Final Review

Process Overview

1. Pattern Transfer
   1. Deposition - over the entire wafer
   2. Lithography - optical mask
   3. Etching material through openings in photoresist
2. Self Alignment
   1. Using previous step to create alignment with prior layers
   2. S/D masked with gate polysilicon
   3. reduce tolerances

Lithography

1. Optical Systems
   1. Diffraction limit
   2. Step and Repeat
   3. Magnifcation reduction onto wafer
   4. Modulation Transfer Function
2. Photoresist
   1. Abosrption of light variable with time - AM+B
   2. PAC Concentration reaction with light dM/dt = -ItC
   3. Development
      1. M' = M exp (-R3 * (1-M) )
      2. Development Rate R = 1 / ((1-M')/R1 + M'/R2))
3. Contrast Enhancement through absorption

Deposition

1. CVD Systems
2. Isotropic - large surface migration
3. Collection Angle determines
   1. LMFP
   2. SMFP

Etching

1. RIE Systems
2. Neutrals - Isotropic Component
3. Sputtering - Complex Angular dependence
4. Reactive Ions - anisotropic component oriented along DC plasma field
5. Spacer Formation - Technology

Device Physics

1. Threshold Voltage changes due to S/D fields
2. Current saturates for different reason
3. Turnoff difficult - thin oxide to control
4. Gate to Drain is never zero

Isolation Technology

1. Oxide Growth - Deal Grove law of growth
2. LOCOS technology
   1. pad oxide to relieve stress
   2. nitride masks growth of oxide
3. Shallow trench
   1. Cut a trench
   2. Grow thin oxide
   3. Deposit oxide and CMP to planarize
   4. Stress is major concern
   5. Stress influences oxidation growth rate

Gate Dielectric

1. Thin oxide gives greater control of channel, off current
2. Leakage, Reliability limit thickness of oxide
   1. Gate current proportional to exp( -1 / tox )
   2. Reliability proportional to gate current, trap generation
3. Boron Penetration
   1. boron diffuses from poly through gate dielectric to channel
   2. changes threshold voltage
4. Nitrogen
   1. limits boron penetration
   2. change permittivity
5. Metal Gates
   1. needs to prevent buried channels
   2. eliminates boron penetration problem
6. Alternate Materials
7. Thermal Stability

Implant

1. Stopping Powers
   1. Nuclear
   2. Electronic
2. Projected Ranges, Straggle, Gaussian Profiles
   1. Should be able to compute these
   2. Estimate range
3. Damage Calculations
4. Channeling
   1. Techniques to avoid

Annealing

1. Dopant Diffusion though point defects
2. Simplified solutions of diffusion equation
3. TED
   1. +1 factor
   2. Clusters of Defects - {311}
   3. Dissolution to surface
4. Activation
   1. Solid Solubility
   2. Segregation and Dose Loss
5. Alternate Annealing
   1. RTA
   2. Plasma Doping
   3. Spike Anneals
6. Silicides
   1. Metal reaction with silicon to form a phase
   2. Salicide

Process Integration

1. Channel Engineering
   1. Wells
   2. Channel Stop
   3. Threshold Adjust
2. Wells
   1. Single Well
   2. Twin Well, Epi technology
   3. Gettering
3. SOI
   1. buried oxide
   2. SIMOX, Smart Cut
   3. Advantages, Disadvantages
4. Dual Gate Devices
   1. FINFET
   2. Pagoda
   3. Vertical Replacement