Sulphur hexafluoride is used to produce chips (processors and memories) on mono-crystalline silicon wafers, or solar cells on poly-crystalline wafers. On a different substrate, e.g. glass, those silicon circuits are manufactured on thin deposited films of different silicon materials and take the more familiar form of solar panels or flat screen TVs.
Fluorinated gases, such as sulphur hexafluoride (SF6), play two very important roles in the manufacturing of silicon devices.
Firstly, they are used to selectively remove materials through a process which is called ‘etching’. The fluorinated gases are activated in plasma and the fluorine radicals that are generated react with the silicon giving volatile species. In this way they pattern the different elements of the circuit on the base. SF6 is especially efficient in the production of MEMS (Micro Electro Mechanical Systems), because the high energy and reactivity of its ions allow an unbeatable etching rate. SF6 is employed in the production of integrated circuits for the so called ‘isotropic etching’, because it reacts in any direction and can pattern round cavities.
Secondly, fluorinated gases are used to clean the production tools from unwanted Si-based layers and particles. SF6 is an optimum gas to generate the F radicals that etch and thus efficiently remove the deposits on the walls of the plasma chamber. This process is known as ‘chamber cleaning’.
Gas purity is of key importance in this market segment, because any possibility of contamination has to be minimized. For this purpose Solvay offers N5.0 material.
