Chrome Etch Research Articles

Electron flux controlled switching between electron beam induced etching and deposition

Electron beam induced deposition (EBID) and etching (EBIE) are promising methods for the fabrication of three-dimensional nanodevices, wiring of nanostructures, and repair of photolithographic masks. Here, we study simultaneous EBID and EBIE, and demonstrate an athermal electron flux controlled transition between material deposition and etching. The switching is observed when one of the processes has both a higher efficiency and a lower precursor partial pressure than the other. This is demonstrated in two technologically important systems: during XeF2-mediated etching of chrome on a photolithographic mask and during deposition and etching of carbonaceous films on a semiconductor surface. Simultaneous EBID and EBIE can be used to enhance the spatial localization of etch profiles. It plays a key role in reducing contamination buildup rates during low vacuum electron imaging and deposition of high purity nanostructures in the presence of oxygen-containing gases.

Formation of plasma induced surface damage in silica glass etching for optical waveguides

Ge, B, P-doped silica glass films are widely used as optical waveguides because of their low losses and inherent compatibility with silica optical fibers. These films were etched by ICP (inductively coupled plasma) with chrome etch masks, which were patterned by reactive ion etching (RIE) using chlorine-based gases. In some cases, the etched surfaces of silica glass were very rough (root-mean square roughness greater than 100 nm) and we call this phenomenon plasma induced surface damage (PISD). Rough surface cannot be used as a platform for hybrid integration because of difficulty in alignment and bonding of active devices. PISD reduces the etch rate of glass and it is very difficult to remove residues on a rough surface. The objective of this study is to elucidate the mechanism of PISD formation. To achieve this goal, PISD formation during different etching conditions of chrome etch mask and silica glass was investigated. In most cases, PISD sources are formed on a glass surface after chrome etching, and metal compounds are identified in theses sources. Water rinse after chrome etching reduces the PISD, due to the water solubility of metal chlorides. PISD is decreased or even disappeared at high power and/or low pressure in glass etching, even if PISD sources were present on the glass surface before etching. In conclusion, PISD sources come from the chrome etching process, and polymer deposition on these sources during the silica etching cause the PISD sources to grow. In the area close to the PISD source there is a higher ion flux, which causes an increase in the etch rate, and results in the formation of a pit.

Testing new chemistries for mask repair with focused ion beam gas assisted etching

In modern photolithography mask repair, shorter exposure wavelengths, smaller dimensions, and tighter process latitudes pose new challenges. We have systematically investigated focused ion beam (FIB) gas assisted etching (GAE) of chrome and mask transmission at 193 nm ultraviolet (UV) irradiation for various FIB parameters. The gases, used either alone or in binary combinations, include XeF2, Cl2, NH3, CO, CO2, Br2, H2O, and O2. While the bromine GAE appears to be the most effective among single gases in etching chrome, the quartz transmission after chrome removal remains ∼50% compared with unexposed material, and residue is present. The gas mixtures NH3/Br2 and CO2/Br2 were found to reduce the amount of residue and to enhance the chromium mask etching rate compared to Br2-only etching. This enhancement occurs in a narrow range of gas partial pressures, and the FIB process may need to be optimized further. The best transmission at 193 nm UV irradiation of the FIB GAE repaired regions achieved to date with no postprocessing is ∼95% of the transmission of a blank mask. We also applied laser power to heat the area where the ion beam is incident. No increase in Cr removal rate was seen for the Br based chemistries. Some increase in removal rate was seen for Cl2+O2 and XeF2 but the overall rate with both gas and laser power was barely higher than sputtering alone.

Precise Chrome Etching in Downstream Chlorine Plasmas with Electron Depletion Through Negative Ion Production

In micropatterning down to 0.1 μm class devices, photolithography requires highly accurate microfabrication of chrome (Cr) reticle masks. In this paper we report the vertical chrome etching using electron beam (EB) resist masks in downstream chlorine plasmas, where the resist damage during etching can be suppressed because of the reduced electron density through negative ion production. Though the Cr etch rate in pure downstream plasmas was only 15 Å/min, slight oxygen addition of 1% resulted in a great increase of Cr etch rates as large as 20 times, while resist etch rates increased only twice. Though isotropic Cr etching reactions with chlorine and oxygen radicals caused undercut features, appropriate substrate biasing allows vertical patterning of 0.2 μm wide lines and spaces due to sidewall protection by redeposition of by‐products from etched Cr and resists. © 2000 The Electrochemical Society. All rights reserved.

Fountain pen nanochemistry: Atomic force control of chrome etching

In this report we demonstrate a general method for affecting chemical reactions with a high degree of spatial control that has potentially wide applicability in science and technology. Our technique is based on complexing the delivery of liquid or gaseous materials through a cantilevered micropipette with an atomic force microscope that is totally integrated into a conventional optical microscope. Controlled etching of chrome is demonstrated without detectable effects on the underlying glass substrate. This simple combination allows for the nanometric spatial control of the whole world of chemical reactions in defined regions of surfaces. Applications of the technique in critical areas such as mask repair are likely.

Molybdenum silicide based attenuated phase-shift masks

The use of phase shifting masks (PSMs) causes revolutionary improvements of the performance of existing wafer steppers. Nowadays the attenuated PSM, also referred to as halftone, is found to be most attractive, as the technique is self-aligned. Moreover, the number of additional process steps in mask fabrication is limited to a dry etching step. Typically, both focus and exposure latitudes for contact holes of 0.35 μm are improved by a factor of 1.5–2 over a conventional mask. As linewidths on mask shrink towards 1 μm (a critical dimension of 0.25 μm, at 4× magnification) and below, the required critical dimension control becomes much tighter. It becomes more and more clear that the accuracy cannot be met anymore with wet etching of chrome. Sputtered molybdenum silicide (MoSi) is easier to dry etch than chrome and is therefore an important candidate as alternative opaque material on masks. The use of MoSi for attenuated PSMs is discussed. This approach has the advantage over the use of an SOG/Cr combination in that only a single dry etch process is required to etch the stack, since both materials can be etched using fluorine based plasmas. This is in contrast to chrome/shifter attenuated masks where chrome and shifter are etched separately, either wet/dry or both dry but in different chemistries. Recently published work describes the application of a single layer of a MoSiO or MoSiON with the required opacity and phase shift, by careful tuning of the refractive index and extinction coefficient. A comparison to these so-called embedded PSMs is included. For the latter an important disadvantage is the lack of conductivity of the layer, such that an extra (sacrificial) layer is required for charge dissipation during electron-beam exposure. An intermediate solution, referred to as partially embedded, is suggested as a compromise.

The manufacture of rim phase shiftin reticles

Abstract RIM Phase Shifting is one of a number of Phase Shifting Techniques being considered to bring potential advantages of improved resolution and better process latitude to optical projection printing in the volume production of high density MB DRAMS with minimum feature sizes down to 0.3μm(1,2,3). This paper describes a production process developed under the ISL project capable of manufacturing rim shifted PSMs for use at g line, i line and DUV wavelengths. The formidable issues of inspection and repair for all types of PSMs are not discussed. The ISL technique uses quartz substrate Reactive Ion Etching, (R.I.E) for the phase shift, and wet chrome etching for the production of the rim. Optical and E-beam resists were used for reticle manufacture.

Mask fabrication for VLSI using an electron beam exposure system

This study describes the results of feature size distribution, pattern location accuracy, and level-to-level registration error on chrome master masks fabricated by an Ee−BES-40 electron beam exposure system. The system has the capability of high speed electron beam blanking at 40 MHz, the capacity for large size masks (with 6 in. mask cassettes), and an automatic cassette handling system. OEBR-100 (PGMA), as the electron beam negative resist, is used for 5 and 6 in. chrome masks. Both wet processing and dry plasma technology are used for chrome etching. Test patterns and 64 K DRAM TEG, as the practical pattern, are used in this study. More than 40 measurements are taken, uniformly distributed over 96 and 112 mm squares, and the feature size distribution is measured by a laser interferometer x–y measuring system. Pattern location accuracy and level-to-level registration error are obtained using the Ee−BES-40 quality assurance programs called market and plotmarket. market operates by scanning over the resist image of the test pattern, utilizing the normal fiducial mark location hardware. The following results are obtained: (1) Feature size distribution within the 6 in. mask: ±0.1 μm, (2) Level-to-level registration error: less than 0.1 μm. High quality masks with about 0.02 defects/cm2, and rapid throughput of ten masks in 6 h using the automatic ten cassette handling system are obtained.