GaN Device-on-Silicon Stiffener Layer for Substrate Removal
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Solution Overview
Problem
Group III-nitride based devices formed on silicon substrates face strain-induced bowing and cracking due to lattice mismatch, and the opaque silicon substrate needs to be removed for optical applications, necessitating a method to enhance mechanical stability and facilitate substrate removal.
Innovation Solution
A method involving the formation of a silicon-based stiffener layer over the group III-nitride device on a silicon substrate, followed by flipping and bonding to a submount, which includes through-silicon vias for electrical contact, allowing the silicon substrate to be removed while maintaining mechanical support and reducing stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If group III-nitride layers are grown on silicon substrate to reduce manufacturing cost, then manufacturing cost is reduced, but strain-induced bowing and cracking occur due to lattice mismatch
Solution Approach 1:
The patent segments the device structure by introducing a stiffener layer that is selectively removed in specific regions. This segmentation allows the stiffener to provide mechanical support where needed while being removed to enable optical access where required, resolving the contradiction between maintaining structural integrity and enabling optical functionality.
Solution Approach 2:
The stiffener layer is formed preliminarily during the device fabrication process, before the device is completed and before substrate removal is needed. This preliminary action provides mechanical support during critical fabrication and handling stages, preventing bowing and cracking, while the stiffener is subsequently removed to enable optical access.
2Reliability
If silicon substrate is kept for mechanical support, then mechanical stability is improved, but optical applications are prevented due to substrate opacity
Solution Approach 1:
The stiffener layer is segmented into regions that are retained and regions that are removed. The retention regions provide mechanical support, while the removal regions enable optical access, thus simultaneously achieving both mechanical stability and optical compatibility in different parts of the device.
Solution Approach 2:
The stiffener layer exhibits local quality by having different presence/absence in different regions of the device. In some regions, it provides mechanical support, while in other regions, it is removed to allow optical functionality, thus adapting to local requirements of the device.
3Reliability
If stiffener layer is formed to reduce strain-induced bowing, then mechanical stability is improved, but device complexity increases due to additional fabrication steps
Solution Approach 1:
The formation of the stiffener layer is merged with existing fabrication processes. The stiffener layer is formed using standard semiconductor manufacturing techniques that are already part of the device fabrication flow, thus adding minimal complexity while providing significant mechanical stability benefits.
Data Source
AI summary
A method for flip chip bonding a GaN device formed on a silicon substrate is described. The method includes providing a silicon substrate having a GaN device thereon, the GaN device comprising at least one gallium-nitride layer near the silicon substrate and remote from the silicon substrate a dielectric layer comprising at least one via configured to electrically contact the at least one gallium-nitride layer, forming a stiffener layer over the GaN device leaving the at least one via exposed, flip chip bonding the GaN device to a submount, wherein the stiffener layer physically contacts the submount and the submount is electrically connected to the at least gallium-nitride layer through the via, and completely removing the silicon substrate exposing the GaN device. Preferably, the material of the stiffener layer comprises silicon, such as silicon, silicon-germanium, or silicon-carbide.