欧姆接触金属退火对应力AlGaN/GaN异质结构中电子迁移率的影响

The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas （2DEG） is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors （AlGaN/GaN HFETs）. Current-voltage （I-V） characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage （C-V） characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.     

Monolithically integrated enhancement/depletion-mode AlGaN/GaN HEMT D flip-flop using fluorine plasma treatment

Depletion-mode and enhancement-mode AlGaN/GaN HEMTs using fluorine plasma treatment were integrated on one wafer.Direct-coupled FET logic circuits,such as an E/D HEMT inverter,NAND gate and D flip-flop,were fabricated on an AlGaN/GaN heterostructure.The D flip-flop and NAND gate are demonstrated in a GaN system for the first time.The dual-gate AlGaN/GaN E-HEMT substitutes two single-gate E-HEMTs for simplifying the NAND gate and shrinking the area,integrating with a conventional AlGaN/GaN D-HEMT and demonstrating a NAND gate.E/D-mode D flip-flop was fabricated by integrating the inverters and the NAND gate on the AlGaN/GaN heterostructure.At a supply voltage of 2 V,the E/D inverter shows an output logic swing of 1.7 V,a logic-low noise margin of 0.49 V and a logic-high noise margin of 0.83 V.The NAND gate and D flip-flop showed correct logic function demonstrating promising potential for GaN-based digital ICs.     

大面积非光刻纳米电极间隙的制备

A lithography-independent and wafer scale method to fabricate a metal nanogap structure is demonstrated. Polysilicon was first dry etched using photoresist （PR） as the etch mask patterned by photolithography. Then, by depositing conformal SiO2 on the polysilicon pattern, etching back SiO2 anisotropically in the perpendicular direction and removing the polysilicon with KOH, a sacrificial SiO2 spacer was obtained. Finally, after metal evaporation and lifting-off of the SiO2 spacer, an 82 nm metal-gap structure was achieved. The size of the nanogap is not determined by the photolithography, but by the thickness of the SiO2. The method reported in this paper is compatible with modern semiconductor technology and can be used in mass production.     

GaN自支撑衬底的化学机械抛光研究

Chemical mechanical polishing （CMP） has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square （RMS） surface roughness of 0.565 nm, as measured by atomic force microscopy.     

RF-MBE Grown AlGaN/GaN HEMT Structure with High Al Content

A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE.The structural and electrical properties of the heterostructure are investigated by the triple axis Xray diffraction and Van der PauwHall measurement,respectively.The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.The high 2DEG mobility in excess of 1260cm2／（V·s） is achieved with an electron density of 1.429e13cm－2 at 297K,corresponding to a sheet-densitymobility product of 1.8e16V－1·s－1.Devices based on the structure are fabricated and characterized.Better DC characteristics,maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer.The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.     

Impact of barrier thickness on gate capacitance—Modeling and Comparative analysis of GaN based MOSHEMTs

A mathematical model is developed predicting the behavior of gate capacitance with the nanoscale variation of barrier thickness in AlN/GaN MOSHEMT and its effect on gate capacitances of AlInN/GaN and AlGaN/GaN MOSHEMTs through TCAD simulations is compared analytically. Al N/GaN and AlInN/GaN MOSHEMTs have an advantage of a significant decrease in gate capacitance up to 108 fF/ m2 with an increase in barrier thickness up to 10 nm as compared to conventional AlGaN/GaN MOSHEMT. This decrease in gate capacitance leads to improved RF performance and hence reduced propagation delay.     

化学抛光处理和低温退火对硅异质结太阳电池性能的影响

Amorphous/crystalline silicon heterostructure solar cells have been fabricated by hot wire chemical vapor deposition （HWCVD） on textured p-type substrates. The influence of chemical polish （CP） etching and the post annealing process on the solar cell performance have been studied. The CP treatment leads to a reduction of stress in the i-layer by the slight rounding of the pyramid peaks, therefore improving the deposition coverage and the contact by each layer, which is beneficial for the performance of the solar cells. An optimized etching time of 10-15 s has been obtained. A post annealing process leads to a considerably improved open voltage （Voc）, filled factor （FF）, and conversion efficiency （η） by restructuring the deposited film and reducing the series resistance. An efficiency of 15.14% is achieved that represents the highest result reported in China for an amorphous/crystalline heterostructure solar cells based on the textured p-type substrates.     

Minimization of leakage current of recessed gate AlGaN/GaN HEMTs by optimizing the dry-etching process

The backward current of Schottky contacts on unintentionally doped GaN samples prepared by different dry-etching methods was investigated. It was found that an ion beam etching (IBE) process with an accelerating voltage of 250 V under an angle of 20 degrees to minimize channeling achieves the best results. The backward current in this case is 4 × 10⁻¹⁰ A/μm² compared to the backward current of the unetched sample of 1 × 10⁻⁷ A/μm² at −100 V. With this process, recessed gate HEMTs on AlGaN/GaN heterostructures grown by low pressure MOVPE were fabricated and compared to HEMTs without recess. The applied gate recess etching technique improves the leakage current by nearly a factor of two. The maximum transconductance is improved from 40 mS/mm to 60 mS/mm at a gate length of 4 μm.     

AlGaN/GaN double-channel HEMT

正The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported.Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure.The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region.The buffer trap is suggested to be related to the wide region of high transconductance.The RF characteristics are also studied.     

Analysis of the growth of GaN epitaxy on silicon

Due to the great potential of GaN based devices,the analysis of the growth of crack-free GaN with high quality has always been a research hotspot.In this paper,two methods for improving the property of the GaN epitaxial layer on Si (111) substrate are researched.Sample A,as a reference,only has an AlN buffer between the Si substrate and the epitaxy.In the following two samples,a GaN transition layer (sample B) and an AlGaN buffer (sample C) are grown on the AlN buffer separately.Both methods improve the quality of GaN.Meanwhile,using the second method,the residual tensile thermal stress decreases.To further study the impact of the two introduced layers,we investigate the stress condition of GaN epitaxial layer by Raman spectrum.According to the Raman spectrum,the calculated residual stress in the GaN epitaxial layer is approximately 0.72 GPa for sample B and 0.42 GPa for sample C.The photoluminescence property of GaN epitaxy is also investigated by room temperature PL spectrum.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.