Impact of both metal composition and oxygenitrogen profiles on p-channel metal-oxide semiconductor transistor threshold voltage for gate last high-k metal gate

摘要

As transistor size continues to shrink, SiO_2/polySi has been replaced by high-k/metal gate (HKMG) to enable further scaling. Two different HKMG integration approaches have been implemented in high volume production: gate first and gate last-the latter is also known as replacement gate approach. In both integration schemes, getting the right threshold voltage (V_t) for NMOS and PMOS devices is critical. A number of recent studies have shown that V_t of devices is highly dependent on not just the as deposited material properties but also on subsequent processing steps. In this work, the authors developed an advanced high-resolution electron energy loss spectroscopy method capable of accurate measurement of material composition on device structures. Using this method, the nitrogen and oxygen concentration at the HKMG interface on p-channel field-effect transistor (PFET) transistors with slightly different metal gate stacks were studied. The authors demonstrated that the correct amount of nitrogen and oxygen at the HKMG interface is required to get the right PFET V_t.