Yasuhiro Koizumi

Practical phase‐shifting mask technology for 0.3 μm large scale integrations

An i‐line phase‐shifting mask technology intended for practical use has been developed. The new technology can provide defect‐free phase‐shifting masks and can produce 0.3 μm large scale integration with large lithographic latitudes. The phase‐shifting masks manufactured here apply the following two major techniques. The first technique is to form phase‐shifting patterns on the chrome mask. This technique features single‐layer shifters using an organic spin on glass (SOG), a simple patterning process of the SOG, and a focused ion beam gas‐assisted etching repair process of shifter defects. The second technique is to create half‐micron chrome patterns using a high‐accuracy e‐beam writing system ‘‘EB‐MX’’ and high‐resolution chemically amplified e‐beam resist ‘‘PSR’’.

Practical method of phase-shifting mask fabrication

Phase-shifting mask (PSM) fabrication techniques have been investigated in order to use PSMs in the manufacturing of 0.3 micrometers memory devices. Comparison of various PSM methods resulted in selection of the SOG (spin on glass)-on-chrome structure. The alternating-type method is used for the wiring layer and the outrigger-type method is used for the hole layer. New techniques are needed for fabricating the PSMs, and the following technologies have been developed or are under development: (1) e-beam writing and process, (2) SOG process, and (3) inspection and repair. Defect free SOG-on-chrome PSMs are available because SOG process is a low defect density process. PSMs and negative i-line resist have been used to experimentally manufacture 0.35 micrometers memory devices, thus demonstrating that SOG-on- chrome PSMs are currently the most practical for memory device manufacturing.

Investigation of phase-shift mask shifter defect printability and inspection techniques

Establishing an effective inspection method for PSMs shifter defects is a very important factor in successful production of PSM under i-line and DUV for 0.25 μm process rules. We have used a PSM with programmed shifter defects to confirm the minimum printable defect size under 0.25 μm rule process environment using i-line and DUV steppers. The same plate was then inspected by a special-detection experimental transmitted and reflected(ETR) and KLA3O1 D/D inspection system which KLA has developed in cooperation with Hitachi to evaluate its detection performance on those printable defects. We report that characteristic of this inspection system, which uses both transmitted and reflected light and special detection algorithm, is an effective tool. We will be able to supply defect free PSM for reliable process of 0.25 μm rule.

Development of a particle-detection system for phase-shifting masks

Particles as small as 0.34 micrometers are detected on phase-shifting masks for 0.3 micrometer LSIs by the particle detection system PS-6000. The system detects the forward- scattered light from the particles using illumination through the rear surface of the masks.

Laser microformation of thin film on glass substrate for repair of transparent defects on high-density masks

Summary A new technique is developed for repairing transparent defects on high density masks for VLSI. A thin Ag-Ta organometallic film is first spin-coated onto a photomask and baked. Then an Ar laser microspot is applied to a small area on this film. After rinsing the mask with a solvent, an opaque layer remains at the laser-irradiated spot and the rest of the organometallic material is washed away. The opaque film formed locally by laser irradiation is dense enough to prevent light transmission and durable enough to withstand repeated washing with strong alkali and acid solutions.