Etch characteristics of GaN and BN materials in chlorine-based plasmas

Reactive ion etching (RIE) was performed on GaN and BN thin films using chlorine-based plasmas. The optimum chemistry was found to be BCl₃/Cl₂/N₂/Ar and Cl₂/Ar at 30 and 40 mtorr for GaN and BN etching, respectively. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analysis of the GaN and BN etched surfaces show a decrease in the surface nitrogen atomic composition and an increase in chlorine impurity incorporation with increasing self-dc bias. A photo-assisted RIE (PA-PIE) process using an IR filtered Xe lamp beam was then used and resulted in improved etch rates and surface composition. Optical emission spectroscopy (OES) measurements have also shown photoenhancement of the etch process.     

ECR plasma etch fabrication of C-doped base InGaAs/InP DHBT structures: A comparison of CH4/H2/Ar vs BCl3/N2 plasma etch chemistries

We compare ECR plasma etch fabrication of self-aligned thin emitter carbondoped base InGaAs/InP DHBT structures using either CH₄/H₂/Ar or BCl₃/N₂ etch chemistries. Detrimental hydrogen passivation of the carbon doping in the base region of our structure during CH₄/H₂/Ar dry etching of the emitter region is observed. Initial conductivity is not recovered with annealing up to a temperature of 500°C. This passivation is not due to damage from the dry etching or from the MOMBE growth process, since DHBT structures which are ECR plasma etched in BCl₃/N₂ have the same electrical characteristics as wet etched controls. It is due to hydrogen implantation from the plasma exposure. This is supported with secondary ion mass spectroscopy profiles of structures which are etched in CH₄/D₂/Ar showing an accumulation of deuterium in the C-doped base region.     

N2O treatment enhancement-mode InAlN/GaN HEMTs with HfZrO2 High-k insulator

A normally-off InAlN/GaN MIS-HEMT with HfZrO₂ gate insulator was realized and investigated. By using N₂O plasma treatment beneath the gate region, 13 nm InAlN Schottky layer was oxidized to AlON_x + 4 nm InAlN Schottky layer. The strong polarization induced carriers in traditional InAlN/GaN 2 DEG quantum well was reduced for enhancement-mode operation. High-k thin film HfZrO₂ was used for gate insulator of E-mode device to further suppress gate leakage current and enhance device gate operation range. The maximum drain current of E-mode InAlN/GaN MIS-HEMT was 498 mA/mm and this value was higher than previous published InAlN/GaN E-mode devices. The measurement results of low-frequency noise also concluded that the low frequency noise is attributed to the mobility fluctuation of the channel and N₂O plasma treatment did not increase fluctuation center of gate electrode.     

Plasma damage effects in InAlN field effect transistors

During gate mesa plasma etching of InN/InAlN field effect transistors the apparent conductivity in the channel can be either increased or decreased through three different mechanisms. If hydrogen is part of the plasma chemistry, hydrogen passivation of the shallow donors in the InAlN can occur, we find diffusion depths for ²H of ≥ 0.5 micron in 30 mins at 200°C. The hydrogen remains in the material until temperatures ≥ 700°C. Energetic ion bombardment in SF₆/O₂ or BCl₃/Ar plasmas also compensates the doping in the InAlN by creation of deep acceptor states. Finally the conductivity of the immediate InAlN surface can be increased by preferential loss of N during BCl₃ plasma etching, leading to poor rectifying contact characteristics when the gate metal is deposited on this etched surface. Careful control of plasma chemistry, ion energy and stoichiometry of the etched surface are necessary for acceptable pinch-off characteristics.     

Inductively coupled plasma etching of InGaP, AllnP, and AlGaP in Cl2 and BCl3 chemistries

Dry etching of InGaP, AlInP, and AlGaP in inductively coupled plasmas (ICP) is reported as a function of plasma chemistry (BCl₃ or Cl₂, with additives of Ar, N₂, or H₂), source power, radio frequency chuck power, and pressure. Smooth anisotropic pattern transfer at peak etch rates of 1000–2000Å·min^?1 is obtained at low DC self-biases (?100V dc) and pressures (2 mTorr). The etch mechanism is characterized by a trade-off between supplying sufficient active chloride species to the surface to produce a strong chemical enhancement of the etch rate, and the efficient removal of the chlorinated etch products before a thick selvedge layer is formed. Cl₂ produces smooth surfaces over a wider range of conditions than does BCl₃.     

Etching characteristics of ZnO thin films in chlorine-containing inductively coupled plasmas

This study examined the plasma etching characteristics of ZnO thin films etched in BCl₃/Ar, BCl₃/Cl₂/Ar and Cl₂/Ar plasmas with a positive photoresist mask. The ZnO etch rates were increased in a limited way by increasing the gas flow ratio of the main etch gases in the BCl₃/Ar, BCl₃/Cl₂/Ar and Cl₂/Ar plasmas at a fixed dc self-bias voltage (V_dc). However, the ZnO etch rate was increased more effectively by increasing the V_dc. Optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS) analyses of the ZnO surfaces etched at various Cl₂/(Cl₂ + Ar) mixing ratios revealed the formation of the ZnO_xCl_y reaction by-products as a result of the increased etch rate with increasing Cl₂ addition, compared with 100% Ar⁺ sputter etching. This suggests that at Cl₂/Ar flow ratios ⩾20%, the ZnO etch process is controlled by an ion-assisted removal mechanism where the etch rate is governed by the ion-bombardment energy under the saturated chlorination conditions.     

Characterization of GaN films etched using reactive ion etching technique by secondary ion mass spectrometry

We investigated GaN films etched by using reactive ion etching (RIE) technique to fabricate the GaN-based devices. The samples were grown on sapphire substrate by metal organic chemical vapor deposition (MOCVD), and Ti/Al contacts were formed on n-GaN surfaces after etching processes. The effects of the kinds of reactive gases were evaluated by secondary ion mass spectrometry (SIMS). The results showed that in the sample etched using BCl₃ gas, the signal from boron contaminations was strongly detected at the interface between the contact metal and n-GaN, and we found that additional etching in Cl₂ plasma after etching with BCl₃ gas was essential to make a good contact.     

Characterization of reactive ion etching-induced damage to n-GaN surfaces using schottky diodes

Dry etch-induced damage has been investigated using Pd Schottky diodes fabricated on n-type GaN surfaces that were etched by reactive ion etching in SiCl₄ and Ar plasmas. Damage was evaluated by measuring the current-voltage, current-voltage-temperature, and capacitance-voltage characteristics of the diodes. A plasma chemistry that includes a chemical etching component (SiCl₄) was found to significantly reduce the degree of induced damage in comparison to a chemistry that uses only a physical component (Ar). The effective barrier height, ideality factor, reverse breakdown voltage, reverse leakage current, and the effective Richardson coefficient of diodes etched under various plasma conditions are presented. The degree of etch-induced damage was found to depend strongly on the plasma self-bias voltage but saturates with etch time after an initial two-minute etch period. Rapid thermal annealing was found to be effective in improving the diode characteristics of the etched GaN samples.     

The fabrication and dry etching of poly-Si/TaN/Mo gate stack in the metal inserted poly-Si stack structure

The Mo-based metal inserted poly-Si stack (MIPS) structure is an appropriate choice for metal gate and high-k integration in sub-45 nm gate-first CMOS device. A novel metal nitride layer of TaN or AlN with high thermal stability has been introduced between Mo and poly-Si as a barrier material to avoid any reaction of Mo during poly-Si deposition. After Mo-based MIPS structure is successfully prepared, dry etching of poly-Si/TaN/Mo gate stack is studied in detail. The three-step plasma etching using the Cl₂/HBr chemistry without soft landing step has been developed to attain a vertical poly-Si profile and a reliable etch-stop on the TaN/Mo metal gate. For the etching of TaN/Mo gate stack, two methods using BCl₃/Cl₂/O₂/Ar plasma are presented to get both vertical profile and smooth etched surface, and they are critical to get high selectivity to high-k dielectric and Si substrate. In addition, adding a little SF₆ to the BCl₃/O₂/Ar plasma under the optimized conditions is also found to be effective to smoothly etch the TaN/Mo gate stack with vertical profile.     

Etching of As- and P-based III–V semiconductors in a planar inductively coupled BCl<Subscript>3</Subscript>/Ar plasma

A parametric study of the etch characteristics of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors in BCl₃/Ar planar inductively coupled plasmas (ICPs) was performed. The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of the As, Ga, and Al trichloride, etch products relative to InCl₃. The ratio of BCl₃ to Ar proved critical in determining the anisotropy of the etching for GaAs and AlGaAs, through its effect on sidewall passivation. The etched features in In-based materials tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square (RMS) roughness and similar stoichiometry to their unetched control samples, while the surfaces of In-based materials are degraded by the etching. The practical effect of the Ar addition is found to be the ability to operate the ICP source over a broader range of pressures and to still maintain acceptable etch rates.     

Dry etch selectivity of Gd2O3 to GaN and AlN

Gd₂O₃ is a promising gate dielectric for GaN, but little is known of its dry etching characteristics. We achieved Gd₂O₃ etch rates up to ～600 Å · min^?1 in high density Cl2-based discharges, with maximum selectivities of ～15 over GaN and ～4 over AlN. Pure Cl₂ discharges produced reverse selectivities for both Gd₂O₃/GaN and Gd₂O₃/AlN, with typical values between 0.1–0.4. When a rare gas additive such as Ar or Xe was added to the plasma chemistry, the nitrides etched faster than the oxide. This indicates that volatile etch products (GaCl₃, AlCl₃, N₂) form in Cl₂-based plasmas once the GaN or AlN bonds are broken by ion bombardment, but that GdCl_x species are not volatile. In conjunction with the low efficiency for Gd₂O₃ bond-breaking at low ion energies, this leads to low selectivity.     

Wet Etching of (0001) GaN/Al2O3 grown by MOVPE

H₃PO₄, NaOH, and KOH solutions are found to be useful for removing nitrogen depleted layers or damage induced by high temperature annealing or dry etching of metalorganic chemical vapor deposition-grown (0001)GaN/Al₂O₃. Solutions are selective to the (0001)plane of GaN. However, certain flat planes etched without etch pits are exposed by wet etching.     

Iron nitride mask and reactive ion etching of GaN films

One of the major GaN processing challenges is useful pattern transfer. Serious photoresist mask erosion and hardening are often observed in reactive ion etching of GaN. Fine pattern transfer to GaN films using photoresist masks and complete removal of remaining photoresist after etching are very difficult. By replacing the etch mask from conventional photoresist to a sputtered iron nitride (Fe-8% N) film, which is easily patterned by wet chemical etching and is very resistive to Cl based plasmas, GaN films can be finely patterned with vertical etched sidewalls. Successful pattern transfer is realized by reactive ion etching using Cl (H) containing plasmas. CHF₃/Ar, C₂ClF₅/Ar, C₂ClF₅/Ar/O₂, SiCl₄, and CHCl₃ plasmas were used to etch GaN. The GaN etch rate is dependent on the crystalline quality of GaN. Higher crystalline quality GaN films exhibit slower etch rates than GaN films with higher dislocation and stacking fault density.     

Study of Surface Treatments on InAs/GaSb Superlattice LWIR Detectors

We report on the comparison of mesa sidewall profiles of InAs/GaSb strained-layer superlattice (SLS) detector structures (λ _{50% cutoff} ≈ 14 μm at V _bias = 0 V and T = 30 K) obtained after (a) a conventional BCl₃-based inductively coupled plasma etch, (b) a chemical etch (H₂O₂:HCl:H₂O, 1:1:4), and (c) a combination of both etches. We found that the smoothest sidewall profile with reasonable undercut (~5 μm) was obtained after chemical etch only. The chemical etch was optimized primarily using an n-type GaSb substrate. During this process, numerous chemical etchants were examined. GaSb n-type substrates were chosen for this study in preference over InAs substrates due to their high chemical reactivity and the complicated composition of the native oxide. In addition, SLS detectors are usually grown on GaSb substrates and, after hybridization of the focal-plane array to the readout integrated circuit, the GaSb substrate is etched away using a combination of wet and dry etching techniques. We found that H₂O₂:HCl:H₂O (1:1:4) etching solution provided the smoothest etched surface of GaSb, with a root-mean-square roughness of 1.59 nm.     

Reactive sputter etching of Al in BCl3

Etching of Al is studied in pure BCl₃ as well as in mixtures with other gases in the reactive sputter etching mode in a cryopumped system. Etch rate, selectivity with respect to positive photoresist, SiO₂ and Si and etch profiles are investigated as a function of gas composition, gas pressure, flow rate and plasma power. Plasma chemical processes are monitored by quadrupole mass spectroscopy as well as by optical emission spectroscopy. Perfectly square Al-profiles can be etched if etch rates are kept below 1000 A/min. Al-patterns running over steep steps can also be clearly defined if a certain amount of overetching can be tolerated. The experimental data indicate that the etch process is reactant supply limited. Anisotropic etching is achieved by either a ‘surface inhibitor mechanism’ or the formation of a sidewall protecting film.     

Role of N2 during chemical dry etching of silicon oxide layers using NF3/N2/Ar remote plasmas

In this work, the role of N₂ gas during the chemical dry etching of silicon oxide layers in NF₃/N₂/Ar remote plasmas was investigated by analyzing the species in the plasma, the reaction by-products in the exhaust, and the chemical properties of the etched surface. Increasing the N₂ gas flow rate resulted in an initial increase in the oxide etch rate up to a maximum value, followed by a subsequent decrease. The increased etch rate of the silicon oxide layers was not ascribed to the increased surface arrival rate of fluorine, but to the enhanced oxygen removal from the silicon oxide caused by the formation of NO₂ molecules. Presumably, the NO radicals formed from the added N₂ gas react chemically with the oxygen in the oxide, leading to the breaking of the Si-O bonds and the effective removal of oxygen, which in turn enhances the formation of SiF₄ resulting in an increased etch rate.     

On the etching mechanism of ZrO2 thin films in inductively coupled BCl3/Ar plasma

The etching mechanism of ZrO₂ thin films in BCl₃/Ar plasma was investigated using a combination of experimental and modeling methods. It was found that an increase in the Ar mixing ratio causes the non-monotonic behavior of the ZrO₂ etch rate which reaches a maximum of 41.4 nm/min at about 30-35% Ar. Langmuir probe measurements and plasma modeling indicated the noticeable influence of a BCl₃/Ar mixture composition on plasma parameters and active species kinetics that results in non-linear changes of both densities and fluxes for Cl, BCl₂ and . From the model-based analysis of surface kinetics, it was shown that the non-monotonic behavior of the ZrO₂ etch rate can be associated with the concurrence of chemical and physical pathways in ion-assisted chemical reaction.     

Effect of reactive ion etch-induced damage on the performance of 4H-SiC schottky barrier diodes

The effect of reactive ion etch (RIE) induced damage on 4H-SiC surfaces etched in fluorinated plamas has been investigated and characterized using Ni Schottky diodes and x-ray photoelectron spectroscopic surface analysis. The diodes were characterized using current-voltage, current-voltage-temperature, and capacitance-voltage measurements with near ideal forward characteristics (n=1.07) and forward current density as high as 9000 A/cm² from the control (unetched) devices. High current handling capability was observed in diodes with etched surfaces as well. Diodes with surfaces etched in CHF₃ containing plasmas showed a significant reduction in the barrier height compared to the diodes with surfaces etched in CF₄ containing plasma. Control devices exhibited high leakages when reverse biased, which is attributed to the presence of a thin (∼2 nm) oxide layer at the metal-semiconductor interface. However, under reverse bias diodes with CHF₃-etched surfaces showed improvement in leakage current compared to diodes with CF₄-etched surfaces and the control diodes.     

以非晶硅为硬掩膜的TaN金属栅的选择性湿法腐蚀

提出了一种在HfSiON介质上,采用非晶硅为硬掩膜的选择性去除TaN的湿法腐蚀工艺。由于SC1(NH4OH:H2O2:H2O)对金属栅具有合适的腐蚀速率且对硬掩膜和高K材料的选择比很高,所以选择它作为TaN的腐蚀溶液。与光刻胶掩膜和TEOS硬掩膜相比,因非晶硅硬掩膜不受SC1溶液的影响且很容易用NH4OH溶液去除（NH4OH溶液对TaN和HfSiON薄膜无损伤）,所以对于在HfSiON介质上实现TaN的选择性去除来说非晶硅硬掩膜是更好的选择。另外,在TaN金属栅湿法腐蚀和硬掩膜去除后, 高K介质的表面是光滑的,这可防止器件性能退化。因此,采用非晶硅为硬掩膜的TaN湿法腐蚀工艺可以应用于双金属栅集成,实现先淀积的TaN金属栅的选择性去除。     

Etch damage evaluation on (Bi4−xLax)Ti3O12 thin films during the etch process using inductively coupled plasma sources

The etching mechanism of (Bi_4−xLa_x)Ti₃O₁₂ (BLT) thin films in Ar/Cl₂ inductively coupled plasma (ICP) and plasma-induced damages at the etched surfaces were investigated as a function of gas-mixing ratios. The maximum etch rate of BLT thin films was 50.8 nm/min of 80% Ar/20% Cl₂. From various experimental data, amorphous phases on the etched surface existed on both chemically and physically etched films, but the amorphous phase was thicker after the 80% Ar/20% Cl₂ process. Moreover, crystalline “breaking” appeared during the etching in Cl₂-containing plasma. Also the remnant polarization and fatigue resistances decreased more for the 80% Ar/20% Cl₂ etch than for pure Ar plasma etch.