Engineering Module: Integrated Circuits & Microprocessors

International & Access Foundation Programmes: Engineering Module, Semester 1

• The module covers Integrated Circuits & Microprocessors, part of Electronic & Electrical Engineering.
• The lecturer is Dr Nevan Bermingham.

Integrated Circuits (ICs)

• ICs are collections of electronic components (transistors, diodes, resistors).
• These components are fabricated and interconnected on a small silicon (Si) semiconductor chip.
• Silicon is the most widely used semiconductor due to its properties and cost.
• Other semiconductor materials include germanium (Ge) and gallium arsenide (GaAs).
• The term "solid-state electronics" describes circuits made from a single solid piece of material.

Levels of Integration in Microelectronics

• Integrated circuits evolve over time, increasing in complexity and the number of devices on a chip.
• This progression includes Small Scale Integration (SSI), Medium Scale Integration (MSI), Large Scale Integration (LSI), Very Large Scale Integration (VLSI), Ultra Large Scale Integration (ULSI), and Giga scale integration.
• Data on the number of devices and approximate year of integration is included in the course.

Overview of IC Technology

• ICs contain hundreds, thousands, or millions of microscopic electronic devices.
• These devices are fabricated and interconnected on a silicon chip.
• The chip is a thin rectangular plate, usually 5-25mm on a side and 0.5mm thick.
• Different layers with distinct electrical properties form each electronic component (e.g., transistor).
• These layers work together to accomplish the device's functions.

Packaging of ICs

• ICs are packaged outside the clean room to prevent environmental damage.
• Packaging involves attaching the chip to leads and enclosing it in a protective package.
• This package protects from factors like moisture, corrosion, temperature fluctuations, vibration, and shock.
• The package includes leads that connect the IC to external circuits.

Processing Sequence for Silicon-based ICs

• Sand is refined into pure silicon, forming wafers.
• Fabrication involves creating, altering, and removing layers to form electronic devices.
• Lithography defines the processing regions on the wafer's surface.
• Packaging processes test, divide into units, and encapsulate the chips.

Clean Rooms

• IC fabrication occurs in controlled environments called clean rooms to minimize foreign particle contamination.
• Cleanliness is crucial for maintaining feature size; standards are measured by the number of particles per cubic foot of air (e.g., class 100 or 10).
• The level of cleanliness is directly related to the size of microscopic features on the integrated circuits and is decreasing annually.

Silicon Processing

• Electronic-grade silicon (EGS) is the main material for microelectronic chips.
• It makes up over 95% of semiconductor devices worldwide.
• Purification, crystal growing, and wafer shaping are critical steps in substrate fabrication.

Crystal Growing

• Silicon substrates for microelectronic chips require single-crystal structure with specific unit-cell orientations.
• Semiconductor device fabrication demands ultra-high-purity silicon.
• The Czochralski process is a common technique for pulling a single crystal boule from molten silicon.

Wafer Slicing

• Wafer slicing uses a diamond-grit saw to cut silicon ingots into individual chips.
• Slicing happens at the internal diameter of the blade to ensure uniform thickness, parallelism, and flatness.
• Wafer accuracy and reduction of kerf loss are crucial during slicing.

Wafer Preparation

• Wafer rims are rounded to prevent chipping.
• Chemical etching removes damage, followed by polishing for smooth surfaces.
• Chemical cleaning removes residues and contaminants.

Lithography

• ICs have microscopic regions on the wafer.
• Planar processes involve adding, altering, or removing layers to create a specific pattern on the wafer.
• Lithography transfers circuit design information to the wafer surface.

Lithographic Technologies

• Various lithography techniques exist (photolithography, electron lithography, X-ray lithography, and ion lithography) using different radiations to transfer the mask pattern to the wafer surface.

Photolithography

• Light radiation exposes a photoresist coating on the wafer to transfer the mask pattern.
• UV light is common for high-resolution imaging.
• A mask prevents unwanted exposure.
• Photoresist is an organic polymer, sensitive to light (UV).
• Patterned mask exposure controls photoresist solubility.

Photoresists

• Photoresist is an organic polymer which is sensitive to light
• UV exposure impacts photoresist's solubility and is controlled by the pattern on the mask.
• Photoresists selectively alter the wafer surface during processing.

Contact Printing, Proximity Printing, and Projection Printing

• Contact printing presses the mask directly against the resist for high resolution but can cause wear.
• Proximity printing separates the mask from the resist, reducing wear but slightly reducing resolution.
• Projection printing projects the mask pattern onto the wafer using lenses for higher resolution and less mask wear.

Processing Sequence in Photolithography

• The wafer surface is oxidized to form SiO2, preparing it for photolithography.
• Photolithographic steps follow the processes.

IC Packaging

• Packaging is the final IC fabrication step connecting components to external circuits and protecting from environmental damage.

Design Issues in IC Packaging

• Electrical connections to external circuits.
• Protection from factors like humidity, corrosion, temperature, and heat dissipation.
• Manufacturing cost is critical.
• Issues involve separating the chips from the wafer, connecting them to packages, and encapsulating them.

Input/Output (I/O) Terminals

• Interconnecting internal to external circuits is challenging due to the high numbers of devices and reduced size.
• Device size reduction and more devices increase interconnection complexity.

IC Package Materials

• Ceramic (alumina – Al2O3) is a common material for IC packages.

Yield Testing

• After packaging, each IC undergoes tests for damage and functional characteristics.
• IC yield loss and variations during fabrication are significant factors.
• High yield is critical to profitability.

Wafer Processing

• High-quality production requires pure starting materials, modern processes, well-maintained clean rooms, and effective testing procedures.