Growth Of Silicon Films Research Articles

Growth of high-crystallinity silicon films by a combination of intermittent pulse heating and plasma-enhanced chemical vapor deposition

We have developed a process to grow high-crystallinity silicon films on insulators by intermittent pulse heating (IPH)-assisted plasma-enhanced chemical vapor deposition to address a drawback of incubation layer formation at the early stage of growth. By applying electrical pulses (22 V, 5 Hz, 10% duty ratio) to a Mo strip underneath a SiO2 layer, the surface is instantaneously heated to 1050 K while maintaining a steady substrate temperature of 670 K. The growth mechanism similar to that of solid-phase epitaxy enhanced its growth rate up to 1.2 nm s−1, which is five times greater than that of a-Si grown outside the Mo strip. The grown films assisted with IPH also showed a 97% crystalline volume fraction with no incubation layer.

Electronic modification of wet-prepared Si surfaces by a dichlorosilane reaction at elevated temperature

Silicon growth using chemical vapor deposition (CVD) is omnipresent in electronic device technology. CVD reactions of different precursor molecules on Si have been the focus of research for decades. Renewed interest in the CVD growth of silicon films has been spurred by the need for high-quality, ultrathin films for fabrication of novel electronic devices. In this work, we have formulated an experimental nanoscale approach to analyze the modification of wet-prepared Si(001) surfaces by dichlorosilane (SiH2Cl2, DCS) reactions at low pressure and 500–650 °C performed in a thermal CVD reactor connected to a scanning tunneling microscopy and spectroscopy (STM/STS) system. The DCS dissociation reaction resulted in a decrease of the Si surface potential due to the creation of chlorine-induced electric dipoles. Employing the ability of the scanning tunneling spectroscopy (STS) to recognize specific adsorption sites, we have carried out a comparative analysis of the relative coverage by Cl and Si as a function of exposure conditions. The existence of an intermediate reaction state of the DCS molecule was confirmed by the STS spectra and further supported by Si XPS data and ab initio calculations. This experimental nanoscale approach shows great promise for the CVD growth of ultrathin films.

Effect of Bipolar Charging of SiH4 on the Growth Rate and Crystallinity of Silicon Films Grown in the Atmospheric Pressure Chemical Vapor Deposition Process

Increasing the growth rate of thin films and enhancing the film quality have been an issue in the semiconductor manufacturing process. To improve those properties, conventionally the deposition temperature in reactor was increased or a catalyst was added to decompose precursors at low temperature. Here, a new technology utilizing a bipolar carbon fiber ionizer (CFI) was used to achieve a high growth rate and quality of silicon films. The deposition behavior of atmospheric pressure chemical vapor deposition silicon films deposited with and without the bipolar CFI system was compared. The growth rate of silicon films deposited at 450 °C, 500 °C, 700 °C, 900 °C and 1100 °C with the bipolar CFI system was 3.4, 5.6, 3.2, 3.3 and 1.3 times higher than deposited silicon film without the bipolar CFI system. The bipolar CFI system could also improve the crystallinity of the silicon film deposited at 900 °C.

Synthesis of Boron-Doped Silicon Film Using Hot Wire Chemical Vapor Deposition Technique

Boron-doped polycrystalline silicon film was synthesized using hot wire chemical vapor deposition technique for possible application in photonics devices. To investigate the effect of substrate, we considered Si/SiO2, glass/ITO/TiO2, Al2O3, and nickel tungsten alloy strip for the growth of polycrystalline silicon films. Scanning electron microscopy, optical reflectance, optical transmittance, X-ray diffraction, and I-V measurements were used to characterize the silicon films. The resistivity of the film was 1.3 × 10−2 Ω-cm for the polycrystalline silicon film, which was suitable for using as a window layer in a solar cell. These films have potential uses in making photodiode and photosensing devices.

Diffusion of hydrogen atoms in silicon layers deposited from molecular beams on dielectric substrates

In the paper, the processes occurring during low-temperature growth of non-hydrogenated amorphous Si and polycrystalline Si films on multilayer Si3N4/SiO2/c-Si substrates from molecular beams under conditions of ultrahigh vacuum are studied in detail. Diffusion of hydrogen atoms from a dielectric layer into the growing film is shown to accompany the growth of a silicon film on a Si3N4 layer deposited by CVD or on a SiO2 layer obtained by thermal oxidation of a silicon wafer. The process of hydrogen migration from the dielectric substrates into the silicon film is studied using FTIR spectroscopy. The reduction of IR absorption at the bands related to the NH bonds vibrations and the increase of IR absorption at the bands relating to the SiN bonds vibrations in IR spectra demonstrate that hydrogen atoms leave Si3N4 layer during Si deposition from a molecular beam. The absorption band assigned to the valence vibrations of the SiH bond at ∼2100 cm–1 emerging in IR spectra obtained at samples deposited both on Si3N4 and SiO2 layers indicates the accumulation of hydrogen atoms in silicon films. The difference in chemical potentials of hydrogen atoms in the dielectric layer and the silicon film explains the transfer of hydrogen atoms from the Si3N4 or SiO2 layer into the growing silicon film.

Transition mechanism of the thin Si-films obtained by the CW laser lateral crystallization from the grain-boundary free highly {100} oriented crystal to the twinned {211} crystal depending on the laser power

Surface texture transition from grain-boundary free {100} crystals to twinned {211} was observed with increasing laser power in the crystal growth of low-temperature silicon films by the cw laser lateral crystallization of a-Si. This transition is explained by two step mechanism. Firstly a crystal having ∼{110} texture grows in the scan direction (SD) rotated from {100} texture keeping the {100} surface normal texture with increasing laser power, and secondly the deformation twinning occurs in the solidified crystal having an in-plane rotation angle of 35°–45° by the compressive stress due to the Si volume expansion with further increasing power, but the twinning does not occur even with the same compressive stress in the crystal having an in-plane rotation angle of 0°–33.5°, where the rotation angle is defined as the angle between 〈100〉 axis of the grown crystal and the SD. The reason is explained by the Schmidt factor calculated as a function of the in-grain rotation with the laser power, assuming the compressive stress is applied parallel to the isotherms. The maximum value in the Schmidt factors for possible partial dislocation glides was 0.471 for the crystal having {110} texture in the SD and 0.236 for the crystal having {100} texture in the SD. Resolved stress to move the twinning partial dislocation in the crystal having {110} texture in the SD is higher than that in the crystal having {100} texture in the SD by a factor of 2.

Evolution of medium-range order and surface compositions by mechanism-driven model with realistic network

To elucidate the evolution of structural topology with the medium-range order of growing silicon films fabricated by plasma enhanced chemical vapor deposition with highly diluted hydrogen, we established a the model for a realistic network of growth films based on continuous random networks. We combined the kinetic Monte Carlo method with the interactions of various atomic-scale mechanisms from first-principles density-functional-theory computations and molecular-dynamics computations. To quantitatively characterize the short- and medium-range order, in addition to the higher order of the structural network, we applied a fluctuation transmission electron microscopy simulation and the pair correlation function to measure information about local order regions in film network. Interestingly, we found that the inflexion temperature of surface SiH3 coverage directly affected the silicon hydride crystallization process by forming much chemisorption from physisorption of surface hydride species. More interestingly, based on the atomic-scale chemical mechanism of the growth process of film, our results first realistically rendered the continuous disorder-order phase transition from structural topology, which is differed from previous knowledge that the amorphous to polycrystalline transition is a discontinuous short-range-order to long-range-order phase transition. Especially, we predicted the temperature dependence of evolution of structural network of the film and elucidated that the growing silicon film formed a nanocrystalline structural network at very low temperatures, relative to those of thermal annealing. This result was ascribed to interactions and competitions between various mechanisms and critically due to the dissociation mechanism and H-induced crystalline mechanism of silicon hydride, which isn’t depend on only one of the model mechanisms of surface diffusion model, etching model and annealing model. These results provide significant new physical insight into an experimentally relevant process for optimizing a strategy of deposition condition.

Directed Atom-by-Atom Assembly of Dopants in Silicon.

The ability to controllably position single atoms inside materials is key for the ultimate fabrication of devices with functionalities governed by atomic-scale properties. Single bismuth dopant atoms in silicon provide an ideal case study in view of proposals for single-dopant quantum bits. However, bismuth is the least soluble pnictogen in silicon, meaning that the dopant atoms tend to migrate out of position during sample growth. Here, we demonstrate epitaxial growth of thin silicon films doped with bismuth. We use atomic-resolution aberration-corrected imaging to view the as-grown dopant distribution and then to controllably position single dopants inside the film. Atomic-scale quantum-mechanical calculations corroborate the experimental findings. These results indicate that the scanning transmission electron microscope is of particular interest for assembling functional materials atom-by-atom because it offers both real-time monitoring and atom manipulation. We envision electron-beam manipulation of atoms inside materials as an achievable route to controllable assembly of structures of individual dopants.

Free-standing epitaxial silicon thin films for solar cells grown on double porous layers of silicon and electrochemically oxidized porous silicon dioxide

A process for fabricating free-standing epitaxial silicon thin films for low-cost, high efficiency silicon solar cells is proposed. The films are first grown (via chemical vapor deposition) on double porous layers consisting of a silicon layer (low porosity) and an electrochemically oxidized silicon dioxide layer (high porosity) and then detached by etching the silicon dioxide layer. This double porous layer structure was fabricated by the electrochemical fabrication of a double-layer porous silicon in HF solution followed by additional electrochemical oxidation in HCl solution. Because this additional oxidation mainly occurred on the high-porosity silicon dioxide bottom layer that was used as a sacrificial layer in the detachment of the grown epitaxial thin film. Annealing the structures in hydrogen prior to the epitaxial growth removed the surface oxide on the top low-porosity silicon layer. The double porous layers of silicon and silicon oxide could be appropriate seed layers for epitaxial silicon growth. EDS and SEM analysis of the grown silicon film on the double porous layer structure revealed that the high-porosity bottom layer remains oxidized, and that the grown silicon film can be detached by etching the electrochemically oxidized porous silicon oxide in HF solution. Characterization of the grown films shown epitaxial and monocrystalline structure with a carrier lifetime of 3μs.

Electron-enhanced atomic layer deposition of silicon thin films at room temperature

Silicon thin films were deposited at room temperature with electron-enhanced atomic layer deposition (EE-ALD) using sequential exposures of disilane (Si2H6) and electrons. EE-ALD promotes silicon film growth through hydrogen electron stimulated desorption (ESD) that creates reactive dangling bonds and facilitates Si2H6 adsorption at low temperatures. Without hydrogen ESD, silicon growth relies on thermal pathways for H2 desorption and dangling bond formation at much higher temperatures. An electron flood gun was utilized to deposit Si films over areas of ∼1 cm2 on oxide-capped Si(111) substrates. The silicon film thickness was monitored in situ with a multiwavelength ellipsometer. A threshold electron energy of ∼25 eV was observed for the Si film growth. A maximum growth rate of ∼0.3 Å/cycle was measured at electron energies of 100–150 eV. This growth rate is close to the anticipated growth rate assuming dissociative Si2H6 adsorption on dangling bonds on representative single-crystal silicon surfaces. The Si growth rate also displayed self-limiting behavior as expected for an ALD process. The silicon growth rate was self-limiting at larger Si2H6 pressures for a fixed exposure time and at longer electron exposure times. The silicon growth rate versus electron exposure time yielded a hydrogen ESD cross section of σ = 5.8 × 10−17 cm2. Ex situ spectroscopic ellipsometry showed good conformality in thickness across the ∼1 cm2 area of the Si film. Si EE-ALD should be useful for a variety of applications.

Deposition of micro crystalline silicon films using microwave plasma enhanced chemical vapor deposition

A microwave plasma enhanced chemical vapor deposition (microwave PECVD) process has been investigated to deposit micro crystalline silicon films with a high growth rate from silane (SiH4). A three-layer Bruggeman-Effective-Medium-Approximation (BEMA) model was developed to describe the complex structure of the grown films. The model was confirmed by Raman and spectroscopic ellipsometry measurements. In addition the surface evolution was characterized by AFM (Atomic Force Microscopy) and spectroscopic ellipsometry data. Particular emphasis is given to the correlation between the structural film properties and the deposition parameters. Besides chemical reactions, it is shown that ion bombardment plays an important role for the crystallinity of the grown silicon films. In the presence of ions, hydrogen radicals are able to etch silicon, which significantly improves the crystallinity of the deposited films. If just radicals are present, the deposited films become amorphous.

Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface

Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface

Evolution of surface morphology during the growth of amorphous and polycrystalline silicon films

The evolution of the surface morphology of LPCVD poly-Si films (deposition temperature 620°C), a-Si films (deposition temperature 550°C) and poly-Si films, obtained by the crystallization of a-Si is investigated in the thickness range 40–500 nm. It is found that upon an increase in the thickness from 40 to 500 nm, the surface roughness (parameters S q , S z , S v ) is increased for poly-Si, while in the case of a-Si and poly-Si obtained by crystallization a-Si, on the contrary, decreases. The correlation length (S al ) increases for all three types of silicon films. Poly-Si films, obtained by the crystallization of a-Si, as compared to LPCVD poly-Si films have a significantly lower surface roughness, respectively, S q two times less at a thickness of 40 nm and sixteen times less at 500 nm. In contrast to thick films, thin a-Si films (at thicknesses of less than 40 nm) have a granular structure, which is especially pronounced at an average thickness of about 20 nm and there is a maximum on the dependence of the roughness S q on the thickness.

CVD silicon film growth on powder substrates using an inline optical system

This paper presents the results achieved with an inline optical chemical vapor deposition (CVD) system operating at atmospheric pressure and at low temperatures (<600° C). Using silane as the gaseous precursor, microcrystalline silicon layers were grown on compressed silicon micrometric powder substrates, moving at constant speed, and crossing three hot deposition regions several times. Microcrystalline silicon (µc-Si) ribbon samples measuring up to 25×70 mm were obtained with growth rates (GR) varying from 13 to 53 µm/min. Grain size of silicon powder has a great influence in GR. It was observed that using lower grain size powders as substrates, higher GR were obtained. Also, it was observed that for the larger grain size powders used, after deposition the silicon films grown were stuck to the quartz substrate holder and could not be removed pristine.

Crystalline silicon growth on aluminum substrate for photovoltaic application

In this work, we investigate the direct formation of crystalline silicon thin films using ECR-PECVD process on aluminum substrates for solar cells applications. The aluminum substrate offers the advantages of being flexible and highly reflective in addition to serve as the back contact for the cell device. The substrates were pure aluminum or silicon rich aluminum sheets. Monocrystalline silicon substrates were used as reference substrates. Silane and hydrogen were used as precursor gases. Silicon growth was done at different substrate temperatures. The grown silicon films were characterized by Raman spectroscopy, SIMS and XRD techniques. Silicon thicknesses between 230 and 1370 nm were obtained on different types of aluminum substrates. The analyses show that the grown silicon films formed at 480 °C under SiH4: 40 sccm and H2 = 10 sccm are amorphous silicon at the initial stage and become nanocrystalline (nc-Si:H) as the deposition proceeds. The crystalline fraction of those films extracted from Raman spectra is found around 40–60% and XRD analysis shows grain silicon size between 41 and 83 A. Finally, SIMS analysis have revealed graded doping distribution profiles which is indicative of the formation of a nc-Si:H(i)/nc-Si:H (p+)/Al substrate, well suited for solar cell structures.

Influence of excitation frequency and electrode separation on the growth of microcrystalline silicon films and their application in single junction microcrystalline solar cell

In this paper we present the role of plasma excitation frequency and electsrode separation on the growth of microcrystalline silicon thin films at two different hydrogen dilutions of silane and different power densities. We optimized the process conditions to develop device quality microcrystalline material. Optoelectronic and structural properties of the developed material have been correlated with the solar cell properties. Growth rate ~7 A/s has been achieved using plasma excitation frequency of 27.12 MHz at 15 mm electrode separation. We have noticed the positive effects after reducing the electrode separation in higher frequency (27.12 MHz). Optimized microcrystalline film of activation energy 0.55 eV and grain size of 14.61 nm has been developed and is applied to fabricate single junction microcrystalline solar cell. Solar cell with initial cell efficiency of 7.75% with short circuit current density of 24.98 mA/cm2 and open circuit voltage of 0.47 V and fill factor of 0.66 has been achieved.

Controlled Fluxes of Silicon Nanoparticles to a Substrate in Pulsed Radio-Frequency Argon–Silane Plasmas

It has been hypothesized that high-energy impact of very small silicon nanoparticles on a substrate may lead to epitaxial growth of silicon films at low substrate temperature. A possible means for producing such energetic nanoparticle fluxes involves pulsing an RF silane-containing plasma, and applying a positive DC bias to the substrate during the afterglow phase of each pulse so as to collect the negatively charged particles generated during the RF power on phase. We here report numerical modeling to provide a preliminary assessment of the feasibility of this scheme. The system modeled is a parallel-plate capacitively-coupled RF argon–silane plasma at pressures around 100 mTorr. Simulation results indicate that it is possible to achieve a periodic steady state in which each pulse delivers a controlled flux of nanoparticles to the biased substrate, that average particle sizes can be kept below 2–3 nm, that impact energies of the negatively-charged nanoparticles that are attracted by the applied bias can be maintained in the ~1 eV/atom range thought to be conducive to epitaxial growth without causing film damage, and that the volume fraction of neutral nanoparticles that deposit by low-velocity diffusion can be kept well below 1 %. The effects of several operating parameters are explored, including RF voltage, pressure, the value of the applied DC bias, and RF power on and off time during each pulse.

Suppression of the epitaxial growth of Si films in Si heterojunction solar cells by the formation of ultra-thin oxide layers

The epitaxial growth of silicon (Si) films during the catalytic chemical vapor deposition (Cat-CVD) of intrinsic amorphous Si (i-a-Si) passivation films on crystalline Si (c-Si) wafers is suppressed by the oxidation of c-Si surfaces simply by dipping the c-Si wafers in hydrogen peroxide (H2O2). This oxidation treatment is also effective for (111)-oriented c-Si surfaces particularly at high a-Si deposition temperatures. The suppression of the epitaxial growth leads to the better effective minority carrier lifetime (τeff) of c-Si wafers passivated with Cat-CVD i-a-Si films. SHJ solar cells show remarkably high open-circuit voltage (Voc) exceeding 0.7 V. These results clearly show the effectiveness of the insertion of SiOx layers on the improvement in Cat-CVD a-Si/c-Si interfaces.

비정질 규소막의 공정조건이 HSG-Si 형성에 미치는 영향

본 논문은 비정질 규소막 성장의 공정 조건이 저장 전극의 표면에 HSG-Si를 형성할 때 미치는 영향을 조사하였다. 그 결과 비정질 규소막의 인 농도가 <TEX>$5.5{\pm}0.1E19atoms/cm^3$</TEX> 이상이면 HSG-Si가 제대로 형성되지 않는 인 농도 의존성을 나타내었다. 또한 HSG 두께가 <TEX>$500{\AA}$</TEX> 이상에서는 전극과 전극을 단락시키는 비트 불량을 유발하기 때문에 비정질 규소막의 인농도는 <TEX>$4.5E19atoms/cm^3$</TEX>, HSG 임계 두께는 <TEX>$450{\AA}$</TEX>이 최적 조건임을 확인하였다. In this paper, the processing conditions of the amorphous silicon film growth were investigated the effect in forming the HSG-Si on the surface of the storage electrode. As a result, when the amorphous silicon film phosphorus concentration is greater than <TEX>$5.5{\pm}0.1</TEX><TEX>E19atoms/cm^3$</TEX>, HSG-Si is not formed correctly and showed the concentration dependency of HSG formation. Also, the optimum condition of the phosphorus concentration for amorphous silicon and HSG thickness are <TEX>$4.5E19atoms/cm^3$</TEX> and <TEX>$450{\AA}$</TEX>, respectively, because of the HSG thickness over the <TEX>$500{\AA}$</TEX> create to bit failure according to a short of the electrodes and the electrode.

Study of deposition temperature on high crystallinity nanocrystalline silicon thin films with in-situ hydrogen plasma-passivated grains

This paper studies the effect of deposition temperature on the growth of nanocrystalline silicon (nc-Si) films deposited by 13.56MHz plasma enhanced chemical vapor deposition (PECVD) with in-situ hydrogen (H) passivation. A high crystalline volume fraction (XC) of 80% was found in the ~100nm nc-Si film deposited at 260°C with 99% H2 diluted SiH4 at intermediate RF power between the power-limited and precursor-limited regimes. Based on these optimized deposition conditions, 300–400nm nc-Si films deposited at 75–260°C also showed a high XC of 82–85%, an intrinsic-like dark-conductivity (σdark) of ~10−6S/cm, and even a low mean oxygen content (CO) of 1017–1018at./cm3. Although material properties were similar, deposition temperature appeared to change the qualitative structure of the nanocrystalline grains. The preferred grain orientation changed from 〈111〉 to 〈220〉 as the deposition temperature was increased from 75 to 260°C due to enhanced surface diffusion of deposition precursors. This reflected in more compact and lateral columnar growth of nc-Si films with increasing deposition temperature. We successfully demonstrated high field-effect hole and electron mobilities of 33.8 and 225cm2/Vs, respectively, in top-gate thin-film transistors (TFTs) employing the ~100nm nc-Si channel layer deposited at 260°C.