I. What is a wafer?
A wafer is a thin sheet of silicon substrate used in the manufacture of integrated circuit chips. It is one of the fundamental materials for electronic devices and integrated circuit manufacturing. Wafers are made of single-crystal silicon and have a flat surface and highly pure structure. During chip manufacturing, wafers are cut into hundreds or even thousands of small squares, each of which becomes an independent chip.
A wafer has extremely high purity and flatness. It is typically made of monocrystalline silicon and formed into a large-scale disk shape through a special growth process. Wafers are typically 4 inches (about 10 centimeters), 6 inches, 8 inches, or 12 inches in diameter; the larger the size, the more chips can be manufactured.
The wafer fabrication process involves selecting silicon single crystals of appropriate purity, dissolving and recrystallizing them, and then performing multiple grinding and polishing processes to obtain a highly smooth surface. The surface quality of the wafer is crucial to the success of chip manufacturing, as any tiny defect or contamination can affect the chip's performance and reliability.
What is the relationship between wafers and chips?
1. Wafers as the Foundation of Chips: Wafers are the foundation of chip manufacturing. They provide a flat and highly clean surface on which integrated circuits are built. Each wafer can be diced into hundreds or even thousands of small squares, each of which becomes an independent chip. Therefore, the quality of the wafer and the precision of the fabrication process directly affect the quality and performance of the chip.
2. Wafer Fabrication Processes: Chip manufacturing on a wafer involves multiple process steps. These steps include photolithography, thin film deposition, ion implantation, chemical etching, and metal deposition. Through these steps, complex integrated circuit structures are gradually built on the wafer. Each step requires high-precision equipment and process control to ensure the reliability and quality of the chip.
3. The Relationship Between Wafers and Chips: Wafers are the starting point for chip manufacturing. During chip manufacturing, wafers are cut into small cubes, each of which becomes an independent chip. These chips undergo subsequent process steps, including circuit design, packaging, and testing, to ultimately form a complete electronic product. Therefore, the relationship between wafers and chips is that the former serves as the foundation and raw material for the latter.
II. Wafer Testing
(I) Purpose of Wafer Testing
1. As the name suggests, this testing phase checks whether the dies on the wafer meet design requirements and possess the basic characteristics of each die, including voltage, current, and functionality. Dies that fail to meet standards or are defective are identified and marked during this process. In the semiconductor industry, yield is determined through CP testing.
2. Some chips may have certain pins sealed inside the chip during packaging, making it impossible to test their functionality after packaging. Therefore, testing must be performed at this stage, before the chip is packaged.
3. Cost savings. For a chip, the earlier a defect is detected, the better. This prevents it from proceeding to subsequent manufacturing processes and causing waste.
4. In a sense, the CP test is also a test of the process capabilities of the fab plant.
(II) Hardware required for wafer testing
The following three hardware components must be used together to achieve the desired CP test results.
1. Test Equipment (ATE)
Currently, the global testing equipment market is still dominated by two major giants: Teradyne of the United States and Advantest of Japan.
In recent years, domestic testing machines have sprung up like mushrooms after rain, such as Huafeng Test & Control, Hefei Yuexin, Nanjing Hongtai, Hangzhou Changchuan, Hangzhou Jiasu, and Hangzhou Guolei. Each testing machine has different preferences for chip types, such as power semiconductor dedicated testing machines from Shanghai Chenxin and Suzhou Lianxun. The functions of testing machines are not entirely the same, and the appropriate testing machine is mainly selected based on the type and function of the chip.
2. Probe Card
As a customized fixture in the chip testing process, the probe card is an indispensable product for testing the chips of design companies. The relationship between the tester and the probe card is like that between a printer and a printer cartridge. There are also many types of probe cards, which are divided into three types according to different chip types and semiconductor manufacturing processes: cantilever probe cards, vertical probe cards, and MEMS probe cards.
3. Probe station
It controls the movement of the wafer and provides a high-precision device for testing the internal environment.
Several leading global manufacturers of probe stations, including FFI (USA), TEL (Japan), and TSK (Japan), provide 12-inch fully automated high and low temperature probe stations. Domestically, several companies such as Senmei Xieer, Zhongke Precision, and Siasun have also emerged as manufacturers of fully automated probe stations.
