Thermodynamics in Chip Processing Terry Ring

Silicon Wafers

Chip Feature Scaling

Moore’s Law please see http://developer.intel.com/update/archive/issue2/focus.htm

What is a semiconductor? Metal Insulator Ceramic (oxides) Semiconductor Diamond Silicon Germanium Gallium Arsenide Host of others

Intrinsic Silicon Silicon has four valence electrons. When a group of Silicon atoms bond together to produce a pure lattice structure, the material is referred to as Intrinsic Silicon.

Silicon Doping This pure silicon configuration (intrinsic silicon) is a poor conductor because none of its electrons are available to serve as carriers of electric charge. The fabrication of integrated circuits requires that the substrate (the wafer surface) be somewhat conductive. This process is known as doping. Boron (B), Phosphorus (P), and Arsenic (As) are the most common dopant atoms used in the industry.

Dopant Chemistry By looking at the Periodic Table, we can determine the number of electrons that Boron and Phosphorus have in their outer orbit.

N-Type P Si Si Si Si Si P Si Si Si

P-Type Si Si Si B Si Si B Si Si Si

Anatomy of a Memory Chip One Die or Chip

Building Blocks of the DRAM memory cell

READ +

WRITE -_

Basic DRAM memory cell - 1T Transistor Capacitor

DRAM memory Array

MOSFET-Gate, Source, Drain Metal-Oxide-Semiconductor-Field-Effect-Transistors A MOSFET is composed of three main components; a gate, a source, and a drain. The gate is a physical structure built on the wafer surface to control the opening and closing of a source-to-drain channel. To create this structure, a metal and oxide layer are formed on a semiconductor surface (MOS). The source and drain regions are just highly doped, shallow pockets in the wafer surface next to the gate.

The Transistor(continued) Doing the dishes requires that we access a Source (or reservoir) of water. Channel (or pipe) connects the reservoir to the sink. Don’t want a continuous flow of water to our drain (or sink). . . Need a gate (or valve) to block the water flow.

Next Step Deposit Metal

Wafer with Photoresist Lithography Light Source Light passes thru die mask Light imaged on wafer Stepper to new die location Re-image Mask Reduction Lens Wafer with Photoresist

MS&E vs ChE How is a Materials Science and Engineering Education Different from Chemical Engineering Education? Focus on Solids Processing What Crystal Structure Higher Purity Materials Impurities Control Properties Semiconductors Grain Boundaries Where atoms are in structure determines properties

Where Thermodynamics Comes into Chip Processing Evaporation Rate during Spin Coating Evaporation Rate during Photoresist Drying Metal Physical Deposition Chemical Vapor Deposition Feed of TEOS Rxn of TEOS Etching - SiF4 vapor pressure CMP Solution Equilibria Dissolution/Precipitation

Wafer with Photoresist Lithography Light Source Light passes thru die mask Light imaged on wafer Stepper to new die location Re-image Mask Reduction Lens Wafer with Photoresist

PhotoLythography PhotoResist UV light =193 nm 80 nm Line

Photoresist -Sales $1.2 billion/yr. in 2001 Resins phenol-formaldehyde, I-line Solvents Photosensitive compounds Polymethylmethacrylate or poly acrylic acid = 638 nm RED LIGHT diazonaphthoquinone Hg lamp, = 365 nm, I-line o-nitrobenzyl esters – acid generators Deep UV, = 248 nm, KrF laser Cycloolefin-maleic anhydride copolymer Poly hydroxystyrene =193 nm gives lines 100 nm = 157 nm F laser Additives

Photoresist Spin Coat wafer Dry solvent out of film Expose to Light Develop Quench development Dissolve resist (+) or developed resist (-)

Spin Coating Cylindrical Coordinates Navier-Stokes Continuity

Newtonian Fluid- non-evaporating If hois a constant film is uniform For thin films, h  -1 t-1/2

Evaporation Model - Heuristic Model CN non-volatile, CV volatile e = evaporation rate of volatile component ei = kMA(Psolvent-I - 0) q = flow rate

Evaporation Rate What is Psolvent-i in a mixture? Other solvents and non-volatile components fil = fiv equilibrium condition fiv =yiP fil = γ i xi Pisat ln γ i =GiE/(RT)

Vapor Pressure of 2 solvent mix P =Σ γ i xi Pisat = γ 1 x1 P1sat + γ 2 x2 P2sat y1 =P1/P= γ 1 x1 P1sat /(γ 1 x1 P1sat + γ 2 x2 P2sat ) Pisat obtained from Normal Boiling Point & Heat of vaporization (Claperon Equation) Eqs 12.10 a Margules equation, GE/(x1x2RT)=A21X1+A12X2

See MathCad Example Vapor Pressure of Solvent Mix.mcd Binary Solvent Mixture Ternary mixture of Solvent plus Non-volatile Resin

Next Step Dissolve Edge of Photoresist So that no sticking of wafer to surfaces takes place Wafers are stored in a rack on edge So that no dust or debris attaches to wafers Wafer with Photoresist

How would you set up this problem? fil = fis equilibrium condition fis = γsi zi fsi fil = γli xi fli same a previous example of solvent mix ln γl i =GiE/(RT) same a previous example of solvent mix γli xi fli = zi γsi fsi γli xi = zi γsi Ψi Chapter 14 Ψi = exp{(ΔHisl/R)[(1/Tm) - (1/T)]} Chapter 14 ΔHisl =Heat of fusion, Tm melting temperature zi γsi=1 for ideal solid (misicible) zi= mole fraction of mix in solid

Break Second lecture is next What did we learn Calculate the partial pressure Used to calculate the evaporation rate of a component of a solvent mixture Calculate the solubility of a solid in a solvent mixture

Lecture 2 Metal Deposition on the wafer Wires to connect the transistors and capacitors To each other To outside world 2 Mb memory chip has > 1 km of wire 8 layers of wiring on top

Deposition Methods Growth of an oxidation layer Spin on Layer Chemical Vapor Deposition (CVD) Heat = decomposition T of gasses Plasma enhanced CVD (lower T process) Physical Deposition Vapor Deposition Sputtering

Physical Vapor Deposition Evaporation from Crystal (metal) Deposition on Wall

Physical Deposition Reactor Wafers in Carriage (Quartz) Carrier Gasses enter Pumped out via vacuum system Furnace Metal evaporated Sublimation No liquid phase Furnace Vacuum Chamber at lower Temp s l v P V

Deposition Rate Ratei = Km A {Pi(TF) - Pi(TC)} What is the sublimation partial pressure of metal as a function of temperature? fiv = fis equilibrium condition fis = γsi zi fsi= γsi zi Pisat exp[VMi(P - Pisat)/(RT)] Poynting Factor fiv =yiP

Metal Saturation Pressure Sublimation Vapor Pressure Claperon Equation ΔHS is the heat of sublimation ΔHS = ΔHF + ΔHV solid to liquid then liquid to vapor

MathCad File Sublimation Vapor Pressure of Alloy.mcd