Wafer back cooling is a cooling technique mainly used to cool the back of a wafer. Basically, helium gas is used for cooling because the gaseous helium gas has outstanding chemical inertness, and its thermal conductivity and specific heat capacity are greater than any other gas except hydrogen.

      What is chemical inertness? Chemical inertness refers to the extremely low ability to react with other substances under normal conditions, making it difficult to undergo chemical reactions. Substances with chemical inertness are usually less likely to react with acids, bases, salts, and many other chemical reagents. Helium (He) is an inert gas. As a back cooling gas, there is no need to worry about corroding the facial mask layer on the wafer surface.

      What is thermal conductivity? The magnitude of thermal conductivity determines the rate at which a substance conducts heat, and the higher the thermal conductivity, the greater the rate at which heat is transferred. Generally speaking, metals have higher thermal conductivity due to the presence of free electrons inside the metal, which can effectively conduct heat; Helium, although its thermal conductivity is lower than that of solids and liquids, is the second highest in gases, making it very suitable as a back cooling gas.

      What is specific heat capacity? Specific heat (specific heat capacity) refers to the amount of heat per unit mass of a substance that needs to be absorbed when its temperature rises by one degree. Specific heat is a physical quantity that measures the ability of a substance to store thermal energy. The greater the specific heat, the less the temperature of a substance increases when it receives a large amount of heat. The use of helium can effectively prevent excessive temperature rise on the wafer and damage to the chip.

      Due to its unique physical and chemical properties, helium has significant advantages in wafer back cooling applications. Therefore, helium gas is chosen as the gas for cooling the back of the wafer.

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