Minoru Komada

Manufacturing of half-tone phase-shift masks III: inspection, repair, and quality assurance

Half-tone phase shift masks with Cr-based shifters have been developed for i-line lithography. The printability of defects is determined with test marks for the four categories of defects: clear defects (pinholes and intrusions) and opaque defects (pinspots and extrusions) under the conditions that a normal hole of 0.40-micrometers width is formed by an i-line stepper with NA equals 0.57. The detectability with a KLA219HRL-PS and that of a KLA331 are also evaluated. The minimum detectable defect size is found to be smaller than the minimum intolerable defect size for each category. Clear defects are repairable by covering them with carbon patches deposited by a focused-ion-beam repair system. On the basis of the consideration of both the shielding effect and the halo effect of the patch, the deposition conditions are optimized: the thickness is 150 nm and the patch edge should be placed just on the hole edge. Opaque defects are repairable by removing them with a laser repair system without any printable damage. A KLA219HRL-PS is used for inspection both before repair and before shipment. It is confirmed that the well repaired (i.e., unprintable) defects are undetectable. Quality assurance tools are summarized.

Development of advanced process for halftone phase-shift mask fabrication with electron-beam exposure systems

A new fabrication process for halftone phase-shift masks (HPSMs) with electron beam writers has been developed for mass production. It has a resist critical dimension (CD) measurement step before dry etching and it gives the determination of etching time using the relationships between CD shift (Chrome CD - resist CD) and overetch ratio. As a result, it shows a good mean CD controllability within a range of 0.03 μm for over 90% of our production HPSMs.

EBR900 processes in e-beam and laser beam lithographies for photomask fabrication

The performance of EBR900 (Toray) as a resist used for e-beam and laser beam lithographies has been investigated. EBR900 has high sensitivity to both e-beam and laser beam exposures. It has high resolution and good dry-etch durability. The e-beam process was optimized by designing a new type of developer, MA50, which is composed of an amine and an aqueous solution of potassium hydroxide. The addition of the amine was found to be effective in improving the performance with regard to profile, CD uniformity, and defect quality. Its performance is stable (e.g., CD deviation is less than 0.03 micrometers for a shelf time of a month); this makes CD control easier. Its CD linearity in the laser beam process is down to 0.6 micrometers , being better than that in the e-beam one (down to 1.0 micrometers ). Its dissolution rate and conversion yield of the photosensitizer were estimated in order to explain the superiority of the laser process. A comparison of its performance between e-beam and laser beam processes for next generation photomask fabrication was presented. In conclusion, EBR900 meets the requirements for 64 Mb DRAM reticles for the use in e- beam and laser beam lithographies.