Designing single chamber hwcvd system for high deposition rate device quality A-Si:h thin films and solar cells

A new single chamber HWCVD with vertically mounted substrates and filaments has been designed for depositing device quality a-Si:H films with high deposition rate. Optimization studies on films deposited in this chamber under a variety of deposition conditions yielded uniform films at more than 7Å/sec deposition rate and with very low oxygen content. These films show a photoconductivity gain of more than 105. The working pressure has been kept quite low at 15 mtorr compared to earlier studies. i-layers of a p-i-n single junction solar cells were deposited on the TCO (Asahi-U type) glass in this reactor. The initial p-layer and the final n-layer were deposited in another system with separate chambers for these doped layers thus exposing the p-layer as well as the i-layer to the atmosphere during the transfer. Using this optimized intrinsic layer, a-Si:H based p-i-n solar cell showed a conversion efficiency of 4.7 %. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2789

Designing single chamber hwcvd system for high deposition rate device quality A-Si:h thin films and solar cells

A new single chamber HWCVD with vertically mounted substrates and filaments has been designed for depositing device quality a-Si:H films with high deposition rate. Optimization studies on films deposited in this chamber under a variety of deposition conditions yielded uniform films at more than 7Å/sec deposition rate and with very low oxygen content. These films show a photoconductivity gain of more than 105. The working pressure has been kept quite low at 15 mtorr compared to earlier studies. i-layers of a p-i-n single junction solar cells were deposited on the TCO (Asahi-U type) glass in this reactor. The initial p-layer and the final n-layer were deposited in another system with separate chambers for these doped layers thus exposing the p-layer as well as the i-layer to the atmosphere during the transfer. Using this optimized intrinsic layer, a-Si:H based p-i-n solar cell showed a conversion efficiency of 4.7 %. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2789

Enhancement of moisture resistance of spin-on low-k HSQ films by hot wire generated atomic hydrogen treatment

Spin on hydrogen silsesquioxane (HSQ) is a material with low dielectric constant (k) and shows potential as intermetal dielectric (IMD) layers for future VLSI circuits. One major challenge in the integration of these films is the moisture uptake with time, which degrades the electrical performance and hence limits their application. In the present work, we show (under accelerated conditions) that the as deposited films absorb moisture significantly which is reflected in the related signatures in the infrared (IR) spectroscopic data. Subsequently there is an increase in the leakage current with a concurrent decrease in the electrical breakdown field. Upon treatment with atomic hydrogen generated by a hot filament (TF = 1900 °C), drastic reduction in the moisture absorption is observed. Also there is almost a 2 orders of magnitude reduction in the leakage current and no indication of any electrical breakdown within the range of applied field.© Elsevie

Resisting oxygen plasma damage in low-k hydrogen silsesquioxane films by hydrogen plasma treatment

Low-density materials, such as the commercially available hydrogen silsesquioxane (HSQ) offer a low dielectric constant. Thus, HSQ with a low value of k (not, vert, similar 2.85) can be spin-coated if the density of Si–H bonding is maintained at a high level and the formation of –OH bonds and absorption of water in the film is minimized. O2 plasma exposure on HSQ film increases leakage current. Also the dielectric constant shows a significant increase after O2 plasma exposure. Another consequence of the O2 plasma exposure is the significant decrease in the contact angle of the HSQ surface, which is not desirable. In this paper, we demonstrate that the surface passivation by hydrogen followed by oxygen plasma treatment of HSQ film for 30 min each leads to a regain of leakage current density and dielectric constant. These results show that the H2 plasma treatment is a promising technique to prevent the damage in the commercially available and highly applicable low-k materials and it also increases the visibility of its use at the 0.1-μm technology. The more hydrophilic nature of the HSQ surface after O2 plasma exposure leads to an increased moisture absorption with a subsequent increase in the dielectric constant.© Elsevie

Gas Phase Chemistry Study During Deposition of a-Si: H and μc-Si: H Films by HWCVD using Quadrupole Mass Spectrometry

Amorphous and microcrystalline silicon films were deposited by HWCVD under different deposition conditions and the gas phase chemistry was studied by in situ Quadrupole Mass Spectrometry. Attempt is made to correlate the properties of the films with the gas phase chemistry during deposition. Interestingly, unlike in PECVD, partial pressure of H2 is higher than any other species during deposition of a-Si:H as well as μc-Si:H. Effect of hydrogen dilution on film properties and on concentration of various chemical species in the gas phase is studied. For low hydrogen dilution [H2]/ [SiH4] from 0 to 1 (where [SiH4] is 10 sccm), all films deposited are amorphous with photoconductivity gain of ∼ 106. During deposition of these amorphous films SiH2 was dominant in gas phase next to [H2]. Interestingly [Si]/[SiH2] ratio increases from 0.4 to 0.5 as dilution increased from 0 to 1, and further to more than 1 for higher hydrogen dilution leading to [Si] dominance. At hydrogen dilution ratio 20, consequently films deposited were microcrystalline

Revisiting the B-factor variation in a-SiC:H deposited by HWCVD

In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (αE)1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (Ts), filament temperature (TF) and C2H2 fraction. Our results indicate that the B-parameter varies considerably with process conditions such as TF, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD

Preliminary results on a-SiC:H based thin film light emitting diode by hot wire CVD

Preliminary results on the first hot wire deposited a-SiC:H based thin film light emitting p–i–n diode having the structure glass/TCO(SnO2:F)/p-a-SiC:H/i-SiC:H/n-a-SiC:H/Al are reported. The paper discusses the results of our attempts to optimize the p-, i- and the n-layers for the desired electrical and optical properties. The optimized p-layers have a bandgap Eg∼2 eV and conductivity a little lower than 10−5 (Ω cm)−1. On the other hand, the optimized n-type a-SiC:H show a conductivity of ∼10−4 (Ω cm)−1 with bandgap 2.06 eV. The highest bandgap of the intrinsic layer is approximately 3.4 eV and shows room temperature photoluminescence peak at approximately 2.21 eV. Thin film p–i–n diodes having i-layers with Eg from 2.7 to 3.4 eV show white light emission at room temperature under forward bias of >5 V. However, the 50-nm thick devices show appreciable reverse leakage current and a low emission intensity, which we attribute to the contamination across the p–i interface since these devices are made in a single chamber with the same filament

Photoluminescent, wide-bandgap a-SiC:H alloy films deposited by Cat-CVD using acetylene

Hydrogenated amorphous silicon/carbon films (a-Si-C:H) are deposited from a silane and acetylene gas mixture by the catalytic chemical vapour deposition (Cat-CVD) technique. It is observed that under certain conditions of total gas pressure and filament temperature (TF), the optical bandgap varies non-linearly with the acetylene to silane (C2H2/SiH4) ratio, having a maximum value of 3.6 eV for a C2H2/SiH4 ratio ≥0.8. However, the deposition rate drastically reduces with an increase in acetylene fraction. FTIR spectra indicate that the total hydrogen content is lower compared to samples deposited by PECVD using similar gas mixtures, with hydrogen being preferentially attached to carbon rather than silicon atoms. The photoluminescence (PL) spectra of these films show PL in the visible spectral region at room temperature. The films with larger bandgap (>2.5 eV) exhibit PL at room temperature, with the emission having peak energy in the range 2.0–2.3 eV

Low temperature silicon nitride deposited by Cat-CVD for deep sub-micron metal–oxide–semiconductor devices

Silicon nitride as a gate dielectric can improve the performance of ULSI CMOS devices by decreasing the gate leakage currents. In this paper we report a a-SiN:H gate dielectric fabricated using Cat-CVD at a relatively low substrate temperature of ∼250°C, using silane and ammonia as the source gases. The films were deposited at various gas pressures, (NH3/SiH4) flow rate ratios and at different filament temperatures (TF). The deposition parameters, i.e. total gas pressure and gas composition (silane+ammonia) were optimized to deposit insulating and transparent films with high breakdown strength. The structural properties of these films were studied by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. Films with bandgap as high as 5.5 eV were obtained. The optimized conditions were used to deposit ultrathin films of the order of 8 nm thickness for deep-submicron CMOS technology. Electrical properties such as C–V and I–V measurements were studied on metal–nitride–semiconductor (MNS) capacitor structures. These characterization results on MNS capacitors show breakdown fields of the order of 10 MV cm−1 and good interface properties

Photoluminescent, wide-bandgap a-SiC:H alloy films deposited by Cat- CVD using acetylene

Hydrogenated amorphous silicon/carbon films (a-Si-C:H) are deposited from a silane and acetylene gas mixture by the catalytic chemical vapour deposition (Cat-CVD) technique. It is observed that under certain conditions of total gas pressure and filament temperature (TF), the optical bandgap varies non-linearly with the acetylene to silane (C2H2/SiH4) ratio, having a maximum value of 3.6 eV for a C2H2/SiH4 ratio ≥0.8. However, the deposition rate drastically reduces with an increase in acetylene fraction. FTIR spectra indicate that the total hydrogen content is lower compared to samples deposited by PECVD using similar gas mixtures, with hydrogen being preferentially attached to carbon rather than silicon atoms. The photoluminescence (PL) spectra of these films show PL in the visible spectral region at room temperature. The films with larger bandgap (>2.5 eV) exhibit PL at room temperature, with the emission having peak energy in the range 2.0–2.3 eV.© Elsevie