SiH4 Flow Research Articles

Investigation of the Growth of Si-Ge-Sn Pseudomorphic Layers on 200 mm Ge Virtual Substrates: Impact of Growth Pressure, HCl and Si2H6 Flows

The implementation of new materials on Si substrates has been a subject of intensive research since decades. Recently, group IV germanium tin (GeSn) and silicon germanium tin (SiGeSn) have triggered huge scientific interest due to the unique features of these materials [1,2]. However, their epitaxial growth is a complex task due to the low solid solubility of Sn in Ge and the limited thermal stability of such alloys. The aim of this work was first to set up a relatively fast and non-destructive experimental protocol to characterize SiGeSn ternary layers by combining X-ray diffraction (XRD) with wavelength dispersive X-ray fluorescence (WDXRF). The surface morphology of the grown layers was otherwise assessed through atomic force microscopy (AFM). Afterwards, different growth conditions were tested in order to optimize growth conditions. Binary and ternary alloys were grown on 2.5 µm thick strain relaxed Ge buffers on 200 mm Si(001) substrates in a reduced pressure chemical vapor deposition reactor from Applied Materials. Close to 30 nm thick GeSn and GeSi pseudomorphic layers were characterized first through XRD. Figure 1 shows the omega-2theta scans around the symmetric (004) reflections. Through these scans, the layer thickness and composition could be calculated. Afterwards, WDXRF measurements were carried out on the same samples and the intensity of the specific element drawn as function of the layer thickness multiplied by this element composition in the layer, as shown in Figure 2. The fitting lines served afterwards to find the composition of each element in the SiGeSn alloys. Ternary alloys were then grown at 349°C and 100 Torr using Si2H6, SnCl4 and Ge2H6 precursors and H2 as a carrier gas. In that first set of samples, we investigated the influence of the Si2H6 flow. Thus, we varied the F(Si2H6 )/F(H2) mass-flow ratio from 0 up to 5.2×10-3. Figure 3 shows the omega-2theta scans around the (004) XRD order for the various SiGeSn/Ge/Si(001) heterostructures grown. Interestingly, the SiGeSn XRD peak did not significantly shift even though the Si2H6 flow varied considerably. Using Figure 2 XRF calibration curves and the layer thickness extracted from XRD scans, the concentration of Si and Sn in the layers could be calculated. Resulting values are shown as functions of the F(Si2H6)/F(H2) mass-flow ratio in Figure 4. As expected, the increase of the Si2H6 flow leads to an increase of the Si content in the layers (from 0% up to nearly 21%). However, this increase is accompanied by an increase of the Sn content in the layer, from ~ 5% up to ~ 11% (Figure 4). This likely explains the stability of the SiGeSn peak’s angular position in XRD profiles. The initial compressive strain in the layer (for Si2H6 = 0 sccm i.e. for the GeSn layer) is kept despite Si2H6 flux variations. Figure 5 shows the growth rate as a function of the F(Si2H6)/F(H2) mass-flow ratio. There is a clear drop of the growth rate when the Si2H6 flux increases (from ~ 32 down to ~ 20 nm min.-1). The surface morphology was otherwise assessed using AFM. Results are provided in Figure 6 and Figure 7. The AFM images highlight that the surface roughness increases when the Si2H6 flux increases. Above a certain F(Si2H6)/F(H2) value, a catastrophic degradation of the surface morphology occurred which could be related to Sn segregation (cf. Figure 6f). In order to better understand the growth of ternary SiGeSn pseudomorphic layers, we have explored a wide range of growth conditions. First, the growth temperature was varied from 313°C to 409°C in 12°C steps, all the other parameters being fixed (pressure (100 Torr), fluxes…). This study allowed us to determine the optimal growth temperatures. Afterwards, three growth temperatures were selected (349°C, 337°C and 325°C) and the Si2H6 flow varied, while keeping constant the SnCl4 and Ge2H6 flows. The layers grown under these conditions are currently under investigations and detailed results will be presented during the conference. [1] S. Wirths et al, Nat. Photonics 9 (2015) 88. [2] S. Wirths et al, Thin Solid Films 557 (2014) 183. Figure 1

(Invited) Structural Properties and Carrier Transport in Axial Silicon-Germanium Nanowire Heterojunctions

Recent advances in forming semiconductor heterojunctions within spatially confined nanoscale objects, including nanowires (NWs), show that the traditional limitations in the lattice-mismatched hetero-growth can be challenged. In various III-V semiconductor NWs, abrupt heterojunctions have been successfully demonstrated using the vapor-liquid-solid (VLS) growth for GaAs/InAs (7% mismatch) and InAs/InP (3% mismatch) heterojunctions. In group IV semiconductors, the approach is complicated not only by the 4.2% lattice mismatch between Si and Ge but also because Si and Ge both have a quite high solubility in the Au-Si catalyst. During chemical vapor deposition (CVD) based VLS growth using SiH4 and GeH4 (or similar gases), a supply of Si remains effectively “on” in the catalyst, and Si effectively intermixes with the arriving Ge even if the SiH4 flow is already switched “off”. One way to address this problem is to choose a catalyst with a lower Si solubility, e.g. AlAu2 and AgAu. Another possibility is to significantly reduce growth temperature before turning a GeH4 source “on”. Using the latter technique, we fabricated Si-Ge heterojunction NWs with nearly ideal interface and only an 8 nm thick SiGe transition layer between straight and nearly micron-long Si and Ge NW segments and analyzed their structural and electrical properties. The observed changes in the photoluminescence and Raman spectra as function of temperature, non-linear and rectifying current-voltage characteristics, strong flicker noise and damped current oscillations with frequencies of 20-30 MHz are explained using the proposed SiGe heterojunction NW energy band diagram including the energy states associated with the NW surface (and near-surface) structural imperfections revealed by transmission electron microscopy and a mismatch in Si and Ge coefficients of thermal expansion.

SiH4 enhanced dissociation via argon plasma assistance for hydrogenated microcrystalline silicon thin-film deposition and application in tandem solar cells

We investigate the influence of argon plasma assistance on the depletion of SiH4 in the preparation of μc-Si:H films via plasma-enhanced chemical vapor deposition (PECVD). From optical emission spectrometry (OES) data of the μc-Si:H deposition, we infer that the excited Ar+ and metastable Ar* states enhance the dissociation of SiH4 and H2 molecules to generate ultra-depletion of SiH4. The ultra-depletion of SiH4 increases the μc-Si:H thin-film deposition rate from 4.5 Å/s to 23.4 Å/s at 6-sccm flow of SiH4. This ultra-depletion condition facilitates the gradual substitution of H2 by Ar, which leads to reduced crystallinity at low argon fractions (far), preferential crystallographic orientation along the (111) direction, and fluctuation of the hydrogen content and microstructure factor (R). Thus, the properties of the μc-Si:H thin films can be controlled via control of the atomic hydrogen generation and physical sputtering effects. The highest photosensitivity (2.2 × 103) is observed at far = 56%. Furthermore, we fabricate an a-Si:H/μc-Si:H tandem solar cell with a total thickness of 1450 nm. The cell exhibits an initial efficiency of 11.44%, and the efficiency reduces to 10.24% after 1000 h of light soaking. The cell also exhibits a significantly higher Voc × FF stability over that of Jsc.

Effect of Pressure and Flow Rates on Polymorphous Silicon‐Germanium (pm‐SixGe1−x:H) Thin Films for Infrared Detection Applications

In this paper, the characterization and optimization of polymorphous silicon‐germanium (pm‐SixGe1−x:H) thin films prepared by plasma‐enhanced chemical vapor deposition (PECVD) are reported in order to use them as thermo‐sensing films on infrared detectors. Two series of pm‐SixGe1−x:H thin films are fabricated and characterized. In the first series, the pressure is varied in a wide range (600–2000 mTorr) using the same SiH4 and GeH4 flow rates, while in the second series the flow rate of GeH4 is varied in the range of R = 10–90%. Fourier transform infrared spectroscopy (FTIR) confirms the large incorporation of germanium (Ge) in the solid phase. The aim is to optimize the films in terms of the temperature coefficient of resistance TCR (% K−1), room temperature conductivity, and noise. A significant variation in the TCR values from 3.1 to 9.9% K−1 and in the room temperature conductivity by about six orders of magnitude is observed. Finally, noise spectral density characterization is performed to evaluate the application of the pm‐SixGe1−x:H films as thermo‐sensing elements in high performance infrared detectors (microbolometers).

Surface morphology evolution and optoelectronic properties of heteroepitaxial Si-doped β-Ga2O3 thin films grown by metal-organic chemical vapor deposition

Heteroepitaxial growth of conductive Si-doped β-Ga2O3 films on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD) was successfully performed. The effect of Si content on the structural, morphological, electrical and optical properties of Si-doped β-Ga2O3 films was investigated in detail. Distinctive surface morphology evolution of films depending on Si content was observed and presented. The Si-doped β-Ga2O3 films exhibited high transmittance in the ultraviolet-visible regions. The temperature-dependent PL was carried out especially to discuss the photoluminescence properties of Si-doped β-Ga2O3 films. More importantly, the results suggested that the conductivity of heteroepitaxial Si-doped β-Ga2O3 films by MOCVD could be realized and controlled by adjusting the Si content. The minimum resistivity of 1.79×10−1Ω·cm was obtained for the films grown under the SiH4 flow rate of 0.08 sccm.

Synthesis of Nanoparticles Using Low Temperature Plasmas and Its Application to Solar Cells and Tracers in Living Body

Plasma is a promising method for synthesis of nanoparticles which are drawn much attention for opt-electric and medical applications such as solar cells and drug delivery systems. The method can control agglomeration of nanoparticles by utilizing their charge and can produce high purity nanoparticles. Wide variety of plasmas have been developed for synthesizing nanoparticles, allowing us to produce them of many kinds of materials and with a high yield. So far, we have employed three types of plasmas: multi-hollow discharge reactive plasmas for Si nanoparticles, high pressure rf sputtering for Ge ones, and plasma in water for In ones. We have firstly succeeded in demonstrating multiple exciton generation in Si and Ge nanoparticles to realize the third generation solar cells. Using In nanoparticles, we have realized high sensitive tracers for understanding nanoparticle kinetics in living body. For the multi-hollow discharge reactive plasma [1, 2], discharges were sustained in 8 holes of 5 mm in diameter and 7 mm in length. Nanoparticles were nucleated and grow in the H2+SiH4 discharges and they were transported to the downstream region by gas flow. The discharge frequency and power were 60 MHz and 180 W. The crystallinity and size of Si nanoparticles were controlled by H2 dilution ratio and working pressure [3, 4]. We found crystalline Si nanoparticles can be formed at high H2 dilution ratio and larger size of them are produced for higher pressure. Crystalline Si nanoparticles of 4 nm in size were fabricated under SiH4 and H2 gas flow rate of 2 and 448 sccm, respectively, and pressure of 266 Pa. They were collected by stainless mesh grids located at the downstream region. Transparent conductive oxide/Si nanoparticles/Al structured Schottky cells were employed for characterization of quantum effects. Carrier generation evaluation showed quantum efficiency of the cells show 100 % or more for incident photon energy above two times larger than the bandgap energy of Si nanoparticles. Consequently, multiple exciton generation by synthesized Si nanoparticles was firstly demonstrated [4]. Ge nanoparticles have more outstanding quantum confinement effects than Si nanoparticles due to the larger excitonic Bohr radius of 24.3 nm for Ge nanoparticle than 4.9 nm for Si ones. Ge is also known to exhibit larger absorption coefficient of infrared light than Si. We have fabricated Ge nanoparticle composite films using a high pressure rf sputtering method [5]. X-ray diffraction (XRD) and Raman spectra of the films showed the films with high crystallinity of 0.8. Fourier transform infrared measurements revealed Ge-H and Ge-H2 stretching bonds in the films. These results suggest the crystalline Ge nanoparticles of 6 nm in size are covered by hydrogenated amorphous Ge. We fabricated Ge nanoparticles solar cells in the TiO2/Ge/polysulfide electrolyte system. We found that the incident photo-to-current conversion efficiency increases with decreasing the wavelength, and it reaches 10 % at 400 nm [6]. The result suggests that excitons generated in Ge nanoparticles were separated into electrons and holes, and such carriers successfully extracted to the outer circuit. For medical applications of nanoparticles, their toxic effects are frequently pointed out. We have employed indium-contained nanoparticles for studying kinetics of nanoparticles in the living body because no In compound exists in living body. For In nanoparticle synthesis, In rod and plate electrodes were immersed into pure water. Discharges were generated by applying pulsed voltage between the electrodes. The discharge voltage and frequency was 9.2 kV and 10 kHz, respectively. The size of primary and secondary nanoparticles was 7 nm and 315 nm, respectively. The yield was 42 mg/min. Energy dispersive X-ray spectroscopy and XRD measurements showed that indium crystalline and indium hydroxide crystalline particles were generated with the mass ratio of 8:2. Preliminary subcutaneous administration of nanoparticles to mice shows that indium is transported from subcutaneous to blood. Comparing with In-contained nanoparticles of 150 nm in primary particle size, nanoparticles for smaller primary particle size indicated more prompt transportation. These results show that synthesized indium-containing nanoparticles are useful for analyzing kinetics of nanoparticles in living body [7]. In summary, plasma expands the capability of the nanoparticle synthesis towards opt-electronics and life science.[1] T. Kakeya, et al., The Solid Films 506-507, (2006)288.[2] G. Uchida et al., Thin Solid Films 544 (2013) 93.[3] H. Seo, et al., Electrochemi. Acta. 87 (2013) 213.[4] H. Seo, et al., Sci. Adv. Mater. 8 (2016) 636.[5] D. Ichida, et al., J. Phys. Conf. Ser. 518 (2014) 012002.[6] M. Shiratani et al., Materials Science Forum 783-786 (2014) 2022.[7] T. Amano et al., J. Nanosci. Nanotechnol. 15 (2015) 9298.

(Invited) Hot Carrier Reliability of High Voltage HVMOSFETs in BCD (Bipolar-CMOS-DMOS) Technology

This paper discusses three important issues in hot carrier (HC) reliability of LDMOSFET ((Laterally Diffused MOSFETs) in BCD technology. One of the main reliability issues encountered during development of the LDMOSFET is optimizing the trade-offs between specific on-resistance (Rdson) and hot carrier (HC) degradation [2]. For instance, Rdson can be reduced by increasing the drift region doping concentration or shrinking the drift region length. Both of these changes result in higher lateral electric field in the drift region which lead to increased HC degradation. The second issue is how to reduce HC degradation in LDMOS due to Back-End-Of-Line (BEOL). It has been reported for CMOS devices that HC performance can be degraded by BEOL processes such as interlayer dielectric film deposition, etch, metal deposition and etch process [3, 4]. The BEOL processes in BCD technology may have a worse impact on LDMOS HC performance than on CMOS’s since it has such as higher energy implants and thicker metal deposition and etch. The third issue is the influence of self heating on the measurement of HC degradation in high gate voltages stress for HC SOA (safe-operating-area) in high voltage LDMOS [5, 6]. To address the first issue, we have compared the thin gate oxide (11.5nm) and thick gate oxide (60nm) LNDMOS hot carrier degradation results as shown in Fig.1 (b). The HC degradation has been significantly reduced in thick gate oxide LNDMOS. The main reason for the reduction may be due to drift region oxide thickness. Based on the results, we proposed a new LDMOS structure in a BCD technology that improves HC degradation without sacrificing the device breakdown voltage or Rdson [1]. The process to form the thick oxide in drift region-I in the LNDMOS is the same as to form thick gate oxide MOSFET, so only a layout change is required. The 11.5nm gate oxide thickness in the channel region remains the same for both LNDMOS structures. The maximum lateral electric field Emax in drift region-I would be reduced by over 94% if the oxide thickness increased to 60nm from 11.5nm based on our calculation. TCAD simulations clearly show that impact ionization rate for the 30V LNDMOS with the thick oxide in drift region-I has been significantly reduced, and also its peak location has been pushed away from the surface into the bulk of the silicon within drift region-I as shown in Fig.2(b). For the second issue, we demonstrated a modified SiN barrier layer which can improve device hot carrier performance in the LDMOSFET. We show experimentally that using a barrier layer of SiN or SiON which is engineered to have a relatively high refractive index (RI) and electrical conductivity can reduce the BEOL effect on hot carrier performance. Increasing the SiH4 flow rate during deposition increases the film’s RI and also its electrical conductivity [9]. The increased electrical conductivity of the SiN barrier layer allows charge from plasma processing to be dissipated into the silicon. At 4000C, a typical BEOL dielectric deposition temperature, the conductivity of the SiN barrier layer is much higher. Thus, the SiN barrier layer can reduce the PPID for the oxide in drift region resulting in reduced HC degradation. The HC Idlin degradation for the LNDMOS device with thick oxide in drift region and high RI SiN or SiON barrier layer has been significantly reduced to less than 1/3 the degradation observed in the standard LNDMOS as shown in Fig.2 (a). The reduced HC Idlin degradation is about 68% due to the thick oxide in drift region-I, and about 32% from the high RI SiN barrier layer. The HC Vth (threshold voltage) degradation exhibited very small degradation after the HC stress. Our data shows self heating, caused by HC stress in the thick gate oxide HV LNDMOS, significantly affected Idlin/Rdson electrical parameter and HC degradation characteristic. The change in delay time between the removal of the HC stress after each stress cycle and the parameter measurement resulted in a significant difference in HC Idlin/Rdson degradation [6]. For a longer delay time, lower Idlin degradation was observed, see Fig.3 (a). The difference or recovery of degradation was mainly due to the self heating effect from Idlin degradation vs junction temperature change (Fig3.(b)) and temperature monitor data. The Idlin degradation from self heating effect seems to be more than from HC effect in packaged HV LNDMOS. In the final paper, we will include some methods to eliminate the self heating effect, and to separate the self heating and local HC injection effect. Figure 1

Influence of SiH4 and pressure on PECVD preparation of silicon films with subwavelength structures

Silicon films with subwavelength structures were prepared on flexible polyimide by plasma deposition. Resulting films exhibited high photosensitivity and high stability. The varied parameters were pressure and silane (SiH4) flow, while power, frequency, temperature, and hydrogen (H2) flow were fixed. Pressure was set at 0.7 or 1.3 Torr, while the SiH4 flow rate was set at 10, 50, or 100 sccm. Similar characteristics were observed for the films when the same SiH4 flow rate was used, despite pressure variations. Deposition rate from 0.94 to 5.86 Å/s, optical gap from 1.6 to 2 eV, and embedded nanocrystals in the range of 2–6 nm were the main characteristics of our films. Subwavelength structures from 102 to 287 nm in diameter were observed. These structures scatter the photons and thus improve absorptance, photosensitivity, and mobility-lifetime product. The structural and optoelectronic properties of these films showed a high correlation with the silane concentration obtained from the partial pressure of SiH4 and H2.

Material and optical properties of low-temperature NH3-free PECVD SiNx layers for photonic applications

SiNx layers intended for photonic applications are typically fabricated using LPCVD and PECVD. These techniques rely on high-temperature processing (>400 °C) to obtain low propagation losses. An alternative version of PECVD SiNx layers deposited at temperatures below 400 °C with a recipe that does not use ammonia (NH3-free PECVD) was previously demonstrated to be a good option to fabricate strip waveguides with propagation losses <3 dB cm−1. We have conducted a systematic investigation of the influence of the deposition parameters on the material and optical properties of NH3-free PECVD SiNx layers fabricated at 350 °C using a design of experiments methodology. In particular, this paper discusses the effect of the SiH4 flow, RF power, chamber pressure and substrate on the structure, uniformity, roughness, deposition rate, refractive index, chemical composition, bond structure and H content of NH3-free PECVD SiNx layers. The results show that the properties and the propagation losses of the studied SiNx layers depend entirely on their compositional N/Si ratio, which is in fact the only parameter that can be directly tuned using the deposition parameters along with the film uniformity and deposition rate. These observations provide the means to optimise the propagation losses of the layers for photonic applications through the deposition parameters. In fact, we have been able to fabricate SiNx waveguides with H content <20%, good uniformity and propagation losses of 1.5 dB cm−1 at 1550 nm and <1 dB cm−1 at 1310 nm. As a result, this study can potentially help optimise the properties of the studied SiNx layers for different applications.

A Benchmark of Germane and Digermane for the Low Temperature Growth of Intrinsic and Heavily in-situ Boron-Doped SiGe

We have recently demonstrated the interest of using Si2H6 + GeH4 for the 450°C-500°C epitaxy of (i) intrinsic SiGe layers and (ii) SiGe:B raised sources and drains [1-4]. One way of further increasing performances (in terms of growth rates at really low temperatures and Ge contents reachable) could be to use a higher order Ge precursor, such as digermane (Ge2H6). We have thus benchmarked GeH4 and Ge2H6 for the Reduced Pressure–Chemical Vapor Deposition (RPCVD) of SiGe and SiGe:B in an Applied Materials 200 mm Epi Centura 5200 tool. We have first of all compared the impact of the GeH4 and Ge2H6 mass-flows on the SiGe growth kinetics (at 500°C, 20 Torr and with a fixed Si2H6 flow). Whatever the source of Ge atoms, we had a linear increase of the SiGe growth rate with the Ge flow (cf. Figure 1, top). This was due to the catalysis of H desorption by Ge surface atoms, freeing sites for incorporation. Because of its higher reactivity, the SiGe growth rate was 8 to 10 times higher with Ge2H6 than with GeH4, however. We were also faced with a sub-linear increase of the Ge content x with F(Ge)/F(Si) (bottom of Figure 1). Using Ge2H6 instead of GeH4 otherwise yielded much higher Ge contents for a given disilane flow: in the 35-48% range instead of 20-33% only. The evolution of x with the F(Ge) flow was well accounted for by x2/(1-x)=nF(Ge)/F(Si) relationships (F(Ge) = F(GeH4) or 2F(Ge2H6)), with n = 0.47 for germane and n = 1.74 for digermane. We have then studied the evolution of the SiGe growth rate with temperature (Figure 2), for both types of Ge precursors. The use of GeH4 led to an exponential increase of the 20 Torr SiGe growth rate with temperature (with a 42 kcal.mol.-1 activation energy), together with a slight linear decrease of the Ge concentration. The situation was very different with Ge2H6. As the growth temperature increases, we were faced with a slow exponential increase of the SiGe growth rate (Ea = 15 kcal.mol.-1), together with a huge linear decrease of the Ge content. We have also quantified the impact HCl, an etchant gas, had on the growth kinetics of intrinsic SiGe with fixed amounts of disilane and digermane. Adding HCl led at 500°C, 20 Torr to a significant decrease of the growth rate (from 7.8 down to 4.2 nm min.-1), together with a significant Ge concentration increase (from 35% up to 55%). We have otherwise studied the impact of the B2H6 flow on the SiGe:B growth kinetics at 500°C, 20 Torr. The SiGe:B growth rate and the real or “apparent” Ge contents associated with such SiGe:B layers are plotted in Figure 3 as a function of the B2H6 mass-flow. Adding small amounts of diborane to Si2H6 + Ge2H6 + HCl led to a dramatic increase of the SiGe:B growth rate, from 5.8 up to 13.2 nm.min.-1. H desorption was indeed catalysed by the presence of B surface atoms. The “apparent” Ge concentration is coming from X-Ray Diffraction when supposing that an in-situ boron-doped SiGe layer behaves as an intrinsic one. This is however not true for high doping levels. Boron atoms, which are much smaller than Si or Ge atoms, then compensate the compressive strain in SiGe layers, yielding Ge concentrations artificially lower than the real ones. The concentration difference thus reflects the compressive strain compensation by substitutional B atoms. There is in Fig. 3 a definite decrease of the real and “apparent” Ge concentration with the B2H6 flow, from 47% down to 15% and 20%, respectively. We have also performed SIMS depth profiling of the B atoms in those SiGe:B layers. Their concentration increased linearly with the B2H6 mass-flow, reaching at most 3.6x1020 cm-3 in single crystalline layers (Figure 4, left) The associated resistivity (Figure 4, right) was as low as 0.43 mΩ.cm. For higher B2H6 flows, we had a resistivity increase, which was likely due to the crystalline quality degradation then the transformation into poly-SiGe:B evidenced in X-Ray Diffraction. Small islands were otherwise present in limited numbers on the surface of those SiGe:B layers, with no clear dependence on the B2H6 flow. [1]J.M. Hartmann et al. ECS J. Sol. State Sci. and Technol. 3 (11) P382 (2014). [2] J.M. Hartmann et al. Thin Sol. Films 557, 19 (2014). [3] J. Aubin et al. Thin Sol. Films 602, 36 (2016). [4] J. Aubin et al. Semicond. Sci. Technol. 30, 115006 (2015). Figure 1

Effect of precursors on propagation loss for plasma-enhanced chemical vapor deposition of SiN_x:H waveguides

This work investigates the role of precursor gas chemistry, SiH4/NH3/N2, on hydrogen incorporation into PECVD H:SiNx for optical applications. The largest reduction in of N-H bond density is shown to respond from SiH4 flow, indicating that all precursor gases must be optimized for low loss waveguides. A linear correlation of N-H bond density with propagation losses in SiNx waveguides is observed, allowing for a propagation loss to be estimated by N-H bond density without waveguide fabrication. With proper optimization of process parameters, we are able to obtain propagation losses as low as −1.6 dB/cm at 1550 nm without a thermal anneal.

Selective Boron Elimination from B2H6–SiH4 Gas Mixtures for Purifying Si

A boron elimination method based on the difference in the pyrolysis temperatures of SiH4 and B2H6 is proposed for purifying metallurgical grade Si feedstock for photovoltaic applications through direct hydrogenation using high-pressure hydrogen plasma. A simple kinetic model is constructed to estimate the proposed boron elimination filter performance. The filter performance is experimentally evaluated. It is confirmed that there is a significant temperature difference between the B2H6 and SiH4 transmission behavior through the filter. However, when SiH4 and B2H6 gases are simultaneously supplied to the filter at the same flow rate of a few standard cubic centimeters per minute, the SiH4 transmission curve is affected by B2H6 and almost overlaps with the B2H6 curve. In contrast, by decreasing the B2H6 flow rate to one thousandth the SiH4 flow rate, B2H6 co-supply has little influence on the SiH4 transmission curve. The type of carrier gas (H2 and He) also affects the transmission curve. With increasing filter temperature, the B elimination effect of the filter becomes greater. The B concentration in Si films prepared by a single elimination process can be reduced to about 1/3000 of the value estimated from the concentration ratio in the unfiltered gas mixture.

CMOS Compatible Growth of High Quality Ge, SiGe and SiGeSn for Photonic Device Applications

Germanium films were deposited on silicon substrate by an ultra-high vacuum chemical vapor deposition system using GeH4 as Ge precursor and different carrier gases (Ar, N2 and H2). Silicon-germanium and SiGeSn films were deposited using optimized growth conditions of Ge growth. Silane and SnD4 were used as precursors for Si and Sn, respectively. A complete study of SiGe growth at chamber pressure from 0.1 to 1.0 torr and at temperatures from 350-450ºC for different SiH4 flow rate is performed. Silicon incorporation in Ge films varied from 1% to 17%. Tin incorporation of 2% was observed in the films with 17% Si incorporation. Investigation of film quality has been done using etch pit measurement, scanning electron microscopy and transmission electron microscopy. Threading dislocation density for Ge, SiGe and SiGeSn films were 1.7×107 cm-2, 2.3 ×107 cm-2 and 4.0 ×107 cm-2 , respectively.

On the Origin of the Gate Oxide Failure Evaluated by Raman Spectroscopy

1. Background and purpose In the miniaturization of the large-scale integrated-circuit (LSI), gate oxide thinning is one of the most important techniques for the performance improvement. However, the ultimately thinned gate oxide causes in the failure with high leakage current. Thus, the evaluation and control of the gate oxide integrity is indispensable in the present LSI technology. In this study, we evaluated the origin of the gate oxide failure by Raman spectroscopy in conjunction with optical beam induced resistance change (OBIRCH) analysis. 2. Experiments Metal-oxide-semiconductor (MOS) capacitors were used as the samples. The 2.8 nm thick gate oxinitrid insulator film and the poly-Si gate electrode layer were formed on a P type Si substrate. The poly-Si layer was deposited at 620 oC with the SiH4 flow rate of 150 or 350 sccm. The gate oxide integrity was evaluated by the test element group (TEG) measurements. The failure was observed only for the 150 sccm SiH4 flow. The current-voltage (I-V) characteristics were shown in Fig. 1. The positions with high leakage current were specified by OBIRCH, and evaluated by Raman spectroscopy. One-dimensional measurements were performed for the Raman spectroscopy by using a quasi-line excitation source at the same time. Excitation laser was Nd:YAG laser (wavelength: 532 nm), and the focal length of the spectrometer was 2,000 mm. The length of the quasi-line laser was approximately 100 μm. We investigated the origin of the gate oxide failure by Raman Spectroscopy obtained at the leakage position determined by OBIRCH. 3. Result s and Discussion Figure 2 shows the light emission image obtained by OBIRCH at the MOS capacitor with gate oxide failure fabricated with 150 sccm SiH4 flow. We confirmed that there are two defect points in the MOS capacitor. Figure 3 shows the Raman intensity distribution across the leakage position in the sample. The higher Raman intensity than the surroundings was confirmed at the failure position. Figure 4 shows the distribution of the Raman shift and the full width at half maximum (FWHM) across the failure position. As shown in Fig. 4, we verified that the Raman peaks at the defect positions shifted toward the lower wave number compared with the other positions. It can be considered that the gate oxide failure was induced by the high tensile strain in the poly-Si layer, probably due to the lack of the SiH4 supply during the deposition. Furthermore, FWHM of Raman spectra were not different comparing with the other position. Thus, there is no difference in the crystallinity and the grain size of the poly-Si. In conclusion, we have evaluated the gate oxide failure with leakage current by Raman spectroscopy and found that the origin was high tensile strain in the gate poly-Si.

Effect of Hydrogen on Silicon Nitrides Formation by Microwave Excited Plasma Enhanced Chemical Vapor Deposition

1. Introduction High quality silicon nitride films (SiNx) formed at low temperature is strongly required because new materials such as Ge, high-k gate dielectrics, gate electrodes metals, etc. are introduced in advanced integrated circuit[1, 2]. The gas composition is very important for reducing process temperature of PECVD. We have reported the SiH4 flow rate is most important parameter for controlling the deposition rate and the film quality in the PECVD using N2, H2, SiH4 gasses. The deposition rate strongly depends on the SiH4 flow rate; however the film quality was degraded with the increase of the flow rate [3]. The other parameters are considered to be also important in the PECVD. In this presentation, we describe effect of hydrogen on SiNx formation by the PECVD. 2. Experimental After native oxide was removed of silicon surface by HF solution, silicon nitride was deposited. The temperature set at 400 ̊C. Ar gas was used as the plasma excitation, and SiH4/N2/H2 mixture gases were used for the source gases. The microwave power, the deposition pressure were 2000 W and 1.7 Pa, respectively. The flow rates of SiH4, N2, and Ar were 0.5, 75, and 20 sccm, respectively. The gas flow rate of H2was varied from 0 to 45 sccm. The film density were measured by the X-ray reflectometry (XRR), and the N-H bonds in SiNx films were measured by Fourier transform infrared spectroscopy (FTIR), respectively. 3. Results and discussions Fig. 1 shows the deposition rate and refractive index of SiNx films as a function of H2 flow rate. The deposition rates for all H2 flow rates are almost the same and the refractive index increases with H2 flow rate in H2 flow rate less than 15 sccm, and the index decreases with H2 flow rate in the flow rate larger than 15 sccm. We have reported that the deposition rate strongly depends on the SiH4 flow rate and the deposition rate is proportional to the SiH4 flow rate and the film quality degrades as the increase of SiH4 flow rate in this PECVD [3]. This suggests that the film quality are controlled by the H2flow rate without the deposition rate. Fig. 2 shows the film density of SiNx films measured by XRR for various H2 flow rates. The density is independent of the H2 flow rates. Fig. 3 shows the N-H bond concentration measured by FTIR for various H2 flow rates. The N-H bond concentration of 0 sccm case is much less than the others, and the concentration of other cases are almost the same. The Si/N ratio of SiNx measured by XPS of 0sccm case is 1-2 % less than the others. It is considered that the hydrogen effectively dissociate the SiH4 gas and makes the nitridation species (NHx), as the result, the hydrogen improves the reaction efficiency of SiH4and NHx. 4. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 22000010 and the synchrotron radiation experiments were performed at the BL46XU of SPring-8 with the approval of JASRI (Proposal No. 2012B1725). 5.

Characterization of Ge Epitaxial Growth on Si1-XGeX Buffer Layer

Ge has higher electron and hole mobility than Si. Therefore, it has been considered as a new channel material in metal oxide semiconductor devices to replace Si. However, Ge substrates are of high cost as well as are difficult to work with. Epitaxial growth of Ge on Si is therefore preferred for fabricating Ge films. Heteroepitaxy of Ge films on bulk silicon is challenging because the lattice constant of Ge is 4.18% greater than that of Si. We investigate epitaxial growth of Ge on SiGe buffer layers. Ge epilayers and SiGe buffer layers were grown on a Si (001) substrate using ultrahigh vacuum chemical vapor deposition with Si2H6 and GeH4 as precursors at the growth temperature of 600 °C. For the SiGe buffer layer, the Si2H6 flow rate was fixed at 20 standard cubic centimeters per minute (sccm) and the GeH4 flow rate was varied from 30 to 70 sccm. The Ge epilayer was grown at the GeH4 flow rate of 200 sccm. Scanning electron microscopy (SEM) images show that the roughness of the SiGe layer increases with the GeH4 flow rate. The SiGe layer forms islands at the GeH4 flow rate of 70 sccm. The Ge epilayer was continuous when grown on the SiGe buffer layer at the GeH4 flow rate of 30 sccm. For the growth over the SiGe buffer layer at the GeH4 flow rate of over 50 sccm, the Ge epilayer formed islands.

Self-compensation effect in Si-doped Al0.55Ga0.45N layers for deep ultraviolet applications

The self-compensation effect in Si-doped Al0.55Ga0.45N layers was investigated using different SiH4/III ratios. The degree of compressive strain changed with SiH4 flow rate during growth. With a low SiH4/III ratio of 2.46 × 10−6, compressive strain was increased in comparison with the un-doped case. However, above this SiH4/III ratio, compressive strain decreased from εxx = −5.07 × 10−3 to 4.28 × 10−3 when the ratio was increased to 4.1 × 10−5. For higher SiH4/III ratios, the compressive strain again increased, which is attributed to the self-compensation effect of Si atoms. A similar tendency was observed in Photo-luminescence (PL) results. While the UV-to-violet ratio (IUV/IVL) of room-temperature PL remained to be almost constant for SiH4/III ratios below 8.2 × 10−5, IUV/IVL decreased rapidly above this value, as a result of self-compensation of Si atoms. These results were in good agreement with the Hall effect measurements.

Effects of SiH4 flow rate on microstructure and mechanical properties of TiSiN nanocomposite coatings by cathodic arc ion plating

TiSiN nanocomposite coatings were deposited on Si and cemented carbide substrates by cathodic arc ion plating in SiH4 ambient. The effects of SiH4 flow rate on microstructure, mechanical and tribological properties of the coatings were investigated systemically. Transmission electron microscopy and X-ray diffraction were employed to probe the crystalline microstructure and X-ray photoelectron spectroscopy was used to investigate the chemical bonding states. Microhardness testers and tribometer were used to evaluate the mechanical and tribological properties of TiSiN nanocomposite coatings. The results showed that the structure of TiSiN coating changed from columnar grain to nanocrystalline with increasing SiH4 flow rate. The hardness increased up to 4100 HV0.025 at the SiH4 flow rate of 42 sccm (9.5 at.% Si in the coating), but it decreases with further addition of SiH4 gases. Friction coefficients of TiSiN composite coatings in the range of 0.6–0.7 were obtained when tested against Si3N4 balls.

On the Origin of the Gate Oxide Failure Evaluated by Raman Spectroscopy

The metal-oxide-semiconductor-field-effect-transistor (MOSFET) has been miniaturized for the high performance large-scale integrated-circuit (LSI). However, in the ultimately miniaturized MOSFET, the gate oxide failure with high leakage current is inevitable. In this study, we evaluated the origin of the gate oxide failure by Raman spectroscopy in conjunction with optical beam induced resistance change (OBIRCH) analysis. MOS capacitors were used as the samples. The 2.8 nm thick gate oxinitrid insulator film and the poly-Si gate electrode layer were formed on a P type Si substrate. The cobalt (Co) silicide film was formed on the poly-Si electrode. The SiH4 flow rate was 150 sccm or 350 sccm. The gate oxide integrity was evaluated by the test element group (TEG) measurements. As a result, Raman intensity increased at the failure position compared with the other positions in the sample deposited with 150 sccm of SiH4 flow rate. We consider that higher Raman intensity at the gate oxide failure positions reflects the irregular structure of poly-Si. Furthermore, the Raman peaks at failure positions shifted toward the lower wavenumber while the FWHMs are approximately constant with other positions. Thus, we found that there is no difference in the crystallinity of the poly-Si. The origin of the gate oxide failure was high tensile strain in the gate poly-Si electrode. In conclusion, we have successfully evaluated the gate oxide failure by Raman spectroscopy with a quasi-line excitation source.

Effect of Hydrogen on Silicon Nitrides Formation by Microwave Excited Plasma Enhanced Chemical Vapor Deposition

The gas composition is one of the most important parameters for reducing process temperature of the plasma enhanced chemical vapor deposition. We investigate the effect of the gas flow rate of SiH4, H2, and N2 on the quality and the deposition rate of the silicon nitride films (SiNx) formed by the microwave excited PECVD. The SiH4 flow rate is most important parameter for controlling the deposition rate and the film quality in the PECVD using N2, H2, SiH4 gasses. The deposition rate strongly depends on the SiH4 flow rate; however the film quality was degraded with the increase of the flow rate. The hydrogen has an optimum flow rate for the high deposition rate and high quality film formation. The hydrogen effectively dissociates the SiH4 gas and makes the nitridation species (NHx), as the result, the optimal hydrogen improves the reaction efficiency of SiH4 and NHx.