In this paper the possibilities of focused ion beam (FIB) applications in microsystem technology are reviewed. After an introduction to the technology and the operating principles of FIB, two classes of applications are described. First the subject of FIB for microsystem technology inspection, metrology and failure analysis is outlined. A procedure for cross sectioning on samples is presented, as well as some examples of how this technique can be applied to study processing results. The second part of the paper is on the use of FIB as a tool for maskless micromachining. Both subtractive (etching) and additive (deposition) techniques are discussed, as well as the combination of FIB implantation of silicon with subsequent wet etching. We will show the possibility to fabricate three-dimensional structures on a micrometre scale, and give examples of recent realizations thereof.

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A review of focused ion beam applications in microsystem technology

Methods for forming or patterning nanostructure arrays are provided. The methods involve formation of arrays on coatings comprising nanostructure association groups, formation of arrays in spin-on-dielectrics, solvent annealing after nanostructure deposition, patterning using resist, and/or use of devices that facilitate array formation. Related devices for forming nanostructure arrays are also provided, as are devices including nanostructure arrays (e.g., memory devices). Methods for protecting nanostructures from fusion during high temperature processing are also provided.

Methods and devices for forming nanostructure monolayers and devices including such monolayers

A method and apparatus for electron beam processing using an electron beam (101) activated gas to etch or deposit material. The invention is particularly suitable for repairing defects in lithography masks. By using an electron beam (101) in place of an ion beam, the many problems associated with ion beam mask repair, such as staining and riverbedding, are eliminated. Endpoint detection is not critical because the electron beam and gas will not etch the substrate. In one embodiment, xenon ditluoride gas is activated by the electron beam (101) to etch a tungsten, tantalum nitride, or molybdenum silicide film on a transmission or reflection mask. To prevent spontaneous etching by the etchant gas in processed sites at which the passivation layer was removed, processed sites can be re-passivated before processing additional sites.

Electron beam processing

Extreme ultraviolet lithography (EUVL) and three dimensional integrated circuit (3D IC) were thoroughly reviewed. Since proposed in 1988, EUVL obtained intensive studies globally and, after 2000, became the most promising next generation lithography method even though challenges were present in almost all aspects of EUVL technology. Commercial step-and-scan tools for preproduction are installed now with full field capability; however, EUV source power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 200 W in-band power at IF, current tools can supply only approximately 40–55 W. EUVL resist has improved significantly in the last few years, with 13 nm line/space half-pitch resolution being produced with approximately 3–4 nm line width roughness (LWR), but LWR needs 2× improvement. Creating a defect-free EUVL mask is currently an obstacle. Actual adoption of EUVL for 22 nm and beyond technology nodes will depend on the extension of current optical lithography (193 nm immersion lithography, combined with multiple patterning techniques), as well as other methods such as 3D IC. Lithography has been the enabler for IC performance improvement by increasing device density, clock rate, and transistor rate. However, after the turn of the century, IC scaling resulted in short-channel effect, which decreases power efficiency dramatically, so clock frequency almost stopped increasing. Although further IC scaling by lithography reduces gate delay, interconnect delay and memory wall are dominant in determining the IC performance. 3D IC technology is a critical technology today because it offers a reasonable route to further improve IC performance. It increases device density, reduces the interconnect delay, and breaks memory wall with the application of 3D stacking using through silicon via. 3D IC also makes one chip package have more functional diversification than those enhanced only by shrinking the size of the features. The main advantages of 3D IC are the smaller form factor, low energy consumption, high speed, and functional diversification. EUVL, if adopted, will continue to enable IC performance improvement at a slower rate, but 3D IC provides an alternative way to improve the system performance. The best scenario is the adoption of both EUVL and 3D IC. However, the possible further delay of EUVL could enhance the realization of 3D IC for IC system improvement.

Extreme ultraviolet lithography and three dimensional integrated circuit—A review

To provide a reflective mask blank for EUV lithography having an absorber layer, which presents a low reflectance to a light in the wavelength ranges of EUV light and pattern inspection light, and which is easily controlled to have desired film composition and film thickness. A reflective mask blank for EUV lithography, comprising a substrate, and a reflective layer for reflecting EUV light and an absorber layer for absorbing EUV light formed in this order on the substrate, wherein the absorber layer contains tantalum (Ta), boron (B), silicon (Si) and nitrogen (N), and in the absorber layer, the B content is at least 1 at% and less than 5 at%, the Si content is from 1 to 25 at%, and the compositional ratio of Ta to N (Ta:N) is from 8:1 to 1:1.

Reflective mask blank for euv lithography

An ion beam structure includes a gas container (16), such as a cylindrical can having first (12) and second apertures (14) through the center of the top and bottom walls respectively of the container such that a narrow ion beam (20) is passed through the apertures and the center axis of the can and onto a target specimen (22) such as a mask or chip or other article of manufacture disposed closely below the bottom of the can The can may further include deflection (42) means for applying voltages and/or magnetic fields to locations on the can (ie, top, bottom, sides) to direct secondary charged particles such as electrons emitted from the specimen onto an electron detection means (30) such that the structure functions as an imaging system The electric and/or magnetic fields may be employed to increase the collection efficiency of the detector and thereby improve the quality of the image by increasing the signal to noise ratio When the collected image produced by the secondary charged particles indicates that a repair or other modification be performed, a gas is introduced into the can from a gas reservoir (24) via a tube The gas, which contains first type particles (ie gold atom, tungsten atom, etc) leaves the can via the bottom aperture and is adsorbed onto the nearby target specimen surface The ion beam, containing second type particles (ie gallium ions) passes through the gas with minimum interaction and strikes the target specimen surface to decompose the adsorbed gas and the decomposed first type particles to provide the modification such as repair to the specimen (mask or chip) surface

Gas delivery for ion beam deposition and etching

A method for marking a mask set to insure minimum mismatch between the masks when they are assembled into a set. Each mask in the set is evaluated against a known fixed standard, identified and marked such that when the set is assembled and utilized to produce an integrated circuit minimum mismatch between each element in each mask in the set will be realized.

Mask set mismatch

Currently the mask blanks used in extreme ultraviolet lithography cannot be fabricated free of defects. A rapid method of determining the optimum placement of mask patterns on the blank to avoid these defects is described. Using this method, the probability of fabricating defect-free masks, when the pattern is (1) randomly placed on the mask blank or (2) positioned optimally to avoid defects, is determined for a variety of integrated circuit designs, defect densities, and defect sizes. In addition to circular defects, oval and clusters of defects are also considered. Finally, simple analytical expressions for the probability of obtaining a defect-free mask in the case of random placement of the mask pattern is presented and compared to Monte Carlo simulations.

Mitigation of extreme ultraviolet mask defects by pattern shifting: Method and statistics

An extreme ultraviolet lithography (EUVL) mask structure and associated method of formation. A first conductive layer is provided between a buffer layer and an absorber layer such that the buffer layer is on a multilayer stack. The multilayer stack is adapted to substantially reflect EUV radiation incident thereon. The absorber layer is adapted to absorb essentially all of EUV radiation incident thereon. A mask pattern is formed in the absorber layer. Formation of the mask pattern in the absorber layer is accompanied by inadvertent formation of a defect in the absorber layer. The defect is subsequently repaired. The mask pattern may be extended into the first conductive layer and into the buffer layer in a substantially defect-free process that exposes a portion of the multilayer stack. A second conductive layer may be provided on the absorber layer, wherein the mask pattern is also formed in the second conductive layer.

EUVL mask structure and method of formation

A transmission grid is disposed in a conventional focussed ion beam system which includes an ion beam source emitter or ion gun, electrodes to turn the ion beam off and on, a beam defining aperture and electrostatic lenses to focus the ion beam onto a target. The elements of the ion beam system are disposed in a chamber which is provided with an inlet port and an outlet port. Gas is introduced into chamber via the inlet port where it is ionized by the ion beam into an ion plasma to be used to deposit materials onto the target. The transmission grid, is interposed which is a fine mesh, passive element is located in the path of the ion beam and reduces the ion beam current density by a desired value. The transmission grid may be configured with a variety of different transmissions so the current density can be adjusted in different increments depending on the gas/type of deposition to be performed.

James P. Levin

Papers

Gas delivery for ion beam deposition and etching

Mask set mismatch

Mitigation of extreme ultraviolet mask defects by pattern shifting: Method and statistics

EUVL mask structure and method of formation

Grid structure for reducing current density in focussed ion beam