Etch Rate Ratio Research Articles

UVC irradiation of alpha particles tracks and empirical equation of bulk etch rate in CR-39 detector

The first empirical equation is presented in this paper to characterize the behavior of the bulk etch rate (Vb) with the UVC dose. The Vb value increased nonlinearly with UVC irradiation during the initial dose of up to 13 J, then remained almost constant with prolonged UVC doses from 13 to 45 J. The alpha track depths in CR-39 were analyzed with UVC irradiation (λ = 254 nm). Samples exposed to UVC radiation achieved the maximum track depth with a shorter etching time than samples not exposed to UVC radiation. The Vt values increased significantly for samples exposed to UVC up to 7.1, 7.0, and 6.9 µm/h, respectively, at alpha energies of 2.5, 3.5, and 4.5 MeV. While the etch rate ratio decreased for the same samples.

The Etching Effect Methods in Registration Properties on CR-39 Nuclear Track Detector

In this work, we use three different etching techniques—water bath, microwaves, and hotplate stirrer devices—in an effort to confirm the optimal etching time and conditions for tracks in the CR-39 solid-state nuclear track detector following irradiation to an alpha particle source (241Am). The research shows that the water bath’s maximum track density is 57596 tracks/cm2, appearing at 90 and 150 minutes. On the other hand, the hotplate stirrer’s maximum track density is 28050 tracks/cm2, appearing at 90 and 150 minutes. The microwave is the best etching method since it generated the tracks (65076 tracks/cm2) in a relatively short amount of time (10 min). The computation of the etching parameters, which are the bulk etch rates (VB), track etch rate (VT) and track etch ratio (V), was investigate in the etching properties. The time for the appearance of all traces of the microwave device is at a time of 10 minutes, followed by a hotplate stirrer at a time of 90 minutes, then a water bath at a time of 120 minutes.

Necking Reduction at Low Temperature in Aspect Ratio Etching of SiO2 at CF4/H2/Ar Plasma.

This study investigated the effect of temperature on the aspect-ratio etching of SiO2 in CF4/H2/Ar plasma using patterned samples of a 200 nm trench in a low-temperature reactive-ion etching system. Lower temperatures resulted in higher etch rates and aspect ratios for SiO2. However, the plasma property was constant with the chuck temperature, indicated by the line intensity ratio from optical emission spectroscopy monitoring of the plasma. The variables obtained from the characterization of the etched profile for the 200 nm trench after etching were analyzed as a function of temperature. A reduction in the necking ratio affected the etch rate and aspect ratio of SiO2. The etching mechanism of the aspect ratio etching of SiO2 was discussed based on the results of the surface composition at necking via energy-dispersive X-ray spectroscopy with temperature. The results suggested that the neutral species reaching the etch front of SiO2 had a low sticking coefficient. The bowing ratio decreased with lowering temperature, indicating the presence of directional ions during etching. Therefore, a lower temperature for the aspect ratio etching of SiO2 could achieve a faster etch rate and a higher aspect ratio of SiO2 via the reduction of necking than higher temperatures.

(Invited) Novel Surface Reactions in Low-Temperature Regime for High-Aspect-Ratio Dielectric Etching

The most critical issue to achieve High-Aspect-Ratio (HAR) dielectric etching is the transport of both radicals and ions to the bottom of a feature [1]. Current HAR dielectric etching uses fluorocarbon and hydrofluorocarbon gases combined with high applied bias power. However, the etch rate drastically decreases at high depth due to the decline of radicals being supplied to the etch front. Alternative methods have long been required to solve this problem. To address the radical transport issue, we propose adopting a novel precursor with low molecular weight to enhance Knudsen transport. In addition, cryogenic temperature regimes are also known to enhance etch rates [2][3] but have not yet been implemented for HAR dielectric etching. In this work we evaluated a novel precursor in cryogenic temperature regime for HAR dielectric etching. For the first time, we demonstrate a synergy effect between cryogenic temperature and this novel precursor by successfully developing an innovative HAR dielectric etch process. We confirmed that this process is capable of etching beyond a ten-micron depth for a 3D-NAND channel hole with a hundred nanometer critical dimension in diameter, thus an aspect ratio of over one hundred to one. The key to enabling high etch rate is strongly correlated with the adsorption of the precursor on the surface, which is enhanced at cryogenic temperature. Detailed surface adsorption reaction mechanisms will be described in the conference. This new process not only enables higher etch rate, higher selectivity and higher aspect ratio etching capability, but also significantly shortens the process time with 84% carbon footprint reduction of greenhouse gas emissions.[1] K. Ishikawa, et al., Jpn. J. Appl. Phys. Vol. 57, No. 6S2, 06JA01, (2018).[2] T. Ohiwa, et al., Jpn. J. Appl. Phys. Vol.31, p.405, (1992).[3] R Dussart, et al., J. Phys. D: 47, 123001, (2014).

Front-side releasing oriented clamped–clamped beams for piezoresistive sensors

Front-side releasing suspended structures made using bulk micromachining processes have the advantages of simplifying vacuum or hermetic packaging processes and reducing squeeze-film damping. This paper studies the effect of doping concentration on the etching rate (ER) of the (111) plane. The experimental results show that increasing the boron doping concentration (but to less than the self-stop etching concentration) significantly increases the ER of the (111) plane and the ER ratio of the (111) and (100) planes. This phenomenon is used to speed up the undercutting and release <110> oriented clamped–clamped beams, which can be used as piezoresistive sensitive elements. The etching depth when the microbeams have just been released and the silicon wedges under single beams, double beams and triple beams disappear is deduced and verified by experiments. This has a certain guiding significance for designing piezoresistive sensors.

Fabrication of ultra-high aspect ratio silicon grating using an alignment method based on a scanning beam interference lithography system.

The high-aspect-ratio silicon grating (HARSG) is an important X-ray optical device that is widely used in X-ray imaging and spectrum detection systems. In this paper, we propose a high-precision alignment method based on the scanning beam interference lithography (SBIL) system to realize precise alignment between the <111> orientation on the (110) wafer plane and the grating lines direction, which is an essential step in HARSG manufacture to obtain the high-aspect-ratio grating structure. After the location of the <111> orientation through fan-shaped mask etching and reference grating fabrication, a two-step method that combines static preliminary alignment and dynamic precision alignment is used to align the reference grating lines direction with the interference field fringes of the SBIL system through the interference of the diffracted light from the reference grating near the normal direction, which can realize a minimal alignment error of 0.001°. Through the overall alignment process, HARSGs with groove densities of 500 gr/mm, 1800 gr/mm, and 3600 gr/mm were fabricated through anisotropic wet etching in KOH solution, producing ultra-high aspect ratios and etch rate ratios greater than 200.

Bevel contamination management in 3D integration by localized SiO2 deposition

This paper investigates silicon oxide bevel deposition to manage contamination in 3D integration with intermediate Back-End Of Lines (iBEOL) levels. Bevel etching and cleaning techniques are now sufficiently mature to remove efficiently contamination on wafer bevel area. However, 3D integration with iBEOL could require encapsulating metal lines, which emerge on the bevel area. This paper explores the efficiency of bevel deposition to answer contamination issues in 3D integration. Films are deposited on the bevel area of 300 mm wafers thanks to a torus shaped Plasma Enhanced Chemical Vapor Deposition (PECVD) configuration allowing encapsulation of the last few mm of the wafer frontside, backside and the apex in a single processing step. Deposition is carried out at 350 °C from mixture of SiH4 and N2O at 2 Torr. When the gap between wafer and top insulator increases from 0.4 to 0.7 mm, the frontside deposition profile is shifted by 0.5 mm inward. In accordance with refractive index of 1.55 measured by ellipsometry, surface analysis by X-ray Photoelectrons Spectroscopy (XPS) show a film composition of SiO1.8N0.3 with a quasi-constant composition from 147 to 149 mm wafer radius. The film resistance, evaluated by wet etch in 2% HF, leads to Wet Etch Rate (WER) ratio to thermal oxide of 4–5. We demonstrate that such films are compatible with oxide bonding. Thanks to a proper integration scheme, minimal impact on the bonding edge quality with bonding limit of 147.7 mm on real product Complementary Metal Oxide Semiconductor with 4 Metal levels (CMOS+M4) is reported. Finally, the effectiveness of the strategy to keep the metallic contamination at 1 × 1010 at.cm-2 or below is verified by either specific Liquid Phase Decomposition bevel Inductively Coupled Plasma Mass Spectrometry (LPD bevel-ICPMS) on BEOL wafers or by Vapor Phase Decomposition (VPD)-ICPMS standard process control on Front-End Of Line (FEOL) wet tool just after having cleaned BEOL wafers.

Fine hole drilling of alkali-containing silicate glass substrate using preferential penetration of etchants around silver precipitates

Solid-state ion exchange is a metal doping method used for alkali-containing glass materials. When an additional voltage is applied to the silver-doped glass surface, it yields nanometer-sized dendritic precipitates in the doped area. The silver precipitation is accompanied by crack formation, which causes the formation of a network of micro-cracks in the glass substrate. These crack networks can be a penetration path for the etchants in removal processes. In this study, we evaluated the effect of etching conditions on the dissolution characteristics of silver-precipitated and un-precipitated areas. Furthermore, fine hole drilling of glass with a higher aspect ratio was performed. When hydrofluoric (HF) acid was used as an etchant, the etching rate of these areas increased with an increase in the etchant temperature and concentration. However, there was no significant change in the etching rate ratio (etching rate of silver-precipitated area per that of un-precipitated area). Similarly, the effect of the etchant concentration on the etching rate ratio was small in the case of potassium hydroxide (KOH) solution. However, the etching rate ratio in the KOH solution was more than three times higher than that of the HF solution. This demonstrates that the KOH solution was suitable for the preferential removal of the silver-precipitated area. Additionally, fine hole drilling of the glass substrate was performed using patterned silver plating film as a silver ion source. Consequently, through-glass hole array was successfully formed.

Numerical Study of SF6/O2 Plasma Discharge for Etching Applications

SF6/O2 plasma discharge has extensive applications in semi-conductor industry for anisotropic etching of silicon. Herein, a self-consistent fluid model has been used to investigate the capacitive coupled SF6/O2 plasma discharge. A complete set of reactions in gas phase which include electron impact reactions, ion-ion reactions, neutral–neutral reactions and charge transfer reactions in tandem with the primary processes such as dissociation excitation, and ionization were incorporated in the model. The densities of dominant plasma species (both neutral and charged) were calculated. Furthermore, the impact of O2 concentration on the plasma characteristics was studied. The results showed a bell shape distribution for neutral species while uniform distribution for charged species at center of the discharge. Moreover, it was demonstrated that the dominant etching species in the discharge were F, O, S, SF5+, FO, F+, O+, O2+ and S+. With the increase of O2 concentration in the plasma, there is a decrease in the ratio of neutral species (i.e., F/ O) and overall etch rate, signifying that chemical etching is the prominent process for the discharge. In conclusion, the anisotropic etching of Si substrate can be efficiently achieved using the optimum input parameters for SF6/O2plasma discharge.

Study of nuclear track parameters of normal incident alpha particles on CR-39 detector

In this paper, Solid State Nuclear Detector (SSNTD) CR-39 was broken into many fragments with areas of (1x1) cm2. The samples were irradiated using 241Am source. The measurements were taken at normal incident angle of the alpha particles for energies (3.17, 3.59 and 4.13) MeV respectively. The samples were etched using sodium hydroxide solution (NaOH 6N, 70±1 oC) for time interval of 0.25 h. The optical microscope provided with digital camera was used to preview the track profile formed in CR-39. This allowed measurement of the track length and in turn the track length as a function of the etching time . The track growth rate, track etch rate and track rate ratio were also investigated as a function of many parameters such as etching time, track depth and residual range. The study showed a good consistency among the investigated parameters . The curves of the track etch rate and track etch ratio manifested a consistency with Brack curve who interested in studying the linear energy loss in materials where the maximum energy loss occurs at the end of the alpha particle range.

Track parameters investigate of oblique incident of alpha particles irradiated CR-39 detector

In this work, the track etch-rate VT and etch-rate ratio V of CR-39 detector irradiated by alpha particles was investigated at different incident angles. The change of the track etch-rate and etch-rate ratio along the particle trajectories showed that these functions are not affected by the inclination of the particle trajectory with respect to the normal on the detector surface.

High-selectivity dry etching for p-type GaN gate formation of normally-off operation high-electron-mobility transistor

Selective dry etching of GaN to AlGaN was studied to form a p-type GaN gate on an AlGaN/GaN high-electron-mobility transistor (HEMT). The epitaxial layer consists of Mg-doped GaN, 15 nm thick Al0.25GaN, GaN channel, and buffer layers on a Si substrate. The inductively coupled plasma (ICP) etching technique was employed with the ICP and bias powers of 120 and 7 W, respectively, using Cl2 and Ar gases with flow rates of 20 and 5 sccm, respectively. Then, the O2 addition effects were investigated for the etching of GaN and AlGaN by changing the O2 flow rate. At the rate of 1 sccm, the etching rate ratio of GaN to AlGaN was found to be about 50 with a smooth surface. Using the etching condition obtained, the p-GaN gate HEMT with the positive threshold voltage of 1.2 V and high drain current of 440 mA mm−1 was successfully fabricated.

Causes of anisotropy in thermal atomic layer etching of nanostructures

In this work, the authors have investigated the dependence of the anisotropy level in an atomic layer etching (ALE) process of Al2O3 on form factor constraints when the ALE process involves etching in non-line-of-sight locations beneath a silicon nitride mask. In the experiments described here, thermal etching of Al2O3 without the use of any direction-inducing plasma components was explored utilizing the well characterized hydrogen fluoride/dimethyl-aluminum-chloride atomic layer etching process. The degree of anisotropy was quantified by measuring the ratio of lateral etch rate of this process in comparison to the vertical etch rate as a function of process step time inside 60 nm holes of aluminum oxide. Inside these holes, the authors determined that the horizontal etch rates slowed to an amount of 19% compared to the vertical rate when short process times were used. For process times operating in the saturation mode of the ALE process, horizontal etch rates per cycle could be sped up to 71% of the vertical rate but never reached parity with the latter. The authors propose a simple mechanism for explaining the anisotropy dependence on process step time and applied a reduced-order algorithm to model it. In this model, the authors introduced fitting parameters for surface modification depths and reaction times to match the experimentally found etch results. Conclusions could be drawn regarding topological hindrance or tortuosity for reactants to reach surfaces in shaded areas under the mask and for reaction by-products to escape from these locations and the impact on etch rate. In addition, the authors recognize that this mechanism could explain the unwanted depth dependence of the etch rate per cycle in high aspect ratio structures.

V-function to investigate tracks of the alpha particle irradiated CR-39 detector

In this work, the etch-rate ratio V of CR-39 detector irradiated by alpha particles was investigated at different alpha particle energies. The study involved a new empirical equation for V as a function of residual range R'. The introduced equation encompassed five free parameters ɑ1 = 0.098 μm−1, ɑ2 = 1.86, ɑ3 = 37.78 μm, ɑ4 = 36.98 μm and ɑ5 = 0.98 which showed good agreement with the experimental data. Moreover, the equation agreed well with other V functions illustrated elsewhere.

A comparative study of Cx(x = 4, 5, 7)F8 plasmas for dry etch processing

In this study, the SiO2 etch characteristics of perfluorocarbon such as C4F8, C5F8, and C7F8 were investigated using inductively coupled plasmas (ICPs) to study the effect of a high C/F ratio on the etch characteristics of SiO2 for the ICP. The SiO2 rates and etch selectivities over Si3N4 and amorphous carbon layer (ACL) were measured by using the mixtures of Cx(x = 4, 5, 7)F8/Ar/O2. The higher C/F ratio of perfluorocarbon showed lower SiO2 etch rate but exhibited higher etch selectivities over Si3N4 and ACL due to the higher C2 while keeping the similar F in the plasma as observed by optical emission spectroscopy and due to the thicker fluorocarbon layer with more carbon-rich fluorocarbon on the materials surface as observed by X-ray photoelectron spectroscopy. Especially, C7F8 is environmentally benign material because it not only has a relatively low global warming potential but also can be captured easily using a capture system (a liquid state at the room temperature). Therefore, C7F8 could be applicable as one of the next generation perfluorocarbon etching materials.

Formation of SiC Mesastructures with Gently Sloping Sidewalls by Dry Selective Etching through a Photoresist Mask

We have demonstrated that SiC mesastructures with gently sloping sidewalls form with the help of selective reactive ion etching (RIE) of silicon carbide through a photoresist mask (slanted walls are formed during simultaneous etching of SiC and the resistive mask with the edge in the shape of a sharp wedge). A simple geometrical model of etching predicts that the resultant slope of the mesastructure wall must be specified by two parameters, i.e., initial angle of the resistive wedge and the selectivity of SiC etching relative to the photoresist (ratio of etching rates of SiC and photoresist). For experiments, we used polished 4H–SiC wafers with the (0001) orientation. Photoresist regions with an edge angle of 22° were deposited using photolithography onto the Si side of the wafers. Then etching of mesastructures was performed in nitrogen trifluoride in a setup with an inductively coupled plasma. We selected RIE parameters ensuring SiC and photoresist etching with rates of 55 and 160 nm/min, respectively (etching selectivity was 1 : 3). The SiC mesastructures formed by etching have a height of 3.2 μm and gently sloping sidewalls with a slope of about 8°. This technology can be used for preparing high-voltage SiC devices with a straight bevel.

Deep, vertical etching for GaAs using inductively coupled plasma/reactive ion etching

Deep etched structures in GaAs have many applications in optoelectronics and MEMS devices. These applications often require an anisotropic etch profile with smooth sidewalls as well as a high etch rate and high aspect ratio. Developing an etch process that demonstrates high selectivity for the etch mask is critical as etch times for deep grooves can be protracted due to the effect of RIE lag. In this work, the authors describe etching deep, vertical grooves in GaAs using Inductively Coupled Plasma/Reactive Ion Etching. The effects of RF power, pressure, and gas composition on mask selectivity, etch rate, and anisotropy are discussed. Using a SiO2 etch mask and Cl2 as the main etchant gas, grooves with a vertical sidewall and depths of &amp;gt;120 μm (aspect ratio of 9) have been achieved.

Effects of p-GaN gate structures and fabrication process on performances of normally-off AlGaN/GaN high electron mobility transistors

Performances of AlGaN/GaN high electron mobility transistors (HEMTs) with various p-GaN gates structures were investigated. With the HEMT wafer surmounted by a p-GaN layer, the gates were formed utilizing inductively coupled plasma reactive ion etching. The etching rate ratio for GaN to AlGaN was obtained to be 50 employing O2 with added Cl2 and Ar gases. Three types of HEMTs with etched regions of p-GaN removed, AlGaN etched slightly, and p-GaN remained were fabricated. All HEMTs showed the same threshold voltage of 1.2 V. High drain currents were obtained for HEMTs of p-GaN removed and AlGaN etched slightly, while the p-GaN remained showed low drain current. On-resistances of p-GaN removed and AlGaN etched slightly HEMTs were 7.3 and 8.6 Ω mm, and electron mobilities were 1600 and 1100 cm2/(V·s). The higher on-resistance of the HEMT with AlGaN etched slightly is ascribed to the deteriorated electron mobility.

ANGULAR DEPENDENCE OF TRACK-ETCH DETECTOR HARZLAS TD-1.

Track-etched detectors are commonly used also for radiation monitoring onboard International Space Station. To be registered in track-etched detectors, the particle needs to meet several criteria-it must have linear energy transfer above the detection threshold and strike the detector's surface under an angle higher than the so-called critical angle. Linear energy transfer is then estimated from calibration curve from the etch rate ratio V that is calculated from parameters of individual tracks appearing on the detector's surface after chemical etching. It has been observed that V can depend on the incident angle and this dependence can vary for different detector materials, etching and evaluating conditions. To investigate angular dependence, detectors (Harzlas TD-1) were irradiated at HIMAC by several ions under angles from 0° to 90°. The correction accounting not only for critical angle but also for dependence of V on the incident angle is introduced and applied to spectra measured onboard International Space Station.

Two-step potassium hydroxide etching to enhance aspect ratio in trench fabrication

Among various grating structure fabrication techniques, potassium hydroxide (KOH) wet anisotropic etching of Si(110) wafers offers low cost and impressive aspect ratio over large areas with high etch uniformity. The aspect ratio is ultimately limited by lateral etching that constantly widens the trenches. In this paper, the authors demonstrated a method to double the achievable aspect ratio using two-step KOH etching. After first KOH etching, the grating structure was grown with a thermal oxide; and after removing the oxide from the trench bottom using reactive ion etching, a second KOH etching was carried out with the original trench sidewall protected by the thermal oxide. The authors achieved the highest anisotropy [etching rate ratio of (110) and (111)] of 247 with 50 wt. % KOH at room temperature. Using the two-step KOH etching, it is possible to increase the aspect ratio by more than a factor of 2 while keeping the trench width almost unchanged.