导图社区 5. Etching
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5. Etching
这是一篇关于5. Etching的思维导图，主要内容包括：Considerations for Dry Etching，Etch Rate Dependence，Dry Plasma Etching，Wet Chemical Etching，requirements and tradeoffs。
编辑于2024-10-07 12:03:16- 制造技术
- Etching
- 5. Etching
这是一篇关于5. Etching的思维导图，主要内容包括：Considerations for Dry Etching，Etch Rate Dependence，Dry Plasma Etching，Wet Chemical Etching，requirements and tradeoffs。
- 1. Introduction and Overview of nanotechnology
这是一篇关于1. Introduction and Overview o的思维导图，主要内容包括：Applications of Nanotechnology to Devices and Microsystems，Scaling Devices to Nanometer Range，Why Nanotechnology for Advanced Microelectronics and Bi
5. Etching
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- 5. Etching
这是一篇关于5. Etching的思维导图，主要内容包括：Considerations for Dry Etching，Etch Rate Dependence，Dry Plasma Etching，Wet Chemical Etching，requirements and tradeoffs。
- 1. Introduction and Overview of nanotechnology
这是一篇关于1. Introduction and Overview o的思维导图，主要内容包括：Applications of Nanotechnology to Devices and Microsystems，Scaling Devices to Nanometer Range，Why Nanotechnology for Advanced Microelectronics and Bi
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5. Etching
requirements and tradeoffs
lithography-pattern etch mask(图案刻蚀掩膜)；Etching- selectively remove materials to form functional devices
requirements
Flexibility to Optimize Processes
Low Cost and High Throughput System With Low Downtime
Uniform Etching Better Than 5%
Minimize Etch Rate Dependence on Feature Size, Wafer Size, Etch Depth, Aspect Ratio, Adjacent Features, Position on Wafer
High Selectivity to Mask and Layer Below
Good Profile Control to Avoid Undercutting
Low Device Damage With Low Ion Energy and Uniform Plasma
Low Particle Generation
Environmental Issues to Reduce Chemical Waste(化学废物)
etching classification
wet etching
dry etching
etching profile
isotropic
Same Etch Rates in Vertical and Horizontal Directions, Undercut(削弱) with Lateral Etching(横向刻蚀) under Etch Mask
anisotropic
completely anisotropic
Completely Anisotropic – No Lateral Etching, only Etch in Vertical Direction with Vertical Profile, Preferred for Small Features
etch selectivity
Etch Rate Ratio between Material to be Etched and Etch Mask
Etch Mask Holds up with High Etch Selectivity
Not Etching Layer Underneath
Wet Chemical Etching
Usually for Surface Cleaning and Complete Removal of a Layer (e.g. Photoresist, Oxide)
Advantages
Low Cost, Simple System
Highly Selective to Mask and Underlying Layer
Batch Processing(批处理) With Larger Number of Wafers (>24) at a Time for High Throughput
Disadvantages
Isotropic Etch With Undercut Profile(削弱轮廓)
For Small and High Aspect Ratio Features, Difficult to Get Solvents in and Out, Can Cause Non-Uniform Etch
Need to Provide Waste Treatment for Large Quantity of Solvents
isotropic ethcing
similar etch rates in the vertical and horizontal directions
Features Become Larger with Rounded Profile After Etching
Difficult to Control Exact Dimension or Profile
Surface Roughness Developed due to Preferential Etching
Solutions
Anisotropic Wet Etching
Faster Etch Rate in One Direction than the Other
Etch Stop or Selectivity based on Doping(参杂)
Etch Rate Depends on Crystalline Structure(晶体结构)
Dense Crystal Planes(<111> in Si, Etch Slower than Less Dense Planes (<100> or <110>))
Anisotropic Si Etching
(111) Si Planes have the Highest Atomic Density compared to (100) or (110) Planes
Etch Rates (110) : (100) : (111) = 600:400:1
Vertical Profile on (110) Si
Tapered Profile(锥形) with 54.74° on (100) Si (V-Groove)
When 2 <111> Planes Meet, Etching Stops
Minimum Opening Size Needed to be able to Etch Through given Thickness
Able to form Devices with Sharp Pointed Tips (e.g. Field Emission Tips) and Openings with Tapered Sidewalls(锥形侧壁)
Comparisons
KOH
Common Solution, Easy Disposal; Orientation Dependent Etch, Smooth Surface; Mobil Ion (K+) Contamination
Alkali Metals(碱金属): Contamination for Integrated Circuits
Highly Selectivity
Etch Stop – Boron Doped(硼参杂) >2X10^19 cm-3
Typical Mixture
EDP
Selective Etch with p++ Etch Stop; Metal Etch Mask (e.g. Cr, Cu, Ta, ...) Except Al; dangerous, Reflux Condenser (回流冷凝)Needed
TMAH
No Mobile Ion, Safer, Easier to Setup; Al as Etch Mask with Si Added or Lower pH; Rougher Surface
Maximum Etch Depth Depends on Feature Size
Dry Plasma Etching
overview
Plasma – Reactive Neutrals (Chemical) and Ions (Physical)
Control Reactions with Materials to be Etched to get Vertical Profile
Plasma Generation
Gas Ionized by external energy (Rf/Microwave Power)
Contains Ions (Positive And Negative), Neutrals, Electrons, Photons
Only 0.1-10 % of the Gas is Ionized
Still mostly Gas Molecules
Reactive Species(反应物质) Generated by Impact Ionization(碰撞电离), Dissociation(解离), Excitation, Relaxation, and Recombination
Electron Impact(轰击) Ionization-Remove Electrons from Atom/Molecule (Ions can be Directional)
Ionization Potential (Minimum Energy to Remove Most Weakly Bound Electrons) for Ar = 15.8 eV; Multiplication of Electrons Maintains Plasma and Keeps the Processes Going
Excitation - Electrons Jump to a Higher Energy Level within an Atom
Excitation potential (lower than ionization Potential, Easier to Excite within Same Atom) for Ar = 11.56 eV
Relaxation - Unstable Excited State Returns to Ground State by Emission of Photons of Energy Equal to ▲E
Color in Plasma Depends on Characteristics of Atoms/Molecules.
Optical Emission Spectrum: Consists of Excited Etch and product species. Can be Used to Monitor Reactive Species in Plasma and Etch Products
Photon Energy – Identify Species
Light Intensity – Concentration of Species
wavelength
Recombination - Electrons and Ions Recombine to Form Neutral Species, Makes Stable Plasma with Fixed Number of Electrons and Ions. Otherwise Electron and Ion Density will Keep Increasing
Dissociation - Break Apart Molecules
Electron Attachment: Generate Reactive Ions
Ion-Neutral Collisions: Charge Transfer(电子转移) or Further Ionization, Change Energy Distribution of Ions and Neutrals in Reactor
Voltage Distribution Across Electrodes
High Density Plasma Systems (e.g. Inductively Coupled Plasma Source or ICP) Can Be Used to Reduce Vdc and Increase Concentration(浓度) of Reactive Species
More Flexible – Separate Power Supplies for Source (Reactive Species Concentration) and Stage (Reactive Ion Energy)
High Ion Density, Lower |Vdc|
Barrel Etcher
Minimum Ion Bombardment, Isotropic Dry Etch
Use mainly for Removal of Photoresist using O2 Plasma
faster: because of light weight of electrons
Controllable Parameters
Gases - Flow, Mixture
Pressure - Residence Time(停留时间)
Power - Power Coupled In; Frequency; Pulsing
Cycling - Switching Gases, Power, Pressure
Temperature - Activation Energy(活化能), Adsorption, Desorption
Chamber Materials And Conditions
Uncontrollable Parameters
Sample Variation-Material, Mask, Oxide, Residue
Residual Gases - Leak(泄露), Adsorption on Wall, Gases From Previous Cycles
Stabilization – Gas Flow, Pressure, Power
Power Loss - Inefficient Coupling
Wafer Temperature Variation - Poor Thermal Conductance
Meter Offset(仪表偏移) - Recalibration(重新校准) Needed
Pump Speed Variation - Oil and Filter Replacement
Reactions on Wafer Surface
Transport of Reactive Species and Etch Products
Surface Reactions
Physical, Chemical, Ion Assisted; Bottom Surface vs. Sidewall; Etching vs. Deposition(沉积)
Radiation Effects
Charging Related to Plasma Uniformity and High-Density Charged Particles
Defect Generation due to High Energy Photons
Mechanisms
Sputter Etching(溅射刻蚀)
Lower Pressure/Less Chemicals; More Directional, Less Selective, More Damage
Ion-Assisted Etching (Both Physical and Chemical)
Both Physical and Chemical Etching
Chemical Plasma Etching (No Physical)
Higher Pressure/More Chemicals, Less Directional, More Selective, Less Damage
Three Principal Mechanisms
Chemical Etching (Isotropic, Selective)
Etching done by Reactive Neutral Species, such as “free radicals”(自由基)
Additives(添加剂) like O2 can be used which react with CF3 and reduce CF3 + F recombination
More Reactive Species
Higher Etch Rate (More F, Less CF3)
purely Chemical, so isotropic and selective, like wet etching with Undercut Profile
Physical Etching (Anisotropic, Less Selective)
Ion Etching is much More Directional to Form Vertical Profile(electric field)
Etching Species are Ions like CF3+ or Ar+ which Remove Material by Sputtering
Not Selective since All Materials Sputter at about the Same Rate
Physical Sputtering can Cause Damage to Materials, depending on Ion Energy
Faceting(刻面)
Preferential, Faster Etching at Certain Angles (Ion Incidence and Material Removal)
Facets Form at having Angles with Fastest Etch Rate
Faceting can be used to Form Sharp Tips
Trenching due to Enhanced Ion Flux related to Ion Scattering
Redeposition on Sidewalls can be reduced by Stage Rotation
Chemical Reactions Increase Etch Rate
Simplest Case: No Ions Needed (No Plasma)
(High pressure, Chemical only)
Fast
No Ion Damage
Isotropic
Highly Selective
CMOS Compatible
Ion-assisted Etching (Anisotropic, Selective)
Presence of Ions and Reactive Neutrals
Etch Rate Enhancement due to Ions and Reactive Neutrals is Substantial, not just two added together
Anisotropic and High Etch Selectivity
Ion-Assisted Etching with Both Reactive Ions (F+) and Reactive Neutrals (F)
Effects of Gas Chemistry
Formation of Volatile Etch Products(挥发性) (Solid to Gases)
Addition of Inert(惰性) Gases (e.g. Ar, He)
Changes Electron Distribution and Composition of Reactive Species
Dilution(稀释); Stabilization; Cooling; Sputtering
Enhance Reactive Species Generation
Etch Rate Increases due to High [F] and Less Polymer Deposition
Enhance Polymer Formation
Etch Rate Decreases due to More Polymer Deposition and Less [F]
F vs. Cl for Metal Etching
F – Etch Products with Lower Boiling Point are Easier to Remove with Faster Etch Rate and Perhaps More Undercut(底切)
Presence of Ions can Enhance Etch Product Removal
Ion Energy Reduces at High Pressure
Higher Pressure – Lower Ion Energy due to More Collisions
low pressure hel etching product remove
Ions and Reactive Neutrals do not Increase with Pressure due to Recombination
Affect Distribution of Reactive Species, Adsorption(吸附), Desorption
Etch Rate
Etch Rate Decreases as Aspect Ratio(纵横比) Becomes Higher
Limited by Transport of Reactive Species and Etch Products
Comparisons of Si Dry Etching Using F- and Cl-based Gases
Cycling between Etching and Passivation(钝化)
Using F-based Gases
Repeated Many Cycles; Deep Etching with Good Profile; Sidewall Roughness
Scalloping(扇形)
Vertical Striations(条纹)
Insufficient Passivation
Vary with Aspect Ratio
Advantages
Fast Etch Rate
High Selectivity
Flexible Profile Control
Disadvantages
Surface Roughness
Sensitive Process that Requires Precise Balance Between Etching and Passivation
Etch Rate and Profile vary with Etch Depth and Feature Size
Frequent Switching of Instruments
Etch Rate Dependence
Sputtering
Physical Bombardment by Ions only, No Chemical Reaction, Simplest Dry Etching
Sputtering Kinetics(动力学)
Energy Transfer between Incoming Ions (mi, vi) and Target Atoms (mt, vt) through Series of Collisions
Sputtering Yield (S) - Number of Target Atoms Ejected(射出的) Per Incident Ion.
S Depends on Ion Energy, Atomic Mass(原子质量) of Incoming Ion and Target Atoms, Surface Binding Energy(表面结合能) of Target, and Angle of Ion Incidence. High S will Provide High Etch Rate
Eth = Threshold Energy(阈值能量) (~10-50 eV) – Minimum Energy for Etching
Sputtering Yield (S) Increases with mi and Eion
Etch Efficiency
S also depends on angle of incident ions
Ejection of Target Atoms in Forward Direction is Easier with Less Directional Change of Momentum
Off Normal Incidence Confine Action to Surface rather than Deep in Substrate
When θi is too Large (e.g. // to surface), not Sufficient Energy/Momentum Transfer. The Ions just Slide // to Surface at Glazing Angle
Maximum etch rate occurs ~45°, not at normal incident 90°
Etch Rate
Ion Assisted Etching
Considerations for Dry Etching
Deposition During Etching
Charging
Undercut due to Neutrals and Ion Scattering
Mask Erosion
Trenching
Dry Etch Induced Damage
Etching Summary
Precise Control in Feature Size, Etch Depth, Etch Profile, and Uniformity
Low Damage and Minimum Electrical Degradation(电气退化)
High Throughput
Trade-Offs among Multiple Factors
High-Density Dry Etching Systems with Independent Control of Ion Density and Ion Energy (Both Chemical and Physical Etching)
Cycling between Etching and Deposition to Maintain Fast Etch Rate with Vertical Profile
Depends on Lithography and Film Properties
Endpoint-Detection
Etch Should Proceed to End-Point But Not Beyond - Selectivity
Timed-Etch: Inaccurate
End-Point Detection
Optical-Reflection
Emission-Spectroscopy(发射光谱法)
Temperature Controlled Stage
Wafers Pulled-Flat to Chuck(卡盘)
Better Cooling-Efficiency
Less Particle-Generation
Wet vs. Dry Etching
Chemical Consumption and Disposal: liquid vs. gas
Profile Control
Directional Reactive Species(定向反应物) for Vertical Profile
Tapered, Rounded, Mirrors, Lenses
Chemical vs. Physical
Directionality and Density of Neutral Species vs. Charged Particles
Damage
Charging, Ion Bombardment(离子轰击), Contamination