Substrate Recess Formation with Alternating Etching for Vertical Sidewalls
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Solution Overview
Problem
The semiconductor industry faces challenges in forming deep recesses such as trenches in semiconductor substrates with desired shapes and profiles, as existing methods result in rough and inclined sidewalls, leading to undesirable signal transmission losses when optical fibers are accommodated.
Innovation Solution
A method involving the formation of a mask, a protection layer, and alternating anisotropic and isotropic etching processes to create a recessed portion with uniform and consistent concaves on the sidewall, ensuring the sidewall is substantially perpendicular to the bottom surface, and maintaining a controlled depth within 160 nm to 400 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to form deep recesses, then the etching process is simple and fast, but the sidewalls become rough and inclined
Solution Approach 1:
The etching process is segmented into multiple alternating steps (anisotropic etching followed by isotropic etching) rather than using a single continuous etching process. This segmentation allows the anisotropic step to create vertical sidewalls while the isotropic step smooths the surface, resolving the contradiction between sidewall quality and process simplicity
Solution Approach 2:
The method employs periodic alternation between anisotropic and isotropic etching processes. The anisotropic etching provides vertical directionality, while the isotropic etching provides lateral smoothing. This periodic action continues until the desired depth is achieved, producing smooth and vertical sidewalls without requiring overly complex single-step processes
2Reliability
If deep recesses are formed with inclined sidewalls, then the etching process is simpler, but signal transmission losses increase
Solution Approach 1:
The etching process is divided into anisotropic and isotropic components that work together to achieve vertical sidewalls. The anisotropic etching establishes the vertical geometry necessary for proper optical fiber alignment, while the isotropic etching refines the surface, ensuring both manufacturing precision and signal transmission reliability
Solution Approach 2:
The method changes the etching parameters by alternating between anisotropic and isotropic conditions. This parameter change allows control over the etching direction and rate, achieving the vertical sidewalls needed for reliable signal transmission while maintaining manufacturing feasibility
3Manufacturing precision
If alternating anisotropic and isotropic etching processes are used, then sidewall uniformity improves, but the number of process steps increases
Solution Approach 1:
The alternating etching processes are implemented as periodic cycles rather than separate independent steps. Each cycle consists of a brief anisotropic etching followed by a brief isotropic etching, repeating until the target depth is reached. This periodic approach maintains sidewall uniformity while minimizing the total number of steps compared to traditional multi-step processes
Solution Approach 2:
The alternating etching process maintains continuous useful action by ensuring that each etching step contributes to the final sidewall quality. The anisotropic step creates vertical structure while the isotropic step smooths the surface, with both actions being essential and non-redundant, thereby maintaining productivity despite the alternating nature of the process
4Manufacturing precision
If the recessed portion etches too deeply or widens, then the etching process is more aggressive, but the shape control and verticality are compromised
Solution Approach 1:
The etching process is segmented into anisotropic and isotropic steps that alternate to provide both depth control and shape control. The anisotropic etching provides the primary etching rate and vertical direction, while the isotropic etching provides shape refinement and sidewall smoothing, preventing unwanted widening and maintaining precise shape control throughout the etching process
Solution Approach 2:
The method dynamically changes etching parameters by switching between anisotropic and isotropic conditions. This allows the process to maintain an overall high etching rate while periodically adjusting the etching characteristics to control the recessed portion shape and prevent excessive widening, achieving both speed and precision
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 method achieves a higher etching rate and smoother, more uniform sidewalls, enhancing signal transmission efficiency by maintaining the sidewall's verticality and consistency, preventing the recessed portion from widening during etching, and improving light transmission in optical communication devices.
Implementation Method 1
performing a first anisotropic etching process to etch the substrate to a desired depth
Implementation Method 2
performing a second isotropic etching process to smooth a surface of the recessed portion
Data Source
AI summary
A recessed portion in a semiconductor substrate and a method of forming the same are provided. The method comprises: forming a mask on the semiconductor substrate; forming a protection layer on a top surface of the mask and on at least one sidewall of the mask, and on at least one surface of the semiconductor substrate exposed by the mask; performing a first etching process to remove the protection layer on the top surface of the mask and on a bottom surface of the semiconductor substrate exposed by the mask; and performing a second etching process to remove the remaining protection layer and to etch the semiconductor substrate to form the recessed portion. In this way, a recessed portion with relatively smooth and vertical sidewalls can be realized.