Sequential Substrate Etching for Flat Thinning Profiles
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Solution Overview
Problem
Existing substrate processing methods struggle to effectively flatten the surface profile of a substrate while thinning it, particularly when dealing with uneven surfaces that can lead to damage during subsequent etching steps.
Innovation Solution
A substrate processing method involving multiple etching steps with adjustable parameters, including rotating the substrate and applying etching liquids like hydrofluoric acid, TMAH, and ammonium hydroxide, with controlled scanning and fixed discharges to achieve a flat surface profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single etching step is used to thin the substrate, then processing time is reduced, but the surface profile cannot be flattened effectively
Solution Approach 1:
The etching process is divided into multiple sequential steps: a first etching step using hydrofluoric acid-containing liquid to remove a large portion of the substrate, followed by a second etching step using TMAH-containing liquid to flatten the surface profile. This segmentation allows each step to be optimized for its specific function, achieving both efficient thinning and high surface flatness.
Solution Approach 2:
Different etching parameters are used in different steps: the first etching step uses hydrofluoric acid with specific concentration and temperature to achieve high removal rate, while the second etching step uses TMAH with adjusted parameters to achieve surface flattening. The etching liquid composition, temperature, and flow rate are changed between steps to optimize both productivity and precision.
2Productivity
If etching liquid is supplied at high speed to increase productivity, then processing time is reduced, but the surface profile becomes uneven
Solution Approach 1:
The high-speed etching and surface flattening functions are separated into different steps. The first etching step uses high etching rate parameters to remove material quickly, while the second etching step uses lower etching rate parameters with optimized liquid supply to flatten the surface, ensuring uniformity without sacrificing overall productivity.
Solution Approach 2:
The first etching step performs preliminary material removal to reduce the substrate to near-final thickness, creating a pre-flattened surface that requires minimal additional processing in the second step. This preliminary action allows the second step to focus on surface uniformity rather than both thinning and flattening simultaneously.
3Manufacturing precision
If the substrate is etched to achieve thinning, then the desired thickness is reached, but the underlying layers may be damaged due to surface unevenness
Solution Approach 1:
The first etching step performs preliminary thinning to bring the substrate close to the target thickness, and the second etching step performs preliminary surface flattening before any subsequent processing. This ensures that when the substrate reaches final thickness, the surface is already uniform, preventing concentration of stress that could damage underlying layers.
Solution Approach 2:
The etching parameters are changed between steps to control both thickness and surface quality. The second etching step uses TMAH with parameters optimized for gentle, uniform removal that flattens the surface without creating the unevenness that would lead to underlying layer damage during subsequent processing.
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 surface flatness of not more than 1.5 µm, ensuring precise thinning and minimizing damage to underlying layers by flattening the surface profile effectively.
Implementation Method 1
a first etching step of supplying a first etching liquid that contains hydrofluoric acid and nitric acid to the principal surface during execution of the substrate rotating step
Implementation Method 2
a substrate rotating step of rotating a substrate, having a principal surface that has been ground or polished for substrate thinning, around a rotational axis perpendicular to the principal surface
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A substrate processing method includes a substrate rotating step of rotating a substrate, having a principal surface that has been ground or polished for substrate thinning, around a rotational axis perpendicular to the principal surface, a first etching step of supplying a first etching liquid that contains hydrofluoric acid and nitric acid to the principal surface during execution of the substrate rotating step, and a second etching step of supplying a second etching liquid that contains TMAH (tetramethylammonium hydroxide) to the principal surface during execution of the substrate rotating step after the first etching step. A second etching parameter applied in the second etching step is adjusted such as to flatten a first surface profile formed on the principal surface resulted by the first etching step.