Multi-step Etching Process Research Articles

Cyclic deep reactive ion etching with mask replenishment

A multi-step reactive ion etching (MS-RIE) process for silicon was developed for the fabrication of deep anisotropic, closely packed structures with vertical sidewalls. This process used repeated cycles of etching and the replenishment of masking layers, similar to the Bosch process (Laermer and Schilp 1996 US Patent 5,498,312) [1] that is employed in specialized etching tools. The process described here, however, can be used on conventional RIE tools, and is based on the isotropic deposition of an etch-inhibiting polymer to protect sidewalls, its anisotropic removal from the bottom etch front, and a subsequent isotropic etch into deeper layers. A conventional parallel plate etcher without fast gas management, cryogenic substrate cooling, or inductively coupled plasma density enhancement, produced these steps. Each process step was optimized for the maximal etch rate, minimal mask erosion, deposition of the thinnest polymer required to protect the sidewalls, and was tailored for use with 2 µm thick photoresist as the initial mask layer. This cyclic RIE process was used to fabricate photonic devices with high aspect ratios of etched depths over 100 µm and etch widths near 1 µm.

DEVELOPMENT OF ENDPOINT DETECTION ALGORITHM IN THE MULTI-STEP PLASMA ETCHING PROCESS

An endpoint detection algorithm based on principal component regression is developed for the multi-step plasma etching process with the whole optical emission spectra data. Because many endpoint detection techniques use a few manually selected wavelengths, noise render them ineffective and it is hard to select important wavelengths. Furthermore, the smaller the open area changes, the more difficult this single wavelength method detection the endpoint. In this paper, the principal component regression between two wafers was used for the real-time endpoint detection In case study, we applied our multiple models to the multi-step plasma etching process, which consisted of continuous polysilicon etching after the bottom anti-reflective coating etching. So we could obtain the simple and clear information for the more effect endpoint detection, which can be used for the improved process monitoring afterwards.

Fabrication and Characterization of Flexible, Microfabricated Neural Electrode Arrays Made from Liquid Crystal Polymer and Polynorbornene

ABSTRACTThis paper reports the development of flexible, neural electrode arrays made from liquid crystal polymer (LCP) and a polynorbornene (PNB) known by its trade name AvatrelTM. Each array consists of a single flexible, polymeric structure composed of an 8 mm-wide pad supporting eight Pt contacts connected to an ASIC mounting pad by a 5 cm-long, 2 mm-wide shaft carrying eight, 50 μm-wide Pt interconnect lines. The Pt conductors sit atop a 50 μm-thick base layer and are isolated from the environment except at the contacts by a capping layer of the same material as the base. In both cases, the devices were fabricated using conventional microfabrication techniques adapted for the particular polymeric material. In the case of LCP, the base structure was fabricated on 50 μm-thick sheets that were laminated and etched into the final structure. In contrast to LCP, PNB is spin castable and photodefinable, which enabled conventional photolithographic patterning techniques to be employed in a straightforward manner. The PNB-based devices could readily be fabricated, however issues related to LCP etching necessitated the development of a multi-step etch process to form the vias that expose the contacts. Electrodes made from both polymers could support electrical loads typical of stimulation applications without failing. A simple cell culture test suggests that Avatrel™ may be biocompatible, at least for short term applications.

A novel low-temperature method to fabricate MEMS resonators using PMGI as a sacrificial layer

A method to fabricate microelectromechanical systems (MEMS) clamped–clamped resonators using polymethylglutarimide (PMGI) as a sacrificial release layer has been developed. Control of the critical air-gap dimension between the resonator beam and drive electrode was maintained by varying the sacrificial PMGI thickness, allowing fabrication of devices with resonator-to-electrode gaps as small as 100 nm. The resonator beam was constructed by depositing a low stress, low temperature bi-layer alpha-TaN/SiON (50/2000 nm) film over the PMGI layer, followed by a multi-step etch process. Physical characterization of devices with varying beam lengths was performed via focused ion beam and scanning electron microscopy analyses to verify complete release of the resonator structures. Electrical testing showed a resonant frequency of 11.3 MHz, which agreed well with simulated results. The measured RF characteristics are fitted with a lumped element model that used Young's modulus and the device quality factor as adjustable parameters. Young's modulus of the individual components of the TaN/SiON bi-layer was measured and found to be in good agreement with the values used to fit the measured resonance.

圧電薄膜を利用する浮上量制御型アクティブスライダに関する研究(情報機器コンピュータメカニクス2 -機構・制御,IIP2004 情報・知能・精密機器部門講演会)

This paper describes a novel active head slider equipped with micro-actuator using PZT thin films for flying height control. The active head slider is a breakthrough technology for achieving ultra-low spacing of less than 10nm. The position of a read/write magnetic head is gone above and below because an unimorph cantilever build in the slider bends by PZT thin film, and flying height is controlled. The multi-step silicone etching process by ICP-RIE or RIE is important to fabricate active head sliders. Therefore, the fabrication process of a silicone slider structure was completed by optimizing etching conditions.

Improvement of the porous silicon sacrificial-layer etching for micromachining applications

Using porous silicon (PS) as a sacrificial layer, freestanding structures with a large distance to the bulk can be obtained. The very high specific surface area of PS allows its removal using dilute alkaline solutions. However, a critical equilibrium between a non-violent and a complete etch reaction is necessary, A solution to this problem is a multi-step etching process using solutions of different concentrations. To avoid this disadvantage, different technological conditions are studied in order to optimize the removal of the PS by using a one-step process with a 0.1% KOH solution. The effects of adding ethanol, ultrasonic stirring and polarization during the etching process are evaluated. Optimization of the etching procedure allows good-quality freestanding polysilicon structures featuring a smooth substrate surface to be obtained.

Physical and magnetic properties of submicron lithographically patterned magnetic islands

We have developed a procedure for high-resolution patterning of magnetic thin films using direct-write electron beam lithography and a multistep sputter etching process [New et al., J. Vac. Sci. Technol. B 12, 3196 (1994)]. Using this patterning procedure we have defined large arrays of 0.2 by 0.4 μm magnetic islands out of a 200-Å-thick polycrystalline film of cobalt. The physical and magnetic structure of these islands has been examined using atomic and magnetic force microscopy, as well as transmission electron microscopy. Hysteresis loop measurements have been taken from large arrays of weakly interacting islands. The particles are not single domain and show considerable nonuniformity of magnetization when they are completely demagnetized. However, after application and removal of a large field along the long axes of the islands, most of the particles do relax into an almost uniform magnetization state.

Submicron patterning of thin cobalt films for magnetic storage

We are investigating the feasibility of a recording medium in which each bit of information is stored in a single-domain magnetic particle. To this end we have developed a procedure for high-resolution patterning of magnetic recording films using direct write electron-beam lithography and a multistep sputter etching process. We have used this procedure to define small islands of polycrystalline magnetic thin film with feature sizes down to 0.1 μm. The patterning process is suitable for many different kinds of magnetic films, including single-crystal epitaxially grown films, and is designed to minimize physical and chemical damage to the magnetic material being patterned. Both atomic force microscopy and x-ray photoemission spectroscopy have been used to establish that the magnetic islands patterned using this process are physically isolated from each other.

Electron beam lithography with monolayers of alkylthiols and alkylsiloxanes

Self-assembled monolayers have been modified with focused electron beams of energy 1–50 keV and scanning tunneling microscopy (STM) based lithography with energies of ∼10 eV. Modifications ∼15 nm in size have been formed by STM and ∼25 nm in size by 50 keV beams. The fact that these materials work as self-developing electron beam resists is demonstrated by both atomic force microscopy imaging and pattern transfer using conventional wet etchants. Patterns have been transferred to silicon substrates to a depth of ≳120 nm with a multistep wet etching process. The mechanism of electron beam modification has also been explored to better design future monolayer processes.

A process for improved Al(Cu) reactive ion etching

The standard reactive ion etching (RIE) process for etching Al and its alloys in a single-wafer tool is basically a high-pressure (>100 mTorr), multistep etching process. A significant modification to this process is reported which incorporates the standard high-pressure Al(Cu) etch followed by a low-pressure overetch step. The etch gases used for Al(Cu) etching are a mixture of (BCl3/Cl2/CHCl3/N2). At pressures <100 mTorr, the cathode dc self-bias voltage is increased, enhancing the ion bombardment energy and hence directionality normal to the substrate. Then the component of etching by ion assisted or reactively sputtered etching increases relative to the reactive component, increasing the ability to remove Cu-rich residues. The low-pressure overetch step also exhibits a factor of 2 smaller etch bias than the standard process. This is estimated to be 0.05 μm/image in RIE of 1-μm-thick Al(Cu) films. We have demonstrated that lowering the pressure of the overetch step, hence increasing the ion energies but keeping the same reactive species, offers a more effective clearing process. Combining this clearing process with the overetch does not increase the total time required for the process. Using this process, 1.5-μm-thick metal lines of Ti/A1(2.5% Cu)/Si 0.6 μm wide were obtained with vertical sidewalls.