What is it about?

Many people think that protecting reticles from electrostatic damage is no different from protecting semiconductor devices from ESD damage during their manufacture. This is a false presumption, and applying some of the countermeasures taken to reduce the risk of damage to manufactured devices can actually increase the risk of damage to a reticle! This paper explains this, and shows that the electrostatic risk is everywhere. Common misperceptions about reticle protection are explained and technically correct procedures that should be used to protect reticles are described.

Featured Image

Why is it important?

Reticles are essential elements for semiconductor production - they are the "master" blueprint that is replicated in the manufacturing process to create a working semiconductor device. Therefore, if any part of the reticle is damaged it will create a defect that will be repeated in every device printed from that reticle. Whether this causes the device to fail at final test or merely introduces a parametric deviation in device operation, such avoidable damage is serious - it can cost anything up to over a million dollars in lost production (actual case) if a reticle is damaged in this way. So understanding the risk and knowing how to correctly avoid it is important.

Perspectives

The semiconductor industry was plagued by serious reticle electrostatic damage problems in the 1990s owing to the introduction of plastic single reticle boxes and reticle pods. These insulating plastic boxes could become charged during handling and the static charge would induce damage in the reticles inside. ESD consultants were employed to fix the problem and "conventional" ESD countermeasures were adopted throughout the industry. However, it was not appreciated at the time that the electrostatic risk to reticles is unique, and some of the countermeasures introduced to address the reticle damage problem were not fully effective at reducing the risk - some actually made the risk to a reticle worse! In 2003 a new cumulative damage mechanism called EFM that causes damage to a reticle under electric field exposure more than 100 times weaker than that which causes ESD in reticles was discovered. It became apparent that the ESD countermeasures that had been adopted by the industry, while generally being quite successful at reducing the ESD risk, were making cumulative damage more likely. Therefore, a new approach was needed to properly address the newly identified risk. This was published in SEMI Standard E163, but the industry has not widely adopted this new approach because EFM is not easily identified in a semiconductor production environment. If the workers in a semiconductor factory cannot see it happening, they don't know that they need to protect against it. Failing to do so can result in huge financial losses - in one case in 2004 a semiconductor factory lost over $1 million following repeated EFM damage to a critical production reticle. For this reason I continue to publish papers describing the risk and presenting new evidence to show why the industry needs to change its approach to reticle protection. The two most common "protective" approaches that have been adopted - namely equipotential bonding during handling and the use of static dissipative plastics for making reticle boxes and pods - actually make the risk of cumulative reticle damage WORSE! This situation needs to be corrected if further losses by the industry are to be avoided.

Dr Gavin C Rider

Read the Original

This page is a summary of: Electrostatic risk to reticles in the nanolithography era, Journal of Micro/Nanolithography MEMS and MOEMS, April 2016, SPIE,
DOI: 10.1117/1.jmm.15.2.023501.
You can read the full text:

Read

Contributors

The following have contributed to this page