An oxide layer is grown on silicon wafer by dry oxidation. The layer is coated with negative photoresist. The mask is shown in figure. Which one of the following structures we will get after exposure followed by development and HF dip (before acetone dip)? Consider green layer as oxide layer and orange layer as photoresist.
To determine the resulting structure after exposure followed by development and HF dip, let's examine each step of the process and the effect it has on the photoresist layer.
1. Exposure: During the exposure step, the photoresist layer is exposed to UV light through a mask. Areas that are transparent in the mask allow the UV light to penetrate the resist, while areas that are opaque in the mask block the UV light.
2. Development: After exposure, the wafer is developed using a developer solution. The developer selectively removes either the exposed or unexposed areas of the photoresist, depending on whether it is positive or negative resist. In this case, it is mentioned that the photoresist is negative, so the unexposed areas will be removed.
3. HF Dip: The wafer is then immersed in a hydrofluoric acid (HF) solution. HF is commonly used to selectively etch silicon dioxide (oxide layer) without significantly affecting other materials. Therefore, the HF dip step will remove the oxide layer in areas where the photoresist has been removed.
Given this information, let's analyze the mask provided in the figure:
- The green layer represents the oxide layer on the silicon wafer.
- The orange layer represents the negative photoresist.
By evaluating the mask, we can deduce that the areas where the photoresist is present (orange) will be protected during the HF dip step. Conversely, the areas where the photoresist is absent (transparent regions) will have the underlying oxide layer removed.
Therefore, after exposure, development, and HF dip, the resulting structure will be defined by the remaining photoresist. In this case, the photoresist forms parallel lines, so the resulting structure will be a pattern of parallel oxide lines on the silicon substrate.
It's important to note that further steps, such as the acetone dip mentioned, may involve additional processes that can influence the final structure. However, based on the information provided, we can determine the immediate effect of exposure, development, and the HF dip.