Deposition Mask Opening Geometry for Uniform Thin Film Thickness
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Solution Overview
Problem
Conventional vacuum deposition methods face challenges in achieving uniform thin film thickness on large substrates, leading to non-uniform luminance and increased risk of short-circuits in organic EL displays, due to mask size and weight issues, which hinder high-definition patterning and productivity.
Innovation Solution
A deposition mask with varying opening sizes along its length, where the openings at the ends are larger than in the central portion, is used to compensate for thickness differences, ensuring uniform film deposition by adjusting the scanning direction and gap between the mask and substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large-sized mask is used for deposition on large substrates, then the deposition area is increased, but the mask weight increases and causes bending or extension leading to positioning errors
Solution Approach 1:
The mask is divided into multiple segments that can be independently supported and positioned. Each segment is held by separate support means, allowing the large mask area to be maintained while distributing the weight load and preventing bending or extension that would cause positioning errors.
2Manufacturing precision
If the mask and substrate are held with a constant gap, then deposition uniformity is improved, but the deposition time increases due to scanning motion
Solution Approach 1:
The system transitions from static mask-substrate positioning to dynamic scanning motion. The mask unit scans across the substrate while maintaining a constant gap through coordinated movement of support means, enabling uniform deposition across the entire substrate area within a reasonable time frame.
Solution Approach 2:
The emission angle of the deposition source is pre-configured to match the scanning geometry and gap distance. By satisfying the relation tan(90-θ/2)=H/W where θ is the emission angle, H is the gap distance, and W is the mask width, the system ensures optimal deposition uniformity is achieved during the scanning process.
3Manufacturing precision
If the opening amount at ends of the mask is increased, then the thin film thickness at ends is improved, but the mask structure complexity increases
Solution Approach 1:
The mask opening amount is made non-uniform, with larger openings at the ends and smaller openings in the central portion. This local variation in opening size compensates for the reduced deposition amount at the ends during scanning, ensuring uniform film thickness across the entire substrate without requiring complex additional structures.
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 enhances the uniformity of thin film thickness, improving image display quality and long-term reliability of organic EL displays by ensuring consistent film deposition across large substrates, thus addressing the limitations of conventional methods.
Implementation Method 1
a deposition source (53) that emits deposition particles (3) forming the thin film (3) toward the substrate (10)
Data Source
AI summary
A deposition mask 601 is used to form a thin film 3 in a prescribed pattern on a substrate 10 by deposition. Each of a plurality of improved openings 62A of the deposition mask 601 has a protruding opening portion 64, and is formed so that the opening amount at an end in a lateral direction is larger than that in a central portion in the lateral direction. In a deposition apparatus 50, the deposition mask 601 is held in a fixed relative positional relation with a deposition source 53 by a mask unit 55. In the case of forming the thin film 3 in a stripe pattern on the substrate 10 by the deposition apparatus 50, deposition particles are sequentially deposited on the substrate 10 while relatively moving the substrate 10 along a scanning direction with a gap H being provided between the substrate 10 and the deposition mask 601.