Semiconductor Fabrication Basics
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Questions and Answers

What is the purpose of the Siemens technique in silicon purification?

  • To reduce the amount of silicon dioxide in the silicon by using carbon mixtures.
  • To increase the purity of silicon from 98% to 99.9999% by depositing silicon on a heated filament. (correct)
  • To convert metallurgical grade silicon to chlorosilanes, which are then purified.
  • To remove impurities from silicon by using a vacuum chamber.

    • What is the typical thickness of the native oxide layer formed on a silicon wafer?

  • 17 micrometers
  • 17 nanometers
  • 17 angstroms (correct)
  • 17 millimeters

    • What is the primary purpose of a cleanroom in semiconductor fabrication?

  • To provide a controlled environment with low humidity for wafer processing.
  • To minimize the contamination of wafers during processing. (correct)
  • To regulate the temperature and airflow for optimal wafer growth.
  • To protect workers from hazardous chemicals used in wafer fabrication.

    • What are the primary steps involved in the RCA cleaning process for silicon wafers?

    <p>Removing organic contaminants, removing metal impurities, and forming a native oxide layer. (A)</p> Signup and view all the answers

    What is the main purpose of gettering in semiconductor fabrication?

    <p>To trap impurities that might contaminate the active device regions. (B)</p> Signup and view all the answers

    Why are HEPA filters used in cleanrooms?

    <p>To filter out large particles and dust from the air. (C)</p> Signup and view all the answers

    Which of the following is NOT a key factor in the design and operation of a cleanroom?

    <p>Electromagnetic shielding (C)</p> Signup and view all the answers

    What is the significance of the Czochralski (Cz) and Kyropoulos (Ky) crystal growth techniques?

    <p>They are used to produce high-quality single-crystal silicon wafers used in the semiconductor industry. (B)</p> Signup and view all the answers

    What is the primary difference between the Czochralski (Cz) and Kyropoulos (Ky) crystal growth techniques?

    <p>Cz uses a rotating crucible, while Ky uses a stationary crucible. (D)</p> Signup and view all the answers

    Which of the following is NOT a type of gettering used in semiconductor fabrication?

    <p>Vacuum gettering (B)</p> Signup and view all the answers

    Flashcards

    Siemens Technique

    A technique used in silicon purification to remove impurities by converting silicon into volatile chlorosilanes. High-purity silicon is then deposited onto heated filaments.

    Czochralski Crystal Growth

    The process of growing a single crystal of silicon from a molten silicon pool. A seed crystal is dipped into the melt and slowly pulled out.

    Vacancy

    A point defect in a crystalline lattice where an atom is missing from its normal position.

    Interstitial Atom

    A point defect in a crystalline lattice where an extra atom is located in a space between lattice sites.

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    Controlling Contaminants in Silicon Wafer Fabrication

    The use of clean rooms, wafer cleaning and gettering to prevent or control contaminants during silicon wafer fabrication.

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    Clean Rooms

    Highly controlled manufacturing environments with air filtration systems to minimize airborne particles.

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    RCA Cleaning

    A standard cleaning procedure used to remove impurities and oxides from silicon wafers. It involves several steps using chemicals like ammonia, hydrogen peroxide and hydrochloric acid.

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    Gettering

    A technique used to trap and deactivate impurities within the silicon wafer. This can be achieved by using getters, which are materials that have a strong affinity for the contaminants.

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    Polysilicon Backside Gettering

    A type of gettering where a layer of polycrystalline silicon is deposited on the back surface of a wafer to act as a trap for impurities.

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    Metal Gettering

    A type of gettering where a layer of metal (like gold or platinum) is deposited on the back surface of the wafer to trap impurities.

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    Study Notes

    Semiconductor Fabrication

    • Semiconductor materials: Silicon (Si) is the primary material used for integrated circuits (ICs). It has a diamond crystal structure.
    • Crystal structure: Crystals are characterized by repeating unit cells in x, y, and z directions. Planes and directions are defined using an x, y, z coordinate system with Miller indices.
    • Silicon purification: Silicon is purified from silicon dioxide (SiO2) using methods like high-temperature melting and chlorosilanes. The goal is to achieve extremely high purity (e.g., 99.9999%).
    • Czochralsky (CZ) method: A common method for producing single-crystal silicon. Raw materials are melted, and a single-crystal seed is introduced to initiate crystal growth.
    • Control parameters in CZ: Pull rate, temperature, and rotation rate are key control parameters.
    • Float zone (FZ) method: An alternative technique for refining and growing single-crystal silicon.
    • Wafers: Silicon crystals are sliced into thin wafers for IC manufacture. The wafers must be polished to achieve high surface quality.
    • Impurities: Oxygen (O) and carbon (C) are common impurities in silicon. O and C in CZ silicon typically reach concentrations on the order of 1018 cm-3 and 1016 cm-3, respectively.
    • Defects: High-temperature processing and other manufacturing steps can introduce defects (e.g., point defects, dislocations) into crystals. These can affect device performance.

    Clean Rooms and Wafer Cleaning

    • Clean rooms: Critical environments to minimize particle contamination during IC fabrication and processing.

    • Cleaning protocols: Wafer cleaning procedures utilizing chemicals like those in RCA cleans ("standard process"). Removal of organics, heavy metals and alkali ions are crucial.

    • Methods for removing contamination: Cleaning techniques include using ultrasonic agitation combined with appropriate chemicals.

    • RCA clean: A typical "standard process" for removing contaminants from silicon wafers. This process uses different mixtures of chemicals (e.g., hydrogen peroxide, sulfuric acid, nitric acid, ammonium hydroxide) to clean off organic, metal, and other components on the surface.

    • Gettering: A process designed to remove unwanted metal ions and alkali ions from device active regions.

      • Intrinsic gettering: Employing Si wafers, precipitation of SiO2, through temperature cycles.
      • Extrinsic gettering: Utilising dielectric layers and metal traps on backside of wafer.

    • Contaminants: Particles, organic films (e.g., photoresist), and heavy metals are contaminants that can affect device performance.

    • Important control parameters: Air quality, temperature, and humidity are strictly controlled parameters during wafer processing within clean rooms.

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    Διεργασίες Κατασκευής Ολοκληρωμένων Κυκλωμάτων

    Description

    Explore the fundamental concepts of semiconductor fabrication, including the properties of silicon, crystal structures, and purification methods. Learn about the Czochralsky and Float Zone methods, essential for producing single-crystal silicon. This quiz will test your knowledge on the key techniques and parameters involved in the semiconductor manufacturing process.

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