A scanner in photolithography works by projecting a circuit pattern from a mask onto a silicon wafer coated with photoresist using a precisely controlled optical system.
In the semiconductor manufacturing process, after preparation steps like thermal bake-out, the substrate (wafer) is moved into an optical projection tool known as a scanner (or stepper/scanner). This tool is crucial for transferring the desired design pattern onto the wafer surface.
Here's a breakdown of the core mechanism, as described in the process:
- Light Source: A specific wavelength of light is generated.
- Mask (Reticle): This light beam then passes through a mask, which contains the desired circuit pattern. The mask acts like a stencil, blocking light in some areas and allowing it to pass through in others.
- Reduction Lens System: After passing through the mask, the light beam enters a sophisticated reduction lens system. This system focuses the light and shrinks the pattern from the mask (which is typically larger than the final feature size on the wafer) down to the required dimensions.
- Wafer Exposure: The focused, reduced image is then projected onto the surface of the silicon wafer, which is covered with a light-sensitive material called photoresist. The areas of the photoresist exposed to light undergo a chemical change.
As the reference states:
A light beam passing through the mask is focused on the wafer through a reduction lens system to produce the desired image in the photoresist.
Unlike a traditional stepper that exposes the entire pattern area (or a segment) in one flash before stepping to the next area, a photolithography scanner typically exposes the pattern by moving the mask and the wafer simultaneously relative to a narrow slit of light. This scanning motion allows for larger exposure areas and can help mitigate certain optical distortions.
Think of the process like using a high-tech slide projector to shrink and project a complex image onto a very small, light-sensitive surface. The scanner ensures this projection is done with extreme precision, layer by layer, building up the intricate structures of a microchip.
Key Components Involved
| Component | Function |
|---|---|
| Light Source | Provides the light used for exposure. |
| Mask (Reticle) | Holds the circuit pattern to be transferred. |
| Reduction Lens | Shrinks and focuses the pattern onto the wafer. |
| Wafer | The semiconductor substrate being processed. |
| Photoresist | Light-sensitive coating on the wafer. |
| Stage (Wafer/Mask) | Precision mechanics for positioning and scanning. |
By orchestrating the movement of the wafer and mask while projecting the light through the reduction optics, the scanner accurately transfers the intricate patterns required for creating integrated circuits onto the wafer surface.
