Device Layer Cavities for Alignment Mark Placement
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Solution Overview
Problem
Existing processes for locating devices after transferring a useful layer to a carrier substrate make alignment marks inaccessible, requiring large apertures to be drilled, which consume excessive space and are imprecise.
Innovation Solution
The process involves placing alignment marks in cavities within the device layer, allowing through-holes to form naturally during transfer, enabling precise device location without additional hole formation steps, using direct bonding under low pressure and heat treatment to maintain cavity integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If apertures are formed in the useful layer to expose alignment marks, then alignment marks become accessible, but aperture size must be large (250 μm) which consumes excessive space
Solution Approach 1:
The alignment marks are moved from the surface level to a lower dimension by placing them at the bottom of cavities formed in the device layer. This vertical displacement allows the useful layer to remain intact at the surface while still providing access to alignment marks through the cavity openings, eliminating the need for large surface apertures.
Solution Approach 2:
The alignment marks are nested within cavities in the device layer, which are themselves positioned on the carrier substrate. This nested structure allows the alignment marks to be contained within the device layer architecture rather than requiring separate surface features, enabling precise location without large apertures.
2Measurement precision
If photolithography is used to define aperture positions, then alignment mark locations are determined, but precision is limited to +/−100 μm without reference points
Solution Approach 1:
Cavities are formed in the device layer before the useful layer is transferred. This preliminary action establishes precise reference structures that will guide the subsequent alignment and transfer processes, eliminating the need for high-precision photolithography alignment since the cavities themselves serve as the alignment references.
Solution Approach 2:
The cavities in the device layer serve dual purposes: they provide structural features for the device architecture and simultaneously serve as alignment references for locating devices after transfer. This self-service function eliminates the need for separate alignment mark structures and complex photolithography alignment procedures.
3Ease of operation
If additional photolithography and etching steps are added to form apertures, then alignment marks can be exposed, but process complexity and manufacturing time increase
Solution Approach 1:
The cavity formation step is merged with the device layer fabrication process, and the alignment mark exposure is achieved through the same cavity structure. This combines multiple functions (device structure creation and alignment reference provision) into a single process step, eliminating the need for separate photolithography and etching steps that would be required to create surface apertures.
Solution Approach 2:
The alignment marks are extracted from the surface level and placed within the cavities of the device layer. This extraction allows the useful layer to remain continuous at the surface while still providing access to alignment marks through the cavity openings, eliminating the need for additional aperture-forming steps.
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 allows for precise device location with smaller apertures, eliminating the need for additional hole formation and maintaining alignment mark visibility, thus improving spatial efficiency and precision.
Implementation Method 1
fracturing the donor substrate in the weak zone so as to transfer the useful layer to the device layer
Implementation Method 2
using direct bonding under low pressure and heat treatment to maintain cavity integrity
Data Source
AI summary
The disclosure relates to a process for locating devices, the process comprising the following steps:a) providing a carrier substrate comprising:a device layer; andalignment marks;b) providing a donor substrate;c) forming a weak zone in the donor substrate, the weak zone delimiting a useful layer;d) assembling the donor substrate and the carrier substrate; ande) fracturing the donor substrate in the weak zone so as to transfer the useful layer to the device layer;wherein the alignment marks are placed in cavities formed in the device layer, the cavities having an aperture flush with the free surface of the device layer.