A projection exposure apparatus including an irradiation optical system including a light source and irradiating a mask with irradiation light beams, a projection optical system for projecting an image of a pattern of the mask on a substrate, a plurality of first fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed surface with respect to the pattern of the mask in the irradiation optical system or on a plane adjacent to the same and having a center located at a plurality of positions which are eccentric from the optical axis of the irradiation optical system, a plurality of second fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed plane with respect to the incidental end of each of a plurality of the first fly-eye type optical integrators or on a plane adjacent to the same and being disposed to correspond to a plurality of the first fly-eye type optical integrators, and a light divider for dividing and causing the irradiation light beams from the light source to be incident on each of a plurality of the second fly-eye type optical integrators.

Projection exposure apparatus

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

Process gas discharged from a bypass pipe to a gas exhaust system can be prevented from diffusing back to the inside of a process chamber without having to install a dedicated vacuum pump at the downstream side of the bypass pipe. The substrate processing apparatus includes a process chamber accommodating a substrate, a gas supply system supplying process gas from a process gas source to the process chamber for processing the substrate, a gas exhaust system configured to exhaust the process chamber, two or more vacuum pumps installed in series at the gas exhaust system, and a bypass pipe connected between the gas supply system and the gas exhaust system. The most upstream one of the vacuum pumps is a mechanical booster pump, and the bypass pipe is connected between the mechanical booster pump and the rest vacuum pumps located at a downstream side of the mechanical booster pump.

Substrate Processing Apparatus

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

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

In order to markedly improve the resolution of photolithography without improving the resolution of exposure systems, the authors propose a simple and effective phase shifting mask technology. The mask has self-aligned phase shifters which do not require assistant patterns and/or complicated design of the phase shifter patterns, which are essential to the conventional phase shifting mask. The mask with a phase shifter size of 0.5 mu m reduces the width of photointensity to 60% of that without phase shifters, while keeping high contrasts. The authors have fabricated the phase shifting mask and obtained 0.2- mu m line resist patterns with a high-contrast resist profile by a KrF excimer laser stepper with resolution capability of 0.4 mu m. The proposed phase shifting mask method is extremely attractive for a future ULSI lithography tool in 256-Mb DRAM (dynamic RAM) and beyond. >

New phase shifting mask with self-aligned phase shifters for a quarter micron photolithography

A projection exposure apparatus is constituted by a first focusing optical system for focusing light from a mercury-vapor lamp as a light source, a uniforming optical system for uniforming the focused light, a second focusing optical system for focusing the uniformed light and radiating the light onto a reticle mask, and a projection optical system for projecting the light, transmitted through the reticle, onto a wafer. A special stop is arranged as a secondary source for uniformly illuminating the mask. The special stop serves to set an intensity distribution within the exit plane of the secondary source so that intensities of both peripheral and central portions are larger than an intensity of an intermediate portion. In addition, the apparatus includes a halftone mask which allows an amplitude transmittance T of the translucent film and an amplitude transmittance T0 of the light-transmitting substrate to satisfy 0.01×TO<or=T<or=0.30×TO. The phase difference between light passing through the light-transmitting substrate is represented by 180×(2n+1)+or -30 (degree) (where n is an integer).

Projectin exposure apparatus

In order to improve remarkably the resolution of photolithography without improving the resolution of exposure systems, we propose a new simple and effective phase shifting mask technology. The new mask has self-aligned phase shifters to need no assistant patterns and no complicated designing the phase shifter patterns, which are essential to the conventional phase shifting mask. The new mask with phase shifter size of 0.5μm reduces the width of photo-intensity to 60% of that without phase shifters, while keeping high contrasts. We have succeeded in fabricating the new phase shifting mask and obtained 0.2pm line resist patterns with a high contrast resist profile even by a KrF excimer laser stepper with the resolution capability of 0.4μm. This new method is extremely attractive for enhancing optical lithography resolution in ULSI region.

Optimization for various phase-shifting masks to fabricate 0.25-µm isolated resist patterns was carried out, and their performances were compared among themselves by simulation. They were evaluated under the assumptions that isolated patterns were located on the same layer with 0.25-µm lines and spaces with the Levenson-type phase-shifters and that the exposure dose was adjusted to the dense patterns. It was found that isolated patterns need to be designed with regard to unavoidable errors in the feature size. None of the isolated line masks studied is effective in improving resolution, except in the case where the Levenson-type phase shifter (shifter edge) can be located. All isolated space masks with optimized dimensions, in contrast, are effective in improving depth of focus for the 0.25-µm isolated pattern.

Simulation Study on Phase-Shifting Masks for Isolated Patterns

When an alignment mark and first and second overlay deviation inspection marks as well as a device pattern are successively formed on a wafer using a first photomask and a second photomask, each of the alignment mark and the overlay deviation inspection marks are formed to have a part of the device pattern or marks having sizes and shapes similar to those of the device pattern, whereby these marks receive a deviation error caused by the influence given by the aberration of the light projection optical lens used for performing the pattern transfer and an error in the following processing steps in substantially the same degree as the device pattern, and an amount of the overlay deviation error is measured correctly so as to achieve an alignment of the photomasks in a high accuracy.

Takashi Sato

Papers

New phase shifting mask with self-aligned phase shifters for a quarter micron photolithography

Projectin exposure apparatus

New phase shifting mask with self-aligned phase shifters for a quarter micron photolithography

Simulation Study on Phase-Shifting Masks for Isolated Patterns

Alignment method, overlay deviation inspection method and photomask