离子色谱法测定蚀刻槽废氢氟酸中的六氟硅酸

建立了一种新的检测蚀刻槽废氢氟酸中六氟硅酸的离子色谱方法。色谱柱为Metrosep A Supp 7阴离子交换柱,流动相为3.2 mmol/L碳酸钠-1.0 mmol/L碳酸氢钠,流速为0.7 mL/min。六氟硅酸经过抑制型电导检测器后进行衍生化反应,在360 nm波长下用紫外检测器检测。六氟硅酸的线性范围为2.4~120 mg/L,相关系数r²大于0.999,定量限为0.24 mg/L,平均加标回收率为97.2%。本方法还可以同时利用电导检测器检测废氢氟酸中的氢氟酸、醋酸、盐酸、硝酸、磷酸和硫酸的含量。该方法快速、准确,适用于蚀刻槽液中六氟硅酸的检测。     

Titrimetric determination of silicon dissolved in concentrated HF-HNO3-etching solutions

The wet chemical etching of silicon by concentrated HF-HNO₃ mixtures in solar and semiconductor wafer fabrication requires the strict control of the etching conditions. Surface morphology and etch rates are mainly affected by the amount of dissolved silicon, that is continuously enriched in the etching solution with each etching run. A fast and robust method for the titrimetric determination of the total dissolved silicon content out of the concentrated etching solution is presented. This method is based on the difference between the two equivalence points of the total amount of acid and the hydrolysis of the hexafluorosilicic anion. This approach allows a silicon determination directly from the etching process in spite of the presence of dissolved nitric oxides in the etching solution. The influences of different acid mixing ratios and of the etching solution density depending on the silicon content is considered and discussed in detail.     

Single etch patterning of stacked silver and molybdenum alloy layers on glass using microcontact wave printing

Stacked thin layers of silver alloy (AgPdCu) and MoCr layers on 10 x 15 cm2 glass substrates were patterned by microcontact wave printing and etching. Patterns of etch-resistant octadecanethiol self-assembled monolayers (SAMs) were wave printed with regular backplane stabilized PDMS stamps. Pattern development was achieved by etching both metal layers in a single step, employing a nitric acid-based etching bath. Trifluoroacetic acid and a nitrite salt were identified as essential bath components for a homogeneous etching process. Etch defects could be eliminated by the addition of a decanesulfonate, which stabilizes the SAM resist via a defect healing mechanism.     

Chemical analysis of acidic silicon etch solutions: I. Titrimetric determination of HNO3, HF, and H2SiF6

The chemical etching of silicon using HF-HNO₃ mixtures is a widely used process in the processing of silicon wafers for microelectronic or photovoltaic applications. The control of the etch bath composition is the necessary condition for an effective bath utilization, for the replenishment of the consumed acids, and to maintain a certain etch rate. The present paper describes two methods for the total analysis of the individual etch bath constituents HF, HNO₃, and H₂SiF₆. Both methods start with an aqueous acid-base titration determining the total acid concentration and the concentration of H₂SiF₆. The first method is an acid-base titration using a 0.1 mol L⁻¹ methanolic solution of cyclohexylamine (CHA) as non-aqueous titrant to determine the content of nitric acid. Then, the amount of hydrofluoric acid is calculated from the difference between the total acid and nitric acid content. The second method is based on the determination of the total fluoride concentration using a fluoride ion-selective electrode (F-ISE). The content of hydrofluoric acid is obtained from the difference between the total fluoride content and the amount of fluoride bound as H₂SiF₆. The amount of nitric acid results finally calculated as difference to the total acid content.     

硅(100)晶面上硅和二氧化硅的横向与纵向腐蚀速率

The method established previously for studying the etching rates of micro-scale silicon and silica was used to study the etching process of silicon and silica on the Si（100）surface. Photolithography was used to pattern a positive photoresist mask to confine the etching area,and the atomic force microscopy was used to probe the etched surface. The lateral etching rate of silicon or silica on the silicon surface was defined,and the lateral and longitudinal etching rates of silicon and silica on the Si（100）surface in 40% ammonium fluoride aqueous solution were measured. The effect of the dissolved oxygen on the etching rates was studied by bubbling the solution with high purity nitrogen. The lateral and longitudinal etching rates of silicon and silica on the（100）surface increase with temperatures except for the lateral etching rate of silica in a N2 -bubbled solution which probably reaches the limit of diffusion controlled reaction. The etching rates of silicon and thermal silica on the Si（100）surface show remarkable difference with that on the Si（111）surface in both air-saturated and N2 -bubbled solutions. The apparent activation energies for the silicon and silica etching processing in ammonium fluoride solution were obtained from the etching rates at different temperatures in the range 20. 6-34. 1℃. The similarity of the apparent activation energies for the etching processing of silicon and silica on the（100）surface to that on the（111）surface probably suggests that the rate-determined-step is the same in both cases. A lot of gas bubbles are seen to aggregate on the surface in silicon dissolution process at 38. 2℃,and it is found that the gas bubbles have great influence on the silicon etching rate. The formation of bubbles accelerates the silicon dissolution at the beginning but blocks the etching as the bubbles gradually aggregate on the surface.     

Influence of laser microfabrication on silicon electrochemical behavior in HF solution

Influence of direct laser writing with femtosecond pulses on electrochemical etching of n-type low conductivity (>1,000 Ωcm) silicon is demonstrated. It has been shown that thermal 1-μm-thick SiO₂ layer on silicon surface can be used as a protective layer in the electrochemical etching process. It has been found that laser ablation changes not only the surface morphology and structure of silicon samples but also the character of their anodic etching in aqueous solution of hydrofluoric acid. Formation of microvoids and caverns of irregular shape has been observed at the laser-ablated sites. It is proposed that the change of silicon conductivity from n- to p-type takes place at the laser fabricated regions. Processes of Si anodic oxidation and electrochemical etching are discussed.     

Anisotropic etching of silicon in hydrazine

This paper contains a detailed discussion of the practical issues related to the anisotropic etching of single crystal silicon using a 5050 hydrazinewater solution. Characteristics of the etchant, etching reactor design, etch procedures, safety precautions, etch rate data for typical samples and appropriate etch-masks are among the topic discussed. The etching process is carried out in a atmospheric reflux reactor, continuously purged with nitrogen. The etch rate of (100) silicon at 115°C in this hydrazine solution is nearly 3 μm/min, which is much higher than that of ethylenediaminepyrocatecholwater (EDP) solutions. Silicon dioxide, silicon nitride and most metallic thin films, except aluminium, can be used to mask the etching process. The etch rate is reduced significantly in highly-boron-doped silicon; a boron concentration of 1.5 × 10²⁰ cm⁻³ practically stops the etch. The use of the hydrazine solution for micromachining thin silicon diaphragms, cantilevers and fibers is demonstrated.     

Determination of metallic impurities in a silicon wafer by local etching and electrothermal atomic absorption spectrometry.

An etching technique for the determination of the metallic impurities distribution in silicon wafers has been developed. An area of 10 mmphi and 10 microm depth was etched by 100 microL of an etching solution with a HF and HNO3 mixture. The acid matrix was evaporated on the wafer surface by IR lamp illumination and vacuum exhaust. Metallic impurities remaining on the wafer surface were redissolved into the collection solution, which was measured by electrothermal atomic absorption spectrometry (ET-AAS). The recovery invested by local etching/ET-AAS was within 95 - 112% for Fe, Cu and Ni. The detection limit (3sigma) for Fe, Cu and Ni in silicon was 1 x 10(13) atoms/cm3. To confirm the applicability, local etching was applied to evaluate the effects of metallic impurities in a gettering study and the electronic properties of semiconductor devices. It was found that local etching is a useful sample preparation technique for the analysis of metallic impurities in a specific area on a silicon wafer.     

Enhancement and stabilization of the photoluminescence from porous silicon prepared by Ag‐assisted electrochemical etching

In this paper, we present the results of studies on the photoluminescence (PL) of porous silicon (PSi) samples obtained by etching with the assistance of silver metal in different ways. If the Si sample, after being coated with a layer of silver nanoparticles, is electrochemically etched, its PL intensity becomes hundreds of times stronger than the PL intensity when it is chemically etched in the similar conditions. The difference in the PL intensities is explained partly by the anodic oxidation of silicon which occurs during the electrochemical etching process. The most obvious evidence that silicon had been oxidized anodically in the electrochemical etching process is the disappearance of the PSi layer and the appearance of the silicon oxide layer with mosaic structure when the anodization current density is large enough. The anodic oxidation has the effect of PSi surface passivation. Because of that, the PL of obtained PSi becomes stronger and more stable with time. Copyright © 2012 John Wiley & Sons, Ltd.     

Superhydrophobic silicon surfaces with micro-nano hierarchical structures via deep reactive ion etching and galvanic etching

An effective fabrication method combining deep reactive ion etching and galvanic etching for silicon micro-nano hierarchical structures is presented in this paper. The method can partially control the morphology of the nanostructures and enables us to investigate the effects of geometry changes on the properties of the surfaces. The forming mechanism of silicon nanostructures based on silver nanoparticle galvanic etching was illustrated and the effects of process parameters on the surface morphology were thoroughly discussed. It is found that process parameters have more impact on the height of silicon nanostructure than its diameter. Contact angle measurement and tilting/dropping test results show that as-prepared silicon surfaces with hierarchical structures were superhydrophobic. What's more, two-scale model composed of micropillar arrays and nanopillar arrays was proposed to study the wettability of the surface with hierarchical structures. Wettability analysis results indicate that the superhydrophobic surface may demonstrate a hybrid state at which water sits on nanoscale pillars and immerses into microscale grooves partially.     

Bulk electrochemical etching of semiconductor single-crystal silicon in HF-containing solutions

Effect of the component composition of an HF-containing electrolytic aqueous solution on the polishing electrochemical etching of semiconductor single-crystal silicon was studied. Propanol-2, SV-1017, and NH₄F served as additional components of solutions used for this purpose. The conditions in which this process can be employed to form elements with 3D structure in microsystems devices were determined. An analysis of the results obtained led to an assumption that the hydrogen passivation of the surface of semiconductor single-crystal silicon is the rate-determining factor affecting the development of a bulk polishing electrochemical etching of this material. Because the process of polishing electrochemical etching of silicon wafers is preserved during approximately 20 min, the method is acceptable for formation of shallow grooves in microsystems devices.     

金属辅助化学刻蚀法制备硅纳米线及应用

金属辅助化学刻蚀是近些年发展起来的一种各向异性湿法刻蚀,利用该方法可以制备出高长径比的半导体一维纳米结构。 本文综述了金属辅助化学刻蚀法可控制备硅纳米线的最新进展,简要概述了刻蚀的基本过程与机制,重点阐述了基于不同模板的金属辅助化学刻蚀可控制备高度有序、高长径比的硅纳米线阵列的具体流程与工艺,并介绍了其在锂离子电池、太阳能电池、气体传感检测和仿生超疏水等方面的潜在应用,探讨了目前存在的问题及其今后的研究发展方向。     

Mechanisms of particle removal from silicon wafer surface in wet chemical cleaning process

A quantitative mechanism of particle removal from silicon wafer surfaces by a wet chemical cleaning process is proposed. The particles are removed from the surface due to the combined effects of chemical etching and a net repulsive interaction between the particle and surface. The mechanism suggests that a critical etching depth, which has been determined theoretically, and an optimal etching rate, which can be determined from etching profile calculation, are required for particle removal. The study will help in the optimization of cleaning processes and formulation of superior cleaning solutions.     

Chemical etching of silicon: Smooth, rough, and glowing surfaces

Scanning Force Microscope images of silicon surface morphology are presented for samples exposed to various oxidizing environments followed by oxide removal. These are contrasted with samples exposed to HNO₃/HF solutions. The former samples consistently produced surface roughness on the order of a few nanometers, while the latter solution exhibited surface roughness of several hundred to over a thousand nanometers. This rough surface is photoluminescent and is known as porous silicon. Careful observation of the onset of the reaction (which is proceeded by a concentration dependent induction period) suggests that the reaction mechanism is autocatalytic; some etchant product species catalyzes the further attack of the surface. Surface features of co-existing fluorescing and non-fluorescing regions emphasize the heavy etching present in the porous silicon region. Local control of the porous silicon formation by a photoinduced etching process is reported for the first time suggesting the possibility of a non-resist lithographic procedure.     

Specific features of the bulk etching of single-crystal semiconducting silicon in aqueous KOH solutions

Bulk chemical etching of single-crystal semiconducting silicon in aqueous alkaline solutions of KOH was studied at various solution temperatures, alkaline component concentrations, and microscopic amounts of a potassium ferricyanide additive. Specific effects of these factors on the process of silicon etching are explained by comparing the corresponding activation energies. The possibility of using alkaline aqueous solutions of KOH with a potassium ferricyanide additive for fabrication of elements in microsystem technology devices is assessed.     

3D NAND制程中选择性刻蚀工艺的SiO2回沾问题研究进展

作为半导体市场中主要存储芯片之一,NAND已从2D发展到3D.3D NAND的立体存储结构提高了芯片容量、性能和可靠性.在3D NAND的交替堆栈结构中,需通过氮化-物氧化物的选择性刻蚀获得层间介质层,堆栈层数越多,芯片性能越好,但高层堆栈的刻蚀均匀性也更难保持,此时易出现SiO2在氧化层端头再沉积的回沾现象,层间结构...     

Extremely superhydrophobic surfaces with micro- and nanostructures fabricated by copper catalytic etching

We demonstrate a simple method for the fabrication of rough silicon surfaces with micro- and nanostructures, which exhibited superhydrophobic behaviors. Hierarchically rough silicon surfaces were prepared by copper (Cu)-assisted chemical etching process where Cu nanoparticles having particle size of 10-30 nm were deposited on silicon surface, depending on the period of time of electroless Cu plating. Surface roughness was controlled by both the size of Cu nanoparticles and etching conditions. As-synthesized rough silicon surfaces showed water contact angles ranging from 93° to 149°. Moreover, the hierarchically rough silicon surfaces were chemically modified by spin-coating of a thin layer of Teflon precursor with low surface energy. And thus it exhibited nonsticky and enhanced hydrophobic properties with extremely high contact angle of nearly 180°.     

Novel Electroless Deposition of Cu<Subscript>3</Subscript>Se<Subscript>2</Subscript> Film on Silicon Substrate by a Simple Galvanic Displacement Process

A novel electroless deposition method for depositing highly uniform adhesive thin films of copper selenide (Cu₃Se₂) on silicon substrates from aqueous solutions is described. The deposition is carried out by two coupled galvanic reactions in a single deposition bath containing copper cations, hydrogen fluoride, and selenous acid: the galvanic deposition of copper on silicon and the subsequent galvanic reaction between the deposited copper with selenous acid in the deposition bath. The powder X-ray diffraction and scanning electron microscopy are used to characterize and examine the deposited films.     

Depth profiles of arsenic in semiconductor silicon by chemical etching and non-dispersive atomic fluorescence spectrometry with hydride generation

An improved non-dispersive atomic fluorescence spectrometric determination of arsenic by sodium tetrahydroborate reduction is described. A new burner on which a small argon-hydrogen-entrained air flame can be maintained at a low hydrogen flow rate (0.15 1 min^-1) is reported. The detection limit ($\text{S}\text{N}$ = 2) is 10 pg of arsenic, and the analytical working curve is linear over four decades of concentration from the detection limit. The system is applied to depth profiling of arsenic in silicon slices. The silicon is anodized, the silica film is removed by hydrofluoric acid and the arsenic in the etching solution determined. The depth of silicon removed is measured by determining the silicon content in the etching solution by inductively-coupled plasma atomic emission spectrometry. The method permits determinations of ?10¹⁸ atoms As cm^-3 in 30-nm sections of a silicon slice with a diameter of 5.1 cm.     

Fabrication of nanostructured silicon by metal-assisted etching and its effects on matrix-free laser desorption/ionization mass spectrometry

A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300 s then decreases until 600 s for both low resistance (0.001–0.02 Ω cm) and high resistance (1–100 Ω cm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance.