Jennifer Braggin

Further analysis of the effect of point-of-use filtration on microbridging defectivity

In a 2009 analysis of microbridging defectivity, a design of experiment methodology was used to show the effect of filtration parameters on microbridging defectivity, specifically focusing on filter retention rating, filter media and design, filtration rate, and controlled filtration pressure. In that analysis it was shown that different filter architectures provide the most effective filtration of microbridging and that different filter architectures show different levels of microbridging defects even when optimally tuned. Ultimately, filter choice and filtration setup matter in removal of microbridging defects. In the new analysis, a similar approach was taken with additional filter types. However, in the new study the retention rating of the filters was kept constant at 10nm while other filter parameters were varied, including membrane material and design. This study will show the specific effect of the membrane material and design on microbridging defectivity in addition to the effects of filtration setup.

Characterization of filter performance on contact-hole defectivity

The effect of filtration on defectivity has been studied extensively with line-space patterns. However, the ability to have defect free contacts is equally as important. Resist materials are specifically designed for contact holes, and therefore it is important to also study their varied sources of defectivity. In this study, unpatterned and patterned wafer defectivities have been studied as a function of point of use filter. The filter retention rating was held constant at 10 nm while the filter membrane material was varied, including ultra-high molecular weight polyethylene (UPE), Nylon and composite filters. A recommendation will be made as to which point-of-use filter performed best with the contact hole specific resists tested.

Defect performance of a 2X node resist with a revolutionary point-of-use filter

In todays competitive lithography market, resist manufacturers are always striving to create a product to meet lithographic challenges while maintaining a low inherent defect level. While bulk filtration used in resist manufacturing removes a majority of the inherent defectivity, point-of-use filtration is still required to ensure that defects are not passed from the bottle to the wafer. As Moores law drives lithographers to ever decreasing dimensions, resist manufacturers must find new ways of filtering their chemistries to make sure that the smallest defects cannot create the biggest yield detractors. In addition, IDMs must use new innovations to explore point-of-use filtration techniques to protect their valuable patterns. This paper will show the conditions that can reduce defectivity in an immersion lithography scheme. More specifically, advanced point-of-use filtration techniques, including revolutionary filter membrane technology and advanced filtration settings, will be explored to understand potential 22nm node defect performance. By thinking ahead about the filtration needs of the future, resist manufacturers, IDMs, and equipment manufacturers can all work toward an understanding of the complex nature of filtration, ultimately yielding a new, low defectivity regime at the smallest pattern sizes.

Lithography cost savings through resist reduction and monitoring program

Photolithography has been one of the primary processes driving semiconductor advances for the past few decades. In order to make faster, more reliable devices, designers drive circuit scaling to its limits. Equipment and material suppliers must create products to meet the throughput and lithographic performance standards required of advanced devices. Track equipment performance and process architecture have improved to meet throughput considerations, and therefore the cost of lithography tracks has remained relatively constant and few equipment changes are remaining which will drastically reduce the cost of lithography. On the other hand, the cost of photolithography materials has drastically increased due to the complexity of the chemistries required to resolve shrinking critical dimensions. In addition, new technology nodes have often required additional processing layers, adding to the high cost of materials in the lithography process. These increased costs are directly delivered to the wafer for processes where high volumes of chemical or multiple layers are needed to properly coat a wafer for further processing. By fine tuning the coating process, a track equipment engineer can reduce resist cost per wafer by reducing the volume dispensed on the wafer. While reducing the resist volume to extremely low levels is attractive, it can also introduce risks into the coating process. Any interruption in the low volume dispense can cause a poor coating or no-coat situation, thus creating a wafer that requires rework or scrap. If the event is detected at the point of dispense, the wafer can be reworked. If the wafer escapes undetected until a post-lithography metrology step, it must be scrapped. This paper evaluates the cost benefits of utilizing an advanced dispense system, such as the IntelliGen® Mini, made by Entegris, Inc., combined with an every-wafer point-of-dispense monitoring strategy. This paper will discuss the means to reduce resist dispense volumes by up to 60% and the ability to track every dispense, decreasing overall scrap and the need for some routine metrology. In addition, the authors will show a return-on-investment summary for undertaking such a project.

Preventing Lithography-Induced Maverick Yield Events With A Dispense System Advanced Equipment Control Method

As semiconductor manufacturers march to the drum beat of Moores law there is very little room for yield mavericks, especially those that can be prevented. Critical process errors are costly and photolithography is one of the few processes in semiconductor manufacturing where there is an opportunity to correct errors. Small changes in photo resist dispensed volume may have severe impact on film thickness uniformity and can ultimately affect patterning. It is important to monitor photo-dispense conditions to detect real-time events that may have a direct negative impact on process yield and be able to react to these events as quickly as possible. This paper presents an evaluation of the IntelliGenreg Mini, a photo resist dispense system manufactured by Entegris, Inc. This system utilizes advanced equipment control software, known as dispense confirmation, to detect variations in photo dispense. These variations, caused by bubbles in the dispense line, valve errors, and accidentally changed chemistries can all create maverick yield events that can go undetected until metrology, defect inspection, or wafer final test. The ability of an advanced dispense system to detect events and create alerts is a very powerful tool, but it can be most effective when that information is collected and analyzed by an automated system. In a modern fabricator this is most likely a statistical process control chart that is monitoring a tracks progress and is ready to stop the track when a maverick event occurs or alert personnel to trends they may not otherwise catch with other inline metrology data. Dispense confirmation, when combined with networking capabilities, can meet this need. After a brief description of the pump, data from simulated yield-affecting events will be examined to evaluate the IntelliGenreg Minis ability to detect them. This discussion will conclude with a brief analysis of the ultimate time and cost savings of utilizing dispense confirmation with networking capabilities to detect and eliminate poorly coated wafers.

Strategy for yield improvement with sub-10 nm photochemical filtration

Process and equipment engineers are always seeking ways to improve yield quickly and efficiently, especially on newly developing processes. These engineers have many tools at their disposal – equipment enhancements, software upgrades, and materials improvements. Many of these tools come from OEMs (other equipment suppliers) and materials suppliers who all benefit from close collaboration with IDMs to improve yield. This paper will discuss the strategies utilized to improve yield on 32 nm BEOL (back end of line) lithography processes with sub-10 nm photochemical filtration. This collaboration generated electrical yield data that validated the performance of several sub-10 nm photochemical filters on various resist and ancillary chemicals used in a tri-layer stack. Examples of yield enhancement include the use of 5 nm UPE (ultra high molecular weight polyethylene) in OPL (optical planarizing layers) which showed a 69% improvement in overall median yield for an OPL material used in the first metallization layer, and a 26% improvement for a second OPL material used in subsequent metallization processes . In addition, this paper will present data studying pre-wetting of a 5 nm point-of-use filter before track installation. Building on the success of this collaboration, an example filtration roadmap is also explored to show the benefits of using advanced filtration in 32 nm technologies and beyond.

Point-of-use filtration methods to reduce defectivity

While immersion lithography has been rapidly implemented in manufacturing environments around the world, a few defect challenges still remain. Bubble and watermark defects are well understood and have been addressed by equipment manufacturers. However, a few defects still bewilder the lithography community, including residues and microbridging. These defects are difficult to completely eliminate as they may have many root causes. However, through effective point-of-use filtration, they can be greatly reduced. Point-of-use filtration has traditionally focused on selecting a filter membrane at a specific pore size that is compatible with the resist chemistry being utilized in the process. The research hereby discussed indicates that in addition to these important point-of-use filter choices, careful filtration parameter setup can improve defectivity results and impact the coating process.

Improving material-specific dispense processes for low-defect coatings

Minimizing defects in spin-on lithography coatings requires a careful understanding of the interactions between the spin-on coating material and the filtration and dispense system used on the coating track. A wet-developable bottom anti-reflective coating (BARC) was examined for its interaction with polyamide and UPE media when utilizing the Entegris IntelliGen Mini dispense system. In addition, a new method of priming the filter and pump is described which improves the wetting of the filter media, preventing bubbles and other defect-generating air pockets within the system. The goal is to establish plumb-on procedures that are material and hardware specific to avoid any defect problems in the coating process, as well as to gain a better understanding of the chemical and physical interactions that lead to coating defects. Liquid particle counts from a laboratory-based filtration stand are compared with on-wafer defects from a commercial coating track to establish a correlation and allow better prediction of product performance. This comparison in turn will provide valuable insight to the engineering process of product filtration and bottling at the source.

Micro-bridge defects: characterization and root cause analysis

Defect review of advanced lithography processes is becoming more and more challenging as feature sizes decrease. Previous studies using a defect review SEM on immersion lithography generated wafers have resulted in a defect classification scheme which, among others, includes a category for micro-bridges. Micro-bridges are small connections between two adjacent lines in photo-resist and are considered device killing defects. Micro-bridge rates also tend to increase as feature sizes decrease, making them even more important for the next technology nodes. Especially because micro-bridge defects can originate from different root causes, the need to further refine and split up the classification of this type of defect into sub groups may become a necessity. This paper focuses on finding the correlation of the different types of micro-bridge defects to a particular root cause based on a full characterization and root cause analysis of this class of defects, by using advanced SEM review capabilities like high quality imaging in very low FOV, Multi Perspective SEM Imaging (MPSI), tilted column and rotated stage (Tilt&Rotation) imaging and Focused Ion Beam (FIB) cross sectioning. Immersion lithography material has been mainly used to generate the set of data presented in this work even though, in the last part of the results, some EUV lithography data will be presented as part of the continuing effort to extend the micro-bridge defect characterization to the EUV technology on 40 nm technology node and beyond.

Pressure control for reduced microbubble formation

Microbubbles in leading-edge photoresist materials create a challenge to the demanding yield requirements of todays shrinking circuit designs. When microbubbles are dispensed onto a wafer surface, they can act as an additional lens in the exposure path, ultimately distorting the pattern and affecting yield. Proper filter selection, filter priming, and dispense settings chosen during process startup are critical to reducing microbubbles, but certain chemistries can continue to cause problems even if the process has been optimized. This paper presents the results of applying a small amount of positive pressure on the chemistry before the dispense nozzle to reduce microbubbles in top anti-reflective coating (TARC). A two-stage technology dispense system was utilized to adjust the pressure on the chemistry in the dispense line while an in-line optical particle counter monitored the microbubbles generated during the dispense process.