EUV Optical Element Capping Layer Defect Prevention
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Solution Overview
Problem
Existing methods for producing capping layers in optical elements, particularly for EUV projection exposure apparatuses, result in short service life due to defects such as blister formation, layer detachment, and oxidation, leading to reduced reflectivity and operational reliability.
Innovation Solution
A method involving the application of a capping layer formed from a stoichiometrically pure capping material with sharp boundaries, using sputtering techniques enhanced by defect-preventing methods like facing-targets sputtering and Penning ionization, to minimize defects and ensure a virtually defect-free capping layer with optimized thickness and composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sputtering methods are used to apply capping layers, then the coating process can be completed, but the capping layers develop defects such as blisters, layer detachment, and oxidation leading to short service life
Solution Approach 1:
The patent applies a preliminary cleaning step using oxygen plasma treatment before depositing the capping layer. This preliminary action removes organic contaminants and oxidizes the surface to improve adhesion, preventing later defects like layer detachment and blisters that would reduce service life.
Solution Approach 2:
The patent uses a controlled atmosphere during the sputtering process, maintaining vacuum conditions and introducing specific gases (oxygen, nitrogen, or inert gases) to prevent oxidation and contamination of the capping layer during deposition, thereby eliminating oxidation defects and extending service life.
2Manufacturing precision
If the capping layer is made thinner to maintain sharp boundaries, then optical performance is improved, but the layer becomes more susceptible to defects and damage
Solution Approach 1:
The patent optimizes multiple parameters including layer thickness (5-50 nm), sputtering power (50-200 W), oxygen flow rate (10-100 sccm), and substrate temperature (room temperature to 200°C) to achieve the desired balance between sharp boundaries and defect resistance. By carefully controlling these parameters, the thin capping layer maintains both optical performance and durability.
3Productivity
If higher sputtering power is used to increase deposition rate, then productivity is improved, but the kinetic energy of particles increases causing more defects and damage
Solution Approach 1:
The patent employs pulsed or periodic sputtering cycles, alternating between deposition phases and plasma treatment phases. This periodic action allows the capping layer to form with controlled particle energy, preventing defect accumulation while maintaining acceptable deposition rates through repeated cycles.
Solution Approach 2:
The patent introduces oxygen or inert gases during sputtering to create a protective atmosphere that reduces particle damage. The gas molecules act as buffers, reducing the kinetic energy transfer to the growing film and preventing defects even at higher sputtering powers that increase productivity.
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
The approach results in long-lived, high-performance capping layers with reduced defects, enhancing the optical element's durability and reliability by preventing flaking and maintaining reflectivity, thus extending the operational life of EUV projection exposure apparatuses.
Implementation Method 1
a coating device (4) configured to individualize particles (5) of the target material (3) with an ionized working gas (6) for coating of a main body (7)
Implementation Method 2
individualize particles (5) of the target material (3) with an ionized working gas (6)
Data Source
AI summary
A method for producing an optical element (2), in particular for a projection exposure system (400), according to which a protective layer (11) consisting of a protective material is applied to a surface of a main body (7) until a protective layer thickness is obtained. The main body (7) has a substrate (17) and a reflective layer (18) applied to the substrate (17). The protective layer (11) is at least substantially defect-free.