Wafer Level Shim Processing for Focal Plane Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wafer processing techniques, such as using epoxy for die level shims, often result in voids at the bond interface and can risk damaging delicate optical surfaces during bow compensation, which is critical for achieving flatness in sensing devices like focal plane arrays.
Innovation Solution
The method involves bonding a first wafer with a detector to a second wafer with a read-out integrated circuit (ROIC) using an oxide layer, followed by the deposition of a bonding oxide on the ROIC wafer. A shim is then bonded to the assembly using low-temperature oxide bonding, which reduces wafer bow and enhances flatness without damaging the optical surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epoxy application is used for die level shim, then shimming can be achieved, but voids are created in the bond interface layer
Solution Approach 1:
The patent replaces the conventional epoxy-based mechanical bonding system with an oxide-to-oxide bonding system. This substitution eliminates the need for epoxy application and curing processes, thereby preventing void formation in the bond interface while achieving precise shim flatness through controlled oxide layer deposition and annealing processes.
Solution Approach 2:
The patent changes the bonding parameters from epoxy-based chemical bonding to oxide-based thermal bonding. By controlling oxide layer thickness, annealing temperature, and atmosphere, the process achieves superior bond interface quality without voids while maintaining the required shim flatness, resolving the contradiction between manufacturing precision and reliability.
2Manufacturing precision
If weights are used to flatten the device after epoxy application, then die flatness can be improved, but the assembly is put at risk due to weight contact with optical surface
Solution Approach 1:
The patent performs preliminary oxide layer deposition and annealing on the wafer backside before any flatness correction is needed. This preliminary action creates a robust oxide bond that inherently provides the required flatness, eliminating the need for subsequent weight-based flattening operations that could damage the optical surface.
Solution Approach 2:
The patent replaces the mechanical weight-based flattening system with a controlled oxide bonding process that achieves flatness through material property control rather than external mechanical force. This substitution eliminates the harmful contact between weights and the optical surface while achieving the required die flatness.
3Reliability
If oxide layer is deposited before thinning, then wafer surface protection is achieved, but process complexity increases
Solution Approach 1:
The patent merges the oxide layer deposition step with the wafer thinning process sequence. By depositing the oxide layer before thinning, the process combines surface protection and subsequent handling into a single integrated flow, where the oxide layer serves dual purposes of protection and bonding, thereby reducing overall process complexity despite the additional deposition step.
Solution Approach 2:
The oxide layer acts as an intermediary between the wafer surface and the external environment during processing. This intermediary layer protects the wafer surface during thinning and handling operations, and simultaneously serves as the bonding interface for shim attachment, thereby simplifying the overall process by combining protection and bonding functions in one layer.
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
This approach effectively reduces wafer bow by up to 96%, achieving ultra-flat optical surfaces and minimizing voids, thereby improving the performance and reliability of sensing devices like focal plane arrays.
Implementation Method 1
a first wafer bonded to a second wafer with an oxide layer
Implementation Method 2
creating a bonding oxide on a second surface of the second wafer
Implementation Method 3
annealing the circuit assembly
Implementation Method 4
polishing the bonding oxide on the second surface of the second wafer
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
Methods and apparatus for proving a sensor assembly. Embodiments can include employing a circuit assembly having a first layer bonded to a second layer with an oxide layer, depositing bonding oxide on the second layer of the circuit assembly, and thinning the first layer of the circuit assembly after depositing the bonding oxide. A coating can be applied over at least a portion of the first layer of the circuit assembly after annealing the circuit assembly. After polishing the bonding oxide on the second surface of the second layer of the circuit assembly, a shim can be secured to the bonding oxide on the second surface of the second layer of the circuit assembly to reduce bow of the assembly. Embodiments can provide a sensor useful in focal plane arrays.