3. HKMG transistors

The third application of ALD in microelectronics concerns the latest generation of transistors, with the introduction of high permittivity oxide stacks and metal gates, commonly known in semiconductor circles as HKMG for High-K Metal Gate.

Since the invention of the first transistor in 1947, integrated circuit manufacturers have used silicon oxide for the gate insulator of CMOS transistors. Polycrystalline silicon, on the other hand, has been used to manufacture the gate. One of the performance criteria for transistors is to have enough charge carriers (electrons or holes) in the channel. This requires a sufficiently high capacitive coupling between the channel and the transistor gate. So, since the beginning of integrated circuits, for each new technology, the oxide thickness has been reduced to increase the structure's capacitance, but this has led to an exponential...