Corey J. Cochrane

Atomic-Scale Defects Involved in the Negative-Bias Temperature Instability

This paper examines the atomic-scale defects involved in a metal-oxide-silicon field-effect-transistor reliability problem called the negative-bias temperature instability (NBTI). NBTI has become the most important reliability problem in modern complementary-metal-oxide-silicon technology. Despite 40 years of research, the defects involved in this instability were undetermined prior to this paper. We combine DC gate-controlled diode measurements of interface-state density with two very sensitive electrically detected magnetic-resonance measurements called spin-dependent recombination (SDR) and spin-dependent tunneling (SDT). An analysis of these measurements provides an identification of the dominating atomic-scale defects involved in NBTI in pure- and plasma-nitrided oxide (PNO)-based devices. We are also able to observe atomic-scale defects involved in HfO2-based devices (although a definitive identification of the dominating defects structure was not possible). Our results in pure- devices indicate an NBTI mechanism which is dominated by the generation of Pb0 and Pb1 interface-state defects. (Pb0 and Pb1 are both silicon dangling-bond defects, in which the central silicon is back-bonded to three other silicon atoms precisely at the interface). This observation is consistent with what most NBTI researchers have assumed. However, our observations in PNO devices contradict with what most NBTI researchers had previously assumed. We demonstrate that the dominating NBTI-induced defect in the plasma-nitrided devices is fundamentally different than those observed in pure-based devices. Our measurements indicate that the new plasma-nitrided NBTI-induced defects physical location extends into the gate dielectric. The defect participates in both SDR and SDT. Our SDR results strongly indicate that the plasma-nitrided defect has a density of states which is more narrowly peaked than that of centers and is near the middle of the band gap. The high sensitivity of our SDT measurements allow an identification of the physical and chemical nature of this defect through observations of hyperfine interactions. The defects are silicon dangling bonds, in which the central silicon is back-bonded to nitrogen atoms. We call these NBTI-induced defects centers because of the similarities to the centers observed in silicon nitride (the silicon-nitrided center is also a silicon dangling bond in which the silicon atom is back-bonded to nitrogen atoms). The defect identification in plasma-nitrided devices helps to explain the following phenomena: (1) NBTIs enhancement in plasma-nitrided devices; (2) conflicting reports of NBTI-induced interface states and/or bulk traps; and (3) fluorines ineffectiveness in reducing NBTI in plasma-nitrided devices. We also observe the atomic-scale defects involved in NBTI in HfO2-based devices and find that short- and long-term stressing generates different defects and that these defects are different than those observed in the SiO2 and plasma-nitrided devices. Our results also suggest that the NBTI-induced defects in these devices are physically located in the interfacial layer (not at the interface).

An electrically detected magnetic resonance study of performance limiting defects in SiC metal oxide semiconductor field effect transistors

In this study, we utilize electrically detected magnetic resonance (EDMR) techniques and electrical measurements to study defects in SiC based metal oxide semiconductor field effect transistors (MOSFETs). We compare results on a series of SiC MOSFETs prepared with significantly different processing parameters. The EDMR is detected through spin dependent recombination (SDR) in most cases. However, in some devices at a fairly high negative bias, the EDMR likely also involves spin dependent trap-assisted tunneling (SDT) between defects on both sides of the SiC/SiO2 interface. At least three different defects have been detected in the magnetic resonance measurements. The defects observed include two at the SiC/SiO2 interface or on the SiC side of the SiC/SiO2 interface: one is very likely a vacancy center with a distribution which extends into the bulk of the SiC and the other is likely a “dangling bond” defect. A third defect, located on the SiO2 side of the SiC/SiO2 interface, has a spectrum very similar to...

Identification of a silicon vacancy as an important defect in 4H SiC metal oxide semiconducting field effect transistor using spin dependent recombination

A spin dependent recombination (SDR) spectrum observed in a wide range of SiC metal oxide semiconducting field effect transistors (MOSFETs) has previously been only tentatively linked to a silicon vacancy or vacancy related defect. By resolving hyperfine interactions in SDR detected spectra with 13C nuclei, we provide an extremely strong argument identifying the SDR spectrum with a silicon vacancy. Since the silicon vacancy spectrum dominates the SDR response in a wide variety of SiC MOSFETs, silicon vacancies are quite important traps in this technology.

Defects and electronic transport in hydrogenated amorphous SiC films of interest for low dielectric constant back end of the line dielectric systems

Back end of line dielectrics with low dielectric constants are needed for current and future integrated circuit technology. However, an understanding of the defects that cause leakage currents and limit reliability in these films is not yet developed. We utilize conventional electron paramagnetic resonance (EPR), electrically detected magnetic resonance (EDMR), and leakage current measurements, complimented by Fourier transform infrared spectroscopy and Rutherford back scattering results, to investigate a-SiC:H dielectrics which have great potential use for back end of line dielectrics. We observe a strong correlation between conventional EPR defect density measurements and leakage currents. There is also a very strong correlation between hydrogen content and both leakage current and EPR defect density. The close correspondence between the EPR results and the leakage currents strongly indicates that the defects observed by EPR are largely responsible for the leakage currents and likely limit the dielectri...

Spin counting in electrically detected magnetic resonance via low-field defect state mixing

The work herein describes a method that allows one to measure paramagnetic defect densities in semiconductor and insulator based devices with electrically detected magnetic resonance (EDMR). The method is based upon the mixing of defect states which results from the dipolar coupling of paramagnetic sites at low magnetic fields. We demonstrate the measurement method with spin dependent tunneling in thin film dielectrics; however, the method should be equally applicable to paramagnetic defect density measurements in semiconductors via the more commonly utilized EDMR technique called spin dependent recombination.

Zero-field detection of spin dependent recombination with direct observation of electron nuclear hyperfine interactions in the absence of an oscillating electromagnetic field

Electrically detected magnetic resonance (EDMR) involves the electron paramagnetic resonance (EPR) study of spin dependent transport mechanisms such as spin dependent tunneling and spin dependent recombination (SDR) in solid state electronics. Conventional EPR measurements generally require strong static magnetic fields, typically 3 kG or greater, and high frequency oscillating electromagnetic fields, typically 9 GHz or higher. In this study, we directly demonstrate that, in the absence of the oscillating electromagnetic field, a very large SDR response (≈1%) can be detected at zero magnetic field with associated hyperfine interactions at extremely low magnetic fields in a silicon carbide (SiC) diode at room temperature. The zero-field SDR (ZFSDR) response that we detect is unexpected in the conventional detection scheme of SDR via EDMR. We believe that our observations provide fundamental physical understanding of other recently reported zero-field phenomena such as singlet triplet mixing in double quant...

Observation of negative bias stressing interface trapping centers in metal gate hafnium oxide field effect transistors using spin dependent recombination

The authors combine metal oxide semiconductor (MOS) gated diode measurements and very sensitive electrically detected electron spin resonance measurements to detect and identify negative bias temperature instability (NBTI) generated defect centers in fully processed HfO2 pMOS field effect transistors. Both short and long term stressing defects are different from those generated by NBTI in Si∕SiO2 devices. The spectra generated by long term stressing differ from the short term stressing signals and are somewhat similar to those observed in plasma nitrided oxide Si∕SiO2 devices. The results suggest that NBTI defects are located in the interfacial SiO2 layer of these HfO2 devices.The authors combine metal oxide semiconductor (MOS) gated diode measurements and very sensitive electrically detected electron spin resonance measurements to detect and identify negative bias temperature instability (NBTI) generated defect centers in fully processed HfO2 pMOS field effect transistors. Both short and long term stressing defects are different from those generated by NBTI in Si∕SiO2 devices. The spectra generated by long term stressing differ from the short term stressing signals and are somewhat similar to those observed in plasma nitrided oxide Si∕SiO2 devices. The results suggest that NBTI defects are located in the interfacial SiO2 layer of these HfO2 devices.

The effect of nitric oxide anneals on silicon vacancies at and very near the interface of 4H SiC metal oxide semiconducting field effect transistors using electrically detected magnetic resonance

We use three electrically detected magnetic resonance (EDMR) approaches to explore nitric oxide (NO) annealing in 4H SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). One approach is sensitive to defects at the interface and those extending into the SiC. Two of these approaches are particularly sensitive to SiC/SiO2 interface defects. They show that NO anneals decrease the EDMR response. Since this and earlier studies indicate the ubiquitous presence of silicon vacancy centers in SiC MOSFETs, our results provide strong circumstantial evidence that these defects play an important role in limiting device performance and that NO anneals are effective in reducing their populations.

Direct observation of lifetime killing defects in 4H SiC epitaxial layers through spin dependent recombination in bipolar junction transistors

We have identified a magnetic resonance spectrum associated with minority carrier lifetime killing defects in device quality 4H SiC through magnetic resonance measurements in bipolar junction transistors using spin dependent recombination (SDR). The SDR spectrum has nine distinguishable lines; it is, within experimental error, essentially isotropic with four distinguishable pairs of side peaks symmetric about the strong center line. The line shape is, within experimental error, independent of bias voltage and recombination current. The large amplitude and spacing of the inner pair of side peaks and three more widely separated pairs of side peaks are not consistent with either a simple silicon or carbon vacancy or a carbon or silicon antisite. This indicates that the lifetime killing defect is not a simple defect but a defect aggregate. The spectrum is consistent with a multidefect cluster with an electron spin S=12. (The observed spectrum has not been reported previously in the magnetic resonance literatu...

Relationship Between the 4H-SiC/SiO 2 Interface Structure and Electronic Properties Explored by Electrically Detected Magnetic Resonance

In this paper, an exceptionally sensitive form of electron paramagnetic resonance called electrically detected magnetic resonance (EDMR) is utilized to investigate performance limiting imperfections at and very near the interface of 4H-silicon carbide MOSFETs. EDMR measurements are made over an extremely wide range of frequencies, 16 GHz-350 MHz. Multiple interface/near interface defects are identified and strong evidence for significant disorder at the interface region is presented.