JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV MEMS DESIGN Previous Question Paper (September - 2020 - R16)

The fabrication of microelectronics requires a highly controlled environment and precise processes to ensure the functionality and reliability of integrated circuits. The primary requirements include:

• Cleanroom Environment: Fabrication must occur in cleanrooms with strictly controlled air quality, temperature, humidity, and vibration levels. Airborne particles must be minimized using HEPA or ULPA filters to prevent defects in the sub-micron features.
• High Purity Materials: The use of electronic-grade silicon wafers and high-purity chemicals (photoresists, etchants, dopants) is essential to prevent contamination that could alter electrical properties.
• Precision Lithography: The ability to transfer complex patterns onto the wafer with nanometer-scale resolution is critical, requiring advanced light sources and precise alignment systems.
• Process Uniformity: Techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and ion implantation must provide uniform layer thickness and doping concentrations across the entire wafer surface.
• Cleanliness and Contamination Control: Strict protocols for wafer handling, including chemical mechanical polishing (CMP) and wet cleaning, are necessary to remove residues and surface defects between processing steps.

Etching is a fundamental process in microfabrication used to remove material from the wafer surface. The comparison between wet and dry etching is as follows:

While wet etching is simple, cost-effective, and highly selective, its isotropic nature makes it unsuitable for high-density, high-aspect-ratio structures. Conversely, dry etching (such as Reactive Ion Etching) provides the vertical sidewalls and precise control required for modern microelectronics, despite the higher equipment costs and complexity of vacuum systems.