Reactive ion etching for VLSI

Reactive Ion Etching (RIE) is a dry etching technique that is used to etch 1-µm and submicrometer patterns into films of silicon and silicon compounds. RIE is suitable for VLSI applications because etching is anisotropic and proceeds via chemical reactions with the substrate. Anisotropic etching allows faithful reproduction of resist patterns into the films that make up a device, and chemical etching allows development of selective etching by manipulating the composition of the plasma. The RIE reactor is described and examples of its use to fabricate 1-µm MOSFET's are given. Concerns arising from the presence of a voltage between the substrates and the plasma, radiation damage of SiO2and contamination of silicon, are discussed.     

Reactive ion etching of trenches in 6H-SiC

In this paper, we report the reactive ion etching (RIE) of trenches in 6H-silicon carbide using SF₆/O₂. The plasma parameters: etchant composition, gas flow rate, chamber pressure, and radio frequency power were optimized to obtain a maximum etch rate of 360Å/min. The etch rate of SiC was found to exhibit a direct correlation with the dc self bias except when the O₂ percentage was varied. Trenches were fabricated using the optimized conditions. It was found that the trench surface was extremely rough due to the aluminum micromasking effect. To overcome this effect, a Teflon^TM sheet was used to cover the cathode during the experiment. The trenches fabricated using this modification were found to have smooth etched surfaces and sidewalls. The angle of anisotropy of these trenches was approximately 80° which is suitable for device applications.     

Reactive ion etching of gallium nitride films

Reactive ion etching (RIE) was performed on gallium nitride (GaN) films grown by electron cyclotron resonance (ECR) plasma assisted molecular beam epitaxy (MBE). Etching was carried out using trifluoromethane (CHF₃) and chloropentafluoroethane (C₂ClF₅) plasmas with Ar gas. A conventional rf plasma discharge RIE system without ECR or Ar ion gun was used. The effects of chamber pressure, plasma power, and gas flow rate on the etch rates were investigated. The etch rate increased linearly with the ratio of plasma power to chamber pressure. The etching rate varied between 60 and 500Å/min, with plasma power of 100 to 500W, chamber pressure of 60 to 300 mTorr, and gas flow rate of 20 to 50 seem. Single crystalline GaN films on sapphire showed a slightly lower etch rate than domain-structured GaN films on GaAs. The surface morphology quality after etching was examined by atomic force microscopy and scanning electron microscopy.     

Reactive ion etching of dielectrics and silicon for photovoltaic applications

This paper investigates the reactive ion etching of SiO₂, Si₃N₄, and Si using CHF₃/O₂ plasma. In particular, we have characterized the time and rf power dependence of the carrier lifetimes in n‐ and p‐type FZ Si. The time dependence of reactive ion etching (RIE) at different rf powers provide insight into the two competing processes of damage accumulation and damage removal in the near‐surface region of the Si during plasma etching. The carrier lifetime, measured using the quasi‐steady‐state photoconductance (QSSPC) technique, has a quadratic dependence on the rf power, which can be related to changes in the dc self‐bias generated by the plasma at different rf powers. The change in carrier lifetime is similar in both n‐ and p‐type Si of the same doping concentration. Using this fact, together with the electronic properties of defects obtained by deep level transient spectroscopy (DLTS), we have modeled the injection‐dependence of the measured carrier lifetimes using the Shockley–Read–Hall model. The isochronal annealing behavior of plasma etched Si has also been studied. Copyright © 2006 John Wiley & Sons, Ltd.     

Reactive ion etching and characterization of p-silk ultra low-k film

Reactive ion etch (RIE) of p-SiLK, a spin-on polymer based ultra low-k (ULK) material with a k value of /spl sim/2.2 was characterized and its influence on electrical yield and dielectric breakdown is presented here. Material characterization was done using blanket films after curing and the effect of exposure to different conventional plasma etch gas mixtures was studied for surface composition, roughness and dielectric constant. Trench etch process was developed for 130-nm technology node for single damascene process integration. Dual hard mask approach was taken and two etch schemes viz., etching under hardmask and etching under photoresist were evaluated. In both schemes, trench etch profiles were near vertical and critical dimension (CD) control was within 10%. RIE lag and the carbon depletion at the sidewalls were found to be insignificant confirming acceptable etch process performance. Etching under photoresist scheme was found advantageous in terms of trench profile for isolated structures, reduced cycle time making the process cost effective and reduced post-CMP defects. However, from the comparison of electrical test results, etch under hardmask scheme showed higher electrical yield and better performance than etch under PR scheme. Although trench sidewalls were exposed to plasma during both schemes, sidewall damage did not contribute to overall leakage. The RIE process developed and the characterization results have confirmed the compatibility of material and RIE process for successful process integration.     

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.     

反应离子刻蚀InSb芯片引入的损伤研究

应用CH₄/H₂/Ar作为刻蚀气源对InSb微台面阵列进行了反应离子刻蚀,并对刻蚀后引入的损伤进行了分析。实验证实利用干法刻蚀与湿法腐蚀相结合的方法能有效地减少刻蚀引入的缺陷和损伤,获得较好的电学特性,达到低损伤刻蚀InSb材料的目的。     

钛扩散铌酸锂平面波导的反应离子刻蚀

Reactive ion etching（RIE） of LiNbO₃（LN） in SF₆ plasma atmosphere was studied for optimizing the preparation conditions for LN ridge waveguides.The samples to be etched are Ti-diffused LN slab waveguides overlaid with a chromium film mask that has a Mach-Zehnder interferometer（MZI） array pattern.The experimental results indicate that the LN-etching rate(R_LN) and the Cr-etching rate(R_Cr) as well as the rate ratio R_LN/R_Cr increase with either increasing the radio-frequency（RF） power at a given SF₆ flow rate or increasing the SF₆ flow rate at a fixed RF power.The maximum values of R_LN = 43.2 nm/min and R_LN/R_Cr = 3.27 were achieved with 300 W RF power and 40 sccm SF₆ flow.When the SF₆ flow rate exceeds 40 sccm,an increase in the flow rate causes the etching rates and the rate ratio to decrease.The scanning electron microscope images of the LN ridge prepared after～20 min etching show that the ridge height is 680 nm and the sidewall slope angle is about 60°.     

离子束刻蚀法制作菲涅耳透镜

由于衍射光学元件独特色的色散特性及体积小、重量轻可进行复制等优点,它在国防、生产及科研等领域的作用越来越重要,应用于光学成像系统,不仅能改善系统成像质量,而且能实现系统的轻量化、小型化,增加系统设计的自由度。使用离子束刻蚀法制作的16阶菲涅耳透镜应用于折衍混合CCD相机;测量菲涅耳透镜的衍射效率并分析了影响衍射效率的因素。     

Raising the quantum efficiency of AlGaInN flip-chip LEDs by Reactive ion etching of the outer side of SiC substrates

A method for creating a light-scattering microprofile on the outer side of SiC substrates in order to diminish the light extraction loss caused by the effect of total internal reflection in light-emitting AlGaIn/GaN structures has been further developed. It is suggested to use thin photoresist layers as random masks for reactive ion etching of silicon carbide substrates. A microprofile with the required parameters has been obtained on the substrate surface by optimizing the etching modes, with the result that the external quantum efficiency of light-emitting crystals increased by more than 25%.     

Identification of subsurface damage of 4H-SiC wafers by combining photo-chemical etching and molten-alkali etching

In this work, we propose to reveal the subsurface damage (SSD) of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as the ridge-like defect. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of scratches. This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).     

Reactive ion etching of copper in an RF N2 + BCl3 + Cl2 Plasma

Reactive ion etching (RIE) of copper in a cold-wall reactor is described. When the rf discharge power is sufficiently high, the etch surface temperature becomes sufficient for reaction product removal due to plasma-wafer heat exchange. The etching process can easily be controlled by monitoring the line intensity in the CuCl emission spectrum. For example, the 435.8-nm line allows operators to fix the instant of etch completion and to keep track of the process     

Uniformity in HgCdTe diode arrays fabricated by reactive ion etching

Two-dimensional, midwavelength infrared (MWIR) HgCdTe detector arrays have been fabricated using reactive ion etching (RIE). Detector-to-detector uniformity has been studied in the devices fabricated with CdTe- and ZnS-passivation layers. Mapping of the doping profile, passivant/HgCdTe interface electrical properties, and diode impedance-area product (R₀A_j) in a two-dimensional array of diodes has been carried out. Temperature and perimeter/area dependence of the dark current are studied to identify the bulk and surface current components. Maximum R₀A_j=2×10⁷ Θcm² was achieved in CdTe-passivated, 200×200 μm² diode arrays. It demonstrates that CdTe-passivated, RIE-processed HgCdTe is a feasible technology.     

Reactive ion etching of SiC using C2F6/O2 inductively coupled plasma

The inductively coupled plasma-reactive ion etching (ICP-RIE) of SiC single crystals using the C₂F₆/O₂ gas mixture was investigated. It was observed that the etch rate increased as the ICP power and bias power increased. With increasing sample-coil distance, O₂ concentration, and chamber pressure, the etch rate initially increased, reached a maximum, and then decreased. Mesas with smooth surfaces (roughness ≤1 nm) and vertical sidewalls (∼85°) were obtained at low bias conditions with a reasonable etch rate of about 100 nm/min. A maximum etch rate of 300 nm/min could be obtained by etching at high bias conditions (≥300 V), in which case rough surfaces and the trenched sidewall base were observed. The trenching effect could be suppressed by etching the samples on anodized Al plates, although mesas with sloped (60–70°) sidewalls were obtained. Results of various surface characterization indicated little contamination and damage on the etched SiC surfaces.     

Considerations on high resolution patterns engraved by ion etching

The theoretical model of a surface contour evolution under ion bombardment is applied to the study of the behavior of a mask during ion etching. Two new parameters are defined. The first gives an upper limit of the etching time when distortion-free patterns are needed. The second gives the lateral shift of the pattern if the previous limit is exceeded. Values of mask parameters were measured for various thin metal films under the following conditions: 1) Argon ion energy = 1 keV, 2) ion current density = 0.6 mA/cm², and 3) oxygen pressure in the sputtering chamber = 10^-4torr. It is shown that the introduction of oxygen improves the mask parameters.     

Investigations on the damage caused by ion etching of SiO2 layers at low energy and high dose

The radiation damage caused by argon ion bombardment during ion etching of thermally grown SiO₂ films at an energy below 1 keV and a dose of about 10¹⁸ cm^?2 has been studied by evaluating MOS C-V curves, FET characteristics, as well as Rutherford ion backscattering spectra. The bombarded samples revealed that ion beam etching in this energy range causes a damaged layer of 5–10 nm thickness at the single crystal silicon surface. Moreover, traces of metal atoms are found in the damaged layer together with argon atoms (≈ 10²¹cm^?3).     

Reactive ion etching of Ta-Si-N diffusion barriers in CHF3+O2

Reactive ion etching of Ta₃₆Si₁₄N₅₀ diffusion barrier layers was performed in CHF₃+O₂ plasmas. Etch depths and rates were determined as a function of etch gas composition, cathode power, and etching time. Etching proceeds only after an initial delay which depends on gas composition and cathode power. This delay is attributed to the presence of a native surface oxide which must first be removed before etching can commence. Maximum etch rate was attained at 62.5% O₂ concentration, which also corresponds to minimum delay     

GaAs vertical-cavity surface emitting lasers fabricated by reactive ion etching

GaAs quantum well vertical-cavity surface emitting lasers fabricated using low damage reactive ion etching are discussed. Lasers which are partially and completely etched through their structure are compared. The surface recombination velocity of exposed GaAs is not exacerbated in deep etched lasers; other loss mechanisms in shallow etched lasers have comparable impact on laser performance. Etched lasers exhibit low voltage and small differential series resistance at threshold, while devices fabricated by a combination of etching and ion implantation possess lower threshold current. It is found that reactive ion etching has little additional effect on laser operation, whereas the different device structures considered do influence laser performance.<>     

A collimation mirror in polymeric planar waveguide formed by reactive ion etching

We fabricated and characterized an integrated optical mirror in a polymeric waveguide. A parabola-shaped cavity is etched in fluorinated polyimide using oxygen reactive ion etching. The vertically etched sidewall of the planar waveguide works as a highly reflecting total-internal-reflection mirror, which collimates a diverging beam from its focus. The estimated mirror insertion loss of the demonstrated device is 2.4 dB or less.