Fluoroelastomer Specialists
Triboelectricity is defined as a charge of (static) electricity generated by friction. The concept was first applied in the 1940s for electrostatic painting and is now widely used in photocopy machines. This phenomenon becomes a concern in wafer manufacturing processes since water is a polar molecule and deionized water (~18MOhm) is a good insulator [1, 2].
When working at the nanoscale of microchip production, even low levels of contamination have the capacity to alter the electrical characteristics of the device and affect the reliability of the end product. Operational hygiene has always been an issue due to the sensitivity of semiconductors to contaminants, but the threat of trace metal contamination specifically is significant. This is mainly true for front end processing but, due to the high mobility of many of these contaminants, it remains a threat at all stages of the manufacturing process flow.
Trace metal constituents of elastomer seals can be released as byproducts during erosion of the seal in aggressive plasma or chemical environments that are part of routine process tool operation. Contamination of semiconductor devices by trace metals adversely affects device performance and as linewidths decrease, the allowable levels of metal contamination reduce. This article explores where trace metals come from, the impact they have on the industry and what can be done to reduce the risks.
Background
Semiconductor microchips, which provide inexpensive, fast computing power for electronic devices, are made from millions or even billions of transistors. The transistor is fundamentally an electronic switch that contains no moving parts but uses an applied low voltage to the gate which in turn allows electrons to move from the source to the drain.
The overall chip making process involves many repeating steps to form the transistor at the front end, and subse- quent formation of the back end interconnect including multiple metal and dielectric levels and several etch steps in between. In the process of building these layers, many transistors are created and interconnected. When completed, a single wafer will contain hundreds of identical chips that must pass rigorous testing. The chip is then mounted onto a metal or plastic package that undergoes final testing, ready to be assembled into final products [1,2].
During routine operation, many components within the process tools and ancillary equipment will be subject to wear and abrasion, particularly those components within the process module that are directly exposed to harsh physical and chemical environments. The most critical locations are those where components are exposed to such environments and in proximity to the substrate being processed.
Equipment consumable items that can sometimes be overlooked are elastomer seals or O-rings. These materials have a certain lifetime proportional to the mechanical and chemical properties of the operating environment and the physical constraints of the groove and location. While an elastomer in a critical location may not actually determine the maintenance cycle of the process tool, byproducts and elastomer constituents will be released into the process environment during active operation. Therefore, whatever constitutes the elastomer can contaminate the wafer and this applies equally to the trace metals.
Read more: Trace metal contamination: Choosing elastomer materials for critical operations
