Wafer edge defects are currently considered a major problem as they negatively impact device yields in integrated circuit
manufacturing, especially in immersion lithography. A primary source of edge defects is from particles of photoresist
originating from the edge bead of resist caused by spin coating. In this paper, photoresist edge bead removal (EBR) is
studied in a series of experiments using a laser and gas cleaning system. One goal of the experiments was to reduce the
edge exclusion by gradually reducing the area cleaned by the laser and gas system. Reduction of EBR width will increase
die yield. A number of varying exposure algorithms were tested, and are described along with microscope and SEM
photos of the resulting edge geometry and surface condition. Another goal of these experiments is time-efficient removal
of thick edge beads, a problem for conventional expose/develop methods. A matrix of varying laser parameters and gas
types was run to produce a best-known-method (BKM) to meet these goals.
The implementation of 193nm laser lithography for IC manufacturing is partially dependent on establishing energy efficient laser beam delivery systems of 'beamlines' in wafer steppers and other lithography and metrology tools. The objective of this work is to study the parameters that most critically impact 193nm UV energy efficiency, specifically the elimination of ozone from the beampath by providing an inert gas positive pressure ambient around the laser optics, and the use of 193nm optimized mirrors for beam delivery. An experimental 193nm laser beamline was set up with an ozone monitor and several UV detectors used throughout the optical system. 193nm-optimized laser mirrors were tested in comparison with standard laser mirrors. Three different inert gases were introduced and at various pressures while firing the laser at 50 Hz, 100 Hz, and 200 Hz reprates. Laser pulse energies are reported under these varying conditions as a function of ozone concentration. Overall laser beamline energy transmission is given as a function of laser mirror type.
This paper describes the design, operation, and performance of a small-field, step-and-repeat deep-UV projection exposure system for photoresist evaluation and advanced IC process research. Description of the basic sub-systems is given, including the 10X mirror-based projection optics, focus and dose control systems, and the control system user interface that facilitates photoresist characterization experiments. Imaging and characterization results are presented on promising 193 nm photoresist materials. Finally, future work on new resists and on a newly designed, high NA catadioptric lens (patent pending) for sub-quarter micron imaging are described.
This paper describes the use of a 193 nm surface imaging resist in a new small-field, deep-UV projection exposure system. The 193 nm surface imaging technology utilizes commercial photoresists, in conjunction with a small field step-and-repeat exposure system. Typical processing characteristics of the imaging chemistry are presented, along with a detailed description of the projection exposure system. The resist uses vapor phase silylation with oxygen RIE developing and has been shown to provide wide focus latitude and better than 0.2 micrometers resolution. The imaging system uses a catadioptric lens with 0.5 NA for 0.20 images.
Increased resolution in optical imaging is desirable for a number of important applications, including advanced integrated circuit development. In sub-micrometer optical lithography, the wavelength of the exposing radiation is a main determinant of pattern resolution, given by the Rayleigh equation R equals k1 (DOT) lambda/NA. There is an upper limit on lens numerical aperture imposed by optical design criteria; k-factors are also restricted by the physical limits of photosensitive material chemistry and practical limits of production processes; reducing the exposing wavelength is left as a logical pathway for achieving increased pattern resolution. This paper presents a novel imaging system for the use of 248 nm and 193 nm lithography. The system is designed to characterize resist materials used in advanced memory (64 Mb, 256 Mb) and high density bipolar IC manufacturing. The imaging system and its optics will be described along with process conditions used to pattern deep-UV sensitive photoresists. SEM photos of imaged wafers will be presented, and methods to further improve deep-UV pattern resolution will be discussed.
Excimer-laser-based steppers have matured to a production-worthy state. Widefield high-NA lenses have been developed and characterized for imaging down to 0.35 micron and below. Excimer lasers have attained practical levels of performance capability and stability, reliability, safety, and operating cost Excimer stepper system integration and control issues such as focus, exposure, and overlay stability have been addressed. Enabling support technologies - resist systems, resist processing, metrology and conventional mask making - continue to progress and are becoming available.
This paper will discuss specific excimer stepper design challenges, and will present characterization data from several field installations of XLS™ deep-UV steppers configured with an advanced lens design.
Krypton Fluoride exciTner laser-based wafer steppers are now expected to extend optical microlithography to sub-0. 5pra design rules in VLSI chip fabrication. The performance and operational requireraents for the excinter laser for this application are very stringent and different from conventional excimer lasers. For practical reasons the stepper requires that the spectral bandwidth of the laser be reduced to less than 3pm while the wavelength is stabilized to better than +/0. Spm. This paper will discuss these issues and the design features of such an excimer laser. This paper also addresses issues relating to the integration of this laser with a wafer stepper and operation in a wafer fabricatio''n environment
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