Dry etching characteristics of GaN using Cl2/BCl3 inductively coupled plasmas

ICP power/RF power, operating pressure, and Cl₂/BCl₃ gas mixing ratio are altered to investigate the effect of input process parameters on the etch characteristics of GaN films. The etch selectivity of GaN over SiO₂ and photoresist is studied. Although higher ICP/RF power can obtain higher GaN/photoresist etch selectivity, it can result in faceting of sidewall and weird sidewall profile due to photoresist mask erosion. Etch rates of GaN and SiO₂ decrease with the increase of operating pressure, and etch selectivity of GaN over SiO₂ increases with the increasing operating pressure at fixed ICP/RF power and mixture component. The highest etch selectivity of GaN over SiO₂ is 7.92, and an almost vertical etch profile having an etch rate of GaN close to 845.3 nm/min can be achieved. The surface morphology and root-mean-square roughness of the etched GaN under different etching conditions are evaluated by atomic force microscopy. The plasma-induced damage of GaN is analyzed using photoluminescence (PL) measurements. The optimized etching process, used for mesa formation during the LED fabrication, is presented. The periodic pattern can be transferred into GaN using a combination of Cl₂/BCl₃ plasma chemistry and hard mask SiO₂. Patterning of the sapphire substrate for fabricating LED with improved extraction efficiency is also possible using the same plasma chemistry.     

Optimized ICP etching process for fabrication of oblique GaN sidewall and its application in LED

Inductively coupled plasma (ICP) etching of GaN is systemically investigated by changing ICP power/RF bias power, operating pressure, and Cl₂/BCl₃ gas mixing ratio. The hexagonal etch pits related to screw dislocation existing along GaN epitaxial layer were observed on the etched GaN surface after ICP etching. The intensity of band-edge emission is significantly reduced from the etched n-GaN surface, which reveals that plasma-induced damage are generated after ICP etching. The oblique sidewall is transferred into GaN using a combination of Cl₂/BCl₃ plasma chemistry and hard mask SiO₂. By adjusting ICP etching process parameters, oblique sidewalls with various oblique angles can be formed, allowing for conformal metal lines coverage across the mesa structures, which can play an important role in the interconnection of multiple microchips for light emitting diodes (LEDs) fabrication.     

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (R_a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.     

Dry etching of ITO by magnetic pole enhanced inductively coupled plasma for display and biosensing devices

The dry etching of indium tin oxide (ITO) layers deposited on glass substrates was investigated in a high density inductively coupled plasma (ICP) source. This innovative low pressure plasma source uses a magnetic core in order to concentrate the electromagnetic energy on the plasma and thus provides for higher plasma density and better uniformity. Different gas mixtures were tested containing mainly hydrogen, argon and methane. In Ar/H₂ mixtures and at constant bias voltage (−100 V), the etch rate shows a linear dependence with input power varying the same way as the ion density, which confirms the hypothesis that the etching process is mainly physical. In CH₄/H₂ mixtures, the etch rate goes through a maximum for 10% CH₄ indicating a participation of the radicals to the etching process. However, the etch rate remains quite low with this type of gas mixture (around 10 nm/min) because the etching mechanism appears to be competing with a deposition process. With CH₄/Ar mixtures, a similar feature appeared but the etch rate was much higher, reaching 130 nm/min at 10% of CH₄ in Ar. The increase in etch rate with the addition of a small quantity of methane indicates that the physical etching process is enhanced by a chemical mechanism. The etching process was monitored by optical emission spectroscopy that appeared to be a valuable tool for endpoint detection.     

A study on the wet etching behavior of AZO (ZnO:Al) transparent conducting film

This paper studies the wet etching behavior of AZO (ZnO:Al) transparent conducting film with tetramethylammonium hydroxide (TMAH). The optimum optoelectronic film is prepared first using designated RF power, film thickness and controlled annealing heat treatment parameters. The AZO film is then etched using TMAH etchant and AZ4620 photoresist with controlled etchant concentration and temperature to examine the etching process effect on the AZO film optoelectronic properties. The experimental results show TMAH:H₂O = 2.38:97.62 under 45 °C at the average etch rate of 22 nm/min as the preferred parameters. The activation energy drops as the TMAH concentration rises, while the etch rate increases along with the increase in TMAH concentration and temperature. After lithography, etching and photoresist removal, the conductivity of AZO film dramatically drops from 2.4 × 10⁻³ Ω cm to 3.0 × 10⁻³ Ω cm, while its transmittance decreases from 89% to 83%. This is due to the poor chemical stability of AZO film against AZ4620 photoresist, leading to an increase in surface roughness. In the photoresist postbaking process, carbon atoms diffused within the AZO film produce poor crystallinity. The slight decreases in zinc and aluminum in the thin film causes a carrier concentration change, which affect the AZO film optoelectronic properties.     

Backside etching of fused silica with Nd:YAG laser

The laser-induced backside etching of fused silica with gallium as highly absorbing backside absorber using pulsed infrared Nd:YAG laser radiation is demonstrated for the first time. The influence of the laser fluence, the pulse number, and the pulse length on the etch rate and the etched surface topography was studied. The comparable high threshold fluences of about 3 and 7 J/cm² for 18 and 73 ns pulses, respectively, are caused by the high reflectivity of the fused silica-gallium interface and the high thermal conductivity of gallium. For the 18 and 73 ns long pulses the etch rate rises almost linearly with the laser fluence and reaches a value of 350 and 300 nm/pulse at a laser fluence of about 12 and 28 J/cm², respectively. Incubation processes are almost absent because etching is already observed with the first laser pulse at all etch conditions and the etch rate is constant up to 30 pulses.The etched grooves are Gaussian-curved and show well-defined edges and a smooth bottom. The roughness measured by interference microscopy was 1.5 nm rms at an etch depth of 0.6 μm. The laser-induced backside etching with gallium is a promising approach for the industrial application of the backside etching technique with IR Nd:YAG laser.     

Investigation of etch characteristics of non-polar GaN by wet chemical etching

We characterized the surface defects in a-plane GaN, grown onto r-plane sapphire using a defect-selective etching (DSE) method. The surface morphology of etching pits in a-plane GaN was investigated by using different combination ratios of H₃PO₄ and H₂SO₄ etching media. Different local etching rates between smooth and defect-related surfaces caused variation of the etch pits made by a 1:3 ratio of H₃PO₄/H₂SO₄ etching solution. Analysis results of surface morphology and composition after etching by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that wet chemical etching conditions could show the differences in surface morphology and chemical bonding on the a-plane GaN surface. The etch pits density (EPD) was determined as 3.1 × 10⁸ cm⁻² by atom force microscopy (AFM).     

Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching

In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K₂S₂O₈ solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K₂S₂O₈ solution has been proposed.     

Photoluminescence activity of Yang and Secco etched multicrystalline silicon material

Ultraviolet and blue-green photoluminescence (PL) was investigated on multicrystalline silicon (mc-Si) samples chemically etched by Secco and Yang solutions. The samples were characterized by dislocation density (10⁵-10⁶ cm⁻²). The form of etched pits is triangular with Yang etch and like a honeycomb with Secco etch as observed with a scanning electron microscope (SEM). These textures of mc-Si wafers give a PL activity similar to that obtained with nanostructures of porous silicon (PS) as reported in the literature. The ultraviolet PL spectra observed with Yang etch shift to the blue-green spectrum range when applying Secco etch. In our experiments we have observed 3-5 μm diameter macro pores separated by a high density of nanowalls. These observations suggest that the origin of the PL activity are quantum dots resulting from the silicon nanocrystallites obtained after few minutes of chemical etching.     

Effects of nitrogen addition on methane-based ECR plasma etching of gallium nitride

The effects of nitrogen addition on methane-based ECR plasma etching of GaN were studied. The etch rate 30 nm/min and r.m.s. roughness 2.6 nm were obtained when the GaN sample was etched by a methane-based gas mixture without N₂. The addition of N₂ gas resulted in a decrease of etch rate and a smoother etched surface. The r.m.s. roughness became less than 0.4 nm even only 1.5 sccm N₂ gas was added to the mixture. In situ XPS measurements showed that, without N₂, heavy N-depletion took place on the etched surface, resulting in appearance of Ga metal on the surface. In contrast, the loss of N was compensated when the N₂ gas was added, and the etched surface approached the stoichiometric one with the increase of N₂ gas flow. This suppression of preferential loss of N was considered to be the main reason that improved the etched surface morphology.     

Dry etching of MgCaO gate dielectric and passivation layers on GaN

MgCaO films grown by rf plasma-assisted molecular beam epitaxy and capped with Sc₂O₃ are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs), respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively coupled plasmas of CH₄/H₂/Ar produced etch rates only in the range 20-70 Å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (∼100 Å/min) were obtained with Cl₂/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH₄/H₂/Ar plasma chemistry produced a selectivity of around 2 for etching the MgCaO with respect to GaN.     

Effect of radio frequency power on the inductively coupled plasma etched Al0.65Ga0.35N surface

The etching effects on the surface and electrical characteristics of high Al mole fraction Al_xGa_1−xN (x = 0.65) have been characterized by X-ray photoelectron spectroscopy (XPS) and transfer length method (TLM) as a function of radio frequency power. XPS results show that the Ga-N and Al-N peaks move to the lower energy after ICP etchings. An increase in the amount of oxygen and a decrease in the amount of nitrogen are observed for the etched samples along with the RF power. The annealing at 450 °C is partly effective on removing the oxygen amount which would come from the C-O component and recovering the N deficiencies on the surface of etched sample. The extracted sheet resistance of the AlGaN layer from TLM increases gradually after ICP etching with an increase of RF power. The correlation between the XPS peaks and the electrical properties of the etched samples has been discussed and the annealing effect on the inverse leakage current of the p-i-n AlGaN solar blind UV detector is examined.     

The effect of hydrogen as an additive in reactive ion etching of GaAs for obtaining polished surface

The effect of hydrogen on the reactive ion etching (RIE) of GaAs in the CF₂Cl₂ plasma is discussed. The addition of hydrogen into the reaction mixture improves the sharpness of etch borders; the etched surface is smooth for etching depth > 1 μm, etching rate is time-constant.     

Effect of surface modification by thermally oxidization and HF etching on UV photoluminescence emission of porous silicon

Photoluminescence of porous silicon (PS) is instable due perhaps to the nanostructure modification in air. The controllable structure modification processes on the as-prepared PS were conducted by thermal oxidization and/or HF etching. The PL spectra taken from thermally oxidized PS showed a stable photoluminescence emission of 355 nm. The photoluminescence emission taken from both of PS and oxidized porous silicon (OPS) samples etched with HF were instable, which can be reversibly recovered by the HF etching procedure. The mechanism of UV photoluminescence is discussed and attributed to the transformation of luminescence centers from oxygen deficient defects to the oxygen excess defects in the thermal oxidized PS sample and surface absorbed silanol groups on PS samples during the chemical etched procedure.     

Laser etching of transparent materials at a backside surface adsorbed layer

The laser etching using a surface adsorbed layer (LESAL) is a new method for precise etching of transparent materials with pulsed UV-laser beams. The influence of the processing parameters to the etch rate and the surface roughness for etching of fused silica, quartz, sapphire, and magnesium fluoride (MgF₂) is investigated. Low etch rates of 1 nm/pulse and low roughness of about 1 nm rms were found for fused silica and quartz. This is an indication that different structural modifications of the material do not affect the etching significantly as long as the physical properties are not changed. MgF₂ and sapphire feature a principal different etch behavior with a higher etch rate and a higher roughness. Both incubation effects as well as the temperature dependence of the etch rate can be interpreted by the formation of a modified near surface region due to the laser irradiation. At repetition rates up to 100 Hz, no changes of the etch rate have been observed at moderate laser fluences.     

Effect of H2 and O2 plasma etching treatment on the surface of diamond-like carbon thin film

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O₂) and hydrogen (H₂) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H₂ and O₂ was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H₂ plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O₂ plasma. The surface roughness of plasma etching-treated DLC with H₂ or O₂ was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O₂ plasma was hydrophilic as well as smooth.     

Indirect laser etching of fused silica: Towards high etching rate processing

The indirect laser processing approach (LIBWE) laser-induced backside wet etching allows defined microstructuring of transparent materials at low laser fluences with high quality. The optical and the thermal properties of the solid/liquid interface determine the temperatures and therefore the etching mechanism in conjunction with the dynamic processes at the interface due to the fast heating/cooling rates. The exploration of organic liquid solvents and solutions such as 0.5 M pyrene/toluene results in low etch rates (∼20 nm/pulse). By means of liquid metals as absorber here, demonstrated for gallium (Ga), etch rates up to 600 nm/pulse can be achieved. Regardless of the high etch rates a still smooth surface similar to etching with organic liquid solutions can be observed. A comparative study of the two kinds of absorbing liquids, organic and metallic, investigates the etch rates regarding the fluence and pulse quantity. Thereby, the effect of incubation processes as result of surface modification on the etching is discussed. In contrast to pyrene/toluene solution the metallic absorber cannot decompose and consequently no decomposition products can alter the solid/liquid interface to enhance the absorption for the laser radiation. Hence, incubation can be neglected in the case of the silica/gallium interface so that this system is a suitable model to investigate the primary processes of LIBWE. To prove the proposed thermal etch mechanism an analytical temperature model based on a solution of the heat equation is derived for laser absorption at the silica/gallium interface.     

干法刻蚀影响应变量子阱发光的机理研究

采用感应耦合等离子体刻蚀技术对InAsP/InP应变多量子阱和InAsP/InGaAsP应变单量子阱材料的覆盖层进行了不同厚度的干法刻蚀. 实验结果表明，干法刻蚀后量子阱光致荧光强度得到了不同程度的增强. 干法刻蚀过程不仅增加了材料表面粗糙度，同时使其内部微结构发生变化. 采用湿法腐蚀方法去除表面变粗糙对量子阱发光特性的影响，得到干法刻蚀覆盖层20 nm后应变单量子阱微结构变化和其表面粗糙度变化两个因素分别使荧光强度提高1.8倍和1.2倍的结果. 关键词： 干法刻蚀 应变多量子阱 光致发光谱 损伤     

Shallow surface etching of organic and inorganic compounds by electrospray droplet impact

The electrospray droplet impact (EDI) was applied to bradykinin, polyethylene terephthalate (PET), SiO₂/Si, and indium phosphide (InP). It was found that bradykinin deposited on the stainless steel substrate was ionized/desorbed without the accumulation of radiation products. The film thickness desorbed by a single collisional event was found to be less than 10 monolayers. In the EDI mass spectra for PET, several fragment ions were observed but the XPS spectra did not change with prolonged cluster irradiation. The etching rate for SiO₂ by EDI was measured to be ∼0.2 nm/min. The surface roughness of InP etched by EDI was found to be one order of magnitude smaller than that etched by 3 keV Ar⁺ for about the same etching depths. EDI is capable of shallow surface etching with little damage left on the etched surface.