3D Semiconductor Etching Using Sub-Bandgap Laser Control
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Solution Overview
Problem
Conventional microfabrication techniques for ICs and MEMS are complex, time-consuming, and costly, limited to creating two-dimensional structures, and struggle with small feature sizes and three-dimensional geometries.
Innovation Solution
A system and method for selective semiconductor etching using sub-bandgap-energy lasers to create holes in the semiconductor lattice through multi-photon absorption, allowing for controlled etching of three-dimensional features by directing holes to specific locations within the semiconductor using a computing device that models charge-carrier transport and electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional microfabrication techniques are used, then manufacturing process is well-established, but device complexity increases and manufacturing precision is limited to 2.5D geometries
Solution Approach 1:
The patent replaces conventional mechanical lithographic patterning and etching processes with a laser-based system that uses optical fields to generate carriers and electrochemical fields to direct etching. The laser system with computational control substitutes for complex multi-step lithographic toolchains, enabling direct 3D fabrication without mechanical contact or layered deposition.
Solution Approach 2:
The patent changes the fundamental parameters of the fabrication process by using sub-bandgap laser wavelengths that penetrate the semiconductor bulk, combined with controlled electrochemical etching parameters. This allows etching to occur throughout the bulk material rather than only at surfaces, enabling true 3D geometries with precision unattainable by conventional surface-based methods.
2Productivity
If conventional layer-by-layer fabrication is used, then process control is straightforward, but productivity decreases due to multiple sequential steps
Solution Approach 1:
The patent performs preliminary computational modeling of charge-carrier transport and electrochemical etching processes to predict the exact laser parameters and electrode configurations needed for desired 3D structures. This pre-calculation eliminates the need for iterative trial-and-error fabrication steps, allowing direct fabrication of complex geometries in a single controlled process.
Solution Approach 2:
The patent merges carrier generation, carrier transport control, and etching execution into a single integrated laser-based electrochemical process. Instead of separate lithography, etching, and deposition steps, the system combines these functions by using the laser to simultaneously generate carriers and the electrochemical field to direct material removal, dramatically reducing process time.
3Manufacturing precision
If sub-bandgap energy laser is used for selective etching, then manufacturing precision improves for 3D structures, but use of energy increases due to multi-photon absorption requirements
Solution Approach 1:
The patent applies laser energy locally only where etching is desired by focusing the sub-bandgap laser to specific spatial positions within the semiconductor bulk. The electrochemical field is similarly localized to direct carriers only to regions where material removal is needed. This localized application of energy and field avoids wasteful bulk heating and enables precise 3D etching with controlled energy consumption.
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
Enables the precise etching of three-dimensional structures with smaller feature sizes than conventional methods, improving resolution and reducing complexity and cost by selectively controlling the etching process.
Implementation Method 1
Holes are selectively created by illumination of the semiconductor by an illumination source (e.g., a laser) that has an energy below the bandgap energy of the semiconductor. Single sub-bandgap energy photons do not have sufficient energy to move electrons in the semiconductor from the valence band to the conduction band. Thus, ordinarily sub-bandgap energy light is unable to create holes in the atomic lattice of the semiconductor. The sub-bandgap energy light emitted by the illumination source is focused to a sufficiently intense focal spot to cause multi-photon absorption (MPA) within the semiconductor.
Implementation Method 2
A semiconductor is etched by way of electrochemical reactions at a surface of the semiconductor that is exposed to an etchant solution. The exposed surface of the semiconductor is etched selectively based upon controlled creation of holes in the atomic lattice of the semiconductor (i.e., absences of electrons in the lattice that are commonly modeled as positively-charged particles called holes). In the etching reaction, holes at the exposed surface of the semiconductor cause oxidation of the semiconductor, which oxidation is subsequently etched by the etchant solution.
Implementation Method 3
Holes can be selectively created in a region near the focal spot of the illumination source where etching is desirably performed, thereby limiting the etching to a region near the focal spot. A computing device controls the illumination source based upon a model of charge-carrier transport within the semiconductor.
Implementation Method 4
A voltage is applied between a first surface of the semiconductor and a second surface of the semiconductor. The computing device controls the illumination source based upon a model of charge-carrier transport within the semiconductor, including an electric field induced by the applied voltage.
Data Source
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AI summary
Various technologies are described herein pertaining to electrochemical etching of a semiconductor controlled by way of a laser that emits light with an energy below a bandgap energy of the semiconductor.