Blockages and Halos – VLSI Basics

Blockages and Halo: The limits of photolithography, the method used to pattern a circuit on a substrate, give birth to two different types of design difficulties in VLSI (Very Large Scale Integration), known as blockages and halo.

Blockages

In the context of photolithography, a blockage is a barrier that keeps light from reaching a particular region of the substrate. This may result in the production of undesirable patterns on the substrate or a partial transfer of patterns. Blockages may be brought on by actual components like reticles or photomasks or by the circuits’ angular configuration on the substrate.

Halo

A halo is a pattern of light that surrounds a feature on a substrate, giving the appearance that the feature is larger than it actually is. Due to the higher feature size on the substrate as a result, there may be issues with circuit scaling and circuit performance. Light diffraction, lens aberrations, and substrate material characteristics are only a few of the causes of halo.

The performance and yield of VLSI circuits can be significantly impacted by both blockages and halo. Designers frequently employ specialized methods and equipment to get around these difficulties, such as optical proximity correction (OPC) and phase-shift masks, which increase photolithography accuracy and lessen blockage and halo effects.

Optical Proximity Correction (OPC)

In order to increase the precision of the pattern transfer process, optical proximity correction, or OPC, is a technique used in VLSI (Very Large Scale Integration) photolithography. To transfer the intended layout of a circuit onto a substrate, photolithography is utilized. However, because of the constraints of photolithography, undesirable patterns or fluctuations in feature size, sometimes known as “proximity effects,” may be produced.#

By altering the design of the photomask or reticle used in photolithography, OPC corrects these proximity effects. In the OPC process, the design is examined, the anticipated proximity effects are calculated, and then correction algorithms are applied to the photomask or reticle to mitigate these effects.

This enhances the performance and yield of VLSI circuits by transferring the intended pattern onto the substrate more precisely, lowering the possibility of pattern distortion.

As the scaling of feature sizes continues to push the boundaries of photolithography technology, OPC is a important phase in the photolithography process for contemporary VLSI circuits. The ongoing development of VLSI technology is made possible by the use of OPC, which enables designers to build circuits that are more accurate and efficient while also being smaller and more complicated.

Advantages of Optical Proximity Correction

Optical Proximity Correction (OPC) provides several advantages in VLSI (Very Large Scale Integration).

• Better yield.
• Smaller feature size.
• Enhanced performance.
• Improved pattern accuracy.
• Improved manufacturability.