SiC Etch Rate Research Articles

Development of SiC Etching by Chlorine Fluoride Gas

Amorphous SiC and 4H-SiC were etched by chlorine fluoride (ClF), chlorine trifluoride (ClF3), fluorine (F2) and chlorine (Cl2) gases, in order to evaluate the etching capability of various reactive gases. The gaseous byproducts of SiC etching were observed by the quadrupole mass spectrometry. The ClF showed slow etching rate of amorphous SiC and 4H-SiC, while ClF3 and F2 quickly etched them. By the ClF gas, the etching rate of amorphous SiC was 120 nm/min at 400 °C. The ClF gas was expected to be suitable for a shallow etching, because of its moderate etching rate even at high temperatures.

Dry etching of silicon carbide in ICP with high anisotropy and etching rate

A detailed study of the influence of technological parameters of the plasma chemical etching process in inductively coupled plasma on the etching rate of single-crystal silicon carbide is presented. The physicochemical substantiation of experimentally revealed patterns is given. The optimal gas mixture was determined in terms of the etching rate of SiC. It was experimentally established that the dependence of the etching rate of silicon carbide on the percentage of oxygen in the total gas mixture is non-linear. Thus, with an increase in the percentage of O2 up to 23%, the etching rate of SiC gradually increases to 560 nm/min, a further increase in the percentage of O2 leads to a sharp decrease in the etching rate of SiC up to 160 nm/min at an oxygen content of 31%. The effect of the distance between the sample and the plasma generation zone on the etching rate of SiC was studied. It was shown that the greatest increase in speed is caused by an increase in the bias voltage, so at Ubias = - 50 V the etching rate is 300 nm/min, and at Ubias = - 150 V the value of the etching rate is 840 nm/min. The optimal parameters of the plasma-chemical etching process were selected for high-speed directional etching of single-crystal silicon carbide substrates.

Study of the effect of substrate holder temperature on the etching rate of monocrystalline silicon carbide

The paper touches upon the features of thermal stimulated plasma chemical etching (PCE) 6H-SiC in fluorine-containing inductively coupled plasma (ICP) in the temperature range from 50 °C to 300 °C. It was found that the etching rate of silicon carbide increases linearly from 0.9 µm/min to 1.3 µm / min with an increase in the temperature of the substrate holder from 50 °C to 150 °C, and further temperature increase to 300 °C does not contribute to an increase in the etching rate of SiC. On the basis of the obtained experimental data, the physicochemical regularities of plasma chemical etching of silicon carbide at elevated values of the substrate temperature were determined.

Fabrication technology for high light-extraction ultraviolet thin-film flip-chip (UV TFFC) LEDs grown on SiC

The light output of deep ultraviolet (UV-C) AlGaN light-emitting diodes (LEDs) is limited due to their poor light extraction efficiency (LEE). To improve the LEE of AlGaN LEDs, we developed a fabrication technology to process AlGaN LEDs grown on SiC into thin-film flip-chip LEDs (TFFC LEDs) with high LEE. This process transfers the AlGaN LED epi onto a new substrate by wafer-to-wafer bonding, and by removing the absorbing SiC substrate with a highly selective SF6 plasma etch that stops at the AlN buffer layer. We optimized the inductively coupled plasma SF6 etch parameters to develop a substrate-removal process with high reliability and precise epitaxial control, without creating micromasking defects or degrading the health of the plasma etching system. The SiC etch rate by SF6 plasma was ∼46 μm hr–1 at a high RF bias (400 W), and ∼7 μm hr–1 at a low RF bias (49 W) with very high etch selectivity between SiC and AlN. The high SF6 etch selectivity between SiC and AlN was essential for removing the SiC substrate and exposing a pristine, smooth AlN surface. We demonstrated the epi-transfer process by fabricating high light extraction TFFC LEDs from AlGaN LEDs grown on SiC. To further enhance the light extraction, the exposed N-face AlN was anisotropically etched in dilute KOH. The LEE of the AlGaN LED improved by ∼3× after KOH roughening at room temperature. This AlGaN TFFC LED process establishes a viable path to high external quantum efficiency and power conversion efficiency UV-C LEDs.

Influence of neutron irradiation on etching of SiC in KOH

The effect of reactor neutron irradiation on the etch rate of SiC in potassium hydroxide has been studied. In the case of high irradiation doses (1019–1021 cm–2), the etch rate of silicon carbide has been shown to drastically rise, especially in the [0001]Si direction. This considerably mitigates the orientation anisotropy of polar face etching. After high-temperature annealing (up to 1200–1400°C), a higher etch rate of irradiated crystals persists. The results have been explained by the high concentration of radiation-induced (partially clustered) defects they contain.

4H–SiC homoepitaxy on nearly on-axis substrates using TFS-towards high quality epitaxial growth

We report high quality homoepitaxial growth on nearly on-axis (±0.5°) 4H–SiC substrates by chemical vapor deposition (CVD) using Tetrafluorosilane and Propane as Si and C-precursors, respectively. N-type unintentional doping (1017–1014cm−3) was obtained for 0.6<C/Si<2.5, displaying site-competition behavior. Epilayers showing varying degrees of step flow/spiral growth were obtained at growth rates Rg- 5–14μm/h, which was found to be C-controlled. At C/Si<2, Rg was weakly dependent on the ratio, with a clear transition from step-controlled growth (0.6<C/Si<1) to spiral growth as C/Si increases, as observed by others previously. For C/Si>2.0, a linear dependence on C-flow is established, with a return to step-mediated growth, shown by the surface morphology (RMS roughness ∼1nm), and high polytype uniformity from Raman at high Rg- 14μm/h. These two behaviors were ascribed to a decrease in the etch rate of SiC by SiF4 with increasing C/Si due to C-aided decomposition of SiF4, both of which make available a greater amount of elemental Si at the surface, thereby suppressing spiral growth. Use of on-axis or near on-axis substrates can eliminate/reduce basal plane dislocations which limit the performance of SiC bipolar electronic devices.

SiC Homoepitaxy, Etching and Graphene Epitaxial Growth on SiC Substrates Using a Novel Fluorinated Si Precursor Gas (SiF4)

Tetrafluorosilane (SiF4 or TFS), a novel precursor gas, has been demonstrated to perform three primary operations of silicon carbide-related processing: SiC etching, SiC epitaxial growth and graphene epitaxial growth. TFS etches SiC substrate vigorously in a H2 ambient by efficient Si removal from the surface, where SiC etch rate is a function of TFS gas concentration. In this SiC etching process, Si is removed by TFS and C is removed by H2. When propane is added to a H2 and TFS gas mixture, etching is halted and high-quality SiC epitaxy takes place in a Si droplet-free condition. TFS’s ability to remove Si can also be exploited to grow epitaxial graphene in a controllable manner in an inert (Ar) ambient. Here, TFS enhances graphene growth by selective etching of Si from the SiC surface.

Effects of UV light intensity on electrochemical wet etching of SiC for the fabrication of suspended graphene

We report on the effects of UV light intensity on the photo assisted electrochemical wet etching of SiC(0001) underneath an epitaxially grown graphene for the fabrication of suspended structures. The maximum etching rate of SiC(0001) was 2.5 µm/h under UV light irradiation in 1 wt % KOH at a constant current of 0.5 mA/cm2. The successful formation of suspended structures depended on the etching rate of SiC. In the Raman spectra of the suspended structures, we did not observe a significant increase in the intensity of the D peak, which originates from defects in graphene sheets. This is most likely explained by the high quality of the single-crystalline graphene epitaxially grown on SiC.

ICP Etching of 4H-SiC Substrates

Due to its inert chemical nature, plasma etching is the most effective technique to pattern SiC. In this paper, dry etching of 4H-SiC substrate in Inductively Coupled Plasma (ICP) has been studied in order to evaluate the impact of process parameters on the characteristics of etching such as etch rate and trenching effect. Key process parameters such as platen power and ICP coil power prove to be essential to control the SiC etch rate. On the other hand, the ICP coil power and the working pressure mainly master the trenching effect. Our results enlighten that high etch rate with minimal trenching effect can be obtained using high ICP coil power and low working pressure.

Formation technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors

The technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors is studied. The dependences of the reactive ion etch rate of SiC in the inductively coupled plasma discharge on the pressure of the SF6/O2/Ar gas mixture (5–40 mTorr), the high-frequency power applied to the bottom electrode (200–300 W), the working gas flow ratio (5 : 1 : (0–10)), and the bottom electrode temperatures (5–50°C) are studied. Based on these dependences, the hole etching process on 76-mm-diameter SiC substrates 50 and 100 μm thick is developed. The process features smooth etched-surface morphology, a high rate (1 μm/min), and low high-frequency power deposited into the inductively coupled plasma discharge (1000 W). The developed process of hole etching in SiC substrates is characterized by the selectivity coefficient S = 12 and the anisotropy coefficient A = 13. Films based on NiB are recommended as masks for etching through holes into SiC substrates. The processes of through-hole metallization by the electrochemical deposition of Ni and Au layers are developed.

Plasma Resistance and Etch Mechanism of High Purity SiC under Fluorocarbon Plasma

Etch rates of Si and high purity SiC have been compared for various fluorocarbon plasmas. The relative plasma resistance of SiC, which is defined as the etch rate ratio of Si to SiC, varied between 1.4 and 4.1, showing generally higher plasma resistance of SiC. High resolution X-ray photoelectron analysis revealed that etched SiC has a surface carbon content higher than that of etched Si, resulting in a thicker fluorocarbon polymer layer on the SiC surface. The plasma resistance of SiC was correlated with this thick fluorocarbon polymer layer, which reduced the reaction probability of fluorine-containing species in the plasma with silicon from the SiC substrate. The remnant carbon after the removal of Si as volatile etch products augments the surface carbon, and seems to be the origin of the higher plasma resistance of SiC.

Etching characteristics and mechanisms of SiC thin films in inductively-coupled HBr-Ar, N2, O2 plasmas

Etch characteristics and mechanisms of SiC thin films in HBr-Ar, HBr-N2, and HBr-O2 inductively-coupled plasmas were studied using a combination of experimental and modeling methods. The etch rates of SiC thin films were measured as functions of the additive gas fraction in the range of 0–100% for Ar, N2, and O2 at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using Langmuir probe diagnostics and a global (zero-dimensional) plasma model. The good agreement between the behaviors of the SiC etch rate and the H atom flux could suggest that a chemical etch pathway is rather controlled by the gasification of carbon through the CHx or CHxBry compounds.

Determination of Etch Rate Behavior of 4H–SiC Using Chlorine Trifluoride Gas

The etch rate of single-crystalline 4H–SiC is studied using chlorine trifluoride gas at 673–973 K and atmospheric pressure in a cold wall horizontal reactor. The 4H–SiC etch rate can be higher than 10 µm/min at substrate temperatures higher than 723 K. The etch rate increases with the chlorine trifluoride gas flow rate. The etch rate is calculated by taking into account the transport phenomena in the reactor including the chemical reaction at the substrate surface. The flat etch rate at the higher substrate temperatures is caused mainly by the relationship between the transport rate and the surface chemical reaction rate of chlorine trifluoride gas.

Characteristics of Silicon Carbide Etching Using Magnetized Inductively Coupled Plasma

In this study, SiC etching was carried out using fluorine-based magnetized inductively coupled plasmas. The SiC etch rates and etch selectivities of SiC to Cu and Ni were investigated for the purpose of obtaining high etch rates in the application of SiC etching to various optical devices and micro-electromechanical systems (MEMS). Among SF6, CF4 and NF3, SF6 showed the highest SiC etch rates and etch selectivities to Cu and Ni, due to its highest F atomic density and to the formation of nonvolatile fluoride on Cu and Ni. Cu generally showed higher etch selectivity than Ni, possibly due to the easier formation of fluoride in this case. The application of a weak axial magnetic field ranging from 0 to 80 G showed maximum SiC etch rates at 40 G, possibly due to the formation of a resonance mode. When a field of 40 G was applied, the SiC etch rate was increased approximately two times and, in this condition, the F atomic density and ion densities in the plasma were also at a maximum. The highest SiC etch rate obtained in our experiment was 2020 nm/min with an inductive power of 1400 W, a bias voltage of -600 V, a pressure of 10 mTorr of SF6, and a magnetic field of 40 G. The etch selectivity to Ni obtained in this condition was about 40.

Fabrication of SiC micro-lens by plasma etching

SiC micro-lenses were fabricated by a plasma etching method by controlling the etch selectivities between photoresist and SiC. To etch SiC, inductively coupled plasmas were used with CF4, HCl, and HCl/HBr as the etch gases. When CF4 and HCl were used to etch SiC, the etch selectivities of SiC over photoresist were remained near 0.4 and 0.6, respectively. However, by using HCl/HBr, the selectivity was changed from 0.6 to 1.1. The SiC etch rates for HCl/HBr were in the range from 345 to 500 nm/min. The curvature radius of SiC micro-lenses fabricated with HCl/HBr was in the range from 20 to 27.54 μm and the roughness of the fabricated lenses was in the range from 1.7 to 2.65 nm.

Dry etching of SiC in inductively coupled Cl2/Ar plasma

Inductively coupled Cl2/Ar plasma etching of 4H–SiC has been studied. The SiC etch rate has been investigated as a function of average ion energy, Ar concentration in the gas mixtures, inductively coupled plasma power, work pressure and substrate temperature. The etch mechanism has been investigated by correlating the ion current density and relative atomic chlorine content to the etch rate under various etch conditions. For the first time, it has been found that the etch rate of SiC increases by about 50% at lower substrate temperatures (−80°C) than at high substrate temperatures (150°C) with the highest SiC etch rate of 230 nm min−1 being achieved at a substrate temperature of −80°C.

Impact of Ar addition to inductively coupled plasma etching of SiC in SF6/O2

The influence of Ar addition to SF 6 /O 2 gas mixtures has been investigated for inductively coupled plasma (ICP) etching of SiC with a view to improve both etch rate and etched surface microstructure. SiC etch rates have been studied as a function of Ar concentration, gas flow rates, applied ICP power, chuck power and chamber pressure. SiC etch rate, surface morphology, surface chemistry and etch profiles obtained in SF 6 /O 2 /Ar gas mixtures have been compared with those of SiC-etched in SF 6 /O 2 gas mixtures under similar conditions. It was found that, compared with SF 6 /O 2 (4:1) ICP-etched SiC in our studies, smoother surfaces and significant reduction of fluorine-related etch residues can be obtained by optimum Ar addition. SiC etch rate in SF 6 /O 2 gas mixtures can be increased by over 5% with optimum Ar%. The highest SiC etch rate achieved here is approximately 500 nm/min in SF 6 /O 2 /Ar gas mixtures. The influence of Ar addition on the SiC etch profile has also been studied.

Impact of Ar addition to inductively coupled plasma etching of SiC in SF 6/O 2

The influence of Ar addition to SF 6/O 2 gas mixtures has been investigated for inductively coupled plasma (ICP) etching of SiC with a view to improve both etch rate and etched surface microstructure. SiC etch rates have been studied as a function of Ar concentration, gas flow rates, applied ICP power, chuck power and chamber pressure. SiC etch rate, surface morphology, surface chemistry and etch profiles obtained in SF 6/O 2/Ar gas mixtures have been compared with those of SiC-etched in SF 6/O 2 gas mixtures under similar conditions. It was found that, compared with SF 6/O 2 (4:1) ICP-etched SiC in our studies, smoother surfaces and significant reduction of fluorine-related etch residues can be obtained by optimum Ar addition. SiC etch rate in SF 6/O 2 gas mixtures can be increased by over 5% with optimum Ar%. The highest SiC etch rate achieved here is approximately 500 nm/min in SF 6/O 2/Ar gas mixtures. The influence of Ar addition on the SiC etch profile has also been studied.

Transformer coupled plasma etching of 3C-SiC films using fluorinated chemistry for microelectromechanical systems applications

Polycrystalline 3C-SiC films are etched by oxygen-mixed sulfur hexafluoride transformer coupled plasmas for microelectromechanical systems (MEMS) applications. Silicon dioxide is employed as etching masks, which avoids the micromasking phenomena and chamber contamination commonly involved when using metals as masks. The etch rate, selectivity, and profile are characterized as functions of O2 percentage in the etching gas. Etch rates of SiC remain almost unchanged at about 3600 Å/min up to 50% O2, but decrease significantly when more than 50% O2 is used. Etch selectivity of SiC over SiO2 reaches maximum of 2.6 when using 50% O2. The chemical composition and the topography of the etched SiC films are also examined. By integrating the etching process with conventional surface micromachining technology, functional SiC-based MEMS resonators are fabricated.

High rate etching of 6H–SiC in SF 6-based magnetically-enhanced inductively coupled plasmas

In this study, the etch characteristics of 6H–SiC were investigated in magnetically-enhanced SF 6 inductively-coupled-plasmas (ICP) with and without magnetic field. The etch characteristics of various metal films such as Ni, Al and Cu were also investigated to apply as the etch mask to the highly selective SiC etching process. With the magnetic field, the etch rates of SiC were increased 60% compared to those without the magnetic field. With the magnetic field, the etch rates of Ni and Al were also increased white the etch rates of Cu decreased. In fact, in the case of Cu etching using SF 6, deposition instead of etching occurred through the formation of etch products such as copper fluoride on the surface with fluorine in the plasma. Therefore, among the investigated mask materials, Cu showed infinite etch selectivity over SiC during etching using SF 6. The highest etch rate obtained for SiC was greater than 1500 nm/min at 1500 W of inductive power, −350 V of bias voltage, and 1.33 Pa of SF 6. SiC etching with the Cu mask showed highly anisotropic etch profiles.