This PDF file contains the editorial “Successors of ArF Water-Immersion Lithography: EUV Lithography, Multi-e-beam Maskless Lithography, or Nanoimprint?” for JM3 Vol. 7 Issue 04

It was shown previously that the double line and space formation method (DLFM) is superior to other methods for forming a dense contact hole (C/H) resist pattern by simulation, and a 0.30-k₁ 1:1 C/H resist pattern was formed experimentally. A through process of C/H formation from resist patterning to metal filling is presented. The oxide square C/Hs transferred from the resist pattern formed by the DLFM could be filled with metal, although the transferred C/Hs had square corners in comparison with the conventional C/H resist patterning. On the other hand, the combination of the DLFM and the “pack and cover process” makes it possible to form resist random C/Hs on grids. So, the possibility of forming random C/Hs filled with metal is shown. Moreover, the resolution limit of the DLFM is discussed. The 0.29-k₁ (half pitch 65-nm) and 0.27-k₁ (half pitch 56-nm) 1:1 C/H resist patterns could be formed with optimized dipole illumination. So, random C/Hs with k₁ below 0.30 are expected to be formed.

Two-photon polymerization (2PP) is an effective technique for the fabrication of complex polymeric 3-D micro/nanofeatures and structures using ultrashort pulses from a NIR laser source. The interaction of laser pulses with photoresponsive resin creates a voxel (volumetric pixel) that defines the resolution of the 2PP process. In this work, we present a mathematical model of the 2PP process that considers the effects of radical diffusion and polymerization kinetics on polymerization dynamics. The increase in temperature during the polymerization process and its effect on polymerization kinetics are considered in the model. The developed model is solved numerically to obtain a better understanding of the polymerization dynamics at various time scales. The effects of diffusion and polymerization kinetics on the growth of voxels are analyzed from the presented simulations. A comparison between high and low pulse repetition rate systems is also presented, showing different polymerization dynamics.

A small sized, low power consuming, shock proven optical scanner with a capacitive comb-type rotational sensor for the application of mobile projection display is designed, fabricated, and characterized. To get a 2-D video image, the present device horizontally scans a vertical line image made through a line-type diffractive spatial optical modulator. To minimize, device size as well as power consumption, the mirror surface is placed on the opposite side of the coil actuator. To prevent thermal deformation of the mirror, the mirror is partially connected to the center point of the coil actuator. To be shock proof, mechanical stoppers are constructed in the device. The scanner is fabricated from two silicon wafers and one glass wafer using bulk micromachining technology. The packaged scanner consists of the scanner chip, a pair of magnets, yoke rim, and base plate. The fabricated package size is 9.2×10×3 mm (0.28 cc) and the mirror size is 3×1.5 mm. The scanner chip receives no damage under the shock test with an impact of 2000 G in 1 ms. In the case of a full optical scan angle of 30 deg at 120-Hz driving frequency, linearity, repeatability, and power consumption are measured at 98%, 0.013 deg, and 60 mW, respectively, which are suitable for mobile display applications.

Advances of electron storage rings to beam currents of above 1 A and tabletop sizes make possible the development of a synchrotron-based source for EUV lithography (EUVL) at ~13.5-nm wavelength. The MIRRORCLE storage rings can provide on average 3-A electron beam current, 1-min lifetime, 15-ms radiation damping, and beam size ~3*3 mm2. MIRRORCLE-20SX, MIRRORCLE-6X, and MIRRORCLE-CV4 store electrons with energies of 20 MeV, 6 MeV, and 4 MeV, respectively. These machines can emit EUV from a tiny target, hit by the circulating beam, via transition radiation or diffusive radiation. Using a multilayer microelectromechanical system (MEMS) target allows enhancement and spectral purification of the emitted EUV. Aligning many such MEMS along the electron beam orbit and radiation collection by only one quasi-elliptical EUV mirror can provide EUV satisfying the joint requirements for an EUVL source.

The use of conventional thermal cross-link materials such as negative resists, antireflective coating, and planarizing layers does not lead to excellent planarization for multilevel interconnects and specially via arrays prior to trench patterning for an advance lithography. The large thicknesses bias between the blanket areas and interconnect areas, and between the blanket areas and via arrays are usually observed. Large thickness bias creates problems during next lithography by narrowing the process latitude. Recently, chemical mechanical polishing (CMP) technology has been proposed to achieve the planarization. However, CMP planarization technique is very sensitive to pattern density, and there is a strong possibility that chemical etching reaction will increase the dielectric constant. The current CMP technique still requires a new investment in the equipment. We report another novel approach for global planarization using UV cross-link material (XUV^TM) and the dielectric UV exposure unit in coater equipment (Clean Track). This planar technique provides benefits for reducing the thickness bias observed in the 22- to 65-nm generation lithography and imprint processes. Using this technique, XUV^TM TNG076 has achieved global planarization of 10-nm thickness bias in 85-nm diameter via topography when the blanket film thickness was only 110 nm.

Poly(dimethylglutarimide) (PMGI) is a resist that is commonly used in bilayer and trilayer imaging applications. PMGI can be exposed using various radiation sources including deep UV. Currently, there are only two developers for PMGI reported in the literature: tetramethylammonium hydroxide and tetraethylammonium hydroxide. We introduce a new developer for PMGI, a mixture of isopropanol (IPA) and water. Samples were irradiated with deep UV at 254 nm. The IPA/water developer exhibits rapid dissolution of exposed PMGI, of many microns per minute. However, PMGI exhibits high absorption at 254 nm, so the development depth is limited. The depth limit, after a critical dose, increases linearly with the exposure dose.

A low-temperature wet-release process for low stiffness structures fabricated using material of low Young's modulus has been developed and presented. The release process is described in the light of different forces that cause stiction during release. This technique is successfully demonstrated for different low stiffness structures with gold as the membrane material and positive photoresist or SiO₂ as the sacrificial layer.

We previously proposed a new method to correct critical dimension (CD) errors appearing in large-scale integrated circuit (LSI) fabrication processes, such as long range loading effect, local flare, and micro loading effect. The method provides high accuracy correction dimensions when using the pattern modulation method (method correcting CD errors by controlling figure sizes of LSI patterns). Now the case that several processes cause CD errors when a layer of an LSI pattern is fabricated on a wafer is discussed. These CD errors are corrected by generalizing the method proposed previously and taking the sequence of processes into account. It is shown from numerical calculation that the method can suppress the CD error to less than 0.01 nm with three iterations, under the condition that the maximum CD errors by micro loading effect and flare are 10 nm and 20 nm, respectively. It is strongly suggested that our methods will provide the necessary CD accuracies in the future.

One annoying problem that degrades high-fidelity pattern images in mask-defect inspection systems is the generation of ghost images in the imaging process. Ghost images arise from spatial coherence periodicity on the mask plane, which is due to periodic and discrete arrangements of fly-eye elements in mask inspection optics. By considering the contrast of ghost images under partial coherence illumination, we can derive the condition that represents the necessary number of fly-eye elements to substantially suppress ghost images in the image field. In addition, we confirm this theoretically derived condition of suppressing ghost images by numerical calculations. As a result, we prove that this suppresing condition is effective, and that the nonuniformity in distribution of image intensity can also be reduced in this way.

A method for rapid fabrication of mold masters for soft-molding of polydimethylsiloxane (PDMS) microfluidic devices is successfully developed and tested. The method involves laser micromachining and a hot-intrusion process, and produces mold masters from polymethylmethacrylate (PMMA) substrates. A metallic mask with microchannel line features of various widths (25 to 200 µm) is initially created by laser micromachining a 75-µm-thick brass sheet. Under the hot-intrusion process, a 2-mm-thick solid PMMA substrate is then heated and molded under pressure to force the softened material through the shaped microfeatures in the mask. The height of the extruded microrelief is determined by the pressure, temperature, and time profile of the hot-intrusion process. A mathematical model that characterizes the rapid fabrication process and enables the operator to select appropriate process parameters is described. The derived empirical model is based on experimental observations where extruded microrelief heights were varied from 5 to 75 µm with aspect ratios from 0.1 to 0.46, and radii of the extruded profile from 12 to 270 µm. The proposed model is developed to describe the relationship between key process parameters and the extruded heights of the microreliefs. Furthermore, the model provides the operator with simple guidelines for selecting the process parameters. An example of PDMS microfluidic devices replicated by the rapid micromold fabrication methodology is presented to illustrate the quality of the resultant features of microchannels.

The existing research on interface properties between heterogeneous materials mainly focuses on semiconductor-metal and dielectric materials, but little on organic-inorganic ones. In recent years, the nanoscale phenomena related to the mechanical properties of organic/inorganic material interfaces is gaining a lot of attention and becoming a new area of nanorelated research. Since gold (Au) exhibits excellent optical, electrical, and mechanical properties, it can be applied to nanooptics, mechanics, and electronics. This study explores the nano effect of the mechanical properties between the interface of Au and heterologous polymethyl methacrylate (PMMA) with different side groups, i.e., isotactic-PMMA, syndiotactic-PMMA, and atactic-PMMA. These heterologous PMMA thin films are prepared using a spin-coater to deposit the different side groups of PMMA upon Au thin film. A sputter technique is used to form Au thin films with different thicknesses. An indenter probe is applied by adding different forces on its tip into the PMMA and Au thin films to realize the interface mechanical properties such as hardness and Young's modulus. Finally, the time-dependent properties of viscoelastic materials are evaluated by using this harmonic nanoindentation test.

We describe two fabricated microthermal shear stress sensors by antiadhesion surface technology and anodic bulk-bonding technology. Two sensors are based on thermal transfer principles with adiabatic structures. The thermal sensor element is a titanium—platinum alloy resistor sputtered on the top of a low pressure chemical vapor deposited (LPCVD) silicon nitride diaphragm with an adiabatic vacuum cavity underneath. The surface micromachined thermal shear stress sensor uses microbumps on the silicon substrate in the sacrificial layer technology to prevent the silicon nitride diaphragm's stiction to the substrate. Microbumps formed by isotropic silicon etching in HNA (the system HF, HNO₃, and HC₂H₃O₂) are arrayed in several points on the silicon substrate with distances of 147 µm in the (200×250)-µm²×1.5-µm vacuum cavity. This cavity is formed by LPCVD silicon nitride film sealing with 30-Pa vacuum degree. The anodic bulk-bonding micromachined thermal shear stress sensor uses bulk silicon substrate etching and anodic bonding to form the (200×250)-µm²×400-µm high aspect ratio cavity with 5×10^-2 Pa vacuum degree. The titanium platinum alloy resistor, (5×150)-µm²×0.2 µm, sputtered on the top of the 1.5-µm-thick LPCVD silicon nitride diaphragm with this bonding chamber, has a temperature coefficient of resistance (TCR) value of 0.33%/°C. According to the comparison of the adiabatic characteristics among three cases—a titanium platinum alloy resistor located over the high aspect ratio 5×10^-2 Pa vacuum cavity, over the 30-Pa vacuum cavity, and directly on top of the substrate—the first case has the best adiabatic characteristic: the titanium platinum alloy resistor located over the 5×10^-2-Pa vacuum cavity has the maximum thermal resistance of 5362 °C/W. Besides the sensor sensitivity performances, it has a comparatively short time constant with value of 0.1 ms under the constant current (CC) mode driving circuit.

An in-plane rotary comb drive actuator was designed for variable optical attenuators (VOAs) that achieved large attenuation with fast response at low driving voltage. Actuator performance was improved by using a higher density of comb fingers for a smaller moment of inertia, serpentine flexure springs for a larger rotational angle, and symmetric spring arrangement for a higher radial shock resistance. A rotation of a tilted reflective mirror was used to further enhance the optical attenuation of VOA. The actuator, proposed with the size of 2 mm × 2 mm, achieved the bandwidth of 350 Hz and the deflection angle of 2.5 deg at 5 V, resulting in the maximum attenuation of 57 dB.

The mechanical properties of the structural layer play an important role in the design and optimization of microelectromechanical system structures. The pull-in measurement is a popular technique used to measure the mechanical properties of a material, but its success depends on the accurate measurement of the gap (g) between the beam and the ground plane and its uniformity. We propose a novel technique that does not require accurate knowledge of the value of g. In our proposed method, a large number of beams with different lengths (L) are to be fabricated simultaneously and the off-capacitance (C_off) in addition to pull-in voltage (V_pi) measured in the same setup. To get accurate results, the range of length of beams must be properly chosen. We show, with the help of simulations, that by using our method the material properties can be extracted very accurately even when the gap (g) is nonuniform.

Electrothermal actuation has been used in microelectromechanical systems where low actuation voltage and high contact force are required. Power consumption to operate electrothermal actuators has typically been higher than with electrostatic actuation. A method of designing and processing electrothermal actuators is presented that leads to an order of magnitude reduction in required power while maintaining the low voltage, high force advantages. The substrate was removed beneath the actuator beams, thereby discarding the predominant power loss mechanism and reducing the required actuation power by an order of magnitude. Measured data and theoretical results from electrothermally actuated switches are presented to confirm the method.

This study presents a rotary micromotor with low-friction and large-step displacement driven by a scratch drive actuator (SDA) with bounceback driving mechanism. The present SDA device has a shorter plate and wider bushing compared to those of the existing SDA, resulting in a new electrostatic scratch-and-bounceback driving mechanism with larger stepping size. The new scratch-and-bounceback actuating mechanism markedly reduces the friction and damping effect between the SDA plate and the nitride insulator surface and eliminates effectively the sudden reverse rotation of SDA-based micro rotary motor. This investigation incorporated three design features (corners-rounded supporting-beam, flanged cover, and corrugated/ribbed/dimpled inside ring) into the structure of a SDA-based rotary micromotor to further decrease the rotating abrasion between the rotor inside ring and the cover, the anchor, and the inside rail. The bouncing SDA-based micromotors developed in this work (with 398 µm diam) were fabricated using the MEMSCAP^® Poly-MUMPs process and achieved many improvements, including low friction, large stepping size (196 nm), small damping effect, and no sudden reverse rotation phenomenon (from dc to 25 kHz).

A novel triaxis microgyroscope is proposed. Three orthogonal axis angular rates for pitch, yaw, and row can be detected simultaneously by the presented microgyroscope. The coupling effect of the triaxis angular rates due to Coriolis response and nonlinearity of the high-frequency modes can be efficiently reduced by the decoupled mechanical structure design. First, a 8×8 linearized state-space representation with a “holonomic” constraint is established and the relative stability of the dynamic system is investigated. Second, the mathematical description and discussion upon performance indices for a microgyroscope, such as sensitivity, bandwidth, and resolution, are addressed. In addition, the quality factor is verified to be a significant design parameter for microgyroscopes. The performance and stability of the gyroscope could be degraded by choosing inappropriate quality factors. Moreover, the trade-off among performance indices for the gyroscope is theoretically evaluated and discussed. Finally, in order to meet most performance specifications, a pole/zero mapping design method is proposed to satisfy either large bandwidth or high-resolution requirements.

A microheater array device is designed and fabricated using the SwIFT-Lite^TM process at Sandia National Laboratories. The device contains 18 individually controllable microheaters in a 3×6 array on a silicon substrate. The microheater array device was designed for use as a biosensor platform with a waveguide for real-time detection of DNA hybridization and melting as well as microfluidics for sample delivery. The design process including modeling, fabrication, and characterization of the heaters and waveguide is detailed. A FRET (florescence resonance energy transfer) system for DNA melting experiments is described, and the associated surface chemistry and microfluidic systems are discussed.