How molybdenum discs support the manufacturing of chips
On the grand stage of chip manufacturing, lithography machines and other equipment always stand out as the stars under the spotlight. However, behind the scenes, there is a type of seemingly simple yet crucial material that silently supports the silicon wafers, enduring repeated high-temperature roasting of thousands of degrees Celsius, ensuring that countless transistors "grow" and "activate" precisely on the wafers. It is this, the molybdenum wafer - an indispensable cornerstone in the field of semiconductor high-temperature processing.
During the chip manufacturing process, high-temperature diffusion, annealing and chemical vapor deposition (CVD) are the key steps that define the performance of transistors. These processes typically need to be carried out in an inert gas or vacuum environment ranging from 1000°C to 1300°C to achieve precise doping of impurities, repair of lattice defects, and deposition of high-quality films.
The material must remain in a solid state at temperatures far above the processing temperature, without softening or deforming. Under long-term high-temperature and thermal cycling conditions, the material structure must be stable and should not produce volatile substances that could contaminate the silicon wafers or the processing chamber. It must be able to transfer heat quickly and uniformly, ensuring that all silicon wafers are heated uniformly and guaranteeing process uniformity. Its thermal expansion coefficient should be as close as possible to that of the silicon wafers, avoiding stress on the wafers due to different expansion/contraction rates during heating and cooling, which could cause warping or cracking. In a vacuum environment, the material itself hardly volatilizes, preventing impurity atoms from contaminating the high-purity silicon wafers. There are only a few materials that can meet all these conditions simultaneously, and molybdenum wafers are among the best.
The reason why molybdenum discs can become the "preferred" carriers for high-temperature processes lies in their inherent excellent physical and chemical properties. The melting point of metallic molybdenum is as high as 2622℃, which is much higher than the maximum temperature required for semiconductor processes. This means that even at 1300℃, the molybdenum discs can still maintain extremely high strength and shape stability, like an "iron throne" that never bends even in the midst of intense heat.
Molybdenum has a high thermal conductivity, enabling rapid and uniform heating. What's more, its coefficient of thermal expansion (approximately 4.8×10⁻⁶/℃) is very close to that of silicon (approximately 3.5×10⁻⁶/℃). This characteristic is of crucial importance as it ensures that the molybdenum wafer and the silicon wafer can "synchronously" expand and contract throughout the process from room temperature to the process temperature, significantly reducing the risk of the silicon wafer warping or cracking due to thermal stress.
High-purity molybdenum discs have extremely low vapor pressure at high temperatures, making them difficult to volatilize and thus not introducing harmful impurities into the processing chamber. At the same time, they can form a dense oxide layer at high temperatures, further preventing the continuous oxidation and volatilization of the internal materials, ensuring a highly clean processing environment.
This is the most direct application of molybdenum discs. Multiple molybdenum discs are precisely processed and assembled into a carrier called "Wafer Boat". The silicon wafers are vertically inserted into the slots of the molybdenum discs. Throughout the entire process, the molybdenum disc tray is responsible for safely and smoothly transporting the silicon wafers to the high-temperature area, and ensuring that each silicon wafer receives a uniform distribution of heat and process gas.
In some rapid thermal processing (RTP) or single-chip processing equipment, the molybdenum disc is designed as a resistance heater, or heating plate. By passing a large current through the molybdenum disc, it generates heat on its own, thereby rapidly heating the silicon wafer placed on its surface to the target temperature within an extremely short period of time. This application directly utilizes the conductive, high-temperature-resistant and rapid heat-conducting properties of the molybdenum disc.
Inside the vacuum chamber, in order to reduce heat loss, improve thermal efficiency and protect the cold walls of the chamber, multiple layers of thermal insulation and reflective screens are usually installed. Molybdenum discs or molybdenum plates processed from them, due to their smooth surfaces and stability at high temperatures, are ideal materials for manufacturing these screens. They reflect thermal radiation and firmly "lock" the heat within the processing area, achieving efficient energy utilization and precise control of the process temperature.
It can be said that without the stable support of molybdenum wafers, the efficient and precise high-temperature processes of modern semiconductors would be impossible. Although it is not a direct material constituting the chip, it is a key consumable and component inside the "mother machine" for manufacturing chips. From micrometers to nanometers, and even to more advanced processes, as the control requirements for process temperatures become increasingly precise, higher standards have been set for the purity, flatness, microstructure and lifespan of molybdenum wafers.
In the future, as semiconductor technology progresses towards the third-generation wide-bandgap semiconductors (such as silicon carbide and gallium nitride), the processing temperatures will often be even higher. Molybdenum wafers, as one of the few known materials that can withstand such harsh conditions, will further strengthen their position. This "metal heart" hidden deep within a temperature of thousands of degrees will continue to silently support each operation and leap in the information age with its unchanging stability and resilience.
The molybdenum disc is in high demand in various parts of the world, such as: USA, Canada, Chile, Brazil, Argentina, Colombia, Germany, France, United Kingdom, Italy, Sweden, Austria, Netherlands, Belgium, Switzerland, Spain, Czech Republic, Poland.
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