Trench Profile Research Articles

Cryogenic DRIE processes for high-precision silicon etching in MEMS applications

Cryogenic deep reactive ion etching (Cryo DRIE) of silicon has become an enticing but challenging process utilized in front-end fabrication for the semiconductor industry. This method, compared to the Bosch process, yields vertical etch profiles with smoother sidewalls not subjected to scalloping, which are desired for many microelectromechanical systems (MEMS) applications. Smoother sidewalls enhance electrical contact by ensuring more conformal and uniform sidewall coverage, thereby increasing the effective contact area without altering contact dimensions. The versatility of the Cryo DRIE process allows for customization of the etch profiles by adjusting key process parameters such as table temperature, O2 percentage of the total gas flow rate (O2 + SF6), RF bias power and process pressure. In this work, we undertake a comprehensive study of the effects of Cryo DRIE process parameters on the trench profiles in the structures used to define cantilevers in MEMS devices. Experiments were performed with an Oxford PlasmaPro 100 Estrelas ICP-RIE system using positive photoresist SPR-955 as a mask material. Our findings demonstrate significant influences on the sidewall angle, etch rate and trench shape due to these parameter modifications. Varying the table temperature between −80 °C and −120 °C under a constant process pressure of 10 mTorr changes the etch rate from 3 to 4 μm min−1, while sidewall angle changes by ∼2°, from positive (<90° relative to the Si surface) to negative (>90° relative to the Si surface) tapering. Altering the O2 flow rate with constant SF6 flow results in a notable 10° shift in sidewall tapering. Furthermore, SPR-955 photoresist masks provide selectivity of 46:1 with respect to Si and facilitates the fabrication of MEMS devices with precise dimension control ranging from 1 to 100 μm for etching depths up to 42 μm using Cryo DRIE. Understanding the influence of each parameter is crucial for optimizing MEMS device fabrication.

Post-trench restoration for vertical GaN power devices

The impact of the post-trench restoration on the electrical characteristics of vertical GaN power devices is systematically investigated in this work. Following the achievement of microtrench-free GaN trench structure with modified dry etching conditions, the post-trench tetramethylammonium hydroxide (TMAH)-based wet etching and UV/Ozone-based oxidation process are employed to further refine the trench profile. It is shown that the c-plane trench bottom is restored to the level of unetched surface, as evidenced by the improved Schottky interface. Additionally, the post-trench treatment exhibits the anisotropic characteristics with the preferred rounded corner profile on m-plane sidewall compared to a-plane sidewall. The simulations and experimental results demonstrate that the trench MOS barrier Schottky (TMBS) rectifier based on m-plane sidewall could suppress the electric field crowding at the trench corner and, hence, reduce the reverse leakage current by 1–2 orders of magnitude. Furthermore, the MOSCAP test structures were fabricated on the trenches. The extracted interface trap density (Dit) confirms the effective restoration of trench bottom. However, the sidewall surface exhibits the relatively large Dit, which emphasizes the necessity of optimizing the sidewall, particularly for devices incorporating sidewall channel. The demonstrated post-trench restoration technique improves the surface quality and trench structure for the significantly enhanced electrical performances, which is essential for the development of vertical GaN power devices.

Incorporation of the riser-seabed-seawater interaction effects into the trench formation and fatigue response of steel catenary risers in the touchdown zone

The existing Steel Catenary Riser (SCR)-seabed interaction models do not account for the contribution of seawater as a key influential factor. The present study has examined the effect of SCR-seabed-seawater interaction on the trench enlargement and consequently on the fatigue performance of the SCR in the touchdown zone (TDZ). Coupled Eulerian-Lagrangian (CEL) analysis with three domains of SCR, seabed soil, and seawater were performed using ABAQUS. A parametric study was conducted to investigate the impact of seawater interaction along with incorporation of the shear strain rate and softening effects. The conventional bearing capacity approach for analysing pipe penetration into the seabed was also reviewed, and modifications were proposed to account for the effects of water entrainment into the trench. The results obtained from CEL analysis were integrated with a global SCR model to incorporate the SCR-seabed-seawater interaction effects into the fatigue analysis. The study showed that the entrainment of seawater into the trench can be coupled with SCR oscillations to further soften the seabed and erode the trench resulting in an enlarged trench profile affecting the fatigue damage in the TDZ.

Numerical prediction of potential 3-dimensional seabed trench profiles considering complex motions of mooring line

Seabed trenches near deep-sea anchors bring risks to the mooring system's safety. The prediction of 3-dimensional (3-D) trench profiles is a key task to reduce the risk. However, the trench width related to the trench wall collapse and lateral movement of the mooring line has not been well studied. This paper first proposes a 3-D mooring line-seabed dynamics model to consider the mooring line lateral movement in the soil. Then, a seabed trenching model to simplify 3-D trench profiles is developed based on the field data. By combining the above models, a novel method to predict 3-D trench profiles around embedded mooring lines is established by considering trench wall collapse and integrating dynamics of mooring line. Based on the verified method, both static and dynamic responses of mooring lines are investigated, then a series of parametric sensitivity studies are carried out. The simulation results reveal that dynamic movement of mooring lines at fairlead may result in remarkable seabed trenches, and lateral motion of mooring lines enlarges the disturbed zone near the mooring line touchdown area. The proposed method in this paper provides a reasonable assessment of the 3-D trench profiles and reduces risks in the operation of mooring systems.

Pattern Collapse Simulation in CMOS Image Sensors Devices

Pattern collapse in CMOS image sensors is discussed, where silicon pillars are separated by trenches of few microns deep. Both analytical and numerical models are given and match experimental results. The trench profile is also taken into account to predict such collapse.

A Framework for Mooring and Anchor Design in Sand Considering Seabed Trenches Based on Floater Hydrodynamics

Seabed trenches reduce anchor capacity. However, the adverse influence is not considered in the current design, and no guideline is found in engineering practice. This paper presents a framework for mooring and anchor design in sand considering seabed trenches based on floater hydrodynamics. First, a hydrodynamic calculation of the studied floater coupled with the mooring system was conducted. Then, the potential trench profile was assessed using a mooring line–seabed dynamic model. Third, after assessing the suction anchor performance based on its installation and capacity, a refined anchor, caisson–plate gravity anchor (CPGA), was proposed, and the capacity mechanisms were analyzed. It was found that the tensions of mooring lines l1 and l2 resist maximum loads under a 45° load condition. Due to the sand’s high strength, a trench is difficult to form in this mooring type. The suction anchor is not suitable as an anchor for the carbonate sand, considering its installation and capacity. The analyses indicate that the increase in soil stress and soil mobilized range in front of the caisson promotes the capacity of CPGA. This paper provides a framework/example to design moorings and anchors considering potential trenches and provides a solution to the anchor design in carbonate sand.

A hybrid model to simulate the trench effect on the fatigue analysis of steel catenary risers in the touchdown zone

The gradual trench formation of steel catenary risers (SCRs) in the touchdown zone is known to significantly affect the SCR’s fatigue life. However, there is still no coherent agreement among researchers on the beneficial or detrimental effects of the trench on fatigue. Recent studies have shown that a potential source of contradictory fatigue results could be the methodology to incorporate the trench in the numerical simulations. Since the predefined mathematical trench profiles create non-realistic contact pressure hot spots in the seabed, and the nonlinear hysteretic seabed interaction models may cause premature trench stabilization, both methods distort the damage distribution. To resolve these problems, a new model called the Hybrid Trench Model (HTM) has been developed in this study by combining the linear soil stiffness and nonlinear hysteretic seabed interaction model. This hybrid model provides an equivalent stiffness distribution in the touchdown zone to simulate the trench profile obtained from a nonlinear riser–seabed interaction model. HTM’s capability in developing deep trenches, e.g., 5D, was examined along with perfect compatibility with the natural catenary shape of the riser, exhibiting the reliability of this method to incorporate the trench effect into the fatigue analysis.

Palaeoenvironmental evolution of the Badain Jaran Desert hinterland during the Early to Middle Holocene: A multi-proxy reconstruction on Taoerlegetu paleolake, northwest China

In this paper, we examine the Early to Middle Holocene evolution of a prominent group of ground-water fed lakes in the southeastern hinterland of the Badain Jaran Desert (BJD) of northwest China. Specifically, we describe a sediment profile record from the Taoerlegetu (TR) palaeolake basin using multiple proxies of total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13Corg, grain size and mineral composition based on a well-dated trench profile. As C/N values suggest that sedimentary organic matter mainly originated from aquatic plants, δ13Corg values can be used as a qualitative proxy for water level because aquatic plants in different biotopes (water depth) have different δ13C values. Our results show that from 10.9 to 9.1 cal kyr B.P., water level rose slowly, and aquatic macrophytes occupied the lake basin. From 9.1 to 5.5 cal kyr B.P., water level reached an even higher level and phytoplankton replaced macrophytes as the major contributor to organic matter. The humid episode of the lakes in the hinterland of the BJD in the early Holocene might be related to the increased groundwater supply from the northeast region of the Tibet Plateau. These findings are consistent with earlier studies of lacustrine and peat sediments found in periphery of the modern lake group, which indicate that their geographic extent may have been larger in the past. A relative drought period recorded in the studied succession from 8.5 to 8.0 cal kyr B.P. marks an interval of reduced ground-water transport from the Tibet Plateau. This interval probably corresponds to the “8.2 ka cold event” and provides evidence that this widespread climate episode influenced groundwater processes across inland Asia.

Study on the Transformation of Si Trench Profile With Low Pressure of SF₆/O₂ Containing Plasmas

The reason for the change of trench sidewall profile under low pressure of SF6/O2 containing plasma was explored by studying the trench morphology under different etching conditions. The result shows that the Si undercut decreases with the decreasing of pressure and the uniformity will become better. However, the sidewall of the trench presents a negatively tapered under low pressure. The reasons for different profile of trench are explored by the thickness of sidewall protective layer for the first time. The TEM results show that the trench sidewall forms a protective film with a thickness of about 100Å. The thickness of the oxide layer decreases from top to bottom. And the EDX results show that the main elements of the protective film are Si and O. Due to the decrease of oxide thickness, the width of trench bottom will become larger and larger, resulting in negatively tapered morphology. It is worth noting that the profile of trench changes to positively tapered again under the condition of low ratio of SF6/O2. Based on this, an optimized trench etching process is proposed and the etch rate is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.15{\mu }\text{m}$ </tex-math></inline-formula> /min and the selectivity to the oxide mask is 14.

Industrial Hemp Root Length Density and Distribution under Polyethylene Mulch with Drip Irrigation

Delineating the depth and extent of the industrial hemp (Cannabis sativa L.) root zone assists with proper irrigation management and minimizes nutrient leaching. The objective of this 3-year field study was to measure root distribution and root length density of industrial hemp cultivars produced for cannabinoids grown under polyethylene mulch with drip irrigation. Root length density (RLD) was measured from 75-cm-deep soil cores obtained during vegetative growth, at early bloom, and at flower harvest. Cores were taken in-row and 15 cm to the side of each plant. In addition to root cores, the trench profile method was used during 2020 to observe in situ gross root architecture of a direct-seeded cannabinoid cultivar. RLD was significantly greater in the 0- to 30-cm soil depth and dropped dramatically below 30 cm; RLD was not significantly affected by cultivar. These findings suggest that the effective root zone depth for industrial hemp cultivars produced for cannabinoids is 0 to 30 cm and that the cultivars tested in this study do not differ in root system size or location.

High performance carrier stored trench bipolar transistor with dual shielding structure

We propose a novel high performance carrier stored trench bipolar transistor (CSTBT) with dual shielding structure (DSS-CSTBT). The proposed DSS-CSTBT features a double trench structure with different trench profiles in the surface, in which a shallow gate trench is shielded by a deep emitter trench and a thick oxide layer under it. Compared with the conventional CSTBT (con-CSTBT), the proposed DSS-CSTBT not only alleviates the negative impact of the shallow gate trench and highly doped CS layer on the breakdown voltage (BV), but also well reduces the gate-collector capacitance C GC, gate charge Q G, and turn-off loss E OFF of the device. Furthermore, lower turn-on loss E ON and gate drive loss E DR are also obtained. Simulation results show that with the same CS layer doping concentration N CS = 1.5 × 1016 cm−3, the BV increases from 1312 V of the con-CSTBT to 1423 V of the proposed DSS-CSTBT with oxide layer thickness under gate (T og2) of 1 μm. Moreover, compared with the con-CSTBT, the C GC at V CE of 25 V and miller plateau charge (Q GC) for the proposed DSS-CSTBT with T og2 of 1 μm are reduced by 79.4% and 74.3%, respectively. With the V GE increases from 0 V to 15 V, the total Q G for the proposed DSS-CSTBT with T og2 of 1 μm is reduced by 49.5%. As a result, at the same on-state voltage drop (V CEON) of 1.55 V, the E ON and E OFF are reduced from 20.3 mJ/cm2 and 19.3 mJ/cm2 for the con-CSTBT to 8.2 mJ/cm2 and 9.7 mJ/cm2 for the proposed DSS-CSTBT with T og2 of 1 μm, respectively. The proposed DSS-CSTBT not only significantly improves the trade-off relationship between the V CEON and E OFF but also greatly reduces the E ON.

RACINE2.2: A Software Application for Processing and Mapping Spatial Distribution of Root Length Density and Potential Root Extraction Ratio from Root Counts on Trench Profiles.

A method has been developed to measure root intersection density (RID) on a trench-profile in field conditions. Here we describe how 2D spatial distribution mapping of RID can be processed and converted into root length density (RLD) and root distances (ARD) using a new freeware named RACINE2.2. The software also allows a simple modeling of potential root extraction ratio in the soil (PRER). The software contains models calculating RLD, ARD, and PRER from RID for several crops (maize, sorghum, sugarcane, rice, pearl millet, pineapple, eucalyptus). Models may be changed or added into RACINE2.2. RLD, ARD, and PRER are calculated for each spatial unit and can be used to generate 2D maps using RACINE2.2. Data can be exported to a spreadsheet or a surface mapping software for further analysis. It is also possible to import data into RACINE2.2 from a spreadsheet. This application thus makes studies about root-soil interactions, root growth, and root uptake easier. It opens new avenues to characterize root systems to improve root water and nutrient uptake in field conditions.

Dynamic analysis of steel catenary riser on the nonlinear seabed using vector form intrinsic finite element method

The dynamics of a steel catenary riser (SCR) are highly nonlinear and strongly affected by the interaction between riser and seabed. Possessing the advantages of robustness and high efficiency, the vector form intrinsic finite element (VFIFE) method is applied to solve this problem. The nonlinear hysteretic riser-seabed interaction is integrated into the model. Simulation results are compared to the commercial software Ocraflex, and high similarities prove the capability of VFIFE to simulate the dynamics of SCR on the nonlinear seabed. In dynamic analysis, a larger mass damping coefficient should be applied in the touchdown zone (TDZ) and flowline part to increase the stabilization. In contrast, the coefficient in the catenary part has only minor influences on the behavior of SCR. To improve the computation efficiency, the effect of using coarse meshes with different densities in the catenary part has been investigated, while the fine meshes are applied in the TDZ and flowline part. In the dynamic analysis of TDZ, the distribution of seabed reaction force and stress range are present and discussed. Furthermore, the effects of different loading parameters and hanging-off positions on the trench profiles and fatigue damage of SCR have been studied in detail.

Vertical root distribution in Himalayan trees: about half of roots occur below 30 cm, the generally sampled depth

Almost nothing is known about the vertical root distribution for Himalayan forest trees. By providing an analysis of vertical distribution of root density of ten important central Himalayan tree species (two evergreen conifers, five evergreen broadleaf species and three deciduous broadleaf species), this paper attempts to address this gap. We used trench profile method to measure tree root density, both of fine (≤ 3 mm diameter) and coarse (> 3 mm diameter) roots. Principal Component Analysis was performed to identify the major sources of variation among species in root distribution. In ten study tree species (eg., sal, oaks, pine and Cupressus torulosa) the rooting depth varied from 90 to 150 cm. On average across the study species, about 49% total roots (all diameter classes) occurred below 30 cm depth and 20.6% below 60 cm depth. These percentages are almost identical to that of tropical rain forest of Amazon. The tree species varied in root density (in entire soil column) from 26.04 ± 2.66 root/100 cm2 in Q. floribunda to 52.7 ± 4.96 root/100 cm2 in Machilus duthei. The ordination graph indicated that tree species of a growth form and even a genus did not form groups and differed markedly in root characters. Tree water status and roots were related only partially and in a complex way. The study has shown that (1) root density measured by digging trenches gives a reasonable estimate of proportional root distribution of trees, and (2) studies which consider only top 30 cm depth can grossly misrepresent root distribution and its consequence.

DESIGN AND CONSTRUCTION OF LINEAR MAIN PIPELINE ON WATER-LOGGED GROUNDS

The paper shows that the linear segments of the main pipelines laid on water-logged grounds are characterized by the floating parts 150–300 m long, with arch blowouts with a deflection of 1.0–1.5 m. This occurs due to the vertical axial loads and the temperature difference. The buckling stability of the floating part is calculated for the pipeline laid in a bog. It is shown that the loss of the buckling stability in the form of the floating parts and arch blowout can be explained by the fact that the project on the water-logged ground construction has no the analysis of the buckling stability under axial loads with regard to the topography of the trench bottom that describes the stress-strain state of the pipeline. At a design stage, it is necessary to conduct more detailed surveys on the pipeline laying with regard to the trench profile in calculating the pipeline buckling stability on water-logged grounds.

Seabed trenching near the mooring anchor: History cases and numerical studies

The floating platform with taut or semi-taut mooring systems is the main option for oil and gas exploitations in deep sea. However, it has been reported that the reciprocating motion of the mooring line tends to induce the seabed trench near the anchor, which consequently reduces the anchor capacity. In this paper, two parts of work have been carried out to enhance the understanding of the seabed trench. Firstly, the dimensions of reported trenches in the field as well as their formation conditions are summarized, and four feature points are proposed to describe the trench profile. Secondly, a numerical method considering mooring line dynamics to predict the final trench profiles is proposed, which contains two simulation modules, i.e. mooring line dynamics and seabed trenching. The method is verified using the data from the field and centrifuge tests. The influences of the mooring line tension and soil strength on trench profiles are comprehensively investigated further. The results show that obvious trenches are likely to form when the amplitude of mooring line tension variation is large and the soil shear strength is low. The main impact of the formed trenches is that the loading direction at the pad-eye tends to be horizontal.

Micro-trench free 4H-SiC etching with improved SiC/SiO2 selectivity using inductively coupled SF6/O2/Ar plasma

SiC dry etching process for formation of a trenched-gate structure in trench metal-oxide-semiconductor field-effect-transistors employing bottom protection p-well (BPW) has been investigated. SF6/O2/Ar based inductively-coupled-plasma reactive-ion-etching were utilized with various variations in process parameters, such as bias power, ICP power, kind of gas species, working pressure and temperature. The effects of process parameters on trench profiles were analyzed by a cross-sectional scanning electron microscope and profilometer to suppress micro trenches at a bottom corner of the trench and improve SiC/SiO2 etch selectivity. We successfully demonstrated the micro-trench free SiC trench structure with high SiC/SiO2 etch selectivity of 3.7 at bias power of 1 kW, ICP power of 4 kW, SF6/O2/Ar flows of 6/6/8 sccm, working pressure of 15 mTorr and temperature of 20 °C.

Experimental comparison of material removal rates in abrasive waterjet cutting and a novel droplet stream technique

The use of abrasive waterjets (AWJ) to machine metal surfaces is prevalent through-out industry. AWJ requires the purchase and disposal of costly abrasive particles which increases manufacturing costs and environmental-footprint. This motivates the exploration for low-cost, eco-friendly alternatives. A novel method which utilizes a stream of high-speed water droplets (WD) travelling through a sub-atmospheric pressure environment to remove material without using abrasive grit is presented. In this paper, the efficacy of this new process is investigated and compared to AWJ and pure water jet (WJ) (i.e., without abrasive particles) by measuring the material removal rates (MRR) of each process on a hard-to-machine steel, DP 1180, for equivalent water-flow conditions. Trench profiles are created by traversing each of the jets across a metal sample, from which the MRR and trench profiles are obtained. The MRR results reveal that WD is significantly faster than WJ, but is subordinate compared to AWJ for MRR efficiency. This identifies a trade-off between manufacturing cost and time.

A Deep Learning-Based Phenotypic Analysis of Rice Root Distribution from Field Images.

Root distribution in the soil determines plants' nutrient and water uptake capacity. Therefore, root distribution is one of the most important factors in crop production. The trench profile method is used to observe the root distribution underground by making a rectangular hole close to the crop, providing informative images of the root distribution compared to other root phenotyping methods. However, much effort is required to segment the root area for quantification. In this study, we present a promising approach employing a convolutional neural network for root segmentation in trench profile images. We defined two parameters, Depth50 and Width50, representing the vertical and horizontal centroid of root distribution, respectively. Quantified parameters for root distribution in rice (Oryza sativa L.) predicted by the trained model were highly correlated with parameters calculated by manual tracing. These results indicated that this approach is useful for rapid quantification of the root distribution from the trench profile images. Using the trained model, we quantified the root distribution parameters among 60 rice accessions, revealing the phenotypic diversity of root distributions. We conclude that employing the trench profile method and a convolutional neural network is reliable for root phenotyping and it will furthermore facilitate the study of crop roots in the field.

Intensive Cultural Resources Survey of the Proposed Dripping Springs Wastewater System Improvements Project (EID 1), Dripping Springs, Hays County, Texas

Intensive Cultural Resources Survey of the Proposed Dripping Springs Wastewater System Improvements Project (EID 1), Dripping Springs, Hays County, Texas