Semiconductor Wafer Porosification for Selective Substrate Removal
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Solution Overview
Problem
Conventional methods fail to precisely remove a semiconductor substrate from a wafer while preserving the semiconductor layer formed on top, as etching or polishing processes often result in unintended removal of the substrate and alteration of the layer thickness.
Innovation Solution
A method involving porosification of the semiconductor substrate, where a porous region is formed with a higher doping concentration than the adjacent layer, allowing for selective etching of the substrate without affecting the epitaxial layer, using a porosifying agent and controlled voltage to create a porous region that can be easily removed, leaving the epitaxial layer intact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching or polishing processes are used to remove the substrate, then the substrate can be removed, but the thickness of the semiconductor layer cannot be preserved and unintended removal occurs
Solution Approach 1:
The substrate is segmented into two distinct regions: a first semiconductor layer with higher doping concentration that will be removed, and a second semiconductor layer with lower doping concentration that will be preserved. This segmentation allows selective removal of only the substrate portion while maintaining the semiconductor layer integrity.
Solution Approach 2:
Different regions of the substrate are given different doping concentrations to create distinct local properties. The first semiconductor layer has a higher doping concentration making it susceptible to porosification and removal, while the second semiconductor layer has a lower doping concentration that protects it from the same process, enabling precise local removal.
2Ease of manufacture
If the substrate is completely removed to allow device region formation, then device fabrication can proceed, but the semiconductor layer thickness cannot be maintained
Solution Approach 1:
The substrate is pre-modified by forming a porous region in the first semiconductor layer before the actual removal process. This preliminary porosification creates a structure that is easily removable while protecting the second semiconductor layer, allowing subsequent easy removal without affecting the layer thickness.
Solution Approach 2:
The doping concentration parameter is changed across different regions of the substrate to create selective removability. By establishing a doping concentration gradient or step function, the substrate becomes differentially susceptible to porosification and removal, enabling precise control over what is removed and what is preserved.
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 method enables precise removal of the substrate while maintaining the thickness and integrity of the epitaxial layer, facilitating the formation of semiconductor devices with desired electric characteristics by ensuring minimal impact on the epitaxial layer during the substrate removal process.
Implementation Method 1
The process of forming the porous region in the first semiconductor layer comprises removing material from the first semiconductor layer with a porosifying agent, wherein the porosifying agent removes material from the first semiconductor layer through electrochemical etching
Data Source
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AI summary
A method is disclosed. The method includes: in a semiconductor wafer comprising a first semiconductor layer (10) and a second semiconductor layer (20) adjoining the first semiconductor layer (10), forming a porous region (12) extending from a first surface (11) into the first semiconductor layer (10); and removing the porous region (12) by an etching process, wherein with regard to a doping of the first semiconductor layer (10) and a doping of the second semiconductor layer (20) at least one of the following applies: a doping concentration of the second semiconductor layer (20) is less than 10-2 times a doping concentration of the first semiconductor layer (10); a doping type of the second semiconductor layer is complementary to a doping type of the first semiconductor layer (10).