Structure Of Silicon Oxide Research Articles

Electrical properties of metal–oxide–silicon structures with LaAlO3 as gate oxide

In this paper, electrical investigations performed on complex metal–oxide–semiconductor (MOS) structures with amorphous LaAlO3 deposited as gate oxide on a rapid thermal processed SiO2 buffer layer are presented. Current–voltage (I–V) measurements at different temperatures and high frequency room-temperature capacitance–voltage (C–V) measurements indicate the presence of a non-equilibrium state in p-type Si (100) substrate under reverse polarization of the structure. The asymmetry in I–V characteristics is opposite to the expected one for the high-κ/interfacial layer stack behavior. Different indications for the non-equilibrium MOS state are inferred from the experimental data, and the extraction of MOS physical parameters by using the classical C–V method is shown to be unreliable. For small and large applied forward voltages defect-related charge transport and tunneling currents dominate, respectively.

Self-aligned mechanical attachment of carbon nanotubes to silicon dioxide structures by selective silicon dioxide chemical-vapor deposition

A self-aligned thin-film deposition technique was developed to mechanically attach carbon nanotubes to surfaces for the fabrication of structurally robust nanotube-based nanomechanical devices. Single-walled carbon nanotubes were grown by thermal chemical-vapor deposition (CVD) across 150-nm-wide SiO2 trenches. The nanotubes were mechanically attached to the trench tops by selective silicon tetraacetate-based SiO2 CVD. No film was deposited on the nanotubes where they were suspended across the trenches.

Relationships Between Gas-Phase Film Deposition, Properties and Structures of Thin SiO2 and BPSG Films

This paper is devoted to the analysis of relationships between chemical vapor deposition (CVD) features and silicon dioxide and silicate glass film properties and structures. Deposition processes have been quantitatively characterized using an empirical parameter the effective constant of the deposition rate, The observed CVD kinetic features are explained by using a simplified multiroute and multistep kinetic scheme of the silicon-based thin-film gas-phase deposition processes, and a classification of the studied processes. The basic physical and chemical properties of thin glass films are explained in terms of the glass structural disordering, which defines the oxide film density, wet etch rate, shrinkage, and intensity of film-moisture interaction. The structure disordering depends in reverse order with respect to It is shown that the borophosphosilicate glass (BPSG) film structure and properties are affected by the quantity of boron atoms with a threefold coordination with respect to the oxygen atoms. The boron coordination in BPSG film tends to change from threefold to fourfold coordination along with the increase of phosphorus to boron ratio in the film. The best BPSG structural ordering and the best film properties correspond to the boron concentrations defined by an empirical equation The respective glass film structure is supposed to consist of and tetrahedra. © 2003 The Electrochemical Society. All rights reserved.

Investigation of the Near-Surface Silicon Layers in SiO2–Si Structures

The regularities of formation of the near-surface silicon layers in the SiO2–Si structures are established using currently available investigation methods. The structural and impurity compositions of the layers are determined. The results can be used for studying the dynamics of postirradiation boosting charge storage in the silicon–silicon oxide structures and photoluminescent properties of silicon with a developed surface.

Low field stress induced double donor defect in metal oxide silicon structures

A variable frequency light pumping (VFLP) effect is presented which describes the energetic induced photon generation mechanism in the stress metal oxide silicon (MOS) system. It is shown that the VFLP occurs, when both the tunneling electrons and the induced photons are coherent. Both the tunneling electrons and the induced photons in the MOS system from the light pumping can gain the energy required to break the Si–O bonds and to excite interstitial oxygen and to lead then to create the intrinsic point defects in the oxide, and the surface silicon, and at the interfaces. Based on the hybrid sixfold ring of the continuous random network model for SiO 2, the intrinsic point defect generation under low field and its basic properties have been studied.

Lithography-free fabrication of sub-100 nm structures by self-aligned plasma etching of silicon dioxide layers and silicon

A general scheme for the fabrication of silicon and silicon dioxide structures with lateral dimensions of less than 100 nm is introduced that avoids high-resolution lithography processes. For the self-aligned formation of extreme small openings in silicon dioxide layers at sharpened surface structures the angle dependent etch rate distribution of silicon dioxide against plasma etching with a fluorocarbon gas (CHF3) was exploited. Subsequent anisotropic plasma etching of the silicon substrate material through the perforated silicon dioxide masking layer results in high aspect ratio trenches of approximately the same lateral dimensions. The latter can be reduced and precisely adjusted between 0 and 200 nm by thermal oxidation of the silicon structures owing to the volume expansion of silicon during oxidation.

LATERALLY ISOLATED POLYSILICON BEAM PROCESS

This paper describes a process technology to make MEMS devices with laterally integrated polysilicon beam as the structural material instead of single crystal silicon for sensors/ actuators. The process consists of fabricating deep silicon trenches, which are then seamlessly filled with the layers of thermal oxide and polysilicon. The polysilicon on the surface is etched back, leaving behind the polysilicon only inside the trenches. The beams are then released by isotropically etching away the silicon surrounding the polysilicon/ silicon oxide structure. This results in free standing polysilicon beams, which form the MEMS structures. The thermal oxide surrounding the polysilicon can be removed by wet HF etch or by isotropic plasma etch. This process can serve as a general platform for realising various types of high aspect ratio MEMS devices. The various stages of the process development, in realising a low stress polysilicon beams and electrical isolation structures are described in the paper.

The protective effect of thin amorphous hydrogenated carbon a-C:H films during metallisation of metal–carbon–oxide–silicon (MCOS) diodes

Capacitance–voltage (C–V) characteristics of the as-grown metal(Al)–carbon–oxide(SiO2)–semiconductor(Si) structures are examined at the frequency of 1 MHz and compared with the C–V characteristics of the conventional metal(Al)–SiO2–Si (MOS) structures. The density of the oxide charge Qo/q is extracted from the experimental results. Qo/q was found to be 1×1012cm−2 for the MOS structures and 7×1011cm−2 for the metal–carbon–oxide–silicon structures. This difference can be attributed to the presence of the carbon layer which acts as a protective coating during metallisation of the wafers.

High-Permittivity-Insulator EEPROM Cell Using Al2O3 or ZrO2

A theoretical investigation is carried out into memory cells based on a polysilicon–oxide–nitride–oxide–silicon structure in which a high-permittivity dielectric is used instead of SiO2 as the gate insulator. The dielectric is taken to be Al2O3 or ZrO2. Write/erase (W/E) cycles are simulated numerically. It is shown for the first time that changing to a high-permittivity insulator reduces the unwanted carrier injection from the gate region and allows one to employ lower and/or shorter W/E pulses; specifically, the W/E time can be decreased from 1 ms to 10 μs. It is concluded that high-permittivity insulators might be useful in carrier-trapping EEPROMs and RAMs.

Impact of the band–band tunneling in silicon on electrical characteristics of Al/SiO 2/p +-Si structures with the sub-3 nm oxide under positive bias

Measurements of current–voltage and capacitance–voltage characteristics were performed for metal––tunnel oxide––silicon structures on p +-silicon wafers doped to 2×10 18–2×10 19 cm −3. Obtained results show at least two striking points. First, the forward (metal “+”) current is amazingly high and comparable in value with the reverse-bias current (metal “−”). Second, capacitance–voltage curves exhibit a distortion in the depletion regime and a hump indicating the onset of inversion. The hump is accentuated with decreasing frequency. These features are suggested to appear due to a tunneling of the valence band electrons within the forbidden gap of silicon and further into metal. Eventually, such electrons may enter the conduction band of silicon where a fraction of them can be temporarily captured at the interface and impurity defects forming thereby an inversion layer.

Band alignments in metal–oxide–silicon structures with atomic-layer deposited Al2O3 and ZrO2

The energy barrier height Φ for electrons at the interfaces of various metals (Mg,Al,Ni,Cu,Au) with nanometer-thin Al2O3 and ZrO2 layers grown on (100)Si by atomic layer deposition has been directly measured using internal photoemission of electrons into the insulator. The behavior of the metal/Al2O3 contacts with increasing metal electronegativity XM resembles that of the metal/SiO2 interfaces with ideality factor dΦ/dXM≈1. The metal/ZrO2 contacts exhibit a less ideal behavior with dΦ/dXM≈0.75. The metal–silicon work function differences in structures with Al2O3 and ZrO2 insulators appear to be considerably larger than in the structures with thermally grown SiO2, suggesting the presence of a negative dipole layer at the metal/deposited oxide interface.

Band alignment at the interfaces of Al2O3 and ZrO2-based insulators with metals and Si

Internal photoemission of electrons was used to determine the band alignment in metal (Mg, Al, Ni, Cu, Au)-oxide-silicon structures with Al2O3- and ZrO2-based insulators. For Al2O3- and ZrO2 layers grown on Si by atomic layer deposition the barrier height between the Si valence band and the oxide conduction band was found to be 3.25 and 3.1 eV, respectively. Thermal oxidation of the Si/oxide stacks results in a barrier height increase to ≈4 eV for both cases due to formation of a silicate interlayer. However, there is a significant sub-threshold electron emission both from silicon and metals, indicating a high density of states in the band gap of the insulators. These states largely determine the electron transport across metal oxides and may also account for a significant dipole component of the potential barrier at the metal/ZrO2 and metal/Al2O3 interfaces.

Increasing the Strength of Refractory Granules by Applying Protective Silicate Coating

The fundamental possibility of increasing the strength of refractory granules by 1.5 – 2 times by applying coatings based on organosilicon compounds at elevated temperatures is demonstrated. It is established that the increase in strength is to a large extent achieved by producing coating with a finely crystalline structure of sodium silicate, silicon oxide, or glass; the strength of granules increases as the coating thickness increases; at the same time, the hydrophoby of granules becomes higher.

Dislocation Locking by Intrinsic Point Defects in Silicon

ABSTRACTDislocation pileups with abnormally weak inter-dislocation repulsion have been observed in locally oxidized silicon structures. To verify if this could be attributed to elastic interaction of dislocations with intrinsic point defects, distributions of self-interstitials in dislocation stress fields have been studied using theoretical calculations and computer simulations. According to the obtained results, self-interstitials can form atmospheres about dislocations causing dislocation stress reduction and therefore screening of dislocations from interaction with external stresses. This may represent an additional mechanism of dislocation locking in silicon alternative to oxygen pinning.

Correlation between the gate bias dependence of the probability of anode hole injection and breakdown in thin silicon dioxide films

Hole injection from the anode in thin silicon dioxide (SiO2) films in n+-polycrystalline silicon gate–oxide–silicon structures has been theoretically investigated during high-field Fowler–Nordheim electron injection from both substrate (positive gate bias) and gate (negative gate bias). Theoretical results of the gate bias dependence of the probability of anode hole injection per injected electron αh as a function of electric field or injection current density are shown to be directly correlated to experimentally observed polarity dependence of destructive breakdown in thin SiO2 films.

Electrical characterization of Pb centers in (100)Si–SiO2 structures: The influence of surface potential on passivation during post metallization anneal

Capacitance–voltage measurements were made on Cr-gated metal–oxide–silicon structures with ultrathin (∼30 Å) thermal oxides. Using an empirical model, activation energies for the passivation of the Pb center were determined and found to be dependent on the charge state of the defect. Depassivation was found to occur at positive gate biases.

Electroluminescence at Si band gap energy based on metal–oxide–silicon structures

Room-temperature electroluminescence corresponding to Si band gap energy from metal–oxide–semiconductor structures on both p-type and n-type Si is observed. With very thin oxide grown by rapid thermal oxidation, the metal–oxide–semiconductor structures behave like light emitting diodes. Luminescence is observed under forward bias even with a current density as low as 0.67 A/cm2. The physical reason for the electroluminescence is discussed and attributed to the localized wave function that leads to the spread of momentum. As a result, the spread momentum causes the electron–hole radiative recombination to occur relatively easily.

Novel process integration for reduction of subquarter-micron contact resistance

In this article, etching of subquarter-micron contact holes with a film structure of silicon dioxide (SiO2)/silicon nitride (Si3N4)/silicide (TiSix) in dual-frequency capacitively coupled plasmas is investigated. The etch process scheme here uses a highly selective chemistry to remove SiO2 film first, then the process switches to another chemistry with high etch selectivity of Si3N4-to-TiSix. The author found that the polymer film deposited inside contact holes during SiO2 etching severely degraded the selectivity of Si3N4-to-TiSix. This can cause open or high contact resistance. Different process integration schemes with the goal of increasing the etch selectivity of Si3N4-to-TiSix were initiated and developed. Electrical parametric data of contact chain resistance will be presented.

Study of the SiO2-to-Si3N4 etch selectivity mechanism in the presence of polymers in fluorocarbon plasmas

The polymerization effects in 27/2 MHz capacitively coupled fluorocarbon plasmas during high selectively subquarter-micron contact hole etching, with the film structure of silicon dioxide (SiO2)/silicon nitride (Si3N4)/silicide (TiSix), are investigated. A high etch selectivity chemistry is first used to remove SiO2, then Si3N4 is removed with another chemistry with high selectivity of Si3N4-to-TiSix. To obtain good etch selectivity of SiO2-to-Si3N4, fluorocarbon plasmas containing a high carbon to fluorine (C/F) ratio is usually employed. Polymerization readily occurs in chemistries having a high C/F ratio. These unsaturated polymers are reactive and stick easily to contact hole sidewalls and bottoms, creating thick polymer films. While the chemistry used to etch Si3N4 has shown acceptable selectivity as measured on a patterned singular film, fluorine from the polymer will severely degrade the etch selectivity of Si3N4-to-TiSix on fully processed wafers. Process developments started with a design of experiment on real production wafers in order to understand the roles of fluorocarbon polymer during the Si3N4 etching. Scanning electron microscope analysis of this polymer film and its effects are included as well as the electrical parametric testing data of contact resistances. Different polymer removing methods to restore the Si3N4-to-TiSix etch selectivity back were initiated and will be briefly discussed. While this investigation pertains to contact etch, this phenomenologically observed result could be applied to any highly selective etching of oxide versus nitride.

Characterization of conductive oxides on silicon using non-contact surface charge profiling

The density of charge associated with the silicon-oxide structure remains a figure of merit for the process as well as an indicator of the eventual MOS device performance. As the effective oxide thickness drops below 2 nm significant currents limit the effectiveness of oxide charge determination from CV measurements. One potential solution is the SPV-based SCP (Surface Charge Profiler) method which allows measurement of total oxide/interfacial charge without making a contact to the oxide. In this paper the effectiveness of the SCP in measuring charges in ultra-thin thermal SiO 2 and conductive Ta 2O 5 films is evaluated.