Laser produced plasma (LPP) systems have been developed as the primary approach for use in EUV scanner light sources for optical imaging of circuit features at 20nm nodes and beyond. This paper provides a review of development progress and productization status for LPP extreme-ultra-violet (EUV) sources with performance goals targeted to meet specific requirements from ASML. We present the latest results on power generation and collector
protection for sources in the field operating at 10W nominal power and in San Diego operating in MOPA (Master Oscillator Power Amplifier) Prepulse mode at higher powers. Semiconductor industry standards for reliability and source availability data are provided. In these proceedings we show results demonstrating validation of MOPA Prepulse operation at high dose-controlled power: 40 W average power with closed-loop active dose control meeting the requirement for dose stability, 55 W average power with closed-loop active dose control, and early collector
protection tests to 4 billion pulses without loss of reflectivity.
Laser produced plasma (LPP) systems have been developed as the primary approach for the EUV scanner
light source for optical imaging of circuit features at sub-22nm and beyond nodes on the ITRS roadmap. This
paper provides a review of development progress and productization status for LPP extreme-ultra-violet
(EUV) sources with performance goals targeted to meet specific requirements from leading scanner
manufacturers. We present the latest results on exposure power generation, collection, and clean transmission
of EUV through the intermediate focus. Semiconductor industry standards for reliability and source
availability data are provided. We report on measurements taken using a 5sr normal incidence collector on a
production system. The lifetime of the collector mirror is a critical parameter in the development of extreme
ultra-violet LPP lithography sources. Deposition of target material as well as sputtering or implantation of
incident particles can reduce the reflectivity of the mirror coating during exposure. Debris mitigation
techniques are used to inhibit damage from occuring, the protection results of these techniques will be shown
over multi-100's of hours.
This paper describes the development of laser-produced-plasma (LPP) extreme-ultraviolet (EUV) source
architecture for advanced lithography applications in high volume manufacturing. EUV lithography is
expected to succeed 193 nm immersion technology for sub-22 nm critical layer patterning. In this paper we
discuss the most recent results from high qualification testing of sources in production. Subsystem
performance will be shown including collector protection, out-of-band (OOB) radiation measurements,
and intermediate-focus (IF) protection as well as experience in system use. This presentation reviews the
experimental results obtained on systems with a focus on the topics most critical for an HVM source.
Laser produced plasma (LPP) systems have been developed as a viable approach for the EUV scanner light sources to
support optical imaging of circuit features at sub-22nm nodes on the ITRS roadmap. This paper provides a review of
development progress and productization status for LPP extreme-ultra-violet (EUV) sources with performance goals
targeted to meet specific requirements from leading scanner manufacturers. The status of first generation High Volume
Manufacturing (HVM) sources in production and at a leading semiconductor device manufacturer is discussed. The
EUV power at intermediate focus is discussed and the lastest data are presented. An electricity consumption model is
described, and our current product roadmap is shown.
With the advent of advanced 193 nm systems processing 300 mm wafers, the production lithography cell is about to undergo a technology shift. This is because processing 300 mm wafers requires introduction of several new technologies. These include technologies that enable increasing light source power at 193 nm - the NA of the projection lens and the speed of scanner stages. Coupled with the need to maintaining high wafer throughput, the scanners must also deliver very tight CD control to within few nm, (typically less than 3 nm). Cymer, Inc. believes that certain key technologies - traditionally ignored at 248 nm for 200 mm wafers - must be revisited. This paper pertains to one such technology: the mechanism to deliver stable light from the light source to the input of the scanner. We refer to this as the Beam Delivery Unit (BDU). To support these changes, Cymer has developed a BDU that will guarantee a stable beam at the scanner entrance, during exposure. There are three aspects to beam stability: 1. Optical transmission, 2. Beam positioning and, 3. Beam angle. Position stability impacts dose stability (energy per pulse integrated over several pulses) at the wafer and pointing instability adversely affects the illumination uniformity at the reticle. To the lithography process engineers, the effects of beam stability are not new; both result in loss of CD control. At 130 nm node, the loss of CD control due to beam instability was insignificant, therefore ignored. However, below that node, we will show that unless the beam exiting the BDU is stabilized in position and pointing, the loss in CD control is of the order or 1 nm, which is a significant portion of the total CD control budget. For example, for MPU gate node of 65 nm, the ITRS roadmap allocates CD control of 3.7 nm. Thus, the 1 nm loss of CD control due to aforementioned instability alone is considered to be very significant. To address this critical loss in CD control, Cymer has implemented a novel beam stabilization control system in the BDU. Such beam stabilization maintains beam position and pointing during exposure of a die of a wafer, virtually eliminating CD control errors. Cymer has also incorporated reliable BDU materials technology that maintains stable transmission over several years of operation. Cymer's beam stabilization control system is the subject of this paper.
With the advent of 193 nm systems processing 300 mm wafers, the production lithography cell is about to undergo a technology shift. The mechanism for delivering the beam from the light source to the illumination system, here referred to as a Beam Delivery Unit (BDU), must change to meet the challenges imposed by this shift. To support these changes, Cymer is developing a BDU that will guarantee a stable beam at the scanner entrance during exposure. The beam stabilization control system has been implemented in a test BDU. We shall present results from experiments that demonstrate our ability to significantly improve short and long term “Beam Stability”.
Excimer lasers are now being used in the manufacturing ofultra-large scale integrated devices that require feature widths ofless than O.25?m. The excimer laser for microlithography, since its introduction in 1987 has evolved from a laboratory instrument to a manufacturing tool. We will trace the history of the excimer laser in this industry and explain why it is and remains the total solution for the present and for many years in the future.
Exposure tools for 193nm lithography are expected to use Argon-Fluoride lasers at repetition rates of at least 2kHz. We are showing that, by revisiting several key technologies, the performance and reliability of ArF lasers at 2 kHz are trending towards a level comparable to KrF lasers.
Exposure tools for 248nm lithography have reached a level of maturity comparable to those based on i-line. With this increase in maturity, there is a concomitant requirement for greater flexibility from the laser by the process engineers. Usually, these requirements pertain to energy, spectral width and repetition rate. By utilizing a combination of laser parameters, the process engineers are often able to optimize throughput, reduce cost-of-operation or achieve greater process margin. Hitherto, such flexibility of laser operation was possible only via significant changes to various laser modules. During our investigation, we found that the key measure of the laser that impacts the aforementioned parameters is its F2 concentration. By monitoring and controlling its slope efficiency, the laser's F2 concentration may be precisely controlled. Thus a laser may tune to operate under specifications as diverse as 7mJ, (Delta) (lambda) FWHM < 0.3 pm and 10mJ, (Delta) (lambda) FWHM < 0.6pm and still meet the host of requirements necessary for lithography. We discus this new F2 control technique and highlight some laser performance parameters.
The phenomenon of compaction of fused silica is a major concern in 193nm lithography. Numerous studies have shown that as a result, the cost-of-operation of 193nm lithography is expected to be significantly higher than at 248nm due to the degradation of scanner optics. Recent studies have also shown that compact could be reduced by increasing the pulse length of the ArF laser since the magnitude of compaction reduced as 1/(Tis)0.6. Here, Tis is the integral square pulse duration and is given.
We report the performance of a very high repetition rate ArF laser optimized for next generation, high NA, high throughput scanner. The laser's repetition rate exceeds 4kHz, at 5mJ, and at bandwidths of less than 1.2 pm. We discuss the complexity of high power operation, and make some estimates about the robustness of this technology. In particular, we discuss the risks of scaling to this high repetition rate, and prospects of exceeding 4kHz to near 6kHz with 95 percent bandwidths of less than 1pm.
The spectral shape requirements for an ArF laser for 193 nm microlithography are expected to be about 2X tighter than at 248nm. This is in part due to the dispersion of fused silica and CaD2 at 193nm and in part due to the push by the lens designers towards higher NA lenses. However, unlike 248nm, it is likely that the process engineer may not be satisfied with simple spectral bandwidth measurements of Full-Width-At-Half-Maximum. Instead, the knowledge of the compete spectral shape may be required, since it is the total shape that has an impact on the lens performance. This requirement may have significant impact on corresponding metrology tools. These tools should be either portable or built into the laser. They should be able to provide continuous feedback to the process engineer as far as the lens performance is considered. Present paper discuses recent developments in 193nm metrology which can be implemented as a part of laser on-board diagnostics or as a field service tool, and is capable of accurately measuring the laser spectrum shape. This information, together with propriety lens parameters, will allow process engineer to accurately evaluate the aberrations due to the laser line shape.
A molecular fluorine laser, specifically tailored for photolithography needs, was developed. Single line operation at 157.6nm was achieved by means of a prism assembly. Laser operation at repetition rates up to 1 kHz without signs of power saturation results in an average power of 15W. The energy stability was equal to comparable ArF laser. Proper choice of materials and corona pre-ionization enabled gas lifetimes in line with current ArF laser technology, without any need for cryogenic purification.
Now that 1000 Hz KrF excimer laser based DUV lithography tools are firmly established in production, emphasis is shifting from development towards improving the productivity and profitability of the manufacturing process, thereby reducing the cost per wafer. In this arena, laser manufacturers are competing now not only on performance but also on cost and productivity enhancements that the laser can offer to the lithography process.
Today, commercial line-narrowed ArF lasers for Deep-UV lithography are typically producing spectral bandwidth of 0.6 pm FWHM. This value forces the stepper/scanner manufacturers to use large amount of CaF2 in the lens design as well as fused silica in order to compensate for chromatic aberrations. We describe in this paper the parameters - such as pulse duration, fluorine concentration and divergence - which influence the line-narrowing efficiency of ArF laser. We are also presenting result obtained using a new optical cavity design using an etalon as output coupler that provides bandwidth of 0.3 pm at FWHM and 0.8 pm for 95 percent of the energy, performance that could allow to greatly reduce the need for CaF2.
The use of higher NA lenses of next generation 248 nm microlithography system sets tight requirements on the spectral purity of the laser, especially because these lenses are not chromatically corrected. Present day KrF excimer lasers are equipped with etalon-based spectrometers that can measure the laser linewidth at full-width-at-half maximum, at nearly every pulse. Both, experience and analysis have shown that the (Delta) (lambda) FWHM may not be the optimum measure of laser spectral purity, and that a better characterization would be the width of the line that contains 95 percent of the laser energy, (Delta) (lambda) 95 percent int. Therefore, the lithography is at risk of losing the image quality if the line shape, characterized by (Delta) (lambda) 95 percent int is outside its limit, even if the laser signals that the (Delta) (lambda) 95 percent measurements of laser line shape. The measurements can be done on a pulse-to-pulse basis or with averaging over an exposure window. Several different configurations and their comparable analysis are presented. These new spectrometers are compact, and can be integrated with a deep UV laser or used as a portable field service tool Despite the small size, the spectrometers have a resolution of about 0.1 pm when measuring FWHM values and about 0.3 pm when measuring 95 percent integral values. The implementation of these new metrology tools provides the lithography with a correct measure of the laser spectral purity during exposure and during process optimization.
The use of higher NA lenses and higher throughput of the next generation 248 nm microlithography systems sets tight requirements on the spectral properties of the laser as well as its power output and dose stability. We demonstrate that such scaling of spectral widths, power and repetition rates is possible by revisiting some of the dynamics of evolution of laser spectrum and stability of laser discharge. In the following, we present results of several optical configurations, that result in spectral widths between 1.0 and 2.0 pm (95% integrated linewidth). The optical configurations are derivatives of Cymer's standard Littrow grating and prism expander configuration. Thereby, the other parameters (beam size, coherence, etc.) are not impacted. Simultaneously, we provide results of scaling a laser to 2 kHz with a dose stability of less than plus or minus 0.5% over a 16 ms window. The resulting laser is now capable of meeting the technical requirements of the next generation microlithography scanners.
Chip makers are gearing up for 686-class micro-processors and 64 Mb production. These require producing < 0.30 micrometers critical features. They are also focusing on 256 Mb DRAMs that require below 0.25 micrometers design rules. Therefore, the shift from mercury lamp based i-line to 248 nm Deep-Ultra- Violet (DUV) steppers has begun in earnest. Current KrF laser models from several suppliers satisfy the optical requirements necessary for pilot production. However, as the move from DUV lithography R&D environment to production occurs, the laser's manufacturability, uptime requirements and cost-of-operation (CoO) become more demanding. The chip maker requires reliability, availability and maintainability data from laser manufacturers to support uptime and CoO estimates. Often, such data are required long before the lasers actually go into production.
In response to the requirement for higher wafer throughput and increased dosage accuracy in DUV lithography steppers and scanners, Cymer has developed a 1 kHz KrF laser optimized for this application. We shall describe its performance and design features.
As applications have evolved out of the research areas, laser beam properties and component lifetimes have become critical to achieving low operating cost in a manufacturing environment. We will discuss the development of a 110 watt KrF laser using an all solid-state pulsed power system. Solid state pulsed power enables a significant reduction in system operating costs by greatly extending the exchange interval of the pulsed power and discharge chamber modules. Beam properties of the laser using both stable and unstable resonator configurations will be discussed.
The operation of 1 kHz KrF lasers for DUV lithography applications requires a design which minimizes perturbations to the optical and electrical properties of the gas present, at one millisecond intervals in the lasing region and vicinity. The optimum design results from a compromise between electrical and fluid dynamic requirements, since these cannot be simultaneously fully satisfied. Other constraints on a commercially viable design are those rooted in issues such as manufacturability, safety, cost, compatibility with fluorine, and service lifetime of the resulting structure. CYMER has successfully engineered a laser which produces linear average power output scaling with pulse repetition rates to 1 kHz at a line- narrowed bandwidth of less than 0.8 pm. The stabilized pulse energy is 10 mJ with a FWHM of approximately 15 nS, producing an average power of 10W at 1 kHz pulse repetition rate. The 3(sigma) value of pulse energy stability is 5 percent. In addition, the chamber exhibits low fluorine consumption and a lifetime in excess of 2 billion shots. Measured performance data are presented along with a general system layout and facilities requirements.
A KrF excimer laser using an all solid state Pulse Power Modulator (PPM) has been studied. This PPM configuration replaces the commonly used thyratron switch with a Silicon Controlled Rectifier (SCR) switch combined with a pulse compression-voltage multiplication circuit. Use of this PPM has extended the useful chamber life of a line-narrowed KrF excimer laser from 1.5 billion to 2.5 billion pulses. Broadband KrF laser performance, optimized for mirror based scanner systems, has also been investigated. A minimum broadband chamber life of 5 billion pulses has been demonstrated with this solid state PPM. While a thyratron-based PPM exhibits an expected lifetime of 3 billion pulses, the solid state PPM used in these experiments has been operated for greater than 6 billion pulses without any decrease in performance. Since 72% of the replacement parts cost for the ELS-4000D line-narrowed excimer laser is due to periodic chamber and PPM replacement, significant cost of ownership reduction is realized by extending the lifetime of the chamber and the PPM.