Fast release process of metal structure using chemical dry etching of sacrificial Si layer

An ultra-fast removal process of a silicon sacrificial layer for the selective release of a metal structure on a Si substrate was studied, which uses a chemical dry etching method. The chemical dry etching of a Si layer was performed in an NF₃ remote plasma with the direct injection of additive nitric oxide (NO) gas. When the NO gas was injected into the chamber into which F radicals were supplied from a remote plasma source using NF₃ input gas, the silicon layer was removed selectively and the metal structure could be released easily. It was found that the etch rate on the sidewall (up to ≅ 18.7 μm/min for an opening width of 100 μm) and the bottom (up to ≅ 24.5 μm/min for an opening width of 100 μm) depends on the NO/(NO + Ar) gas flow ratio, time duration, and opening width. The developed dry etching process could be used to release a Ni structure with near infinite selectivity in a very short time. The process is well suited for fabricating various devices which require a suspended structure, such as in radio-frequency microelectromechanical system switches, tunable capacitors, high-Q suspended inductors and suspended-gate metal-oxide semiconductor field-effect transistors.     

Comparison of dry etching of PMMA and polycarbonate in diffusion pump-based O2 capacitively coupled plasma and inductively coupled plasma

We report a comparison of dry etching of polymethyl methacrylate (PMMA) and polycarbonate (PC) in O₂ capacitively coupled plasma (CCP) and inductively coupled plasma (ICP). A diffusion pump was used as high vacuum pump in both cases. Experimental variables were process pressure (30-180 mTorr), CCP power (25-150 W) and ICP power (0-350 W). Gas flow rate was fixed at 5 sccm. An optimized process pressure range of 40-60 mTorr was found for the maximum etch rate of PMMA and PC in both CCP and ICP etch modes. ICP etching produced the highest etch rate of 0.9 μm/min for PMMA at 40 mTorr, 100 W CCP and 300 W ICP power, while 100 W CCP only plasma produced 0.46 μm/min for PMMA at the same condition. For polycarbonate, the highest etch rates were 0.45 and 0.27 μm/min, respectively. RMS surface roughnesses of PMMA and PC were about 2-3 nm after etching. Etch selectivity of PMMA over photoresist was 1-2 and that of PC was less than 1. When ICP power increased from 0 to 350 W, etch rates of PMMA and PC increased linearly from 0.47 to 1.18 μm/min and from 0.18 to 0.6 μm/min, while the negative self bias slightly reduced from 364 to 352 V. Increase of CCP power raised both self bias and PMMA etch rate. PMMA etch rates were about 3 times higher than those of PC at the same CCP conditions. SEM data showed that there was some undercutting of PMMA and PC after etching at 300 W ICP, 100 W CCP and 40 mTorr. The results also showed that the etched surface of PMMA was rough and that of PC was relatively smooth.     

Comparative study on dry etching of polycrystalline diamond thin films

The reactive ion etching (RIE) technique was used to etch polycrystalline diamond thin films. In this study we investigate the influence of process parameters (total pressure, rf power, gas composition) of standard capacitively coupled plasma RIE system on the etching rate of diamond films. The surface morphology of etched diamond films was characterized by Scanning Electron Microscopy and the chemical composition of the etched film part was investigated by Raman Spectroscopy.We found that the gas composition had a crucial effect on the diamond film morphology. The use of CF₄ gas resulted in flatter surfaces and lateral-like etching, while the use of pure O₂ gas resulted in needle-like structures. Addition of argon to the reactant precursors increased the ion bombardment, which in turn increased the formation of non-diamond phases. Next, increasing the rf power from 100 to 500 W increased the etching rate from 5.4 to 8.6 μm/h. In contrast to this observation, the rise of process pressure from 80 to 150 mTorr lowered the etching rate from 5.6 down to 3.6 μm/h.     

Formation and optimization of undercut-microholes in InGaN light emitting diodes by using wet chemical etching

We report on the formation and optimization of undercut-microholes (UM) generated by a wet etching process. GaN epilayers with 6 μm and 15 μm polygonal holes (PH) were grown by using selective metal organic chemical vapor deposition under identical growth conditions. The samples were wet etched with either a KOH solution or a mixed H₃PO₄:H₂SO₄ solution. Both kinds of etching solution produced the formation of UM. In the case of the etching produced with the mixed H₃PO₄:H₂SO₄ solution, the angle of UM was varied with an increase of H₂SO₄ in the solution. The etching produced by the KOH solution was very simple, and it formed a clear UM with an angle of 62°. This was achieved without etching the hard mask because of the selective etching and crystallographic characteristics of the GaN. UM were optimized through etching with PH structures, and the results showed formation of clear UM in a 15 μm PH structure.     

Nanowhiskers formation by radio frequency Ar/O2 plasma etching of aluminum coated diamond films

Diamond nanowhiskers were fabricated by etching as-grown and aluminum coated diamond films in radio frequency (RF) Ar/O₂ plasma. It was found that diamond nanowhiskers could be obtained by anisotropic etching of both kinds of films. For the as-grown diamond film, the whiskers randomly formed on the diamond surface with higher etching rate. However, for the Al-coated diamond film, an energy dispersive X-ray spectroscopy measurement revealed that the distribution of the whiskers was the same as that of the coated Al particles. During the etching process, Al particles served as masks contributing to restraining the etching of the film underneath. It was found that the distribution of the whiskers was significantly influenced by the Al coating. The whiskers (1 μm in height and 50 nm in diameter) could be obtained under the optimum etching condition. In addition, the dependence of the distribution of the whiskers on Al coating time was demonstrated.     

Doping optimization and surface modification of aluminum doped zinc oxide films as transparent conductive coating

Aluminum doped zinc oxide (ZnO:Al) films were grown using spray pyrolysis technique. Effect of doping on structural, electrical, optical and morphological properties was studied. Aluminum doping improved the prominence of [002] growth while maintaining the grain size ~ 48 nm. Using an intermediate Al/Zn atomic ratio in precursor (1.5:100), we could achieve a low resistivity ρ ~ 7 × 10^− 4 Ωcm. These films possessed an average visible transmittance ~ 88%, an optical gap ~ 3.7 eV and plasma wavelength at 1.87 μm. A simultaneous use of methanol and iso-propanol in the precursor lead to a moderate surface roughness ~ 12 nm. The films were surface modified using wet chemical etching in diluted hydrochloric acid, for varied time intervals (5 s-15 s) and etchant concentrations (0.125%-1%). The etching experiments could be used to know the building of the film as also to modify the surface for desired optical and morphological properties.     

Hydrogen plasma etching of silicon dioxide in a hollow cathode system

Chemical etching of various materials has been observed when hydrogen plasmas are used in material processing. In the case of the deposition of diamond films the preferential etching of sp² bonded carbon is considered to be of fundamental importance. A few papers have been published which have indicated that etching by hydrogen ions is different to that by hydrogen atoms. In this paper we describe the etching of silicon dioxide by hydrogen which was plasma-activated in a molybdenum-lined RF hollow cathode. The etch rate was seen to be thermally activated but decreased with increasing plasma power. The addition of a few percentage of helium increased the etch rate. The application of a − 50 V bias to the sample holder almost doubled the etch rate indicating the importance of ion bombardment for the chemical reaction. At high plasma powers and substrate temperatures in excess of 450 °C a thin molybdenum deposit was formed on the quartz samples.     

Nanoindentation of laser micromachined 3C-SiC thin film micro-cantilevers

Single crystalline thin films of 3C-SiC with a thickness of 1.7 ± 0.2 μm were deposited on Si (100) substrate using atmospheric chemical vapor deposition technique. A Q-switched Nd:YAG laser in the fundamental wavelength with a pulse duration of 100 ns and average power of 1 W was then used to pattern 50 μm wide and 150 μm long cantilever beams in direct-writing mode. Following laser patterning, wet chemical etching using KOH anisotropic etchant was carried out to remove the underlying Si and form free-standing 3C-SiC cantilever beams. The cantilevers were subjected to nanoindentation test to obtain deflection versus load curves. The average Young’s modulus and fracture strength were determined to be 423 GPa and 1.5 GPa respectively which are comparable to those obtained by the reactive ion etching. Laser patterning thus offers nearly identical properties as that of ion etching with the added benefit of much higher etch rates.     

Dual etch processes of via and metal paste filling for through silicon via process

We investigated the etched slope control of silicon via and the filling of the through silicon via (TSV) with nano-scale Ag paste. Patterns for a 10 μm-diameter hole and line were etched using the Bosch process in a deep reactive ion etching system (the first etching process). The diameter of via_(Top) and the depth of the via were about 10.6 μm and 80 μm, respectively, with a nearly vertical profile. In sequence, the tapered via and the removal of the scallops were obtained using an inductively-coupled etching system (the second etching process). We investigated the effects of gas pressure and input power on the slope of the TSV during the second etching process. In the second etching process, as the process pressure increased from 10 to 80 mTorr, the diameter of via_(Top) decreased from 13 to 12.2 μm. Meanwhile, the expansion of via_(Top) increased with increasing source power from 200 to 600 W. We found that the expansions of the via_(Top) size were related to the desorption of by-product and the arrival of ion flux. We achieved a smooth surface and a slope angle of about 86° using the dual etch process. Finally, the depth of the 80 μm via was filled with nano-scale Ag paste using a vacuum-assisted filling method.     

Random phase mask as a model of a rough surface: Part II. Experiment

Artificial roughness was created on sample surfaces by etching through a two-dimensional orthogonal grating with a stochastic distribution of square "defects" of size. "Defects" depth was varied from 0.02 μm up to 1.005 μm. The experimental dependences of the scattering of polarized light were studied on four types of surface roughness for two materials: quartz and aluminum. The defect sizes of the random phase mask were 25 × 25 μm and 2.5 × 2.5 μm. The impacts of the sizes and density of artificial defects of rough surfaces on the polarization of reflected light were investigated by multiple-angle-of-incidence (MAI) ellipsometry at a wavelength of 0.63 μm.     

A combined top-down and bottom-up approach to fabricate silica films with bimodal porosity

We report a method to fabricate silica films with bimodal porosity based on the surfactant-directed self-assembly process followed by post-treatment with reactive ion etching (RIE). By RIE of a surfactant-templated mesoporous silica film with a 3D hexagonal structure, vertically-etched pores with the size of several tens of nanometers and the depth of ca. 60 nm are generated, while the original caged mesopores (ca. 5 nm in size) are still retained in the unetched parts of the film. Pre-treatment of the mesoporous silica film by wet-etching to expose the pores on the surface, followed by sputter deposition of a Pt layer for partial masking, is crucial for the anisotropic etching of the film. Such a combined top-down and bottom up approach offers an opportunity to fabricate silica films with hierarchical pore architectures.     

Low threading dislocation Ge on Si by combining deposition and etching

Blanket and selective Ge growth on Si is investigated using reduced pressure chemical vapor deposition. To reduce the threading dislocation density (TDD) at low thickness, Ge deposition with cyclic annealing followed by HCl etching is performed. In the case of blanket Ge deposition, a TDD of 1.3 × 10⁶ cm^− 2 is obtained, when the Ge layer is etched back from 4.5 μm thickness to 1.8 μm. The TDD is not increased relative to the situation before etching. The root mean square of roughness of the 1.8 μm thick Ge is about 0.46 nm, which is of the same level as before HCl etching. Further etching shows increased surface roughness caused by non-uniform strain distribution near the interface due to misfit dislocations and threading dislocations. The TDD also becomes higher because the etchfront of Ge reaches areas with high dislocation density near the interface. In the case of selective Ge growth, a slightly lower TDD is observed in smaller windows caused by a weak pattern size dependence on Ge thickness. A significant decrease of TDD of selectively grown Ge is also observed by increasing the Ge thickness. An about 10 times lower TDD at the same Ge thickness is demonstrated by applying a combination of deposition and etching processes during selective Ge growth.     

Thinning of CIGS solar cells: Part II: Cell characterizations

In this paper, the influence of reducing the thickness of the CIGSe absorber layer by bromine etching from 2.5 μm to 0.5 μm on electrical and optical solar cell properties is addressed. We observe a decrease in efficiency which is mainly caused by a reduced short circuit current, whereas the fill factor and the open circuit voltage are stable. Even without deliberate light trapping or anti-reflection coating, an efficiency of 10.3% is obtained for a 0.5 μm thick CIGSe absorber. A smoothing of the absorber surface is observed during the etching, its influence on the cell parameters will be discussed.     

UNCD electron emitters using Si nanostructure as a template

The electron field emission (EFE) properties of silicon nanostructures (SiNSs) coated with ultra-nanocrystalline diamond (UNCD) were characterized. The SiNS, comprising cauliflower-like grainy structure and nanorods, was generated by reaction of a Si substrate with an Au film at 1000 °C, and used as templates to grow UNCD. The UNCD films were deposited by microwave plasma-enhanced chemical vapour deposition (MPECVD) using methane and argon as reaction gases. The UNCD films can be grown on the SiNS with or without ultrasonication pretreatment with diamond particles. The EFE properties of the SiNS were improved by adding an UNCD film. The turn-on field (E₀) decreased from 17.6 V/μm for the SiNS to 15.2 V/μm for the UNCD/SiNS, and the emission current density increased from 0.095 to 3.8 mA/cm² at an electric field of 40 V/μm. Ultrasonication pretreatments of SiNS with diamond particles varied the structure and EFE properties of the UNCD/SiNS. It is shown that the ultrasonication pretreatment degraded the field emission properties of the UNCD/SiNS in this study.     

Pr_(6)O_(11)对合成金刚石单晶各向异性的刻蚀EI北大核心CSCD

为了探究稀土氧化物对合成金刚石单晶的各向异性刻蚀,在氮气保护下,在750~950℃内用Pr_(6)O_(11)对合成金刚石单晶进行刻蚀。采用扫描电子显微分析、热重分析、X射线衍射和拉曼光谱等技术对刻蚀后金刚石单晶不同晶面的表面形貌、物相组成和刻蚀机理进行表征与分析。采用最大刻蚀深度、单颗粒抗压强度和冲击韧性来表征刻蚀前后金刚石性能的变化。结果表明:Pr_(6)O_(11)对金刚石{100}面和{111}面的刻蚀程度和形貌均不同;当温度为750℃时,Pr_(6)O_(11)对金刚石单晶已有一定程度的刻蚀,随刻蚀温度的增加,刻蚀加剧,且金刚石{111}面的刻蚀程度比{100}面严重;{111}面刻蚀坑形貌从三角形变为层状结构三角形,{100}面由轻微的四边形变为类蜂窝状刻蚀坑;{111}面最大刻蚀深度从1.12μm增加到12.54μm,而{100}面只从0.30μm增加到2.11μm;金刚石单颗粒的抗压强度由未刻蚀金刚石的576.25 N降低到最小530.06 N,冲击韧性由92.94 J/cm^(2)减小到88.53 J/cm^(2);Pr_(6)O_(11)对金刚石单晶的刻蚀机理在885℃前为催化石墨化,885℃后为催化石墨化和氧化。     

Nanostructured GaN on silicon fabricated by electrochemical and laser-induced etching

Nanostructured GaN layers have been fabricated by electrochemical and laser-induced etching (LIE) processes based on n-type GaN thin films grown on the Si (111) substrate with AlN buffer layers. The effect of varying current and laser power density on the morphology of the GaN layers is investigated. The etched samples exhibited a dramatic increase in photoluminescence intensity as compared to the as grown samples. The average diameter of the GaN crystallites was about 7-10 nm, as determined from the PL data The Raman spectra also displayed stronger intensity peaks, which were shifted and broadened as a function of etching parameters. A strong band at 522 cm^− 1 is from the Si (111) substrate, and a small band at 301 cm^− 1, due to the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 cm^− 1 and 568 cm^− 1due to E2 (low) and E2 (high) respectively.     

Raman spectroscopy characterization of diamond films on steel substrates with titanium carbide arc-plated interlayer

Diamond chemical vapour deposition (CVD) on steel represents a difficult task. The major problem is represented by large diffusion of carbon into steel at CVD temperatures. This leads to very low diamond nucleation and degradation of steel microstructure and properties. Recent work [R. Polini, F. Pighetti Mantini, M. Braic, M. Amar, W. Ahmed, H. Taylor, Thin Solid Films 494 (2006) 116] demonstrated that well-adherent diamond films can be grown on high-speed steels by using a TiC interlayer deposited by the PVD-arc technique. The resulting multilayer (TiC/diamond) coating had a rough surface morphology due to the presence of droplets formed at the substrate surface during the reactive evaporation of TiC. In this work, we first present an extensive Raman investigation of 2 μm, 4 μm and 6 μm thick diamond films deposited by hot filament CVD on TiC interlayers obtained by the PVD-arc technique. The stress state of the diamond was dependent on both the films thickness and the spatial position of the coating on the substrate. In fact, on the top of TiC droplets, the stress state of the diamond was much lower than that of diamond in flatter substrate areas. These results showed that diamond films deposited on rough TiC interlayers exhibited a wide distribution of stress values and that very large compressive stress exists in the diamond film grown on flat regions of steel substrates with a TiC interlayer. Diamond films could accommodate stresses as large as 10 GPa without delamination.     

Nucleation and initial growth processes of diamond thin films for stripper foils

Carbon ion beam stripper foils were fabricated from diamond films synthesized on silicon via chemical vapor deposition. Fine-grained polycrystal diamond foils with decent surface flatness were obtained using a nucleation enhancement pretreatment process. Freestanding diamond foils were formed by etching a portion of the silicon substrate on which the diamond films well-adhered. In preliminary lifetime evaluations, the 1–3 μm-thick diamond foils lasted between 20 and 420 min for 3.2 MeV Ne⁺ion-beam charge stripping.     

Influence of the contacting scheme in simulations of radial silicon nanorod solar cells

Silicon nanorod solar cells were simulated using the Silvaco Technical Computer Aided Design (TCAD) software suite. For reasons of speed optimization the simulations were performed in cylinder coordinates taking advantage of the model's symmetry. Symmetric doping was assumed with a dopant density of 10¹⁸ cm⁻³ in the p-type core and in the n-type shell, and the location of the pn-junction was chosen such that the space charge region was located adjacent to the shell surface. Two contact configurations were explored. In configuration A the cathode contact was wrapped around the semiconductor nanorod, while in configuration B the cathode was assumed just on top of the nanorod. In both cases the anode was located at the bottom of the rod. Cell efficiency was optimized with regard to rod radius and rod length. Optimization was performed in a three-step procedure consisting in radius optimization, length optimization and again radius optimization. A maximum in efficiency with respect to rod length L was visible in configuration A, leading to an optimum value of L = 48 μm. This maximum is explained by the combination of an increase of short-circuit current density J_sc and a decrease of open-circuit voltage U_oc with L. In configuration B, J_sc also increases with L, but U_oc stays rather constant and the maximum in efficiency only appears at very large values of L ≈ 12 mm. We restricted the rod length to L ≤ 100 μm for further optimization, in order to stay in an experimentally feasible range. During the optimization of rod radius R in configuration A the open circuit voltage increased continuously, while short circuit current density stayed rather constant. This leads to an increase in efficiency with R, which only stops at very large radii, where R starts to be comparable with L. In configuration B efficiency is almost independent of R, provided that the radius is large enough to comprise a well-formed space charge region, here only a shallow maximum can be estimated. With the demand of rod lengths being smaller than 100 μm, optimum parameters L = 48 μm, R = 32 μm and L = 96 μm, R = 2 μm were extracted for configuration A and B, respectively.     

Modification of AZO thin-film properties by annealing and ion etching

Effects of annealing and ion etching on the structural, electrical and optical properties of sputtered ZnO:Al (AZO) thin films were investigated. The post-deposition annealing at temperatures T_A = 200-400 °C in the forming gas (80% N₂/20% H₂) for 1 h and ion RF-sputter etching after annealing were used. Ion-sputter etching rate was 7 nm/min. The surface topography changed noticeably after ion-sputter etching: the surface of the sample was rougher (R_a = 33 nm) in comparison with annealed sample only (R_a = 9 nm). After the post-deposition annealing temperature T_A = 400 °C and ion-sputter etching thin films have higher integral transmittance (in the range of λ = 400-1000 nm) than non-etched samples. The figure of merit (F) became higher with increase of annealing temperature and the maximum value was F = 8%/Ω at T_A = 400 °C (R_s = 10 Ω, T_int = 86%).