Hiroyuki Iwashita

Photomask technology for 32nm node and beyond

193nm-immersion lithography is the most promising technology for 32nm-node device fabrication. At the 32nm technology-node, the performance of photomasks, not only phase-shift masks but also binary masks, needs to be improved, especially in resolution and CD accuracy. To meet sub-100nm resolution with high precision, further thinning of resist thickness will be needed. To improve CD performance, we have designed a new Cr-on-glass (COG) blank for binary applications, having OD-3 at 193nm. This simple Cr structure can obtain superior performance with the conventional mask-making process. Since the hardmask concept is one of the alternative solutions, we have also designed a multilayered binary blank. The new COG blank (NTARC) was fully dry-etched with over 25% shorter etching time than NTAR7, which is a conventional COG blank. Thinner resist (up to 200nm) was possible for NTARC. NTARC with 200nm-thick resist showed superior resolution and CD linearity in all pattern categories. On the other hand, the multilayered binary stack gives us a wide etching margin for several etching steps. Super thin resist (up to 100nm) was suitable by using a Cr-hardmask on a MoSi-absorber structure (COMS). The COMS blanks showed superior performance, especially in tiny clear patterns, such as the isolated hole pattern. We confirmed that these new photomask blanks, NTARC and COMS, will meet the requirements for 32nm-node and beyond, for all aspects of mask-making.

The ultimate chrome absorber in photomask making

193nm-immersion lithography is the most promising technology for 32nm-node device fabrication. A new Cr absorber (TFC) for 193-nm attenuated phase-shift blanks was developed to meet the photomask requirements without any additional process step, such as hardmask etching. TFC was introduced with a design concept of the vertical profile for shorter etching time, the over etching time reduction. As a result, the dry-etching time was dramatically improved by more than 20% shorter than the conventional Cr absorber (TF11) without any process changes. We confirmed that 150nm-resist thickness was possible by TFC. The 32nm technology-node requirement is fully supported by TFC with thinner CAR, such as resolution and CD performance.

The art of photomask materials for low-k1-193nm lithography

The resolution of photomask patterns were improved with a hardmask (HM) system. The system which is thin Sicompounds layer is easily etched by the hyper-thin resist (below 100nm thickness). The HM material has sufficient etching selectivity against the chrome-compounds which is the second layer chrome absorber for the phase-shifter. This hardmask layer has been completely removed during the phase-shifter etching. It means that the conventional phase-shit mask (PSM) has been made with the ultimately high-resolution without configuration changes. Below 50nm resolution of PSM was made with 90nm thickness resist on HM layer in this paper. The CD bias between a resist feature CD and a chrome feature CD was almost zero (below 1nm) in the optimized etching condition. We confirmed that the mask performances were the equal to COMS (Cr-HM on MoSi binary mask) in resolution and CD linearity. The performances of hardmask blanks will be defined by resist performance because of almost zero bias.