In this work, the authors will review the laser operation and imaging fundamentals behind a new method of alternating wavelengths in a single exposure and the application to Customer use cases. Two focal positions are created that are averaged over the exposure field, which can be turned on and off, thus eliminating any potential scanner calibration issues. The main focus of this work is the application of this imaging method (single exposure with two focus positions) to significantly improve the sidewall angle linearity of features in extremely thick photoresist applications. This novel technique, called MFI (multi-focal imaging), can be tuned specifically to provide the required amount of focus offset for a specific thick photoresist application. There are several Customer use cases that have been evaluated in simulation and demonstrated on wafer.
Over the years, lithography engineers have continued to focus on CD control, overlay and process capability to meet node requirements for yield and device performance. Previous work by Fukuda1 developed a multi-exposure technique at multi-focus positions to image contact holes with adequate DOF. Lalovic2 demonstrated a fixed 2-wavelength technique to improve DOF called RELAX. The concept of multi-focal imaging (MFI) was introduced3 demonstrating two focal positions are created that are averaged over the exposure field, this wavelength “dithering” approach which can be turned on and off, thus eliminating any potential scanner calibration issues.
In this work, the application of this imaging method (1 exposure-2 focus positions) can be used in thick photoresist and high aspect ratio applications. An example of thick photoresist imaging is shown in figure 1. We demonstrate 5um line and space features in 10um of photoresist at 3 different imaging conditions. On the left, single focus imaging (SFI) at best dose and focus, the center image which is also SFI but at a defocus of +3.2um. On the right is MFI with 2 focus positions of 0 and 2.8um. Here we can see a significant improvement in the SWA linearity and image profile quality. A second example of high aspect ratio imaging using MFI is shown in figure 2. The aspect ratio of 13:1 is shown for this. The use of Tachyon KrF MFI source – mask optimization flow will be reviewed to demonstrate optimum conditions to achieve Customer required imaging to meet specific layer requirements.
Key sustainability opportunities have been executed in support of corporate initiatives to reduce the environmental footprint and decrease the running cost of DUV light sources. Previously, substantial neon savings were demonstrated over several years through optimized gas management technologies. Beyond this work, Cymer is developing the XLGR 100, a self-contained neon recycling system, to enable minimal gas consumption. The high efficiency results of the XLGR 100 in a production factory are validated in this paper.
Cymer has also developed new light source modules with 33% longer life in an effort to reduce raw and associated resource consumption. In addition, a progress report is included regarding the improvements developed to reduce light source energy consumption.
Cymer continues to address several areas of sustainability within the semiconductor industry by reducing or eliminating consumption of power and specific types of gas (i.e. neon, helium) required by DUV light sources in order to function. Additionally, Cymer introduced a new recycling technology to reduce the dependence on production of raw gases. In this paper, those initiatives that reduce the operational cost, environmental footprint, and business continuity risk will be discussed.
Cymer has increased the efficiency of its light sources through improvements that have resulted in energy output increase while maintaining the same or requiring less power consumption. For both KrF and ArF systems, there have been component [1], system, and architecture improvements [2] that allowed customers to increase energy efficiency and productivity. An example of module improvements is the latest MO chamber that helped reduce power consumption by ~15%. Future improvements aim to continue reducing the power consumption and cost of operation of the install base and new systems.
The neon supply crisis in 2015 triggered an intensive effort by the lithography light source suppliers to find ways to minimize the use of neon, a main consumable of the light source used in DUV photolithography. Cymer delivered a multi-part support program to reduce natural resource usage, decrease overall cost of operation, and ensure that chipmaker’s business continuity risk is minimized. The methods used to minimize the use of neon for 248 nm and 193 nm photolithography that offered significant relief from supply constraints and reduction of business continuity risk for chipmakers were described in previous work [3]. In this paper, results from the program will be presented.
In addition, techniques to capture the neon effluent and re-purify it within the semiconductor fabs have been pursued. For example, Cymer has developed and validated a neon recycling system for ArF light sources that resides within the chipmaker’s fab. Cymer has partnered with a global gas supplier to develop a system capable of capturing, recycling and delivering <90% of the total neon gas required by multiple ArF light sources through automated operation, including online analysis. In this paper, the neon recycle system performance as demonstrated by a quantitative analysis of facility-supplied gas versus the recycled neon in ArF light source performance will be discussed.
Similarly, DUV light sources have historically used helium as a purge gas in the critical line narrowing module (LNM) to achieve stable wavelength and bandwidth control. Helium has a low coefficient of index of refraction change vs. temperature relative to nitrogen and provides efficient cooling and purging of critical optics in the LNM. Previous work demonstrated how helium consumption can be reduced and still achieve stable performance under all operating conditions [1]. In this paper, results of eliminating the use of helium will be described.
In response to significant neon supply constraints, Cymer has responded with a multi-part plan to support its customers. Cymer’s primary objective is to ensure that reliable system performance is maintained while minimizing gas consumption. Gas algorithms were optimized to ensure stable performance across all operating conditions.
The Cymer neon support plan contains four elements: 1. Gas reduction program to reduce neon by >50% while maintaining existing performance levels and availability; 2. short-term containment solutions for immediate relief. 3. qualification of additional gas suppliers; and 4. long-term recycling/reclaim opportunity. The Cymer neon reduction program has shown excellent results as demonstrated through the comparison on standard gas use versus the new >50% reduced neon performance for ArF immersion light sources. Testing included stressful conditions such as repetition rate, duty cycle and energy target changes. No performance degradation has been observed over typical gas lives.
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