Roel Moors

Plasma sources for EUV lithography exposure tools

The source is an integral part of an extreme ultraviolet lithography (EUVL) tool. Such a source, as well as the EUVL tool, has to fulfil extremely high demands both technical and cost oriented. The EUVL tool operates at a wavelength in the range 13–14 nm, which requires a major re-thinking of state-of-the-art lithography systems operating in the DUV range. The light production mechanism changes from conventional lamps and lasers to relatively high temperature emitting plasmas. The light transport, mainly refractive for DUV, should become reflective for EUV. The source specifications are derived from the customer requirements for the complete tool, which are: throughput, cost of ownership (CoO) and imaging quality. The EUVL system is considered as a follow up of the existing DUV based lithography technology and, while improving the feature resolution, it has to maintain high wafer throughput performance, which is driven by the overall CoO picture. This in turn puts quite high requirements on the collectable in-band power produced by an EUV source. Increased, due to improved feature resolution, critical dimension (CD) control requirements, together with reflective optics restrictions, necessitate pulse-to-pulse repeatability, spatial stability control and repetition rates, which are substantially better than those of current optical systems. All together the following aspects of the source specification will be addressed: the operating wavelength, the EUV power, the hot spot size, the collectable angle, the repetition rate, the pulse-to-pulse repeatability and the debris induced lifetime of components.

First performance results of the ASML alpha demo tool

The ASML EUV alpha demo tool is operational! The alpha demo tool is a 0.25NA fully functional lithography tool with a field size of 26×33 mm2, enabling process development at the 40-nm technology node. In this paper we describe the tool performance, show that vacuum is achieved in a few hours, and demonstrate that our optics contamination strategy mitigates degradation of the optics. Additional data shows the Sn source cost-of-ownership to be comparable to state-of-the-art ArF source systems, by implementing a collector contamination mitigation strategy that includes cleaning. And, we present our first 35-nm dense lines and spaces (half pitch) resist images.

Relationship between an EUV source and the performance of an EUV lithographic system

The light source is a critical factor when Extreme Ultra Violet Lithography (EUVL) is used. This paper shows the link between the light source and the customers requirements. These are: Throughput, Cost of Ownership (CoO) and imaging quality (e.g. CD uniformity). Also shown is how customer requirements dictate the necessary performance specifications for light sources. To be competitive with other New Generation Lithography technologies, EUVL tools should show a potential for high throughput. This puts a high requirement on the collectable in-band power produced by an EUV source. CD control requirements, together with restrictions of reflective optics, are discussed. This means that the pulse-to-pulse repeatability, the spatial stability control and the repetition rates, must be substantially better than those of current optical systems. It is essential, in the early stages of the development of potential light sources, to understand the source limitations. It is also essential to see the way the light source or the total source/lithographic system could be improved, in the development time, to meet the lithography tool requirements. Although there are no light sources currently under development that comply with the requirements for an EUVL production tool, future improvement in the performance of light sources seems possible. This paper shows detailed analyses of the way to meet (beta) and production tool requirements, including the increase in repetition rate, for all of the sources. The decrease in energy per pulse will also be discussed. The performance requirements for the light source for the first lithographic tool, together with the timeline for its choice, will be shown.

Detection and characterization of carbon contamination on EUV multilayer mirrors

In this paper, we detect and characterize the carbon contamination layers that are formed during the illumination of extreme ultraviolet (EUV) multilayer mirrors. The EUV induced carbon layers were characterized ex situ using spectroscopic ellipsometry (SE) and laser generated surface acoustic waves (LG-SAW). We show that both LG-SAW and SE are very sensitive for measuring carbon layers, even in the presence of the highly heterogeneous structure of the multilayer. SE has better overall sensitivity, with a detection limit of 0.2 nm, while LG-SAW has an estimated detection limit of 2 nm. In addition, SE reveals that the optical properties of the EUV induced carbon contamination layer are consistent with the presence of a hydrogenated, polymeric like carbon. On the other hand, LG-SAW reveals that the EUV induced carbon contamination layer has a low Youngs modulus (<100 GPa), which means that the layer is mechanically soft. We compare the limits of detection and quantification of the two techniques and discuss their prospective for monitoring carbon contamination build up on EUV optics.

Extreme-ultraviolet source specifications: tradeoffs and requirements

Although progress has been reported, the extreme-ultraviolet (EUV) source remains one of the largest challenges for EUV lithography production to be economically viable. This article gives an update on the high-level source requirements, including the origin of these specifications. All requirements are driven by litho system cost-of-ownership considerations and the imaging capabilities. Attention will be paid to conflicting requirements and the consequent tradeoffs that have to be made in making conceptual source decisions and in designing an EUV system. Finally, we will look into the future of the top-level source requirements with the conclusions that not only EUV power requirements will keep on increasing, but that this increase has to be accompanied with a high availability and reliability of the source. Furthermore, an operation mode has to be found that is chemically, particulately, and spectrally clean so that the cost-of-ownership and imaging capabilities of the total system remain intact over its lifetime.

Particle cleaning of EUV reticles

Due to absorption of EUV light, EUV reticles are not likely to have pellicles for particulate contamination protection, thus even nanosize particles on the reticle could result in fatal defects in every printed die. Consequently, measures must be taken to detect and remove particles above a certain critical size that are deposited on the reticle in the course of its use. In this paper we first present the very stringent requirements that a cleaning technique must satisfy in order to be employed for EUV reticle cleaning. The main challenges consist in the capability of removing very small particles (sub-100 nm), in principle of any type (organic/inorganic) and without damage to the reticle. We then focus on two of the techniques that we are investigating, laser shockwave cleaning (LSC) and high voltage cleaning (HVC). Both of them are dry techniques, which is a necessary requirement in view of their potential integration in the lithography tool. We finally present cleaning and damage tests results, including cleaning of 40-nm polystyrene-latex (PSL) spheres on large areas.

EUV for HVM: towards an industrialized scanner for HVM NXE3400B performance update

With the introduction of its fifth-generation NXE:3400B scanner, ASML brought EUV to High- Volume Manufacturing for 7 nm node lithography and beyond with full support of pellicle. This paper presents an update on lithographic performance results obtained with the NXE:3400B, characterized by an NA of 0.33, a Pupil Fill Ratio (PFR) of 0.2 and throughput capability of 125 wafers per hour. Advances in source power and system availability have enabled a continued increase of productivity. To maximize the number of yielding dies per day excellent Overlay, Focus, and Critical Dimension (CD) control have been realized, combining intrinsic tool stability with holistic control schemes. We will also show matching performance for both Overlay and Imaging, and further improvements in Focus Process Dependencies for the 5nm node.

Ellipsometric and surface acoustic wave sensing of carbon contamination on EUV optics

Carbon contamination layers, deposited on extreme ultraviolet (EUV) multilayer mirrors during illumination were characterized ex situ using spectroscopic ellipsometry (SE), laser generated surface acoustic waves (LG-SAW), and by their EUV reflectance loss. We show SE is more sensitive to the deposition of carbon layers than the EUV reflectance loss, even in the presence of the highly heterogeneous structure of the multilayer. SE has better overall sensitivity, with a detection limit of 0.2 nm, while LG-SAW has an approximate detection limit < 5 nm.