Research On Atomic Hydrogen Cleaning Carbon Contaminations On EUV Multilayer

Extreme ultraviolet(EUV) lithography is the mainstream technology for the next generation lithography target below the 22 nm node. During the exposure process, carbon contamination will be deposited on the surface of the EUV multilayer film inside the lithography machine, which will not only result in the decrease of the reflectivity of the optical element and the decrease of the chip yield, but also affect the lithography quality. With the continuous improvement of light source power, the carbon contamination of EUV multilayers is becoming more and more serious. How to reduce the harm of carbon pollution to optical components has become the focus of all relevant laboratories. The current solution of removing the carbon contamination on the surface of the EUV multilayer films is mainly by way of cleaning technologies, such as Radio Frequency(RF)-O2/H2, UV/O2, EUV/O2 and atomic hydrogen. By comparing the advantages and disadvantages of different techniques, atomic hydrogen is chosen as the method of cleaning carbon contaminants in this paper, because it has little oxidation or other damage to the surface of the multilayer films.In this paper, the mechanism of cleaning carbon contaminants on the surface of multilayer optical elements by atomic hydrogen is studied. A cleaning model is established based on molecular dynamics, which could be used to estimate the cleaning rate of carbon contaminants. An experimental platform for atomic hydrogen cleaning is built, and the experiments of cleaning of carbon contamination on the surface of multilayer optical elements are performed. The main contents are as follows:1. Based on molecular dynamics, this paper studies the mechanisms of cleaning carbon contaminants on surface of multilayer optical elements by atomic hydrogen from the points of physics and chemistry. A cleaning model is established which would be used to estimate the cleaning rate of carbon contaminants and provide theoretical guidance for cleaning experiments.2. An experimental platform for cleaning is set. The graphite carbon layers are deposited on the substrate(EUV multilayer optical elements, quartz and sapphire, etc.) by physical vapor deposition(PVD) method to simulate real carbon contaminants. Cleaning experiments under different cleaning conditions(working distance, substrate temperature and atomic hydrogen excitation source power, etc.) are designed, and the velocity variation was measured with a quartz balance. The effects of cleaning conditions on the cleaning rate are obtained based on in-depth analysis of the experimental results and comparison with the model.3. According to the influence of cleaning condition factors on atomic hydrogen cleaning rate, combined with other limiting factors, the optimal cleaning scheme is proposed. The EUV multilayer samples with carbon contaminants are cleaned with the optimal cleaning program and evaluated by comparing the reflectance and the surface roughness before and after cleaning.4. Based on ellipsometry, the method of measuring the carbon contamination thickness on the surface of EUV multilayer film is studied, which will provide a theoretical basis for real-time measuring and evaluating the thickness change during carbon contamination cleaning. The structure model is established based on multilayer samples, and the corresponding dispersion models are chosen according to film coating materials. Carbon contaminants thicknesses are measured by ellipsometer based on the model established above and the accuracy of measurement results of different dispersion models are compared, the model with high accuracy is selected.In this paper, the mechanism of cleaning carbon contaminants on surface of multilayer optical elements by atomic hydrogen is studied. The conditions and factors that affect the cleaning rate and effect are analyzed by experiments. Based on ellipsometry, the method of measuring the carbon contamination thickness on the surface of EUV multilayer film is studied. It provides a theoretical basis for cleaning the surface of EUV multilayer optical elements by atomic hydrogen, and it is of great significance for the future development of on-line cleaning of EUV multilayer optical elements.