Plasma-enhanced Chemical Vapor Deposition SiN Research Articles

Low temperature PECVD SiN x films applied in OLED packaging

Plasma Enhanced Chemical Vapor Deposition (PECVD) SiN x films deposited at the substrate temperatures from 20 to 180 °C and at the RF powers from 10 to 30 W were investigated. It is found that the films' properties such as density, refractive index, composition and bonding configuration are varied with the substrate temperature and RF power. The moisture resistant ability of the deposited SiN x films was investigated by the water vapor permeation (WVP) measurement. Even at the low substrate temperature such as 50 °C, the moisture resistance of SiN x films keeps quite good. Our results can be applied in Organic Light Emitting Devices (OLED) packaging effectively.

Orientation and dielectric overlayer effects in InGaP/GaAs heterojunction bipolar transistors

Emitter orientation effects in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) in which DC current gain was greater for the [0 1 1] emitter orientation compared to the [0 1 1 ̄ ] orientation were previously attributed to the piezoelectric effect, however no effects of dielectric overlayers were examined. In this work, we establish that for InGaP/GaAs HBTs, dielectric passivation effects can be as important as the piezoelectric effect. Non-self-aligned InGaP/GaAs HBTs with ECR SiON dielectric deposited at 25 °C exhibited greater stress and showed less current gain difference and lower base current ideality factors for these orientations than identical HBTs that were passivated with plasma enhanced chemical vapor deposition (PECVD) SiN dielectric. Non-self-aligned HBTs with ECR SiON passivation also showed slightly better rf performance for the [0 1 1] orientation with f t of 48 GHz compared to f t of 44 GHz for the [0 1 1 ̄ ] orientation. These differences in dielectrics are attributed to higher dielectric-induced damage in emitter–base space-charge region for the PECVD SiN film.

Low Dielectric Constant 3MS α-SiC:H as Cu Diffusion Barrier Layer in Cu Dual Damascene Process

The primary candidate for the barrier/etch stop layer in damascene process is silicon nitride. However, silicon nitride has a high dielectric constant. To reduce the effective dielectric constant in the copper damascene structure, silicon carbide, which is prepared by plasma enhanced chemical vapor deposition (PECVD) using 3 methyl silane source (Z3MS), is studied for the dielectric copper diffusion barrier. The dielectric constant of PECVD α-SiC:H is varied from 4.0 to 7.0 and the fourier transform infrared (FTIR) spectra peak intensity ratio of Si–CH3 bond to Si–C is also examined. The reduction in dielectric constant of α-SiC:H using 3MS gas seems to be related to the decreased density upon incorporation of Si–CH3 groups. The value of capacitance with α-SiC is 8–10% lower than that with PECVD SiN. The leakage current with α-SiC:H barrier is lower by 1 order of magnitude than that with PECVD SiN barrier.

Optimization of PECVD SiN:H films for silicon solar cells

We have grown silicon nitride (SiN:H) thin films on silicon and glass by the Plasma Enhanced Chemical Vapor Deposition (PECVD) Method at low temperature in order to study their electro-optical properties and correlate these properties to the chemical composition of the layers, so that optimum films may be achieved for silicon solar cells. By varying the silane to ammonia ratio in the plasma gas we have been able to modify the index of refraction, the optical band gap and the silicon surface state passivation properties of the films. From this information we have determined that the optimum silane to ammonia ratio, with other constant parameters in our system, should be 20/65. Our results indicate that the mid-gap surface state density in silicon can be reduced down to 10 10 cm −2 eV −1 when this optimum (silane to ammonia) ratio is used for depositing SiN:H layers. We have confirmed this optimal ratio by making quantum efficiency measurements on silicon solar cells having their emitter passivated with SiN:H layers deposited with different silane to ammonia ratios. A great reduction of the surface recombination velocity was achieved, as observed from the internal quantum efficiency measurements, for cells with optimal SiN:H layers as compared to those with non-optimum SiN:H layers.

Enhancement of Etching Rate of SiN Films by Addition of Gases Containing Hydrogen to CF 4 / O 2

We studied a method for increasing the etching rate of SiN films in downflow plasma. It was confirmed that the etching rate of SiN films deposited by plasma‐enhanced chemical vapor deposition (PE‐CVD) was 50‐200 times higher than that of the films deposited by low‐pressure chemical vapor deposition (LP‐CVD). The activation energy for PE‐CVD SiN (PE‐SiN) was 0.62 kcal/mol and that for LP‐CVD SiN (LP‐SiN) was large, 5.3 kcal/mol, indicating that different etching reactions occurred. Assuming that the difference is caused by the many H atoms contained in PE‐SiN, we compared the etching rates by adding gaseous , water, and methanol, which include H atoms, to . The results show that the etching rate increased by a maximum factor of 10 for LP‐SiN and approximately a factor of 1.5 times for PE‐SiN. From these results, we propose the following etching mechanism for the enhancement in the etching rate. Hydrogen added to reacts with N atoms on the SiN films to form , which is then removed as a volatile component. With the removal of these N atoms, the SiN surface becomes Si rich; therefore, the etching reaction of Si atoms and the F radicals is accelerated, thereby increasing the etching rate. © 1999 The Electrochemical Society. All rights reserved.

Low temperature polycrystalline silicon thin film transistors

Low temperature polycrystalline silicon (poly-Si) thin film transistors (TFTs) fabricated using laser crystallized poly-Si, as-deposited poly-Si by plasma process, and metal-induced crystallized (MIC) poly-Si were reviewed on the basis of recent results. The as-deposited and laser crystallized poly-Si TFTs have been fabricated in the present work together with Ni-MIC poly-Si using plasma enhanced chemical vapor deposition (PECVD) silicon nitride as a gate insulator. The as-deposited poly-Si TFT fabricated with a maximum process temperature of 280°C exhibits a field effect mobility of 12 cm 2/V s when the thickness of the poly-Si is ∼300 nm. The laser crystallized poly-Si TFT using Ni silicide source/drain and gate electrodes exhibits a field effect mobility of 262 cm 2/V s. However, the MIC poly-Si TFT using PECVD SiN x gate insulator exhibits a field effect mobility of ∼12 cm 2/V s.

Optimization of saturation current density of PECVD SiN coated phosphorus diffused emitters using neural network modeling

Emitter surface passivation by low temperature plasma enhanced chemical vapor deposition (PECVD) silicon nitride is investigated and optimized in this paper. We have found that the saturation current density of a 90±10 μ/sq phosphorus diffused emitter with Ns ≈3 x 1019 and Xj ≈0.3 µm can be lowered by a factor of eight by appropriate PECVD silicon nitride deposition and photoassisted anneal. PECVD silicon nitride deposition alone reduces the emitter saturation density (Joe) by about a factor of two to three, and a subsequent photoanneal at temperatures ≥350°C reduces Joe by another factor of three. In spite of the larger flat band shift for direct PECVD silicon nitride coating, the silicon nitride induced surface passivation is found to be about a factor of two inferior to the thermal oxide plus PECVD silicon nitride passivation due to higher interface state density at the SiN/SiO2 interface compared to SiO2/Si interface. A combination of statistical experimental design and neural network modeling is used to show quantitatively that lower radio frequency power, higher substrate temperature, and higher reactor pressure during the PECVD deposition can reduce the Joe of the silicon nitride coated emitter.

Enhanced disordering of GaAs/AIGaAs multiple quantum well by rapid thermal annealing using plasma enhanced chemical vapour deposited SiN capping layer grown at high RF power condition

The multiple quantum well (MQW) structure is a good candidate to monolithically integrate lasers and waveguides for realizing photonic integrated circuits. For such an application, selective disordering techniques are required, because these can make it possible to define a waveguide section laterally by inducing local changes in absorption and refractive indices of a MQW structure, which is needed to fabricate waveguide devices including laser. There are several techniques to selectively disorder the I I I -V MQW structures. These are impurity induced disordering [1,2], ion implantation disordering [3, 4], and impurity-free disordering [5-12] followed by thermal treatment. Impurity induced disordering and ion implantation disordering can disorder MQW structure perfectly, but these techniques introduce many defects and high doping concentrations which may deteriorate the performances of waveguide devices because of losses from scatterings by defects and free carrier absorption in the waveguide. Impurity-free techniques employ dielectrics, such as SiO2 or SiN, a capped annealing technique, which employs rapid thermal annealing (RTA) [5-10] or sealed ampoule annealing with an As overpressure [11, 12]. Impurity-free techniques do not disorder MQW structure completely, but disorder it enough to fabricate waveguides and lasers [9-12]. For impurity-free disordering, there are various film growth techniques, such as chemical vapour deposition (CVD) [11], e-beam evaporation [6, 8, 9], sputtering [5], and plasma enhanced chemical vapour deposition (PECVD) [7, 10, 12], which can deposit SiN and/or Si te films on a MQW structure. The behaviour of disordering is affected by the film quality used in the impurity-free disordering technique. Therefore, if an optimum film growth condition can be found by varying process conditions, then selective disordering can be achieved with the same material without surface degradation which should be accompanied in the disordering process without an encapsulation. The characteristics of film deposited by the PECVD technique can be varied by varying process conditions, such as substrate temperature, ratio of reactant gas, and RF power [13]. As a first step to finding a process-dependent impurity-free disordering, we varied the RF power. We carried out impurity-free disordering using a PECVD SiN cap layer with RTA. We found that this technique could disorder the GaAs/A1GaAs MQW structure and the disordering was enhanced by using SiN film grown at high RF power. We used a GaAs/A1GaAs MQW laser structure which was grown by a metal organic chemical vapour deposition (MOCVD) technique on Si-doped n ÷ GaAs substrate. The structure has the following layers from the top of the substrate: 0.5/xm of n (1018 cm -3) GaAs buffer, 1/zm of n (1017 cm -3) A10.4~Ga0.s3As, 0.1/xm of undoped A10.24Ga0.76As, four 7 nm undoped GaAs quantum wells with 10 nm A10.24Ga0.76As barrier, 0.1/xm of undoped A10.24Ga0.76As, 1/zm of p (1017 cm -3) A10.47Ga0.53As, and 0.2/xm of p+ (10 ~8 cm -3) GaAs. In the substrate design, separate confinement design is chosen to enhance the optical confinement in the quantum wells. SiN films were deposited by a PECVD technique for cap layers. We used dilute silane (5% Sill4 in N:) and high purity NH 3 (99.999%) and N2 (99.9999%) as a reactant gas. During plasma deposition, the ratio of partial pressure (PNH3/Psi~,) was kept at 1, total pressure was kept as 120 Pa by adding N2 gas and the substrate temperature was 300 °C. SiN films were grown with various RF powers (0 W, 60 W and 90 W). The thicknesses and refractive indices, for each RF power condition, were determined by an ellipsometer (Gaertner, Ll17) and a surface profiler (Tencor, alpha step 200). Disordering of MQW samples was accomplished by RTA at 850 °C for 35 s in Ar atmosphere with a heating rate of 65 °C/s. Disordering of MQW

Plasma-enhanced chemical-vapor-deposited oxide for low surface recombination velocity and high effective lifetime in silicon

It is shown that plasma-enhanced chemical-vapor deposition (PECVD) of thin SiO2 on Si wafers followed by rapid thermal annealing (RTA) can result in very high effective carrier lifetime (≳5 ms) and extremely low surface recombination velocity (≤2 cm/s). Thin SiO2 (∼100 Å) layers were prepared by direct PECVD at 250 °C and RTA was performed at 350 °C in forming gas. Detailed metal-oxide-semiconductor analysis and model calculations showed that such a low recombination velocity is the result of moderately high positive oxide charge (5×1011–1×1012 cm−2 ) and relatively low midgap interface-state density (5×1010–1×1011 cm−2 eV−1). RTA was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very low surface recombination velocity. Some degradation in the surface recombination velocity or effective lifetime was observed. It is found that a PECVD SiN cap on top of the thin SiO2 not only suppressed this degradation but also enhanced the effective lifetime.

Hydrogen in plasma-enhanced chemical vapour deposition insulating films

There exists a strong interdependence between deposition conditions, thin film composition (especially hydrogen concentration) and thin film parameters in the case of plasma-enhanced chemical vapour deposition (PECVD) silicon nitrides deposited in quartz tube reactors in the kilohertz frequency range. Besides deposition temperature and total pressure, the composition of the reacting gas mixture exerts a significant influence on the hydrogen concentration of PECVD SiN. Low partial pressures of hydrogen do not necessarily lead to low hydrogen concentrations in the layers. The combined influence of N:Si ratio and hydrogen content may lead to contrary changes of technologically relevant parameters as seen in the case of SiN(N 2) and SiN(NH 3) according to the etch rate in HF solutions. Hydrogen concentrations above 30 at.% lead to a hardening effect of PECVD SiN surfaces. The same effect can be obtained by phosphorus doping of PECVD silicon nitrides and especially oxynitrides, whereas PECVD oxides tend to become softer with increasing phosphorus doping. Hydrogen diffusion coefficients in PECVD SiN and SiO were derived from hydrogen concentration profiles in these layers. Hydrogen effusion during thermal stress can be a reason for remarkable changes and severe degradation of technologically relevant parameters of PECVD thin films. Therefore in this work emphasis was laid on the reasons, mechanisms and effects of incorporation and movement of hydrogen in PECVD SiN thin films.