Behind wafer technology: How are semiconductors made?

The starting point of all semiconductor processes are thin polished wafers in specific diameters. Bosch primarily uses 200 mm and 300 mm diameter wafers. For silicon-based products, these raw material wafers are manufactured by our suppliers using the sophisticated Czochralski process.

It all starts with high-quality quartz, sourced from specialized deposits. Although silicon is widely available, the semiconductor industry relies on special quartz sand (silicon dioxide). This sand undergoes processing to extract pure silicon, a semi-metal that forms the foundation for semiconductors. The material is further refined to meet the extreme requirements for silicon wafers, then transformed into monocrystalline silicon with a purity of 99.999999999%. The Czochralski process begins with a silicon melt obtained by chemically reducing silicon dioxide with carbon, separating the silicon from oxygen.

Purity is critical in semiconductor production. Even the tiniest pollutant can disrupt the flow of electrons, affecting a chip’s ability to process billions of calculations per second. To ensure flawless crystal growth, operators carefully control the temperature and other conditions as they grow single silicon crystals at temperatures above 1,400°C.

Once formed, the purified silicon ingots are sliced into thin wafers and polished to achieve an atomically smooth surface. To fine-tune the electrical properties of the wafers, a process called doping is used. This involves introducing small amounts of specific elements – phosphorus for n-type silicon and boron for p-type silicon. Doping allows precise control over how electrical charges move through the material, making modern semiconductor circuits possible.

While traditional silicon semiconductors form the backbone of many applications, advanced materials like silicon carbide (SiC) offer superior performance for specialized needs, particularly in automotive and power applications. SiC chips enable power devices that can operate at higher temperatures and voltages while reducing switching losses and overall system size. The manufacturing process for SiC – which Bosch has been mass-producing since 2021 – differs significantly from conventional silicon.

SiC does not melt at high temperatures; instead, it sublimates – meaning it turns from solid to gas above 1,600°C. This property prevents the use of the standard Czochralski process for crystal growth. The preferred method is physical vapor transport (PVT), which consists of three steps: SiC source sublimation, sublimate transport, and crystallization on the seed crystal surface.

Raw silicon and raw carbon are placed on the bottom of a high-purity graphite crucible as the starting material. A high-quality SiC seed crystal is attached to the top of the crucible. The quality of this seed crystal plays a key role in determining the subsequent crystal quality. Everything is contained in a closed environment at low pressure and heated to temperatures above 2,000°C using induction or resistance heaters.

The central element of the PVT method is maintaining a specific temperature difference between the source material at the bottom and the seed crystal at the top of the crucible. This temperature difference is critical because of the partial pressure difference of the various gases between the hot SiC source and the slightly cooler SiC seed crystal. The gaseous silicon and carbon atoms migrate into the cooler area, where they attach to the seed crystal and are incorporated into the existing crystal lattice structure. This is how the crystal grows atom by atom.

After successful crystal growth, the resulting SiC crystal is cut into wafers, serving as the foundation for semiconductor production. However, as SiC is a very hard material, the wafering process is difficult and requires special tools and materials. Some of this wafering is performed by suppliers, but Bosch also purchases SiC ingots and performs the process in its own plants using a laser separation process. This approach allows Bosch to prepare wafers that ideally match the requirements of its device manufacturing lines.

The semiconductor industry has one of the most complex and specialized supply chains in modern manufacturing. Key production stages for semiconductors from Bosch are located in different regions of the world, combining expertise in wafer production, chip design, and advanced manufacturing processes. Through continuous research and innovation in silicon technologies, Bosch is creating opportunities for next-generation mobility solutions. Stay tuned to find out where this technology is heading next.

Fill out the form below to download your free copy

The white paper is currently available in English, German, and Chinese language.