Structure and electrical properties of polysilicon films doped with ammonium tetraborate tetrahydrate

Here,p-type polysilicon films are fabricated by ex-situ doping method with ammonium tetraborate tetrahydrate(ATT)as the boron source,named ATT-pPoly.The effects of ATT on the properties of polysilicon films are comprehensively analyzed.The Raman spectra reveal that the ATT-pPoly film is composed of grain boundary and crystalline regions.The preferred orientation is the(111)direction.The grain size increases from 16−23 nm to 21−47 nm,by~70%on average.Comparing with other reported films,Hall measurements reveal that the ATT-pPoly film has a higher carrier concentration(>10^(20)cm^(−3))and higher carrier mobility(>30 cm2/(V·s)).The superior properties of the ATT-pPoly film are attributed to the heavy doping and improved grain size.Heavy doping property is proved by the mean sheet resistance(Rsheet,m)and distribution profile.The R_(sheet,m)decreases by more than 30%,and it can be further decreased by 90%if the annealing temperature or duration is increased.The boron concentration of ATT-pPoly film annealed at 950℃ for 45 min is~3×10^(20)cm^(−3),and the distribution is nearly the same,except near the surface.Besides,the standard deviation coefficient(σ)of Rsheet,m is less than 5.0%,which verifies the excellent uniformity of ATT-pPoly film.

Fabrication of n^+ Polysilicon Ohmic Contacts with a Heterojunction Structure to n-Type 4H-Silicon Carbide

Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si-faced p-type 4H-SiC epilayer. The polysilicon is deposited using low-pressure chemical vapor deposition （LPCVD） and doped by phosphorous ions implantation followed by diffusion to obtain a sheet resistance of 22Ω/□. The specific contact resistance pc of n^＋ polysilicon contact to n-type 4H-SiC as low as 3.82 × 10^-5Ω· cm^2 is achieved. The result for sheet resistance Rsh of the phosphorous ion implanted layers in SiC is about 4.9kΩ/□. The mechanisms for n^＋ polysilicon ohmic contact to n-type SiC are discussed.

Resistivity Instability in Polysilicon Resistors Under Metal Interco-nnects and Its Suppression by Compensating Ion Implantation

The resistivity instability of the boron-doped polysilicon resistors being a line resistance element of ICs is within the range of several kΩ's,especially when our running the underneath metal interconnects.Polysilicon resistors have been fabricated under various processing conditions as well as some electrical and crystallographic characteristics have been obtained.It is shown the resistivity instability mainly results from the variational carrier mobility.By analyzing the Seto's model,the barrier height and trapped charge density are observed reducing under the Al over layer.Therefore,the resistance instability is also caused by both the charge trapping/detrapping occurring at polysilicon grain boundaries and the resultant variation in the potential barrier height.The formation of high-stability polysilicon resistors in the range of several kΩ's has been decided by compensating the ion implantation,which makes the charge trapping/detrapping at the grain boundary less susceptible to the hydrogen annealing.

Polysilicon Over-Etching Time Control of Advanced CMOS Processing with Emission Microscopy

The emission microscopy （EMMI） test is proposed as an effective method to control the polysilicon over-etching time of advanced CMOS processing combined with a novel test structure, named a poly-edge structure. From the values of the breakdown voltage （Vbd） of MOS capacitors （poly-edge structure） ,it was observed that,with for the initial polysilicon etching-time, almost all capacitors in one wafer failed under the initial failure model. With the increase of polysilicon over-etching time, the number of the initial failure capacitors decreased. Finally, no initial failure capacitors were observed after the polysilicon over-etching time was increased by 30s. The breakdown samples with the initial failure model and intrinsic failure model underwent EMMI tests. The EMMI test results show that the initial failure of capacitors with poly-edge structures was due to the bridging effect between the silicon substrate and the polysilicon gate caused by the residual polysilicon in the ditch between the shallow-trench isolation region and the active area, which will short the polysilicon gate with silicon substrate after the silicide process.

MECHANICAL DEFLECTION OF POLYSILICON MICROCANTILEVER BEAMS USING NANOINDENTATION

The validity of a novel, direct and convenient method for micromechanical property measurements by beam bending using a nanoindenter is demonstrated. This method combines a very high load resolution with a nanometric precision in the determination of the microcantilever beam deflection. The method is described clearly. In the deflection of microbeams, the influence of the indenter tip pushing into the top of the microbeams and the curvature across its width must be considered. The measurements were made on single-layer, micro-thick, several kinds of width and length polysilicon beams that were fabricated using conventional integrated circuit (IC) fabrication techniques. The elastic of a polysilicon microcantilever beam will vary linearly with the force and the deformation is thought to be elastic. Furthermore, it suggests that Young modulus of the beam can be determined from the slope of this linear relation. From the load deflection data acquired during bending the mechanical properties of the thin films were determined. Measured Young modulus is 137 GPa with approximately a ±2.9%～±6.3% difference in Young modulus.

Numerical simulation of chemical vapor deposition reaction in polysilicon reduction furnace

Three-dimensional model of chemical vapor deposition reaction in polysilicon reduction furnace was established by considering mass, momentum and energy transfer simultaneously. Then, CFD software was used to simulate the flow, heat transfer and chemical reaction process in reduction furnace and to analyze the change law of deposition characteristic along with the H_2 mole fraction, silicon rod height and silicon rod diameter. The results show that with the increase of H_2 mole fraction, silicon growth rate increases firstly and then decreases. On the contrary, SiHCl_3 conversion rate and unit energy consumption decrease firstly and then increase. Silicon production rate increases constantly. The optimal H_2 mole fraction is 0.8-0.85. With the growth of silicon rod height, Si HCl3 conversion rate, silicon production rate and silicon growth rate increase, while unit energy consumption decreases. In terms of chemical reaction, the higher the silicon rod is, the better the performance is. In the view of the top-heavy situation, the actual silicon rod height is limited to be below 3 m. With the increase of silicon rod diameter, silicon growth rate decreases firstly and then increases. Besides, SiHCl_3 conversion rate and silicon production rate increase, while unit energy consumption first decreases sharply, then becomes steady. In practice, the bigger silicon rod diameter is more suitable. The optimal silicon rod diameter must be over 120 mm.

Organic field-effect transistor floating-gate memory using polysilicon as charge trapping layer

In this study,we present an organic field-effect transistor floating-gate memory using polysilicon(poly-Si)as a charge trapping layer.The memory device is fabricated on a N^+-Si/SiO2 substrate.Poly-Si,polymethylmethacrylate,and pentacene are used as a floating-gate layer,tunneling layer,and active layer,respectively.The device shows bidirectional storage characteristics under the action of programming/erasing(P/E)operation due to the supplied electrons and holes in the channel and the bidirectional charge trapping characteristic of the poly-Si floating-gate.The carrier mobility and switching current ratio(Ion/Ioff ratio)of the device with a tunneling layer thickness of 85 nm are 0.01 cm^2·V^-1·s^-1 and 102,respectively.A large memory window of 9.28 V can be obtained under a P/E voltage of±60 V.

MODEL AND MODELING OF LOW TEMPERATURE CURRENT GAIN OF POLYSILICON EMITTER BIPOLAR TRANSISTORS

A unified model of low temperature current gain of polysilicon emitter bipolar transistors based on effective recombination method is presented, incorporating band-gap narrowing, carrier freezing-out, tunneling of holes through polysilicon/silicon interface oxide layer and reduced mobility mechanism in polysilicon. The modeling results based on this model are in good agreement with experimental data.

The Antioxidation Properties of the In-situ Ceramic from Pyrolyzing Polysilicone Preceramic

A systematic research on the pyrolysis process of polymethysilicone (SAR-2) and the thermostability of the pyrolysis residue was made by the thermogravimetric analysis, DTA and infrared spectroscopy.The experimental results indicate that the pyrolysis residue of SAR-2 converted into the amorphous SiC_xO_(4-x) phase above 900 ℃,the residue at 1200 ℃ is the most thermostable and antioxidant.It is suitable to be used as polysilicone preceramic.

SIZE EFFECT ON THE BENDING AND TENSILE STRENGTH OF MICROMACHINED POLYSILICON FILMS FOR MEMS

The bending strength of microfabricated polysilicon beams was measured by beam bending using a nanoindenter. Also, the tensile strength of microfabricated polysilicon thin ?lms was measured by tensile testing with a new microtensile test device. It was found that the bending strength and tensile strength of polysilicon microstructures exerts size e?ect on the size of the specimens. In such cases, the size e?ect can be traced back to the ratio of surface area to volume as the governing parameter. A statistical analysis of the bending strength for various specimen sizes shows that the average bending strength of polysilicon microcantilever beams is 2.885 ± 0.408 GPa. The measured average value of Young’s modulus, 164 ± 1.2 GPa, falls within the theoretical bounds. The average fracture tensile strength is 1.36 GPa with a standard deviation of 0.14 GPa, and the Weibull modulus is 10.4 -11.7, respectively. The tensile testing of 40 specimens on failure results in a recommendation for design that the nominal strain be maintained below 0.0057.

Numerical simulation study of organic nonvolatile memory with polysilicon floating gate

A polysilicon-based organic nonvolatile floating-gate memory device with a bottom-gate top-contact configuration is investigated,in which polysilicon is sandwiched between oxide layers as a floating gate.Simulations for the electrical characteristics of the polysilicon floating gate-based memory device are performed.The shifted transfer characteristics and corresponding charge trapping mechanisms during programing and erasing（P/E） operations at various P/E voltages are discussed.The simulated results show that present memory exhibits a large memory window of 57.5 V,and a high read current on/off ratio of ≈ 10~3.Compared with the reported experimental results,these simulated results indicate that the polysilicon floating gate based memory device demonstrates remarkable memory effects,which shows great promise in device designing and practical application.

THE SURFACE EFFECT ON THE TENSILE STRENGTH OF MICROMACHINED POLYSILICON FILMS FOR MEMS

In order to accomplish reliable mechanical design of MEMS, the infuences of surface roughness and octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on the mechani- cal properties of micromachined polysilicon flms for MEMS are investigated. Surface efect on the fracture properties of micromachined polysilicon flms is evaluated with a new microtensile testing method using a magnet-coil force actuator. Statistical analysis of the surface roughness efects on the tensile strength predicated the surface roughness characterization of polysilicon flms being tested and the direct relation of the mechanical properties with the surface roughness features. The fracture strength decreases with the increase of the surface roughness. The octadecyltrichlorosi- lane self-assembled monolayers coating leads to an increase of the average fracture strength up to 32.46%. Surface roughness and the hydrophobic properties of specimen when coated with OTS flms are the two main factors infuencing the tensile strength of micromachined polysilicon flms for MEMS.

Polysilicon Prepared from SiCl_4 by Atmospheric-Pressure Non-Thermal Plasma

Non-thermal plasma at atmospheric pressure was explored for the preparation of polysilicon from SiCl4. The power supply sources of positive pulse and alternating current （8 kHz and 100 kHz） were compared for polysilicon preparation. The samples prepared by using the 100 kHz power source were crystalline silicon. The effects of H2 and SiCl4 volume fractions were investigated. The optical emission spectra showed that silicon species played an important role in polysilicon deposition

Numerical simulation of granular silicon growth and silicon fines formation process in polysilicon fluidized bed

Operating conditions strongly affect the yield and quality of polysilicon in a polysilicon fluidized bed.In this study,a new model of polysilicon fluidized bed was established using the Euler-Euler model coupled with population balance model(PBM),which was combined with fluid flow,heat,and mass transfer models,while considering the scavenging effect of silicon fines.The effects of different operating conditions on the deposition and formation rates of silicon fines were investigated.Results show that the model can correctly describe the particle growth process in the fluidized bed of polysilicon.The silicon fines and the interphase velocity difference show"N"-and"M"-shaped distributions along the axial direction,respectively.The particle temperature and concentration near the wall are higher than those in the central region.The decomposition of silane in the bottom region of the bed is dominated by het-erogeneous deposition.The scavenging of silicon fines occurs in the dilute-phase region.The effects of operating conditions,i.e.inlet gas temperature,silane composition,and gas velocity,on the reactor performance were also explored comprehensively.Increasing the inlet gas composition and velocity enhances the formation rates of solid silicon and fines.Increasing the inlet gas temperature promotes the growth of solid silicon and inhibits the formation of silicon fines.High fluidization ratio,low inlet silane concentration,and high inlet gas temperature enhance the selectivity of silicon growth.

The algorithm for the piezoresistance coefficients of p-type polysilicon

In order to improve the piezoresistance theory of polysilicon, based on the tunneling piezoresistance model, using the mechanisms of approximate valence band equation and shifts of the hole transfer and hole con- duction mass by stress, a novel algorithm for the piezoresistance coefficients of p-type polysilicon is presented. It proposes three fundamental piezoresistance coefficients π11,π12 and π44 of the grain neutral and grain boundary regions, separately. With those piezoresistance coefficients, the gauge factors of the p-type polysilicon nanofilm and the p-type common polysilicon film are calculated, and then the plots of the gauge factor as a function of doping concentration are given, which are consistent with the experimental results.

Investigation of the polysilicon p-i-n diode and diode string as a process compatible and portable ESD protection device

The polysilicon p-i-n diode displays noticeable process compatibility and portability in advanced tech- nologies as an electrostatic-discharge （ESD） protection device. This paper presents the reverse breakdown, current leakage and capacitance characteristics of fabricated polysilicon p-i-n diodes. To evaluate the ESD robustness, the forward and reverse TLP I-V characteristics were measured. The polysilicon p-i-n diode string was also investigated to further reduce capacitance and fulfill the requirements of tunable cut-in or reverse breakdown voltage. Finally, to explain the effects of the device parameters, we analyze and discuss the inherent properties ofpolysilicon p-i-n diodes.

多晶硅装置尾气回收工艺研究进展

综述了改良西门子法多晶硅制备工艺及尾气回收研究现状,从回收率、回收效果及能耗等方面阐述了湿法回收、膜分离回收和干法回收3种尾气回收工艺。重点概述了多晶硅尾气干法回收工艺各个单元的研究进展,并根据现状总结了未来的研究方向。

42对棒环形布棒还原炉能量耗散研究

由于无法对大型还原炉环状硅棒排布方式对能耗的影响做出准确判断,对42对棒西门子多晶硅还原炉进行仿真模拟计算,建立两种环状硅棒布棒方式(三环排布、四环排布)的还原炉模型。通过对还原炉的炉行为及棒行为分析发现,硅棒直径加大能耗也会相应加大,且这种变化受炉内流场和温度场共同影响;同时,还原炉内内环硅棒辐射能耗随硅棒直径的增大呈先增大后减小的变化趋势,而排列在外环的硅棒辐射损耗则随硅棒直径的增大而不断增大。针对42对棒西门子还原炉内硅棒的排布方法,提出选用硅棒三环排布的方式可达到降低该还原炉总能耗的目的。

碳中和背景下我国多晶硅产业现状及发展趋势

在碳中和、碳达峰的重大时代背景下,加速能源结构转型、改变当前能源结构已成共识。本文简述了目前多晶硅主要的生产工艺流程,从多方面对比了各工艺的优缺点,详述了改良西门子法与硅烷流化床法工艺的发展趋势,指出硅烷流化床法仍有巨大改进空间,有望给我国多晶硅行业带来崭新局面。多晶硅产业逐渐向我国转移,我国市场占有率不断提升,推动双碳目标的实现也更加离不开多晶硅产业的发展。

多晶硅企业事故大气环境次生污染物影响分析

本文以某企业三氯氢硅储罐泄漏、燃烧引发次生污染物氯化氢气体在大气环境中扩散的风险事故情形为例,利用AFTOX模型进行大气环境风险的分析、预测,为此类风险事故的防范、应急与减缓措施提供了建议。