Jason T. Ryan

The effect of interfacial layer properties on the performance of Hf-based gate stack devices

The influence of Hf-based dielectrics on the underlying SiO2 interfacial layer (IL) in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.

Breakdown in the metal/high-k gate stack: Identifying the “weak link” in the multilayer dielectric

We apply a systematic approach to identify a high-k/metal gate stack degradation mechanism. Our results demonstrate that the SiO2 interfacial layer controls the overall degradation and breakdown of the high-k gate stacks stressed in inversion. Defects contributing to the gate stack degradation are associated with the high-k/metal-induced oxygen vacancies in the interfacial layer.

Origin of the Flatband-Voltage Roll-Off Phenomenon in Metal/High-

The effect of flatband-voltage reduction [roll-off (R-O)], which limits fabrication options for obtaining the needed band-edge threshold voltage values in transistors with highly scaled metal/high- k dielectric gate stacks, is discussed. The proposed mechanism causing this R-O phenomenon is suggested to be associated with the generation of positively charged oxygen vacancies in the interfacial SiO2 layer next to the Si substrate. The vacancies in the interfacial layer are induced by oxygen outdiffusing into the overlying high-k dielectric. The model is consistent with the variety of observations of R-O dependence on the electrode and substrate type, high-k dielectric composition and thickness, temperature, etc. The models predictions were experimentally verified.

k

We demonstrate “on the fly” electron spin resonance (ESR) in which the defect generation process in the negative bias temperature instability (NBTI) can be observed without recovery contamination. Elevated temperature and modest negative gate bias generates ESR spectra due to E′ center defects. The NBTI generated E′ center spectrum disappears upon stress condition removal, a result consistent with recovery. Our observations support the idea that NBTI is triggered by inversion layer hole capture at an E′ precursor site which leads to depassivation of nearby interface trap precursors.We demonstrate “on the fly” electron spin resonance (ESR) in which the defect generation process in the negative bias temperature instability (NBTI) can be observed without recovery contamination. Elevated temperature and modest negative gate bias generates ESR spectra due to E′ center defects. The NBTI generated E′ center spectrum disappears upon stress condition removal, a result consistent with recovery. Our observations support the idea that NBTI is triggered by inversion layer hole capture at an E′ precursor site which leads to depassivation of nearby interface trap precursors.

Gate Stacks

We have identified the structure of three atomic scale defects which almost certainly play important roles in radiation damage in hafnium oxide based metal oxide silicon technology. We find that electron trapping centers dominate the HfO/sub 2/ radiation response. We find two radiation induced trapped electron centers in the HfO/sub 2/: an O/sub 2//sup -/ coupled to a hafnium ion and an HfO/sub 2/ oxygen vacancy center which is likely both an electron trap and a hole trap. We find that, under some circumstances, Si/dielectric interface traps similar to the Si/SiO/sub 2/ P/sub b/ centers are generated by irradiation. Our results show that there are very great atomic scale differences between radiation damage in conventional Si/SiO/sub 2/ devices and the new Si/dielectric devices based upon HfO/sub 2/.

Observations of negative bias temperature instability defect generation via on the fly electron spin resonance

Conventional electron spin resonance measurements indicate gross processing dependent differences in the densities of paramagnetic oxygen deficient silicon sites, E′ centers, in the interfacial layer of unstressed hafnium oxide based metal-oxide-silicon structures. (E′ centers are not usually observed in unstressed oxides.) The volume densities of these centers can be quite high (∼1×1019cm−3). Electrically detected magnetic resonance measurements suggest that related oxygen deficient sites may significantly degrade device performance and reliability.

Identification of the atomic scale defects involved in radiation damage in HfO/sub 2/ based MOS devices

The amphoteric nature of Si/SiO2 interface states in submicron sized metal-oxide-silicon-field-effect-transistors is observed using an enhanced spectroscopic charge pumping method. The method’s simplicity and high sensitivity makes it a powerful tool for interrogating the true nature of electrically measured interface states in samples which exhibit extremely low defect densities. The spectroscopic results obtained clearly illustrate a signature “double peak” density of states consistent with amphoteric Pb center data obtained from electron spin resonance measurements. Since the method is a hybrid of the commonly used charge pumping methodology, it should find widespread use in electronic device characterization.

Electron spin resonance observations of oxygen deficient silicon atoms in the interfacial layer of hafnium oxide based metal-oxide-silicon structures

We demonstrate a very powerful electrically detected magnetic resonance (EDMR) technique, spin dependent charge pumping (SDCP) and apply it to 4H SiC metal-oxide-semiconductor field-effect-transistors. SDCP combines a widely used electrical characterization tool with the most powerful analytical technique for providing atomic scale structure of point defects in electronic materials. SDCP offers a large improvement in sensitivity over the previously established EDMR technique called spin dependent recombination, offering higher sensitivity and accessing a wider energy range within the bandgap.

Spectroscopic charge pumping investigation of the amphoteric nature of Si/SiO2 interface states

We show that a Si∕HfO2 interfacial layer defect with an electron spin resonance spectrum similar to that of some E′ center variants responds to oxide bias consistent with an amphoteric defect. The spectrum is weakly orientation dependent indicating that the defect does not reside in a completely amorphous matrix. The defect’s spin lattice relaxation time is much shorter than that of conventional E′ centers suggesting that the defect involves some coupling of a Hf atom to a nearby oxygen deficient silicon dangling bond defect. This defect very likely plays an important role in widely reported instabilities in HfO2 based transistors.

Spin dependent charge pumping in SiC metal-oxide-semiconductor field-effect-transistors

We demonstrate an electron paramagnetic resonance technique which simply links point defect structure and energy levels in a very direct way. The technique’s simplicity and the robust character of the response make it, at least potentially, of widespread utility in the understanding of defects important in solid state electronics. Since the specific defect observed is generated in silicon oxynitride by high electric field stressing, an important device instability problem in present day integrated circuitry, the observations are of considerable importance for microelectronics technology.