Effects of various additive gases on chemical dry etching rate enhancement of low-k SiOCH layer in F2/Ar remote plasmas

N₂ and NO gas addition to F₂/Ar remote plasmas during chemical dry etching (CDE) of low-k SiOCH layer was effective in increasing the etch rate, but the addition of O₂ decreased the etch rate. And, the injection of NO gas directly into the reactor increased the SiOCH etch rate most significantly. The addition of N₂ or NO gas contributes to an effective removal of oxygen in the SiOCH layer, by forming NO₂ and HNO₃ by-products, and of carbon species in the SiOCH layer by forming CF₄ by-product, which leads to enhancement of SiF₄ formation and in turn increase in the SiOCH etch rate.     

Anodic etching of p-type cubic silicon carbide

p-Type cubic silicon carbide was anodically etched using an electrolyte of HF:HCl:H₂O. The etching depth was determined versus time with a fixed current density of 96.4 mA cm^–2. It was found that the etching was very smooth and very uniform. An etch rate of 22.7 nm s^–1 was obtained in a 1:1:50 HF:HCl:H₂O electrolyte.     

Etch characteristics of CoFeB magnetic thin films using high density plasma of a H2O/CH4/Ar gas mixture

Etch characteristics of CoFeB magnetic thin films patterned with TiN hard masks were investigated using inductively coupled plasma reactive ion etching in H₂O/Ar and H₂O/CH₄ gas mixes. As the H₂O concentration in the H₂O/Ar gas increased, the etch rates of CoFeB and TiN films decreased simultaneously, while the etch selectivity increased and etch profiles improved slightly without any redeposition. The addition of CH₄ to the H₂O gas resulted in an increase in etch selectivity and a higher degree of anisotropy in the etch profile. X-ray photoelectron spectroscopy was performed to understand the etch mechanism in H₂O/CH₄ plasma. A good pattern transfer of CoFeB films masked with TiN films was successfully achieved using the H₂O/CH₄ gas mix.     

Wet etching of sputtered tantalum thin films in NaOH and KOH based solutions

In this paper, a wet chemical etching technique to selectively etch tantalum thin film in sodium hydroxide and potassium hydroxide based solutions was developed. Tantalum thin films were deposited by a DC-magnetron sputtering technique on silica and yttria-stabilized zirconia (YSZ) substrates. After deposition, the films were etched in hot NaOH/ H₂O₂ and KOH/H₂O₂ based solutions with Au/Cr film as a hard mask. The etch rate was studied as a function of temperature and concentration of the etchants.     

Etching of MgO crystals in acids: kinetics and mechanism of dissolution

Kinetics of etching of MgO crystals have been studied in H₂SO₄, HNO₃ and HCl. The effects of etching time, acid concentration and temperature on the growth of hillocks, on the selective etch rate and on the rate of overall dissolution are demonstrated. It is observed that etch rates are independent of time, but are determined by the temperature and concentration of the acid. The etch rate-concentration curves show maxima which are characteristic of an acid. The values of activation energy for the processes of dissolution, selective etching and hillock growth and the corresponding frequency factors are computed. It is established that the process of dissolution in concentrated H₂SO₄ is diffusion controlled, while in H₂SO₄ with concentrations below 18 N and in HNO₃ and HCl it is reaction rate controlled. The pre-exponential factor is found to be a function of acid concentration. The results are discussed from the standpoint of chemistry. A comment on the data published on MgO by previous workers is made.     

On the use of a neural network to characterize the plasma etching of SiON thin films

Using a generalized regression neural network (GRNN), plasma etching of oxynitride thin films was modeled. The etch process was characterized by means of a statistical experiment. A genetic algorithm was employed to improve prediction performance by optimizing multiparameterized training factors. Compared to a conventional GRNN model, the constructed etch rate model demonstrated an improvement of about 60% in the prediction performance. 3-D plots were generated to qualitatively interpret etch mechanisms while validating the predictions with experimental data. In separating physical and chemical effects, both dc bias and profile angle variations were effectively utilized. The source power affected significantly the etch rate irrespective of changes in the bias power or C₂F₆ flow rate. For pressure variations, the etch rate was estimated to be dominated by chemical etching. The complex effect of C₂F₆ flow rate could be explained by dominant chemical etching or polymer deposition.     

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 (C₆H₁₂) and propylene (C₃H₆) 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 C₆H₁₂ and C₃H₆ was 5050 Å/min and 6360 Å/min. Although the deposition rate of ACL deposited from C₆H₆ was lower than that from C₃H₆, normalized deposition rate of ACL deposited from C₆H₁₂ was 1.64 times higher than that from C₃H₆. 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 C₆H₁₂ was 0.51 and that from C₃H₆ was 0.48. The density of ACL deposited at 550 °C from C₆H₁₂ was 1.48 g/cm³ and that from C₃H₆ was 1.45 g/cm³. The dry etching rate of ACL deposited at 550 °C from C₆H₁₂ was 1770 Å/min and that from C₃H₆ 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 C₆H₁₂ with the increase of deposition temperature was the same as those of ACLs from C₃H₆. The high density and low dry etch rate of ACL from C₆H₁₂ 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.     

Analyses of interface adhesion between porous SiOCH low-k film and SiCN layers by nanoindentation and nanoscratch tests

In this study, an Si/PEOX/SiCN/SiOCH/SiCN multilayered film stack has been prepared by chemical vapor deposition. The bonding configurations between porous SiOCH film and SiCN etch stop layers have been analyzed by X-ray photoelectron spectroscopy, and the interface adhesion has been investigated by nanoindentation and nanoscratch tests. Elements of Si, C, N, and O constructed an interlayer region of about 10 nm with mixing bonds of Si to C, Si to N and Si to O at the interface between the porous SiOCH film and SiCN layers. During nanoindentation and nanoscratch tests, interface delamination occurred between SiOCH and SiCN layers due to the accumulation of sufficient shear stresses around the indented regions. The interface adhesion energy was accordingly measured as 1.68 J/m² by nanoindentation test with an applied load of 30 mN. With higher applied loads, the measured interface adhesion energy decreased. By the nanoscratch test, the interface adhesion energy was measured as about 0.91 J/m², lower than that obtained by nanoindentation test due to the mode mixity effect.     

Infinitely high etch selectivity during CH4/H2/Ar inductively coupled plasma (ICP) etching of indium tin oxide (ITO) with photoresist mask

Under certain conditions during ITO etching using CH₄/H₂/Ar inductively coupled plasmas, the etch rate selectivity of ITO to photoresist (PR) was infinitely high because the ITO films continued to be etched, but a net deposition of the α-C:H layer occurred on the top of the PR. Analyses of plasmas and etched ITO surfaces suggested that the continued consumption of the carbon and hydrogen in the deposited α-C:H layer by their chemical reaction with In and Sn atoms in the ITO resulting in the generation of volatile metal-organic etch products and by the ion-enhanced removal of the α-C:H layer presumably play important roles in determining the ITO etch rate and selectivity.     

Effect of doping elements on ZnO etching characteristics with CH4/H2/Ar plasma

Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH₄ flow ratio and self-bias voltage, V_dc, in inductively coupled CH₄/H₂/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH₄/H₂/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CH_x)_y etch by-products.     

Influence of impurities on the etching of NaCl crystals

The effect of CdCl₂, CuCl₂·2H₂O, MnCl₂·4H₂O and FeCl₃·6H₂O impurities and undersaturation on the rates of macroscopic dissolution,v _p, lateral etching away from a dislocation line,v _t, and normal etching along the dislocation line,v _n, and on the surface micromorphology of the {100} face of NaCl single crystals in water, methanol and 96% ethanol is investigated. The dependence of etch rates on impurity concentration,c _i, showed that the addition of a salt to the solvent always leads to a decrease inv _p, which attains a minimum value after a particular value ofc _i. The concentration dependence ofv _t andv _n is relatively complex, but often both decrease or increase simultaneously. A change in etch-pit morphology is caused by increasing the concentrations of all additives in ethanol and methanol. The dependence of etch rates on the undersaturation of methanol and methanol containing 10^–3 M CdCl₂ showed that dislocation etch pits are formed only for undersaturations greater than 0.02 and 0.06, respectively. These results as well as the roughening of etched surfaces at low impurity concentrations, the formation of terraced etch pits and the difference between etch pits at aged and fresh dislocations are discussed.     

The dissolution of Na2O-MgO-CaO-SiO2 glass in aqueous HF solutions

The dissolution (or etching) of a multicomponent (Na₂O-MgO-CaO-SiO₂) silicate glass in aqueous HF solutions is studied. The solutions were chosen in the systems HF-HNO₃-H₂O, HF-HCl-H₂O and HF-H₂SO₄-H₂O, and the temperatures varied from 25 to 60° C. SEM micrographs of the glass surface after etching show an orange peel surface structure which develops during etching and which originates from surface flaws. The dissolution rate of the glass was found to increase with higher HF concentration, higher strong-acid concentrations and higher temperatures. The dissolution rate is determined by the reaction of HF molecules and HF₂ ions with the Si-O-Si grouping surrounding the SiO₄ tetrahedron. In the multicomponent glass some of these bonds are non-bridging due to the presence of Na₂O, CaO and MgO, increasing the dissolution rate significantly. H⁺ ions introduced by adding strong acids to the etch solution adsorb on the surface and catalyse the dissolution reaction. Several models used to describe the relation between the dissolution rate and the H⁺ concentration are discussed.     

Etch pit observations on the habit faces of gel grown nickel molybdate crystals

The results obtained from etching experiments on the habit faces of NiMoO₄·xH₂O are described. Dilute solutions of chemical reagents such as HNO₃, CH₃COOH, NaOH, KOH are found to be the best etchants for revealing dislocation etch pits. The shape and nature of the etch pits are also described.     

Kinetics of etching and dissolution of gel-grown CdC2O4·3H2O crystals

The kinetics of etching and dissolution of cadmium oxalate trihydrate single crystals in selective etchants such as 1 M HCl, 1 M HNO₃, 10% chromic acid, 4M NH₄Cl, 4M CdCl₂ and 4 M NH₄Cl-1 M HCl solutions are studied. Contrary to a previous report on semiconductor etching, in the present investigation the activation energy of etching in solvents having a reaction-rate controlled mechanism of dissolution was lower than in those having a diffusion-rate controlled dissolution mechanism. Three 3-component etch systems, i.e., HCl-NH₄Cl-H₂O, HCl-CdCl₂-H₂O, and NH₄Cl-CdCl₂-H₂O, are employed and constant etch rate contours are plotted which enable the part played by each component in association with the other components in the system to be understood.     

Study for amorphous silicon etching process using dielectric barrier discharge

Characteristics of amorphous silicon (a-Si) etching using atmospheric pressure plasma discharge had been studied. Dielectric barrier discharge (DBD) plasma with nitrogen gas was employed for the study. The active chemical agent for etching was generated by mixing a small quantity of sulfur hexafluoride (SF₆) gas into the plasma. The two distinguishable plasma zones are generated with the specially designed DBD plasma generator. The one is the main discharge zone generated between the two parallel plate electrodes. And the other one is downstream plasma zone extracted from the main discharge zone through the holes perforated on the bottom electrode. A test specimen was etched located at the plasma zone and moved the zone several times for etching on a temperature controlled stage. The etch rate of a-Si and the selectivity to silicon nitride (SiNx) were improved by addition of hydrogen (H₂) or methane (CH₄) gas into the plasma. However, when the specimen temperature was lower than 100 °C with H₂ or CH₄ gas added plasma condition, a-Si layer was not etched at all, but in the range of 100-140 °C of specimen temperature, the a-Si layer started to be etched while the influence of the specimen temperature on etching of a-Si was ignorable in that temperature range. At the optimized condition, the a-Si etch rate was up to 3000 A/min in the downstream plasma zone with the 3 mm of the distance between the surface of the specimen and the bottom side of the DBD plasma generator module. And the etch rate ratio between a-Si and SiNx was more than 100:1.     

RIE of SiO2 in doped and undoped fluorocarbon plasmas

SiO₂ and Si₃N₄ on top of polycrystalline silicon, titanium silicide and gallium arsenide have been selectively etched by reactive sputter etching in glow discharges of CF₄ and CHF₃. It is observed that for SiO₂ an infinite degree of selectivity can be obtained by admixing minor amounts of methane (<5%) to CHF₃. By a proper adjustment of the operating conditions, i.e. power, gas-flow, total pressure and the CH₄ to fluorocarbon ratio, we are able to control the rate of carbon deposition in such a way that etching takes place in exposed areas, releasing oxygen or nitrogen under the influence of energetic particle bombardment. The ion-assisted chemical reaction between oxygen or nitrogen and the polymerizing species, forming volatile products, together with the physical sputtering, makes these areas accessible to fluorine-containing species responsible for the chemical etching of SiO₂. The importance of carbon deposition and oxygen release under energetic particle bombardment is demonstrated by resting the samples on different cathode materials and by sputter etching in an argon/methane atmosphere.These experiments confirm that prevention of carbon build-up by released oxygen is the main mechanism responsible for the high etch rate ratio between SiO₂ and Si in reactive ion etching.     

A study on the etch characteristics of HfAlO3 dielectric thin film in Cl2/Ar gas chemistry using inductively coupled plasma system

Thin films of HfAlO₃, a high-k material, were etched using inductively-coupled plasma. The dry etching mechanism of the HfAlO₃ thin film was studied by varying the Cl₂/Ar gas mixing ratio, RF power, direct current bias voltage, and process pressure. The maximum etch rate of the HfAlO₃ thin film was 16.9 nm/min at a C1₂/(C1₂ + Ar) ratio of 80%. Our results showed that the highest etch rate of the HfAlO₃ thin films was achieved by reactive ion etching using Cl radicals, due to the high volatility of the metal-chlorides. Consequently, the increased chemical effect caused an increase in the etch rate of the HfAlO₃ thin film. Surface analysis by x-ray photoelectron spectroscopy showed evidence that Hf, Al and O reacted with Cl and formed nonvolatile metal-oxide compounds and volatile metal-chlorides. This effect may be related to the concurrence of chemical and physical pathways in the ion-assisted chemical reaction.     

Characteristics of the etching of undoped silica in MCVD-fabricated optical fibers with buffered hydrofluoric acid

The etching reaction between the undoped silica cladding in MCVD-fabricated fibers and buffered hydrofluoric acid (BHF) has been studied by examining the outer diameter decrease of the fibers in a given etching time. The study has revealed that the etching reaction is not diffusion limited. The etch rate is determined and compared with values published for SiO₂ - films. We have also determined the activation energy of the process, which agrees well with values reported for SiO₂ - films.     

Optimized inductively coupled plasma etching for poly(methyl-methacrylate-glycidly-methacrylate) optical waveguide

Optical loss is a crucial quality for the application of polymer waveguide devices. The optimized oxygen inductively coupled plasma etching conditions, including antenna power, bias power, chamber pressure, O₂ flow rate and etching time for the fabrication of smooth vertical poly(methyl-methacrylate-glycidly-methacrylate) channel waveguide were systematically investigated. Atomic force microscopy and scanning electron microscopy were used to characterize the etch rate, surface roughness and vertical profiles. The increment of etch rate with the antenna power, bias power and O₂ flow rate was observed. Bias power and chamber pressure were found to be the main factor affecting the interface roughness. The vertical profiles were proved to be closely related to antenna power, bias power and O₂ flow rate. Surface roughness increment was observed when the etching time increased.     

Inductively coupled plasma reactive ion etching of titanium thin films using a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of titanium thin films patterned with a photoresist using Cl₂/Ar gas was examined. The etch rates of the titanium thin films increased with increasing the Cl₂ concentration but the etch profiles varied. In addition, the effects of the coil rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and gas pressure. The degree of anisotropy in the etched titanium films improved with increasing coil rf power and dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy revealed the formation of titanium compounds during etching, indicating that Ti films etching proceeds by a reactive ion etching mechanism.