This paper discusses the current performance and the evolution of five generations TWINSCAN immersion scanning
exposure tools. It is shown that production worthy overlay and focus performance can be achieved at high scan speeds.
The more critical part for immersion tools is related to defects, but also here improvements resulted in production
worthy defect levels. In order to keep the defect level stable special measures are needed in the application of wafers.
Especially Edge Bead Removal (EBR) design and wafer bevel cleanliness are important.
Defectivity has been one of the largest unknowns in immersion lithography. It is critical to understand if there are any immersion specific defect modes, and if so, what their underlying mechanisms are. Through this understanding, any identified defect modes can be reduced or eliminated to help advance immersion lithography to high yield manufacturing. Since February 2005, an ASML XT:1250Di immersion scanner has been operational at IMEC. A joint program was established to understand immersion defectivity by bringing together expertise from IMEC, ASML, resist vendors, IC manufactures, TEL, and KLA-Tencor. This paper will cover the results from these efforts. The new immersion specific defect modes that will be discussed are air bubbles in the immersion fluid, water marks, wafer edge film peeling, and particle transport. As part of the effort to understand the parameters that drive these defects, IMEC has also developed novel techniques for characterizing resist leaching and water uptake. The findings of our investigations into each immersion specific defect mechanism and their influencing factors will be given in this paper, and an attempt will be made to provide recommendations for a process space to operate in to limit these defects.
This paper discusses the types and formation of immersion defects. It is shown that drying stains and water marks are the main immersion defects. The immersion defects are related to resist leaching, water penetration and droplet formation. It is shown that scanner immersion hood design based on an actuated air gap and air curtain droplet clean-up minimizes defect counts. Additionally, pre-and post soaks steps in the track can reduce drying stains and water marks. The defect performance is evaluated on XT:1250i and XT:1400i systems. It is shown that the immersion defect density can go as low as 0.01 /cm2, which is well below the ITRS 2005 number of 0.03 /cm2.
Immersion Lithography is now the most important technique for extending optical lithography's capabilities and meeting the requirements of the Semiconductor Industry Association (SIA) roadmap. The introduction of water as an immersion fluid will allow optical lithography to progress as far as the 45nm (half pitch) node using ArF scanning systems such as the XT1700i. Developments are under way to explore the use of immersion lithography beyond this performance level and toward the 32nm (half pitch) node. This paper examines the progress that has been made, particularly with the use of 2nd-generation immersion fluids. The requirements of the exposure system are defined. Issues associated with achieving the requirements are reviewed and discussed. Special attention is given to clarifying the optical materials and the issues associated with extending optical designs to hyper-numerical aperture (NA) levels. A number of threshold levels for the numerical apertures are set by the refractive index of the available materials in the lithographic film stack. These are defined. The requirements of high refractive index fluids are detailed. The performance of experimental samples is compared to system requirements. Fluid interaction with photoresists and topcoats are examined. The results of stain tests and soak tests for fluid samples on resist are reported. Data is supplied on resist imaging for 32nm line and space L/S.
In less than two years immersion lithography has been developed from curiosity to viable technology for IC manufacturing. With water as immersion fluid ArF immersion offers the potential to extend conventional optical lithography to at least the 45-nm node. By slightly modifying “dry lenses” it is possible to use the immersion option as enhancement for the focus window. With immersion the DOF can be increased with 50% and more. ASML has developed and shipped ArF immersion TWINSCAN systems with lens NA’s of 0.75 and of 0.85. In the near future immersion systems with 0.93 NA and >1.1NA will become available.
In this paper we discuss the experimental results obtained on the TWINSCAN immersion systems. In the first part we discuss the experimental results obtained with the 0.75 NA and 0.85 NA immersion systems. It is demonstrated that basic system performance is maintained in case of immersion, while the imaging performance is improved significantly. We present data on resolution capability, full wafer CD uniformity, lens aberrations and single machine overlay. In the last part of the paper we will give an outlook to the next generations of immersion systems. This will include a discussion on the possible use of high index fluids and what resolution can be reached ultimately.
For 193-nm lithography, water proves to be a suitable immersion fluid. ArF immersion offers the potential to extend conventional optical lithography to the 45-nm node and potentially to the 32-nm node. Additionally, with existing lenses, the immersion option offers the potential to increase the focus window with 50% and more, depending on actual NA and feature type. In this paper we discuss the results on imaging and overlay obtained with immersion. Using a 0.75 NA ArF projection lens, we have built a proto-type immersion scanner using TWINSCAN technology. First experimental data on imaging demonstrated a large gain of depth of focus (DoF), while maintaining image contrast at high scan speed. For first pilot production with immersion, a 0.85 NA ArF lens will be used. The resolution capabilities of this system will support 65 nm node semiconductor devices with a DOF significantly larger than 0.5 um. Early imaging data of such a system confirms a significant increase in focus window.
As the semiconductor industry looks to the future to extend manufacturing beyond 100nm, ASML have developed a new implementation of an old optical method for lithography. Immersion lithography can support the aggressive industry roadmap and offers the ability to manufacture semiconductor devices at a low k1. In order to make immersion lithography a production worthy technology a number of challenges have to be overcome. This paper provides the results of our feasibility study on immersion lithography. We show through experimental and theoretical evaluation that we can overcome the critical concerns related to immersion lithography. We show results from liquid containment tests focussing on its effects on the scan speed of the system and the formation of micro-bubbles in the fluid. We present fluid-to-resist compatibility tests on resolution, using a custom-built interference setup. Ultimate resolution is tested using a home build 2 beam interference setup. ASML built a prototype full field scanning exposure system based on the dual stage TWINSCAN platform. It features a full field 0.75 NA refractive projection lens. We present experimental data on imaging and overlay.
Liquid immersion has been used for more than 100 years to increase the numeric aperture (NA) and resolution in optical microscopy. We explore the benefits and limitations of immersion technology in lithography. Immersion optical lithography has the potential to extend the resolution below 40 nm. The theory of immersion is decribed. Simulations show that a 193-nm immersion system at NA = 0.95 can double the depth of focus as compared to a dry system. Also, an immersion 193-nm system at NA = 1.05 has slightly more depth of focus than a 157-nm dry system at NA = 0.85. However, the exposure latitude at 193 nm is decreased due to the impact of polarization in imaging. Design schemes are presented to realize an immersion step and scan system. Two configuration approaches are proposed and explored. A localized shower type solution may be preferred over a bath type solution, because the impact on the step and scan platform design is significantly less. However, scanning over the wafer edge becomes the main design challenge with a shower solution. Studies are presented that look at the interaction of immersion fluids with the lens and the photoresist. Water seems to be a likely candidate, as it does not impact productivity of the step and scan system; however, focus and aberration levels need to be carefully controlled. For 157 nm, per-fluor-polyether (PFPE) materials are currently being studied, but their characteristics may limit the productivity of the exposure system. Further research on fluid candidates for 157-nm immersion is required.
With the delivery of 193nm exposure tool to several production fabs in the past year, we are now able to identify potential issues with this technology. For 193 nm lithoghpray, lifetime issues associated with the optical elements have been a big concern in the industry. Early learnings of optical component lifetimes for a 193nm step- and-scan system in pilot lien operation are reviewed. The performance and stability of line-narrowed ArF excimer lasers have also been unknowns in a production fab until now. High voltage and pulse length trends on the ArF laser are discussed. Data for lens heating effects on focus is presented. Stray light data will also be included in this paper. Observations related to the practical operation of a 193nm exposure tool as well as 193nm specific error modes will be shared. Finally, key areas where improvement is needed to ensure that 193nm lithography will be a cost- effective manufacturing technology are identified.
In this paper, the intra-field critical dimension (CD) control of a KrF step&scan and step&repeat system are investigated and compared. The scanners are expected to replace the conventional steppers in the manufacturing of integrated circuit generation of 0.18 micrometer and beyond, because of the larger field size and the intrinsic improvement in intra- field CD and overlay control using comparable lens design, complexity and cost. The work has been focused on sub-0.25 micrometer critical dimensions. A reticle design for both top- down CD measurements and electrical linewidth probing has allowed massive data collection and investigation of the impact of the metrology technique in CD control studies. From this study, it can be concluded that the stepper and scanner exhibit similar CD control at best focus, but the scanner improves the CD control of the stepper if the considered focus range increases. The CD control is governed by the reticle CD non-uniformity. Focus budget calculations indicate that reticle CD ranges of 40 nm (4x) are needed to bring the CD control of 0.2 micrometer grouped lines within acceptable ranges for realistic gate levels. For isolated lines, dedicated deep-UV resists and resolution enhancement techniques will be needed on top of this to obtain similar CD control.
Commercially available photoresists from the major photoresist vendors are investigated using a PAS 5500/300 wafer stepper, a 31.1 mm diameter field size high throughput wafer stepper with variable NA capability up to 0.63. The critical dimension (CD) investigated is 0.25 micrometers and lower for dense and isolated lines and 0.25 micrometers for dense contact holes. The photoresist process performance is quantified by measuring exposure-defocus windows for a specific resolution using a CD SEM. Photoresists that are comparable with or better than APEX-E with RTC top coat, which is the current base line process for lines and spaces imaging performance, are Clariant AZ-DX1300 and Shin Etsu SEPR-4103PB50. Most recent photoresists have much improved delay performance when compared to APEX without top coat. Improvement, when an organic BARC is applied, depends on the actual photoresist characteristics. The optimal photoresist found for 0.25 micrometers contact holes is TOK DP015 C. This process operates at optimal conditions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.