Evaluation of fluorinated polyimide etching processes for optical waveguide fabrication

This paper reports the etching process of fused silica by inductively coupled plasmas (ICP) for through glass via (TGV) applications. Mixed C4F8 and Ar were used as etching gases in present experiments. The effects of key factors, including etching gases, chamber pressure and substrate temperatures, on etch rate and via profile were studied. Results showed that a high etch rate of about 0.75 μm/min with smooth and vertical sidewall of TGVs can be obtained. Compared to Ar flux and chamber pressure, the effect of C4F8 flux on etch rate is more remarkable. Vertical vias (>89°) can be achieved by increasing the substrate temperature and decreasing the mixing ratio of C4F8 and Ar. Besides, micro-pillars at the bottom of via were observed when the substrate temperature was set at 0 °C. As the substrate temperature reached to 80 °C, micro-pillars were removed clearly. Optimized results indicate that the ICP etching is an effective method for fabricating TGV.

AlGaN is am important ultraviolet optoelectronic material and inductively coupled plasma (ICP) etching plays an important role in fabrication of mesa structures of AlGaN-based photodiodes. In this work, we investigate ICP etching processes of Al_0.32Ga_0.68N and Al_0.47Ga_0.53N. The Al_0.32Ga_0.68N and Al_0.47Ga_0.53N materials were firstly tested by transmission spectra and it indicates that they are different materials with different epitaxial quality. Cl₂/Ar/BCl₃ were used as the ICP gases, and Cl₂/Ar mixing ratio was fixed at 4:1. Etching behaviors were characterized by varying the ICP power, the dc bias, Cl₂/Ar/BCl₃ mixing ratio. ICP power influences etching rates. Dc bias heavily influences the etching rates, and the etching rates increase monotonously with dc bias, which suggests that the ion-bombardment effect is an important factor of these etching processes. BCl₃ is the effective removal of oxygen during the etching, and also influences etching rates. The surface rms roughness was measured by an at omic force microscope. The ICP etching surface morphologies were studied by Scanning Electron Microscope (SEM). The results show dc bias and BCl₃ are important to electrical characteristics of epitaxial materials. At a relative high dc bias and more BCl₃, the etching rate is low, but the damage is low. These results have direct application to the fabrication of AlGaN-based ultraviolet optoelectronic devices.

High speed anisotropic etching of Pyrex ® for microsystems applications

Dry etch of wafer-bonded AlGaInP/mirror/Si light-emitting diodes (LEDs) with planar electrodes was performed by high-density plasma using an inductively coupled plasma (ICP) etcher. The etching characteristics were investigated by varying process parameters such as Cl2/N2 gas combination, chamber pressure, ICP power and substrate-bias power. The corresponding plasma properties (ion flux and dc bias), in situ measured by a Langmuir probe, show a strong relationship to the etch results. With a moderate etch rate of 1.3 μm/min, a near vertical and smooth sidewall profile can be achieved under a Cl2/(Cl2+N2) gas mixture of 0.5, ICP power of 800 W, substrate-bias power of 100 W, and chamber pressure of 0.67 Pa. Quantitative analysis of the plasma-induced damage was attempted to provide a means to study the mechanism of leakage current and brightness with various dc bias voltages (−110 to −328 V) and plasma duration (3–5 min) on the wafer-bonded LEDs. It is found that the reverse leakage current increases and the brightness decreases rapidly as the dc bias increases, which is a clear indication of severe damage accumulation in the sidewall. However, once a low-etch-rate condition (long duration of plasma treatment) is chosen to facilitate smooth sidewall and profile, the accumulated charge on the etched surface may not have enough time to relieve and make the leakage current increase. Finally, an effective recovery method is developed, where the plasma-induced damage can be partially restored after rapid thermal annealing at 450 °C in N2 ambience.

Dry etching of undoped, n- and p-type GaN films was carried out in Cl2-based inductively coupled plasmas (ICPs) using different rf excitation frequencies of 100 kHz and 13.56 MHz, in which the rf chuck power source operates. The etch rates with lower frequency of 100 kHz are somewhat greater than those with a higher frequency of 13.56 MHz due to higher ion bombarding energy with lower frequency. The highest etch rates with the 100 kHz frequency were obtained at moderately high ICP power of 700 W: ∼9300 Å/min of n-GaN, ∼5300 Å/min of p-GaN, and ∼7100 Å/min of undoped GaN. The 13.56 MHz frequency of rf chuck power source produced maximum etch rates of ∼7900 Å/min of n-GaN, ∼5800 Å/min of p-GaN, and 6100 Å/min of undoped GaN at 20 mTorr, 700 W ICP, and 150 W rf power. The surface roughness was relatively independent of the chuck power up to 150 W in 13.56 MHz and showed fairly smooth morphology (rms 1.1–1.3 nm), while etching at higher rf power (>200 W) produced rougher surface.

Among rare-earth ion-doped crystals that are of high interest for quantum technologies, yttrium orthosilicate [Y2SiO5 (YSO)] crystal has demonstrated the longest coherence times. Etching optical guiding structures enables the creation of complex structures offering the advantage of technological scalability. We report on the dry etching of YSO crystal wafers performed by inductive coupled plasma (ICP) reactive ion etching. The material etching rate, the etch rate selectivity versus the material mask, and the etched side wall’s shape have been measured for various ICP process parameters and gas combinations including Ar-alone, Cl2:Ar, and Cl2:N2 plasma chemistry. These gas-combination choices have enabled identifying the etching mechanisms involved. Etching results have evidenced that Ar ions are the primary contributors for YSO etching, with Cl ions being also efficient, while Cl neutrals play a marginal role. ICP YSO etching is predominantly a physical process carried out by ions. Several ICP powers and RF powers have been investigated. The highest 80 nm/min etch rate is obtained under the Ar-alone plasma, but at the expense of trenching, while chlorine-based etching provides no trenching and smooth side walls. The choice of the dielectric material mask is also discussed.

Reactive ion etching of ferroelectric (Bi 4 m x La x )Ti 3 O 12 (BLT) thin films has been studied using C 2 F 6 and HBr etch gases in an inductively coupled plasma (ICP). BLT thin films with bismuth layered-perovskite structure were prepared by chemical solution deposition method. Etch rate and etch selectivity of BLT films were investigated for each gas. The etch rate of 700∼900 Å were obtained for C 2 F 6 gas while the etch rate by HBr gas were in the range of 700∼1100 Å under the etch conditions used in this study. The etch profiles and surface morphologies of BLT films etched by each gas were observed using field emission scanning electron microscopy (FESEM). HBr chemistry turned out to be more effective in obtaining high etch rate and clean etch profile than C 2 F 6 chemistry.

Inductively coupled plasma (ICP) etching has distinct advantages over reactive ion etching in that the etching rates are considerably higher, the uniformity is much better, and the sidewalls of the etched material are highly anisotropic due to the higher plasma density and lower operating pressure. Therefore, ICP etching is a promising process for pattern transfer required during microelectronic and optoelectronic fabrication. Resonator-quantum well infrared photodetectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). To fabricate R-QWIP focal plane arrays (FPAs), two optimized ICP etching processes are developed. Using these etching techniques, we have fabricated R-QWIP FPAs of several different formats and pixel sizes with the required dimensions and completely removed the substrates of the FPAs. Their QE spectra were tested to be 30 to 40%. The operability and spectral non- uniformity of the FPA is ∼99.5 and 3%, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10

Inductively coupled plasma (ICP) chemistry based on a mixture of CH₄, Ar, and H₂ was investigated for the purpose of delineating HgCdTe mesa structures and vias typically used in the fabrication of second and third generation infrared photo detector arrays. We report on ICP etching uniformity results and correlate them with plasma controlling parameters (gas flow rates, total chamber pressure, ICP power and RF power). The etching rate and surface morphology of In-doped MWIR and LWIR HgCdTe showed distinct dependences on the plasma chemistry, total pressure and RF power. Contact stylus profilometry and cross-section scanning electron microscopy (SEM) were used to characterize the anisotropy of the etched profiles obtained after various processes and a standard deviation of 0.06 &mgr;m was obtained for etch depth on 128 x 128 format array vias. The surface morphology and the uniformity of the etched surfaces were studied by plan view SEM. Atomic force microscopy was used to make precise assessments of surface roughness.

GaN‐based ridge waveguides with very smooth and vertical sidewalls are fabricated by combined inductively coupled plasma (ICP) etching and wet chemical etching. The height of GaN waveguide is precisely controlled by ICP dry etching, while smooth and vertical sidewalls are realized by wet chemical etching. Compared with waveguides with rough sidewalls just after ICP etching, the propagation loss of waveguides with wet‐etched smooth sidewalls was reduced by about 2 dB mm−1 at 1.55 µm. Propagation loss can be further reduced by improving the quality of GaN epitaxial layers.

As the microelectronics industry continues to shrink feature size and increase feature density in the back-end of integrated circuits, the traditional empirical approach to plasma etch process development is becoming prohibitively expensive and time consuming. Fundamental physics based models can prove useful in driving down process development time and cost. In this article, an integrated equipment-feature scale modeling infrastructure for SiO2 and photoresist (PR) etching in fluorocarbon based plasma discharges is described. The model correlates process conditions with plasma properties, surface interactions, and etch results. A validated plasma chemistry for Ar/c–C4F8/CF4 and detailed plasma–surface reaction mechanisms for SiO2/PR etching have been incorporated in the model. Major surface reactions for SiO2 etching include neutral surface passivation, fluorocarbon radical polymerization, and ion assisted etching of volatile products. The mechanism for PR erosion includes energy/angle dependent ion sputtering, ion activation, F atom etching with ion assistance, and fluorocarbon radical deposition. Computed SiO2 and PR etch profiles and rates have been validated by comparing with experimental results in a commercial inductively coupled plasma (ICP) etch tool. The validated model is used for a detailed investigation of SiO2/PR etching in a representative 300 mm wafer ICP tool. It is found that SiO2 etch rate is a nonlinear function of Ar/c–C4F8 ratio, where the highest etch rate is obtained when sufficient neutral passivation takes place while polymer deposition is still small. Deviating from this condition reduces SiO2 etch rate by either excessive polymerization or insufficient passivation. PR etch rate and facet size, however, increase monotonically with Ar/c–C4F8 ratio due to reduced polymer deposition. The effect of CF4 ratio in the Ar/c–C4F8/CF4 source gas on SiO2 etching depends on the Ar fraction. When Ar fraction is large, replacing c-C4F8 with CF4 reduces surface passivation and thereby decreases SiO2 etch rate. However, at small Ar fractions, CF4 addition reduces polymer formation and increases the SiO2 etch rate. For the range of conditions explored, SiO2 etch characteristics are insensitive to bias frequency as the ion energies are well above the threshold energy for etching. The plasma zone height (PZH) impacts the fluxes of etchants to the wafer and consequently the SiO2/PR etch rates. PZH, however, does not influence etch uniformity noticeably as diffusion is dominant at low gas pressures.

We studied dry etching of AlGaAs and InGaP in a planar inductively coupled BCl3 plasma. The process parameters were planar ICP source power (0–500 W), reactive ion etching (RIE) chuck power (0–150 W), and chamber pressure (5–15 mTorr). The process results were characterized in terms of etch rate, surface morphology, and surface roughness. The planar inductively coupled BCl3 plasmas were also monitored with in situ optical emission spectroscopy (OES). BCl3 planar inductively coupled process (ICP) etching of AlGaAs showed very vertical sidewall, clean and smooth surface, while that of InGaP showed somewhat rough surface after etching. Etch rates of AlGaAs were generally higher than those of InGaP in the planar BCl3 ICP etching. It indicated that InClX byproducts had relatively low volatility during InGaP etching in the planar inductively BCl3 plasmas. Increase of ICP source power and RIE chuck power strongly raised etch rates of both AlGaAs and InGaP. That of pressure decreased etch rate of both materials. OES data showed that emission intensity of the planar BCl3 ICP was a strong function of ICP source power and chamber pressure, while it was almost independent of RIE chuck power.

Reactive ion etching (RIE) and inductively coupled plasma (ICP) Cr etch processes have been evaluated for fabrication of extreme ultraviolet lithography masks on 200 mm substrates. Experiments were completed to optimize the Cr etch rate, etch rate uniformity, and Cr to resist selectivity for both etch processes. The best ICP process was found to have superior etch rate, etch rate uniformity, and comparable Cr to resist selectivity to the RIE process. The effect of exposed Cr area on the Cr to resist selectivity, critical dimension (CD) bias, and CD bias 3σ was also investigated. A decrease in exposed Cr area from 95% to 7% was found to dramatically increase the Cr etch rate, leading to an increase in the Cr to resist selectivity. Lower Cr loading was also found to decrease the CD bias and CD bias 3σ. The average CD bias was very high for both processes, with the ICP etch process having a higher CD bias (143 nm) than the RIE process (89 nm). The CD bias uniformity was significantly lower for the ICP process (32 nm, 3σ) when compared to the RIE process (71 nm, 3σ).

Highly anisotropic features of benzocyclobutene, a promising low stress layer for microelectromechanical systems, were achieved by inductively coupled plasma (ICP) etching with fluorine/oxygen based chemistry. The effects of chamber pressure, platen power, ICP power, and SF6/O2 relative concentration were studied on etch rate, selectivity, and sidewall morphology. Highly anisotropic features were achieved with sidewall slopes ∼88° for almost all conditions. Grass-like residue, due to redeposition of etch material, was observed under certain conditions and is shown to be dependent on pressure, ICP power, and feature dimensions.

From measurements of optical emission and silicon etch rate, we are able to separate contributions due to the chemical etching and the ion-bombardment enhanced etching in the CF4+O2 reactive ion etching process. The chemical etching part of undoped polysilicon etch rates is linearly proportional to the ground state fluorine population and the ion bombardment part is proportional to the dc self-bias voltage (V2.3bi). The chemical etching predominates during plasma etching, giving rise to the isotropic etch profile, while both the chemical etching and the ion-bombardment enhanced etching mechanisms coexist during reactive ion etching. A degree of the etch anisotropy in reactive ion etching is determined by competition between the chemical etching and the ion-bombardment enhanced etching, and can be expressed by an equation which only involves two physical quantities, etch rate and fluorine concentration, experimentally measurable in plasma etching and reactive ion etching. The silicon loading effect leads to a substantial decrease in a number density of the ground state fluorine and consequently makes an etch profile more directional by reducing a contribution due to the chemical etching. Also, we have identified important process parameters which influence etch profiles.