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What is a Semiconductor Wafer?

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  • icon2 January 4, 2024
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Semiconductor Wafer

A semiconductor wafer is a thin slice of semiconductor substance, like crystalline silicon, used in electronics for the making of integrated circuits. In the electronics jargon, a thin slice of semiconductor material is called as a wafer. It could be a silicon crystal which is used in the making of integrated circuits and other micro devices.

Wafers are made up of very pure single crystal material. In the Czochralski process a cylindrical ingot of highly pure monocrystalline semiconductor like silicon or germanium is made by pulling of a seed crystal from a melt. Impurity atoms which are donors are added to the molten intrinsic material in exact amounts to ensure doping of the crystal. Thus changing the semiconductor into n type or p type semiconductor. The ingot is then sliced to form wafers.

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Properties of silicon wafer

Silicon wafers are available in a variety of sizes in this case diameters. They are available from 25.4 mm to 450 mm. Semiconductor plants are known by the diameter of wafers they produce. The diameter of the wafers has increased through out to reduce costs with the current gen of fab considered to be 300 mm in diameter. If you are looking to buy silicon wafers online, you can check out our shop page here.

silicon wafer sizes

Wafers that are grown by making use of materials other than silicon will have different thickness from a silicon wafer. The thickness of the wafer is measured by the mechanical strength of the material used. The thickness of the wafer must be enough to support its own weight during handling.

Wafers that are under 200 mm diameter are cut into flats on one or more sides. Which indicates the crystallographic planes of the wafer. The earlier gen of wafers had a pair of flats that were placed at different angles which additionally conveyed the doping type. Wafers that are 200 mm in diameter make use of a single small notch to convey wafer orientation which gives no visual indication of the type of doping used.

Once when one or two flats are ground into the edge of the wafer, indicates crystal orientation which applies to wafers in some diameters. Flats are used to denote crystallographic and doping orientation. The red color represents material that has been removed. Wafers that are grown from crystals have a regular crystalline structure. Where silicon has a diamond cubic structure. this Silicon wafers are not made of 100% silicon. But are formed with impurity doping concentration in the initial stages. Carbon and other metallic contamination is kept to a minimum. Semiconductor doping is a process whereby the intrinsic semiconductor is changed to an extrinsic semiconductor. Extrinsic semiconductors are components of many electrical devices.

Semiconductor Materials

First and foremost, semiconductors themselves are materials that fall somewhere between conductors and insulators. This means they can act as both at times, switching between conducting electricity or providing resistance and acting as an insulator. The most common semiconductor materials used today are silicon and compounds made from elements like gallium or arsenic mixed together (referred to as III-V compound semiconductors).

Pure silicon and other semiconductor materials are not naturally good conductors - they need some modification first. This process is known as “doping” and introduces different impurity atoms to alter the semiconducting properties in useful ways for device functioning. Doped semiconductor materials make up the thin layers built upon the wafer surface.

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Blank Semiconductor Wafers

A bare semiconductor wafer starts as an extremely thin slice cut from a large single crystal ingot of an ultra-pure semiconductor material, typically silicon. Silicon ingots up to 450mm in diameter can be grown using something called the Czochralski process. The cylindrical ingots are then carefully sliced to get the thin circular wafers.

The size of wafers has increased over time, from earlier 25mm options to massive 300mm diameter wafers common in high-volume manufacturing today. Bare wafers are highly polished to an extremely flat and smooth surface. This is vital for later photolithography processes needing tiny component details etched at nearly atomic scale across the surface.

Today’s large wafers allow more dies per wafer ultimately bringing down costs. Even small increases in wafer size significantly increase yields thanks to the extra surface area.

Semiconductor Wafer Specifications

Semiconductor Wafer Specifications

Next let’s overview some key wafer characteristics and parameters:

Dimensions

  • Diameters – From 25mm to the current standard 300mm diameter
  • Thickness – Varies from around 500-900μm (0.5-0.9mm). About as thick as 5-10 human hairs!

Primary Material

  • Silicon – Approximately 90% of fabricated wafers for ICs are silicon. It is abundant, easily forms stable oxides, and ideal for modern CMOS processes.
  • Sapphire – An electrical insulator. Used for specialized devices including RF power, LEDs and sensors.
  • Gallium arsenide – Advantages over silicon include better optoelectronic properties and higher electron velocity/mobility. Used for advanced high speed transistors, lasers and solar cells.
  • Germanium – Semiconductor used for integrated optics and infrared imaging/detection applications.

Crystal Orientation

As mentioned earlier, wafers are cut with specific crystal orientations including:

  • (100) - Most common, especially for CMOS logic
  • (111) for specialized analog, RF, fast switching and high frequency devices
  • (110) - Slightly used for some sensor and power applications

Reclaim & Epitaxy

There are also some advanced wafer types including:

  • Reclaim wafers – Reprocessed from test wafer materials using chemical mechanical planarization
  • Epitaxial wafers – An epitaxial process grows a precise crystalline layer on top of the wafer surface providing superior electrical properties

The Importance of Semiconductor Wafers

a patterned semiconductor wafer

It's incredible to realize that such thin and physically fragile slices of material enable so much of our electronics-based world. Some key areas that depend critically on advanced IC chips built on semiconductor wafers include:

Computing Technology

  • Microprocessors and memory chips power all computing from mobile phones to supercomputers
  • Continual enhancements in speed, efficiency and capability are enabled by new IC innovations

Communications Tech

  • RF, analog and mixed signal chips for wireless and broadband comms are fabricated on wafers
  • Allows connectivity technologies like 5G, WiFi, Bluetooth and more

Advanced Electronics

  • Custom ICs, sensors, power management chips appearing in products from cars to wearables to home automation
  • The Internet of Things (IoT) relies on tiny but powerful ICs on wafers

Space Tech

  • Extreme electronics for satellites and spacecraft depend on very specialized ICs
  • Great efforts are made to ensure these chips work reliably in the harsh conditions

So while chips get most of the glory, we should recognize that none of them would even exist without the wonder that is the semiconductor wafer! The world economy depends critically on the excellent engineering and painstaking fabrication operations carried out on seemingly innocuous discs of silicon.

Semiconductor Wafer Fabrication: A Step-by-Step Process

Semiconductor Wafer Fabrication Process

Semiconductor wafers form the foundation of integrated circuits and semiconductor devices. At WaferPro, we manufacture high-quality semiconductor wafers using an intricate multi-step process. Here, I’ll walk you through the key steps involved in transforming a raw semiconductor material into a polished wafer ready for device fabrication.

Ingot Growth - The process begins with crystal ingot growth. We place a small silicon seed crystal into a quartz crucible filled with molten polysilicon. As the crucible is slowly extracted from the molten silicon, the seed crystal acts as a template for the molten polysilicon to crystallize around into a large single crystal ingot up to 2 meters long. Precise control of temperature gradients and extraction rates allows us to grow almost perfect crystalline structures.

Slicing - The grown cylindrical ingot is sliced into thin discs using a specialized saw with a diamond-impregnated cutting blade. Hundreds of circular wafers can be obtained from a single ingot. During sawing, wafer thickness is precisely controlled to achieve uniformity and enable further processing steps. The wafers are typically between 500-900 microns thick at this stage.

Edge Grinding - Since the cutting process creates small cracks and defects around the wafer edge, the wafer periphery needs to be smoothed out. In the edge grinding step, we use grinding wheels to remove a narrow band of material from the edge until an undamaged, clean “new” edge surface is obtained all around the wafer circumference.

Lapping - Next, the wafer surface is globally planarized through a process called lapping. The wafers are allowed to slowly rotate between two rotating cast iron plates covered with an abrasive slurry. The plates grind away material from the front and back wafer surfaces until they are flat and parallel with each other. Lapping removes saw marks from wafer slicing and also sets wafer thickness close to the target thickness for device manufacturing.

Etching - After lapping, the wafers still have surface damage and contaminants embedded from previous processes. Etching is performed using wet chemicals (such as a mixture of hydrofluoric, nitric and acetic acids) which selectively and evenly remove a few microns from the silicon wafer surface while removing defects, leaving behind a pristine surface layer.

Polishing - At this point, the wafers undergo mechanical-chemical polishing using a silica-based slurry which oxidizes the silicon surface while abrasive particles together with a soft pad physically wear it away. This combined chemical and mechanical polishing produces extremely smooth and damage-free mirror-like wafer surfaces essential for photolithography and other downstream processes.

Cleaning - After polishing, wafers undergo rigorous cleaning in a series of wet chemical baths to remove particles, organic contaminants and metal impurities from wafer surfaces and maintain cleanliness standards. Various analytical techniques are also used to inspect, monitor and qualify the wafers prior to shipment to device fabrication facilities.

Microfabrication Turns Semiconductor Wafers into ICs

That super flat bare semiconductor wafer acts as the foundation for building up numerous layers of tailored materials intersecting in microscopic structures to create integrated circuits (ICs) through an intricate fabrication process known as microfabrication. This highly complex and sophisticated process imprints tiny electronic components and connections layered across the entire surface through steps like:

  1. Photolithography - Using light and masks to project circuit patterns which get etched onto wafer layers.
  2. Doping - Introducing impurities to produce distinct n-type and p-type semiconductor areas.
  3. Deposition - Adding materials layers through processes like chemical vapor deposition.
  4. Etching - Removing selected areas of material layers to leave behind desired circuit & component geometries.
  5. Planarization - Smoothening wafer layers flat through chemical mechanical planarization.

These steps along with others like cleaning and inspection are repeated across 25-100+ sequential processing steps working with remarkable precision. Slowly but surely, extremely intricate microscopic scale electronics components like transistors, capacitors, resistors and their interconnecting wiring build up across the wafer surface.

It’s through this sophisticated, extremely advanced microfabrication process that a bare semiconductor wafer gets transformed into a surface packed with fully functional circuitry - fulfilling the purpose that makes the wafer so vital to begin with!

Dies and Integrated Circuits

integrated circuit

The end goal is ultimately not the wafer itself - but what ends up constructed across its prepared surface. All the microfabrication produces many copies of a single type of integrated circuit design patterned repeatedly across the wafer, each copy called a die.

A single wafer can house anywhere from dozens to thousands of dies depending on:

  • Wafer size - today’s largest standard being 450mm
  • Die size - which ranges from tiny millimeter square chips to flip chip scale packages over 25mm
  • Density - how small and packed the circuit geometries can get

At the leading edge, advanced processes allow packing over a thousand dies onto a single 300mm wafer!

The whole wafer gets sent through fabrication as a unit. But the end goal is all those individual dies packaging what becomes finished ICs once separated and housed in supportive casing. ICs are then put to use powering electronics through being integrated into devices or further circuit assemblies and components.

So in summary - a semiconductor wafer ultimately serves as the foundational platform holding microchips being constructed through intricately layering various materials to imprint integrated circuits which will be individually separated out later on.

Common Semiconductor Wafer Materials

The most common material for semiconductor wafers by far is silicon, making up around 95% of all wafers and ICs produced today. Silicon offers great semiconducting properties and abundance resulting in lower costs over other options.

Alternate wafer materials gaining increasing interest are compound semiconductors from mixtures of elements across the second and third rows of the periodic table. Referred to as II-VI and III-V compounds based on their make up, these compound semiconductor wafers provide wider options in tuning material properties.

Some emerging popular choices for certain applications are gallium arsenide (GaAs), gallium nitride (GaN) and indium phosphide (InP). Their tuned electrical behaviors can enable smaller, faster and more efficient devices. However wafer sizes max out much smaller and costs run higher than ubiquitous silicon.

Silicon carbide wafers also find niche uses when high heat tolerance, voltage handling or other specialized parameters take priority over mainstream requirements met easily with silicon.

Wafer Fabrication Innovations

There’s still much active research pushing semiconductor wafer innovations further to extend abilities in what integrated circuitry can achieve. Milestones seem to come surprisingly regular still thanks to scientific creativity finding ways to circumvent apparent barriers.

Recent years have seen multiple revolutionary breakthroughs already in wafer scale endeavors, like:

  • 5nm process nodes coming to reality thanks to exotic multi-bridge channel FET advancements
  • Integration of carbon nanotubes onto silicon wafers about to bear fruit advancing capabilities
  • Graphene synthetic techniques progressing swiftly to provide paths incorporating graphene’s outstanding properties with standard production methods

And many more wafer focused developments targeting better efficiency, density, speed, connectivity capacities and capabilities seem poised to nurture continued progress in semiconductor accomplishments.

Which all emanates from the thriving ecosystem seeded around these seemingly simple but technologically mighty semiconductor wafers! Their durable reign as the bedrock of integrated circuit innovation continues opened up to encouraging new possibilities ahead.

Semiconductor Wafers Power Our Digital Lives

Nearly all modern electronics require integrated circuits imprinted onto raw silicon. Smartphones, computers, appliances, vehicles - semiconductor wafers power them all!

We have wafers to thank for technologies that enhance every aspect of society:

Communication

Blazing fast 5G networks rely on RF chips built from silicon. Without wafers, we’d still be using wired telegraphs!

Entertainment

GPUs for gaming, video processing chips for streaming shows, audio codec chips for music - all demand advanced semiconductor chips.

Exploration

Space agencies use rugged semiconductor wafers due to their durability and radiation resistance. Good luck exploring Mars without them!

Sustainability

Solar panels, wind turbines, electric vehicles, smart power grids - semiconductor wafers drive greener technologies.

Health

Wearable medical devices, precision drug delivery systems, MRI machines, and other life-saving technologies depend on sophisticated silicon microchips.

The Future of Semiconductor Wafer Technology

The semiconductor industry amazingly keeps finding ways to pack more and more devices into smaller spaces on chips. And since a single wafer contains many identical chips, the value that can be created from one wafer is enormous. However, we are approaching fundamental limits of physics and economics:

Feature Size Limits

  • Chip components eventually cannot be made smaller than atomic dimensions
  • New materials and innovative device designs are needed to advance further

Fabrication Costs

  • State of the art fabs now cost over $10 billion to construct
  • The cost to develop advanced process technologies is rocketing upwards
Challenge Potential Mitigations
Feature size limits Novel nanomaterials, 3D chip integration, advanced packaging
Soaring fab costs Modular equipment, multi-chip technologies

Nevertheless, the industry has a great history of overcoming barriers, and semiconductor wafer technology still has a very exciting future ahead! With processors now permeating virtually all advanced products, humanity is incredibly dependent on the innovations coming from those glossy silicon discs that enable our digital world.

Frequently Asked Questions:

What are the most common materials used for semiconductor wafers?

The most prevalent material used is silicon, accounting for over 90% of all wafers produced. Other materials like gallium arsenide, silicon carbide and gallium nitride are used for specialized high-performance applications.

What size are most semiconductor wafers?

Common wafer sizes range from 100-450 mm in diameter. State-of-the-art fabs now use 300mm wafers, which allows more chips per wafer. The industry is actively developing 450mm wafers for future high-volume manufacturing.

How thin are semiconductor wafers?

Wafer thickness depends on the material and application, but they are typically hundreds of microns thick. Silicon wafers can range from roughly 100-1000 microns (0.1-1.0 mm). This incredibly small thickness uniformity facilitates nanoscale device fabrication across the entire surface.

What are some key wafer fabrication companies?

Major wafer suppliers include companies like Shin Etsu, SUMCO, GlobalWafers and SK Siltron. Many semiconductor manufacturers also produce some portion of their own wafers internally.

How many fabrication steps are required?

Modern microprocessors can require 500 or more fabrication steps! This includes growing the crystal ingot all the way through slicing wafers and processing them into finished chips suitable for packaging. The complexity of designs requires an intricate dance of deposition, lithography, etch, implant, polish and inspection steps repeated sequentially.

How are wafers transported between tools?

Wafers move through the fab either manually by operators wearing specialized protective equipment or by automated material handling systems. Care is taken to avoid any contamination or damage during both automated and manual transport.

So in summary, semiconductor wafers come in different sizes and materials, are extremely thin and pure, and go through an immense number of complex processing steps in order to build the advanced ICs that drive progress in electronics!

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