ICMCTF2016 Session C5-2: Thin Films for Active Devices

Depositing nitrates using N₂ rather than NH₃ requires plasma activation. It has been done successfully for Si3N4 in a PECVD system and for GaN in an MOCVD system. As a result better films without H₂ content depositied at lower temperatures and without the abatment issues relating to NH₃ use. However carrying the earlier learning to atomic deposition systems without sacrificing productivity or cycle time is none trivial. Nano-Master has developed an ALD chamber with ICP source having a minimal volume and therefore shortest cycle time. Here the features of the chamber design and results of depositing GaN films on Si substrates in such a system will be discussed.

For the production of high brightness light-emitting diodes (LEDs) it is essential to have both a high light extraction efficiency (LEE) and high internal quantum efficiency (IQE) of the device. Patterned sapphire substrates (PSS) improve both the LEE and the IQE and hence PSS are often used for high brightness LEDs. The LED itself is built of multi quantum well (MQW) structures containing metalorganic vapor phase epitaxy (MOVPE)-GaN layers. Any defect in these layers results in a decrease of the IQE.

In this work an AlN-buffer layer, using physical vapor deposited (PVD), is used as a template for the MOVPE-GaN growth. All AlN films were deposited on a dedicated high temperature PVD module using an Evatec CLUSTERLINE 200 II. Commercially available patterned and flat sapphire substrates (FSS) were processed simultaneously. Both the deposition temperature and thickness were varied from 400°C to 800°C and from 10 nm to 65 nm respectively.

The following MOVPE processes were performed in an Aixtron 200RF with a horizontal reactor and standard precursors for the GaN deposition. After a low temperature GaN nucleation step at 750°C, the temperature is raised up to 1120°C for the GaN film growth. The thicknesses were varied between approx. 20 nm and 3 µm.

XRD measurements show that the AlN on FSS are of high quality and their FWHM of the AlN(002) rocking curve (RC) is below 20 arcsec. Scanning electron microscope (SEM) images show that the growth pattern of GaN on PSS does not only depend on the RC, but also on the lattice spacing of AlN, which can be slightly varied by temperature and thickness. Depending on this lattice spacing, the GaN-MOVPE layer either shows a side wall or a bottom growth. A process window for the AlN-PVD buffer layer is presented in which the GaN grows only at the bottom of PSS. Hence these AlN templates are suitable for the mass production of high brightness LEDs.

The near-infrared (NIR) emitting lanthanide complexes are gaining much attention all over the world for their potential applications in optical communications, optoelectronic devices and biomedical diagnostic applications. In particular, ytterbium ion is very useful for biomedical probes because it emits light near 1000 nm where the tissues are relatively transparent. The emission at this wavelength can be properly utilized to develop OLEDs using Yb complexes as emitting layers. Although few OLEDs based Yb complexes are available, their efficiency and stability are very low and, is still in question. For this reason, there is a need to develop ytterbium complexes which could enhanced the efficiency and stability of the respective OLEDs.

ScN, CrN, and related ternary nitrides are semiconductors with promising properties for high-temperature electronic, thermoelectric, opto-electric, piezo-electric, and magnetoresistive devices. Epitaxial layers are grown on MgO(001) and Al₂O₃(0001) by reactive magnetron sputtering at 600-1000 ^oC, and their microstructure, surface morphology, and composition analyzed by XRD, XRR, in situ STM, RBS, XPS, and AES. A combination of temperature dependent electron transport measurements, optical analyses, and first principles calculations are employed to determine band gaps, effective masses, mobilities, carrier concentrations, and phonon modes. ScN has a 0.92 eV indirect band gap, direct transitions at the X and Gamma points of 2.07 and 3.75 eV, transport and effective masses of 0.40 and 0.33 m₀, and a carrier concentration which is controlled by F doping ranging from 1.12-12.8x10²⁰ cm^-3. Al_1-xSc_xN exhibits a structural instability with a non-linear composition dependence in bond angle, length, and character that is associated with a transition from the rock-salt to the wurtzite structure, and exhibits a direct band gap of 6.15–9.32x (eV) in the wurtzite structure. CrN is a Mott-Hubbard type insulator with a 0.2+/-0.4 eV band gap, a structural and magnetic phase transition at 280 K, variable-range hopping conduction with a Efros-Shklovskii to Mott transition at 30 K, a lower limit for the effective mass of 4.9 m₀, and a donor ionization energy of 24 meV.

In this research, Quasi-ballistic effect influence Hot carrier-induced degradation (HCD) at different temperature in ultra scale n-channel metal oxide semiconductor field effect transistor (n-MOSFET) was investigated. Since electron-electron scattering (EES) is the dominant mechanism in nanoscale device, which populates the hot carrier fraction more efficiently at elevated temperatures, making HCD more severe. Nevertheless, ballistic effect must be concerned in nanoscale device, but the ballistic effect influence on HCD is still not completely known. In this study, we use a concept of ballistic transport to explain why HCD can be suppressed under low temperature in short channel device. At low temperature, the injection velocity decreases and ballistic is enhanced because the population of the energetic carriers is decreased and scattering probability (ex. EES) is decreased in the channel, respectively.

This study investigates on defect variation from Nitrogen diffuse to hafnium oxide layer in Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) by different metal gate fabrications. By varying fabrications of PVD-TiN, ALD-TiN and ALD-TaN, the work-function can be adjusted leading to apparent differences of threshold voltage (V_th). In addition, the result of the charge pumping shows that the amount of the interface trap in the PVD-TiN device is the highest, ALD-TiN device the second, while the ALD-TaN the least. On the other hand, nitrogen interstitial phenomenon resulting in temporary shift of threshold voltage (V_th) can be observed, PVD-TiN the highest and ALD-TaN the least, through ultra-fast and slow-IV NBTI. To compare with pre- and post-metal annealing effect on ALD-TaN, pre-metal annealing can suppress nitrogen interstitial from thermal diffusion in annealing process.

In this research, the effects of post-metal deposition annealing temperature on the degradation induced by hot carrier stress (HCS) and positive bias stress (PBS) in TiN/HfO₂ n-channel fin field effect transistors (FinFETs) are studied. The initial electrical characteristics possess higher threshold voltage (Vth), transconductance (GM) and on-state current (Ion) in high-annealing temperature devices. Particularly, it is found that the PBS and HCS-induced degradation is more serious in high-annealing temperature devices due to more plenty high-k bulk traps. However, nitrogen diffusion from TiN is not more abundant oxygen vacancies generated within HfO₂ since oxygens are more likely to diffuse toward the interface layer and repair Si/SiO₂ dangling bonds for high-annealing temperature devices. Furthermore, by charge-pumping and C-V measurements, less Nit and thicker IL was found in high-annealing temperature devices, verifying the proposed model.