Low Temperature Polycrystalline-silicon Film Research Articles

Low temperature polycrystalline silicon film formation by metal induced crystallization with nickel salt derived by ultrasonic spray pyrolysis

AbstractSolution‐based nickel induced crystallization of amorphous silicon (a‐Si) films was performed. The nickel solution was prepared by dissolving (CH3CO2)2Ni in deionized water and applied uniformly on a‐Si films by low‐cost ultrasonic spray pyrolysis method. Crystallization could be realized for a‐Si films coated with a 0.2 M nickel solution and annealed at 500 °C. The effect of substrate temperature during nickel solution deposition was analyzed. Micro‐Raman and x‐ray diffraction measurement show that a‐Si is fully crystallized at 550 °C for 7 h with a nickel concentration of 0.8 M. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamical resolidification behavior of silicon thin films during frontside and backside excimer laser annealing

Abstract Excimer laser annealing (ELA) is frequently employed to fabricate low-temperature polycrystalline silicon films on glass substrate. The grain size and crystallinity of polycrystalline silicon films are significantly affected by the resolidification behavior during ELA. A real-time in situ time-resolved optical measurement system is developed to record the rapid phase transformation process during ELA. The average solidification velocity of liquid-Si is calculated from these optical spectra using MATLAB and Excel softwares. Field emission scanning electron microscopy images reveal maximum grain size of poly-Si films with a diameter of 1 μm, which is obtained in the complete melting regime of both frontside ELA and backside ELA. Recrystallization mechanisms of complete melting of Si thin films in frontside ELA and backside ELA are demonstrated. Resolidification scenarios of partial melting, near-complete melting and complete melting in frontside ELA and backside ELA are proposed.

P‐5: Self‐Release Nickel Induced Lateral Crystallized (SR‐NILC) Low Temperature Polycrystalline Silicon Films and Thin Film Transistors

AbstractNickel induced crystallization of a‐Si with a self‐release inducing source was studied. Three main factors affecting the crystallization rate were investigated. The new source possesses an effect of nickel self‐release and the crystallized poly‐Si has obviously lower nickel residua. The p‐channel thin film transistors (TFTs) based on the SR‐NILC poly‐Si film showed lower off‐state current (Ioff) and gate induced drain leakage (GIDL).

Fabrication and Analysis of Nano-Aluminum-Induced Low-Temperature Polycrystalline Silicon Film

In this paper, we successfully fabricate polycrystalline silicon films with very large and uniform-size grains by the method of nanometer thick aluminum induced crystallization (nano-AIC) on the a-Si:H film deposited by plasma enhanced chemical vapor deposition (PECVD). The effect of annealing ramp-up time is discussed. Four different annealing ramp-up time, 1,5,10,20 hours, are tested. The results show the maximum average grain size obtained in this paper is about 60 μm under the condition of 20-hour annealing ramp-up time. The nano-AIC specimens show a much better leakage current characteristics than the AIC specimens since the Al layer in AIC process is much thicker and was not removed completely from the polycrystalline silicon film during Al wet selective etching process.

Hydrogen passivation of ultra-thin low-temperature polycrystalline silicon films for electronic applications

We have investigated the influence of hydrogen passivation on the electronic properties of ultra-thin polycrystalline silicon layers prepared by the aluminum-induced layer exchange process. Hall effect measurements reveal high hole carrier concentrations in the as-grown poly-Si layers up to several times 1019cm−3. We find a drastic increase of the resistivity after hydrogenation for very thin samples, which is attributed to a combination of two effects: (1) the reduction of free holes due to acceptor passivation and (2) compensation of free holes remaining after H-passivation by interface trap states. Temperature-dependent measurements show that the activation energy of the dark conductivity increases strongly after the hydrogenation process. The origin of the compensation was investigated by spin-dependent transport measurements. In addition, the potential of the passivated poly-Si layers for electronic applications was studied. We have demonstrated a normally ON back-gate depletion mode transistor with a two mask process, which exhibits a field-effect mobility of 21cm2/Vs for holes in the 20nm thin channel layer.

Effect of Sputtering Power of Aluminum Film in Aluminum Induced Crystallization of Low Temperature Polycrystalline Silicon Film

In this study we produced a low-temperature polycrystalline silicon (LTPS) film by aluminum induced crystallization (AIC) on a Corning EAGLE2000 glass substrate. Five types of specimen, with the DC sputtering powers of aluminum films of 100, 200, 400, 800, and 1600 W, were prepared. Crystal quality, surface morphology, roughness, and film stress were analyzed. Results show that surface roughness increases proportionally with sputtering power. The numbers of bulges and cracks observed on the polycrystalline silicon (poly-Si) thin film surface increase with sputtering power. The calculated film stresses are tensile when the sputtering powers are 100 and 200 W but they become compressive as the sputtering power is further increased. The optimal aluminum film sputtering power range for inducing the crystallization of amorphous silicon is also discussed.

Low temperature polycrystalline silicon film formation with and without charged species in an electron cyclotron resonance SiH4/H2 plasma-enhanced chemical vapor deposition

We have developed a novel technique to deposit poly-Si films on insulating substrates in an electron cyclotron resonance (ECR) SiH4/H2 plasma-enhanced chemical vapor deposition (PECVD) and investigated the effect of reactive species on polycrystalline silicon (poly-Si) film formation at low substrate temperatures. The charged species incident on the substrate were successfully shut out by using permanent magnets set above the substrate in an ECR SiH4/H2 plasma. As a result, the films formed without charged species were found to have better crystallinity than those formed with charged species at a low substrate temperature of 150 °C. From results of the atomic force microscope, it was found that the surfaces of films formed without charged species were smoother than those of films formed with charged species at a substrate temperature of 300 °C. Therefore, it was clarified that the charged species deteriorated the crystallinity and the surface roughness while the neutral reactive species played an important role for improving them in the poly-Si film formation at low temperatures using the ECR SiH4/H2 PECVD method.

Very low temperature polycrystalline silicon films with very large grains deposited for thin film transistor applications

This paper presents the results of low temperature polycrystalline silicon growth on SiO 2 and glass substrates. The silicon films were deposited with the hydrogen dilution method by electron cyclotron resonance chemical vapor deposition at or below 250°C without any thermal annealing. Hydrogen passivation of the SiO 2 surface was applied to enhance the grain growth of poly-Si deposition. The polycrystallinity of the silicon films was established by transmission electron microscopy (TEM), Raman scattering, and X-ray diffraction. The maximum grain size was about 1 μm. The crystalline fraction of the polycrystalline silicon (poly-Si) films was near 100% as identified by Raman shift spectra. The preferred orientations of the poly-Si film were 〈110〉 and 〈111〉. Poly-Si films with a maximum grain size of 7000 Å were formed at a substrate temperature as low as 100°C.