High Dry Etching Research Articles

Selective Isotropic Dry Etching of SiO2 Using F/H-Based Pulsed Remote Plasma and a Vapor Phase Solvent

Isotropic etching generally employs liquid-based wet etching techniques. However, due to the high integration of devices, conformal etching is challenging in patterns with a high aspect ratio because liquid chemicals struggle to penetrate inside the pattern. Additionally, during the drying process after chemical treatment, pattern collapse is observed due to surface tension. Therefore, there is a need for dry isotropic etching techniques to replace wet etching techniques in next-generation device manufacturing processes.Typically, when high selectivity SiO2 isotropic dry etching is required, F-base/H-based gas mixtures are utilized to form HF, which serves as an etchant for SiO2. SiO2 can be dry etched through two different mechanisms. First, HF reacts directly with H2O or alcohol, etching SiO2. The other way is to produce (NH4)2SiF6 salt from the reaction of NH3, which can be formed in a plasma containing NH3 and NF3. This (NH4)2SiF6 salt is sublimated and removed by a following heating process at a temperature over 100ºC.The process above has some disadvantages, such as lowering the etch selectivity of SiO2 over Si and Si3N4 because Si and Si3N4 can be etched by F radicals remaining in the plasma. This study aimed to overcome these disadvantages by controlling the F radical through pulsing the remote plasma during the discharging of F-based/H-based gas mixtures for the formation of HF. By pulsing the remote plasma, SiO2 could be selectively etched at a higher etch rate relative to those of Si and Si3N4. Additionally, various types of H/F-based gas mixtures that do not contain nitrogen while producing HF were investigated to prevent the formation of ammonium powders, which can be a source of contamination in the chamber. Futhermore, the etching mechanisms were identified through gas phase anlysis and surface analysis. Also, any possible surface damage during the etching process was investigated.

Development of high uniformity Al1-xScxN piezoelectric film stack dry etching process on 8-inch silicon wafers

This paper have investigated the basic properties of inductively coupled plasma reactive ion etching (ICP-RIE) of scandium doped aluminum nitride (Al1-xScxN) thin films on 8-inch silicon wafers, and presented a pretreatment scheme which can effectively improve the etching uniformity and wafer yield in the mass fabrication of Al1-xScxN-MEMS (micro-electromechanical systems) devices. Based on BCl3/Ar pretreatment and Cl2/Ar main etching scheme, an etching rate of 128 nm/min is obtained, with the low nonuniformity, and selectivity of 1.8 with respect to the loss of molybdenum (Mo) electrode is achieved, respectively. The relationship between etching parameters and etching uniformity is revealed in detail by the 5-step Al1-xScxN etching model. Meanwhile, to optimize the etching compatibility in the fabrication of Al1-xScxN-piezoelectric MEMS devices, a variety of etching masks (e.g. photoresist and silicon dioxide) are respectively used to obtain the consistent sidewall profile at different locations, with photoresist of 24° and silicon dioxide of 57°.

InP-Based Grating Antennas for High-Resolution Optical Beam Steering

Optical beam steerers on InP integrated photonics have not been able to offer high angular resolution, due to the technological challenges in realizing a large emission aperture. In this paper, we propose the creation of waveguide-based grating antennas fabricated in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> super-cladding on InP membrane on silicon (IMOS) to achieve simultaneously high resolution and good compatibility with InP-based active devices. By exploiting the high dry etch selectivity between SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and InP, a tolerant fabrication process is proposed and demonstrated, allowing for high controllability in the process. Device parameters including buffer thickness and pitch have been explored to obtain an optimized design. A 2-mm long grating antenna is fabricated and shows a record narrow full-width-half-maximum angular beam width of 0.05° and a high spatial resolution of more than 250 points when the wavelength is tuned over a range of 100 nm.

Plasma-Etched Pattern Transfer of Sub-10 nm Structures Using a Metal-Organic Resist and Helium Ion Beam Lithography.

Field-emission devices are promising candidates to replace silicon fin field-effect transistors as next-generation nanoelectronic components. For these devices to be adopted, nanoscale field emitters with nanoscale gaps between them need to be fabricated, requiring the transfer of, for example, sub-10 nm patterns with a sub-20 nm pitch to substrates like silicon and tungsten. New resist materials must therefore be developed that exhibit the properties of sub-10 nm resolution and high dry etch resistance. A negative tone, metal-organic resist is presented here. It can be patterned to produce sub-10 nm features when exposed to helium ion beam lithography at line doses on the order of tens of picocoulombs per centimeter. The resist was used to create 5 nm wide, continuous, discrete lines spaced on a 16 nm pitch in silicon and 6 nm wide lines on an 18 nm pitch in tungsten, with line edge roughness of 3 nm. After the lithographic exposure, the resist demonstrates high resistance to silicon and tungsten dry etch conditions (SF6 and C4F8 plasma), allowing the pattern to be transferred to the underlying substrates. The resist's etch selectivity for silicon and tungsten was measured to be 6.2:1 and 5.6:1, respectively; this allowed 3 to 4 nm thick resist films to yield structures that were 21 and 19 nm tall, respectively, while both maintained a sub-10 nm width on a sub-20 nm pitch.

(Invited) Proximity Gettering Design of Hydrocarbon Molecular Ion Implanted Silicon Wafers Using Direct Bonding Technique for Advanced CMOS Image Sensors: A Review

Complementary metal oxide semiconductor (CMOS) image sensors have become widely used ubiquitous devices such as smart phone and personal computer type tablets. Consumer markets strongly demands more high sensitivity imaging and more high speed image data processing for achieving advanced CMOS image sensor fabrication. However, there are some serious improvement technical issues in CMOS image sensor fabrication process. Extremely important technical issue is metallic impurity contaminated device active region during device fabrication process such as high temperature rapid thermal annealing, dry etching and plasma heat treatment. Metallic impurities formed deep energy level defects in the silicon band-gap. Thus, these deep energy level defects strongly affects electrical device characteristic such as pn-junction leakage current, recombination lifetime and gate oxide breakdown voltage. Another technical issue is oxygen impurity out-diffused to the device active region from a Czochralski (CZ) grown silicon substrate during device heat process. Oxygen impurity formed oxygen related deep energy level defects in the device active region of photo-diode space charge region and transfer transistor gate channel region. These oxygen related defects strongly influenced on electrical device performance such as image lag. Therefore, in recent years, CMOS image sensor manufacturers have strongly demanded silicon wafers with the highest metal and oxygen impurities gettering capability during CMOS device processes. In response, we have developed a novel gettering wafer production concept using a hydrocarbon molecular ion implantation technique for advanced CMOS image sensors [1][2][3]. This technique can implant a silicon wafer surface simultaneously with carbon and hydrogen elements that form the projection range using a hydrocarbon compound molecular gas source. In our previous study, it was found that a hydrocarbon molecular ion implanted silicon wafer had three unique characteristics for high performance of advanced CMOS image sensors. First, a hydrocarbon molecular ion projection range has high gettering capability of metallic impurities [1][2][4]. Second, this projection range also has a diffusion barrier effect for oxygen impurities out-diffusing to the device active region from a CZ grown silicon wafer substrate [5]. Third, it is expected that diffusing hydrogen to the device active region from the hydrogen of hydrocarbon molecular ions gettered in the projection range during the device fabrication process will have a passivation effect on unreconstructed surface dangling bonds and Si/SiO2 interface state densities such as local oxidation of silicon or shallow trench isolation [6][7]. Moreover, we achieved more improvement for gettering capability of hydrocarbon molecular ion implanted silicon wafer which formed epitaxial layer without epitaxial growth process using room temperature direct bonding technique. In this presentation, we demonstrate that a hydrocarbon molecular ion implanted silicon wafers using room temperature direct bonding technique has high gettering capability characteristics for transition metal and light element impurities such as oxygen, and hydrogen during the CMOS image sensor fabrication process.

Toward realization of small-size dual-band long-wavelength infrared photodetectors based on InAs/GaSb/AlSb type-II superlattices

In this study, we demonstrate 12×12µm2 high-performance, dual-band, long-wavelength infrared (LWIR) photodetectors based on InAs/GaSb/AlSb type-II superlattices. The structure consists of two back-to-back heterojunction photodiodes with 2µm-thick p-doped absorption regions. High quality dry etching combined with SiO2 passivation results in a surface resistivity value of 7.9×105Ωcm for the longer (red) channel and little degradation of the electrical performance. The device reaches dark current density values of 4.5×10−4A/cm2 for the longer (red) and 1.3×10−4A/cm2 for the shorter (blue) LWIR channels at quantum efficiency saturation. It has 50% cut-off wavelengths of 8.3 and 11.2µm for the blue and red channel, respectively, at 77K in back-side illumination configuration and exhibits quantum efficiencies of 37% and 29%, respectively. This results in specific detectivity values of 2.5×1011cm·Hz1/2/W and 1.3×1011cm·Hz1/2/W at 77K.

Inductively coupled plasma etching of bulk, single-crystal Ga2O3

High ion density dry etching of bulk single-crystal β-Ga2O3 was carried out as a function of source power (100–800 W), chuck power (15–400 W), and frequency (13.56 or 40 MHz) in inductively coupled plasma (ICP) systems using Cl2/Ar or BCl3/Ar discharges. The highest etch rate achieved was ∼1300 Å min−1 using 800 W ICP source power and 200 W chuck power (13.56 MHz) with either Cl2/Ar or BCl3/Ar. This is still a comfortably practical set of conditions, where resist reticulation does not occur because of the effective He backside cooling of the sample in the tool and the avoidance of overly high powers in systems capable of 2000 W of source power. The etching is ion-assisted and produces anisotropic pattern transfer. The etched surface may become oxygen-deficient under strong ion-bombardment conditions. Schottky diodes fabricated on these surfaces show increased ideality factors (increasing from 1.00 to 1.29 for high power conditions) and reduced barrier heights (1.1 on reference diodes to 0.86 eV for etched surfaces). This electrically active damage is dependent on ion energy and flux during the etching. An obvious strategy is to reduce plasma powers toward the end of an etch sequence to reduce the disruption to the Ga2O3 surface.

Fabrication of hierarchical anti-reflective structures using polystyrene sphere lithography on an as-cut p-Si substrate

The broadband anti-reflective (AR) properties of hierarchical structures (HSs) have attracted considerable attention in recent years as a means to reduce Fresnel reflection in photovoltaic solar cell materials. This study employed polystyrene sphere lithography in conjunction with high density plasma dry etching in the fabrication of pure sub-wavelength structures and HSs on an as-cut p-Si substrate. Etching parameters, such as RF power, O2, and etching time, were adjusted to alter the surface morphology. Experiment results demonstrate that the resulting hierarchical paraboloidal structures suppress average reflectance to below 0.5% across a spectral range of 500–1000nm.

High rate dry etching of (BiSb)2Te3 film by CH4/H2-based plasma

Etching characteristics of p-type (BiSb)2Te3 films were studied with CH4/H2/Ar gas mixture using an inductively coupled plasma (ICP)-reactive ion etching (RIE) system. The effects of gas mixing ratio, working pressure and gas flow rate on the etch rate and the surface morphology were investigated. The vertical etched profile with the etch rate of 600nm/min was achieved at the optimized processing parameters. X-ray photoelectron spectroscopy (XPS) analysis revealed the non-uniform etching of (BiSb)2Te3 films due to disparate volatility of the etching products. Micro-masking effects caused by polymer deposition and Bi-rich residues resulted in roughly etched surfaces. Smooth surfaces can be obtained by optimizing the CH4/H2/Ar mixing ratio.

High Selectivity in Dry Etching of Silicon Nitride over Si Using a Novel Hydrofluorocarbon Etch Gas in a Microwave Excited Plasma for FinFET

The SiNx gate spacer formation is one of the key processes in the miniaturized MISFETs, because the thickness of the gate spacer and the Si recess after the gate spacer formation etching have large impacts on the electrical properties of MISFETs [1,2]. High selectivity of SiNx over Si is strongly required in MISFETs such as extremely thin silicon on insulator (ETSOI) device and 3 dimensional (3D) MOSFET for the reduction of the series resistance [1,2]. Various etching gases were evaluated in order to obtain high selectivity of SiNx over Si[3-6]. It is considered that a plasma source and etching gases are important in order to obtain high selectivity dry etching of SiNxover Si. We consider that the plasma source with low electron temperature is advantageous in the improvement of selectivity, because it prevents excessive dissociation of the etching gas. The difference of the chemical structures of etching gas with the plasma source can make a difference of the selectivity. In this work, we utilized the microwave excited plasma source that has the characteristic of low electron temperature and a novel gas (SSY525 made by ZEON) [7].Figure 1 shows the selectivity of SiNx to poly Si as a function of O2 flow rate. The flow rate of SSY525 and CH3F are 8 sccm and 10 sccm, respectively. The microwave power, the RF power of bottom electrode and the Ar gas flow rate were 1000 W, 60 W and 200 sccm, respectively. SiNx films were deposited by PECVD and LPCVD. Si/N ratio and density of SiNx by PECVD was lower than those by LPCVD [8]. In the case of SSY525, a higher selectivity of SiNx by PECVD and LPCVD to poly Si was obtained with O2 flow rate from 0 to 50 sccm to CH3F. Low etch rate of poly Si less than 0.3 nm/min and high selectivity of SiNx to Si over 50 were obtained with O2 flow rate of 0 sccm and more than 30 sccm. Figure 2 shows the analysis of poly Si surface by XPS after dry etching using SSY525. A high intensity of C 1s was obtained with O2 flow rate of 0 sccm. It is considered that high selectivity of SiNx to poly Si was obtained due to carbon deposition on poly Si surface. The intensity of C 1s decreases and the intensity of O 1s increases as the O2 flow rate increases. It is considered that High selectivity of SiNx to poly Si is obtained with O2 flow rate more than 30 sccm due to an oxidation of poly Si surface. Figure 3 (a) shows the schematic of 3D-MISFET structure. Figure 3 (b)-(d) show the cross-section SEM images from A to B in Fig. 3 (a) with various SSY525 flow rate. A 40 nm-thick SiNx was overetched at (b) 8 sccm, (c) 12 sccm and (d) 15 sccm. Si near the SiNx sidewall was etched with SSY525 of 8 sccm. It was not etched with SSY525 more than 12 sccm. About 5 nm-thick film containing carbon was deposited on the Si surface with 15 sccm. In the cases of (c) and (d), high selectivity of SiNx over Si was obtained. It is confirmed that SSY525 is effective in order to form the SiNxgate spacer in the miniaturized MISFET.

Atomic layer deposition of aluminum-doped zinc oxide films for the light harvesting enhancement of a nanostructured silicon solar cell

Anodic-aluminum-oxide (AAO) template lithography and atomic layer deposition (ALD) antireflection coating techniques have often been applied for the fabrication of wide-angle antireflection structures on silicon solar cells. In this study, an AAO template was fabricated as a mask to block the high density plasma dry etching from the crystalline silicon to form nanostructures on the surface of the crystalline silicon wafer. Then, a 55-nm-thick aluminum-doped zinc oxide (AZO) film was deposited on the silicon nanostructures using the ALD method. The results show that the application of a nanostructured AZO film can decrease the average reflectivity of the crystalline silicon to 0.83% in the wavelength range from 400 to 850 nm for an incident angle of 8°. The conversion efficiency of the nanostructured silicon solar cell can be enhanced from 6.93% to 8.37%.

Low-Loss GaInAsP Wire Waveguide on Si Substrate with Benzocyclobutene Adhesive Wafer Bonding for Membrane Photonic Circuits

Low-power and compact optical interconnects can be realized using III–V membrane photonic integrated circuits fabricated from thin InP-based films bonded to a Si wafer using benzocyclobutene (BCB) adhesive wafer bonding method. However, the conditions of the bonding and fabrication process strongly affect the propagation loss of waveguides. This study investigated the process conditions during bonding and waveguide fabrication with a view to reducing the propagation loss. It was found that clean, large GaInAsP thin films without air voids or fractures could be obtained by using an appropriate solvent volatilization time of 20–30 min at 200 °C for BCB. Furthermore, by using a resist with high dry etching resistance and an SiO2 mask for the etching process, the sidewall roughness of the waveguide was significantly reduced, which finally afforded a waveguide propagation loss as low as 4 dB/cm.

High rate dry etching of InGaZnO by BCl3/O2 plasma

This paper reports the results of the high-rate dry etching of indium gallium zinc oxide (IGZO) at room temperature using BCl3/O2 plasma. We achieved an etch rate of 250 nm/min. We inferred from the x-ray photoelectron spectroscopy analysis that BOx or BOClx radicals generated from BCl3/O2 plasma cause the etching of the IGZO material. O2 initiates the etching of IGZO, and Ar removes nonvolatile byproducts from the surface during the etching process. Consequently, a smooth etched surface results when these gases are added to the etch gas.

Comparative study on the properties of amorphous carbon layers deposited from 1-hexene and propylene for dry etch hard mask application in semiconductor device manufacturing

Amorphous carbon layers (ACLs) were prepared by plasma enhanced chemical vapor deposition (PECVD) from 1-hexene (C 6H 12) and propylene (C 3H 6) as a carbon source at different temperatures for dry etch hard mask of semiconductor devices manufacturing process. The deposition rate of ACL deposited at 550 °C from C 6H 12 and C 3H 6 was 5050 Å/min and 6360 Å/min. Although the deposition rate of ACL deposited from C 6H 6 was lower than that from C 3H 6, normalized deposition rate of ACL deposited from C 6H 12 was 1.64 times higher than that from C 3H 6. The relative amount of hydrocarbon contents measured by FTIR (Fourier transformation infrared) and TDS (thermal desorption spectroscopy) was decreased with the increase of deposition temperature. Raman results showed that the numbers and size of graphite cluster of ACLs deposited from each source were increased with the increase of deposition temperature. The extinction coefficient of ACL deposited at 550 °C from C 6H 12 was 0.51 and that from C 3H 6 was 0.48. The density of ACL deposited at 550 °C from C 6H 12 was 1.48 g/cm 3 and that from C 3H 6 was 1.45 g/cm 3. The dry etching rate of ACL deposited at 550 °C from C 6H 12 was 1770 Å/min and that from C 3H 6 was 1840 Å/min. The deposition rate, dry etch rate and the amount of hydrocarbon contents of ACLs deposited from each carbon source were decreased with the increase of deposition temperature but extinction coefficient and density were increased with the increase of deposition temperature. We concluded that the variation behavior of the deposition characteristics and film properties of ACLs from C 6H 12 with the increase of deposition temperature was the same as those of ACLs from C 3H 6. The high density and low dry etch rate of ACL from C 6H 12 can be explained by less hydrocarbon incorporation during deposition and these properties are more favorable for the dry etch hard mask application in semiconductor device fabrication.

Nanofabrication of gallium nitride photonic crystal light-emitting diodes

We describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity.

Fabrication of Photonic Wire and Crystal Circuits in Silicon-on-Insulator Using 193-nm Optical Lithography

High-index contrast silicon-on-insulator technology enables wavelength-scale compact photonic circuits. We report fabrication of photonic circuits in silicon-on-insulator using complementary metal-oxide-semiconductor processing technology. By switching from advanced optical lithography at 248 to 193 nm, combined with improved dry etching, a substantial improvement in process window, linearity, and proximity effect is achieved. With the developed fabrication process, propagation and bending loss of photonic wires were characterized. Measurements indicate a propagation loss of 2.7 dB/cm for 500-nm photonic wire and an excess bending loss of 0.013 dB/90deg bend of 5-mum radius. Through this paper, we demonstrate the suitability of high resolution optical lithography and dry etch processes for mass production of photonic integrated circuits.

Very high resolution etching of magnetic nanostructures in organic gases

Two methods for high resolution dry etching of permalloy (NiFe) and iron (Fe) nanostructures are presented and discussed. The first involves the use of carbon monoxide (CO) and ammonia (NH3) as etching gases, the second uses methane (CH4), hydrogen (H2) and oxygen (O2). In both etching processes volatile metallo-organic compounds are the resulting reaction products. The patterned and dry etched thin films were observed with SEM and TEM to study the quality of each of the two processes. It is found that the CO/NH3 process yields higher etch rates, higher selectively with respect to the SiN mask used, and less redeposition than the CH4/H2/O2 process.

Progress towards photonic crystal quantum cascade laser

The paper describes recent progress in the design, simulation, implementation and characterisation of photonic crystal (PhC) GaAs-based quantum cascade lasers (QCLs). The benefits of applying active PhC confinement around a QCL cavity are explained, highlighting a route to reduced threshold current operation. Design of a suitable PhC has been performed using published bandgap maps; simulation results of this PhC show a wide, high reflectivity stopband. Implementation of the PhC for the device is particularly difficult, requiring a very durable metallic dry etch mask, high performance dry etching and a low damage epilayer-down device mounting technique. Preliminary shallow etched PhC QCLs demonstrated the viability of current injection through the metal etch mask and the device mounting technique. Development of the etch mask and dry etching have demonstrated a process suitable for the manufacture of deep etched PhC structures. All the necessary elements for implementing deep etched PhC QCLs have now been demonstrated, allowing for the development of high performance devices.

Thick film resist lithography for a-Si:H devices with high topography and long dry etch processes

In this article, we present an optimized thick film photoresist process to compensate for issues such as step coverage, linewidth variations, and long dry etch resistance for hydrogenated amorphous silicon (a-Si:H) devices, such as vertical thin film transistors (VTFTs) with significant substrate topography (1 μm or higher). This article describes a systematic approach to develop an optical lithographic process along with practical process models to analyze the key parameters that control the process throughput and resist charactersistics. The resist performance in dry etching and linewidth control over the topographic structure of VTFTs accompanied with the electrical characteristics of the fabricated device are demonstrated.

Critical tasks in high aspect ratio silicon dry etching for microelectromechanical systems

The process of pattern transfer of desired topological features into silicon plays a critical role for the production of microelectronic and photonic devices, and micro- and nanoelectromechanical systems. Any deviation from the desired shape of the pattern limits density, yield, and reliability of these devices. Gas reactivity, pressure, ion, electron, and reactant transport to the surface, and product transport away from the surface, have all been identified as important issues that control the microscopic uniformity in high aspect ratio etching. When etch-inhibiting chemistry by the gas chopping deep reactive ion etching (RIE) was employed, it caused enormous complications in the scaling of etching rates, with increasing aspect ratio. Using an energy-resolving quadrupole mass spectrometer assembled into the cathode, specially designed test features, and etching simulation models, we establish the link between etch process parameters such as pressure, rf power, etching gas chemistry, temperature, and the physical and chemical process parameters like energy and angular distribution of ions and neutrals, radical sticking, and surface charging. The most significant effects like RIE lag, notching, bowing, faceting, microtrenching, profile shape dependence, etc. will be discussed in this article. 2003 American Vacuum Society.