This PDF file contains the editorial “Editorial: Chris Mack Takes Over as JM3 Editor-in-Chief in 2012” for JM3 Vol. 10 Issue 02

This manuscript reports on the development of a needle-type sensor for in situ on-site measurement of pH. Conventional pH microelectrode sensors are fabricated by pulling glass pipettes and applying ion-selective films at the tip. However, these sensors suffer from low fabrication yields and short sensor lifetime due to disruption or loss of the ion-selective membrane after repeated use. The developed needle-type sensor is fabricated by meniscus etching and takes advantage of the MEMS batch fabrication techniques. The sensor is based on the ion-selective properties of iridium oxide film, which was deposited at the sensor tip by electrodeposition. The sensor exhibited a Nernstian response with sensitivity of ∼62 mV/pH in the pH 2 to 12 range. The sensor also exhibited a fast 5 s response and a lifetime of ∼2 months when stored in a pH7 buffer solution, which is substantially longer than that of the conventional pulled-pipette sensors.

When a thinner absorber mask is applied to extreme ultraviolet (EUV) lithography for chip production, it becomes essential to a introduce light-shield border in order to suppress the leakage of EUV light from the adjacent exposure shots. In this paper, we evaluate the leakage of both EUV and out-of-band from light-shield border and clarify the dependence of lithographic performance on light-shield border structure using a small field exposure tool with/without spectral purify filter (SPF). Then we evaluate the lithographic performance of a thin absorber EUV mask with light-shield border of the etched multilayer type and demonstrate the merit of its structure using a full-field scanner operating under the currently employed condition of EUV source in which SPF is not installed.

This paper presents a three-dimensional (3D) tapered spot-size converter connecting to silicon wire waveguide and silicon rib waveguide. The silicon 3D structure was essentially formed by a single-step deep anisotropic dry etching of arrayed submicron-scale line patterns with different pitches, resulting in a tailored depth profile which is controlled by the line pattern through loading effect. Subsequent thermal oxidation and removal of the oxidized portion with wet etching led to a bare 3D silicon structure with smooth surface. The optical mode from a 4.6 μm × 3.1 μm silicon rib waveguide was successfully coupled to a 280 nm × 500 nm nanowire waveguide by a silicon 3D tapered spot-size converter, with average coupling loss of 1.52 dB.

In semiconductor industries, controlling and measuring critical dimensions are two important tools to design masks. However, measuring the dimensions with physical tools becomes more challenging, and the traditional method of measuring is slow and has many processes though it is accurate. This paper suggests a method that accurately measures the critical dimension length in a short time based on the digital image processing.

We developed an optimized substrate removal process for GaAs-based opto-electronic devices by establishing a reliable two-step process. In this process, the substrate is first thinned by mechanical lapping and then followed by selective high density plasma etching. The adopted inductively coupled plasma etching, having an optimized boron trichloride (BCl₃)/sulfur hexafluoride (SF₆)/argon composition, shows a nearly infinite etching selectivity for the GaAs substrate over the aluminum gallium arsenide (Al_xGa₁-_xAs) etch-stop layer. The surface of the die is perfectly smooth and mirror-like after processing. In addition to its simplicity, the process is also highly reproducible and shows no damage to the underlying detector material.

Deformable membrane mirrors are promising MOEMS devices for focus control and aberration correction in vital microscopy, offering high speed focus adjustment in an optical system that can be miniaturized for in vivo use. This paper describes mirrors comprising metalized polymer membranes suspended over three concentric circular electrodes for electrostatic actuation. The membranes are 2-μm thick and 3 mm in diameter, made from the fully cross-linked photoset epoxy SU-8 2002. A layer of SU-8 2025 is used to establish a 30-μm thick air gap between the electrodes and the membrane mirror. The membranes are actuated by applying voltage to each electrode individually to achieve displacement as large as 12 μm while minimizing spherical aberration. Surface deflection is studied using phase-shift interferometry under both static and dynamic excitation. Using the deformable MOEMS mirror for focus control in an optical microscope we demonstrate the ability to adjust the location of the focal plane by 85 μm using an N.A. = 0.75 optical system.

Current work on deep-reactive ion etching has primarily focused on creating vertical sidewalls for microelectromechanical system and electronics applications. For micro-optical and micro-optoelectromechanical system structures control of the sidewall angles other than vertical is as important as the ultimate depth. In this work, we investigate the control of sidewall profiles using an inductively coupled plasma technique. The material systems being investigated on blanket samples are silicon and silicon dioxide with CF₄, CHF₃, and SF₆ chemistries. Micro-optic structures are created by photolithography and CHF₃ gas has been explored to achieve a wide range of etch rates, smooth etch profiles, and sidewall angles. The etch profiles are characterized by scanning electron microscopy.

The quadratic aberration model used in optical lithography is a natural extension of the linear model by taking into account interactions among individual Zernike coefficients. Although the model has been tested and verified in many applications, the effects of Zernike coefficients under partially coherent imaging are usually obtained by extensive experiments due to the complexity of the model expression. In this paper, a generalized cross triple correlation (CTC) is introduced and a fast algorithm to simulate the quadratic aberration model is developed. Simulations were performed by the proposed CTC-based algorithm with different input Zernike aberrations for binary and phase shift masks with multiple pitches and orientations, which demonstrate that the proposed approach is not only accurate but also efficient for revealing the influence of different Zernike orders on aerial image intensity distributions under partially coherent illumination.

Textured surfaces have been fabricated in the past using several methods and were characterized for relatively simple texture geometries and especially with static drops on them. Numerical tools may provide an effective alternative to understand the effect of complex texture geometries and help understand the effect of texturing on flowing liquids. This work focuses on the numerical simulation of laminar bulk flow of water through microchannels with textured surfaces and provides a comparison with their smooth counterparts. The interpillar spacing on the textured surfaces is found to influence the pressure drop. This is because the trapped air is able to exit the surface cavities at a relatively high rate for larger interpillar spacings. A decrease in channel height increases the percentage pressure drop reduction because of an increase in the ratio of slip length to channel height. The probability of water penetrating the surface cavities increases with flow velocity. Pressure drop measurements on microchannels with textured surfaces, fabricated using two-step photolithography, show that the theoretical pressure drop for smooth microchannels is marginally closer to the experimental value than those observed with textured microchannels. The study therefore helps understand the effect of individual parameters on the overall flow field and engineering parameters such as wall shear stress.

Optical proximity correction (OPC) methods are resolution enhancement techniques used extensively in the semiconductor industry to improve the resolution and pattern fidelity of optical lithography. During the mask data preparation process, the mask pattern is first fractured into basic rectangles, and then fabricated by the variable-shaped-beam mask writing machine. The rectangle count included in the fractured pattern is preferable to be suppressed to reduce the mask fabricating time and cost. Recently, various pixel-based OPC (PBOPC) approaches have been developed to improve the resolution of optical lithography systems. However, these approaches fall short in controlling the rectangle count in the fractured pattern, thus deteriorating the manufacturability of the mask. This paper focuses on developing gradient-based PBOPC optimization algorithms to improve the resolution of optical lithography, while controlling the manufacturability of the mask. To achieve this goal, a topography filter is designed to analytically formulate the rectangle count in the fractured pattern during the optimization process. The manufacturability cost term is then introduced to constrain the complexity of the mask. Cost sensitivity is applied to speed up the proposed algorithms. A line search method is used to properly choose the parameters, and leads to superior resolution and manufacturability of masks.

Line-edge and linewidth roughness (LER and LWR) is mostly characterized using the edge position data obtained by detecting edges in scanning electron microscope (SEM) images. In order to reduce data errors caused by SEM-image noise, image pixels are usually averaged along or across pattern edges (longitudinal or crosswise averaging) before the edge detection. In the case of the longitudinal averaging, it not only reduces the image-noise-induced additional LWR, but smoothes the real LWR. Because of this smoothing effect, the power spectral density (PSD) of the LWR decreases more markedly at larger wave numbers. A distinct feature of this PSD is oscillatory structures, which depend on the number of averaged pixels. It is difficult to formulate these modifications of PSD in the cases of any LWRs under arbitrary measurement and analysis conditions. By contrast, the crosswise averaging of the image pixels reduces only the image-noise effect without affecting the real LWR, enabling to enjoy the benefits of the methodology developed so far. Accordingly, the authors propose to apply only the crosswise averaging to SEM-image pixels before the edge detection.

The photoelectrical response properties of a linear high-temperature (high-Tc) superconducting sensor coupled with a refractive microlens array are investigated. The theoretical analysis and measurements demonstrate that the photoelectrical response uniformity of superconducting sensors is not always improved simultaneously with the enhancement of the common photoelectrical performances of superconducting sensors, such as the responsivity, the noise equivalent power, and the detectivity, after coupling cylinder microlenses with them. A linear 8-pixel high-Tc YBa₂Cu₃O₇-δ superconducting thin film sensor and a quartz microlens array of 32×64, are designed and then fabricated and finally coupled for detection infrared radiation in the wavelength range of 1 to 5 μm. The superconducting sensors are characterized through a common measurement method.

Resist line-edge/width roughness is one of the most critical aspects in extreme UV lithography for the 32-nm technological node and below. It is originated by the uncertainties which characterize the lithographic process: source speckle effect, mask line and surface roughness, mirror roughness, flare effect, and resist pattern formation all contribute to the final roughness. In this paper mask and resist line-edge roughness were compared by means of frequency analysis on top-down scanning electron microscopy images: it was found that low frequency mask roughness is well correlated with the power spectral density of the resist roughness. Mask high-frequency components resulted less critical due to the natural cut-off of the optical system. Experimental data for both mask and resist were implemented in the PROLITH stochastic resist model simulator to quantify the mask line edge roughness contribution to the final resist roughness: the results showed that, for the particular lithographic setting used during the exposures, 16% of the low frequency resist roughness component is originated at the mask level. For this reason, mask impact was set as 0.6 nm of the overall line edge roughness resist budget.

Double patterning (DP) was investigated for logic layout by using a rigorous three-dimensional (3D) wafer-topography/lithography simulator with water immersion lithography. With increasing complexity of the DP process, the 3D wafer-topography effect of stack structure must be considered, because of its impact to lithography. The main purpose of this paper is to present how to optimize both process and design to ensure overlap and connectivity of split patterns by solving electro-magnetic field distribution in wafer substrate, as well as resist region. A process window was analyzed varying not only focus, dose, and split masking layers, but also considering topography of substrate stack structures, which cause local reflectivity variations. Arbitrary 45 nm logic layout including an L-shaped pattern was analyzed. The process window of the second litho step was analyzed. Due to the reflection from the hard mask (HM, result of the first litho step), the process window was restricted and became smaller. The other option suggests that swapping the first and second litho masks is a better choice, with respect to the impact of wafer topography. The optimization of the stack process condition was analyzed by using the contour plot of reflectivity, as functions of n, k, and thickness of materials inside the bottom anti-reflective coating. The concept of extended normalized image log slope considering local reflectivity variation from wafer process is able to explain the variation of resist sidewall slope and exposure latitude.Therefore, it is useful to analyze connectivity at the stitching point by using a 3D wafer-topography/lithography simulator and to optimize the combination of the DP process and layout stitching design. Furthermore, as a design of an advanced process, litho-develop litho-etch was simulated.

We have developed a new local overlay measurement technique on actual device patterns using a critical dimension scanning electron microscope (CD-SEM), which can be applied to two-dimensional (2D) device structures such as a static random access memory contact hole array. CD-SEM overlay measurement can provide additional local overlay information at the site of device patterns, complementary to the optical overlay. The methodology includes the use of pattern symmetry to cancel out many process effects and reduce measurement uncertainty. CD-SEM overlay metrology was compared with conventional optical overlay metrology in terms of measurement uncertainty and overlay model analysis, and very good correlation was confirmed. The developed methodology was applied to local overlay measurement of double patterning contact hole layers of leading edge devices. The local overlay distribution was obtained across the device area, and spatial correlation of the overlay error vectors was examined over a large range of distances. The applications of CD-SEM overlay metrology were explored, and methodologies were introduced to examine both the overlay of double patterning contacts at the edge of an array and lithographic process-induced overlay shift of contacts. Finally, a hybrid optical CD-SEM overlay metrology was introduced in order to capture a high order, device weighted overlay response.

The silicon anisotropic wet chemical etching technique is widely employed for fabricating various microelectromechanical system structures for advantages such as simple etching equipment and its capability to fabricate special microstructures. In this paper, we consider one of the most frequently used equations of atomistic model of simulation of anisotropic wet etching. Then using a trial and error method we solve the mentioned equations and derive a new equation for calculating the microscopic etch rates of some surface atoms for a new range of concentrations and temperatures. Furthermore, a new equation is presented for the calculation of the microscopic activation energies for some typical surface atoms and a new comparison of activation energies between some atoms is made dividing atoms into three categories. This classification makes it easier to study microscopic etch rates and activation energies of other atoms. The results demonstrate a good agreement with the experimental results.

This PDF file contains the errata for “JM3 Vol. 10 Issue 02 Paper 3576188” for JM3 Vol. 10 Issue 02

This PDF file contains the errata for “JM3 Vol. 10 Issue 02 Paper 3599423” for JM3 Vol. 10 Issue 02