Industrial Electronics

A look at semiconductor manufacturing, testing and packaging

13 March 2024
Source: Beswick

The consumer electronics, appliances, electrical vehicles and internet of things (IoT) that help make modern life so much easier are all products of semiconductor manufacturing, an essential industrial process. Using extremely pure single crystal silicon as a substrate, several nanofabrication procedures are carried out to construct semiconductor devices. Substrates like these are commonly referred to as wafers. Two popular types of wafers are 300 mm and 200 mm. The former allows for the advanced miniaturization needed in modern devices, while the latter is better suited to the mixed-lot production required by IoT devices. The fundamental steps in making a semiconductor chip from silicon are covered in this article.

Silicon wafer manufacturing

The semiconductor starts with a silicon wafer. Semiconducting materials like silicon, gallium arsenide and silicon carbide are used to make semiconductor wafers. The silicon used to make most wafers comes from sand, which is first heated until it turns into a very pure liquid, and then it undergoes crystallization to solidify. The finished silicon rods, or ingots, are then cut into discs of very thin wafers. Sliced wafers have a rough and imperfect surface, which is treated with polishing machines. The rationale behind this is that surface flaws or contamination have the potential to compromise the accuracy of an electronic circuit. Hence, chemical agents are employed to eradicate all forms of contamination, including ultra-fine particles, trace quantities of organic or metallic residues produced during production, and undesired layers of natural oxides caused by exposure to air.

Oxidation and coating

Oxidation creates an oxide layer that insulates semiconductor devices on the inside. The wafer is shielded from damage and unauthorized connections within the device by the insulating oxide layer. In field-effect transistors (FETs), the junction area and the gate terminal are defined by this insulation. Dry oxidation and wet oxidation are two ways to create a thin layer of oxidized material. In addition to preventing current leakage between circuits, this oxide film safeguards the surface of the wafer during the next processes. This film is like a thick armor that keeps out harm.

Photolithography

The process begins with coating the silicon wafer with a light-sensitive material called photoresist. This is usually done by spinning the wafer while dispensing a liquid photoresist, ensuring an even and thin coating. The coated wafer is subjected to a low-temperature bake, which removes any solvent in the photoresist and makes it more stable for subsequent processing.

A mask, which contains the desired circuit pattern, is placed over the photoresist-coated wafer. The entire setup is exposed to ultraviolet (UV) light. The areas on the mask that are transparent allow UV light to pass through and expose the underlying photoresist in a pattern corresponding to the desired circuit layout. After exposure, the wafer undergoes a high-temperature bake, often called a "hard bake." This further stabilizes the exposed areas of the photoresist. The wafer is then immersed in a developer solution that selectively dissolves either the exposed or unexposed regions of the photoresist, depending on whether positive or negative photoresist is used. This step reveals the pattern on the wafer.

Etching

Etching gets rid of any extra material from the surface after printing the circuit diagram on the wafer. There are two ways to go about this: the wet etching process that involves wetting the material with chemical solutions or plasma or gaseous etching in a dry process. In order to make a semiconductor chip, the photolithography and etching procedures are carried out multiple times on each layer of the wafer. To keep the chip structure intact, the entire process necessitates pinpoint accuracy and stringent process control.

Ion implantation

To impart semiconducting characteristics to silicon wafers, impurities (like phosphorous or arsenic ions) are implanted into the material through ion implantation. The next step is activating the ions through heat processing. Using ashing or chemicals, the photoresist material is removed after implantation. It blocks ions from entering areas that could cause defects.

Testing and packaging

After the integrated circuits are fabricated on a silicon wafer, the first level of testing occurs. This is often referred to as wafer probing. Each individual chip on the wafer is tested for functionality, performance and defects. Defective chips are marked, and the information is used in subsequent steps. Some chips undergo a burn-in process, where they are subjected to elevated temperatures and electrical stresses. After the individual chips pass wafer testing and, if applicable, burn-in testing, they are cut from the wafer and assembled into packages. Each packaged chip then undergoes final testing to ensure that it meets the specifications for the intended application. This testing includes functional tests, performance tests and other quality checks.

Conclusion

The three primary steps in making semiconductors are making the wafer, building the circuit and packaging them. It makes use of complex technology, and depending on the product and technology node, it might involve extra steps that aren't covered in this article. Ensuring that only trustworthy and high-quality semiconductor devices make it to market relies heavily on testing and packaging.

To contact the author of this article, email GlobalSpecEditors@globalspec.com


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