Semiconductor Manufacturing Process Overview

Semiconductor Manufacturing Process

• Semiconductor fabrication is crucial
• Fabrication is based on CMOS technology
• CMOS transistors are on silicon wafers
• Silicon is economical, better conductivity, less noise, and easier to format MOSFET transistors
• Silicon is the base material for MOS fabrication

Step-by-Step Fabrication Process

• Process transforms silicon wafers into functional chips
• Wafer manufacturing is a crucial stage in semiconductor industry
• Wafers are thin, flat disks that function as substrates for integrated circuits (ICs), sensors etc
• Key stages in wafer production:
  • Raw material preparation (Si Ingot Production)
  • Ingot Slicing
  • Wafer Polishing
  • Wafer Cleaning

Oxidation

• Oxidation creates an oxide layer (SiO2) or insulating layer to control current flow, isolate components, and boost device performance
• Oxidation furnace operates at 900-1200 degrees Celsius using H2O or O2
• SiO2 is used in bipolar and MOS transistors to isolate devices, provide surface passivation, and act as a barrier against impurity diffusion/implantation in substrates
• SiO2 acts as a component in MOS devices and a dielectric isolation layer between multilevel interconnect layers

Oxidation Techniques

• Thermal Oxidation - Basic process in IC fabrication. Used when low charge density level is required at the interface of silicon and oxide
• Wet Oxidation - Chemical vapor deposition for forming SiO2 layer on top of the metal layer in multilevel structures
• Plasma Oxidation

Lithography

• Lithography transfers geometric patterns from a mask onto a thin layer of radiation-sensitive material (resist) on a semiconductor wafer
• Photolithography uses e-beam and involves:
  • Oxidation Layering
  • Photoresist Coating
  • Stepper Exposure
  • Development and Bake
  • Acid Etching
  • Spin, Rinse, and Dry

Photomask Design

• Photomask is a master template for IC design
• Commonly 6-inch X 6-inch
• Uses quartz or glass substrates with opaque films for more complex masks
• Designs start as a file format, then created in photomask facilities
• Masks are used in lithography scanners to pattern desired features on wafers

Full Mask

• One layer = One mask
• Number of layers = Number of masks

Etching

• Etching removes unwanted materials from a wafer using chemicals or plasma after lithography
• Wet Etching: Selective removal of material using liquid etchants like acids, bases, or solvents
• Dry Etching: Material removal using plasma to selectively remove material on a substrate

Deposition

• Blanket of materials deposited on a surface using multiple techniques, such as:
  • Selective Deposition
  • Atomic-Layer Deposition
  • Chemical Vapor Deposition (CVD)
  • Physical Vapor Deposition (PVD)
• Type of technique depends on the semiconductor process node, type of chip, and time required for the deposition
• The deposition process must be uniform across the wafer

Doping

• Ion implantation and diffusion introduce dopants for semiconductor materials
• Ion Implantation: High-energy ion bombardment of dopants into semiconductor wafers for precise doping profiles in devices like CMOS
• Diffusion: Dopants diffused at high temperatures into semiconductor materials

Diffusion vs. Ion Implantation

• Ion Implantation: Precise control of dopant concentration and depth, but can damage the material and is more costly.
• Diffusion: Simpler, less expensive, but offers less control of dopant profile.

Diffusion

• Adds impurities (N-type or P-type) to silicon wafers for MOSFET transistor regions.
• Impurity (dopant) added to silicon using chemical sources at high temperatures
• Can also use doped oxide source, or ion-implanted source

Ion Implantation

• Process where impurity atoms are accelerated to high velocity and introduced into a single crystal substrate
• Impurity atoms enter lattice, colliding with existing atoms and gradually losing energy until rest at some depth

Metal Wiring

• Crucial process for creating electrical connections on wafers
• Involves depositing, patterning, and etching metal layers for functional electrical connections
• Techniques: metal deposition, lithography for patterning, etching, annealing to improve properties, testing to ensure quality
• The process is crucial for performance and reliability of semiconductor devices

Wafer Dicing

• Cuts a silicon wafer into individual components (chips/dies).
• Process is vital for integrated circuit and semiconductor devices fabrication
• Requires high-quality high precision machinery

IC Packaging

• Encapsulates the semiconductor device protecting it from corrosion and damage and allows mounting to printed circuit boards (PCB).
• Final stage in semiconductor production
• The package protects the IC from damage from external elements and corrosive effects of age

Common IC Package Types

• Pin-grid array (for socketing)
• Lead-frame and dual-in-line packages (for assemblies with pins through holes)
• Chip scale package (single-die, direct surface mountable with area less than 1.2X die area)
• Quad flat pack (leadless variety)
• Quad flat no-lead (tiny package, for surface mounting)
• Multichip package (incorporates multiple ICs, discrete components, and semiconductor dies on a substrate)
• Area array package (maximizes chip surface area for interconnections)

Testing

• Functional testing of fabricated semiconductor chips
• Crucial rules and considerations during the fabrication process:
  • Design Rule Check (DRC)
  • Scalable Design Rule
  • Micron-Rules Process
  • Circuit-Under-Test
  • Packaging ICs Rules
  • Cleanroom Environment
• Different fabrication methods used according to different types of semiconductor devices

Fabrication Process: Inverter

• Sequential steps in creating an inverter chip
• Crucial steps using photolithography to define layers of the chip, including n-well, polysilicon, n+ and p+ diffusion, contacts and metal.

Inverter Cross-Section

• Detailed internal structure of an inverter, showing transistors (nMOS and pMOS), substrate and well connections, layers, and materials.

Fabrication Process: Inverter Mask Set

• Hypothetical sequence of masks used to create an inverter, including n-well, polysilicon, and n+/p+ diffusion layers and metal layers

Fabrication Process: Cross-sections during n-well manufacturing process

• The method of adding dopants, diffusion and ion implantation.
• Diffusion and ion implantation methods for adding dopants

Fabrication Process: Cross-sections during polysilicon and n-diffusion manufacturing process

• Process of creating transistor gates.
• Using Chemical Vapor Deposition
• Patterned polysilicon masks for gates

Fabrication Process: Cross-sections during p-diffusion, contacts, and metal manufacturing process

• P-diffusion mask, oxide is used for masking, patterned, and contact cuts
• Sputtering aluminum for even metal coating
• Metal patterning techniques using metal masks

Layout Design Rules

• Rules for packing and arranging small features in manufacturing processes
• Scaling designs can be difficult across different processes or foundries
• Descriptors for processes: feature size, minimum drawn transistor channel length.
• Typical minimum transistors channel length is half of the feature size.

Layout Design Rules: Inverter

• The layout of transistors is important
• PMOS transistors are typically wider than N-MOS transistors because holes move slower than electrons.

Gate Layouts

• Line of diffusion, which consists of four horizontal strips: metal ground, n-diffusion, p-diffusion and metal power
• Power and ground called supply rails.
• Layout for inverter, showing well and substrate taps placed below power and ground rails.
• Line of diffusion rule widely used

Other

• Links to videos that can further explain the content and provide a better understanding of MOSFETs etc in more detail

This quiz explores the intricacies of the semiconductor manufacturing process, focusing on CMOS technology and silicon wafers. It covers key stages of wafer production, including raw material preparation and oxidation techniques, essential for creating functional chips and integrated circuits.