PATTERN POSITIONING ERROR OF RETICLE WRITING INDUCED BY RETICLE CLAMPING

This article describes the effect of reticle flexure caused by clampin g on pattern positioning accuracy. Reticle flexure causes a pattern sh ift resulting from stretching or compression of the reticle surface. W e focused on the clamping mechanism of the pattern writing system and the measuring machine which held the reticle at four points. By repeat ing the clamping of the reticle, it was recognized that the surface he ight distribution deviates. As a result, pattern shift deviation occur s. To improve the repeatability of clamping, a new three-point clampin g mechanism was developed for electron-beam writing systems, and also a three-point adapter was employed for the measuring machine. The Valu es parameters related to pattern positioning accuracy, x and y scaling , and orthogonality were calculated for several reticles (5 in. sq., 0 .09 in. thick). By clamping the reticle at three points, the deviation s of these three values were reduced to less than 53% that of four-poi nt clamping. Moreover, surface shift caused by three-point clamping wa s precisely compensated by adding a compensation circuit to the electr on-beam writing system. (C) 1995 American Vacuum Society.