Superposition Checking Mark Alignment via Transparent Film
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Solution Overview
Problem
In the lithography process, superposition checking marks on the lower layer cannot be recognized when an opaque film is present between the upper and lower layers, making it difficult to perform alignment and check for misalignment between patterns formed by different masks.
Innovation Solution
A method is developed where a first superposition checking mark is formed with a transparent film on an opaque film, allowing observation of the second step, enabling the measurement of misalignment even when the first mark is obscured by the opaque film. This involves forming a stacked structure with silicon oxide and silicon nitride films, using a carbon film as the opaque layer, and adjusting the film thickness to ensure both the resist pattern and opaque film step are within the same view plane for accurate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an opaque film is formed between upper and lower layers, then the lower layer superposition checking mark cannot be recognized, but the upper layer pattern formation is protected
Solution Approach 1:
A transparent film is introduced as an intermediary layer between the lower layer superposition checking mark and the upper layer opaque film. This transparent film allows optical transmission so that the lower layer mark remains visible through the opaque film region, enabling alignment measurement while maintaining the protective function of the opaque film for upper layer pattern formation.
Solution Approach 2:
The solution transitions from a two-dimensional planar structure to a three-dimensional stacked structure by forming the transparent film as a separate layer above the lower layer mark but below the opaque film. This vertical layering allows simultaneous presence of the opaque film for protection and the transparent film for optical transmission, resolving the visibility contradiction.
2Measurement precision
If the superposition checking mark is formed on the lower layer, then alignment can be performed, but the mark becomes obscured by the opaque film
Solution Approach 1:
The transparent film serves as an optical mediator that allows measurement light to pass through the opaque film region to reach and reflect from the lower layer superposition checking mark. This enables precise misalignment detection while maintaining the opaque film's protective function, as the transparent film's optical transmission property allows the mark to be observed despite the opaque film's presence.
3Difficulty of detecting and measuring
If a transparent film is added to allow observation of the lower layer mark, then the mark becomes visible, but the film structure becomes more complex
Solution Approach 1:
The transparent film performs multiple functions simultaneously: it serves as a structural layer in the film stack, provides optical transmission for mark visibility, and acts as a spacer maintaining vertical separation between layers. By integrating these multiple functions into a single layer, the solution avoids adding excessive complexity while achieving the visibility goal.
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 allows for effective misalignment detection between patterns formed by different reticles, improving the accuracy of alignment and reducing damage to the semiconductor device, while also enabling easy removal and conductivity of the opaque film.
Implementation Method 1
a second superposition checking mark provided with a transparent film allowing observation of the second step is formed on the opaque film
Data Source
AI summary
According to one embodiment, a forming method of superposition checking marks includes forming a first superposition checking mark to have a first step with respect to an arrangement surface for the first superposition checking mark, forming an opaque film having a second step resulting from the first step on the arrangement surface, and forming on the opaque film a second superposition checking mark provided with a transparent film allowing observation of the second step.