Vertical Etching Research Articles

Ordered Al xGa1- xAs Nanopillar Arrays via Inverse Metal-Assisted Chemical Etching.

The ternary III-V semiconductor compound, Al xGa1 -xAs, is an important material that serves a central role within a variety of nanoelectronic, optoelectronic, and photovoltaic devices. With all of its uses, the material itself poses a host of fabrication difficulties stemming from conventional top-down processing, including standard wet-chemical etching and reactive-ion etching (RIE). Metal-assisted chemical etching (MacEtch) techniques provide low-cost and benchtop methods that combine many of the advantages of RIE and wet-chemical etching, without being hindered by many of their disadvantages. Here, inverse-progression MacEtch (I-MacEtch) of Au-patterned Al xGa1 -xAs is demonstrated for the first time and is exploited for the generation of vertical and ordered nanopillar arrays. The etching solution employed here consists of citric acid (C6H8O7) and hydrogen peroxide (H2O2). The I-MacEtch evolution is tracked in time for Al xGa1 -xAs samples with compositions defined by x = 0.55, x = 0.60, and x = 0.70. The vertical and lateral etch rates (VER and LER, respectively) are shown to be tunable with Al fraction and temperature of the etching solution, based on modification of catalytically injected hole distributions. Control over the VER/LER ratio is demonstrated by tailoring etch conditions for single-step fabrication of ordered AlGaAs nanopillar arrays with predefined aspect ratios. Maximum VER and LER values of ∼40 nm/min and ∼105 nm/min, respectively, are measured for Al0.55Ga0.45As at a process temperature of 65 °C. The I-MacEtch nanofabricationmethodology outlined in this study may be utilized for the processing of many devices, including high electron mobility transistors, distributed Bragg reflectors, lasers, light-emitting diodes, andmultijunction solar cells containing AlGaAs components.

(Invited) Light Enhanced Metal Assisted Chemical Etching of Silicon

The study of electrochemicl porosification of silicon has allowed the production of different kinds of porosities in it, ranging from micropores to macropores, and directed by cristallographic planes, or electrical current lines. Additional studies have been on the use of different kinds of electrolytes, to etch faster, or with lower branching. Pore modulation has been also an important development, for a range of applications from photonics to energy storage devices. The modulation can be of either different porosities or different pore diameters, and has been accomplished by the use of different current densities [1], or by the use of different light intensities (mainly for n-type Si) [2]. In particular, the use of light allows the production of electron-hole pairs in semiconductors. This is necessary in n-type Si, since electronic holes are part of the etching reaction, and they are scarce in n-type wafers. Having the availability of more of fewer electronic holes, one can etch wider or narrower pores respectively [1]. Metal Assisted Chemical Etching (MACE) is an alternative etching method, which does not use a power source (it is an electroless method). Nobel metal (commonly Au, Ag or Pt) particles or films are deposited on the surface of Si, and the metallized samples are immersed in an etching solution afterwards. The regions with metal are commonly etched much faster, thus they work as a catalyst [3]. At the metal-semiconductor interface, space-charge-region (SCR) is formed, accelerating electronic holes formed at the electrolyte-metal interface. In this way, there is a higher availability of holes for etching in (or close to) the regions where the metal is present. Having an internal electric field (given by the SCR) in MACE, which is external in the case of electrochemical etching, it is strightforward to think that light may work in a similar way in both etching methods. However, there are just a few reports on the use of light for MACE, and it has been used just at the front-side (the etched face). There are no reports on the use of back-side illumination for MACE. In the present work, evidences of pore modulation or etching conditions through the use of alternating illumination at the back-side will be presented. Illumination induces either lateral or vertical etching, depending on the doping type of Si. [1] E. Quiroga-González, J. Carstensen, C. Glynn, C. O’Dwyer, H. Föll, Phys.Chem.Chem.Phys., 16, 255 (2014). [2] S. Matthias, F. Müller, J. Schilling, U. Gösele, Appl. Phys. A, 80(7), 1391 (2005). [3] X. Li and P.W. Bohn, Appl. Phys. Lett.77, 2572 (2000).

Porous Silicon's fractal nature revisited

Fractal nature of porous silicon (Si), where porous nanowires (NWs) of Si has been observed inside the porous membrane matrix, has been revisited this time by metal assisted chemical etching (MACE) also known as metal induced etching or MIE. While carrying out MACE of Si wafer with silver nanoparticles (AgNPs) as the etching metal, it is observed that non vertical chemical etching take place. An SEM study reveals that the usual well aligned SiNWs, approximately 50 nm thick, consists of nanometer wide pores in themselves. The nanometer sized pores in turn results in Si NSs of a few nanometers in these thick looking SiNWs and are capable of showing quantum confinement effects. The SEM and TEM studies have been consolidated to model the growth mechanism for the observed fractal porous Si.

Investigation on Aerosol Jet Etching for Thin Film Patterning

As the critical dimension of the semiconductor memory device keeps shrinking, new etching method is required to etch nanometer-scale patterned thin film. Accordingly, we propose novel etching method called aerosol jet etching. This etching technique is to use an aerosol jet containing tiny liquid droplets which are made of an etchant. Liquid droplets are generated and accelerated onto the thin film by nozzle expansion into a vacuum chamber where the substrates are located. This method is intended to perform vertical anisotropic etching without redeposition by combining the chemical mechanism of wet etching and physical bombardment of particles in dry etching. Formation of nanometer-scale patterns by nanoetching process of thin films should be developed for the future semiconductor memory devices. Therefore, this new etching technique can be a prospective etching method. Also, this technique can be applied to nano-device, MEMS and various thin-film sensors. In this study, we have investigated the etch characteristics of nanometer-scale patterned thin films using aerosol jets which contain the tiny droplets of proper liquid etchants. We designed and optimized etching equiment for aerosol jet etching, and proceeded the characterization and development of nanometer-scale patterns by using it. As the major experimental parameters, there are the nozzle geometry (nozzle shape and nozzle diameter), nozzle to substrate distance, chamber pressure, and substrate temperature. The etch rates were obtained by the surface profilometer and field emission scanning electron microscopy (FESEM) and etch profiles were observed by FESEM. In addition, X-ray photoelectron spectroscopy were used for the investigation on the etched surfaces for the etch mechanism. Acknowldgments This work was supported by NRF-2017R1D1A1B03033143

Fabrication of Si3N4/SiO2 tiered resonant nanopillars with nickel caps arrays: application for optochemical sensing

A controlled, 3D selective inductively coupled plasma reactive ion etching process (ICP-RIE) was employed to fabricate high aspect ratio tiered resonant nanopillars (TR-NPs) made of two Bragg reflectors consisting of a stack of Si3N4/SiO2 alternate layers, a resonant SiO2 central cavity, and nickel caps. The 3D etching process led to a vertical full etching, and also to a horizontal highly selective etching that preserves SiO2 layers while the Si3N4 layers are slowly etched. Resulting TR-NPs periodic arrays were tested as optical sensors and highlighted a 28% increment in bulk sensitivity (379 nm RIU−1) comparing with conventional Si3N4/SiO2 resonant NPs without metal caps (296 nm RIU−1) considering the resonance feature located in the 580-630 nm wavelength range.

Self-Anchored Catalyst Interface Enables Ordered Via Array Formation from Submicrometer to Millimeter Scale for Polycrystalline and Single-Crystalline Silicon.

Defying text definitions of wet etching, metal-assisted chemical etching (MacEtch), a solution-based, damage-free semiconductor etching method, is directional, where the metal catalyst film sinks with the semiconductor etching front, producing 3D semiconductor structures that are complementary to the metal catalyst film pattern. The same recipe that works perfectly to produce ordered array of nanostructures for single-crystalline Si (c-Si) fails completely when applied to polycrystalline Si (poly-Si) with the same doping type and level. Another long-standing challenge for MacEtch is the difficulty of uniformly etching across feature sizes larger than a few micrometers because of the nature of lateral etching. The issue of interface control between the catalyst and the semiconductor in both lateral and vertical directions over time and over distance needs to be systematically addressed. Here, we present a self-anchored catalyst (SAC) MacEtch method, where a nanoporous catalyst film is used to produce nanowires through the pinholes, which in turn physically anchor the catalyst film from detouring as it descends. The systematic vertical etch rate study as a function of porous catalyst diameter from 200 to 900 nm shows that the SAC-MacEtch not only confines the etching direction but also enhances the etch rate due to the increased liquid access path, significantly delaying the onset of the mass-transport-limited critical diameter compared to nonporous catalyst c-Si counterpart. With this enhanced mass transport approach, vias on multistacks of poly-Si/SiO2 are also formed with excellent vertical registry through the polystack, even though they are separated by SiO2 which is readily removed by HF alone with no anisotropy. In addition, 320 μm square through-Si-via (TSV) arrays in 550 μm thick c-Si are realized. The ability of SAC-MacEtch to etch through poly/oxide/poly stack as well as more than half millimeter thick silicon with excellent site specificity for a wide range of feature sizes has significant implications for 2.5D/3D photonic and electronic device applications.

Fabrication of Suspended III-V Nanofoils by Inverse Metal-Assisted Chemical Etching of In0.49Ga0.51P/GaAs Heteroepitaxial Films.

Metal-assisted chemical etching (MacEtch) has been established as a low-cost, benchtop, and versatile method for large-scale fabrication of semiconductor nanostructures and has been heralded as an alternative to conventional top-down approaches such as reactive-ion etching. However, extension of this technique to ternary III-V compound semiconductor alloys and heteroepitaxial systems has remained relatively unexplored. Here, Au-assisted and inverse-progression MacEtch (I-MacEtch) of the heteroepitaxial In0.49Ga0.51P/GaAs material system is demonstrated, along with a method for fabricating suspended InGaP nanofoils of tunable thickness in solutions of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). A comparison between Au- and Cr-patterned samples is used to demonstrate the catalytic role of Au in the observed etching behavior. Vertical etch rates for nominally undoped, p-type, and n-type InGaP are determined to be ∼9.7, ∼8.7, and ∼8.8 nm/min, respectively. The evolution of I-MacEtch in the InGaP/GaAs system is tracked, leading to the formation of nanocavities located at the center of off-metal windows. Upon nanocavity formation, additional localized mass-transport pathways to the underlying GaAs substrate permit its rapid dissolution. Differential etch rates between the epilayer and substrate are exploited in the fabrication of InGaP nanofoils that are suspended over micro-trenches formed in the GaAs substrate. A model is provided for the observed I-MacEtch mechanism, based on an overlap of neighboring injected hole distribution profiles. The nanofabrication methodology shown here can be applied to various heteroepitaxial III-V systems and can directly impact the conventional processing of device applications in photonics, optoelectronics, photovoltaics, and nanoelectronics.

Size Scaling of Photonic Crystal Surface Emitting Lasers on Silicon Substrates

We report here the lateral cavity size scaling and confinement effects on the lasing performance in defect-free photonic crystal surface-emitting lasers (PCSEL) on silicon substrates. Hybrid PCSELs with different lateral cavity sizes and different lateral confinement geometries have been fabricated using transfer printing technology and controlled selective etching. The measured lasing properties show a strong dependence on the lateral cavity size below 100 μ m. In particular, the finite lateral dimension significantly affects the laser threshold and side mode suppression ratio (SMSR) of the PCSEL devices. On the other hand, by controlling the lateral confinement using vertical etching, a reduction of the laser threshold is observed. The experimental results agree well with theoretical predictions. The work presented here can lead to ultra-compact PCSELs for on-chip integration with excellent energy efficiency.

Reaction control of metal-assisted chemical etching for silicon-based zone plate nanostructures.

Metal-assisted chemical etching (MACE) reaction parameters were investigated for the fabrication of specially designed silicon-based X-ray zone plate nanostructures using a gold catalyst pattern and etching solutions composed of HF and H2O2. Etching depth, zone verticality and zone roughness were studied as a function of etching solution composition, temperature and processing time. Homogeneous, vertical etching with increasing depth is observed at increasing H2O2 concentrations and elevated processing temperatures, implying a balance in the hole injection and silica dissolution kinetics at the gold–silicon interface. The etching depth decreases and zone roughness increases at the highest investigated H2O2 concentration and temperature. Possible reasons for these observations are discussed based on reaction chemistry and zone plate design. Optimum MACE conditions are found at HF : H2O2 concentrations of 4.7 M : 0.68 M and room temperature with an etching rate of ≈0.7 μm min−1, which is about an order of magnitude higher than previous reports. Moreover, our results show that a grid catalyst design is important for successful fabrication of vertical high aspect ratio silicon nanostructures.

Defect sensitive etching of hexagonal boron nitride single crystals

Defect sensitive etching (DSE) was developed to estimate the density of non-basal plane dislocations in hexagonal boron nitride (hBN) single crystals. The crystals employed in this study were precipitated by slowly cooling (2–4 °C/h) a nickel-chromium flux saturated with hBN from 1500 °C under 1 bar of flowing nitrogen. On the (0001) planes, hexagonal-shaped etch pits were formed by etching the crystals in a eutectic mixture of NaOH and KOH between 450 °C and 525 °C for 1–2 min. There were three types of pits: pointed bottom, flat bottom, and mixed shape pits. Cross-sectional transmission electron microscopy revealed that the pointed bottom etch pits examined were associated with threading dislocations. All of these dislocations had an a-type burgers vector (i.e., they were edge dislocations, since the line direction is perpendicular to the [211¯0]-type direction). The pit widths were much wider than the pit depths as measured by atomic force microscopy, indicating the lateral etch rate was much faster than the vertical etch rate. From an Arrhenius plot of the log of the etch rate versus the inverse temperature, the activation energy was approximately 60 kJ/mol. This work demonstrates that DSE is an effective method for locating threading dislocations in hBN and estimating their densities.

The effect of reactive ion etch (RIE) process conditions on ReRAM device performance

The recent surge of research on resistive random access memory (ReRAM) devices has resulted in a wealth of different materials and fabrication approaches. In this work, we describe the performance implications of utilizing a reactive ion etch (RIE) based process to fabricate HfO2 based ReRAM devices, versus a more unconventional shadow mask fabrication approach. The work is the result of an effort to increase device yield and reduce individual device size. Our results show that choice of RIE etch gas (SF6 versus CF4) is critical for defining the post-etch device profile (cross-section), and for tuning the removal of metal layers used as bottom electrodes in the ReRAM device stack. We have shown that etch conditions leading to a tapered profile for the device stack cause poor electrical performance, likely due to metal re-deposition during etching, and damage to the switching layer. These devices exhibit nonlinear I–V during the low resistive state, but this could be improved to linear behavior once a near-vertical etch profile was achieved. Device stacks with vertical etch profiles also showed an increase in forming voltage, reduced switching variability and increased endurance.

Ultradeep electron cyclotron resonance plasma etching of GaN

Ultradeep (≥5 μm) electron cyclotron resonance plasma etching of GaN micropillars was investigated. Parametric studies on the influence of the applied radio-frequency power, chlorine content in a Cl2/Ar etch plasma, and operating pressure on the etch depth, GaN-to-SiO2 selectivity, and surface morphology were performed. Etch depths of >10 μm were achieved over a wide range of parameters. Etch rates and sidewall roughness were found to be most sensitive to variations in RF power and % Cl2 in the etch plasma. Selectivities of >20:1 GaN:SiO2 were achieved under several chemically driven etch conditions where a maximum selectivity of ∼39:1 was obtained using a 100% Cl2 plasma. The etch profile and (0001) surface morphology were significantly influenced by operating pressure and the chlorine content in the plasma. Optimized etch conditions yielded >10 μm tall micropillars with nanometer-scale sidewall roughness, high GaN:SiO2 selectivity, and nearly vertical etch profiles. These results provide a promising route for the fabrication of ultradeep GaN microstructures for use in electronic and optoelectronic device applications. In addition, dry etch induced preferential crystallographic etching in GaN microstructures is also demonstrated, which may be of great interest for applications requiring access to non- or semipolar GaN surfaces.

Vertical and bevel-structured SiC etching techniques incorporating different gas mixture plasmas for various microelectronic applications

This study presents a detailed fabrication method, together with validation, discussion, and analysis, for state-of-the-art silicon carbide (SiC) etching of vertical and bevelled structures by using inductively coupled plasma reactive ion etching (ICP-RIE) for microelectronic applications. Applying different gas mixtures, a maximum bevel angle of 87° (almost vertical), large-angle bevels ranging from 40° to 80°, and small-angel bevels ranging from 7° to 17° were achieved separately using distinct gas mixtures at different ratios. We found that SF6 with additive O2 was effective for vertical etching, with a best etching rate of 3050 Å/min. As for the large-angle bevel structures, BCl3 + N2 gas mixtures show better characteristics, exhibiting a controllable and large etching angle range from 40° to 80° through the adjustment of the mixture ratio. Additionally, a Cl2 + O2 mixture at different ratios is applied to achieve a small-angel bevels ranging from 7° to 17°. A minimum bevel angel of approximately 7° was achieved under the specific volume of 2.4 sccm Cl2 and 3.6 sccm O2. These results can be used to improve performance in various microelectronic applications including MMIC via holes, PIN diodes, Schottky diodes, JFETs’ bevel mesa, and avalanche photodiode fabrication.

Minimizing Isolate Catalyst Motion in Metal-Assisted Chemical Etching for Deep Trenching of Silicon Nanohole Array.

The instability of isolate catalysts during metal-assisted chemical etching is a major hindrance to achieve high aspect ratio structures in the vertical and directional etching of silicon (Si). In this work, we discussed and showed how isolate catalyst motion can be influenced and controlled by the semiconductor doping type and the oxidant concentration ratio. We propose that the triggering event in deviating isolate catalyst motion is brought about by unequal etch rates across the isolate catalyst. This triggering event is indirectly affected by the oxidant concentration ratio through the etching rates. While the triggering events are stochastic, the doping concentration of silicon offers a good control in minimizing isolate catalyst motion. The doping concentration affects the porosity at the etching front, and this directly affects the van der Waals (vdWs) forces between the metal catalyst and Si during etching. A reduction in the vdWs forces resulted in a lower bending torque that can prevent the straying of the isolate catalyst from its directional etching, in the event of unequal etch rates. The key understandings in isolate catalyst motion derived from this work allowed us to demonstrate the fabrication of large area and uniformly ordered sub-500 nm nanoholes array with an unprecedented high aspect ratio of ∼12.

Dry etching of palladium thin films in high density plasmas of CH3OH/Ar, C2H5OH/Ar, CH4/Ar, and CH4/O2/Ar gas mixtures

High density plasma etching of Pd thin films masked with TiN films was performed using CH3OH/Ar, C2H5OH/Ar, CH4/Ar, and CH4/O2/Ar gas mixtures. The etch rates of the Pd films and TiN masks in all the gas mixtures decreased whereas the etch selectivities increased. The etch profiles of the Pd films etched under C2H5OH/Ar gas were better than those obtained with CH3OH/Ar gas. Addition of O2 gas to the CH4/Ar gas mixture considerably improved the etch profiles of the Pd films. CH4, Ar, and O2 were found to play a critical role in obtaining a vertical etch profile with smooth sidewalls. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed the formation of polymeric layers and PdOx compounds on the sidewalls and the film surface. Good etch profiles with a high degree of anisotropy were achieved with the use of C2H5OH/Ar and CH4/O2/Ar gas mixtures.

High Aspect Ratio Machining of Nanocarbon Materials by Reactive Ion Etching

AbstractWe demonstrate anisotropic, vertical deep etching of graphite and densely packed carbon nanotube (CNT) thick layer beyond the micrometer scale, which representing the first step toward nanocarbon bulk micromachining. This micromachining process is compatible with standard lithography and therefore allows the fabrication of graphite and CNT architectures with 1 μm lateral resolution and up to 10 μm scale depth.

(invited) Metal-Catalyzed Etching of Graphene Layers

We present a comparative investigation on the etching of graphene layers catalyzed by Fe and Cu and demonstrate that their strikingly different etching behaviors are governed by their distinct interactions with carbon. Metal thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas or nitrogen, particles are produced due to the dewetting of the metal thin film. The evidence from the low-voltage scanning electron microscopy and Raman spectroscopy reveals that, at 950 oC in forming gas, the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen, indicating that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. Due to the strong Fe-C interactions, graphene and FLG are severely damaged through not only catalytic carbon hydrogenation but also carbon dissolution into Fe alone. By comparing with the etched monolayer and FLG in nitrogen, we identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During carbon hydrogenation, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover. For the Cu case, while no etching takes place for Cu particles on graphite in either gas environment at 1050 oC, Cu particles catalyze the carbon hydrogenation reaction on graphene and FLG. The weak interaction between Cu and graphene, along with the low solubility of carbon in Cu, makes the Cu particles ideal for tracking their etching paths on graphene layers. Further temperature-dependent study shows that no catalytic etching occurs at 850 oC. Both etching from the graphene step edge and on the graphene basal plane are observed for Cu particles at 950 oC and vertical etching takes place in graphite at 1150 oC, resulting in the formation of hexagon pits with all zigzag edges.

The Application of Advanced Pulsed Plasma in Fin Etch Loading Improvement

With the background of general integrated circuit (IC) feature size shrinking designers to get high performance transistors, Self-Alignment-Double-Patterning (SADP) FinFETetch was widely used in 14/16 nm technologies node and beyond. Rigorous process loading control (CD, profile, depth) in reactive ion etch (RIE) becomes more critical and challenging to ensure precise patterning and to avoid performance degradation among different features.[1]However, it’s quite hard to tackle such notorious loading for its inherent high Te induced ionization in traditional continuous wave (CW) plasmas.Thus, significant improvements in controlling plasma properties in a dry etching reactor are essential to satisfy such stringent requirement. Pulsed plasmas have demonstrated several advantages compared to CW plasmas. By varying the pulse frequency and the duty cycle, pulsed plasma provide additional “control knobs” in controlling critical plasma parameters, such as ion and electron densities, electron temperature, flux and energy of the ions and radicals incident on surface. These critical factors affecting overall on-wafer performance during plasma etching processes at both within wafer and within die levels, etching and deposition, vertical and lateral etch rate, profile control, feature sidewall passivation and plasma damage.[2]In view of characters of pulsed plasma noted above, it appears to be a promising approach to improve RIE-lag loading in SADP fin etch. In this paper, we systematically investigated the influence of both bias pulsed plasma and synchronous pulsed plasma to fin CD, profile (sidewall angle) and depth loading performance among dense and semi-isolated lines. It was found that proper duty cycle and frequency of pulsed power could drastically impact the loading performance. Based on the above learning, we finally delivered the overall solution by introducing synchronous pulsed plasma etch in mandrel and shallow trench isolation (STI) to address the rigorous loading control between dense and isolated patterns. [1] Y. Wang, et al, CSTIC, “Process Loading Reduction on SADP FinFET Etch”, 2015 [2] S. Banna, et al, JVST A, “Pulsed High-density Plasmas for Advanced Dry Etching Process”, 2012

SiO2 nanohole arrays with high aspect ratio for InGaN/GaN nanorod-based phosphor-free white light-emitting-diodes

Vertically aligned InGaN/GaN nanorod (NR)-based phosphor-free light emitting diodes (LEDs) using SiO2 nanohole patterns are demonstrated. The highly ordered SiO2 nanoholes were realized on a 2 μm-thick n+GaN template by a two-step dry etching process. The use of C4F8/O2/Ar plasma chemistries under the low pressure is found to greatly enlarge the bottom diameter of each hole, exhibiting high aspect ratio (AR ∼ 9) and vertical etch profile (∼89°). SAG technique was used to define the height of the GaN NRs while the width is determined by the trimethylgallium flow rate and growth temperature. An LED structure consisted of three-pairs of InGaN/GaN quantum well and AlGaN electron blocking layer on the sidewall of the nanorod in a core-shell structure. The wavelengths were successfully tuned by controlling pitches of the rods, which was caused by the different growth rate and indium incorporation of conformally overgrown InGaN multiquantum wells. At the operating current density of 1.5 A/cm2 (65 mA), NR-based single-chip phosphor-free white LEDs with the dimension of 630 × 970 μm2 show highly stable white emission characteristics which are attractive for future solid-state lighting and full-color display applications.

Scalable Fabrication of Integrated Nanophotonic Circuits on Arrays of Thin Single Crystal Diamond Membrane Windows.

Diamond has emerged as a promising platform for nanophotonic, optical, and quantum technologies. High-quality, single crystalline substrates of acceptable size are a prerequisite to meet the demanding requirements on low-level impurities and low absorption loss when targeting large photonic circuits. Here, we describe a scalable fabrication method for single crystal diamond membrane windows that achieves three major goals with one fabrication method: providing high quality diamond, as confirmed by Raman spectroscopy; achieving homogeneously thin membranes, enabled by ion implantation; and providing compatibility with established planar fabrication via lithography and vertical etching. On such suspended diamond membranes we demonstrate a suite of photonic components as building blocks for nanophotonic circuits. Monolithic grating couplers are used to efficiently couple light between photonic circuits and optical fibers. In waveguide coupled optical ring resonators, we find loaded quality factors up to 66 000 at a wavelength of 1560 nm, corresponding to propagation loss below 7.2 dB/cm. Our approach holds promise for the scalable implementation of future diamond quantum photonic technologies and all-diamond photonic metrology tools.