Ralf Schuster

Overlay considerations for 300-mm lithography

Generally, the potential impact of systematical overlay errors on 300mm wafers is much larger than on 200mm wafers. Process problems which are merely identified as minor edge yield detractors on 200mm wafers, can evolve as major roadblocks for 300mm lithography. Therefore, it is commonly believed that achieving product overlay specifications on 300mm wafers is much more difficult than on 200mm wafers. Based on recent results on high volume 300mm DRAM manufacturing, it is shown that in reality this assumption does not hold. By optimizing the process, overlay results can be achieved which are comparable to the 200mm reference process. However, the influence of non-lithographic processes on the overlay performance becomes much more critical. Based on examples for specific overlay signatures, the influence of several processes on the overlay characteristics of 300mm wafers is demonstrated. Thus, process setup and process changes need to be analyzed monitored much more carefully. Any process variations affecting wafer related overlay have to be observed carefully. Fast reaction times are critical to avoid major yield loss. As the semiconductor industry converts to 300mm technology, lithographers have to focus more than ever on process integration aspects.

Selected implications of photoresist processing in 300mm manfacturing

In our paper, we discuss implications currently relevant to 300mm resist processing in lithography. The large size of the wafers, and therefore the large volume of machine modules and media within these modules, demand tighter specifications and a careful re-consideration of design. Firstly, we investigated a novel resist development process based on a new developer dispense nozzle. The CD uniformity across the 300mm wafer thus achieved is compared to a common process. Based on this, we are able to make a preliminary recommendation for the photoresist development technology required for future, high-end semiconductor device manufacturing. Resist thickness fluctuations around the edge area of a silicon wafer typically occur if high spin speeds are applied during the photoresist coating process. 300mm coating processes are particularly prone to the occurrence of such spin marks as the operating range of applicable spin speeds is lower in comparison to processes applied to wafers of lower diameters. We show in our example how such local resist thickness fluctuations impact the product yield. Finally, a special type of micromasking defect was found to be particularly relevant to 300mm lithography layers. This doughnut-type defect detracts the yield of the semiconductor product. The defect has a distinct physical appearance and is precipitated onto the wafer as a hollow resin sphere. This defect has not yet been observed on our 200mm reference process. The occurrence of the defect directly depends on the matching of the air flows entering and leaving the 300mm coater cup. The mechanism of formation involves the presence of a photoresist-solvent aerosol.

Evaluation techniques for 300-mm equipment

As the semiconductor industry begins its transition to its next wafer size threshold of 300mm, several key factors are becoming significant. Solving the problems surrounding these factors is critical to achieving a 30-40 percent cost savings over 200mm wafer integrated circuit manufacturing. These problematic areas involve automation, equipment readiness, and process performance. 300mm factories will differ from 200mm versions due to the automation level, lot size choices, and factory sizing targets in terms of wafer starts. This paper discusses these areas from data acquired at SEMICONDUCTOR300 in processing a 0.25 micrometers 64Mb DRAM device. Current performance is discussed for each semiconductor manufacturing tool functional group. These data include performance cost of ownership, on automation and computer integrated manufacturing, and process capability.

Process performance comparisons on 300-mm i-line steppers, DUV stepper, and DUV scanners

SEMICONDUCTOR300 was the first pilot production facility for 300mm wafers in the world. This company, a joint venture between Infineon Technologies and Motorola, is working to develop a manufacturable 300mm wafer tool set. The lithography tools include I-line steppers, a DUV stepper, and two DUV scanners. These tools are used to build 64M DRAM devices and aggressive test vehicles. Data will be presented on the mix-and-matching performance between DUV scanners and I-line steppers. Process-related data on CD within-field and across wafer sampling for selected tool types were investigated. The process capability of the current tool set for 0.25 micrometers and 0.18 micrometers devices were compared. Resolution performance of the scanner with its 0.68 numerical aperture was studied. Dense and isolated printed pattern performance was measured with in-line metrology. 300mm wafers are sensitive to backside defectivity, and therefore the wafer chuck design plays an important role in achieving the desired pattern transfer performance. The performance of the different chuck types and their sensitivity to incoming backside wafer contamination levels was studied. Rework data was used to assist in characterizing the exposure dose matching and chuck type performance.

Effect of nonlinear errors on 300-mm wafer overlay performance

SEMICONDUCTOR3000 was the first pilot production facility for 300nm wafers in the world. This company, a joint venture between Infineon Technologies and Motorola, is working to develop a manufacturable 300mm wafer tool set. The lithography tools include I-line stepper, and two DUV scanners. These tools are used to build both 64M DRAM devices and aggressive test vehicles. This paper shows the influence of non-linear errors on 300nm wafers is much stronger than on 200mm wafers. The team determined the root causes for the stronger appearance of these effects and proposed solutions to improve the overlay performance.

Is lithography ready for 300 mm

SEMICONDUCTOR300 was the first pilot production facility for 300mm wafers in the world. This company, a joint venture between Infineon Technologies Motorola, started in early 1998 to develop processes and manufacture products using 300mm wafer tool set. The lithography tools include I-line steppers, as I-line scanner, a DUV stepper, and DUV scanners. All of these exposure tools are running in-line with a photoresist coat and develop track. The lithography tools are used to build 64Mb DRAM devices and aggressive test vehicles with design rules of 0.25 micrometers and below, in sufficient quantity to be able to assess the tool readiness. This paper present the history of technical improvements and roadblocks that have occurred on the 300mm lithography tool set since the start-up, and describe a methodology used to assess the tool performance.