Youichi Usui

EUVL practical mask structure with light shield area for 32nm half pitch and beyond

The effect of mask structure with light shield area on the printability in EUV lithography was studied. When very thin absorber on EUVL mask is used for ULSI application, it then becomes necessary to create EUV light shield area on the mask in order to suppress possible leakage of EUV light from neighboring exposure shots. We proposed and fabricated two types of masks with very thin absorber and light shield area structure. For both types of masks we demonstrated high shield performances at light shield areas by employing a Small Field Exposure Tool (SFET).

Process development of 6-in EUV mask with TaBN absorber

6-inch EUV masks consisting of Mo/Si multilayers and patterned CrX buffer and TaBN absorber layers have recently been developed and evaluated. Mo/Si multilayers with a relatively high EUV reflectivity of 66 percent and an excellent uniformity were obtained on the polished ULE substrates by an ion beam sputtering method. The multilayers showed high durability to the acid abased cleaning and baking at 150 degrees C used in the conventional mask-making process. The Cr based film was optimized as a repair buffer to obtain a high reflectivity of 52 percent at 257 nm and low stress within 100 MPa. TaBN absorbers with a low reflectivity were obtained by optimizing the film compositions, which resulted in a high image contrast to the multilayer for DUV inspection. An EUV contrast level of 99 percent was achieved for a thinner, 100-nm thick absorber stack. Using the optimized mask process, EUV mask with patterns of 180-nm width were successfully obtained, without a significant drop in EUV reflectivity.

Particle-free mask handling techniques and a dual-pod carrier

In EUV lithography, particle-free handling is one of the critical issues because a pellicle is impractical due to its high absorption. To investigate this subject, we have developed a mask protection engineering tool that allows various types of tests to be carried out during the transfer of a mask or blank in air and in vacuum. We measured the number of particle adders during the transfer of a mask blank in a dual-pod carrier and in an RSP200 carrier. We found that the number of particle adders (>=46 nm PSL) to a mask blank in a dual pod is less than 0.01 over the whole process from taking the blank out of the load port in air to putting it in the electrostatic chuck chamber in vacuum. Through various experiments, the number of particle adders during any process using a dual pod was found to be very few and very stable. In contrast, for a naked mask, many particle adders were found in large variations. Below one particle were added in over 80% of experiments on a dual pod and in about 20% of experiments on a naked mask. Based on the test results, we can conclude that the use of dual pod is an excellent particle-free transfer technique.

Fabrication of programmed phase defects on EUV multilayer blanks

Programmed phase defects, at desirably specified sizes and known locations, for EUV multilayer blanks were successfully fabricated by the following newly developed simple technique; depositing Cr film on a 6025 glass substrate or a Si wafer, generating Cr patterns of isolated lines and/or dots by EB lithography, and depositing Mo/Si multilayer of 40-bilayers by ion beam sputtering over the Cr patterns. Thereby, programmed bump defects were created on the multilayer surface over the Cr pattern at the bottom. The programmed defects were observed by TEM and AFM, of which images revealed behavior of the multilayer growth on the Cr patterns. The observed images show that height and full width at half maximum (FWHM) of the bump on the multilayer surface strongly depended on the Cr pattern in height and width, and also incident angle of the sputtered molecular flux to the substrate surface. The multilayer coating at near-normal (vertical) incidence provides a significant amount of smoothing near the Cr patterns. A bump phase defect of 2-nm height and 60-nm FWHM, as the result, was obtained on the multilayer surface using a 5-nm thick Cr pattern, which corresponded to a minimum killer defect for EUV lithography at 45-nm node. The multilayer blanks with the programmed phase defects can be effectively used as a standard for defect inspection tool development and defect printability study. This paper describes a simple fabrication process of the programmed phase defects on EUV multilayer blanks, evaluation results on the programmed phase defects, and growth behaviors of multilayer on various patterns (seed of the defects).

Development of a novel EUV mask protection engineering tool and mask handling techniques

We have developed a mask protection engineering tool (MPE Tool) that simulates various types of tests during the transfer of a mask or blank in air and in vacuum. We performed mask transfer experiments to investigate particle-free mask handling techniques using the MPE and mask inspection tools. We measured the number of particles accumulated during the transfer of the mask blanks. Less than 0.3 particles were added over a path from a load port (in air) to an ESC chamber (in vacuum) and more than half the particles accumulated appeared during the pumping down and purging steps in the load-lock chamber. Consequently, we consider that pumping down and purging are the most important steps for particle-free mask handling.

Characterization of small phase defects using a micro-coherent extreme ultraviolet scatterometry microscope

To evaluate defects on extreme ultraviolet (EUV) masks in the blank state of manufacture, we developed a micro-coherent EUV scatterometry microscopy (micro-CSM) system. Its illumination source is coherent EUV light with a 230 nm focus diameter on the defect using a Fresnel zoneplate. This system directly observes the reflection and scattering intensities, which are strongly related to the printability of a defect. After observing pit-type program phase defects with a 60 nm width and 1 nm depth, we estimated the reflection and scattering intensities of each defect using step-and-repeat measurement around the defect. The reflection and scattering intensities from the program defects of the same design fluctuated. This indicates that the actual volumes of all defects differ even for the same design. Additionally, the scattering distributions of 30-nm-wide defects were anisotropic owing to interference with speckle from multilayer scattering. Thus, micro-CSM demonstrates that the scattering distribution depends on the defect position in the multilayer.

Thin-absorber extreme-ultraviolet lithography mask with light-shield border for full-field scanner: flatness and image placement change through mask process

When a thinner absorber mask is practically applied to the extreme ultraviolet lithography for ultra large scale integration chip production, it is inevitable to introduce an extreme ultraviolet (EUV) light shield area to suppress leakage of the EUV light from adjacent exposure shots. We believe that a light-shield border of the multilayer etching type is a promising structure in terms of mask process flexibility for higher mask critical dimension accuracy. We evaluate the etching impact of the absorber and multilayer on the mask flatness and image placement change through the mask process of a thin absorber mask with a light-shield border of the multilayer etching type structure. We clarify the relation between mask flatness and mask image placement shift.

Advanced photomask repair technology for 65nm lithography (4)

Yasutoshi Itou, Yoshiyuki Tanaka, Osamu Suga *Yasuhiko Sugiyama, *Ryoji Hagiwara, *Haruo Takahashi, *Osamu Takaoka, *Tomokazu Kozakai, *Osamu Matsuda, *Katsumi Suzuki, *Mamoru Okabe, *Syuichi Kikuchi, *Atsushi Uemoto, *Anto Yasaka, *Tatsuya Adachi, **Naoki Nishida Semiconductor Leading Edge Technologies, Inc. 16-1, Onogawa, Tsukuba-shi, Ibaraki, 305-8569, Japan *SII NanoTechnorogy Inc. 36-1 Takenoshita, Oyama-cho, Sunto-gun, Shizuoka, 410-1393, Japan **HOYA Co. 1375 Kawaguchi-cho, Hachioji-shi, Tokyo, 193-8525, Japan

At-wavelength observation of phase defect using focused lensless microscope

To evaluate defects on extreme ultraviolet (EUV) masks at the blank state of manufacturing, we developed a micro coherent EUV scatterometry microscope (micro-CSM). The illumination source is coherent EUV light with a 230-nm focus diameter on the defect using a Fresnel zoneplate. This system directly observes the reflection and scattering signals from a phase defect. The scattering distributions of 30-nm-wide defects were anisotropic due to interference with speckle from multilayer scattering. Thus, printability of the defects would depend on the defect position in the multilayer.

Thin absorber EUVL mask with light-shield border for full-field scanner: flatness and image placement change through mask process

When thinner absorber mask is practically applied to the EUVL for the ULSI chip production, it is inevitable to introduce EUV light shield area in order to suppress leakage of the EUV light from adjacent exposure shots. We believe that light-shield border of multilayer etching type is promising structure in terms of mask process flexibility for higher mask CD accuracy In this paper, we evaluate etching impact of absorber and multilayer on mask flatness and image placement change through mask process of thin absorber mask with light-shield border of multilayer etching type structure. And then, we clarify the relation between mask flatness and mask image placement shift.