Investigation on Low Firing Copper for Front Electrode of Si-Based Solar Cell Applications.

Solar cell is one of the most popular alternative energies. The aim of this study is to construct an ohmic contact between front electrode and Si-based solar cell by a Newly-invented low-cost paste and low temperature sintering process. The core-shell of CucoreAgshell powders were prepared for making high solid content paste, then screen printing the fine line on laser-opening H-pattern silicon substrate and applying firing process. Because the silver coverage is more than 95% and silver nanoparticles start to melt at 200 °C. The shell of nanoparticles of silver not only is used to prevent copper from oxidized, but also connected core Cu particles for enhancing the conductivity of CucoreAgshell. TEM, EDS, SEM were used to examine the microstructure of CucoreAgshell. Fourpoint probe and transmission line model were employed to analyze the sheet resistance and the specific contact resistance. The lowest specific contact resistivity is 0.005 Ωcm2, sheet resistance is 0.0138 Ω/ and the lowest resistivity of front electrode measured is 2.65 × 10-5 Ωcm when CucoreAgshell paste with 94 wt% solid content was fired at 550 °C.

Fabrication of In(0.75)Zn(1.5)Sn(1.0) (IZTO) Thin-Film Transistors Using Solution-Processable Materials and PZT Inkjet-Printing.

Recently, Thin Film Transistors (TFTs) have been studied widely because of potential applications in low cost, low-temperature process and flexible displays. They can be fabricated by easy processes based on solution methods. But the mobility of organic TFTs is lower and the threshold voltage is higher than amorphous Si TFTs. In order to enhance the channel mobility and satisfy with the requirement of low-cost fabrication, we prepare a low-cost, mask-free, reduced material wastage, deposited technology using transparent, directly printable, air-stable semiconductor slurries and dielectric solutions. In our investigations, we attempt to obtain a high performance and low-cost TFT via preparing materials, designing device structure, and using PZT inkjet-printing technology. A stable and non-precipitated metal oxide ink with appropriate doping was prepared for the fabrication of an InxZn1.5Sn1.0 (IZTO) by PZT inkjet-printing. The soluble direct-printing process is a powerful tool for material research and implies that the printable materials and the printing technology enable the use of all-printed low-cost flexible displays and other transparent electronic applications. Transparent materials including dielectric PVP, conductive carbon nanotube (CNT) and active IZTO were employed into the fabrication of our PZT inkjet-printing process. After annealed at 180 °C, The experimental all-printed TFT exhibit the carrier mobility of 0.194 cm2/Vs, sub-threshold slope of 20 V/decade, and the threshold voltage of 5 V, initially. All-inkjet-printed films have great transparency, potentially in transparent electronics and the transmittance pattern in visible part of the spectrum (400­700 nm) is over 80%.

Effects of Annealing Pressure on Microstructure and Conversion Efficiency for Electrodeposited CuInSe2 Absorbers.

As-deposited CuInSe2 thin films by electrodeposition method are usually accompanied with amorphous structure which is regarded detrimental for solar cell conversion efficiency. In this work, we proposed an annealing method under high pressure for improving the conversion efficiency of electrodeposited CuInSe2 thin film solar cells, and the microstructure of high-pressure annealed CuInSe2 films were also investigated. The annealing pressure was set from 100 kPa to 250 kPa, and the annealed CuInSe2 thin films were then fabricated into solar cell using standard process. Field-emission scanning electron microscopy (FESEM) images show that CuInSe2 films with higher annealing pressure demonstrate denser and smoother surface morphology. Results from X-ray diffraction (XRD) and Raman spectra indicate that annealing under high pressure enhanced the (1 1 2) preferential orientation of CuInSe2 films and also eliminated binary Cu­Se phases. Finally, through annealing CuInSe2 absorber layer under 200 kPa, the fill factor of the CuInSe2 solar cell was found to be improved from 28.4% to 55% and the efficiency from 2.77% to 6.91%.

Investigation the electroplating behavior of self formed CuMn barrier.

The electrical and material properties of Copper (Cu) mixed with [0-10 atomic% manganese (Mn)] and pure Cu films deposited on silicon oxide (SiO2)/silicon (Si) are explored. Cu electroplating on self formed CuMn barrier was investigated with different Mn content. The electrochemical deposition of the Cu thin film onto the electrode using CuMn barrier was investigated. Scanning electron microscopic (SEM) micrographs of copper electroplating on CuMn films were examined, and the copper nucleation behaviors changed with the Mn content. Since the electrochemical impedance spectroscopy (EIS) is widely recognized as a powerful tool for the investigation of electrochemical behaviors, the tool was also used to verify the phenomena during plating. It was found that the charge-trasfer impedance decrease with the rise in the Mn content below 5%, but increase with the rise in the Mn content higher than 5%. The result was corresponded to the surface energy, the surface morphology, the corrosion and the oxidation of the substrate.

A novel synthesis of a CuInSe2 thin film from electrodeposited Cu-Se-In-Se precursors with three steps annealing.

In this study, copper indium diselenide (CIS) films were synthesized from electrodeposited Cu-Se-In-Se precursors by three step annealing. The Se layer between Cu and In layer was grown to prevent the formation of Cu/In compound. The Cu-Se precursors were first annealed to grow uniform and conductive Cu2Se surface. After deposition of the four layers precursors, two steps annealing was employed to form Cu2Se-In2Se3 precursors. Transforming Cu2Se-In2Se3 to CIS required less thermal energy. Therefore, high quality CIS film can be synthesized by two steps annealing due to its high crystallinity. The properties of the CIS films were characterized by scanning electron microscopy (SEM), X-ray Diffraction (XRD), and Raman Spectra.

Power Molding Inductors Prepared Using Amorphous FeSiCrB Alloy Powder, Carbonyl Iron Powder, and Silicone Resin.

In this study, amorphous FeSiCrB alloy powder, carbonyl iron powder, and high-temperature heat-resistant silicone resin were used to prepare power molding inductors, and the effects of different heat treatment procedures on the magnetic properties were investigated. Two heat treatment procedures were used. Procedure 1: Amorphous FeSiCrB alloy powder was pre-heat-treated, then mixed with carbonyl iron powder and silicone resin and uniaxially pressed to prepare power inductors. Procedure 2: A mixture of amorphous FeSiCrB alloy powder, carbonyl iron powder, and silicone resin was uniaxially pressed. After dry pressing, the compacted body was heat-treated at 500 °C. Heat treatment after compaction can reduce the internal strain caused by high-pressure compaction and promote the crystallization of superparamagnetic nano-grains simultaneously. Therefore, the compacted sample after heat treatment exhibited better magnetic properties.

Using chemical-mechanical polishing for planarizing a high-kappa nanocomposite polyimide insulator for organic thin film transistors application.

To solve the large leakage current of the heavily blended nanocomposite (Polyimide and nano-TiO2 particles) gate dielectric film exhibiting a high-kappa, the chemical-mechanical polishing (CMP) was adopted to flatten the surface of the PI-TiO2 nanocomposite film. An extremely high dielectric constant (is congruent to 13) of the nanocomposite with CMP treatment is obtained and its leakage current is comparable to that of the neat polyimide in our studies. An OTFT based on the nanocomposite gate dielectric exhibiting high capacitance and a smooth surface after CMP treatment shows very promising performance. Compared with the OTFT based on the neat polyimide gate dielectric, the threshold voltage is improved from -22 to -5 (V), the sub-threshold voltage is decreased from 3.44 to 0.50 (V/dec), the current on/off ratio is increased from 1.6 x 10(6) to 3.53 x 10(8), and the mobility is increased from 0.416 to 0.624 (cm2V(-1)s(-1)). Moreover, it is worth noting that the hysteresis effect of OTFT based the nanocomposite can be significantly reduced due to the few charge trapped in the interface when the nanocomposite dielectric surface was further polished by CMP treatment.

Improvement on Conductivity for Thick Film Aluminum Paste.

With the development of thick-film paste, silver and copper are circulating in the market as the electric conductive fillings currently. Unfortunately, the cost of silver is exceedingly high, while the copper has to be sintered in the reducing atmosphere. In this study, we proposed to exert aluminum as the filling due to its low cost, good electrical conductivity, and capability of being sintered in air. By means of the fracture mechanism of the oxidation layer of the Al surface and the liquid phase sintering, the Al paste with high solid content is used to implement high electrical conductivity. Based on that Al powder with large particle size tends to fracture easily, while it is easy for Al powder with small size to fill the gap, we mixed Al powder with large and small particle sizes at different proportion, so that the internal micro-structure and the oxidization are observed. However, when glass frit was added into mixed Al powder, the Al particles are wet by glass frit for bonding Al particles as well as inhibiting oxidation. Effect of the glass frit content and the solid content of Al paste on conductivity are investigated in this study. The sheet resistance of Al paste sintered at 850 °C for 10 min. can be reduced to 4.5 mΩ/□ when Al paste is formulated based on the mixed Al particles with proportion of big to small (4:1) at 10 wt% glass frit content and 80 wt% solid content.

Improvement on Conductivity for Thick Film Aluminum Paste.

With the development of thick-film paste, silver and copper are circulating in the market as the electric conductive fillings currently. Unfortunately, the cost of silver is exceedingly high, while the copper has to be sintered in the reducing atmosphere. In this study, we proposed to exert aluminum as the filling due to its low cost, good electrical conductivity, and capability of being sintered in air. By means of the fracture mechanism of the oxidation layer of the Al surface and the liquid phase sintering, the Al paste with high solid content is used to implement high electrical conductivity. Based on that Al powder with large particle size tends to fracture easily, while it is easy for Al powder with small size to fill the gap, we mixed Al powder with large and small particle sizes at different proportion, so that the internal micro-structure and the oxidization are observed. However, when glass frit was added into mixed Al powder, the Al particles are wet by glass frit for bonding Al particles as well as inhibiting oxidation. Effect of the glass frit content and the solid content of Al paste on conductivity are investigated in this study. The sheet resistance of Al paste sintered at 850 °C for 10 min. can be reduced to 4.5 mΩ/□ when Al paste is formulated based on the mixed Al particles with proportion of big to small (4:1) at 10 wt% glass frit content and 80 wt% solid content.

Influence of Plasma Ultraviolet/Vacuum Ultraviolet Irradiation Damage on Silicon Metal-Oxide-Semiconductor Capacitor During Etching.

In this study, we evaluate the defects and charges caused by the ultraviolet (UV)/vacuum ultraviolet (VUV) irradiation in the high-k/metal gate stack structure, especially in HfO2 layer and at Si/HfO2 interface. First, we measured the photons irradiating to the surface in the neutral beam etching (NBE) system and in the conventional inductively coupled plasma (ICP) system through optical emission spectroscopy (OES), respectively. By using this method, we evaluate the ability of reducing UV/VUV irradiation damage in the NBE system. As a result, photon intensity detected in the ICP system shows larger magnitude as compared to the NBE system, which indicates the UV/VUV irradiation is more severe in the ICP system. Moreover, in order to understand the twisting of electrical characteristics caused by UV/VUV irradiation, we set the prefabricated metal-oxide-semiconductor (MOS) capacitors in both systems to absorb the irradiation of UV/VUV photons respectively. The electrical characteristics of the etched MOS capacitors and its related plasma-induced damage model are discussed. The result of the devices exposed in the ICP system reveals a greater electrical characteristics shift compared to the devices in NBE such as the interface trap density (Dit) in case of NBE is 3.55621×1012 cm-2eV-1 and in case of ICP is higher i.e., 4.19961×1012 cm-2eV-1.

Effect of nanocomposite gate-dielectric properties on pentacene microstructure and field-effect transistor characteristics.

In this study, the effect of surface energy and roughness of the nanocomposite gate dielectric on pentacene morphology and electrical properties of pentacene OTFT are reported. Nanoparticles TiO2 were added in the polyimide matrix to form a nanocomposite which has a significantly different surface characteristic from polyimide, leading to a discrepancy in the structural properties of pentacene growth. A growth mode of pentacene deposited on the nanocomposite is proposed to explain successfully the effect of surface properties of nanocomposite gate dielectric such as surface energy and roughness on the pentacene morphology and electrical properties of OTFT. To obtain the lower surface energy and smoother surface of nanocomposite gate dielectric that is responsible for the desired crystalline, microstructure of pentacene and electrical properties of device, a bottom contact OTFT-pentacene deposited on the double-layer nanocomposite gate dielectric consisting of top smoothing layer of the neat polyimide and bottom layer of (PI+ nano-TiO2 particles) nanocomposite has been successfully demonstrated to exhibit very promising performance including high current on to off ratio of about 6 x 10(5), threshold voltage of -10 V and moderately high filed mobility of 0.15 cm2V(-1)s(-1).

Effect of under-layer treatment of Ta/TaN barrier film on corrosion between Cu seed and Ta in chemical-mechanical-polishing slurry.

Tantalum/tantalum nitride (Ta/TaNx) composite film is widely used as a copper (Cu) diffusion barrier layer. In order to reduce via-resistance, an additional argon (Ar) re-sputtering process is used to thin the barrier thickness at the feature bottom. In this study, the effect of Ar re-sputtering of the under-layer of TaNx barrier films on the corrosion between Cu seeds and upper Ta films in chemical-mechanical-polishing (CMP) slurries was investigated. The results show that Ar re-sputtering of the under-layer of the TaNx barrier has a strong influence on the corrosion of Cu seeds and Ta films. The equivalent circuit, simulated using data from electrochemical analysis, reveals changes in resistance and capacitance elements of the Cu-Ta electrochemical system, proving that the phase transformation of upper Ta films under different TaNx conditions leads to different degrees corrosion of Cu seeds and the Ta films.

Effects of photo-assisted electrodeposited on CuInSe2 thin films.

Photo-assisted one-step electrodeposition has been applied to help in forming smooth and dense CuInSe2 films. The difference in surface morphology and crystalline quality between CuInSe2 films with various photo-assistance has been investigated. In the photo-assisted electrodeposition process, the many kinds of lamps providing maximum light intensity at about 380 to 620 nm were used as light source to be irradiated onto the surface of Mo-coated soda-lime glass substrates. The results suggested effects of photo-assistance including activating surface diffusion and growing high-crystalline quality films with reduced defects during electrodeposition.

A Study of Trimethylsilane (3MS) and Tetramethylsilane (4MS) Based α-SiCN:H/α-SiCO:H Diffusion Barrier Films.

Amorphous nitrogen-doped silicon carbide (α-SiCN:H) films have been used as a Cu penetration diffusion barrier and interconnect etch stop layer in the below 90-nanometer ultra-large scale integration (ULSI) manufacturing technology. In this study, the etching stop layers were deposited by using trimethylsilane (3MS) or tetramethylsilane (4MS) with ammonia by plasma-enhanced chemical vapor deposition (PECVD) followed by a procedure for tetra-ethoxyl silane (TEOS) oxide. The depth profile of Cu distribution examined by second ion mass spectroscopy (SIMs) showed that 3MS α-SiCN:H exhibited a better barrier performance than the 4MS film, which was revealed by the Cu signal. The FTIR spectra also showed the intensity of Si-CH3 stretch mode in the α-SiCN:H film deposited by 3MS was higher than that deposited by 4MS. A novel multi structure of oxygen-doped silicon carbide (SiC:O) substituted TEOS oxide capped on 4MS α-SiC:N film was also examined. In addition to this, the new multi etch stop layers can be deposited together with the same tool which can thus eliminate the effect of the vacuum break and accompanying environmental contamination.