摘要:

We present a review on the state of knowledge of surface phenomena behind adhesion in surface micromechanical structures. After introducing the problem of release-related and in-use adhesion, a theoretical framework for understanding the various surface forces that cause strong adhesion of micromechanical structures is presented. Various approaches are described for reducing the work of adhesion. These include surface roughening and chemical modification of polycrystalline silicon surfaces. The constraints that fabrication processes such as release, drying, assembly, and packaging place on surface treatments are described in general. Finally, we briefly outline some of the important scientific and technological issues in adhesion and friction phenomena in micromechanical structures that remain to be clarified.

ISSN:0734-211X    

DOI:10.1116/1.589247

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Local-density approximation calculations have been used to study the electronic structure of the Al14/n-fold SiO2ring/Si15cluster system forn=3, 4, and 6. The sixfold ring placed between aluminum and silicon has an insulator character with the fundamental band gap of 4 eV and the energetic barrier of 3.5 eV. The fourfold ring has a band gap of 2 eV, however its insulator properties are doubtful because of the very small distance between the Fermi level and the first unoccupied state (0.2 eV). The threefold SiO2ring has not a fundamental gap at all. Considering the Al14/n-fold SiO2ring /Si15H̄18system as a model of the metal-oxide-semiconductor device, we can predict that the thin silica film (d≈7 Å) can be used as an insulator layer. However, if the thickness is less than 5 Å, the insulator properties of silica disappear.

ISSN:0734-211X    

DOI:10.1116/1.589248

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The nanoscale restructuring process induced by the tunneling current was studied on a TiO2(110)1×2 reconstructed surface. The threshold parameters of 0.1 nA and +3.5 V were found. Below the critical voltage (even in the case of two orders of magnitude higher tunneling current), no change of the original surface structure appears. Above the threshold bias, the evolution of the process depends on the current: (i) for lower current (0.1–1 nA), only an outrising feature (average diameter of 3 nm, corrugation 1 nm) appears and the process saturates in the time scale of 10–20 s; (ii) for the higher currents 1–10 nA, the structural transformation begins with an increasing hump formation followed by a developing of a craterlike hollow structure (etching process). According to the results of the spectroscopic measurements, it is very likely that the created humps are composed of more reduced stoichiometric oxide phase. The facts that the presented process starts only above a threshold bias and the intensity of the tunneling current has great influence on the volume of the created structure strongly suggest a mechanism where a resonant electron excitation induced surface decomposition plays an important role.

ISSN:0734-211X    

DOI:10.1116/1.589249

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Tip collection of luminescence is advantageous in low-temperature tunneling-electron luminescence microscopy because it can improve spatial resolution, luminescence collection yield, and thermal isolation. We have developed a novel conductive transparent (CT) tip that injects tunneling electrons into a sample and simultaneously collects tunneling-electron luminescence (TL). Essential features of the CT tip are a multimode fiber with a flame-shape tapered to a point, a gold-on-In2O3double layer that serves as an optically transparent electrode to the apex, and a thick coaxial metal plating on the optical-fiber shaft that reinforces the CT tip allowing it to be firmly screwed onto a holder. The CT tip can easily be changed in a vacuum chamber like an all-metal tip. Using a TL microscope with the CT tip, TL spectra and TL images were successfully obtained on the cross section of GaAs(50 nm)/AlAs(50 nm) multiple quantum wells at 10 K.

ISSN:0734-211X    

DOI:10.1116/1.589250

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Scanning probe lithography has been used for the first time to grow silicon nitride nanostructures on silicon substrates. The lithography was performed by an atomic force microscope (AFM) placed in an evacuated chamber with a partial pressure of annhydrous ammonia. The silicon nitride nanostructures were grown by negatively biasing the silicon tip with respect to the sample. By changing the environment of the AFM, both silicon oxide and silicon nitride can be grown and subsequently processed.

ISSN:0734-211X    

DOI:10.1116/1.589251

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Selective adsorption of disilane, Si2H6, on the Si(111) surface partially terminated by Ga atoms has been investigated by scanning tunneling microscopy in the temperature range from 390 to 480 °C. When the substrate temperature is below 420 °C, disilane is dissociatively adsorbed in Si(111)7×7 regions, whereas it is hardly adsorbed in Si(111)∛×∛-Ga regions due to Ga termination of Si dangling bonds. The migration of precursors dissociated from disilane is not significant on the Si(111)7×7 surface below 420 °C. Consequently, precursors containing Si atoms are not supplied to Ga-terminated regions by the disilane dissociation in the Ga-terminated regions or the surface migration from 7×7 regions. Above 420 °C, precursors dissociated from disilane migrate from Si(111)7×7 regions to Ga-terminated regions, resulting in a two-dimensional island growth of Si in Ga-terminated regions.

ISSN:0734-211X    

DOI:10.1116/1.589252

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The monolayer deposition of nanoscale colloidal particles (Au citrate sols) was demonstrated by employing an aminofunctional silane [3-(2-Aminoethlyamino) propyltrimethoxysilane] as a coupling agent. The compatibility of this colloidal Au deposition method with conventional electron beam lithography techniques was examined, and the two-dimensional patterning of the Au colloidal monolayer was demonstrated. Using this fabrication method, a proposal for a single electron device structure based on nanoscale (2 nm diameter) gold colloidal particles was made.

ISSN:0734-211X    

DOI:10.1116/1.589253

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

An asymmetric double-recessed gate process achieved through a single lithography step and a combination of wet and dry etching techniques is presented. The double-recessed gate process is beneficial in the fabrication of InGaAs/AlGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) because breakdown voltage is enhanced while surface effects on the drain side of the gate are minimized. In contrast to conventional processes that require two lithography steps, the current process requires only a single lithography step for the asymmetric placement of aT-gate in a wide recess trench. The process utilizes a four-layer resist of polymethylmethacrylate (PMMA) and P(MMA-MAA) exposed by electron beam lithography. Upon development of the resist, a wet selective etch (citric acid:H2O2)is used to define the wide recess trench and then a dry selective etch(SiCl4/SiF4)is used to recess a narrow trench (within the wide recess trench) in which the gate foot rests. This technique can achieve gate lengths of0.15μm and drain-side wide recess dimensions from 0.15 to0.55μm while the source-side recess width is kept at or below0.15 μm. Device results show improved breakdown voltages and output conductance with only slight reduction in transconductance and drain current for the PHEMTs fabricated using the technique as compared to PHEMTs fabricated using a trilayerT-gate process.

ISSN:0734-211X    

DOI:10.1116/1.589254

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The peel strength of a copper (Cu) thin film deposited on a polyimide (PI) substrate deteriorates after heat treatment at 150 °C in air. The deterioration involves Cu2O microparticles (10–100 nm) penetrating the PI substrate, both the substrate and film being oxidized. To prevent this penetration and oxidation, we introduced an interfacial layer (vanadium, titanium, or cobalt) at the interface between the Cu thin film and PI substrate. Both titanium and cobalt interfacial layers were effective as barriers against the penetration of Cu2O particles. The quality of the interfacial layers (e.g., quantity of dislocations) influenced their effectiveness. By annealing the cobalt interfacial layers at 280 °C for 1 h in a vacuum before sputter deposition of a Cu thin film, we succeeded in keeping the peel strength between the Cu thin film and the PI substrate above 0.1 N/m even after heat treatment of the laminate at 150 °C for three days.

ISSN:0734-211X    

DOI:10.1116/1.589255

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A subhalf-micron gap filling process for copper (Cu) films was developed by using an electron cyclotron resonance (ECR) plasma sputtering method. The achieved Cu film had a resistivity as low as that of bulk Cu and an excellent, void-free filling property in a 0.5-μm-wide trench. This result is because the distance between the target and wafer was longer than conventional sputtering; the plasma could be generated at low pressure (<1 mTorr); and the ECR plasma sputtering method generates a highly anisotropic particle flux of Cu. Then, a reflow process of the Cu films deposited by using an ECR plasma sputtering method was tried. The reflow phenomenon was observed and the filling property was improved; void-free filling in a 0.4-μm-wide trench was achieved. Moreover, a Cu interconnection of 0.5 μm linewidth was fabricated by a chemical mechanical polishing method without dishing, scratching, and erosion.

ISSN:0734-211X    

DOI:10.1116/1.589256

出版商:American Vacuum Society    

年代:1997

数据来源: AIP