The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Principles of Lithography

Nanofabrication by electron beam lithography and its applications

A lithographic apparatus configured to project a patterned beam of radiation onto a target portion of a substrate is disclosed. The apparatus includes a first radiation dose detector and a second radiation dose detector, each detector comprising a secondary electron emission surface configured to receive a radiation flux and to emit secondary electrons due to the receipt of the radiation flux, the first radiation dose detector located upstream with respect to the second radiation dose detector viewed with respect to a direction of radiation transmission, and a meter, connected to each detector, to detect a current or voltage resulting from the secondary electron emission from the respective electron emission surface.

Lithographic apparatus, and device manufacturing method

The technology of high‐resolution focused ion beams has advanced dramatically in the past 15 years as focusing systems have evolved from laboratory instruments producing minuscule current densities to high current density tools which have sparked an important new process: direct micromachining at the micrometer level. This development has been due primarily to the exploitation of field emission ion sources and in particular the liquid‐metal ion source. Originally developed in the early 1960’s as a byproduct of the development of electrostatic rocket engines, the liquid‐metal ion source was adapted for focused beam work in the late 1970’s, when it was demonstrated that submicrometer focused ion beams could be produced with current densities greater than 1 A cm−2. Ions can be produced with liquid‐metal ion sources from elements including Al, As, Au, B, Be, Bi, Cs, Cu, Ga, Ge, Fe, In, Li, P, Pb, Pd, Si, Sn, and Zn. In the past decade, focused ion beam systems with liquid‐metal ion sources have had a signific...

High‐resolution focused ion beams

The dissolution behavior of a methacrylate polymer was analyzed by the Quartz Crystal Microbalance (QCM) method in order to clarify the dissolution mechanism of ArF resists and control thereof. The QCM analysis provides information on the dissolution rate and the swelling rate of the polymer film by measuring the weight change in polymer films during the development. Poly(isobornylmethacrylate-co-methacrylic acid)s were studied as a model polymer for the resist in ArF excimer laser lithography by the QCM method. It was found that an increase in the bake temperature for the film preparation decreases the dissolution rates and the swelling rates in an alkaline solution, that an increase in methacrylic acid units produces the characteristic surface and interface layers which do not depend upon the bake temperature, and that an increase in isobornylmethacrylate units produces swelling during the development.

Swelling Analysis of Methacrylate Polymers in Aqueous Alkaline Developer

A focused ion beam (FIB) technology has many advantages for submicron structure fabrication and other maskless processes. In order to develop 4–16 M(D) RAM, the FIB technology is strongly desired for its capability of submicron lithography without proximity effects.

Submicron pattern fabrication by focused ion beams

We have proposed the combination of the new transparent phase-shifting mask with the off-axis illumination, and have carried out the feasibility study on it, for the objective of the extension in optical lithography. We have demonstrated that 0.10micrometers lien pattern fabrication is achieved with sufficient process margin by applying the transparent phase-shifting mask to ArF lithography. Especially, this new technology is characterized that the resolution of isolated lien pattern in more strongly enhanced as compared with other resolution enhancement technologies, the combination of the attenuated phase- shifting mask with the off-axis illumination and the alternating phase-shifting mask technology. However, the application of the transparent phase-shifting mask is restricted within limited pattern size less than about 0.15micrometers . For applying this new technology to actual logic device patterns, we have also proposed the embedded transparent phase-shifting mask in which the transparent phase shifter and the opaque layer are assigned to the fine features and the larger features, respectively. In the next stage, we will study the application to logic device patterns.

Feasibility study of an embedded transparent phase-shifting mask in ArF lithography

Damage to silicon implanted with Si++, Au++ and Be++ ions using focused ion beams has been evaluated by a Raman microprobe technique. A quantitative evaluation of damage to ion-implanted silicon was made by comparing the intensities of Raman scattering from implanted and unimplanted areas. The minimum dose at which damage is detectable by Raman measurements is 9×1011 ions/cm2 for Au++, 7.5×1012 ions/cm2 for Si++ and 7.5×1013 ions/cm2 for Be++. From the depth distribution of the damage measured using laser lines of different wavelengths, it is inferred that damage at the near-surface region in Be++ implanted silicon is reduced by self annealing during high-dose-rate implantation and that a channeling effect causes the saturation dose in Be++ implantation to be higher than that in other ion implantations.

https://iopscience.iop.org/article/10.1143/JJAP.26.903/pdf

Characterization of Silicon Implanted with Focused Ion Beam by Raman Microprobe

Attenuated phase-shifting mask with a single-layer absorptive shifter of CrO, CrON, MoSiO or MoSiON films has been developed. The optical parameter of these films can be controlled by the condition of sputtering deposition. These films satisfy the shifter requirements, both the 180-degrees phase shift and the transmittance between 5 and 20% for i-line. MoSiO and MoSiON films also satisfy the requirement for KrF excimer laser light. Conventional mask processes, such as etching, cleaning, defect inspection and defect repair, can be used for the mask fabrication. Defect-free masks for hole layers of 64 M-bit DRAM are obtained. Using this mask, the focus depth of 0.35-micrometers hole is improved from 0.6 micrometers to 1.5 micrometers for i-line lithography. The printing of 0.2-micrometers hole patterns is achieved by the combination of this mask and KrF excimer laser lithography.

Hiroaki Morimoto

Papers

Swelling Analysis of Methacrylate Polymers in Aqueous Alkaline Developer

Submicron pattern fabrication by focused ion beams

Feasibility study of an embedded transparent phase-shifting mask in ArF lithography

Characterization of Silicon Implanted with Focused Ion Beam by Raman Microprobe

Attenuated phase-shifting mask with a single-layer absorptive shifter of CrO, CrON, MoSiO, and MoSiON film