Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: (1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; (2) Si deposition with remote, linear PECVD; (3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first nip a-Si cells were made on steel substrates with flat barrier layer and had initial efficiencies of 6.3%, showing the potential of the concept.     

Thermal stability of atomic layer deposited Ru layer on Si and TaN/Si for barrier application of Cu interconnection

The thermal stability of thin Ru single layer and Ru/TaN bilayers grown on bare Si by plasma enhanced atomic layer deposition (PEALD) have been studied with Cu/Ru, Cu/Ru/TaN structures as a function of annealing temperature. To investigate the characteristics as a copper diffusion barrier, a 50 nm thick Cu film was sputtered on Ru and Ru/TaN layers and each samples subjected to thermal annealing under N2 ambient with varied temperature 300, 400, and 500 degrees C, respectively. It was found that the single 5 nm thick ALD Ru layer acted as an effective Cu diffusion barrier up to 400 degrees C. On the other hand ALD Ru (5 nm)/TaN (3.2 nm) showed the improved diffusion barrier characteristics even though the annealing temperature increased up to 500 degrees C. Based on the experimental results, the failure mechanism of diffusion barrier would be related to the crystallization of amorphous Ru thin film as temperature raised which implies the crystallized Ru grain boundary served as the diffusion path of Cu atoms. The combination of ALD Ru incorporated with TaN layer would be a promising barrier structure in Cu metallization.     

Improvement of the properties and electrical performance on TiCl4-based TiN film using sequential flow chemical vapor deposition process

Sequential flow chemical vapor deposition (SFCVD), utilizing TiCl₄/NH₃ as reactants and immediate NH₃ treatment after film deposition, is applied to produce TiN barrier films in the contact process. Secondary ion mass spectroscopy results indicate that the SFCVD TiN film can effectively block the diffusion of WF₆ into the underlying Ti layer during W deposition. NH₃ treatment immediately after film deposition causes SFCVD TiN films to be less contaminated with carbon than TiN films that are formed by metallic organic compounds chemical vapor deposition (MOCVD) and to contain less chlorine residue than conventional TiCl₄/NH₃ CVD TiN layers even at a low reaction temperature. According to the resistance measurement of Kelvin contacts, the SFCVD process yields a lower resistance and a more uniform distribution than the MOCVD or CVD process. Transmission electron microscopic observations demonstrate that WF₆ can diffuse through the MOCVD TiN to react with the underlying Ti layer, causing a rupture at the Ti/TiN interface and poor W adhesion. The SFCVD TiN can serve as a sufficient diffusion barrier against WF₆ penetration during W CVD deposition.     

柔性高阻隔薄膜材料的研究现状

目的为柔性高阻隔薄膜的应用提供理论指导。方法综述柔性高阻隔膜的应用现状及存在问题,总结热蒸发、化学气相沉积、原子层沉积等制备柔性高阻隔薄膜的方法、原理、特点及应用,展望高阻隔膜包装材料的发展前景。结果高阻隔薄膜制备工艺趋向于单次制备,采用等离子体辅助原子层沉积技术是制备超高阻隔薄膜的首选,原子层沉积(ALD)和分子层沉积(MLD)结合也是获得超高阻隔薄膜的未来发展方向。结论快速、高效地制备柔性高阻隔薄膜是包装工业的发展趋势。     

Root growth of multi-wall carbon nanotubes by MPCVD

This work examines the relationships among the growth and interlayer reactions of carbon nanotubes (CNTs) to develop an effective process for controlling the nanostructure, orientation and characteristics of CNTs. Vertically oriented CNTs were successfully synthesized by microwave plasma chemical vapor deposition (MPCVD) with CH₄/H₂ as source gases. Additionally, the Ti and SiO₂ barrier layers and the Co catalyst were used in an experiment on the growth of CNTs on the Si wafer. Then, the SiO₂ barrier layer was deposited by low-pressure chemical vapor deposition (LPCVD). The Ti barrier layer and Co catalyst films were deposited on the Si wafer by physical vapor deposition (PVD). The deposited nanostructures were characterized by scanning and transmission electron microscopy, the results of which reveal that the deposited MWCNTs were grown under the influence of a catalyst on Si substrates with or without a barrier layer, by MPCVD. Vertically grown, dense MWCNTs attached to a catalytic film demonstrate that various MWCNTs penetrated the root particles. The diameter of the root particles, of approximately in the order of 100 nm, is larger than those of the tube, 10–15 nm. The well-known model of the growth of CNTs includes base- and tip-root growth. The interaction between the catalytic film and the supporting barrier layer is suggested to determine whether the catalytic particles are driven up or pinned down on the substrate during the growth.     

Aluminum alloy film deposition and characterization

A flash evaporation system which utilizes a mechanism for feeding alloy wire onto a heated bar was used for the deposition of aluminum-silicon, aluminum-copper and aluminum-copper-silicon. The effect of deposition conditions and processing procedure on film composition and microstructure was determined. Particular attention was given to the film surface topography and the possible influence of deposition conditions, alloy composition, substrate type, thickness, annealing time and temperature and addition of oxide overlayers. Resistivity, and possible shorting of junctions in silicon as a consequence of silicon dissolution in the metallization, were considered as a function of alloy composition. Metal continuity over steps in the substrate was tested as a function of deposition temperature. These studies yielded recommendations, regarding the general use of alloy metallization on silicon devices and its specific use in two-level metallization configurations, which include: deposition at temperatures down to 275°C and at evaporation rates of about 0.4 g/min; the use of initial layer thickness down to 0.7 μ; post-deposition processing for aluminum-copper or aluminum-copper-silicon not to exceed 525°C; the addition of 1% silicon to prevent junction penetration; and the addition of 4% copper to lend adequate electromigration resistance and inhibit hillock growth during high temperature processing.     

Study on the characteristics of amorphous low-K thin film for solar cells

The most practical solar cells are silicon based crystal silicon solar cells. Phosphorus oxychloride for n+ type doping was diffused on a p+ Si, SiC and poly Si using N2 carrier gas by low pressure chemical vapor deposition. The series resistances on various p type silicon substrates were researched. An n(+)-p+ junction was fabricated by thermal diffusion of phosphorus oxychloride into a p+ Si wafer. For the rear metallization, Al was deposited using screen printing and SiOC film was used instead of SiO2 film as a passivation material for the metal layer. SiOC film was made by the capacitive coupled plasma chemical vapor deposition. When the Fourier transform infrared spectra of SiOC film shows organic properties including a strong peak of the Si-CH3 bond, the efficiency was increased, because of the reduction of the recombination at the back surface.     

A vacuum plasma surface pretreatment for refining seeding of Co in electroless copper plating

In this work, various vacuum plasma types, generated by either single gaseous sources (N₂ or H₂) or mixed sources (N₂-H₂) are incorporated into an aqueous-solution electrochemical seeding process to pre-treat the surfaces of SiO₂ dielectric layers. Under the optimal plasma atmosphere (monitored by optical emission spectroscopy), the dielectric surfaces can be modified to terminate by hydrophilic bonds, accelerating the adsorption of a crowd of catalytic seeds as small as 3 nm. Such a seeding refinement allows for the growth of a Co-based barrier layer with thickness as thin as 10 nm using electroless plating. Moreover, the capacity of integrating the plasma surface pretreatment with the seeding and electroless-plating process steps to deposit an ultrathin copper-stacked metallization layer in a selective and sequential manner on blanket wafers will be demonstrated by the fabrication of copper-gated and barrier-interposed capacitors. Finally, a tentative work of filling the seeds and the barrier layer into trenches of a patterned wafer was carried out, demonstrating the potential of the reported technique for advanced technology nodes of 60 nm or less.     

Arsenic distribution in bilayers of TiSi2 on polycrystalline silicon during heat treatment

The diffusion behaviour of arsenic in bilayers of TiSi₂ on polycrystalline silicon (poly-Si) was investigated by the He⁺ backscattering technique and sheet resistance measurements. The TiSi₂ films were sputtered from a stoichiometric compound target onto poly-Si prepared by low pressure chemical vapour deposition. X-ray diffractometry was used to identify the phases present after the samples had been annealed at various temperatures. The as-deposited silicide layers were found to be amorphous and to recrystallize into orthorhombic TiSi₂ (C54 structure) on heat treatment at and above 800 °C. Arsenic was either implanted into the already formed TiSi₂ films or directly implanted into the poly-Si layer prior to silicide deposition. In the former case the arsenic was observed to redistribute solely within the silicide film without any significant out-diffusion into the underlying poly-Si layer on subsequent heat treatment. The arsenic initially present in the poly-Si layer, however, was found to migrate into the silicide film at temperatures in the vicinity of 900 °C. This feature makes arsenic incompatible with a particular metal/oxide/semiconductor process, where it is desired to carry out poly-Si drain-source doping by a single ion implantation step if TiSi₂/poly-Si is used as the gate level interconnection material. It is concluded that the behaviour of arsenic in a bilayer of TiSi₂/poly-Si is completely different from that reported for the WSi₂/poly-Si system.     

SiOx/PET复合薄膜的力学性能及阻隔性能

目的基于氧化硅(SiO_x)镀层优异的性能,研究不同厚度的SiO_x层对SiO_x/PET复合薄膜力学性能和阻隔性能的影响,以期得到性能较优的SiO_x/PET复合薄膜。方法以自制的聚对苯二甲酸乙二醇酯(PET)薄膜为基材,采用等离子体增强化学气相沉积法沉积得到SiO_x层厚度分别为40,150,230,320 nm的SiO_x/PET复合薄膜,并进行傅里叶变换红外线光谱分析、力学性能和阻隔性能测试,以及薄膜表观形貌分析。结果沉积SiO_x层后,SiO_x/PET复合薄膜拉伸强度和断裂伸长率随SiO_x层厚度的增大先增大后减小,氧气透过率和水蒸气透过率则出现明显衰减而后逐渐平缓的趋势。SiO_x层厚度达150~230 nm时,复合薄膜的力学性能和阻隔性能表现较优,拉伸强度、断裂伸长率、氧气透过率以及水蒸气透过率分别提高了约25.0%,20.9%,79.3%,77.3%。结论适宜厚度的SiO_x层可以使得SiO_x/PET复合薄膜同时具备较优的力学性能和阻隔性能。     

Diffusion barrier property of TiN and TiN/Al/TiN films deposited with FMCVD for Cu interconnection in ULSI

Flow modulation chemical vapor deposition (FMCVD) with titanium tetrachloride (TiCl₄) and ammonia (NH₃) is effective for depositing titanium nitride (TiN) films with conformal morphology, good step coverage, low electrical resistivity, and low chlorine residual contamination. It means that FMCVD TiN film is a good candidate of diffusion barriers for copper interconnection technology in ULSI. But the diffusion barrier property of FMCVD TiN film against Cu diffusion has not been confirmed. So, firstly, we deposited Cu (100 nm)/FMCVD TiN (25 nm)/Si multilayer films and investigated the thermal stability of Cu/TiN/Si structure. Vacuum annealing was done at 400, 500, 550 and 600 °C. For films annealed for 30 min at 400 °C, Cu diffused through the TiN layer and formed copper silicides on the surface of Si substrates. Therefore, FMCVD films formed under such conditions are unsatisfactory diffusion barriers. To enhance the diffusion barrier property of FMCVD TiN films, we used sequential deposition to introduce a monolayer of Al atoms between two TiN films. Etch-pit tests showed that for TiN films with Al interlayer, Cu diffusion through the barrier occurred at 500 °C and that is 100 °C higher than TiN film without Al interlayer. Al atoms formed AlO_x with oxygen atoms present in the TiN films as impurities, and fill up the grain boundaries of TiN film, thereby blocking the diffusion of Cu atoms.     

Barrier capability of Zr–N films with titanium addition against copper diffusion

Zr–Ti–N film prepared by sputtering deposition has been employed as a potential diffusion barrier for Cu metallization. It is thought that the existing states of Ti and Zr in the films are Ti–N and Zr–N phase in Zr–Ti–N films. Material analysis by XRD, XPS and sheet resistance measurement reveal that the failure of Zr–N film is mainly due to the formation of Cu₃Si precipitates at the Zr–N/Si interface by Cu diffusion through the grain boundaries or local defects of the Zr–N barrier layer into Si substrate. In conjunction with sheet resistance measurement, XRD and XPS analyses, the Cu/Zr–Ti–N/Si contact system has high thermal stability at least up to 700 °C. The incorporation of Ti atoms into Zr–N barrier layer was shown to be beneficial in improving the thermal stability of the Cu/barrier/Si contact system.     

Transparente Barriereschichten auf flexiblen Polymersubstraten

Transparent permeation barrier layers on flexible polymer substrates This paper reviews different vacuum based technologies for manufacturing transparent permeation barrier layers and layer stacks on flexible polymer substrates. With plasma assisted reactive evaporation, a cost‐efficient, highly productive process for food packaging applications is presented. Reactive dual magnetron sputtering is a technology for the deposition of oxide layers with a very low water vapor and oxygen transmission rate at a reasonable deposition rate. Many groups suggest multilayer stacks for the encapsulation of flexible electronic devices. In this paper, an all‐in‐vacuum inline concept for manufacturing such multilayers is presented. It is based on the combination of reactively sputtered barrier layers with interlayers grown by using a magnetron based PECVD process (Magnetron‐PECVD). Both, process parameters, such as deposition rate and process pressure, and important layer properties, such as morphology and the water vapor and oxygen transmission rate are compared for the different single and multi layer technologies.     

Nanocrystalline graphite films nucleation by the radio frequency bias pretreatment

New method for nucleation of different nanocrystalline carbon films upon monocrystalline Si substrate was proposed. The process is based on a combination of microwave and radio frequency plasma assisted chemical vapor deposition methods. Potential of the method for nucleation was demonstrated by deposition of nanocrystalline diamond film in pure microwave plasma in one process, immediately after "seeding" procedure. The method was also used for growth of nanocrystalline graphite (NCG) films, which are currently under intensive investigation due to their exceptional electronic properties, particularly fine electron emission characteristics. Deposited NCG films have demonstrated remarkable electron field emission properties having current density of up to 10 A/cm2. The films have also possessed good adhesion to silicon substrate. Carbon films and nucleation layer were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

SiOx包装阻隔薄膜的发展现状及其制备方法

SiOx阻隔薄膜具有优异的阻隔性,并且光透过性和微波透过性好,在阻隔包装领域的应用前景广泛,介绍了SiOx包装阻隔薄膜的制备方法:物理气相沉积,等离子体聚合及大气下等离子体聚合等.     

A Single‐Chamber System of Initiated Chemical Vapor Deposition and Atomic Layer Deposition for Fabrication of Organic/Inorganic Multilayer Films

A single‐chamber system capable of depositing both organic and inorganic layers by initiated chemical vapor deposition (iCVD) and atomic layer deposition (ALD) is demonstrated to facilitate the fabrication of organic/inorganic hybrid thin film encapsulation (TFE). The chamber geometry and the process conditions of iCVD and ALD are similar to each other, which enabled the design of the single‐chamber system. Both organic and inorganic films deposited via the single‐chamber system produces films with their properties equivalent to those deposited in separate iCVD and ALD reactors. Alternating the deposition mode between iCVD and ALD produces organic/inorganic multilayers with outstanding barrier properties as well as optical transparency mechanical flexibility.     

Contact and interconnect formation on compound semiconductor devices by ionized-cluster beam deposition

A new deposition technology, namely the ionized-cluster beam deposition method, was applied to form contacts and interconnects on III–V compound semiconductor devices. Au alloy films deposited by this technology had strong enough adhesion to an insulator layer to be a satisfactory interconnection. A step approximately 8 μm high at an angle of 90° to the semiconductor was covered fully with an Au alloy film obtained by this method. Electrical ohmic contacts for p-type GaP and GaAs were successfully obtained at substrate temperatures of 400 °C and 300 °C respectively without any further annealing process; this resulted in better device characteristics because of the lower process temperatures and also made the device less expensive because of a reduction in fabrication time.     

镍衬底上定向金刚石膜的成核与生长

提出了一种包括晶粒接种、高温退火、成核、生长四过程的薄膜沉积新方法 ,用射频等离子体增强热丝化学气相沉积系统 ,在Ni衬底上制备了定向金刚石膜。通过对成核和生长两过程工艺条件的研究 ,掌握了提高成核密度和金刚石定向生长规律。实验还表明 ,膜与Ni衬底之间未见Ni C H界面层的形成     

几种食品包装用塑料膜阻透性能比较

目的研究不同厚度、不同材质的食品包装用塑料膜透氧量、透湿量的变化情况,为食品包装在阻隔性方面的选材提供依据和指导。方法采用压差法和杯式法分别测试塑料膜的透氧量和透湿量。结果单层塑料膜随厚度的增加,透氧量和透湿量均减小,阻隔性能变好。相同厚度的PE,PET,BOPP,PA这4种单层塑料膜中,PA的透氧量最小,PE的透氧量最大,BOPP的透湿量最小,PA的透湿量最大。复合膜厚度增加,其透氧量、透湿量均减小,但减小幅度逐渐变小。塑塑复合膜外层材料厚度不变时,透氧量、透湿量随总厚度变化不太明显,EVOH塑料复合膜的透氧量值和透湿量值较小,通常在5以下,铝箔塑料复合膜的透氧量值和透湿量值均小于1。结论单层塑料膜PA的氧气阻隔性最好,PE的氧气阻隔性最差,BOPP的水蒸气阻隔性最好,PA的水蒸气阻隔性最差。复合膜中,塑塑复合膜的阻隔性主要取决于外层材料,铝塑复合膜的阻隔性最好,含高阻隔材料EVOH的塑料复合膜的阻隔性比普通塑塑复合膜好,其阻隔性可与铝塑复合膜媲美。