Plasma-enhanced Atomic Layer Deposition System Research Articles

Effects of ammonia and oxygen plasma treatment on interface traps in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors

A HfO2/Al2O3/AlN stack deposited in a plasma-enhanced atomic layer deposition system is used as the gate dielectric for GaN metal–insulator–semiconductor structures. Prior to the deposition, in situ remote plasma pretreatments (RPPs) with O2, NH3, and NH3–O2 (in sequence) were carried out. Frequency-dependent capacitance–voltage (C–V) measurements reveal that for all the RPP-treated samples, the interface trap density Dit was significantly reduced compared to the sample without RPP. In particular, the NH3-treated sample exhibits an extremely low Dit of ∼1011 cm−2·eV−1 from EC − 0.31 eV to EC − 0.46 eV. To characterize the interface traps at deeper levels, the transfer pulsed I–V measurement was employed further. In the energy range of EC − ET > 0.54 eV, the interface trap charge density Qit of various samples demonstrates the following order: NH3 RPP < NH3–O2 RPP < O2 RPP < without RPP. By adjusting multiple pulse widths, the Dit derived from the Qit result matches the C–V measurement precisely. Moreover, X-ray photoelectron spectroscopy analysis of the Ga 3d core-level indicates that NH3 RPP facilitates the conversion of Ga2O into GaN at high RF power of 2500 W, whereas O2 RPP mainly oxidizes GaN to relatively stable Ga2O3. Combined with the C–V and pulsed I–V measurements, it is confirmed that a strong positive correlation exists between Ga2O and the interface traps, rather than Ga2O3.

Spectroscopic study of La2O3 thin films deposited by indigenously developed plasma-enhanced atomic layer deposition system

The spectroscopic study of La2O3 thin films deposited over Si and SiC at low RF power of 25 W by using indigenously developed plasma-enhanced atomic layer deposition (IDPEALD) system has been investigated. The tris (cyclopentadienyl) lanthanum (III) and O2 plasma were used as a source precursor of lanthanum and oxygen, respectively. The [Formula: see text]1.2 nm thick La2O3 over SiC and Si has been formed based on our recipe confirmed by means of cross-sectional transmission electron microscopy. The structural characterization of deposited films was performed by means of X-ray photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD). The XPS result confirms the formation of 3[Formula: see text] oxidation state of the lanthania. The XRD results reveals that, deposited La2O3 films deposited on SiC are amorphous in nature compare to that of films on Si. The AFM micrograph shows the lowest roughness of 0.26 nm for 30 cycles of La2O3 thin films.

Tuning Material Properties of Oxides and Nitrides by Substrate Biasing during Plasma-Enhanced Atomic Layer Deposition on Planar and 3D Substrate Topographies.

Oxide and nitride thin-films of Ti, Hf, and Si serve numerous applications owing to the diverse range of their material properties. It is therefore imperative to have proper control over these properties during materials processing. Ion-surface interactions during plasma processing techniques can influence the properties of a growing film. In this work, we investigated the effects of controlling ion characteristics (energy, dose) on the properties of the aforementioned materials during plasma-enhanced atomic layer deposition (PEALD) on planar and 3D substrate topographies. We used a 200 mm remote PEALD system equipped with substrate biasing to control the energy and dose of ions by varying the magnitude and duration of the applied bias, respectively, during plasma exposure. Implementing substrate biasing in these forms enhanced PEALD process capability by providing two additional parameters for tuning a wide range of material properties. Below the regimes of ion-induced degradation, enhancing ion energies with substrate biasing during PEALD increased the refractive index and mass density of TiOx and HfOx and enabled control over their crystalline properties. PEALD of these oxides with substrate biasing at 150 °C led to the formation of crystalline material at the low temperature, which would otherwise yield amorphous films for deposition without biasing. Enhanced ion energies drastically reduced the resistivity of conductive TiNx and HfNx films. Furthermore, biasing during PEALD enabled the residual stress of these materials to be altered from tensile to compressive. The properties of SiOx were slightly improved whereas those of SiNx were degraded as a function of substrate biasing. PEALD on 3D trench nanostructures with biasing induced differing film properties at different regions of the 3D substrate. On the basis of the results presented herein, prospects afforded by the implementation of this technique during PEALD, such as enabling new routes for topographically selective deposition on 3D substrates, are discussed.

Performance enhancement of MgZnO ultraviolet photodetectors using ultrathin Al2O3 inserted layer

In this study, the magnesium zinc oxide (MgZnO) films and ultrathin alumina (Al2O3) inserted layers were subsequently deposited on sapphire substrates using a plasma-enhanced atomic layer deposition system, and applied in metal-semiconductor-metal ultraviolet (UV) photodetectors (MSM-UPDs). The dark current of the MgZnO MSM-UPDs was decreased from 1 to 0.34 nA with an increase in Al2O3 layer thickness from 0 to 5 nm. The ultrathin Al2O3 inserted layer effectively passivated the dangling bonds on the MgZnO surface and blocked leakage current. At a bias voltage of 5 V, the maximum UV-visible rejection ratio of the MgZnO MSM-UPDs was 1.78 × 103 with 5-nm-thick Al2O3 inserted layer. Furthermore, the noise equivalent power and detectivity of MgZnO MSM-UPDs with 5-nm-thick Al2O3 inserted layer were improved from 1.26 × 10−14 W and 2.50 × 1013 cm Hz1/2 W−1 to 0.93 × 10−14 W and 3.40 × 1013 cm Hz1/2 W−1 in comparison with MgZnO MSM-UPDs without Al2O3 inserted layer. The high performances of MgZnO MSM-UPDs were achieved by using ultrathin Al2O3 inserted layer.

Effect of hydrogen peroxide pretreatment on ZnO-based metal–semiconductor–metal ultraviolet photodetectors deposited using plasma-enhanced atomic layer deposition

In this study, zinc oxide (ZnO) films were deposited on sapphire substrates using a plasma-enhanced atomic layer deposition system. Prior to deposition, the substrates were treated with hydrogen peroxide (H2O2) in order to increase nucleation on the initial sapphire surface and, thus, enhance the quality of deposited ZnO films. Furthermore, x-ray diffraction spectroscopy measurements indicated that the crystallinity of ZnO films was considerably enhanced by H2O2 pretreatment, with the strongest (002) diffraction peak occurring for the film pretreated with H2O2 for 60 min. X-ray photoelectron spectroscopy also was used, and the results indicated that a high number of Zn–O bonds was generated in ZnO films pretreated appropriately with H2O2. The ZnO film deposited on a sapphire substrate with H2O2 pretreatment for 60 min was applied to metal–semiconductor–metal ultraviolet photodetectors (MSM-UPDs) as an active layer. The fabricated ZnO MSM-UPDs showed improvements in dark current and ultraviolet–visible rejection ratios (0.27 μA and 1.06 × 103, respectively) compared to traditional devices.

Microwave remote plasma enhanced-atomic layer deposition system with multicusp confinement chamber.

A microwave remote Plasma Enhanced-Atomic Layer Deposition system with multicusp confinement chamber is established at the Plasma and Beam Physics research facilities, Chiang Mai, Thailand. The system produces highly-reactive plasma species in order to enhance the deposition process of thin films. The addition of the multicusp magnetic fields further improves the plasma density and uniformity in the reaction chamber. Thus, the system is more favorable to temperature-sensitive substrates when heating becomes unwanted. Furthermore, the remote-plasma feature, which is generated via microwave power source, offers tunability of the plasma properties separately from the process. As a result, the system provides high flexibility in choice of materials and design experiments, particularly for low-temperature applications. Performance evaluations of the system were carried on coating experiments of Al2O3 layers onto a silicon wafer. The plasma characteristics in the chamber will be described. The resulted Al2O3 films-analyzed by Rutherford Backscattering Spectrometry in channeling mode and by X-ray Photoelectron Spectroscopy techniques-will be discussed.

Influence of AlN Passivation on Dynamic ON-Resistance and Electric Field Distribution in High-Voltage AlGaN/GaN-on-Si HEMTs

We investigate in detail the influence of AlN passivation on dynamic ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) and electric field (E-field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed I-V measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic RON increase has been significantly suppressed to below 10% at various temperatures ranging from -50 to 200 °C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic RON for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique.

A Remote-Oxygen-Plasma Surface Treatment Technique for III-Nitride Heterojunction Field-Effect Transistors

We present a paper on the influence of an oxygen-plasma treatment technique for III-nitride (III-N) heterojunction field-effect transistors (HFETs) using a plasma-enhanced atomic layer deposition (PE-ALD) system. The oxygen plasma is excited in a remote location to avoid the plasma damage. After the plasma treatment, the threshold voltage was shifted from -0.25 to 0 V and a two-orders-of-magnitude reduction of the drain leakage current was observed in recessed-gate AlGaN/AlN/GaN HFETs. The capacitance-voltage characteristics of gate diodes showed indistinguishable hysteresis. Improved gate-lag and lowered dynamic ON-resistance were also observed in the fabricated AlGaN/AlN/GaN HFETs after the oxygen-plasma treatment. The results indicate that the oxygen-plasma treatment using a PE-ALD system could be a promising approach to improve the device switching performance in III-N HFETs.

Characteristics of SiOC(-H) Thin Films Prepared by Using Plasma-enhanced Atomic Layer Deposition

Low-dielectric-constant SiOC(-H) thin films were prepared on p-type Si(100) substrates by using plasma-enhanced atomic layer deposition (PEALD) with trimethylsilane (TMS; (CH3)3SiH) and oxygen gas as precursors and Ar as a purge gas. The adoption of the atomic layer deposition (ALD) method to deposit low-k materials is a challenge to achieve high-quality films and lowtemperature process conditions. The eect of the radio-frequency (rf) power on the structural and the dielectric properties was studied. RF powers from 100 W to 500 W were applied to the PEALD system to generate the plasma. The films were analyzed by using Fourier-transform infrared (FTIR) spectroscopy and C-V and I-V measurements. FTIR studies were carried out in the absorbance mode in the range of 700 to 4000 cm 1 , and showed various bonding configurations, such as Si-O-Si(C), Si-CH3, -OH, and CHn bonds, in the films. As the rf power was increased, the absorption peaks corresponding to the Si-O-Si and the Si-O-C bonds become sharper; at the same time, the former shifted towards lower wave number (red shift). The dielectric constants of the films were investigated using a Al/SiOC(-H)/p-Si MIS structure. The measured dielectric constant and leakage current density were 2.3 and 10 8 A/cm 2 at 1 MV/cm, respectively. Using the optimized process conditions, we evaluated the PEALD method applied to SiOC(-H) film deposition. The PEALD method without heat treatment for SiOC(-H) film deposition has been shown not only to be comparable to the PECVD method with heat treatment or UV irradiation but also to be applicable to a new applications requiring a low-temperature process.

Plasma Modeling of a PEALD System for the Deposition of TiO2 and HfO2

A PEALD (plasma enhanced atomic layer deposition) system is developed and analyzed by using a uid model in 2-D ICP (inductively coupled plasma) was used as a remote plasma source on the top of an Al deposition chamber for handling 200 mm wafers. TIIP (titanium isoproxide) and TEMA-Hf (tetraethylmethyl amino hafnium) were used for deposition precursors. Ar+O2 and H2O plasmas were used as an oxidant for those precursors. A conventional 100 mm diameter ICP source was replaced with a 33 mm diameter sealed-o glass tube wound with a 6.35 mm-diameter copper tube antenna. The e ects of a 300 { 400 W, 13.56 MHz plasma were analyzed by using OES(optical emission spectroscopy) and the properties of the deposited lms. The uniformity of the lm thickness was very sensitive to the wafer temperature rather than to the plasma parameters for HfO2. Fluid modeling of the plasma showed a 37 mm source had an equivalent radical generating capability as a 100 mm source. The electron density calculated just above the wafer was 1/100 of that in the source region and it could be considered as remote. The heat transfer analysis showed that the rise in the wafer surface temperature could be as high as 100 C with a large diameter plasma source to give large non-uniformity in the lm's thickness for a temperature sensitive precursor like TEMA-Hf.