Simultaneous deep and shallow aluminium diffusion for box structure - has silicon nitride deposited on layer of thermal silicon and top layer of pyrolytic silica of which selective removal is made

摘要

Aluminium is diffused in a silicon plate, notably to form box structures. First, a layer of thermal silica is formed on the silicon plate. A layer of silicon nitride is deposited on the first layer and a layer of pyrolytic silica is deposited on the second layer. Then, the second and third layers are selectively removed in choosen places. The first, second and third layers are selectively removed in other choosen places. The plate is then placed in a sealed tube having an aluminium source and a thermal treatment is applied. As a result, a deep diffusion of aluminium is formed where the three layers have been removed, a shallow diffusion where two layers have been removed and no diffusion elsewhere.