Polyimide Backside Film for Wafer Particle Capture
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Solution Overview
Problem
As semiconductor devices shrink, immersion photolithography becomes sensitive to unwanted particles on the wafer backside, leading to image defocusing and defects, resulting in lowered yields and increased costs due to blurred lines in the exposed photoresist.
Innovation Solution
Applying a polyimide layer, such as KAPTON film, to the wafer backside captures particles during processing steps, which are then removed before subsequent photolithography, preventing contamination of the immersion medium and maintaining image sharpness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If immersion photolithography is used to achieve finer resolution, then resolution is improved, but sensitivity to particles increases causing image defocusing and defects
Solution Approach 1:
The patent segments the wafer into two distinct surfaces: the active side for photolithography and the backside for particle capture. By applying a separate polyimide layer to the backside, particle management is separated from the front-side imaging process, allowing immersion photolithography to maintain high resolution while backside particles are captured and removed independently.
Solution Approach 2:
The polyimide layer acts as an intermediary between the wafer backside and the immersion medium. It captures particles during processing and serves as a removable barrier that prevents particles from contaminating the immersion liquid, thereby protecting the imaging process from particle-induced defocusing while allowing the high-resolution benefits of immersion photolithography to be realized.
2Productivity
If particles are present on wafer backside during processing, then processing can proceed, but particles become mobile and cause blurred lines in exposed photoresist
Solution Approach 1:
The patent applies the polyimide layer to the wafer backside before processing steps that generate particles. This preliminary action ensures that particles are captured at the source during etching and other processing steps, preventing them from becoming mobile and contaminating the immersion medium before they can cause blurred lines in the photoresist.
Solution Approach 2:
The patent converts the potentially harmful presence of particles during processing into a benefit by using the polyimide layer to deliberately capture and contain these particles on the backside. The particles that would otherwise cause blurred lines are instead trapped on the polyimide layer, which is subsequently removed, leaving the photoresist patterns sharp and clear.
3Object-affected harmful factors
If polyimide layer is applied to capture particles, then particle contamination is reduced, but additional process steps are required
Solution Approach 1:
The polyimide layer is applied to the wafer backside, serves its particle-capturing function during processing, and is then discarded in a single removal step. This approach accepts the addition of process steps as a trade-off for dramatically reducing particle contamination, with the polyimide layer being easily removed after serving its protective purpose.
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
Substantially reduces particles on the wafer, improving yield and reducing costs by eliminating defocus issues and maintaining sharp image lines during resist exposure, with fewer than 300 particles per wafer detected post-implementation compared to 1200-2000 without the solution.
Implementation Method 1
a polyimide layer, such as a tape or film, is applied to a backside of the wafer... particles that impinge on the backside during the etching are captured by the polyimide layer
Implementation Method 2
By using a medium instead of air between the lens and the photoresist to be exposed, and in particular a medium having a refractive index greater than one, the achievable resolution may be increased
Data Source
AI summary
Methods for removing particles from a wafer for photolithography. A method is provided including providing a semiconductor wafer; attaching a polyimide layer to a backside of the semiconductor wafer; and performing an etch on an active surface of the semiconductor wafer; wherein particles that impinge on the backside during the etch are captured by the polyimide layer. In another method, includes attaching a layer of polyimide film to a backside of a semiconductor wafer; dry etching a material on an active surface of the semiconductor wafer; depositing of an additional layer of material on the active surface of the semiconductor wafer; removing the layer of polyimide film from the backside of the semiconductor wafer; patterning the layer of material using an immersion photolithography process to expose a photoresist on the active surface of the wafer; and repeating the attaching, dry etching, depositing, removing and patterning steps.