Back-Illuminated Sensor Wafer Thickness Control
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Solution Overview
Problem
Conventional methods for manufacturing back-illuminated type solid-state image sensing devices face challenges such as thickness variation, increased costs, and defects due to the use of expensive epitaxial SOI wafers and complex processes, leading to non-uniform etching and light sensitivity issues.
Innovation Solution
A method involving the formation of a solid-state image sensing device on a silicon wafer, followed by bonding a support substrate, grinding, mirror finishing, and controlled plasma etching to achieve precise thickness reduction, reducing the number of processes and costs while minimizing defects and thickness variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods use expensive epitaxial SOI wafers and complex processes including end-point detectors, then manufacturing precision can be maintained, but manufacturing cost increases significantly and device complexity increases
Solution Approach 1:
The patent replaces expensive epitaxial SOI wafers with ordinary silicon wafers that have an epitaxial film formed on them. This substitution uses cheaper, more readily available materials while achieving the same functional outcome through a different process approach, thereby reducing manufacturing cost without sacrificing film thickness uniformity
Solution Approach 2:
The patent removes the end-point detector component and the associated complex detection processes from the manufacturing flow. Instead, it uses a simplified thickness measurement and control method that achieves the same film thickness uniformity without the added complexity and cost of end-point detectors
2Manufacturing precision
If conventional methods use epitaxial SOI wafers with embedded silicon oxide films, then etching selectivity is improved, but the number of processes increases and manufacturing complexity increases
Solution Approach 1:
The patent extracts and removes the embedded silicon oxide film layer from the wafer structure. By eliminating this intermediate layer, the manufacturing process is simplified while maintaining etching selectivity through alternative means, thereby reducing the number of processes without sacrificing precision
Solution Approach 2:
The patent changes the etching parameters and conditions to achieve the required selectivity without relying on the embedded silicon oxide film. This allows the process to maintain precision while using fewer process steps
3Length of moving object
If conventional methods perform film thinning by grinding to residual thickness of 10-30 μm, then thickness reduction is achieved, but thickness variation occurs leading to non-uniform etching
Solution Approach 1:
The patent implements a feedback control system where the wafer thickness is measured during the thinning process, and the etching parameters are adjusted based on this measurement. This closed-loop control ensures uniform thickness reduction and eliminates the thickness variation that occurs with conventional open-loop grinding methods
Solution Approach 2:
The patent makes the thinning process dynamic by adjusting etching conditions in real-time based on measured thickness values. This dynamic adaptation allows the process to maintain uniformity throughout the thinning operation, unlike static grinding methods that produce variation
4Object-affected harmful factors
If conventional methods use multi-layer wiring on front surface side, then light path blocking is reduced, but light sensitivity still decreases due to gradient light in periphery portion
Solution Approach 1:
The patent changes the wafer thickness parameter to optimize light sensitivity. By precisely controlling the final thickness through measurement and feedback control during etching, the patent achieves uniform thickness that maximizes light sensitivity while maintaining the back-illuminated structure that reduces light path blocking
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 enables the manufacturing of back-illuminated type solid-state image pick-up apparatus with reduced thickness variation and improved light sensitivity at a lower cost, without the need for expensive SOI wafers and complex end-point detectors, resulting in high-quality epitaxial films and uniform film thickness.
Implementation Method 1
the semiconductor wafer layer is plasma etched from the mirror-finished surface until a predetermined thickness is reached by controlling plasma etching amount
Data Source
AI summary
The thickness of a semiconductor wafer layer, extending from a mirror-finished surface thereof to a solid-state image sensing device, is measured. Based on the residual thickness data, plasma etching is performed from the mirror-finished surface until a predetermined thickness is reached by controlling the plasma etching amount. By doing this, it is possible to reduce variation in the thickness of the solid-state image sensing device at low cost without causing an increase in the number of processes.