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

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 charged particle beam includes: a computer that controls a needle actuating mechanism so as to approach a needle to a sample piece using a template formed from an absorbed current image obtained by irradiating the needle with a charged particle beam and a tip coordinate of the needle acquired from a secondary electron image obtained by irradiating the needle with the charged particle beam.

Charged particle beam apparatus

We investigate poly(methylmethacrylate) (PMMA) development processing with cold developers (4–10 °C) for its effect on resolution, resist residue, and pattern quality of sub-10 nm electron beam lithography (EBL). We find that low-temperature development results in higher EBL resolution and improved feature quality. PMMA trenches of 4–8 nm are obtained reproducibly at 30 kV using cold development. Fabrication of single-particle-width Au nanoparticle lines was performed by lift-off. We discuss key factors for formation of PMMA trenches at the sub-10 nm scale.

/pdf/sub-10-nm-electron-beam-lithography-using-cold-development-1ez0lpse16.pdf

Sub-10 nm electron beam lithography using cold development of poly(methylmethacrylate)

In a semiconductor circuit device fabricating process in which a reduction image projection exposure apparatus and an electron beam exposure apparatus are in a mixed use in its exposure process, pattern position shift errors for each exposure apparatus are measured and corrected at the time of drawing by means of an electron beam drawing apparatus, thereby enhancing the alignment accuracy First, a pattern for measuring position shifts is exposed using a stepper and the electron beam drawing apparatus Then, the position shift errors are measured using an identical coordinate position measuring device Accidental errors have been mixed in the measurement result at this time On account of this, measurement data at a certain point are smoothed by taking a summation average with data on the periphery thereof, thus decreasing influences of the accidental errors Moreover, by inverting positive or negative signs of the data on the position shift errors, the data are made into correction data Then, the correction data are stored When an exposure is performed by the electron beam drawing apparatus with the pattern exposed by the stepper as a reference, the correction data for the two apparatuses are transferred to the electron beam drawing apparatus, the two data are added to detected mark positions, and at positions after the addition, pattern position shifts within a wafer surface are determined At the time of exposure, the exposure is performed at positions obtained by subtracting the correction data from the determined pattern position shifts This method makes it possible to correct both position shift errors within the wafer surface due to the stepper and position shift errors due to the electron beam drawing apparatus, thus allowing the alignment accuracy to be enhanced Also, this result makes it possible to enhance yield for products in the fabricating process

Method of fabricating semiconductor circuit devices utilizing multiple exposures

This article proposes a new method for proximity effect correction that utilizes newly developed hardware. The correction algorithm modifies the exposure dose for each exposure point by referring to a pattern area density map. The only additional process in this method is virtual exposure to make the map. The virtual exposure is carried out once at the first use of the large‐scale integration circuit pattern and can be processed in only 30 s. The pattern area density map makes it possible to correct the proximity effect from the lower‐level patterns by the new map calculated from the two maps of lower level and exposing level. The usefulness of this method is verified by experiments using model patterns.

Fast proximity effect correction method using a pattern area density map

The role of ion bombardment in field emission current instability is clarified experimentally by varying the emission current level and pressure over a wide range. It is found that bombarding ions sputter-off adsorbed gas molecules on the emitter surface and this causes field emission current fluctuation. This current fluctuation caused by ion bombardment is larger than that caused by gas molecule migration when the product of the pressure and the emission current is higher than 7×10-12 PaA. The relative fluctuations turn out to be the logarithm of the product of the pressure and the emission current. The ions are mainly generated close to the emitter due to electron collisions with residual gas.

https://iopscience.iop.org/article/10.1143/JJAP.21.1513/pdf

Role of Ion Bombardment in Field Emission Current Instability

An electron‐beam exposure system HL‐800D has been developed for the mass production of both quarter micron large‐scale integrated memories and application specific integrated circuits (ASICs). To achieve a productive level of throughput, the system utilizes a cell‐projection method combined with variable shaped method and a continuously moving stage at variable speed depending on the pattern density. The system is operated at a 50 kV acceleration voltage and a 1 μC/cm2 dosage. Three stage deflectors have been developed to assure high‐speed deflection and highly accurate positioning. A fast pattern controller generates patern data at 200 ns shot‐cycle‐time with the positioning error correction and proximity effect correction. A high‐speed ceramic XY stage and an automatic wafer loder have been developed. The system is operated by a workstation which also provides data conversion. The estimated throughput of the system is 11 wafers/h for 0.3 μm ASICs and 20 wafers/h for quarter micron memories.

Electron‐beam cell‐projection lithography system

A technique and exposure apparatus measures, with a high degree of accuracy, figure and placement errors of individual optical elements constituting optics embedded inside of an exposure apparatus or the like, with the optics kept in an embedded state as they are. The system measures the distribution of wavefront distortions in the optics while changing the positions of a light source and an image point inside an exposure field of the optics being observed. Optimal displacements of reflective surfaces constituting the optics are then found by calculation based on the measured distribution of wave-front distortions. Finally, the positions of the reflective surfaces are corrected in accordance with the calculated optimal displacements. The positions of the reflective surfaces are corrected by individually controlling displacements output by a plurality of actuators attached to each reflective surface and by mechanically modifying appropriate portions of the reflective surfaces.

Norio Saitou

Papers

Method of fabricating semiconductor circuit devices utilizing multiple exposures

Fast proximity effect correction method using a pattern area density map

Role of Ion Bombardment in Field Emission Current Instability

Electron‐beam cell‐projection lithography system

Methods for measuring optical system, and method and apparatus for exposure using said measuring method