Evolving Semiconductor Wafer Technology

Semiconductor wafers are the core material in today’s electronic devices, and their performance directly affects overall device operation and efficiency. Advanced semiconductor wafer technologies using silicon, silicon carbide (SiC), and gallium nitride (GaN) are essential for further improvement of IoT devices and next-generation communication technologies (5G and 6G), not to mention smartphones, personal computers, and automotive driver assistance systems (ADAS). As semiconductors become even finer and more highly integrated, wafer uniformity and low defect count are important factors that directly affect yield and production efficiency. In addition, technological advances in semiconductor wafers have contributed significantly to high-frequency characteristics, improved breakdown voltage, energy savings, and reduced environmental impact. As a result, evolving semiconductor wafers are playing an increasingly important role in the development of next-generation electronic devices for the realization of a sustainable society.

This article provides an overview of semiconductor wafer technology, manufacturing processes, and the latest trends.

What is a semiconductor wafer?

First of all, let’s review semiconductor wafers.

Semiconductor Integrated Circuit (IC)

A semiconductor integrated circuit is an electronic component that integrates a number of elements, such as transistors, capacitors, and resistors, which perform various functions, onto a single chip. Today’s integrated circuits are highly integrated, with miniaturization reaching less than 2 nanometers (one nm is one billionth of a meter).

Semiconductor Wafer

When manufacturing semiconductor integrated circuits (ICs), many circuits are formed on a thin substrate made of materials such as silicon. The thin substrate is called a semiconductor wafer.

Semiconductor wafers are thin disks made from crystals of semiconductor materials. The most common material used is silicon, but compound semiconductors such as gallium arsenide and minerals such as sapphire are also used. Diamond is also being studied as a next-generation material.

Semiconductor wafers are first manufactured from an ingot, which is a block of silicon of high purity. Wafers are cut from the ingot.

The most common wafer sizes are 8 inches (200 mm) to 12 inches (300 mm) in diameter, depending on the material and application.

Along with the evolution of miniaturization technology, semiconductor wafer technology supports higher integration and performance of devices. In particular, the purity and uniformity of silicon wafers have a direct impact on yield and power efficiency, contributing significantly to innovations in cutting-edge electronics and information technology fields, such as next-generation energy efficiency.

Wafer Manufacturing Process

Let’s take a look at the wafer manufacturing process, using silicon wafers as an example.

Making silicon ingots

First, silica stone, the raw material, is melted and reduced to polycrystalline silicon.

The resulting polycrystalline silicon is then refined into a single-crystal silicon ingot with a purity of eleven-nine (99.9999999999%), which contains almost no impurities. The reason for this high purity of eleven nines is that semiconductors have electrical characteristics that are greatly affected by even the slightest impurity.

To increase the purity of polycrystalline silicon, the Czochralski method and the floating zone method are used.

In the Czochralski method (pull-up method), which bears the name of its developer Czochralski, polycrystalline silicon is placed in a quartz crucible and melted at 1000°C or higher. This silicon is then pulled up to create a single-crystal silicon ingot.

In the floating zone method, a portion of the polycrystalline sample rod is heated to form a molten zone between the lower single crystal and the sample rod, and the entire zone is moved downward while the molten zone is supported by surface tension.

Slicing

Cylindrical silicon ingots are sliced into wafers using special saws such as wire saws and slicing machines.

Beveling

Beveling is simply defined as chamfering. The sides of each sliced wafer (the intersection of the cut surfaces and the surface that used to be the circumference of the original cylinder) are beveled and rounded using a diamond grindstone or similar tool to form a perfect circle.

Polishing (lapping)

The surface of the wafer is polished with an abrasive to correct thickness variations, distortion, and scratches caused by the slicing process.

Etching

Etching is a type of surface treatment that uses chemicals (corrosive solutions), reaction gases (fluorine), ions, etc. to dissolve and etch the target area.

Post-lapping wafers still have minute distortions and scratches. Etching is performed to remove particulate impurities (several tens to several hundreds of nanometers in size) that were adhered to the wafer surface in the earlier manufacturing process, and the wafer is finished to the designed dimensions and shape.

Heat treatment (annealing)

This is a method of relieving stress inside a material by heating. When annealing is performed on silicon, oxidation donors in the silicon are removed and crystal defects are reduced, resulting in stable resistance values.

Polishing

Polishing is a more precise polishing process than lapping. Planarization chemical mechanical polishing (CMP) technology is used to polish the wafer surface with ultra-fine particles to achieve a mirror finish with high planarity.

Cleaning

As the final stage of finishing, the wafer surface is chemically cleaned to remove foreign matter and contaminants remaining on the wafer surface using cleaning equipment such as batch cleaning equipment and single wafer cleaning equipment.

Drying

After cleaning, wafers are dried.

Quality Characteristics Inspection

The manufactured wafers are visually inspected and checked by inspection equipment to ensure that the dimensions, shape, flatness, crystal orientation, and resistance are in accordance with the design, and that there are no defects such as scratches or contamination.

Wafer Technology Trends

Semiconductor wafer technology is rapidly evolving to achieve both performance improvement and cost reduction as device integration and miniaturization technologies advance. One of the trends attracting attention today are larger-diameter silicon wafers.

Conventional wafer sizes have been 150 mm, 200 mm, and 300 mm, but now 450 mm wafers are approaching commercialization. Larger silicon wafer diameters will increase the number of semiconductor chips that can be obtained from a single wafer, resulting in lower manufacturing costs and higher production efficiency. Currently, 450 mm wafers are in test production, and efforts toward practical use are accelerating.

There have also been important developments in semiconductor wafer material technology. Silicon wafers currently account for the majority of the market and are used in many familiar devices such as PCs, smartphones, and automobiles. Meanwhile, Silicon carbide (SiC) and gallium nitride (GaN) are expanding their use as next-generation semiconductor materials. These compound semiconductors are resistant to high temperatures and high-voltage environments, and demand for these materials is rapidly increasing in fields such as power electronics, 5G communications, and electric vehicles. With continued research and development aimed at expanding the supply of SiC and GaN and reducing costs, these materials are expected to occupy an important position next to silicon in the future.

The spread of 450-mm wafers and next-generation materials will be an important factor in supporting next-generation high-performance devices.

Applications of Semiconductor Wafers

Let’s take a look at some typical applications of semiconductor wafers at the end of this section.

Processors and memory devices

The most common applications are processors and memory devices. Many of the smartphones, PCs, automobiles, and home appliances that surround us contain semiconductor devices, that support their operation and data processing.

These semiconductor devices are manufactured by forming minute circuits on semiconductor wafers. The performance and efficiency of processors and memory can be maximized by using semiconductor wafers with higher flatness and uniformity. Semiconductor wafer technology is also applied in a wide range of fields, including IC chips used in credit cards and SIM cards.

Power Electronics

Semiconductor wafers also play an important role in the field of power electronics. In particular, power devices using compound semiconductors such as SiC and GaN realize highly efficient power conversion and are widely applied in next-generation energy technologies such as electric vehicles (EV) and renewable energy systems. This enables improved energy efficiency and downsizing of systems, making a significant contribution to the realization of a sustainable society.