Physical mechanism of secondary-electron emission in Si wafers

CMOS-compatible RF/microwave devices,such as filters and amplifiers,have been widely used in wireless communication systems.However,secondary-electron emission phenomena often occur in RF/microwave devices based on silicon(Si)wafers,especially in the high-frequency range.In this paper,we have studied the major factors that influence the secondary-electron yield(SEY)in commercial Si wafers with different doping concentrations.We show that the SEY is suppressed as the doping concentration increases,corresponding to a relatively short effective escape depthλ.Meanwhile,the reduced narrow band gap is beneficial in suppressing the SEY,in which the absence of a shallow energy band below the conduction band will easily capture electrons,as revealed by first-principles calculations.Thus,the new physical mechanism combined with the effective escape depth and band gap can provide useful guidance for the design of integrated RF/microwave devices based on Si wafers.

Challenges in Processing Diamond Wire Cut and Black Silicon Wafers in Large-Scale Manufacturing of High Efficiency Solar Cells

Texturing of diamond wire cut wafers using a standard wafer etch process chemistry has always been a challenge in solar cell manufacturing industry. This is due to the change in surface morphology of diamond wire cut wafers and the abundant presence of amorphous silicon content, which are introduced from wafer manufacturing industry during sawing of multi-crystalline wafers using ultra-thin diamond wires. The industry standard texturing process for multi-crystalline wafers cannot deliver a homogeneous etched silicon surface, thereby requiring an additive compound, which acts like a surfactant in the acidic etch bath to enhance the texturing quality on diamond wire cut wafers. Black silicon wafers on the other hand require completely a different process chemistry and are normally textured using a metal catalyst assisted etching technique or by plasma reactive ion etching technique. In this paper, various challenges associated with cell processing steps using diamond wire cut and black silicon wafers along with cell electrical results using each of these wafer types are discussed.

Development of Low Dark Current SiGe Near-Infrared PIN Photodetectors on 300 mm Silicon Wafers

SiGe offers a low-cost alternative to conventional infrared sensor material systems such as InGaAs, InSb, and HgCdTe for developing near-infrared (NIR) photodetector devices that do not require cooling and can operate with relatively low dark current. As a result of the significant difference in thermal expansion coefficients between germanium (Ge) and silicon (Si), tensile strain incorporated into SiGe detector devices through specialized growth processes can extend their NIR wavelength range of operation. We have utilized high throughput, large-area complementary metal-oxide semiconductor (CMOS) technology to fabricate Ge based p-i-n (PIN) detector devices on 300 mm Si wafers. The two-step device fabrication process, designed to effectively reduce the density of defects and dislocations arising during deposition that form recombination centers which can result in higher dark current, involves low temperature epitaxial deposition of Ge to form a thin p+ seed layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. Phosphorus was then ion-implanted to create devices with n+ regions of various doping concentrations. Secondary ion mass spectroscopy (SIMS) has been utilized to determine the doping profiles and material compositions of the layers. In addition, electrical characterization of the I-V photoresponse of different devices from the same wafer with various n+ region doping concentrations has demonstrated low dark current levels (down to below 1 nA at -1 V bias) and comparatively high photocurrent at reverse biases, with optimal response for doping concentration of 5 × 1019 cm-3.

Determination of Substitutional Carbon in SI-GaAs Thin Wafers by Infrared Microscope

Determination of substitutional carbon in SI-GaAs thin wafers was investigated by FT-IR microscopeat room temperature for the first time.The experimental results showed that the carbon concentration inGaAs thin wafers can be measured directly with simple treatment.The calculation method of carbon concen-tration is in agreement with that for normal IR spectrum with 0.5 cm-1resolution.The resolution of1 cm-1can be taken in order to obtain a high signal-to-noise（S/N）ratio using 2.34×1016cm-2calibration factor for calculating carbon concentration at room temperature.

Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide(a-SiOx:H) on〈100〉- and 〈111〉-orientated c-Si wafers

Hydrogenated amorphous silicon oxide(a-SiOx:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction(SHJ) solar cells. In this paper, a-SiOx:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime(τ(eff)) of 4743 μs and corresponding implied opencircuit voltage(iV(oc)) of 724 mV are obtained on〈100〉-orientated c-Si wafers. While τ(eff) of 2429 μs and iV_(oc) of 699 mV are achieved on 111-orientated substrate. The FTIR and XPS results indicate that the a-SiOx:H network consists of SiOx(Si-rich), Si–OH, Si–O–SiHx, SiO2 ≡ Si–Si, and O3 ≡ Si–Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiOx:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.

INFLUENCE OF NITROGEN ON THERMAL WARPAGE IN CZOCHRALSKI SILICON WAFERS

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Investigation of Inhomogeneity in Single Crystal SiC Wafers Using C-Scan Acoustic Scanning Microscopy

In this work, C-Scan Acoustic Scanning Microscopy (ASM) is used to map the defects of three SiC samples. The acoustic images indicate that numerous defects with different shapes and area?sexist in the wafers. Some of the defects have areas of more than 100,000 μm2. The number of defects ranges from 1 to 50 defects/wafer. Defect mapping is essential for defect repairing or avoidance.?This work shows that ASM can locate the precise positions of the crystallographic defects, which?enables?defects repair and yield enhancement.

Formation of subsurface cracks in silicon wafers by grinding

Single-crystal silicon is an important material in the semiconductor and optical industries.However,being hard and brittle,a silicon wafer is vulnerable to subsurface cracks(SSCs)during grinding,which is detrimental to the performance and lifetime of a wafer product.Therefore,studying the formation of SSCs is important for optimizing SSC-removal processes and thus improving surface integrity.In this study,a statistical method is used to study the formation of SSCs induced during grinding of silicon wafers.The statistical results show that grinding-induced SSCs are not stochastic but anisotropic in their distributions.Generally,when grinding with coarse abrasive grains,SSCs form along the cleavage planes,primarily the{111}planes.However,when grinding with finer abrasive grains,SSCs tend to form along planes with a fracture-surface energy higher than that of the cleavage planes.These findings provide a guidance for the accurate detection of SSCs in ground silicon wafers.

Raman Back-scattering study of Damaged and Strain Subsurface Layers in GaAs Wafers

The damaged and strain subsurface layers of semi insulating(SI) GaAs substrate were characterized non destructively by Raman back scattering.The study shows that the thicknesses of the damaged and strain layers are less than 3μm.The damaged and strain layer can be removed after being etched in H 2SO 4·H 2O 2·H 2O for 1.5 min.

Surface Damage in Wire cut Silicon Wafers

The surface damage and the damage depth in wire cut silicon wafers and inner diameter (ID) cut silicon wafers were studied by means of thickness meter, scanning electron microscopy (SEM) and double crystal X ray diffractometer. The results show that the surface of wire cut silicon wafers is rougher than that of ID cut silicon wafers and the surface damage in wire cut silicon wafers is more serious than that in ID cut silicon wafers, while the damage depth in wire cut silicon wafers is smaller than that in ID cut silicon wafers. The possible reasons for the generation of surface damage in wire cut silicon wafers were also discussed.

Finite Element Analysis for Grinding and Lapping of Wire-sawn Silicon Wafers

Silicon wafers are the most widely used substrates for semiconductors. The falling price of silicon wafers has created tremendous pressure on silicon wafer manufacturers to develop cost-effective manufacturing processes. A critical issue in wafer production is the waviness induced by wire sawing. If this waviness is not removed, it will affect wafer flatness and semiconductor performance. In practice, both lapping and grinding have been used to flatten wire-sawn wafers. Although grinding is not as effective as lapping in removing waviness, it has many other advantages over lapping (such as higher throughput, fully automatic, and more benign to environment) and has great potential to reduce manufacturing cost of silicon wafers. This paper presents a finite element analysis (FEA) study on grinding and lapping of wire-sawn silicon wafers. An FEA model is first developed to simulate the waviness deformation of wire-sawn wafers in grinding and lapping processes. It is then used to explain how the waviness is removed or reduced by lapping and grinding and why the effectiveness of grinding in removing waviness is different from that of lapping. Furthermore, the model is used to study the effects of various parameters including active-grinding-zone orientation, grinding force, waviness wavelength, and waviness height on the reduction and elimination of waviness. Finally, the results of pilot experiments to verify the model are discussed.

THE STUDY ON DEFECTS IN SINGLE CRYSTAL SILICON WAFERS TREATED WITH DOUBLE-GETTERING TECHNIQUE

Investigations on the nature and states of the defeats in single crystal wafers treated with double-gettering technique have been carried out by means of optical microscopy,electron microscopy,electron miaroanalysis and spread resistance.Phosphorus profile in these wafers was measured.And the effect of phosphorus on defects and resistivity was determined.

Subsurface Damage of Monocrystalline Germanium Wafers by Fixed and Free Abrasive Lappings

The subsurface damage(SSD)layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology.Three ways such as ice-fixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers.The SSD depth was measured by a nanoindenter,and the morphology of SSD layer was observed by an atomic force microscopy(AFM).The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer.Compared with thermosetting fixed abrasive and free abrasive lappings,the SSD depth lapped with ice-fixed abrasive is shallower.Moreover,the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.

Malignant Cerebral Edema Secondary to Gliadel Wafers in the Early Postsurgical Period

High grade gliomas are the commonest intrinsic brain tumours and account for more average years of life lost than all the common cancers. It has become the commonest cause of cancer death in men under the age of 45 and women under the age of 35. Although surgical resection can greatly reduce tumour bulk, complete excision is virtually impossible due to the infiltrative nature of these tumours. In an attempt to treat the infiltrating tumour cells, there has been much interest in using local therapies inserted at the time of surgery. The authors report a case of fatal cerebral edema unresponsive to aggressive medical and surgical assessment that finally evolved to premature death in the early postsurgical period, after the craniotomy and implantation of Gliadel wafers. They note that high doses of dexamethasone were insufficient to prevent cerebral edema and death. A search for corticosteroid use and dosing for patients treated with Gliadel wafers in the published literature revealed no recommendations on the doses of steroids to be administered. In our opinion this is a very important issue and maybe the key point for the treatment of this disease, and may need to be addressed with treatment guidelines in the near future in order to ensure better results on patient’s survival. Prior to this case review there had been two similar report but a later presentation. So we think that this is the first case report of acute fulminant cerebral edema secondary to gliadel wafers in the early period.

Optical colorimetric LiTaO_(3)wafers for highprecision lithography on frequency control of SAW devices

Surface acoustic wave(SAW)resonators based on lithium tantalate(LT,LiTaO_(3))wafers are crucial elements of mobile communication filters.The use of intrinsic LT wafers typically brings about low fabrication accuracy of SAW resonators due to strong UV reflection in the lithography process.This hinders their resonance frequency control seriously in industrial manufacture.LT doping and chemical reduction could be applied to decrease the UV reflection of LT wafers for high lithographic precision.However,conventional methods fail to provide a fast and nondestructive approach to identify the UV performance of standard single-side polished LT wafers for highprecision frequency control.Here,we propose a convenient on-line sensing scheme based on the colorimetry of reduced Fe-doped LT wafers and build up an automatic testing system for industrial applications.The levels of Fe doping and chemical reduction are evaluated by the lightness and color difference of LT-based wafers.The correlation between the wafer visible colorimetry and UV reflection is established to refine the lithography process and specifically manipulate the frequency performance of SAW resonators.Our study provides a powerful tool for the fabrication control of SAW resonators and will inspire more applications on sophisticated devices of mobile communication.

Double-sided transistor device processability of carrierless ultrathin silicon wafers

Double-sided metal-oxide-semiconductor field-effect-transistor processing is demonstrated for the first time on an ultrathin crystalline silicon substrate of 6-20μm in a 100 mm diameter wafer format without a carrier wafer,the thinnest freestanding silicon wafers ever fabricated.The compatibility of the flexible material with conventional semiconductor processing tools is enabled by supporting an interior ultrathin silicon with a surrounding thicker ring of silicon.Currentvoltage characteristics of transistors on ultrathin silicon show performance as expected from bulk silicon,with electron mobility^1500 cm^2 V^−1 second^−1.Mechanical measurements quantify the handleability.

尺骨撞击综合征研究进展

尺骨撞击综合征是导致腕关节尺侧疼痛的主要原因,它是由于腕关节尺侧结构中尺骨头、三角纤维软骨复合体、月骨、三角骨之间反复发生撞击,导致腕关节尺侧长期超负荷,影响局部血供和关节润滑液的营养障碍,最终引起一系列病理改变和临床症状的关节退行性疾病。主要临床表现为腕关节尺侧的疼痛,且随着反复强力抓握活动、前臂旋前或腕部的尺偏而逐渐加重。目前该疾病的诊断主要依靠症状、查体、影像学检查及腕关节镜检查。尺骨撞击综合征可选择保守治疗,但效果往往不佳,近年来手术仍为主要的治疗方式。手术方法主要包括尺骨短缩截骨术、Wafer术、Darrach术和Sauvé-Kapandji术等,以前2种手术方式目前最为常用。现就该疾病的诊断及治疗进展进行综述。

Scalable and ultrafast epitaxial growth of single-crystal graphene wafers for electrically tunable liquid-crystal microlens arrays

The scalable growth of wafer-sized single-crystal graphene in an energy-efficient manner and compatible with wafer process is critical for the killer applications of graphene in high-performance electronics and optoelectronics. Here, ultrafast epitaxial growth of single-crystal graphene wafers is realized on singlecrystal Cu90Ni10(1 1 1) thin films fabricated by a tailored two-step magnetron sputtering and recrystallization process. The minor nickel(Ni) content greatly enhances the catalytic activity of Cu, rendering the growth of a 4 in. single-crystal monolayer graphene wafer in 10 min on Cu90Ni10(1 1 1), 50 folds faster than graphene growth on Cu(1 1 1). Through the carbon isotope labeling experiments, graphene growth on Cu90Ni10(1 1 1) is proved to be exclusively surface-reaction dominated, which is ascribed to the Cu surface enrichment in the Cu Ni alloy, as indicated by element in-depth profile. One of the best benefits of our protocol is the compatibility with wafer process and excellent scalability. A pilot-scale chemical vapor deposition(CVD) system is designed and built for the mass production of single-crystal graphene wafers, with productivity of 25 pieces in one process cycle. Furthermore, we demonstrate the application of single-crystal graphene in electrically controlled liquid-crystal microlens arrays(LCMLA), which exhibit highly tunable focal lengths near 2 mm under small driving voltages. By integration of the graphene based LCMLA and a CMOS sensor, a prototype camera is proposed that is available for simultaneous light-field and light intensity imaging. The single-crystal graphene wafers could hold great promising for highperformance electronics and optoelectronics that are compatible with wafer process.

Structural Characterization of Laser Bonded Sapphire Wafers Using a Titanium Absorber Thin Film

Two sapphire substrates were tightly bonded by irradiation with a 1064 nm nanosecond laser and using a sputtered 50 nm-titanium thin film as an absorbing medium.Upon laser irradiation,aluminum from the upper substrate is incorporated into the thin film,forming Ti-Al-O compounds.While the irradiated region becomes transparent,the bond quality was evaluated by scanning acoustic microscopy.

A comparative study of rhenium coatings prepared on graphite wafers by chemical vapor deposition and electrodeposition in molten salts

The purity,preferred orientation,microstructure,microhardness,bonding strength,thickness uniformity and thermal stability of rhenium(Re)coatings prepared on graphite wafers by chemical vapor deposition(CVD)and electrodeposition(ED)in molten salts were comparatively studied in this paper.It was found that carbon(0.0140 wt%)and oxygen(0.0067 wt%)were the primary impurities for CVD and ED Re coatings,respectively.The diffusion of carbon into CVD Re coating caused higher microhardness near the substrate and helped to improve the bonding strength at the same time.The preferred orientation,microstructure and microhardness of ED Re coating were all susceptible to oxygen.The coating deposition uniformity of ED Re is obviously better than that of CVD Re coating,due to its intrinsic characteristics.The(002)-oriented,coarse columnar CVD Re coating exhibited better thermal stability compared with that of the<110>-oriented,fiber-like columnar ED Re coating,while the ED Re grains grew remarkably and the microstructure evolved toward the similar structure of CVD Re after annealing treatment.The diversity of Re coatings in microstructure could be attributed to the mobility of grain boundaries(affected by temperature and impurity)during deposition processes.