J. P. Silverman

Design and performance of an x‐ray lithography beam line at a storage ring

A beam line for x‐ray lithography using synchrotron radiation (SR) has been built at the VUV storage ring of the National Synchrotron Light Source and is now in operation. The high intensity and good collimation of SR overcome the problems of low throughput and resolution‐limiting penumbra associated with using conventional x‐ray sources. The design of a beam line for SR has to deal with two problems. First, the beam line must meet the ultrahigh vacuum standards of the storage ring, and second, the emitted radiation is horizontally uniform but very nonuniform vertically. The beam line optics consist of an oscillating cylindrical mirror that scans the reflected light vertically over the exposure area and collimates the incident radiation horizontally, thus increasing the intensity by a factor of 3. We will describe the vacuum system, the beryllium window that separates the exposure chamber from the beam line, and the vacuum protection of the ring. We will show the measured uniformity of illumination. The e...

Synchrotrom radiation X-ray lithography☆

Abstract X-ray lithography is a shadow printing technique which uses X-rays to transfer a pattern from a mask into a resist-coated wafer. Synchrotron radiation from a storage ring has advantages over the radiation from conventional X-ray sources for this purpose, since it is 2 to 4 orders of magnitude more intense and its natural collimation virtually eliminates penumbra and run-out errors. To take advantage of synchrotron radiation, we have built a beamline for X-ray lithography at the VUV storage ring of the NSLS. This beamline was designed to meet two major requirements: vacuum isolation from the UHV in the storage ring and uniform illumination over the exposure area, to achieve good linewidth control in the resist pattern. To achieve uniform illumination in the vertical direction, we use a scanning grazing-incidence mirror that sweeps the beam over the exposure area. This mirror also collimates horizontally to maximize the exposure flux. In this paper we will describe the basic design including optics, beryllium window and the calculated spectral power distribution. The performance of the beamline will be discussed in terms of experimentally achieved uniformity of illumination, mask contrast and mask substrate transmission, exposure flux and exposure flux and exposure times and resolution. With PMMA resist, features down to 0.25 μm have been copied with an aspect ratio of 16 to 1 using a 40 μm mask to wafer separation. The ultimate resolution is limited by diffraction. We have begun to study a variety of resists to evaluate their suitability for X-ray lithography.

Performance of a wide‐field flux delivery system for synchrotron x‐ray lithography

An x‐ray flux delivery system consisting of a compact storage ring and dedicated beamlines is now in routine use in the IBM Advanced Lithography Facility in East Fishkill, New York. The beamlines have been designed for use with a stepper that scans the mask and wafer vertically through a stationary beam. The performance of the system from a lithographic standpoint is reported. The measured size and stability of the synchrotron x‐ray source will be presented, and the design and performance of the beamlines will be discussed. The beamlines have been designed to provide high intensity, uniform illumination over a wide field. The overall performance of the system has been evaluated by measuring the flux at the mask plane in the stepper. A horizontal uniformity of better than ±2% over a field more than 50 mm wide has been achieved; the vertical uniformity is limited by the uniformity of the stepper scanning mechanism. The delivered mask‐incident flux per milliampere of stored beam current has been found to be ...

Synchrotron Radiation X-Ray Lithography: Recent Results

A beamline for making X-ray lithography exposures using synchrotron radiation has been built and is now in routine operation at Brookhaven National Laboratory. The beamline, its optics, and its control system are described, and results are presented showing the intensity and uniformity of the radiation at the wafer. Results of exposures in a variety of resists are shown and discussed.

X-Ray Lithography Exposures Using Synchrotron Radiation

A beamline for making X-ray lithography exposures using synchrotron radiation has been built and is now in operation at Brookhaven National Laboratory. The characteristics of synchrotron radiation and the reasons for using such a source are discussed. A description of the beamline and its control system is given, and results of early exposures are presented.

Conventional novolak resists for storage ring x‐ray lithography

This paper describes the lithographic processing of several positive novolak‐based resists exposed on the IBM x‐ray lithography system at the Brookhaven National Laboratory 750 MeV storage ring. One of the advantages of the storage ring exposure system has been the ability to use resist development processes which are the same as the corresponding optical or e‐beam processes. The exposure system and the x‐ray mask used for resist evaluation are described elsewhere in this symposium. Determining the best process conditions requires consideration of mask contrast as well as the desired linewidth and profile control, particularly in the presence of topography. Data will be presented and compared with results obtained using other lithographic systems (i.e., e‐beam and conventional source x‐ray). In particular, the relationship of mask absorber thickness to process window will be presented using a simple model of the development process. Using the process window defined by this model, we have exposed test patt...

X-ray lithography beamlines in the IBM advanced lithography facility

In 1991 a storage ring designed as a source of X-rays for X-ray lithography was delivered, installed, and commissioned in the IBM Advanced Lithography Facility (ALF) in East Fishkill, New York. Beamlines of two different designs have been constructed and installed on the ring to deliver the X-rays to the exposure stations. One design is intended for use with a stepper for the fabrication of integrated circuits. The second design is for a general-purpose research and development beamline which is used for unaligned exposures as well as for characterization of beamline components. The design and performance of both are described. Special attention is given to a paraboloid mirror optical system which is used to collimate the radiation from the storage ring. Both the theoretical and the measured performance of the mirror are presented and shown to be in excellent agreement. An exposure nonuniformity of less than ±3%, including contributions from both the mirror and the beryllium exit window, has been achieved.

Evaluation of the Defense Advanced Lithography Program (DALP) x-ray lithography aligner

A state-of-the-art proximity x-ray lithography aligner was developed for the Defense Advanced Lithography Program (DALP) and installed in IBMs Advanced Lithography Facility (ALF) in 1995. This aligner was designed to satisfy the manufacturing requirements for 250 and 180 nm groundrule electronic devices, such as 256 Mbit and 1 Gbit DRAMs, while connected to synchrotron beamlines which use scanning beam systems for x- ray flux delivery. The aligner uses an innovative x-ray image sensor (XRIS) to align the mask by detecting its x-ray actinic image, and uses an off-axis alignment system, similar to the alignment system used in Micrascan-II, to align the wafer. As a result, the same wafer alignment marks can be used by either tool. This facilitates the mix and match between the x-ray aligner and Micrascan-II optical steppers. A stabilized helium environment is maintained from the beryllium window of the beamline to the exposure plane, including the gap between mask and wafer. The aligner can accept x-ray masks that conform to NIST standards, and has a maximum exposure field of 50 mm by 50 mm. The important lithography performance parameters, i.e., overlay, linewidth control and throughput, have been evaluated. The test methodologies and their results are presented in detail. Potential improvements of the systems performance will also be discussed.

X-ray lithography: overview and outlook

Summary form only given. The authors describes X-ray lithography (XRL) and current results from various laboratories around the world. The status and challenges associated with the various technology elements (the source, the optics, the aligner, the mask, and the photoresist) are discussed. Finally, the outlook for successfully inserting XRL into semiconductor manufacturing are assessed.