Hydrogenated polycrystalline SiGe films and their application in Thin Film Transistors

National Congress of Materials (7. 2002. Madrid). © Sociedad Española de Cerámica y Vidrio, Consejo Superior de Investigaciones Científicas. Licencia Creative Commons 3.0 España (by-nc). Trabajo financiado por la CICYT, Proyecto MAT 99-1214.En este trabajo se ha caracterizado el proceso de hidrogenación en un plasma generado por resonancia ciclotrónica de electrones de capas de SiGe policristalino obtenidas mediante cristalización en fase sólida y el efecto de la hidrogenación en las características eléctricas de transistores de película delgada fabricados usando dicho material. Los procesos de hidrogenación se realizaron a 150 y 250 ºC, con duraciones de hasta 11 horas. Los espectros de transmitancia en infrarrojo muestran solamente las bandas de absorción características de los enlaces Si-H. Estas bandas indican que el hidrógeno se incorpora al material enlazándose principalmente con los átomos de silicio. Las medidas de reflectancia en el ultravioleta indican que se crea daño en la superficie de la muestra y que éste aumenta a medida que lo hace el contenido en Ge. Los transistores de película delgada con capa activa de SiGe policristalino muestran un fenómeno de degradación consistente en que la corriente que atraviesa el canal disminuye con el tiempo manteniendo fijas las condiciones de polarización. La hidrogenación de los transistores hace que la degradación sea cada vez más lenta a medida que aumenta el tiempo de proceso en plasma a temperatura constante.The hydrogenation of polycrystalline SiGe layers, obtained by solid phase crystallization, by an electron ciclotron resonance hydrogen plasma and the influence of this hydrogenation process on the electrical characteristics of thin film transistors fabricated using this material as active layer have been studied The hydrogenation processes were carried out at 150 and 250 degreesC for several times, Lip to 11 hours. Infrared transmission spectra of these samples show only the absorption bands corresponding to Si-H bonds, indicating that hydrogen atoms are bonded mainly to silicon atoms. Ultraviolet reflectance measurements show that the surface damage caused by the plasma exposure increases as the Ge content of the film does. The transistors fabricated using polycrystalline SiGe films as active layer show a degradation phenomenon, consisting of a progressive decrease of the drain current at constant gate and drain Has. The degradation slows down as the hydrogenation time increases at constant temperature.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUECICYT of Spainpu

Rapid thermally annealed plasma deposited SiNx : H thin films: Application to metal-insulator-semiconductor structures with Si, In0.53Ga0.47As, and InP

We present in this article a comprehensive study of rapid thermal annealing (RTA) effects on the physical properties of SiNx:H thin films deposited by the electron cyclotron resonance plasma method. Films of different as-deposited compositions (defined in this article as the nitrogen to silicon ratio, x=N/Si) were analyzed: from Si-rich (x=0.97) to N-rich (x=1.6) films. The evolution of the composition, bonding configuration, and paramagnetic defects with the annealing temperature are explained by means of different network bond reactions that take place depending on the as-deposited film composition. All the analyzed films release hydrogen, while Si-rich and near-stoichiometric (x=1.43) ones also lose nitrogen upon annealing. These films were used to make Al/SiNx:H/semiconductor devices with Si, In0.53Ga0.47As, and InP. After RTA treatments, the electrical properties of the three different SiNx:H/semiconductor interfaces can be explained, noting the microstructural modifications that SiNx:H experiences upon annealing

Optical and structural properties of SiOxNyHz films deposited by electron cyclotron resonance and their correlation with composition

SiOxNyHz films were deposited from O-2, N-2, and SiH4 gas mixtures at room temperature using the electron cyclotron resonance plasma method. The absolute concentrations of all the species present in the films (Si, O, N, and H) were measured with high precision by heavy-ion elastic recoil detection analysis. The composition of the films was controlled over the whole composition range by adjusting the precursor-gases flow ratio during deposition. The relative incorporation of O and N is determined by the ratio Q = phi(O-2)/(phi(SiH4) and the relative content of Si is determined by R =[phi(O-2)+phi(N-2)]/phi(SiH4) where phi(SiH4), phi(O-2), and phi(N-2) are the SiH4, O-2, and N-2 gas flows, respectively. The optical properties (infrared absorption and refractive index) and the density of paramagnetic defects were analyzed in dependence on the film composition. Single-phase homogeneous films were obtained at low SiH4 partial pressure during deposition; while those samples deposited at high SiH4 partial pressure show evidence of separation of two phases. The refractive index was controlled over the whole range between silicon nitride and silicon oxide, with values slightly lower than in stoichiometric films due to the incorporation of H, which results in a lower density of the films. The most important paramagnetic defects detected in the films were the K center and the E' center. Defects related to N were also detected in some samples. The total density of defects in SiOxNyHz films was higher than in SiO2 and lower than in silicon nitride films

Thermally induced modifications on bonding configuration and density of defects of plasma deposited SiOx : H films

The bonding configuration, hydrogen evolution, and defect content of rapid thermally annealed (RTA) SiOx:H films of different compositions were studied. Infrared absorption measurements showed that all the hydrogen present in the films is lost at annealing temperatures below 600 degreesC without any change in the oxygen to silicon ratio of the films. The activation energy of the hydrogen release is in the 0.21-0.41 eV range independently of film composition, suggesting that the process occurs via network bond reactions. For annealing temperatures higher than 700 degreesC, a change in the Si-O-Si stretching wave number from the initial unannealed value to the 1070-1080 cm(-1) range was promoted, independently of the initial film composition. Electron spin resonance measurements showed that all the films contain two type of bulk paramagnetic defects: the E-' center (.Si=O-3) and the silicon dangling bond center (.Si=Si-3). The RTA process promotes a general decrease of defect concentration for annealing temperatures below 400 degreesC. At higher temperatures, E' center disappears, and the .Si=Si-3 center increases its concentration up to the 10(17)-10(18) cm(-3) range. This suggests that the RTA at higher temperatures promotes the formation of a high-quality, almost defect-free, SiO2 matrix in which highly defective Si nanocrystals are also formed, where the .Si=Si-3 centers are located

Microstructural modifications induced by rapid thermal annealing in plasma deposited SiOxNyHz films

The effect of rapid thermal annealing (RTA) processes on the structural properties of SiOxNyHz films was investigated. The samples were deposited by the electron cyclotron resonance plasma method, using SiH4, O-2 and N-2 as precursor gases. For SiOxNyHz films with composition close to that of SiO2, which have a very low H content, RTA induces thermal relaxation of the lattice and improvement of the structural order. For films of intermediate composition and of compositions close to SiNyHz, the main effect of RTA is the release of H at high temperatures (T>700degreesC). This H release is more significant in films containing both Si-H and N-H bonds, due to cooperative reactions between both kinds of bonds. In these films the degradation of structural order associated to H release prevails over thermal relaxation, while in those films with only N-H bonds, thermal relaxation predominates. For annealing temperatures in the 500-700degreesC range, the passivation of dangling bonds by the nonbonded H in the films and the transition from the paramagnetic state to the diamagnetic state of the K center result in a decrease of the density of paramagnetic defects. The H release observed at high annealing temperatures is accompanied by an increase of density of paramagnetic defects

High-k gadolinium scandate on Si obtained by high pressure sputtering from metal targets and in-situ plasma oxidation

This article studies the physical and electrical behavior of Gd2-xScxO3 layers grown by high pressure sputtering from metallic Gd and Sc targets. The aim is to obtain a high permittivity dielectric for microelectronic applications. The films were obtained by the deposition of a metallic nanolaminate of Gd and Sc alternating layers, which is afterwards in-situ oxidized by plasma. The oxide films obtained were close to stoichiometry, amorphous and with minimal interfacial regrowth. By fabricating metal-insulator-semiconductor capacitors we found that a moderate temperature annealing is needed to enhance permittivity, which reaches a high value of 32 while keeping moderate leakage. Finally, the feasibility of interface scavenging in this material with Ti gate electrodes is also demonstrated

Si oxidation processes by electron cyclotron resonance plasmas

National Congress of Materials (7. 2002. Madrid). © Sociedad Española de Cerámica y Vidrio, Consejo Superior de Investigaciones Científicas. Licencia Creative Commons 3.0 España (by-nc). Los autores agradecen al C.A.I. de Implantación Iónica (U.C.M.) por las labores técnicas de apoyo, y al C.A.I. de Espectroscopía (U.C.M.) por la disponibilidad del espectrómetro FTIR. Éste trabajo fue parcialmente financiado por el CICYT bajo contrato TIC 01‑1253.Se han fabricado estructuras MIS sobre Si (100) mediante un proceso en dos pasos: una primera exposición del sustrato de Si a un plasma ECR de oxígeno, que da lugar a la obtención de una capa de SiOx (en adelante PO-SiOx), seguido de un depósito de nitruro de silicio (SiN1.55:H) mediante plasma ECR. La estructura MIS resultante es de la forma Al/SiN1.55:H/PO‑SiOx/Si. Los dispositivos han sido caracterizados mediante la medida simultánea de las capacidades a alta y baja frecuencia, lo que permite conocer la calidad de la intercara PO‑SiOx/Si, calcular los espesores de la capa de PO‑SiOx y la velocidad de crecimiento del SiNx:H. Para caracterizar el proceso de oxidación se realizaron varias series de muestras variando en cada una un parámetro del proceso. Estos parámetros fueron: el tiempo de depósito del SiNx:H, el tiempo de oxidación, la temperatura del sustrato y el flujo total de O2. Asimismo, se ha estudiado la estructura de enlaces del dieléctrico apilado mediante espectroscopia infrarroja. El espectro del dieléctrico apilado mostró la superposición de dos picos: uno de menor intensidad asociado al PO‑SiOx con el máximo en 1056 cm-1, y otro debido al SiN1.55:H con máximo en 860 cm-1. Estas medidas mostraron que la ley que rige el crecimiento del PO‑SiOx es dSiO = 2.7 tox 0.26 nm donde dSiO es el espesor de la capa de PO-SiOx y tox es el tiempo de oxidación en min. Por lo que respecta a las características eléctricas, las estructuras presentaron mínimos de la densidad de trampas en la intercara (Dit) cercanos a 1011 eV-1cm-2. Este valor es inferior al que presentaron las estructuras sin oxidar, del tipo SiN1.55:H/Si. Además, los dispositivos apilados mostraron un barrido del nivel de Fermi mayor y una histéresis prácticamente despreciable.MIS structures have been fabricated on Si (111) by a two-step process: first an exposition of the Si substrates to an ECR oxygen plasma was performed, which yields a layer of SiOx (in the following PO-SiOx); this process was followed by an ECR plasma silicon nitride deposition (SiN1.55:H). The resulting MIS structure is Al/SiN1.55:H/PO-SiOx/Si. Devices have been characterized by the simultaneous measurement of the capacitance at high and low frequencies. This measurement lets us know the PO-SiOx/Si interface quality, calculate the thickness of the PO-SiOx layer and the growth rate of SiN1.55:H. To characterize the oxidation process some series of samples were prepared. In each series a process parameter was varied. These parameters were: the SiN1.55:H deposition time, the ECR plasma oxidation duration, the substrate temperature and the total oxygen flux. The bonding structure of the stacked dielectric has been studied by infrared spectroscopy. The stacked dielectrics spectra showed the super-position of two peaks: a less intense peak associated to the PO-SiOx layer with its maximum in 1056 cm(-1), and another one due to the SiN1.55:H film with its maximum in 860 cm(-1). These measurements showed that the PO-SiOx growth law is d(SiO) = 2.71 t(ox)(026) nm where d(SiO) is the PO-SiOx layer thickness and t(ox) is the oxidation time in min. Concerning electrical characteristics, stacked MIS devices showed interface trap density minimums (D-u) close to 10(11) eV(-1)cm(-2). This value is inferior to the one that non-oxydized devices (Al/SiN1.55:H/Si) show. Also, stacked devices presented higher Fermi level sweeps and an electrical hysteresis almost insignificant.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUECICYT of Spainpu

Electrical properties of rapid thermally annealed SiNx : H/Si structures characterized by capacitance-voltage and surface photovoltage spectroscopy

A comparative investigation of the characteristics of the SiNx:H/Si interface has been undertaken by capacitance-voltage measurements and surface photovoltage spectroscopy. By each of these techniques, we have determined the distribution of the interface trap density within the silicon bandgap. The samples were grown by the electron-cyclotron resonance plasma method starting from SiH4 and N-2 as precursor gases whose flow ratio was varied to produce films of three different compositions: silicon rich, near stoichiometric and nitrogen rich. Post-deposition rapid thermal annealing treatments were applied to observe the evolution of interface properties with the annealing temperature in the range from 300 to 1050 degreesC. For thin dielectrics, the interface state density has a U-shaped distribution dominated by hand-tail states. The minimum of this distribution decreases significantly and shifts to midgap for moderate annealing temperatures. For higher annealing temperatures, the trend is reversed. In the silicon-rich films, the percolation of rigidity caused by the chains of Si-Si bonds impedes the initial decrease of the defect density. For thicker films, the strain of the: SiNx:H film produces a higher density of defects that results in increased levels of leakage currents and poorer electrical characteristics