Backside Illuminated Image Sensor Self-Aligned Metal Pad Fabrication
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Solution Overview
Problem
The existing semiconductor image sensor fabrication processes are complex and time-consuming, requiring multiple photolithography steps which increase costs and reduce throughput.
Innovation Solution
The implementation of a self-aligned metal pad structure during image sensor fabrication, which simplifies the process by eliminating the need for additional patterning steps and using shallow trench isolation (STI) structures to electrically separate adjacent image sensors, along with self-aligned patterning processes to form contact plugs and pads, reducing the number of photolithography processes required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple photolithography steps are used to form metal pad structures, then manufacturing precision is improved, but device complexity and production time increase
Solution Approach 1:
The patent combines the formation of contact holes and metal pad openings into a single self-aligned process. The first photolithography step forms both contact holes and the pattern for metal pad openings simultaneously, eliminating the need for separate patterning steps. This merging of operations reduces fabrication complexity while maintaining alignment precision through self-alignment mechanisms.
Solution Approach 2:
The patent performs preliminary patterning of the metal pad region during the contact hole formation step. By pre-defining the metal pad opening locations in the same photolithography step that creates contact holes, the process eliminates subsequent patterning steps. This preliminary action reduces overall device complexity while ensuring precise alignment through self-aligned etching processes.
2Manufacturing precision
If multiple photolithography steps are used, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
The patent merges multiple photolithography operations into fewer steps by using self-aligned processes. The metal pad openings are formed in the same photolithography step as contact holes, and subsequent etching steps use previously formed structures as alignment references. This reduction in photolithography steps directly increases fabrication throughput while maintaining precision through self-alignment.
Solution Approach 2:
The patent performs preliminary patterning of metal pad regions during contact hole formation, eliminating the need for separate metal pad patterning steps. This preliminary action reduces the total number of photolithography cycles required, thereby increasing productivity while ensuring precise alignment through self-aligned etching processes that use previously formed structures as masks.
3Manufacturing precision
If additional patterning steps are added, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The patent combines the patterning of contact holes and metal pad openings into a single photolithography step. By forming both features simultaneously using self-aligned processes, the invention eliminates additional patterning steps that would otherwise be required to achieve precise pad alignment, thereby reducing fabrication cycle time while maintaining manufacturing precision.
Solution Approach 2:
The patent performs preliminary patterning of metal pad openings during the contact hole formation step. This preliminary action defines the metal pad locations without requiring subsequent dedicated patterning steps, reducing overall fabrication time while ensuring precise alignment through self-aligned etching that uses the contact hole patterns as reference.
4Ease of manufacture
If self-aligned structures are used, then ease of manufacture is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent merges contact hole formation and metal pad opening creation into self-aligned processes where previously formed structures serve as alignment masks. This merging simplifies manufacturing by eliminating separate patterning steps while the self-alignment mechanism inherently ensures precise positioning, reducing the need for high-precision photolithography alignment.
Solution Approach 2:
The patent employs self-aligned etching processes where previously formed structures (contact holes, isolation trenches) automatically serve as alignment masks for subsequent etching steps. This self-service mechanism ensures precise alignment without requiring additional photolithography alignment steps, simplifying manufacturing while maintaining precision through the self-aligning nature of the process.
Data Source
AI summary
An image sensor comprises a semiconductor material having a front side and a back side opposite the front side; a dielectric layer disposed on the front side of the semiconductor material; a poly layer disposed on the dielectric layer; an interlayer dielectric material covering both the poly layer and the dielectric layer; an inter-metal layer disposed on the interlayer dielectric material, wherein a metal interconnect is disposed in the inter-metal layer; and a contact pad trench extending from the back side of the semiconductor material into the semiconductor material, wherein the contact pad trench comprises a contact pad disposed in the contact pad trench, wherein the contact pad and the metal interconnect are coupled with a plurality of contact plugs; and at least an air gap isolates the contact pad and side walls of the contact pad trench. The poly layer and the semiconductor material between adjacent two STI structures of a plurality of first and second STI structures are used as hard masks to form the plurality of contact plugs by selectively removing the dielectric materials between a first side of the plurality of first STI structures and the metal interconnect, wherein each of the plurality of contact plugs extends from the first side of each of the plurality of first STI structures through each of the plurality of first STI structures into the interlayer dielectric material and vertically abuts the metal interconnect.