Semiconductor Wafer Manufacturing

Semiconductor Wafers

• A wafer is the base of semiconductor fabrication
• Semiconductor plants transform sand into wafers
• The article discusses silicon wafer production and other materials

What are Semiconductor Wafers?

• A wafer, also known as a substrate or slice, is a thin disk-like round material on which semiconductors are grown
• Wafers are the base for manufacturing semiconductors
• The first stage in semiconductor manufacturing process is to produce a wafer
• Manufacturing processes operate on the wafer surface to build the end product "chip” or integrated circuit (IC)

Wafer Size

• Semiconductor manufacturing plants select different wafer sizes to produce chips
• The first wafers were 25 mm and 51 mm
• Wafer sizes increased to 76 mm, 100 mm, 125 mm, and 150 mm
• Some of these are still in use for specific devices
• Available wafer sizes:
• 200 mm (7.9/8 inch): Extensively used in Foundries
• 300 mm (11.8/12 inch): Extensively used in Foundries
• Proposed wafer sizes:
• 450 mm (17.7/18 inch): Proposed with several limitations
• 675 mm (26.6/27 inch): A theoretical subject of research

Wafer Efficiency

• The goal of semiconductor manufacturing is to offer reliable, low cost, and top-quality chips
• Wafer size, the type of manufacturing process, and IC size (die) determine production numbers
• A single wafer can produce hundreds or thousands of semiconductor chips, depending on the size
• Yield is the ratio of actual operational chips produced to the total number of chips in a wafer
• Eliminating defective chips per wafer
• Yield is an important quantitative parameter to estimate the success of semiconductor manufacturing processes
• Larger wafer sizes can produce more semiconductor chips
• 450 mm and 675 mm wafer sizes are a topic of discussion in the industry
• Larger wafers increase efficiency and minimize cost per die

Wafer Manufacturing Processes

• The wafer manufacturing process includes:
• Selecting wafer material
• Finding raw material
• Raw material goes through chemical procedures for filtration and extraction of the pure material
• The pure material is crystallized to form a hard cylindrical structure called an “ingot”
• The ingot is sliced into thin wafers
• Sending the wafer for polishing and further chemical processes

Wafer Material Section

• The first step in manufacturing semiconductor wafers is selecting the correct wafer material
• Materials include:
• Silicon (Si)
• Gallium arsenide (GaAs)
• Sapphire
• Silicon carbide (SiC)
• Indium phosphide (InP)
• Gallium nitride (GaN)
• Germanium (Ge)
• Silicon is the most common material
• Silicon wafers dominate the semiconductor market at USD13.42 billion
• Gallium arsenide stands at USD1.4 billion
• Silicon carbide wafers are another technology in the semiconductor industry, at USD994.02 million

Other Materials

• Aluminum nitride is the newest wafer in the market
• Fraunhofer IISB launched the 1-inch AIN wafer around March 2023

Raw Material

• The next step is to find the raw material for extraction
• Silicon is the most widely used due to its abundance
• Silica or silicon dioxide is the source of silicon, found in sand and quartz
• A process known as “reduction" enables the extraction of silicon
• Silicon goes through a refinement and heating to obtain 99.999% purity
• The obtained silicon is solidified into polysilicon crystals
• Polysilicon is melted for crystallization

Crystal Growth

• The next stage is to solidify the liquid polysilicon melt
• Crystallization is when a liquid or vapor forms a solid crystal
• In semiconductor manufacturing, the process is known as crystal growth

Czochralski Method

• The Czochralski method is used for Silicon wafer manufacturing
• A seed crystal is put into molten silicon
• As the seed crystal is extracted, a cylindrical shaped silicon crystal (ingot) forms

Kyropoulos Method

• The Kyropoulos method allows a seed crystal to be dipped inside a molten crucible
• The seed crystal is pulled upwards with rotation
• The resulting crystal takes the shape of the crucible

Float-Zone Method

• The float-zone method or zone method is a crystal growth method in semiconductor manufacturing
• Dipping a small molten material in the polycrystalline silicon solution Recrystallizes the rod into a silicon crystal (ingot)

Bridgman-Stockbarger Method

• Used for manufacturing GaAs wafers
• A polycrystalline material is kept in a container along with a seed crystal
• Heated above its melting point and cooled slightly so that it forms the crystal near the seed material

Epitaxy

• Where a thin layer is grown over the substrate
• Epitaxial processes include liquid phase epitaxy, atomic layer epitaxy, molecular beam epitaxy, etc

Ingot Slicing

• Long cylindrical crystals or ingots are sliced into thin wafers
• Each wafer should be:
• A single entity (separated from the ingot)
• Continuous at the edges to maintain the round shape
• Flat
• Ground and polished
• These wafers are then sent for polishing and further chemical processes like oxidation, photolithography, and etching