CMOS Fabrication and Photoresist Layer

In CMOS (Complementary Metal-Oxide-Semiconductor) fabrication, the photoresist layer plays a crucial role in the process of creating intricate patterns and transferring them onto the wafer. The photoresist layer is a light-sensitive material that undergoes chemical changes when exposed to specific wavelengths of light. These changes allow for the selective removal or protection of certain areas during subsequent fabrication steps.

Role of Photoresist Layer

The photoresist layer acts as a mask, protecting certain areas of the wafer while allowing the desired pattern to be transferred onto the exposed regions. This process helps in defining the various components and interconnections that make up the CMOS integrated circuit.

Exposure of Photoresist Layer

To expose the photoresist layer, a photomask is used. A photomask is a transparent plate with the desired pattern etched onto it. When light passes through the photomask and reaches the photoresist layer, it causes a chemical reaction that alters the solubility of the material.

Wavelength of Light

The correct answer to the given question is option B, ultraviolet light. Ultraviolet (UV) light is commonly used in CMOS fabrication for exposing the photoresist layer. The wavelength of UV light used typically falls within the range of 365-436 nanometers. This wavelength range is shorter than visible light but longer than X-rays or gamma rays.

Reason for Using Ultraviolet Light

Ultraviolet light is preferred for several reasons in CMOS fabrication:

1. Resolution: The shorter wavelength of UV light allows for higher resolution and finer feature size, enabling the creation of smaller and more complex integrated circuits.

2. Penetration Depth: UV light has a relatively short penetration depth, meaning it can be used to expose only the top layer of the photoresist without affecting the layers beneath. This allows for better control and accuracy during the fabrication process.

3. Sensitivity: Photoresist materials are specifically designed to be sensitive to UV light, ensuring the desired chemical reactions occur when exposed to the appropriate wavelength.

4. Availability: UV light sources are readily available and commonly used in semiconductor manufacturing.

In conclusion, the photoresist layer in CMOS fabrication is exposed to ultraviolet light. This specific wavelength of light allows for high resolution, controlled penetration, and effective chemical reactions in the photoresist layer, enabling the creation of intricate patterns and structures on the wafer.