Catalytic Chemical Vapor Deposition SiN Research Articles

Tunnel nitride passivated contacts for silicon solar cells formed by catalytic CVD

An ultra-thin silicon nitride (SiN x ) layer formed by catalytic chemical vapor deposition (Cat-CVD) is used to replace the Si dioxide (SiO2) layer of a tunnel oxide passivated contact solar cell. The passivation quality of crystalline Si (c-Si) with a stack of the ultra-thin SiN x and n-type hydrogenated amorphous Si (a-Si:H) or microcrystalline Si (μc-Si:H), also formed by Cat-CVD, is significantly improved by annealing at 850 °C, probably due to the formation of a back surface field layer. Cat-CVD SiN x with thicknesses of up to 2.5 nm can have sufficient tunneling conduction. The ultra-thin SiN x having functions of surface passivation and carrier tunneling, and the unification of the formation method for the tunnel SiN x and conductive layers will lead to the realization of tunnel nitride passivated contact solar cells.

Excellent passivation effect of Cat-CVD SiN x/i-a-Si stack films on Si substrates

We have demonstrated that the surface recombination velocity can be lowered to as low as 1.3 cm/s for n-type c-Si wafers and to 9.0 cm/s for p-type wafers by using amorphous Si (a-Si) and Si nitride (SiN x ) stacked films prepared by catalytic chemical vapor deposition (Cat-CVD). These values are much lower than those of c-Si wafers passivated by same stacked structures formed by low-damage remote plasma-enhanced CVD (PECVD). It is revealed that Cat-CVD a-Si insertion layers play an important role to improve interface quality, and also SiN x films are also essential for reducing the surface recombination velocity down to such low levels.

C–V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Electrical properties of Schottky- and metal–insulator–semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance–voltage ( C–V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance ( g m) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f T compared with that of the Schottky-gate device. In this study, C–V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.

Cat-CVD SiN passivation films for OLEDs and packaging

A Roll-to-roll type catalytic chemical vapor deposition (Cat-CVD) apparatus was developed for the application to flexible organic light-emitting diode (OLED) displays and packaging. Silicon nitride (SiN x ) films were prepared by this roll-to-roll type apparatus at temperatures below 60 °C. It was found that these SiN x films are highly moisture resistant, and the water vapor transmission rate (WVTR) on plastic substrates could be lowered to 0.01 g/m 2 day. Roll-to-roll type Cat-CVD is one of the most promising methods for the preparation of barrier films for OLED displays and packaging.

Effect of hydrogen on SiN x films deposited by Cat-CVD method

This study is aimed at improving the characteristics of silicon nitride (SiN x) film deposited by catalytic chemical vapor deposition (Cat-CVD) method. Cat-CVD method can deposit SiN x films that have low hydrogen content and high density at low temperature without any plasma damage to substrates. Usually silane (SiH 4) and ammonia (NH 3) are used for source gases. Then adding hydrogen (H 2) gas to source gases makes characteristics of Cat-CVD SiN x improved. When using H 2 gas, hydrogen content in SiN x film becomes lower and electronic reliability becomes higher.

GaN-based FETs using Cat-CVD SiN passivation for millimeter-wave applications

We have found that SiN passivation by catalytic chemical vapor deposition (Cat-CVD) can significantly increase an electron density of an AlGaN/GaN heterostructure field-effect transistor (HFET). This effect enables thin-barrier HFET structures to have a high-density two-dimensional electron gas and leads to suppression of short-channel effects. We fabricated 30-nm-gate Al 0.4Ga 0.6N(8 nm)/GaN HFETs using Cat-CVD SiN. The maximum drain current density and extrinsic transconductance were 1.49 A/mm and 402 mS/mm, respectively. Current-gain cutoff frequency and maximum oscillation frequency of the HFETs were 181 and 186 GHz, respectively. These high-frequency device characteristics are sufficiently high enough for millimeter-wave applications.

XPS study of surface potential in AlGaN/GaN heterostructure with Cat‐CVD SiN passivation

AlGaN surface potentials in AlGaN/GaN heterostructures with and without SiN passivation were investigated using x-ray photoelectron spectroscopy (XPS). SiN films were formed on AlGaN surfaces by catalytic chemical vapor deposition (Cat-CVD), which has already been found to increase two-dimensional electron gas (2DEG) density. Based on a simple electrostatic analysis, the 2DEG density is expected to increase as the AlGaN surface potential decreases. This study experimentally demonstrates that a reduction in the AlGaN surface potential is actually induced by Cat-CVD SiN passivation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement-Mode AlN/GaN HFETs Using Cat-CVD SiN

High-performance enhancement-mode (E-mode) AIN (2.5 nm)/GaN heterostructure field-effect transistors (HFETs) were fabricated with a novel method using SiN passivation by catalytic chemical vapor deposition (Cat-CVD). We found that the formation of a 2-D electron gas (2DEG) in the AIN/GaN heterostructure can be controlled by the presence of the Cat-CVD SiN on the barrier layer. Before SiN deposition, the 2DEG at the AIN/GaN heterointerface was completely depleted because of the extremely thin barrier layer. On the other hand, after SiN deposition, the decrease in AIN surface barrier height induced a high-density 2DEG. The E-mode HFETs with gate lengths of 100-180 nm and threshold voltages from +0.14 to +0.55 V showed a maximum drain-current density of 0.70-0.92 A/mm and a maximum extrinsic transconductance of 362-400 mS/mm. A current-gain cutoff frequency of 87 GHz and maximum oscillation frequency of 149 GHz were obtained for the 100-nm-gate devices.

AlN/GaN Insulated-Gate HFETs Using Cat-CVD SiN

The authors fabricated SiN/AlN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) using SiN passivation by catalytic chemical vapor deposition (Cat-CVD). Cat-CVD SiN increased the electron density of AlN/GaN HFETs by compensating the surface depletion of the two-dimensional electron gas. The MIS-HFETs had a maximum drain current density of 0.95 A/mm and a peak extrinsic transconductance of 211 mS/mm. A current-gain cutoff frequency of 107 GHz and maximum oscillation frequency of 171 GHz were obtained for the 60- and 70-nm-gate devices, respectively

Effects of SiN passivation by catalytic chemical vapor deposition on electrical properties of AlGaN∕GaN heterostructure field-effect transistors

We investigated the effects of SiN passivation by catalytic chemical vapor deposition (Cat-CVD) on the electrical properties of AlGaN∕GaN heterostructure field-effect transistors. The two-dimensional electron density (Ns) greatly increased after the Cat-CVD SiN deposition, and the tendency of the increase was enhanced with decreasing AlGaN barrier thickness. As a result of the large increase in Ns, the sheet resistance (Rsh) significantly decreased after the deposition, and it had low values of 320–460Ω∕◻ for extremely thin AlGaN barriers of 4–10nm. The increase in Ns showed little dependence on SiN thickness, indicating that the stress applied to the AlGaN barrier by SiN cannot be the origin of the increase. Cat-CVD SiN also improved the in-plane uniformity of mobility for extremely thin-barrier structures, which in turn improved the uniformity of Rsh. Moreover, we found that Cat-CVD was more effective than plasma-enhanced chemical vapor deposition in increasing Ns. A comparison of theoretical calculations and experimental results indicated that these behaviors can be explained by a decrease in the AlGaN surface barrier height due to the SiN deposition.

Preparation of SiN x gate-insulating films for bottom-gate type TFTs by Cat-CVD method

The properties of SiN x films prepared by catalytic chemical vapor deposition (Cat-CVD) on various gate-metals were studied for application of bottom-gate thin-film transistors (BG-TFTs). Additionally, the gate-insulating properties after rapid thermal annealing (RTA) were investigated for the fabrication of polycrystalline silicon (poly-Si) TFTs by simple RTA of amorphous silicon (a-Si:H) BG-TFTs. It was found that Cat-CVD SiN x on metals can be used as gate-insulating films of a-Si:H BG-TFTs and that the films can also be used even after RTA at 800 °C, when the surface of such metals is slightly oxidized.

Formation of low-resistivity poly-Si and SiN x films by Cat-CVD for ULSI application

In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiN x films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O 2 oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiN x prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiN x films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm −1 of OFF leakage current and ON/OFF ratio of 10 7–10 8 are realized, i.e. the devices can operate similarly to conventional thermal CVD process.