Μm Deep Trenches Research Articles

A double-sided 3D trench electrode detector using an 8-inch CMOS process: 3D simulation and experimental investigation

A double-sided 3D trench electrode detector (DS-3DTED) structure is proposed in this work to investigate the manufacturing process implementation of 3D detectors for high-energy physics, x-ray spectroscopy and x-ray cosmology applications. The device's electrical characterization, including electrostatic potential and electric field distributions, I–V, C–V, full depletion voltage and transient current with x-ray incidence, was performed with Synopsys® Sentaurus TCAD tools. In addition, a manufacturing method to realize the DS-3DTED device is presented. A 311 μm deep trench has been achieved through the Bosch process on the IMECAS 8-inch CMOS platform to verify the feasibility of the device structure. The maximum depth-to-width ratio is close to 105:1 when the trench width is 2 μm, which is an excellent foundation for manufacturing future 3D detector with a large fill factor and small dead region.

(Invited) Bottom-up Gold Filling for Manufacture of X-Ray Gratings: Mechanism and Implications

Over the past four years a process for extreme superconformal deposition of gold has been demonstrated and explored for void-free filling of recessed features on patterned substrates for application in X-ray imaging. Uniform and complete void-free filling was detailed on 100 mm silicon wafers patterned with micrometer pitch vias of aspect ratio (height/diameter) 23 and trenches of aspect ratio (height/width) exceeding 60 as well as trenches more than 300 μm deep and fractal patterns of spatially varying depth. This talk discusses a proposed mechanism and model for the observed behavior. Simulations capture key features of the experimental processes, including not only the bottom-up filling itself but also an extended incubation period of conformal deposition that precedes its start as well as self-passivation of the active deposition that accompanies the completion of filling. Feature filling results with relevant electrochemistry are discussed in the context of predicted behavior for different deposition conditions. Cross-sectioned 60 μm deep trenches Au filled at fixed potentials, the associated current transients, a Au filled grating and a simulation of filling in 50 μm deep trenches are all shown in the figure. Figure 1

Trench Bottom Optical Isolation for Suppressing Lateral Diffusion of Photocarriers in LAPS

Lateral diffusion of photocarriers in substrate causes the cross-talk in light-addressable potentiometric sensor (LAPS), which degrades the performance of LAPS. Surface optical isolation is a useful method to suppress the cross-talk in LAPS of backside irradiation manner, but the remarkable reduction of detection signal is a defect. In this study, a method of trench bottom optical isolation is developed. Main idea of this method is using the trench structure to narrow the diffusion scope of photocarriers, then irradiating the trench bottom by isolation light to locally suppress cross-talk. According to experimental analysis, when using 400 μm thick substrate, 240 μm deep trench and 100 mA drive current of isolation laser, the suppressing ability of trench bottom optical isolation is 1.38 times as strong as surface optical isolation, and 3.14 times as strong as having no isolation. Besides, the detection signal intensity of trench bottom optical isolation is 1.4 times as great as surface optical isolation. Thus, the method of trench bottom optical isolation can effectively suppress the cross-talk and reduce the loss of detection signal.

4H-SiC trench filling by chemical vapor deposition using trichlorosilane as Si-species precursor

4H-SiC trench filling has been accomplished by chemical vapor deposition (CVD) with a gas system composed of trichlorosilane, (TCS:C2H4:H2). The influences of Cl/Si ratio and growth pressure on the coverage distribution across trenches and the corresponding filling efficiency were investigated. Using the optimized process at Cl/Si = 43.5, the 8 μm deep 4H-SiC trenches with an aspect ratio of 3, were completely filled at a filling rate of 2.8 μm/h and acquired a flat end surface without void defects.

Ion assisted near-complete filling of high aspect ratio trenches for 3-D neutron detectors

A single-step process has been developed for the conformal deposition of boron carbide in high aspect ratio trenches fabricated in an n-type (111) silicon substrate. Plasma enhanced chemical vapor deposition was used to deposit boron carbide from ortho-carborane (OC2B10H12) precursor mixed with helium and argon gas. The depositions were carried out under substrate self-bias conditions to achieve a high fill factor using forward-directed ions. Nearly complete filling of 25 µm deep trenches with high-aspect ratio (> 6:1) via conformal coating of side walls has been confirmed from cross-sectional scanning electron microscopy studies. The results presented in this article establish that the process technology developed for achieving conformal deposition of the neutron stopping layer is suitable for the fabrication of Silicon p-i-n based three-dimensional thermal neutron detectors with high neutron detection efficiency.

Effects of Three-Dimensional Platform Stiffness and Layer Dimensions on Separation of Carcinoma Cells

Cancer cell separation is highly desirable for cancer diagnosis and therapy. Besides biochemical methods, engineered platforms are effective alternatives for sorting carcinoma cells from normal cells based on their unique properties in responding to the physical changes of the surrounding microenvironment. In this work, three-dimensional (3D) biomimetic scaffold platforms were developed to separate nasopharyngeal carcinoma 43 (NPC43) cells from immortalized nasopharyngeal epithelial 460 (NP460) cells based on precisely controlled design parameters including stiffness, number of layers, and structural layout. The migration characteristics of NPC43 and NP460 cells on the scaffold platforms revealed that NPC43 cells could squeeze into 10 μm wide, 15 μm deep trenches while NP460 cells could not. The different migration behavior was mainly due to cells having different interactions with the surrounding microenvironment. NPC43 cells had filopodia-like protrusions, while NP460 cells exhibited a sheet-like morphology. Using these 3D biomimetic platforms, 89% separation efficiency of NPC43 cells from NP460 cells was achieved on stiffer two-layer scaffold platforms with a 40/10 μm ridge/trench (R/T) grating on the top layer and a 20/10 μm R/T grid on the bottom layer. Moreover, the separation efficiency was further increased to 93% by adding an active conditioned medium (ACM) that caused the cells to have higher motility and deformability. These results demonstrate the capability to apply biomimetic engineered platforms with appropriate designs to separate cancer cells from normal cells for potential cancer diagnosis and treatment.

Deep reactive ion etching of silicon using non-ICP-based equipment

Deep reactive ion etching (DRIE) technology is one of the most important technologies in the processing of microelectronic devices and microelectromechanical system. As a necessary process in semiconductor integration, it has been widely studied in the past decades. It is known that the traditional DRIE process typically uses a plasma etching reactor equipped with inductively coupled plasma (ICP) sources to generate a high-density plasma so as to achieve high aspect ratio trenches with relatively small roughness. A cryogenic temperature control unit is typically employed as well. Here, however, we use a parallel plate RIE with rather simple structure, which is not usually used for DRIE, to obtain high aspect ratio silicon etching. With no ICP sources and no sophisticated temperature control unit, the system and experiment are now much more cost effective. Through the optimization of the processing, the etching rate of silicon can reach 440 nm/min. Finally, a 45 μm deep trench is etched in silicon with good perpendicularity. This method will greatly reduce the equipment related cost, especially for those applications that do not have extremely stringent requirement on the final etching accuracy.

Traversing behavior of tumor cells in three-dimensional platforms with different topography.

Three-dimensional polydimethylsiloxane platforms were developed to mimic the extracellular matrix with blood vessels by having scaffolds with micropatterns, porous membrane and trenches. Precisely controlled physical dimensions, layouts, and topography as well as different surface chemical treatments were applied to study their influences on nasopharyngeal carcinoma cell (10–15 μm in diameter) migration in mimicked platforms over 15-hour of time-lapse imaging. By placing the pores at different distance from the edges of the trenches, pores with different trench sidewall exposures and effective sizes were generated. Pores right next to the trench sidewalls showed the highest cell traversing probability, most likely related to the larger surface contact area with cells along the sidewalls. Straight grating oriented perpendicular to trenches below the top layer increased cell traversing probability. Pore shape as well as pore size influenced the cell traversing probability and cells could not traverse through pores that were 6 μm or less in diameter, which is much smaller than the cell size. Trench depth of 15 μm could induce more cells to traverse through the porous membrane, while shallower trenches impeded cell traversing and longer time was needed for cells to traverse because 3 and 6 μm deep trenches were much smaller than cell size which required large cell deformation. Hydrophobic surface coating on the top layer and fibronectin in pores and trenches increased the cell traversing probability and reduced the pore size that cells could traverse from 8 to 6 μm, which indicated that cells could have larger deformation with certain surface coatings.

Impact of Si(100) doping methods on TiSi2 formation in vertical and horizontal FET structure areas with increasing aspect ratio

Due to the increasing complexity of FET structures and the preferred high trench aspect ratios, demanding process challenges exist, not only in the structuring of the contact trenches, but also in the uniform doping of the diffusion area. Previous investigations have mainly analyzed the doping of horizontal contact areas. For this reason, this paper demonstrates how vertical and horizontal contact areas can be doped through the side wall at the same time. For this purpose, relationships between structural geometry and doping methods are studied in order to structure a multitude of contact trenches next to each other in a functional way, which can realize source and drain trenches. By means of an ion implanted test structure, high doping concentrations of up to 1019 cm−3 could be achieved at a depth of approx. 250 nm below the 2.5 μm deep contact trench bottom. The concentration which can be obtained by PSG diffusion decreases rapidly with increasing Si depth. For the first time, it is shown that the dopant particle concentration of ion implantation increases with trench height and proximity to the trench side wall. Accordingly, the electrical conductivity is also higher and the SR value lower. A positive effect of the near-surface doping concentrations on the subsequent C49-TiSi2 formation could be demonstrated, which enables uniform film growth. In contrast, dopant deposition generates asymmetric dopant concentrations and prevents uniform silicide formation as the aspect ratio increases, thus causing higher diffusion area resistances.

Inductively coupled CH 4 /H 2 plasma etching process for mesa delineation of InAs/GaSb type‐II superlattice pixels

An inductively coupled plasma etching process for delineation of InAs/GaSb type-II superlattice pixels is presented. An optimised etch recipe without alternate plasma cleaning step showed an etch rate as high as 0.11 μm/min that results in smooth vertical sidewalls for the type-II superlattice pixel arrays with 10 μm pitch size and 2.4 μm deep trenches. At 70 K, the dark current density for the mesa etched + SU-8 polymer passivated type-II superlattice photodiodes was found to be 0.11 A/cm2 at an applied reverse bias voltage of 0.2 V. The activation energy of 13 meV obtained from the Arrhenius plot and a variable area diode array technique showed that the measured dark current is mainly attributed to bulk tunnelling current. This technique of mesa delineation for the type-II superlattice pixel arrays with small pitch size is a viable option in realising next-generation infrared focal plane arrays.

Quality factor improvement of MIS capacitor using side metal coating

A simple process to improve the quality factor of metal–insulator–silicon (MIS) capacitors is introduced. Typically, MIS capacitors show a low quality factor in the gigahertz range because the lower electrode is silicon, which has low conductivity. The electrical conductivity of the lower electrode of the MIS capacitor is improved by the application of side metal coating through a simple process. To make the side metal of the MIS capacitor, a 200 µm-deep trench is formed between each capacitor using a sawing machine, and then the top electrode and side metal coating are added at the same time. Since scribing is performed prior to realisation of the top electrode, no additional dicing process is required. The quality factor of the proposed capacitor is improved from 73.8 to 101.3 at 2 GHz just by the addition of the side metal electrode.

Nano crystalline diamond MicroWave Chemical Vapor Deposition growth on three dimension structured silicon substrates at low temperature

Nano crystalline diamond (NCD) films grown at a temperature below 400 °C can open new applications on temperature sensitive substrates such as polymers or low-melting point alloys. One requirement for the applicative use of NCD is the ability of depositing on a structured substrate having high aspect ratio. This work presents a study on the three dimensional (3D) conformity of NCD deposition at low temperature (350 °C) and low pressure (30 Pa). Silicon wafers have been structured using a mask-less photolithography and (hardmask-less) Deep Reactive Ion Etching (DRIE) process and seeded with nano-diamond particles. The NCD films were grown on these 3D patterned Si substrates with various trench geometries to provide means of determining the limiting geometries of this technique. By measuring the step coverage with changing trench width, a threshold for conformal NCD growth can be determined. The NCD films at the bottom of the 100 μm deep trenches were continuous down to an aspect ratio of 1:7.

Process characterisation of deep reactive ion etching for microfluidic application

The goal of this paper is to investigate the influence of parameters of the Bosch deep reactive ion etching (DRIE) process on etched surface profile, sidewall profile and etch rate of micrometre silicon features. By investigating these parameters, we found the conditions to obtain smooth sidewall, high etch rate and balance of chemical and physical etching in the DRIE process. In this paper, the silicon surface was covered by a thin silver patterning, created by lift-off, as a hard mask for the DRIE process. The etched samples were characterised by optical microscopy and mechanical profilometry. The results show smooth sidewall of 136 μm-deep silicon trenches obtained at a high etch rate of 4 μm/min using 5 sccm C4F8, 8 sccm O2 and 24 W of bias power.

(Invited) Achieving Vertical Trench-Gate GaN MOSFETs via Process Optimization

Gallium nitride is a strong candidate material for advanced power electronics that exceed the capabilities of current Si and SiC technologies. The ideal device structure for GaN power switches is the vertical metal-oxide-semiconductor field effect transistor (MOSFET). Current vertical GaN MOSFETs have not reached theoretical performance limits. Optimization of these devices is required to improve their performance, particularly with respect to the dielectric/semiconductor interface along the device active regions, and processing used to fabricate the vertical channel regions. We have studied two atomic layer deposition precursor systems for ZrO2 dielectrics on both as-grown and plasma-etched c-plane GaN. Piranha etching of GaN surfaces before ALD improved the capacitance-voltage response of the deposited ZrO2. 5-10 µm deep trenches in GaN substrates have also been fabricated, to allow more detailed study of the trench sidewalls and dielectric interfaces on the etched surfaces before and after hydroxide-based wet etching.

Enhancement of vertical integration density by engineered BSOI wafers

The lateral and vertical integration density of bulk microelectromechanical systems (MEMS) using bonded silicon-on-insulator (BSOI) wafers is significantly enhanced if the handle wafer is used as an electrical redistribution layer. Therefore isolated conductive paths should be integrated in the handle wafer, which are connected to the surface of the BSOI-wafer by high aspect ratio contacts (VIAs) through the device layer of the BSOI-wafer. In the present study we report on a fabrication process for customer specific designed BSOI wafers with VIAs from the device to the handle layers. Wafer bonding, wafer edge shaping and thinning of the wafers, which are critical processes for the fabrication of the BSOI-wafers, are discussed. The contacts to the handle wafer through the 75 µm thick device layer are created by 10 µm wide and 75 µm deep trenches filled with highly doped n-type poly-silicon. From current–voltage measurements an ohmic behaviour of the contacts with a resistance of around 120 Ω is demonstrated.

Deep reactive ion etching of 4H-SiC via cyclic SF6/O2 segments

Cycles of inductively coupled SF6/O2 plasma with low (9%) and high (90%) oxygen content etch segments are used to produce up to 46.6 µm-deep trenches with 5.5 µm-wide openings in single-crystalline 4H-SiC substrates. The low oxygen content segment serves to etch deep in SiC whereas the high oxygen content segment serves to etch SiC at a slower rate, targeting carbon-rich residues on the surface as the combination of carbon-rich and fluorinated residues impact sidewall profile. The cycles work in concert to etch past 30 µm at an etch rate of ~0.26 µm min−1 near room temperature, while maintaining close to vertical sidewalls, high aspect ratio, and high mask selectivity. In addition, power ramps during the low oxygen content segment is used to produce a 1:1 ratio of mask opening to trench bottom width. The effect of process parameters such as cycle time and backside substrate cooling on etch depth and micromasking of the electroplated nickel etch mask are investigated.

Superplastic behavior of silica nanowires obtained by direct patterning of silsesquioxane-based precursors

Silica nanowires spanning 10 μm-deep trenches are fabricated from different types of silsesquioxane-based precursors by direct e-beam patterning on silicon followed by release through deep reactive ion etching. Nanowire aspect ratios as large as 150 are achieved with a critical dimension of about 50 nm and nearly rectangular cross-sections. In situ bending tests are carried out inside a scanning electron microscope, where the etch depth of 10 provides sufficient space for deformation. Silica NWs are indeed observed to exhibit superplastic behavior without fracture with deflections reaching the full etch depth, about two orders of magnitude larger than the nanowire thickness. A large-deformation elastic bending model is utilized for predicting the deviation from the elastic behavior. The results of forty different tests indicate a critical stress level of 0.1–0.4 GPa for the onset of plasticity. The study hints at the possibility of fabricating silica nanowires in a monolithic fashion through direct e-beam patterning of silsesquioxane-based resins. The fabrication technology is compatible with semiconductor manufacturing and provides silica nanowires with a very good structural integrity.

A Quick and a Flexible Hydride Vapor Phase Epitaxy Process to Achieve Buried Heterostructure Quantum Cascade Lasers

BH-QCLs were fabricated with regrowth of semi-insulating InP:Fe in hydride vapor phase epitaxy reactor. Two types of lateral ridge QCL designs were considered: (i) closely spaced ridges with double trenches and (ii) widely and uniformly spaced ridges. The etched depth varies from 6 to 15 µm in the former and 6 to10 µm in the latter. Double trenches of about 14 µm deep take only < 40 minutes to planarize while the same time is needed to planarize about 8 µm deep trenches with uniform ridges. In any case the achieved growth rate is higher by at least one order of magnitude than that can be achieved in MBE and MOVPE. Some fabricated BH-QCLs are characterized and they exhibit spatially monomode (TMoo) laser with an output power of as high as 2.4 W and wall plug efficiency of ~8-9% at RT under CW operation.

Mechanical quality factor enhancement in a silicon micromechanical resonator by low-damage process using neutral beam etching technology

The fabrication and evaluation of silicon micromechanical resonators using neutral beam etching (NBE) technology is presented. An etching technique based on a low energy neutral beam of Cl2/F2/O2 is introduced for making nano-trench patterns on 5 µm-thick silicon. The NBE technology has been investigated to form a highly-anisotropic etching shape. A 5 μm-deep trench pattern having smooth side walls with a gap width of 230 nm is achieved by using NBE. Additionally, a fabrication method for silicon resonators using NBE technology is proposed. The resonant frequency of the fabricated devices with a length of 500 μm, width of 440 μm and thickness of 5 μm is 9.66 MHz, and the average quality factor (Q) value is around 78 000. The devices fabricated by both deep reactive ion etching (DRIE) and NBE are evaluated and compared. The devices fabricated by NBE show that the motional resistances are reduced by almost 11 times from 645 kΩ to 59 kΩ and their output signals (insertion loss) are increased by approximately 15 dB in comparison with those fabricated by DRIE. Especially, devices fabricated by NBE provide the higher Q factors (average Q factor value of around 78 000) than those (average Q factor value of around 61 000) fabricated by DRIE in the same resonator parameters and measurement conditions.

Development of a 60 $\mu{\rm m}$ Deep Trench and Refill Process for Manufacturing Si-Based High-Voltage Super-Junction Structures

A unique and novel, 60 μm deep trench and refill process for manufacturing Si-based Super-Junction device structures for high-voltage applications beyond 600 V is discussed on the following pages. We combine an etching-process with a DCS-HCl epitaxial growth method to achieve a homogenous refilling of the generated deep-trench structures with oppositely charged dopants. Utilizing numerical process simulations, we demonstrate the advantage of the trench and refill technological approach as compared to the more established multiple-epitaxy and implantation manufacturing method. In order to experimentally validate the homogeneity of our refilling procedure, we perform secondary electron potential contrast as well as nanoscaled scanning capacitance microscopy measurements on our fabricated micro-structures.