Universal Transfer Printing With Adjustable Polymer Tethers
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Solution Overview
Problem
Existing micro-transfer printing methods are not suitable for processes involving gallium nitride (GaN) or other compound semiconductor materials due to differences in physical and chemical properties, and the lack of an analogous oxide layer that can be etched away like in silicon.
Innovation Solution
A universal transfer printing method using adjustable polymer tethers that can accommodate various semiconductor materials, allowing for the combination of disparate semiconductor devices such as GaN with SiC or BCDMOS, and enabling parallel processing and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional micro-transfer printing methods are used with silicon oxide etching, then silicon-based chiplets can be transferred, but the method cannot be applied to GaN or other compound semiconductor materials due to lack of analogous etchable oxide layers
Solution Approach 1:
The patent introduces a sacrificial adhesive layer as an intermediary between the chiplet and carrier substrate. This layer serves as a universal release mechanism that works with all semiconductor materials regardless of their native oxide properties. The adhesive layer can be selectively removed to release the chiplet, providing a material-agnostic transfer mechanism that resolves the contradiction between versatility and process complexity
Solution Approach 2:
The patent changes the fundamental parameter of the release mechanism from material-specific chemical etching (requiring specific oxide layers) to a universal adhesive-based mechanical release. This parameter change allows the same transfer printing process to be applied to diverse materials including silicon, GaN, and other compound semiconductors without requiring material-specific process adjustments
2Manufacturing precision
If individual chiplets are transferred sequentially, then precise positioning can be achieved, but processing time increases significantly
Solution Approach 1:
The patent segments the transfer process into two distinct phases: a parallel phase where multiple chiplets are transferred simultaneously to achieve high productivity, and a precision phase where the elastomeric stamp provides self-alignment and precise positioning. This segmentation allows both high-speed parallel transfer and accurate positioning to be achieved without compromise
Solution Approach 2:
The patent merges the functions of parallel transfer and precise positioning into a single integrated process step. The elastomeric stamp simultaneously performs bulk transfer of multiple chiplets and provides self-aligning contact that ensures precise positioning, eliminating the need for separate sequential operations and thereby increasing productivity while maintaining manufacturing precision
3Reliability
If larger tether structures are used to hold chiplets during transfer, then chiplet retention is improved, but the tether occupies more space and increases parasitics
Solution Approach 1:
The patent employs thin film tether structures that provide sufficient mechanical strength for chiplet retention during transfer while occupying minimal space. The flexible nature of these thin film tethers allows them to conform to the chiplet surface and provide reliable adhesion without requiring large cross-sectional areas, thereby reducing parasitic effects while maintaining retention reliability
Data Source
AI summary
A transfer printing method is described that can be used for a wide variety of materials, such as to allow for circuits formed of different materials to be integrated together on a single integrated circuit. A tether (18) is formed on dice regions (16) of a first wafer (30), followed by attachment of a second wafer (32) to the tethers. The dice regions (16) are processed so as to be separated, followed by transfer printing of the dice regions to a third wafer (34).