Dry etching of III-V semiconductors in IBr/Ar electron cyclotron resonance plasmas

IBr/Ar plasmas were found to be promising candidates for room temperature dry etch processing of the III-V semiconductors GaAs, AlGaAs, GaSb, InP, InGaAs, and InSb. Results showed fast etch rates (～3,000Å/min) at high microwave power (1000W) and good surface morphology (typical root mean square roughness ～2 nm), while retaining the near-surface stoichiometry. There was little variation of surface smoothness over a wide range of plasma compositions for Gacontaining materials. By contrast, there was a plasma composition window of about 25–50% of IBr in IBr/Ar plasmas for maintaining good morphology of Incontaining semiconductors like InP. Etch rates of the semiconductors generally increased with microwave power (400-1000 W) and rf power (50-250 W), whereas there was little dependence of the rates on the increasing percentage of IBr in the IBr/Ar plasma composition above 30% IBr for In-based, and 50% IBr for Ga-based materials. Those results show the etch rates over 30% of IBr in IBr/ Ar are desorption-limited. Photoresist masks do not hold up well to the IBr under ECR conditions, resulting in poor profile control, whereas SiN_x offers much better etch resistance.     

干法刻蚀InSb时Ar气含量的选取

感应耦合等离子体(ICP)刻蚀技术是目前国际制备InSb台面结型焦平面阵列技术的主流技术之一。文章研究采用ICP刻蚀技术,以CH4/H2/Ar刻蚀气体体系对InSb材料进行干法刻蚀时刻蚀气体体系中Ar气体积组分对材料刻蚀形貌及器件性能的影响。实验方案设置为在控制其他实验变量相同的情况下设置不同Ar气体积分数的刻蚀气体体系对InSb材料进行台面蚀刻,通过扫描电子显微镜(SEM)、激光共聚焦显微镜考察台面刻蚀形貌,通过I-V测试得到的器件性能结果考察刻蚀损伤情况。从实验结果得到,Ar体积占据总气体体积的30%～35%时台面刻蚀形貌良好,表面损伤轻,器件性能良好,刻蚀工艺满足要求。     

Selective dry etching of InGaP over GaAs in inductively coupled plasmas

By exploiting the relatively high volatility of In etch products in CH₄/H₂ discharges, we were able to obtain a maximum selectivity for InGaP over GaAs of ∼20 at low ion energies and fluxes. Three different inert gas additives to CH₄/H₂ were examined, with Ar producing higher selectivities than He or Xe. This process is attractive for selective removal of the InGaP emitter in the fabrication of heterojunction bipolar transistors.     

Comparison of ECR plasma chemistries for etching of InGaP and AlGaP

Etch rates for InGaP and AlGaP are examined under electron cyclotron resonance (ECR) conditions in Cl₂/Ar, BCl₃/Ar, BCl₃/N₂, ICl/Ar, and IBr/Ar discharges. All the plasmas except IBr/Ar provide rapid etching of InGaP at rates above 1 μm min⁻¹. ICl/Ar provides the highest etch rates. Unlike the Cl₂/Ar and BCl₃-based chemistries, the rates in ICl/Ar and IBr/Ar are almost independent of microwave power in the range 400–1000 W. Much lower rates were obtained for AlGaP in every discharge due to the greater difficulties in bond breaking that must precede formation and desorption of the etch products.     

Dry etching of Hg1−xCdxTe using CH4/H2/Ar/N2 electron cyclotron resonance plasmas

An approach is presented which eliminates the problems caused by hydrocarbon polymer deposition during etching Hg_1-x Cd_xTe with CH₄/H₂ based plasmas. We find that the addition of N₂ to the plasma inhibits polymer deposition in the chamber and on the sample. We speculate that atomic nitrogen formed from N₂ in the plasma has several beneficial effects: the elimination of polymer precursors, the reduction of the atomic hydrogen concentration, and a potential increase of methyl radical concentration. Evidence for the reaction between the nitrogen and the polymer precursors is presented. It is also demonstrated that the addition of N₂ to CH₄/H₂ based electron cyclotron resonance (ECR) plasmas used to etch HgCdTe eliminates the roughness normally formed during etching and results in a steadier etch rate.     

Surface cleaning and etching of CdZnTe and CdTe in H2/Ar, CH4/H2/Ar, and CH4/H2/N2/Ar electron cyclotron resonance plasmas

This paper compares H₂/Ar, CH₄/H₂/Ar, and CH₄/H₂/N₂/Ar plasma etch processes for CdZnTe and CdTe substrates in view of their potential to provide high-quality substrate surfaces for subsequent HgCdTe epitaxy. An electron cyclotron resonance source was used as plasma generator, and ellipsometry, angle-resolved x-ray photoelectron spectroscopy and low energy electron diffraction were applied to characterize roughness, composition, and order of the resulting substrate surfaces. It was found that CdZnTe is much more susceptible to evolving surface roughness under H₂/Ar plasma exposure than CdTe. The severe roughening observed at 100°C sample temperature was found to be correlated with a buildup of ZnTe at the surface, which suggests that the roughness formation may result from a preferential etching of the CdTe component. This surface degradation could be reduced by the addition of CH₄ to the process gases. However, only a further addition of nitrogen gas balanced and substantially improved the plasma process so that atomically clean, very smooth, and stoichiometrically composed CdZnTe surfaces of long-range order were eventually obtained.     

Temperature dependence of band gaps in HgCdTe and other semiconductors

Band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures. The calculated temperature variation of gaps agrees with experiments to better than 10% in all materials except InAs and InSb where the deviation is about 50%. While the simple picture that the intra (inter)-band transitions reduce (increase) the gap still holds, we show that both the conduction band edge E_c and valence band edge E_v move down in energy. These shifts in E_v affect the valence band offsets in heterojunctions at finite temperature. The temperature variations of valence band offset and the electron effective mass are also reported.     

Model‐Based Analysis of the ZrO2 Etching Mechanism in Inductively Coupled BCl3/Ar and BCl3/CHF3/Ar Plasmas

The etching mechanism of ZrO₂ thin films and etch selectivity over some materials in both BCl₃/Ar and BCl3/CHF3/Ar plasmas are investigated using a combination of experimental and modeling methods. To obtain the data on plasma composition and fluxes of active species, global (0‐dimensional) plasma models are developed with Langmuir probe diagnostics data. In BCl3/Ar plasma, changes in gas mixing ratio result in nonlinear changes of both densities and fluxes for Cl, BCl2, and BCl2⁺. In this work, it is shown that the nonmonotonic behavior of the ZrO2 etch rate as a function of the BCl3/Ar mixing ratio could be related to the ion‐assisted etch mechanism and the ion‐flux‐limited etch regime. The addition of up to 33% CHF₃ to the BCl₃‐rich BCl3/Ar plasma does not influence the ZrO2 etch rate, but it non‐monotonically changes the etch rates of both Si and SiO2. The last effect can probably be associated with the corresponding behavior of the F atom density.     

Deep dry etching of borosilicate glass using SF6 and SF6/Ar inductively coupled plasmas

Deep reactive ion etching (DRIE) of borosilicate glass was carried out using SF₆ and SF₆/Ar plasmas in an inductively coupled plasma (ICP) reactor. Electroplated Ni on Cu (≅50 nm)/Cr (≅100 nm)/glass structure using patterned SU-8 photoresist mask with a line spacing of 12-15 μm was used as a hard-mask for plasma etching. Plasma etching of borosilicate glass was performed by varying the various process parameters such as the gas chemistry, the gas flow ratio, the top electrode power, and the dc self-bias voltage (V_dc). In the case of using SF₆ gas only, the profiles of the etched channel showed the undercut below the Ni hard-mask due to a chemical etching and the microtrenching at the bottom of the etched channel. An optimized process using the SF₆ plasmas showed the glass etch rate of ≅750 nm/min. The addition of the Ar gas to the SF₆ gas removed the undercut and microtrenching but decreased the etch rate to ≅540 nm/min. The increasing and decreasing time-dependent etch rates with the etch depth in the SF₆ (200 sccm) and SF₆(60%)/Ar(40%) plasmas, respectively, were ascribed to the different ion-to-neutral flux ratios leading to the different etch process regime.     

Dry etching of new phase-change material Al_(1.3)Sb_3Te in CF_4/Ar plasma

正The dry etching characteristic of Al_(1.3)Sb_3Te film was investigated by using a CF_4/Ar gas mixture.The experimental control parameters were gas flow rate into the chamber,CF_4/Ar ratio,the O_2 addition,the chamber background pressure,and the incident RF power applied to the lower electrode.The total flow rate was 50 sccm and the behavior of etch rate of Al_(1.3)Sb_3Te thin films was investigated as a function of the CF_4/Ar ratio,the O_2 addition,the chamber background pressure,and the incident RF power.Then the parameters were optimized.The fast etch rate was up to 70.8 nm/min and a smooth surface was achieved using optimized etching parameters of CF_4 concentration of 4%,power of 300 W and pressure of 80 mTorr.     

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.     

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.     

溅射功率对AlN/ZnO薄膜结构形貌的影响

采用直流反应磁控溅射法以ZnO为缓冲层在Si衬底上制备了AlN/ZnO薄膜。利用台阶仪、X线衍射(XRD)仪和原子力显微镜(AFM)对不同溅射功率下制备的AlN/ZnO薄膜的厚度、结构及表面形貌进行测试表征。结果表明,不同溅射功率下生长的AlN薄膜都沿(002)择优生长,且随着功率的增大,薄膜的沉积速率增加,晶粒长大,AlN薄膜的(002)取向性变好。同时还利用扫描电子显微镜(SEM)对在优化工艺下制得AlN/ZnO薄膜断面的形貌进行表征,结果显示AlN薄膜呈柱状生长。     

Surface morphology and electronic properties of dislocations in AlGaN/GaN heterostructures

Scanning force microscopy was used to examine the surfaces of AlGaN/GaN heterostructures grown by molecular beam epitaxy (MBE) on GaN templates prepared by hydride vapor phase epitaxy (HVPE). Away from dislocations, the MBE growth replicates the surface morphology of the HVPE film, with monolayer steps clarly visible in topographic images. However, the surface morphology near dislocations depends strongly on the MBE growth conditions. Under Ga rich growth the dislocations appear as hillocks, while under stoichiometric growth they appear as pits. A dependence on Al concentration is also observed. Surface contact potential variation near dislocations is consistent with excess negative charges surrounding by a depletion region, but this was observed only for the film grown under stoichiometric conditions.     

Effects of Ar and O2 additives on photopatternable sol-gel etching in an SF6-based plasma for planar lightwave circuit fabrication

We present a novel study of the interaction of SF₆-based plasmas with sol-gel materials in a parallel plate reactive ion etching (RIE) system. The purpose of these experiments was to obtain quantitative measures and optimisation of the RIE parameters, which can be used in the microfabrication of planar lightwave circuit (PLC) devices. The sulfur hexafluoride chemistry is chosen due to its excellent etching properties of SiO₂, which is one of the components of the photopatternable sol-gel materials and is not present in typical photoresist materials. Fast process etching rate and good selectivity is achieved by varying SF₆ flow and power delivered to the electrodes. The study also reveals a marginal influence of oxygen and argon flow on the character of the sol-gel etching. The experimental data obtained can be used as a reference for any sol-gel devices fabricated using widely available RIE reactors.     

Comparison of etching characteristics of SiO2 with ArF photoresist in C4F6 and C4F8 based dual-frequency superimposed capacitively coupled plasmas

In this study, we compared the C₄F₆ and C₄F₈ based plasma etching characteristics of silicon dioxide and ArF photoresist (PR) in a dual-frequency superimposed capacitively coupled plasma (DFS-CCP) etcher under different high- and low-frequency combinations (f_HF/f_LF), while varying the process parameters such as the dc self-bias voltage (V_dc), O₂ flow, and CH₂F₂ flow rate in the C₄F₈/CH₂F₂/O₂/Ar and C₄F₆/CH₂F₂/O₂/Ar plasmas. The silicon oxide etch rates increased significantly in both chemistries with increasing f_HF and O₂ flow rate. The silicon oxide etch rates were higher in the C₄F₈/CH₂F₂/O₂/Ar than in the C₄F₆/CH₂F₂/O₂/Ar plasmas, but the PR etch rate was much higher in the C₄F₆/CH₂F₂/O₂/Ar than in the C₄F₈/CH₂F₂/O₂/Ar plasmas under the present experimental conditions. The slower oxide etch rate in the C₄F₆ based plasmas was attributed to the thicker steady-state fluorocarbon layer on the silicon oxide surface, while the faster PR etch rate in the C₄F₈ based plasmas was ascribed to the higher F radical density in the plasma.     

The role of the V/III ratio in the growth and structural properties of metalorganic vapor phase epitaxy GaAs/Ge heterostructures

GaAs epitaxial layers have been grown on (001) 6† off-oriented toward (110) Ge substrates by metalorganic vapor phase epitaxy. In order to study the influence of V/III ratio on the growth mechanisms and the structural properties of the layers, the input flow of arsine was changed over a wide range of values, while keeping constant all other experimental settings. Optical microscopy in the Nomarski contrast mode, x-ray topography and high resolution diffractometry, transmission electron microscopy and Rutherford backscattering have been used to investigate the epilayers. It has been found that the growth rate increases and the surface morphology worsens with increasing V/III ratio. The abruptness of the layer-substrate interface has also been found to strongly depend on the V/III ratio, the best results being obtained under Ga-rich conditions. The main structural defects within the layers are stacking faults and misfit dislocations. Layers grown under As-rich conditions only contain stacking faults, probably originated by a growth island coalescence mechanism, whereas layers grown under Ga-rich conditions contain both misfit dislocations and stacking faults generated by dissociation of threading segments of interfacial dislocations. In spite of the different defects, the strain relaxation has been found to follow the same trend irrespective of the V/III ratio. Finally, the relaxation has been found to start at a thickness exceeding the theoretical critical value.     

Effect of gas mixing ratio on etch behaviors of Ba2Ti9O20 (BTO) and Pt thin films in Cl2/Ar inductively coupled plasma

An investigation of the Ba₂Ti₉O₂₀ (BTO) and Pt thin films etch mechanism in the Cl₂/Ar inductively coupled plasma was carried out. It was found that an increase in Ar mixing ratio at fixed gas pressure and input power causes a fast decrease in the BTO etch rate (26.9-1.2 nm/min for 0-100% Ar) while the Pt etch rate increases slightly from 17.4-23.0 nm/min. Langmuir probe diagnostics and zero-dimensional plasma modeling provided the data on plasma parameters, steady-state composition and fluxes of active species on the etched surface. From the model-based analysis of etch kinetics, it was shown that the behavior of the BTO etch rate corresponds to the reaction-rate-limited etch regime, where the etch rate is limited neither by physical sputtering of the main material nor by the ion-stimulated desorption of low-volatile reaction products. The etch process of Pt appears in the transitional regime and is controlled by the neutral and ion fluxes together.