Angled Silicon Reflector Using Inverted Etched Mounting
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Solution Overview
Problem
The existing methods for fabricating small-scale mirrors, such as 45 degree mirrors, face challenges in achieving smoothness and repeatability due to the tediousness and subjectivity of the anisotropic etching process, which affects the planarity and reflectivity of the mirror surface.
Innovation Solution
The method involves using the polished surface of a silicon wafer as the reflective surface and the etched surface as the mounting surface, with photolithographic techniques to pattern protective layers and anisotropic etching to form a 45 degree mounting surface, allowing for a metallic coating on the reflective surface to enhance reflectivity, thereby relaxing fabrication tolerances and improving smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If anisotropic etching is used to form the reflective surface, then the mirror can be fabricated with specific angle, but the surface smoothness and planarity deteriorate due to etching-induced roughness
Solution Approach 1:
The patent inverts the conventional approach by using the polished surface as the reflective surface and the etched surface as the mounting surface. This inversion allows the mirror to achieve excellent surface smoothness from the polished side while still utilizing the etched surface for angular orientation and mounting purposes.
Solution Approach 2:
The patent segments the wafer surface into two distinct functional regions: the polished surface serves as the reflective surface requiring high smoothness, while the etched surface serves as the mounting surface providing angular orientation. This segmentation allows each surface to be optimized for its specific function without compromise.
2Manufacturing precision
If photolithographic techniques are used to pattern protective layers, then the etching region can be precisely defined, but the process complexity and subjectivity increase due to alignment requirements
Solution Approach 1:
The patent extracts the critical alignment step from the photolithographic process by using a simpler approach where the etched surface itself serves as the reference for mounting. This eliminates the need for complex photo mask alignment to crystal axes while still achieving precise angular orientation through the etching process.
3Ease of manufacture
If the etched surface is used as the reflective surface, then the mounting process is simplified, but the reflectivity deteriorates due to surface roughness from etching
Solution Approach 1:
The patent applies inversion by assigning the polished surface (with high reflectivity) as the reflective surface and the etched surface (with angular orientation) as the mounting surface. This resolves the contradiction by ensuring that the surface used for reflection has the necessary smoothness while the etched surface provides the mounting functionality.
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 significantly improves the smoothness of the mirror surface, achieving better than 5 nm surface smoothness and simplifying the fabrication process by reducing the need for precise control over the etching conditions, while maintaining effective reflectivity.
Implementation Method 1
exposing a region of a first major surface of a substrate to an anisotropic etchant to form a surface having the specific angle with respect to the first major surface
Implementation Method 2
a metallic coating may be formed along that surface [the second major surface] to enhance reflectivity properties
Data Source
AI summary
In a method of forming a device so as to include a reflective surface at a specific angle to an incident optical axis, a region of a first major surface of a substrate is exposed to an anisotropic etchant to form a surface having the specific angle with respect to the first major surface, but the etched surface is then used as a mounting surface. That is, rather than anisotropically etching a reflective surface, the etching provides the mounting surface and the second major surface of the substrate functions as the reflective surface when the fabricated device is properly mounted. The substrate may be a <100> silicon wafer having a 9.74 degree off-axis cut. Then, a 45 degree mirror is formed by the process. When the reflector is used in an optical device, the <111> crystalline plane will be generally parallel to the surface of the support.