Etching Of Substrate Research Articles

(Digital Presentation) Research on Single Wafer RCA Clean in High Aspect Ratio Trenches

High aspect ratios trench are commonly used in shallow trench isolation (STI) or Gate Poly-silicon structures by dry etching of a silicon substrate. During the dry etching process, polymerization residues are produced inside the trench. These polymerization residues must be removed before the next deposition process. Watermarks might also form by poor drying after the wet cleaning process of high aspect ratio structures, which can seriously affect the next process. In this paper, we show the performance of single wafer RCA cleaning technology in high aspect ratio structures. Polymer residues can be removed by diluted HF and SC1 with megasonic technology, without the appearance of watermarks after drying. This study focuses on polymerization residues and watermarks using inline defect detection to qualify the performance of single wafer RCA clean. Yield is the final verification for proving the single wafer RCA clean.

Stamping colors with solid-state superionic stamping (S4)

Traditional top-down approaches to producing metallic nanostructures are usually indirect; involve ultra-high vacuum processing steps and deep sub-micron lithography such as electron-beam lithography (EBL). Therefore, such pathways are difficult to scale up to high production rates. Additionally, they are too expensive to deploy in the production of single-use, low-cost products like plasmonic biological or chemical sensors, security tags or decorative patterns, all of which involve metallic nanopatterns. Hence, there is a need for more scalable and affordable manufacturing pathways for producing metallic nanostructures. In this work, we demonstrate a scalable manufacturing pathway for patterning silver nanostructures for plasmonic color generation. The pathway begins with the production of a single master pattern. We use commercially available Two-Photon Lithography (TPL) to direct-write a mask on a silicon substrate. Shallow etching of the silicon substrate with this mask by the Reactive Ion Etching (RIE) process (or Deep Reactive-Ion Etching for deeper patterns) produces a silicon master mold with the desired pattern. This master is used for hot embossing AgI-AgPO3 glass, a chemically stable, pure Ag-ion conductor with a low glass transition temperature (of about 100 °C, depending on its stoichiometry), into a stamp. This glass stamp, in turn, is used in the Solid-State Superionic Stamping (S4) process to electrochemically imprint the desired pattern into several substrates. Here, with this direct, facile, and efficient process, we report that a single nano-patterned stamp is capable of producing several high-fidelity replicas of the master.

Comparative study of nanostructured ultra-thin AlGaN/GaN heterostructures grown on hybrid compliant SiC/porSi substrates by molecular beam epitaxy with plasma nitrogen activation

This study demonstrates the advantages of using a hybrid compliant substrate containing a porous silicon (porSi) layer, obtained through electrochemical etching of the original silicon substrate, and a silicon carbide (SiC) layer, formed on its surface through the Kukushkin method, to grow high-quality, ultra-thin nanostructured AlхGa1-xN/GaN heterostructures with nanocolumnar morphology by molecular beam epitaxy with plasma-activated nitrogen.Comparison of our experimental results with information from prior literature illustrates that the use of such a hybrid SiC/porSi substrate has a number of undeniable advantages for the growth of ultra-thin AlхGa1-xN/GaN nanoheterostructures without the use of thick AIIIN buffer layers. Direct growth on a hybrid compliant substrate and SiC/porSi leads to a substantial relaxation of elastic stresses between the epitaxial film, porous silicon, and silicon carbide; this consequently affects the structural quality and optical characteristics of AIIIN nitride-based transistor ultra-thin structures.The experimental and computational data obtained in our research are important for understanding the physics and technology of AlхGa1-xN/GaN nanoheterostructures, and they will contribute to their potential applications in optoelectronics.

Application of a Femtosecond Laser in the Fabrication fused Silica Sensing Elements for MEMS Accelerometers

A group method of manufacturing quartz sensing elements of MEMS Q-flex type accelerometers is known, which is based on sequential liquid and plasma chemical etching in fluorinated plasma. In order to reduce the defects of the final products, labor costs for their manufacture and to obtain a rectangular etching profile of through holes in the section of the sensing element, an alternative technology for forming holes has been developed. The technology is thus the laser radiation pretreatment of fused silica glass with ultrashort pulse duration (about hundreds of femtoseconds) for the entire thickness of the substrate and subsequent liquid etching holes. The conducted studies revealed a local increase in the etching rate of irradiated section of fused silica glass during liquid etching with hydrofluoric acid or alkaline solution. The influence of the etching solution concentration on the change in the etching rate and the roughness of quartz is analyzed. The technology is universal and it can be used for high-precision volumetric processing of product formed from fused silica glass up to 4 mm thick.

Backside wet etching of sapphire substrate by laser-induced carbothermal reduction

Laser-induced backside wet etching is a promising technology to process sapphire substrate. However, the conventional working media including toxic organic and heavy metal salt solutions is not environmentally friendly. In this paper, the backside wet etching of sapphire substrate with ink as a working solution by laser-induced carbothermal reduction is achieved. Raman and XRD analyses demonstrate that ink can provide a stable carbon source and the carbothermal reduction of sapphire occurs during the etching. Numerical calculation reveals that the deposition of the carbon layer plays a crucial role in heating the sapphire to the temperature triggering the carbothermal reduction. The grooves etched by the laser-induced carbothermal reduction have smooth walls and good shape reproducibility. The linearly increase in etching depth with pulse number at the same laser fluence. The high-quality etching based on the carbothermal reduction as the etching mechanism is beneficial for fabricating microstructures on sapphire.

Influence of the asymmetry of the metal mask arrangement on the matching of the lower electrode with a high-frequency displacement generator during reactive-ion etching of massive substrates

The effect of the degree of asymmetry in the arrangement of metal masks on the matching of the lower electrode with a high-frequency displacement generator during selective reactive-ion etching of massive substrates in plasma-forming gas mixtures based on freon-14 is studied theoretically and experimentally. Theoretically, the absence of the influence of the asymmetry of the mask location on the specific reactive power is shown. It is shown that at the edge of the substrate, especially with a mask, there is a sharp increase in the RF current density, which proves mainly the surface (end) nature of its flow. The influence of the mask location on the behavior of the electric charge density, which correlates with the distribution of the RF current density in the near-surface layer of the substrate, is established. No redistribution of the charge density of the chemically active plasma particles at the edge of the mask was detected. In accordance with the theoretical results obtained, it is experimentally shown that metal masks with a side length ratio of 36/0 mm reduce the power reflection coefficient within 5%. Keywords: diffractive optical element, reactive ion etching, inductively coupled plasma, contact mask, lower electrode, simulation Multiphysics.

Wet etching in β-Ga2O3 bulk single crystals

Wet etching is a simple and effective method to identify defects, fabricate patterns, and polish wafers of semiconductors. We highlight recent progress in wet etching of β-Ga2O3 substrates with an aim to comprehensively understand the etching behavior and mechanism.

GaN-based heterostructures with CVD diamond heat sinks: A new fabrication approach towards efficient electronic devices

A new approach to the fabrication of efficient heat sinks for GaN-based transistors is demonstrated. A key feature of this work is the growth of polycrystalline diamond coating on the functional silicon layer of SOI wafers followed by etching of a thick silicon substrate and a thin thermal oxide. As a result, composite epi–ready substrates consisting of a thin (410 nm) monocrystalline silicon functional layer on top of the 150 µm-thick polycrystalline diamond heat sink were fabricated. GaN heterostructures were grown on top of the silicon layer, which resulted in an effective thermal contact between CVD diamond and GaN structure. The packaged ungated transistors were made to analyze the efficiency of the developed heat sink. Improved heat removal structures showed the decrease in surface temperature by more than 50 °C at base temperature of Tb=85 °C and dissipation power of Pdiss=6.9 W/mm compared to conventional GaN-on-SiC technology and by more than 20 °C at Tb=25 °C, Pdiss=6.9 W/mm compared to up-to-date GaN-on-Diamond equivalent transistors reported by other groups. New substrate fabrication technology positively impacts GaN-based device output characteristics and reliability, which is important in improving communication systems, radars, and secondary power supply systems.

An alN-based piezoelectric micromachined ultrasonic transducer with a double-beam suspended structure

ABSTRACT This paper presents an AlN-based piezoelectric micromachined ultrasonic transducer (PMUT) with a double-beam suspended structure. In order to obtain greater deflection displacement and output sound pressure compared to standard systems, a suspended structure is proposed, achieved by utilizing double-sided deep reactive ion etching of the silicon substrate. This structure is capable of greatly reducing the tensile stress caused by deflection on the membrane edge, thereby improving the piezoelectric micromachined ultrasound transducer performance. Simulations are performed using the finite element method and COMSOL software, with results demonstrating that the suspension structure exhibits a lower resonant frequency and a larger membrane deflection displacement than other methods, implying higher penetration and acoustic energy levels. Thus, the sound pressure is improved by changing the PMUT structure. Moreover, a PMUT with a double-beam is fabricated, and the impedance diagram is determined with an impedance analyzer. The resonant frequency of the transducer was 31.88 kHz, while the sound wave received by the standard lead zirconate titanate (PZT) ultrasonic transducer was converted to a voltage of 277.5 mV. In comparison, the proposed PMUT demonstrates an improved acoustic emission performance. In addition, the electromechanical coupling coefficient of the suspended PMUT is observed to be approximately 3.08%, which is significantly better than that of a fully clamped PMUT. This demonstrates the strong electromechanical conversion performance of the proposed PMUT. Results from the transmission and reception air experiments prove that the proposed double-beam PMUT can potentially be used for ranging and wireless energy transmission applications.

Study of nonlinear optical phenomena in silicon nanowires

This work studies generation of second and third harmonics in arrays of vertically oriented silicon nanowires (SiNWs) encapsulated into a silicone membrane and separated from the growth substrate. The structures were produced by plasma-chemical etching of silicon substrate resulting in a formation of homogeneous arrays of SiNWs. Such SiNW-based membranes demonstrated efficient infrared-to-visible light conversion by generation of second and third harmonic signals visible by a naked eye. This study contributes to the development of technology of optical devices based on silicon and presents a new route for visualization of infrared radiation.

Specific Features of Matching of a Lower Electrode and an RF Bias Generator for Reactive Ion Etching of Bulk Substrates

Specific Features of Matching of a Lower Electrode and an RF Bias Generator for Reactive Ion Etching of Bulk Substrates

Self-assembled multifunctional nanostructures for surface passivation and photon management in silicon photovoltaics

Abstract This work reports the fabrication and characterization of multifunctional, nanostructured passivation layers formed using a self-assembly process that provide both surface passivation and improved light trapping in crystalline silicon photovoltaic (PV) cells. Scalable block copolymer self-assembly and vapor phase infiltration processes are used to form arrays of aluminum oxide nanostructures (Al2O3) on crystalline silicon without substrate etching. The Al2O3 nanostructures are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spectroscopic ellipsometry. Injection-level dependent photoconductance measurements are used to determine the effective carrier lifetime of the samples to confirm the nanostructures successfully passivate the Si surface. Finite element method simulations and reflectance measurement show that the nanostructures increase the internal rear reflectance of the PV cell by suppressing the parasitic optical losses in the metal contact. An optimized morphology of the structures is identified for their potential use in PV cells as multifunctional materials providing surface passivation, photon management, and carrier transport pathways.

Improvement of thermal‐type MEMS flow sensor chip via new process of silicon etching with sacrificial polycrystalline silicon layer

AbstractThis paper reports upon a new process for the flow sensor fabrication of a thermal microelectromechanical systems (MEMS) and its performance improvement. A unique feature of the proposed process is the silicon etching, which is a combination of normal crystal‐oriented silicon etching and isotropic etching of polycrystalline silicon (poly‐Si). The poly‐Si layer works as a sacrificial layer and promotes etching of the silicon substrate in the horizonal direction, thereby enabling location of the etching holes in the membrane of the flow sensor without the conventional etching rules. Some designs for the flow sensors, which have been infeasible with normal processes, were thus fabricated and evaluated. Hence, the new process improves the design flexibility of the membrane and enhances flow sensor performance, such as 38.3% reduction in power consumption.

Optimization of TSV Leakage in Via-Middle TSV Process for Wafer-Level Packaging

Through silicon via (TSV) offers a promising solution for the vertical connection of chip I/O, which enables smaller and thinner package sizes and cost-effective products by using wafer-level packaging instead of a chip-level process. However, TSV leakage has become a critical concern in the BEOL process. In this paper, a Cu-fulfilled via-middle TSV with 100 µm depth embedded in 0.18 µm CMOS process for sensor application is presented, focusing on the analysis and optimization of TSV leakage. By using etch process, substrate defect, and thermal processing co-optimization, TSV leakage failure can be successfully avoided, which can be very instructive for the improvement in TSV wafer-level package yield as well as device performance in advanced semiconductor technology.

Dry etching of monocrystalline silicon using a laser-induced reactive micro plasma

Dry etching is a prevalent technique for pattern transfer and material removal in microelectronics, optics and photonics due to its high precision material removal with low surface and subsurface damage. These processes, including reactive ion etching (RIE) and plasma etching (PE), are performed at vacuum conditions and provide high selectivity and vertical side wall etched patterns but create high costs and efforts in maintenance due to the required machinery.In contrast to electrically generated plasmas, laser-induced micro plasmas are controllable sources of reactive species in gases at atmospheric pressure that can be used for dry etching of materials.In the present study, we have demonstrated the laser-induced plasma etching of monocrystalline silicon. A Ti:Sapphire laser has been used for igniting an optically pumped plasma in a CF4/O2 gas mixture near atmospheric pressure. The influence of process parameters, like substrate temperature, O2 concentration, plasma-surface distance, etching duration, pulse energy and crystal orientation on etching rate and surface morphology has been investigated.Typical etching rates of 2–12 µm x min−1 can be achieved by varying mentioned parameters with a decreasing etching rate during the process. Different morphologies can be observed due to the parameters set, smooth as well as rough surfaces or even inverted pyramids.The presented etching method provides an approach for precise machining of silicon surfaces with good surface qualities near atmospheric pressure and sufficiently high material removal rates for ultraprecise surface machining.

Etching of iron and iron–chromium alloys using ICP-RIE chlorine plasma

The dry etching process of Fe, Cr and Fe–Cr alloys under a chlorine-based plasma is studied. The objective is to create new surface functionalities. The approach combines an experimental study of an ICP (Inductively Coupled Plasma) reactor with the development of a multi-scale etching model including kinetic, sheath and surface models. The results from plasma etching of substrates made of Fe, Cr and Fe–Cr alloys are presented. Optical emission spectroscopy and interferometry measurements show strong modifications of the plasma when Fe or Cr samples are present in the reactor. It is shown that Fe is easier to etch than Cr. The study highlights the role of chemical etching by the formation of volatile products such as FeCl3. The Cr content in Fe–Cr alloys has a strong impact on both the lateral and vertical etch rates, as well as on the roughness along the profile. For Fe-Cr alloys, the experimental and calculated values of etch rate are very similar. The concept of hard zones is introduced to get a better agreement between simulation results and experimental ones. This good agreement demonstrates the capability of the developed simulator to implement new phenomena.

The Influence of Metal Masks on Matching of the Lower Electrode and a High-Frequency Bias Generator at Reactive Ion Etching of Large Substrates

The Influence of Metal Masks on Matching of the Lower Electrode and a High-Frequency Bias Generator at Reactive Ion Etching of Large Substrates

Plasma Etching‐Assisted Perpendicular Magnetic Anisotropy

Ferromagnetism with perpendicular magnetic anisotropy (PMA) receives continuous attention. But, the PMA is always limited by materials system, the assistance from suitable buffer layers such as Pt and Ta is essential. A general method for the generation of PMA on various systems is pursued. Herein, it is shown that preparatory plasma etching of oxide substrate produces robust PMA in subsequent grown ferromagnetic multilayers, out‐of‐plane hysteresis loop is rectangular with remanence close to 100%. In contrast, without the preparatory plasma etching, out‐of‐plane hysteresis loop of subsequent grown ferromagnetic multilayers is very oblique, the calculated uniaxial anisotropic constant is one order of magnitude smaller than the former one. The enhancements of PMA are observed in distinct oxide substrates including Si/SiO2, Al2O3, LaAlO3, and MgO, indicating the interfacial plasma etching technique can be used for various oxide substrates to obtain PMA. The promotion of Co–O hybridization is proposed to be the dominant reason for the enhancement of PMA, which is supported by the control experiment. This finding provides opportunity for the formation of interfacial PMA on crystalline oxide substrates, and expands the material selection for achieving PMA.

Effect of backside dry etching on the device performance of AlGaN/GaN HEMTs

AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) have significant advantages of high carrier concentration, high electron mobility, and large breakdown voltage, and show promising potential as power devices. Being widely used in semiconductor manufacturing, dry etching process is capable of fabricating microstructures and thinning substrate from backside, which is good for developing flexible devices. Here, we investigate the effect of backside dry etching of Si substrate on the physical and electrical properties of AlGaN/GaN HEMTs. The physical properties were characterized by scanning electron microscope, Raman spectra, and x-ray diffraction (XRD). After the dry etching process, the peak red-shift of GaN E 2 mode indicates an increase of tensile stress, and the XRD rocking curve of GaN film shows to a certain extent decreased dislocation density. Furthermore, the maximum saturation current density and maximum transconductance of the HEMTs are improved by 21.1% and 25.5%, respectively. The approach of backside dry etching for thinning Si substrate would contribute to the optimization of GaN heterojunction-based devices, and also provide inspirations for the development of flexible and robust power devices.

Deep isotropic chemical etching (DICE) process for fabricating highly symmetric hemispherical silicon molds

This paper introduces the deep isotropic chemical etching (DICE) process developed for wafer-scale manufacturing of highly symmetric hemispherical silicon molds. The DICE process uses silicon nitride concentric rings as a masking layer during hydrofluoric, nitric, acetic etching of silicon substrate. These concentric rings pop up and widen the etch aperture as etch depth increases, thereby allowing control of vertical and lateral etch rates until reaching the desired mold dimensions. Our comparative experiments demonstrate that the pop-up rings are remarkable at creating molds with enhanced symmetry compared to the conventional pinhole masks. We have demonstrated the effectiveness of our approach compared to single pinholes by producing a super-symmetric 0.1 mm hemispherical mold () using two concentric rings surrounding a pinhole. We have then shown how the DICE process can be used to fabricate larger silicon molds and presented the results of a single concentric ring that achieves fabrication of a 0.25 mm-deep mold with an aspect ratio of .