Robert P. Rippstein

X‐ray stepper exposure system performance and status

An integrated x‐ray align and expose system has been installed at Brookhaven National Laboratory National Synchrotron Light Source VUV beam line U2. The system includes the first commercially available x‐ray align and expose system, the Karl Suss XRS‐200 and matched beamline. Subsystem and aligned exposure tests were performed to characterize the entire system. Initial results are presented for key lithographic properties as well as throughput. Improvements and future activities are also described.

Imaging capabilities of proximity X-ray lithography at 70 nm ground rules

This paper discusses the resolution capabilities of proximity x-ray lithography (PXRL) system. Exposure characteristics of features designed at 150 nm pitch size: 75 nm dense lines with 1:1 duty ratio, 2D features at 1:1 and 1:2 duty ratios and isolated lines have been studied. Aerial image simulations were compared to the experimental data. Verification of the aerial image model has been accomplished by measurements of exposure windows of 100 nm and 125 nm nested lines. The PXRL aerial image parameter, equivalent penumbra blur, has been determined from the experimental data. Contributions from the synchrotron radiation x-ray source, stepper and the chemically amplified resist to the degradation of the aerial image have been evaluated. Patterning capability of PXRL at 75 nm feature size is compared to projection optics using the optical k1 factor as a common figure of merit. To facilitate the comparison, optical imagin was at pattern sizes currently manufacturable by the mainstream optical tools while the PXRL imaging was at 75 nm pattern size. Requirements for a PXRL system of manufacturing VLSI at 70 nm minimum feature sizes with the critical dimension control better than 10 percent are also discussed.

Novel single mirror condenser for x‐ray lithography beam lines

In proximity x‐ray lithography (XRL), two types of illumination are used: full field and scanning. We describe a single mirror condenser for XRL beam lines which provides a high flux of soft x rays. The surface is generally aspheric, designed using numerical methods, and described by polynomials. The flexible design approach can be used to find a result with specific imaging characteristics according to the various requirements of the beam line, and thus is of more general application. The performance of the designed condenser is verified with ray tracing. For advanced submicron applications, mirror scanning is preferred because of its higher scanning speed. However, with figured mirrors, a small change of grazing angle may cause a large variation of image shape, so that to provide a uniform beam, the scanning of the mirror is compensated by a lateral shift. A uniform exposure of 50×50 mm2 field can be achieved.

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 ...

Overlay performance of 180 nm ground rule generation x-ray lithography aligner

The 180 nm ground rule production prototype x-ray lithography aligner was developed for the Defense Advanced Lithography Program (DALP) and installed in IBM’s Advanced Lithography Facility (ALF) in 1995. This aligner is designed to satisfy the manufacturing requirement for 250 and 180 nm ground rule electronic devices, such as 256 Mbit and 1 Gbit dynamic random access memories. The acceptance evaluation of this aligner was presented elsewhere (Ref. 12). 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™ (a trademark of Silicon Valley Group Lithography), to align the wafer. From subsystem testing, the alignment repeatability of XRIS is not a significant contributor to the aligner’s contribution of overlay error. As a result, the x-ray alignment sensor technology can be used for future generations of x-ray lithography aligners. This article will specifical...

Design of synchrotron x-ray lithography beamlines

X-ray lithography using a synchrotron light source has received considerable attention in recent years as a method for producing semiconductor device dimensions smaller than 0.35 microns. A number of synchrotrons or Electron Storage Rings (ESR) have been built around the world as possible light sources for lithographic applications. IBM has built its Advanced Lithography Facility (ALF) for the purpose of exploring synchrotron based X-ray lithography for device manufacturing. The ALF has the superconducting HELIOS compact storage ring, built by Oxford Instruments Ltd, at its center. The subject of the present paper is the design of the beamlines which connect this synchrotron light source to the Step- and- Repeat Aligner/exposure (SRA) tool where the device wafers are exposed to the synchrotron light.

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.

ACLV control in x-ray lithography

In this paper, dimensional control of critical features in proximity x-ray lithography is discussed. CD error components attributed to x-ray mask, proximity exposure and resist process are identified. Analysis of linewidth control data at 180 nm and 150 nm ground rules for synchrotron based x-ray proximity lithography is presented. Data have been collected at IBM Advanced Lithography Facility equipped with x-ray stepper built by SVGL and Helios synchrotron radiation x-ray source.