Airborne molecular contaminants continue to pose cost of ownership challenges in photolithography. Recent advances in understanding siloxane removal have led to the development of an innovative filtration configuration utilizing new media that works in concert to increase overall filter life for acids, bases and silicon containing organic contaminants. This paper examines accelerated testing results, for these state-of-the-art filtration assemblies versus legacy products, to demonstrate improved system performance. The state-of-the-art filtration assemblies have been evaluated in production semiconductor fabs and have shown favorable performance.
The focus of airborne molecular contamination (AMC) control within the semiconductor industry, specifically
photolithography, has changed significantly over the past decade. As the focal point of concern has shifted from
ammonia (or base gases), to acid gases, and recently to organic contaminants, the filtration industry has adeptly grown to
provide the necessary filtration solutions. This paper attempts to provide an overview of these changes while reviewing the primary contaminants, how they are removed, the control technologies in use, and how they are applied.
The concern over molecular contamination on the surfaces of optics continues to grow. Most recently, this concern
has focused on siloxane contamination resulting from hexamethyldisilazane (HMDS) which is commonly used as a
wafer treatment to improve photoresist adhesion onto wafers. From this process, HMDS vapor can be found within
FABs and process tools where it has been linked to issues related to lens hazing. This type of surface contamination
is significantly detrimental to the imaging process and is generally corrected by extensive surface cleaning or even
lens replacement. Additionally, this type of repair also requires adjustment of the optical axis, thereby contributing
to an extended downtime.
HMDS is known to be very sensitive to the presence of water and is therefore believed to degrade in humid
airstreams. This research focuses on rationalizing the reaction mechanisms of HMDS in dry and humid airstreams
and in the presence of several adsorbent surfaces. It is shown that HMDS hydrolyzes in humid air to trimethylsilanol
(TMS) and ammonia (NH<sub>3</sub>). Furthermore, it is shown that TMS can dimerize in air, or on specific types of
adsorption media, to form hexamethyldisiloxane (HMDSO). Additionally, we report on the relative impact of these
reaction mechanisms on the removal of both HMDS and its hydrolysis products (TMS, HMDSO and NH<sub>3</sub>).
Airborne molecular contamination (AMC) continues to play a very decisive role in the performance of many
microelectronic devices and manufacturing processes. Besides airborne acids and bases, airborne organic
contaminants such as 1-methyl-2-pyrrolidinone (NMP), hexamethyldisiloxane (HMDSO), trimethylsilanol (TMS),
perfluoroalkylamines and condensables are of primary concern in these applications. Currently, the state of the
filtration industry is such that optimum filter life and removal efficiency for organics is offered by granular carbon
filter beds. However, the attributes that make packed beds of activated carbon extremely efficient also impart issues
related to elevated filter weight and pressure drop. Most of the lower pressure drop AMC filters currently offered are
quite expensive and are simply pleated combinations of various adsorptive and reactive media. On the other hand,
low pressure drop filters, such as those designed as open-channel networks (OCN's), offer good filter life and
removal efficiency with the additional benefits of significant reductions in overall filter weight and pressure drop.
Equally important for many applications, the OCN filters can reconstruct the airflow so as to enhance the operation
of a tool or process. For tool mount assemblies and fan filter units (FFUs) this can result in reduced fan and blower
speeds, which subsequently can provide reduced vibration and energy costs. Additionally, these low pressure drop
designs can provide a cost effective way of effectively removing AMC in full fab (or HVAC) filtration applications
without significantly affecting air-handling requirements. Herein, we will present a new generation of low pressure
drop OCN filters designed for the removal of airborne organics in a wide range of applications.