Source Wafer Etch Stop Layers for Flat Micro-Transfer Printing
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Solution Overview
Problem
In micro-transfer printing, the lack of selectivity in wet chemical etching for removing sacrificial layers results in a bowed bottom surface of device coupons, affecting bonding with host wafers and requiring additional complexities or costs for substrate reuse.
Innovation Solution
Incorporating one or more etch stop layers between the photonic component and the wafer substrate, and optionally between the release layer and the wafer substrate, to improve the flatness of the device coupon's bottom surface and enable substrate reuse without additional polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet chemical etching is used to remove the sacrificial release layer, then the device coupon can be lifted off from the substrate, but the bottom surface of the device coupon becomes bowed and non-flat
Solution Approach 1:
An etch stop layer is introduced as an intermediary between the device coupon and the substrate. This layer is selectively etched by the wet chemical etchant to create a flat bottom surface on the device coupon while still allowing complete removal of the sacrificial release layer for lift-off. The etch stop layer acts as a mediator that enables both the lift-off process and the flatness requirement.
2Productivity
If the substrate is reused after lift off to reduce cost, then manufacturing cost decreases, but additional polishing processes are required to restore substrate flatness
Solution Approach 1:
The etch stop layer serves as a protective intermediary between the substrate and the etching process. When the sacrificial release layer is removed, the etch stop layer remains in place, preventing damage to the substrate and maintaining its flatness. This allows the substrate to be reused immediately without requiring additional polishing or flatness restoration processes.
Solution Approach 2:
The etch stop layer is deposited on the substrate before the device coupon is fabricated and attached. This preliminary action ensures that when subsequent etching occurs to remove the release layer, the substrate is already protected and will not require post-processing. The flatness is preserved in advance, enabling direct substrate reuse.
3Manufacturing precision
If high selectivity wet etching conditions are used to achieve flat bottom surface, then manufacturing precision improves, but process complexity and cost increase
Solution Approach 1:
The etch stop layer is designed with specific material properties that provide high etch selectivity, creating a natural barrier that stops the etching process at the desired depth. This intermediary layer eliminates the need for complex process control conditions, as the etch stop layer inherently defines the etching depth and ensures flat bottom surface formation through its selective removal.
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 etch stop layers enhance the flatness of the device coupon's surface, improving adhesion and yield during micro-transfer printing, while allowing for cost-effective and efficient reuse of substrates.
Implementation Method 1
wet chemical etching, which selectively etches the sacrificial layer
Implementation Method 2
This is usually performed through wet chemical etching, which selectively etches the sacrificial layer
Data Source
AI summary
A source wafer for use in a micro-transfer printing process. The source wafer comprising: a wafer substrate; a photonic component, provided in a device coupon, the device coupon being attached to the wafer substrate via a release layer; and one or more etch stop layers, located between the photonic component and the wafer substrate.