Vapor Generation Techniques

Vapor generation

• Evaporation involves heating a material to its vapor state under a vacuum, where it then condensates on a cooled substrate, creating a thin film.
• Sputtering uses Ar ions to bombard a target material, releasing atoms in the form of vapor that deposit on a substrate.
• Vapor Pressure Curve for various materials shows the relationship between temperature and vapor pressure.
• Evaporation Types include Thermal Evaporation, using resistive heating, and E-Beam Evaporation, using electron beam heating.
• Thermal Evaporation involves heating a material in a crucible by a resistive wire.
• E-Beam Evaporation uses an electron beam to heat the material in a crucible.
• Shadowing Effect is a directional deposition characteristic of evaporation, allowing for lift-off processes.
• Characteristics of Evaporation include:
  • Use of high vacuum (10-5 to 10-6 torr) to minimize contamination.
  • High directionality due to long mean free paths.
  • Shadow effect caused by high directionality.
  • Poor step coverage.
  • Suitability for lift-off processes.
  • E-beam evaporation is effective for high-temperature materials.
  • Higher deposition rates than other methods.
• Sputtering Concept uses accelerated Ar+ ions to bombard a target material, resulting in vapor deposition.
• Type of Sputtering includes DC sputtering, RF sputtering, Reactive sputtering, and Magnetron sputtering.
• DC Sputtering uses a DC bias for depositing metals.
• RF Sputtering uses an AC bias at high frequency for depositing dielectrics.
• Reactive Sputtering introduces reactive gas to deposit oxide or nitride films.
• Magnetron Sputtering uses permanent magnets to enhance electron collision with Ar gas, increasing ionization efficiency.
• Sputtering Operating Procedure involves:
  • Loading the sample wafer and target material.
  • Pumping the chamber down to 10-5 to 10-6 torr.
  • Introducing Argon gas at 1-10 mtorr pressure.
  • Turning on the thickness monitor.
  • Activating the DC or RF power supply.
  • Igniting the plasma.
  • Opening the shutter.
  • Closing the shutter and turning off the power supply when achieving the desired thickness.
  • Venting the chamber and unloading the sample wafer.
• Sputtering Applications include hard disks, compact disks, and hard coatings like TiN, TiC, and TiAlN.

Introduction

• Thin Film Deposition technologies involve growing layers of materials on a substrate.
• Applications include renewable energy, organic electronics, flat panel displays, optics, tribology, optical/magnetic storage, and hard/decorative coatings.
• Mean Free Path is the average distance a molecule travels in a gas before colliding with another molecule.
• Mean Free Path Formula:
  • λ = kT / (2πa²P)
    • k: Boltzmann constant (1.38 × 10-23 m2 kg s-2 K-1)
    • T: Temperature
    • P: Pressure
    • a: Diameter of gas molecule

Evaporation

• Shadowing Effect in evaporation is due to the directional deposition, causing shadowing behind obstacles.
• Evaporation Advantages include high vacuum, directionality, suitability for lift-off processes, and high deposition rates.

Sputtering

• Sputtering Advantages include a broader range of materials, better step coverage, and higher adhesion to the substrate.
• Composite materials deposition can be achieved through co-sputtering or sputtering from a single composite target.
• Sputtering is preferred over evaporation due to its improved characteristics.

Fabrication Flow

• Silicon Substrate as the base material for fabrication processes.
• Deposition is a key step where thin films are added.
• Photolithography used to transfer patterns onto the substrate.
• Etching removes areas to create the desired features.
• Multiple cycles of deposition, photolithography, and etching are often required.
• Inspection is used to control and monitor the process.
• Dicing separates wafers into individual dies.
• Packaging protects and connects the die to external circuitry.
• Final Test verifies functionality before assembling into a product.