Yu-Jen Fan

EUV resist outgassing: scaling to HVM intensity

Typical extreme ultraviolet (EUV) photoresist is known to outgas carbon-containing molecules, which is of particular concern to the industry as these molecules tend to contaminate optics and diminish reflectivity. This prompted extensive work to measure these species and the quantities that they outgas in a vacuum environment. Experiments were performed to test whether the outgassing rate of these carbon-containing molecules is directly proportional to the rate at which the EUV photons arrive and whether a very high power exposure will cause the same amount of outgassing as a much lower power exposure with the dose unchanged.

Effect of carbon contamination on the printing performance of extreme ultraviolet masks

Carbon contamination is a significant issue with extreme ultraviolet (EUV) masks because it lowers throughput and has potential effects on imaging performance. Current carbon contamination research is primarily focused on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and can affect the printed images. In this work, various carbon contamination experiments were performed to study the impact between contamination topography and observed imaging performance. Lithographic simulation using calculated aerial images and experimentally determined resist parameters was performed and compared to the printing results to estimate the allowed carbon thickness with critical dimension compensation applied to the mask.

Benchmarking study of EUV resists for NXE:3300B

EUV lithographers have continued to reduce the barriers to high Volume Manufacturing (HVM) introduction. Tool, mask and photoresist manufacturers have made excellent progress on several fronts, including resolution of many EUV source related issues, resists for early imaging characterization, and defect inspection tooling. In this discussion, we will focus on photoresist development. For many years, the team at SUNY Polytechnic Institute (SUNY Poly) has provided results from a neutral photoresist benchmarking study, which has been quite useful in establishing the limits of currently available photoresist systems [1-5]. New photoresist systems are being developed with improving resolution, but they also have lower coated thicknesses. In an effort to continue to point out potential lithographic problem areas, SUNY Poly has been evaluating the ‘etch compatibility’ of the best performing photoresists available in order to determine if the decreasing aspect ratios would prove a detriment to etch performance. In this paper, we will show data from our most recent benchmark study. We will also include smoothing process results, as well as some post-etch results obtained using the NXE:3300B resident on the SUNY Poly campus.

Carbon contamination of extreme ultraviolet (EUV) masks and its effect on imaging

Carbon contamination of extreme ultraviolet (EUV) masks and its effect on imaging is a significant issue due to lowered throughput and potential effects on imaging performance. In this work, a series of carbon contamination experiments were performed on a patterned EUV mask. Contaminated features were then inspected with a reticle scanning electron microscope (SEM) and printed with the SEMATECH Berkeley Microfield-Exposure tool (MET) [1]. In addition, the mask was analyzed using the SEMATECH Berkeley Actinic-Inspection tool (AIT) [2] to determine the effect of carbon contamination on the absorbing features and printing performance. To understand the contamination topography, simulations were performed based on calculated aerial images and resist parameters. With the knowledge of the topography, simulations were then used to predict the effect of other thicknesses of the contamination layer, as well as the imaging performance on printed features.

Carbon contamination topography analysis of EUV masks

The impact of carbon contamination on extreme ultraviolet (EUV) masks is significant due to throughput loss and potential effects on imaging performance. Current carbon contamination research primarily focuses on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and the printed images, as well as impacting the efficiency of cleaning process. In this work, several different techniques were used to determine possible contamination topography. Lithographic simulations were also performed and the results compared with the experimental data.

Quantitative measurement of EUV resist outgassing

The Mo/Si multilayer mirrors used for extreme ultraviolet (EUV) lithography can become contaminated during exposure in the presence of some hydrocarbons [1-3]. Because this leads to a loss in the reflectivity of the optics and throughput of the exposure tools, it needs to be avoided. Since photoresists are known to outgas during exposure to EUV radiation in a vacuum environment, the careful choice of materials is important to preserving the EUV optics. Work therefore has been performed to measure the species and quantities of molecules that outgas from EUV resists when exposed to EUV radiation [4-7].

Wavelength dependence of carbon contamination on mirrors with different capping layers

Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. In addition to the desired wavelength near 13.5 nm (EUV), plasma sources used in EUV exposure tools emit a wide range of out-of-band (OOB) wavelengths extending as far as the visible region. We present experimental results of contamination rates of EUV and OOB light using a Xe plasma source and filters. Employing heated carbon tape as a source of hydrocarbons, we have measured the wavelength dependence of carbon contamination on a Ru-capped mirror. These results are compared to contamination rates on TiO2 and ZrO2 capping layers.

Extreme ultraviolet resist outgassing and its effect on nearby optics

Extreme ultraviolet (EUV) photoresists are known to outgas during exposure to EUV radiation in the vacuum environment. This is of particular concern since some of the outgassed species may contaminate the nearby EUV optics and cause a loss of reflectivity and therefore throughput of the EUV exposure tools. Due to this issue, work has been performed to measure the species and quantities that outgas from EUV resists. Additionally, since the goal of these measurements is to determine the relative safety of various resists near EUV optics, work has been performed to measure the deposition rate of the outgassed molecules on Mo/Si-coated witness plate samples. The results for various species and tests show little measurable effect from resist components on optics contamination with modest EUV exposure doses.

Dependence of contamination rates on key parameters in EUV optics

Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. Dependence of contamination rates on key EUV parameters was investigated. EUV tools have optics at different illumination angles. It was observed that at shallower angles, the carbon contamination rate and surface roughness was higher on the optics surface. This is a concern in EUV optics as higher roughness would increase the scattering of the EUV radiation. Secondary ion time of flight mass spectrometer (TOF-SIMS) data indicated that the carbon contamination film might be a polymer. Three chemical species were used to investigate the dependence of polymerization and reactivity on the contamination rate. Acrylic acid was found to have a measurable contamination rate above background compared to propionic acid and methyl methacrylate. Secondary electron dissociation is one of the mechanisms considered to be a cause for the growth of the carbon contamination film. Multiple experiments with two substrates having different secondary electron yields were performed. The substrate with the higher secondary electron yield was found to give a higher contamination rate.