SACM-APD Photodiode Fabrication Using Spacer Self-Alignment
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Solution Overview
Problem
Existing methods for fabricating SACM-APD photodiodes in mesa configuration face challenges such as risks of breakdown at the edges due to misalignment and inaccurate peripheral recessing, which affect the optical and electronic properties, and the complexity of multi-step photolithographic processes.
Innovation Solution
A method involving the formation of a photonic chip with a SACM-APD photodiode optically coupled to an integrated waveguide, using spacers to define constant peripheral recessings for the charge and absorption regions, reducing the need for multiple photolithographic steps and enhancing self-alignment, thereby optimizing the photodiode's properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-step photolithographic processes are used to achieve peripheral recessing, then manufacturing precision can be improved, but device complexity and fabrication time increase
Solution Approach 1:
The patent introduces spacers as intermediary elements that define the peripheral recessing of the absorption portion and charge region. These spacers act as physical masks during etching, eliminating the need for multiple photolithographic steps while maintaining precise dimensional control. The spacers are deposited conformally and then anisotropically etched to create the desired recess profiles.
Solution Approach 2:
The fabrication process is segmented into distinct stages: first forming the absorption portion with its peripheral recessing using spacers, then forming the charge region with its peripheral recessing using additional spacers. This segmentation allows each region to be precisely defined independently without requiring complex multi-step photolithographic alignment.
2Ease of manufacture
If peripheral recessing is not properly controlled, then fabrication process is simpler, but breakdown risk at photodiode edges increases
Solution Approach 1:
The spacers are formed preliminarily before the absorption portion and charge region materials are deposited. This preliminary action establishes the precise peripheral boundaries that will contain the subsequent materials, ensuring proper recessing is achieved automatically during the deposition and etching processes without requiring additional corrective steps.
Solution Approach 2:
The patent replaces the mechanical/chemical etching process with multiple photolithographic steps with a physical spacer-based masking approach. The spacers provide mechanical definition of the peripheral recessing boundaries, and anisotropic etching selectively removes material based on the spacer geometry, achieving precise control with simpler processes.
3Measurement precision
If multiple photolithographic steps are used for alignment, then positioning accuracy improves, but manufacturing time and cost increase
Solution Approach 1:
The spacers serve as self-aligning reference structures that automatically define the positions of the absorption portion and charge region peripheries. The conformal deposition and anisotropic etching of spacers create inherent geometric relationships that ensure proper alignment without requiring external photolithographic alignment procedures, thereby improving throughput while maintaining precision.
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 improves the optical and electronic properties of the photodiode by ensuring precise recessing and self-alignment, reducing the risk of breakdown and simplifying the fabrication process, leading to enhanced performance and reliability.
Implementation Method 1
The charge region is bounded laterally by a first spacer made of a first dielectric material extending in contact with the sides of the through-opening such that the charge region has a constant peripheral recessing with respect to an edge of the multiplication portion
Implementation Method 2
the absorption portion is bounded laterally, at the interface with the charge region, by a second spacer made of a second dielectric material distinct from the first dielectric material and extending between and in contact with the first spacer and with the absorption portion such that the absorption portion has a constant peripheral recessing with respect to an edge of the charge region
Implementation Method 3
The waveguide may be optically coupled to the absorption portion in an evanescent manner when it extends in a plane different from that of the absorption portion
Implementation Method 4
an APD is a photodiode whose high reverse biasing causes a multiplication of the charge carriers present in the depletion region by virtue of the impact ionization phenomenon
Data Source
AI summary
The invention relates to a method of fabrication of a photonic chip 1 comprising an avalanche photodiode 20 of the SACM type optically coupled to an integrated waveguide 40, comprising a step for forming a first spacer 24 allowing a constant peripheral recessing drzc of the charge region 23 to be defined later on with respect to an edge of the multiplication portion 22, then a step for forming a second spacer 26 allowing a constant peripheral recessing drpa of the absorption portion 27 to be defined later on with respect to an edge of the charge region 23.