EUV Photomask Ruthenium Oxide Reduction for Reflectivity Recovery
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Solution Overview
Problem
EUV photomasks in the semiconductor industry face significant challenges due to the oxidation of ruthenium capping layers, which reduces reflectivity and shortens their lifespan, leading to increased costs and inefficiencies in EUV lithography processes.
Innovation Solution
The method involves heating the EUV photomask to a controlled temperature and using specific reducing agent gases, such as carbon monoxide, methane, or hydrogen, in conjunction with carrier gases and plasma generation to reduce ruthenium oxides to ruthenium metal, thereby maintaining reflectivity and extending the photomask's life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the EUV photomask is used for lithographic processes, then the photomask performs its function of reflecting EUV light, but the ruthenium capping layer becomes oxidized which reduces reflectivity and shortens lifespan
Solution Approach 1:
The patent applies preliminary anti-action by performing oxide reduction treatment on the ruthenium capping layer before it becomes significantly oxidized during normal use. The reduction process counteracts the oxidation that occurs during lithographic exposure, thereby maintaining reflectivity and extending photomask lifespan. This is achieved by flowing reducing agent gases (such as hydrogen, carbon monoxide, or methane) through the photomask at controlled temperatures (room temperature to 150°C) to remove oxide layers proactively.
2Productivity
If reducing agent gas is flowed at high concentration to increase reduction rate, then oxide removal efficiency increases, but safety risks from explosive gases increase
Solution Approach 1:
The patent uses carrier gases (such as nitrogen, argon, or helium) as intermediaries to deliver reducing agent gases safely. The carrier gas dilutes the reducing agent gas to concentrations below explosive limits while maintaining effective reduction rates. This intermediary approach allows the system to achieve high productivity through efficient oxide removal without compromising safety from explosive hazards.
Solution Approach 2:
The patent controls the concentration parameter of reducing agent gas by adjusting the ratio of reducing agent gas to carrier gas. By maintaining the reducing agent gas concentration within safe limits (below explosive thresholds) while optimizing other parameters such as flow rate, temperature, and exposure time, the system achieves effective oxide reduction without creating explosion risks.
3Productivity
If the photomask is heated to higher temperatures to enhance reduction reaction, then oxide removal efficiency improves, but thermal damage to photomask layers may occur
Solution Approach 1:
The patent optimizes the temperature parameter within a controlled range (room temperature to 150°C) to enhance reduction reaction rates without causing thermal damage. By carefully selecting and controlling this parameter, along with adjusting gas flow rates and composition, the system achieves improved productivity through faster oxide removal while maintaining the structural integrity and reliability of the photomask's sensitive multilayer structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces oxide formation on ruthenium capping layers, enhancing the reflectivity and stability of EUV photomasks, thereby prolonging their performance and reducing production costs by extending their operational life.
Implementation Method 1
gases in the EUV photomask processing chamber react with a ruthenium oxide layer on a Ru capping layer to reduce the Ru oxide layer to Ru metal
Implementation Method 2
generating a plasma in the remote plasma generator using an RF power source, and flowing gases from the remote plasma generator into an EUV photomask processing chamber
Implementation Method 3
heating the EUV photomask to a temperature of approximately 100 degrees Celsius to approximately a thermal budget of the EUV photomask
Implementation Method 4
pressurizing the EUV photomask processing chamber to a process pressure to increase a reducing reaction between the reducing agent gas and the Ru oxide layer on the Ru capping layer
Data Source
AI summary
Methods and apparatus for reducing ruthenium oxide on an extreme ultraviolet (EUV) photomask leverage temperature, plasma, and chamber pressure to increase the reduction. In some embodiments, a method includes heating the EUV photomask with a ruthenium (Ru) capping layer with a top surface which has a Ru oxide layer to a temperature of approximately 100 degrees Celsius to approximately a thermal budget of the EUV photomask, flowing a reducing agent gas into an EUV photomask processing chamber, and pressurizing the EUV photomask processing chamber to a process pressure to increase a reducing reaction between the reducing agent gas and a Ru oxide layer on the Ru capping layer. Other embodiments may incorporate remote plasma generators or atmospheric-pressure plasma generators to enhance the reduction of Ru oxides on the Ru capping layer.