtering
Types and Properties of Multilayer Structures
Types
of architectures Metal/metal Ceramic/ceramic Metal/ceramic Semiconductor/semiconductor Properties With structurally modulated architectures With compositionally modulated architectures High interface volume fraction Large intrinsic stress With structural and/or compositional gradient Exhibiting unique and enhanced electric, dielectric, magnetic, and mechanic properties
Ratio
bombarding ones
1-2 Sputtering System
Typical Types of Sputtering Systems
Direct current
(dc) diode sputtering Used for sputtering conducting materials Radio frequency (rf) diode sputtering Used for sputtering insulating materials Magnetron diode sputtering Most commonly used today Plasma be confined around the target surface by a magnet field Advantages of using magnetron sputtering
V/cm), high leakage current
Aim
of nanolayer structure BaTiO3 film capacitor: high dielectric constant and low leakage current
Realization and effects

具有纳米多层结构的BaTiO3薄膜电容器横截面示意图
Nanolayer MoSi2/SiC
of the materials to be deposited
Substrate
Anode
May
be grounded, floated, or biased
Glow Discharge Medium in Sputtering Chamber
A
gas or a mixture of different gases, most commonly Ar or He
可360度旋转的衬底支架 偏轴溅射系统 陶瓷加热器 衬底 示意图 Schematic of off负离子撞击区 靶 axis sputtering
system
屏蔽闸
空间屏蔽区
衬底
正面溅射 系统 示意图
靶
磁体
Schematic 氩气 of the facing target sputtering system
Condensation:
An Important Concept: Sputtering Yield
A
measurement of the efficiency of sputtering of the number of emitted particles to the number of