Low temperature Si/Si wafer direct bonding using a plasma activated method

Manufacturing and integration of micro-electro-mechanical systems （MEMS） devices and integrated circuits （ICs） by wafer bonding often generate problems caused by thermal properties of materials. This paper presents a low temperature wafer direct bonding process assisted by 02 plasma. Silicon wafers were treated with wet chemical cleaning and subsequently activated by 02 plasma in the etch element of a sputtering system. Then, two wafers were brought into contact in the bonder followed by annealing in N2 atmosphere for several hours. An infrared imaging system was used to detect bonding defects and a razor blade test was carried out to determine surface energy. The bonding yield reaches 90%--95% and the achieved surface energy is 1.76 J/m2 when the bonded wafers are annealed at 350 ~C in N2 atmosphere for 2 h. Void formation was systematically observed and eli-mination methods were proposed. The size and density of voids greatly depend on the annealing temperature. Short O2 plasma treatment for 60 s can alleviate void formation and enhance surface energy. A pulling test reveals that the bonding strength is more than 11.0 MPa. This low temperature wafer direct bonding process provides an efficient and reliable method for 3D integration, system on chip, and MEMS packaging.

EFFECT OF HYDROGEN BONDING ON DIRECTION OF PHOTOISOMERIZATION OF RETINOIDS:THE ORIGIN OF THE SOLVENT POLARITY EFFECT.

Studies of direction of photoisomerization of retinal,retinonitrile,a- retinonitrile and a trienenitrile analog in different solvents with varying wave- lengths of excitation and reaction temperature led to the conclusion that the well known solvent dependent photochemistry of retinoids is due to selective excitation of the hydrogen bonded species.

RECENT DEVELOPMENTS OF DIRECT BONDED COPPER(DBC)SUBSTRATES FOR POWER MODULES

DBC substrates are the standard circuit boardsfor power modules. Using the DBC technologythick copper foils (0.125mm - 0.Tmm) arecladded to Alumina or Aluminum Nitride,The strong adhesion of the copper to ceramicbond reduces the thermal expansion coefficientin horizontal direction only slightly above theTEC of the ceramic itself. This allows directsilicon attach of large dies without using TECcontrolling layers.As DBC technology is using copper foils,integralleads overhanging the ceramic can be realized...

Fabrication of 1.55μm Si-Based Resonant Cavity Enhanced Photodetectors

A novel bonding method using silicate gel as bonding medium is developed.High reflective SiO 2/Si mirrors deposited on silicon substrates by e-beam deposition are bonded to the active layers at a low temperature of 350℃ without any special treatment on bonding surfaces.The reflectivities of the mirrors can be as high as 99 9%.A Si-based narrow band response InGaAs photodetector is successfully fabricated,with a quantum efficiency of 22 6% at the peak wavelength of 1 54μm,and a full width at half maximum of about 27nm.This method has a great potential for industry processes.

All-SiC Fiber-Optic Sensor Based on Direct Wafer Bonding for High Temperature Pressure Sensing

This paper presents an all-SiC fiber-optic Fabry-Perot(FP)pressure sensor based on the hydrophilic direct bonding technology for the applications in the harsh environment.The operating principle,fabrication,interface characteristics,and pressure response test of the proposed all-SiC pressure sensor are discussed.The FP cavity is formed by hermetically direct bonding of two-layer SiC wafers,including a thinned SiC diaphragm and a SiC wafer with an etched cavity.White light interference is used for the detection and demodulation of the sensor pressure signals.Experimental results demonstrate the sensing capabilities for the pressure range up to 800 kPa.The all-SiC structure without any intermediate layer can avoid the sensor failure caused by the thermal expansion coefficient mismatch and therefore has a great potential for pressure measurement in high temperature environments.

Researching the silicon direct wafer bonding with interfacial SiO_2 layer

A silicon wafer direct bonding with a thin SiO2 layer at the interface was investigated. An atomic force microscope （AFM） was employed to characterize the surface roughness and a shearing test was carried out to evaluate the bonding strength. Experiments were performed to analyze the relations of surface roughness and bonding strength with the thickness of SiO2 which was grown by thermal oxidation and plasma enhanced chemical vapor deposition （PECVD） respectively. The bonding strength can reach up to 18 MPa for thermal oxidation and 8 MPa for PECVD after a 2-h 400℃ annealing. Results indicate that the bonding strength is negatively correlated to the thickness of SiO2 at the interface, which is important in designing the MEMS-based devices and other devices built with wafer direct bonding.

Sintering Complexity of Magnesia-chrome Refractories

Magnesia-chrome refractories are appropriate to work under cyclic temperatures or atmospheric conditions because some oxides of chrome ore readily release oxygen(are reduced)upon heating and pick up oxygen(are oxidized)upon cooling or upon changing the atmosphere.They have been ideal lining materials for RH degassers for many years,despite challenging of Cr^(6+) disposal issue after using.The varieties of magnesia-chrome refractories depend on their raw materials and burning temperatures,which could be well demonstrated by their microstructures.But Indian chrome concentrate cannot be directly used in the production of magnesia-chrome bricks because of reducing sintering density.Silicate bonded magnesia-chrome bricks are produced with low purity magnesia after burning at relatively lower temperatures,resulting in liquid film forming as silicate bond around chrome ore particles.Direct bonded and rebonded fused-grains magnesia-chrome refractories are made of high purity magnesia or fused magnesia-chrome grains,forming euhedral and intergranular secondary chromite spinels as the main feature.The amount of secondary spinel increases with the rising burning temperature,leading to increasing hot modulus of rupture and overall hot properties as well.It is important to burn magnesia-chrome bricks under weakly reducing atmosphere.The oxygen content of burning atmosphere from 800℃ to 1650℃ would better controlled below 0.5%to increase the burnt strength and to avoid inner cracks and loose bonding of magnesia-chrome bricks,while the atmosphere contains 3%-6%O_(2) under most economical firing condition.

Fabrication of Si_(3)N_(4)/Cu direct-bonded heterogeneous interface assisted by laser irradiation

Joining of ceramic and metal is a key component in microelectronic device manufacturing,in which the integrity of bonded interface is critical in the performance and stability of the devices.Current methods with a problem of thick transition layer at the interface impeded heat flow,which degraded device service life seriously.Herein,we propose a laser-assisted bonding approach to join ceramic to metal directly without any intermediate material.By focusing the laser on the surface of β-Si_(3)N_(4) ceramic,the Si microcrystalline layer with stacked α-Si_(3)N_(4) nanocrystals was prepared first.The face-centered cubic(fcc)Si and hexagonal close-packed(hcp)β-Si_(3)N_(4) substrate take the coherent orientation relations of[001]_(fcc)║[0001]_(hcp) and(220)_(fcc)║(10■0)_(hcp).Then,the defect-free Si_(3)N_(4)/Cu bonded interface obtained by the reaction of the formed Si and Cu at elevated temperature in the 805-900℃range for 30 min demonstrated a strong and stable joining of ceramic to metal.The introduction of the laser provides a novel approach to join ceramics to metals,and the ceramic/metal component is expected to be a new configuration for package substrate in high-power device applications.

Direct C-H Bond Activation of Benzoxazole and Benzothiazole with Aryl Bromides Catalyzed by Palladium（Ⅱ）-N-heterocyclic Carbene Complexes

Herein, we report that a series of novel palladium（II）-NHC complexes （NHC=N-heterocyclic carbene） were synthesized. The structures of all novel complexes were characterized by ^1H NMR, ^13C NMR, FT-IR spectroscopy and elemental analysis techniques. These palladium（ll）-NHC complexes were tested as efficient catalysts in the direct C-H bond activation of benzoxazole and benzothiazole with aryl bromides in the presence of 1 mol% catalyst loading at 150 ℃ for 4 h. Under the given conditions, various aryl bromides were successfully applied as the arylating reagents to achieve the 2-arylbenzoxazoles and 2-arylbenzothiazoles in acceptable to high yields.

Direct C–H amination for indole synthesis from N-Ts-2-Styrylaniline derivatives catalyzed by copper salt

A direct C–H amination reaction of N-Ts-2-Styrylaniline derivatives to realize the synthesis of indole derivatives was developed in the presence of copper salt. A variety of N-Ts-2-Styrylaniline derivatives were transformed into the corresponding indole products in good to excellent yield under mild conditions with the oxidation of potassium persulfate.

Interface control for pure ultraviolet electroluminescence from nano-ZnO-based heterojunction devices

Realization of pure and stable ultraviolet electroluminescence(UV EL) of ZnO light-emitting diode(LED)is still a challenging issue, due to complicated defects of intrinsic ZnO and the corresponding device interfaces. In this paper, we demonstrated a simple & feasible method to fabricate n-ZnO/AlN/p-GaN heterojunctions light-emitting devices. First, the vertically aligned ZnO nanorods(NRs) have been prepared as high quality active layer, and the nanostructured heterojunction LED arrays were constructed by directly bonding ZnO NRs onto AlN-coated p-GaN wafer. By optimizing the AlN layer thickness to be 20 nm, a strong and pure ultraviolet emission located at 387 nm can be observed. The energy band alignment of n-ZnO/AlN(20 nm)/p-Ga N heterojunction LED has been studied by using X-ray photoelectron spectroscopy(XPS), the valence band offset between AlN and GaN was calculated to be 0.34 eV. On the other side, the conduction band offset(as large as 3.28 eV) between Al N and ZnO can block the flow of electrons from ZnO top-GaN. Thus, electron-hole recombination takes place in the ZnO layer, and a pure UV EL could be observed. Our results provide a significant approach toward future of pure ultraviolet optoelectronic LEDs.

Design and Fabrication of Functional Hydrogels through Interfacial Engineering

Hydrogels have drawn considerable attention in the past two decades due to their excellent biocompatibility and multi-stimuli responsiveness. They have a wide range of applications in the fields related to tissue engineering, sensors and biomedicine. Their applications are strongly influenced by the surface properties of hydrogels and the interfacial interactions between hydrogels and other substrates. In particular, the surface wettability and adhesion of hydrogels decide their applications as drug carriers and wound dressing materials. Nevertheless, there is a lack of systematic discussion on the surface functionalization strategies of hydrogels. Therefore, this review aims at summarizing the strategies of functionalizing the surfaces of hydrogels and bonding hydrogels with other solid substrates. It also explores the challenges and future perspectives of interfacial engineering of hydrogels.