Stressed Ge Photodiode Integration via Substrate Removal
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Solution Overview
Problem
Germanium photodetectors integrated with CMOS silicon photonics platforms have limited optical responsivity in the C-band, and existing methods for introducing stress/strain do not consider the fabrication techniques required for building these detectors, limiting options for depositing stressor materials.
Innovation Solution
A method involving wafer bonding to support the deposition of a stressor material underneath the germanium photodetector, which induces stress and changes the optical absorption edge, improving responsivity by altering the crystal lattice bandgap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stressor material is deposited on the Ge photodetector, then optical responsivity is improved, but fabrication complexity increases due to additional process steps
Solution Approach 1:
The substrate is removed before depositing the stressor material, creating an exposed surface that allows direct deposition underneath the Ge photodetector. This preliminary substrate removal enables the stressor material to be integrated into the device structure without requiring complex post-fabrication processing steps.
Solution Approach 2:
The stressor material is deposited in the vertical dimension underneath the Ge photodetector rather than on the top surface. This dimensional change allows the stressor to be integrated into the device stack without interfering with top-surface contacts or requiring lateral routing, simplifying the overall fabrication process.
2Adaptability or versatility
If substrate is removed to enable stressor deposition, then stressor material options are expanded, but manufacturing process difficulty increases
Solution Approach 1:
The substrate removal is performed as a preliminary step before stressor material deposition, creating the necessary access pathway. By removing the substrate first, the process enables subsequent deposition of various stressor materials (such as silicon nitride, diamond-like carbon, or silicon-germanium) that would otherwise be inaccessible.
Solution Approach 2:
The substrate removal process acts as an intermediary step that bridges the Ge photodetector and the stressor material deposition. This intermediate action creates the structural configuration necessary for integrating diverse stressor materials while maintaining compatibility with existing CMOS fabrication processes.
3Reliability
If stressor material is deposited underneath the Ge photodetector, then optical absorption edge is extended, but device structure complexity increases
Solution Approach 1:
The stressor material is positioned in the vertical dimension underneath the Ge photodetector, allowing optical absorption edge extension without lateral expansion or complex lateral structuring. This vertical integration maintains a compact device footprint while achieving the desired optical performance enhancement.
Solution Approach 2:
The substrate removal and stressor deposition process serves multiple functions: it enables stressor material integration, extends the optical absorption edge, and maintains compatibility with standard CMOS fabrication flows. This multi-functionality reduces the need for separate specialized processing 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
The stressor material, such as silicon nitride or diamond-like carbon, effectively extends the optical absorption edge towards longer wavelengths, enhancing the responsivity of the germanium photodetector in the C-band.
Implementation Method 1
depositing the stressor material induces a stress that changes an optical absorption edge of the germanium photodetector
Implementation Method 2
bonding the first wafer to a second wafer
Data Source
AI summary
The embodiments of the present disclosure describe a stressed Ge PD and fabrications techniques for making the same. In one embodiment, a stressor material is deposited underneath an already formed Ge PD. To do so, wafer bonding can be used to bond the wafer containing the Ge PD to a second, handler wafer. Doing so provides support to remove the substrate of the wafer so that a stressor material (e.g., silicon nitride, diamond-like carbon, or silicon-germanium) can be disposed underneath the Ge PD. The stress material induces a stress or strain in the crystal lattice of the Ge which changes its bandgap and improves its responsivity.