Underneath the nitride mask, the growth is suppressed, and these areas will become the active transistor area. The neutral silicon is converted to a negative or positive conductor by the process of ion implantation. Impurity atoms are ionized and then accelerated by an electric field until they impinge on the silicon surface, where they embed themselves. During subsequent thermal treatment, the impurities redistribute. The concentration of atoms at any point determines the electrical properties of the crystal at that point.
Process simulation is used here to predict the contours of phosphorus concentration in the silicon.
A polysilicon line crosses the active area in the upper left and forms the gate of a transistor. After the transistors are built in the silicon, they must be interconnected using metal layers above the silicon substrate. First an insulating glass layer is deposited to cover the silicon, then contact holes are cut into the glass layer down to the silicon. Metal is deposited on top of the glass, connecting to the devices through the contact holes. Process simulation can be used to predict the hole filling capabilities of different metal deposition techniques.