Pad Positioning in Solid-State Imaging Substrates
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Solution Overview
Problem
Existing solid-state imaging apparatuses face challenges in achieving high reliability and simplicity in the connection between the pad and the circuit due to long electrical routes and complex manufacturing processes, leading to increased connection resistance and sensitivity issues.
Innovation Solution
A solid-state imaging apparatus is designed with a wiring structure between two semiconductor substrates, where the pad is strategically positioned between the substrates to reduce electrical route length and simplify the connection process, allowing for easier formation of a reliable connection between the pad and the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pad is formed on the back-side face of the second substrate after exposure by polishing, then the light receiving area of the photoelectric conversion element is secured, but the electrical route connecting the pad and the first substrate becomes long, resulting in increased connection resistance and degraded reliability
Solution Approach 1:
The pad is repositioned from the back-side face to the front-side face of the second substrate, changing the spatial dimension of pad formation. This dimensional change allows the pad to be formed in a location that shortens the electrical connection route to the first substrate while still maintaining sufficient light receiving area for the photoelectric conversion element.
Solution Approach 2:
A liner is introduced as an intermediary layer between the pad and the second substrate. This liner facilitates the formation of the pad on the front-side face while maintaining proper electrical connection, acting as a mediator that enables both short connection routes and adequate light receiving area.
2Reliability
If the pad is formed on the back-side face of the second substrate, then the connection between pad and first substrate is established, but the manufacturing process becomes complicated requiring liner provision, polishing, and pad formation steps
Solution Approach 1:
The pad is formed on the front-side face of the second substrate before bonding to the first substrate, rather than after bonding and polishing. This preliminary action eliminates the need for subsequent polishing and liner provision steps, simplifying the manufacturing process while maintaining reliable electrical connection.
Solution Approach 2:
The conventional sequence of operations is inverted: instead of bonding substrates first and then forming the pad on the back-side face through polishing, the pad is formed on the front-side face before bonding. This inversion of the process sequence eliminates complicated manufacturing steps while ensuring reliable connection.
3Measurement precision
If pixels are made finer to obtain high definition images, then image definition is improved, but the light receiving area of the photoelectric conversion element decreases, resulting in deterioration in sensitivity
Solution Approach 1:
By repositioning the pad to the front-side face of the second substrate, the light receiving area of the photoelectric conversion element can be maximized even with finer pixels. The pad occupies space that would otherwise interfere with the photoelectric conversion element's light receiving area, allowing high pixel density without sacrificing sensitivity.
Data Source
AI summary
The first face of the pad is situated between the front-side face of the second semiconductor substrate and a hypothetical plane including and being parallel to the front-side face, and a second face of the pad that is a face on the opposite side of the first face is situated between the first face and the front-side face of the second semiconductor substrate, and wherein the second face is connected to the wiring structure so that the pad is electrically connected to the circuit arranged in the front-side face of the second semiconductor substrate via the wiring structure.