MSE4004 Topics for Exam III
Electronic device fabrication
Advanced lithography methods: why do we need them?
Shrinking feature sizes, increased density, improved performance, cost reduction
What are some of the methods and what mechanisms do they use?
EUV: short wavelengths → higher res and finer features (needed for semiconductor nodes)
Nanoimprint lithography → high res, photonics, nanoelectronics, and bioengineering
Electron Beam Lithography (EBL): EBL uses a focused beam of electrons to directly write patterns onto a substrate coated with an electron-sensitive resist material. It offers extremely high resolution
What equipment is necessary to use them? What kind of linewidths can be achieved?
EUV <10nm
Multiple Patterning <20
Nanoimprint Lithography (NIL) <10nm
Directed Self-Assembly (DSA): <10nm
Electron Beam Lithography (EBL): <10nm
Subtractive processing methods: Be familiar with most methods described in class, what are they used for, be able to tell which can be used for device fabrication, which you cannot (Lecture 7)
Wet chemical etching
Electrochemical → redox reactions
Isotropic etching (same rate in all directions, does not depend on orientation of mask)
Anisotropic etching (rate depends upon orientation to crystalline phases, used for complex shapes)
Etch rates are (100) > (110) > (111) for Si
(111) is the stop plane
Process
Transport of reactants to surface, surface reactions, transport of products from the surface
Used in micromachining
Dry chemical etching
Subtractive process that uses plasma (hot ionized gases) for removing materials
Dry etching can yield finer patterns than wet etching
This method is also safer as no corrosive acids or bases are needed
Glow discharge Methods or Ion Beam Methods
Pressures
Low: physical sputtering, unselective, directional, and can cause radiation damage
Medium: reactive ion etching, physical and chemical
High: plasma etching, faster, selective, least damage
Etching of efficiency is dependent on electron energy, density, ion energy and density, and current
Most common materials that are etched in processing IC’s: silicon, SiO, Ti, Al, Photoresist
RIE: Reactive Ion etching
Etched Copper can be done this way
Gas/Vapor Etching, Plasma Etching, Reactive Ion Etching (mostly nanofab), Sputter Etching
Sputter etching, ion milling
FIB
Used to carefully etch specific regions in a specimen
The ion column can be used for selective removal of material by ion beam milling.
The ion beam can also be used for ion-enhanced imaging of fine texture analysis in crystalline materials.
Laser Machining and EDM (electric discharge machining)
Laser:
All classes of materials can be laser machined:
metals, ceramics, plastics
Energy determines the achieved temperature
EDM
Three types:wire,sinker and hole
Most common is wire EDM: Uses a wire to cause dielectric breakdown in air
Can be used for machining any conductive material
Yields excellent surface quality and very high accuracy
Procedure:
charge up an electrode
bring the electrode near a metal workpiece (oppositely charged).
as the two conductors get close enough a spark will arc across a dielectric fluid. This spark will "burn" a small hole in the electrode and workpiece.
4. continue steps 1-3 until a hole the shape of the electrode is formed.
Types:
ICP (Inductive Coupled Plasma)
Electron Cyclotron Resonance (ECR)
Magnetic Confinement RIE
Similarities and differences between wet chemical etching and dry chemical etching, differences between different resist wall profiles
Electronic Packaging (Lecture 9)
Packaging Hierarchy for a PC Board
Packaging Levels:
Wafer level Packaging
Printed Wiring Board Level (PWB) or PCB
Packaging and Assembly
Sealing and Encapsulation
Thermal and Mechanical Reliability
Wafer Level Packaging (Individual Die)
Adhesives
Tab
Solder Bump
Single or Multichip Package
Multichip modules can be similar to single chip modules and have regular die attach, wire bonding and pin grid arrays
They can also be mounted by μBGA ball bump bonding as for single chip cases
Examples of substrates used Acronyms: SMT, PWB, MCM, TAB, PGA, BGA
Surface Mounted Technology (SMT)
Printed Wiring Board Level (PWB)
Multichip Module (MCM)
(TAB)
Pin Ball Grid Array (PGA)
Ball Grid Array (BGA)
Die Attach Film (DAF)
Dual In-line Package (DIP)
Die attachment methods
In the wire bond method (top), the die faces up and is attached to the package via wires.
The flip chip (bottom) faces down and is typically attached via μBGA solder bumps similar to the larger ones that attach BGA packages to the printed circuit board
Advantages of flip chip technology
Mounted upside down
Better connections to the chip as opposed to wire bonding where the wires add extra length, capacitance and inductance that limit signal speed.
More attachment points available since the whole area of the chip is available instead of just the edges
Faster production
Smaller overall package size
Uses μBGA
Current packaging schemes:
Surface mounted resistors, capacitors, inductors
Integrated resistors, capacitors, inductors
Cree/Wolfspeed - SiC single crystal substrates for GaN LEDs
Lumileds thin film flip chip → packaging of GaN LEDs
RF SAW filter SF16 → smallest as of August 2003
Kyocera
Thermal dissipation
As the number of transistors in each chip or integrated circuit increases, more heat needs to be dissipated
Methods used:
Through the substrate
Chip backside
Current thermal solution is sufficient for single chip, not acceptable for stacked high-performance chips
Differences between SOC and SOP
System on Chip VERSUS System on Package
SOP incorporates embedded components(resistors, capacitors, inductors) within the package rather than placing them on top
SOP ADV
Design simplicity
Lower cost
Higher system function integration
Better electrical performance than SOC (system on a chip)
Can stack different types of chips with processors and flash memory .
SOC → ability to place multiple function "systems" on a single silicon chip, cutting
development cycle while increasing product functionality, performance and quality.
Nanoelectronics (Lecture 8)
What determines whether a device is a nanoelectronic device or not?
Can be made from:
Individual nanoparticles, nanorods, nanotubes,etc..
Make contacts using photolithography patterns or soft lithography
Mixing with polymers or other materials
Most made by sol-gel
What are some examples of nanoelectronic devices?
Applications include: single electron transistors, chemical and mechanical sensors, and components for solar cells, displays, etc.
What materials are currently being used?
CdSE Nanocrystals - quantum dots (demonstrate quantum confinement or size effects)
Electrochromic Polymers
Know the differences between graphite, graphene, graphene oxide, reduced graphene oxide, C60 , nanotubes, nanowires, nanobelts
Graphite: carbon hexagonal lattice, good conductor
Graphene: single layer carbon in 2D honeycomb lattice
Graphene Oxide: graphene with oxygen functional groups
Reduced Graphene Oxide: Graphene oxide with additional electrons (removed some oxygen functional groups)
C60: Buckyball
Nanotubes: cylinders of rolled up graphene sheets
Nanowires:1D Carbon in linear fashion
Nanobelts:narrow, belt like structures of carbon in ring like configuration
What methods are normally used to characterize nanomaterials?
SEM, TEM, AFM, XRD, Raman Spec, FTIR
Why is there an emphasis on transparent conductors?
Touchscreens and displays,
Solarcells and photovoltaics
LEDs and windows
Why is there emphasis on flexible electronics?
Form Factor Flexibility (Durability), Wearables, Energy Storage, Space saving
Point defects in materials (Lecture 11)
Defect types
Point defects (vacancies, interstitial and substitutional)
Line Defects (dislocations)
Area Defects (Grain Boundaries)
Electronic Defects (0D)
Point Defects (0D)
Line Defects (1D)
Planar Defects (2D)
Dislocations Loops (2D & 3D)
Grain Boundaries (2D & 3D)
Clusters (3D)
Kroger-Vink notation
ESC
E represents what is on the site, either V for a vacancy or, if occupied by an element, the element symbol
S represents what type of site is occupied by E, either i for an interstitial or, if normally occupied by an element, the symbol for that element
C represents the charge relative to the normal ion charge on the site S, using dots to represent positive relative charges, primes to indicate negative relative charges, and X to indicate zero relative charge
Mass action relations and how to determine equilibrium constants for different defect reactions
Mass balance: can’t create or destroy matter in a reaction to form defect (i.e., mass on the left side of the equation equals that on the right)
Site balance: sites must appear in correct ratio for the stoichiometric crystal on either side of reaction.
Charge balance: crystal must always be electrically neutral (net charge on the left side of the equation equals that on the right)
Low partial pressure of oxygen & High partial pressure of oxygen
Separate into regimes
Brouwer diagrams
Constructing Brouwer Diagrams (as a function of PO2 or similar) requires the meticulous following of several steps.
1. Write all the defect reactions expected in the system with their corresponding equilibrium constant equation.
2. Write the electroneutrality equation.
3. Separate the problem into regimes and write the corresponding Brouwer approximation equation for each case.
4. Cleverly combine the equations in step 3 with the equations in step 1 to solve for each of the defect concentrations and establish their PO2 (or similar) dependence (slopes in the diagram) in each region.
5. Substitute values of K’s (if known) and obtain concentration values for each defect in each regime (if possible).
6. Find the PO2 (or similar) value for the boundaries between two regions.
7. Neatly plot your diagram based on the calculated values from steps 4-6
Effect of defects on electrical conductivity and dominant charge carriers
Mixed Conductors (SrTiO3)
Ionic Conductors (CeO2)
Acceptor Doping (ZrO2)
Temperature dependence behavior for different types of materials, especially how ionic conductors differ from semiconductors and highly conducting materials and what determines their activation energy
Choose at least two other group term paper topics and be able to summarize what you learned from them
Magnetic Levitation
Lithium batteries
Carbon Capture