Author: MARIANO ACEVES MIJARES

Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD

MARIANO ACEVES MIJARES (2007)

A comparative study of compositional and optical properties of silicon-rich oxide (SRO) films deposited by low-pressure chemical

vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) is presented. Infrared spectra revealed the

presence of hydrogen bonded to silicon atoms in the SRO–PECVD films, whereas in SRO–LPCVD films the IR spectra looked like the

stoichiometric thermal silicon oxide. Moreover, X-ray photoelectron spectroscopy (XPS) studies showed that the SRO–PECVD films

contain a higher content of nitrogen than SRO–LPCVD films. In spite of differences, the SRO films obtained by both methods show a

strong room-temperature photoluminescence (PL). However, the highest PL intensity was emitted by SRO films obtained by LPCVD.

Article

Silicon rich oxide Infrared spectroscopy XPS Photoluminescence CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Off Stoichiometric Silicon Oxide Applied to Enhance the Silicon Responsivity up to UV Region

MARIANO ACEVES MIJARES (2007)

Silicon Rich Oxide (SRO) is a material compatible

with silicon integrated technology, besides it has

photoluminescent properties. When SRO is illuminated

with UV radiation emission in the range of 600 to 800

nm take place. This radiation has been applied to a

silicon PN junction in order to expand the capabilities

of silicon improving its detection properties. In this

work a more precise characterization of a sensor made

of silicon and SRO is done. The response of this sensor

goes from 200 nm to standard Si detection range, and

in the range of 200 to 400 nm it increases with the

wavelength.

Conference proceedings

SRO BIOLOGÍA Y QUÍMICA QUÍMICA OTRAS ESPECIALIDADES QUÍMICAS OTRAS

Spectroscopical analysis of luminescent silicon rich oxide films

MARIANO ACEVES MIJARES (2007)

Compositional, structural and optical properties of silicon rich oxide (SRO) films containing different silicon excess were investigated using X ray photoelectron spectroscopy (XPS), Raman spectroscopy, energy filtered transmission electron microscopy (EFTEM) and photoluminescence (PL). The XPS-Si2p peaks fitting showed the presence of Si - Si4 tetrahedra only for the SRO film with the highest silicon excess. Raman spectroscopy revealed amorphous phase silicon in the SRO films with lowest silicon excess; when it was increased, a sharp peak at around 517 cm-1 appeared, which corresponds to crystalline silicon. Si-nanoclusters were slightly observed by EFTEM in the SRO film with the lowest silicon content. They became more evident when the silicon excess was increased, in agreement to Raman spectra. A strong PL was observed in the SRO films with low silicon excess. However, in SRO films with the highest silicon excess, where the silicon agglomeration is greater, the PL practically disappeared. According to these results, we have analysed the dependence of photoluminescence on the composition and structure of the SRO films.

La composición, estructura y propiedades ópticas de películas de óxido rico en silicio (SRO) con diferentes excesos de silicio fueron investigadas usando espectroscopía de fotoelectrones de rayos X (XPS), espectroscopía Raman, microscopía electrónica de transmisión con energía filtrada (EFTEM) y fotoluminiscencia (FL). El ajuste de los picos XPS-Si2p solo mostraron la presencia de tetrahedros Si-Si4 en la película de SRO con más alto contenido de silicio. La espectroscopía Raman reveló una fase de silicio amorfo en películas de SRO con más bajo exceso de silicio, cuando este se incrementó, apareció un pico en 517 cm-1, el cual corresponde a silicio cristalino. Mediante EFTEM, nano-aglomerados de silicio fueron ligeramente observados en las películas con el más bajo exceso de silicio. Estos llegaron a ser más evidentes cuando el exceso de silicio se incrementó, en acuerdo con los espectros Raman. Las películas de SRO con bajo exceso de silicio mostraron una fuerte FL. Sin embargo, para mayor exceso de silicio, donde la aglomeración es mayor, la FL prácticamente desapareció. La dependencia de la FL con respecto de la composición y estructura de las películas de SRO ha sido analizada.

Article

Silicon rich oxide Silicon clusters Raman XPS EFTEM Photoluminescence Óxido rico en silicio Aglomerados de silicio Raman XPS EFTEM Fotoluminiscencia CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

MOS-like electroluminisescent devices using silicon-rich oxide obtained by LPCVD

MARIANO ACEVES MIJARES (2009)

silicon Rich Oxide (SRO) is a multiphase material composed by SiO2, Si and SiOx(0<X<2) SRO characteristics include the photo and cathode emission of visible light. Lastly, big efforts have been devoted to obtain a controllable emission using electroluminescence, but keeping its compatibility with silicon Ic's fabrication technology.

Conference proceedings

Silicon rich oxide BIOLOGÍA Y QUÍMICA QUÍMICA QUÍMICA FÍSICA OTRAS

Charge trapping and de-trapping in Si-nanoparticles embedded in silicon oxide films

MARIANO ACEVES MIJARES (2008)

Electrical properties of silicon nanoparticles (Si-np’s) embedded in a silicon oxide matrix were studied using MOS-like structures. Si-np’s were created after silicon rich oxide (SRO) films were thermally annealed at 1100 ºC. Capacitance– voltage (C–V) characteristics showed downward and upward peaks in the accumulation region. Current–voltage (I–V) measurements exhibited current valleys and downward and upward peaks. Current versus time (I–t) measurements were also done at a negative constant gate voltage. A switching behaviour between two current states (ON and OFF) was observed. These effects have been related to the charge trapping and de-trapping of the Si-np’s embedded in the SRO films.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Estudio de las propiedades de conducción del dispositivo Al/Silicio rico en Silicio/Si, y su posible aplicación a celdas de entrada/salida de circuitos integrados

Research on the conduction properties of the Al/Silicon rich oxide/Si, and the possibility of apply it as an input/output cell in integrated circuits

Mariano Aceves Mijares (1996)

En este trabajo se estudia las características de conducción eléctrica de la estructura AL/SRO/Si con la intención de aplicarla en protecciones de entrada y salida de los circuitos integrados. Estudiamos las características corriente contra voltaje y capacitancia contra voltaje (I-V y C-V) de estructuras AL/SRO/Si. El SRO se depositó sobre obleas de silicio mediante la técnica de depósito químico en fase vapor (CVD). El exceso de silicio se controló mediante la razón (Ro) de presiones parciales de los gases reactantes. Se estudiaron estructuras con varios Ro´s, diversas concentraciones de substrato y tipo P y N. A diferencia de estudios realizados hasta la fecha, se hicieron mediciones considerando que el SRO es un material que puede atrapar carga. De esta forma se hicieron curvas I-V y C-V con muestras vírgenes, es decir, como terminaron el proceso de fabricación. También con muestras que fueron sometidas a un esfuerzo de voltaje, es decir, se cargaron las trampas de SRO, e inmediatamente después se hicieron las mediciones I-V y C-V. Se hicieron mediciones de la repuesta en frecuencia del dispositivo AL/SRO/Si. Para esta prueba se usó al dispositivo como parte de un circuito pasa altas. Se midió la ganancia y la fase en función de la frecuencia. Los dispositivos fueron sometidos a picos de voltaje. Para esta tarea se usó el modelo del cuerpo humano. Las estructuras fueron capacitores y pads. Los capacitores fueron de área más grande que el de las estructuras de tipo pad. Los pads a su vez se dividieron en dos tipos: con conexión a compuertas de transistores y sin ésta. Las características de capacitancia contra voltaje muestran sistemáticamente una variación de la capacitancia en inversión, además de los corrimientos característicos del atrapamiento de carga. Esta variación se explicó como un intercambio de carga entre la región de inversión en la superficie de Si y la carga atrapada en el SRO. Se propusieron dos métodos de estimar lo que hemos llamado la densidad de trampas activas. De la capacitancia en acumulación se estimó la constante de permitividad. A partir de esta se obtuvo (en conjunto con otro trabajo) un método para determinar el exceso de silicio en el SRO. De las gráficas I-V se encontraron tres componentes de corriente: la primera se presenta a bajos voltajes y es debida al intercambio de carga entre el SRO y el silicio este componente puede ser de signo contrario a lo esperado. La segunda componente se debe a la corriente de desplazamiento propia de un capacitor, y dependiendo de la rapidez de cambio del voltaje dominará, o no sobre la de intercambio. Por último, el régimen de alta corriente que se alcanza después del voltaje de encendido Von, en este caso la corriente se debe al arrastre de electrones que tunelean a través de las islas de silicio. Este componente está controlada por las características de conducción de SRO. La corriente es altamente dependiente del tipo, concentración del substrato y de la Ro. El SRO al cargarse puede llevar a la superficie de silicio a estados que proveen los portadores necesarios para que se produzca la conducción, es decir, el régimen de alta corriente es dependiente en los portadores que se encuentran en la superficie de Si. Experimentalmente se encontró que el régimen de alta corriente se puede saturar. En el estado de saturación de corriente se pueden soportar campos eléctricos muy grandes. La saturación depende del tipo y concentración del substrato de la Ro. Experimentalmente se encontraron los siguientes modos de funcionamiento del dispositivo: como un capacitor MOS tanto en equilibrio como fuera de este; como un conductor con voltaje de encendido variable; como un capacitor que hace contacto a una unión P-N inducida. El funcionamiento de uno u otro modo depende del tipo y concentración del substrato y de la Ro. Para explicar los diferentes modos de funcionamiento se propone que al dispositivo AL/SRO/Si como un nuevo dispositivo al que hemos llamado Capacitor-N-P. A partir de las características de corriente del Capacitor -N-P se propone un método para calcular el tiempo de vida de recombinación y la concentración del substrato. Del estudio de respuestas a la frecuencia y voltajes de rompimiento del dispositivo se encontró que éste soporta voltajes de rompimiento más alta que el del SiO2. También se demostró experimentalmente que cuando el dispositivo se coloca en un pad de entrada, sí proporciona protección contra picos de voltaje. Sin embargo, se debe de realizar todavía bastante trabajo para optimizar la estructura de forma que se alcancen voltajes más altos y mejor respuestas a la frecuencia.

In this work we study the conduction properties of the AI/SRO/Si structure aiming at determining if it is possible to use the structure as an input/output pro­tection cell. It was studied the I-V and C-V characteristics of the AI/SRO/Si struc­ture. The SRO was deposited on silicon wafers by CVD, and the excess of silicon was controlled by the ratio Ro of the partial pressure of the reactant gases. Differ­ent Ro's, and different substrate's type and concentrations, were used. In this work a non-traditional approach was used to study these devices. The SRO is a memory material, that is, it traps charge. To see the effects of the trapped charge on the I-V and C-V characteristics, the samples were studied both as they were at the conclusion of fabrication process and after voltage stress was applied to charge the SRO before the current and capacitance were measured. The frequency response of the device as a part of an RC circuit was also measured. That is, the gain and the phase as a function of the frequency was measured. Using the Human Body Model, the device was tested against voltage peaks. Two types of devices were studied: Pads that were formed by AI/SRO/Si and were connected to the Gate of transistors, and unconnected capacitors also made with AI/SRO/Si structures with two different areas. We found, experimentally, that the C-V curves show, besides the normal flat band shifting due to trapped charge, a variation of the inversion capacitance as an effect of the trapped charge. This effect was explained as the exchange of charge between the surface and the SRO. From these experimental results, two methods were proposed to estimated the density of what we call the active traps. The capacitance in accumulation was used to calculate the SRO permittiv­ity. Using the permittivity, a method to estimate the SRO excess of silicon was proposed (this was the result of another joint project). It is important to mention that a big variation was observed for the experimental results related to AI/SRO/Si. So to have accurate results it is necessary to measure a large quantity of samples, in such a way that the average really represents the population measured. For the l-V curves, three current components were found. They are the ex­change component due to the exchange of charge between the silicon surface and the SRO charge; the normal displacement component; and the high regime cur­rent. The first two are observed at low voltages, and depending on the rate of change of the voltage ramp, one or another will dominate. The third one is present after a tum on voltage Von is reached, and is dominated by tunneling trough the silicon islands in the SRO. lt was also found that the surface charge will provide the electrons to sus­tain the current, but the charge trapped in the SRO will affect the surface charge. So the current is altered by the trapped charge in the SRO. Experimentally, it was observed that the high regime current can saturate. The saturation it related to the Ro and the characteristics of the substrate. The following characteristics of the device's behavior were verified experi­mentally: lt behaves as an MOS capacitor in and out of equilibrium, also as a con­ductor with variable Von, and as a device that makes contact to an induced P-N junction. The behavior depends on the SRO Ro and the type and concentration of the substrate. As a device that makes contact to an induced P-N junction, we pro­pose a method to estimate the generation life-time and the concentration of the substrate. Due to the different behavior of the AI/SRO/Si, the structure is proposed as a new device that we call the apacitor-N-P. It behaves as an MOS capacitor in and off equilibrium, as a conductor with a variable VON and as a capacitor that has a contact to an induced P-N junction. Also as an experimental result, it was found that the breakdown voltage of the Capacitor-N-P is higher than the breakdown voltage of the gate oxide, and that the AI/SRO/Si structure positively protects the gate oxide from ESD. However, more work has to be done to increase the breakdown voltage and to improve the frequency response.

Doctoral thesis

Estructura Al/SRO/Si, Obleas de silicio INGENIERÍA Y TECNOLOGÍA CIENCIAS TECNOLÓGICAS TECNOLOGÍA DE LAS TELECOMUNICACIONES

The deposition and control of self assembled silicon nano islands on crystalline silicon

ZHENRUI YU MARIANO ACEVES MIJARES (2008)

The formation of nano sized Si structures during the annealing of silicon rich oxide (SRO) films was investigated. These films were synthesized by low pressure chemical vapor deposition (LPCVD) and used as precursors, a post-deposition thermal annealing leads to the formation of Si nano crystals in the SiO2 matrix and Si nano islands (Si nI) at c-Si/SRO interface. The influences of the excess Si concentration, the incorporation of N in the SRO precursors, and the presence of a Si concentration gradient on the Si nI formation were studied. Additionally the influence of pre-deposition substrate surface treatments on the island formation was investigated. Therefore, the substrate surface was mechanical scratched, producing high density of net-like scratches on the surface. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the synthesized nano islands. Results show that above mentioned parameters have significant influences on the Si nIs. High density nanosized Si islands can epitaxially grow from the c-Si substrate. The reported method is very simple and completely compatible with Si integrated circuit technology.

Article

Si nano islands Self assembly Epitaxial growth Silicon-rich oxide Photoluminescence CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Structural characteristics of a multilayer of silicon rich oxide (SRO) with high Si content prepared by LPCVD

ZHENRUI YU MARIANO ACEVES MIJARES (2009)

Single layer films and a multilayer structure of SRO (Silicon Rich Oxide) have been prepared by LPCVD (Low Pressure Chemical Vapour Deposition) and characterized by FTIR, SIMS, XPS, TEM and AFM measurements. The stacked structure is composed of alternating layers of SRO with high Si content and SRO with low Si content. The layered structure is confirmed by SIMS and TEM measurements. The composition of the materials is discussed. Besides Si nanocrystals, the existence of agglomerates of silicon oxide with structure close to fused silica and the existence of oxynitrides is evidenced in the films with high Si content.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

OPTICAL CHARACTERIZATION OF SILICON RICH OXIDE FILMS

ALFREDO MORALES SANCHEZ MARIANO ACEVES MIJARES (2006)

SRO films obtained by LPCVD have shown a strong visible photoluminescence (PL) after annealed

at 1100°C. Since these materials are robust and efficient, they have shown having potential applications in

optoelectronics. Structural and optical studies on these materials were carried out. The results suggest that the

emission can be related to defects surrounding the Silicon c1usters and nanocrystals.

Conference proceedings

Silicon Rich Oxide BIOLOGÍA Y QUÍMICA QUÍMICA QUÍMICA FÍSICA OTRAS