Nikon Corporation

Shin-etsu Chemical Co., Ltd.

Kabushiki Kaisha Toshiba

Shin-estu Chemical Co., Ltd.

Naoto Kondo

Tsuneyuki Hagiwara

Tsuneo Numanami

Masayuki Mogi

Masayuki Nakatsu

Masamitsu Itoh

In a quadrangular photomask blank substrate with a length on each side of at least 6 inches, which has a pair of strip-like regions that extend from 2 to 10 mm inside each of a pair of opposing sides along an outer periphery of a substrate top surface, with a 2 mm edge portion excluded at each end, each strip-like region is inclined downward toward the outer periphery of the substrate, and a difference between maximum and minimum values for height from a least squares plane for the strip-like region to the strip-like region is at most 0.5 &#x3bc;m. The substrate exhibits a good surface flatness at the time of wafer exposure.

Photomask blank substrate, photomask blank and photomask

A photomask blank substrate is made by polishing a starting substrate to a specific flatness in a principal surface region on a top surface of the substrate so as to form a polished intermediate product, then additionally polishing the intermediate product. Substrates made in this way exhibit a good surface flatness at the time of wafer exposure. When a photomask fabricated from a blank obtained from such a substrate is held on the mask stage of a wafer exposure system with a vacuum chuck, the substrate surface undergoes minimal warping, enabling exposure patterns of small geometry to be written onto wafers to good position and linewidth accuracies.

Method of making photomask blank substrates

Provided that a pair of strip-like regions extend from 2 mm to 10 mm inside each of a pair of opposing sides along an outer periphery of a top surface of a substrate on which a mask pattern is to be formed, with a 2 mm edge portion excluded at each end in a lengthwise direction thereof, the height from a least squares plane for the strip-like regions on the substrate top surface to the strip-like regions is measured at intervals of 0.05-0.35 mm in horizontal and vertical directions, and a substrate in which the difference between the maximum and minimum values for the height among all the measurement points is &#x3bd;o&#x3c4; &#x3bc;o&#x3c1;&#x3b5; &#x3c4;&#x3b7;&#x3b1;&#x3bd; 0.5 &#x3bc;m is selected.

Method of selecting photomask blank substrates

A photomask blank substrate is selected for use in a process where at least a masking film or a phase shift film is deposited on a top surface of a photomask blank substrate to form a photomask blank, the deposited film is patterned to form a photomask, and the photomask is mounted in an exposure tool. The substrate is selected by simulating a change in shape in the top surface of the substrate, from prior to film deposition thereon to when the photomask is mounted in the exposure tool; determining the shape of the substrate top surface prior to the change that will impart to the top surface a flat shape when the photomask is mounted in the exposure tool; and selecting, as an acceptable substrate, a substrate having this top surface shape. The selected substrate has an optimized top surface shape that improves productivity in photomask fabrication.

Growing community of inventors

Tokyo, Japan

Naoto Kondo