The ability to deliver high end photomasks free of printable defects is key to the success of the photomask manufacturing process. Although investment in substrate purity, particulate control, and cleaning capability has increased dramatically, they have proven no match for the defects’ ability to destroy an otherwise ideal mask. It is, therefore, essential to continue to have the capability to repair defects in order to deliver high-end photomasks. The vast variety of potential defects, combined with the different mask substrates, has driven the repair capability to not only be very technically driven, but also versatile and quick.
Between the major defect categories of clear and opaque defects, opaque defects present the greatest challenge. Traditionally, this challenge lies in the reality that there is no perfect full height defect resulting in no one universal removal process. This is compounded with the fact that on any given photomask, these opaque defects can be greater than a micron, sub micron, very numerous, within tight geometries, or out in an isolated region of the photomask. Furthermore, defects identified as opaque defects have the possibility to be foreign material related, presenting a further challenge. They do not respond to repair in the same manner as the opaque defects. The multitude of issues, combined with the need to repair the defects with high throughput, has driven the need for an advanced opaque repair system.
This paper will look into the practical application of a laser-based advanced opaque repair tool. Repair tool capability will show repair performance including substrate damage, transmission effects, and edge placement repeatability. This paper will also present a view of the operations of the repair system including imaging capabilities, and process throughput. This practical review of the advanced opaque repair system will show that technical needs of opaque repair, as well as practical needs of throughput and ease of use, can be achieved within one repair process.
Fabricating masks for extreme ultraviolet lithography (EUVL) is challenging. New design features have been introduced because of the high absorption of most materials at 13.4 nm and the small critical dimension (70 nm and below). The novel mask features introduced with EUVL include the reflective design, new film combinations, and stringent defect specifications. This paper focuses on one aspect of the mask build process that must be detected, understood, and minimized: defects. We obtain our EUV mask blanks with the multi-layers already in place. While the deposition of usable Mo/Si multi-layers is a challenge in itself, our pursuit of a clean EUV mask process begins with the buffer layer. From that point, the basic mechanics of the mask build is: deposit the buffer layer, deposit the absorber layer, apply and pattern the resist, and etch the absorber. The buffer layer is left to protect the multi-layers during inspection and repair. Careful attention to cleaning, inspection, and repair will be required to meet the ITRS Roadmap's 55 nm maximum defect size (at the 70 nm node). Our inspection methodology, defect data and repair options will be presented in detail.
As the wafer industry has driven the minimum feature size on the photomask to the submicron range, an increased focus has been placed on the metrology used to control such features. The most common method of metrology for photomask linewidth measurements is the optical CD metrology tool. However, now that the submicron range of photomask linewidths and features are aggressively pursued, the optical resolution limit of the optical CD measurement tool is limiting the ability to accurately perform photomask linewidth measurements. It is therefore essential to look beyond this limit, to either pursue new technology CD metrology tools, or to develop practical techniques to measure submicron photomask features approaching or extending beyond the optical resolution limit of the metrology tool. This paper investigates the later approach with discussion and evaluation of some techniques used as an attempt to enhance the current optical CD metrology capability in order to measure photomask features well into the submicron range.