Coma measurement by use of an alternating phase-shifting mask mark with a specific phase width

Abstract

The correlation between the coma sensitivity of the alternating phase-shifting mask (Alt-PSM) mark and the mark's structure is studied based on the Hopkins theory of partially coherent imaging and positive resist optical lithography (PROLITH) simulation. It is found that an optimized Alt-PSM mark with its phase width being two-thirds its pitch has a higher sensitivity to coma than Alt-PSM marks with the same pitch and the different phase widths. The pitch of the Alt-PSM mark is also optimized by PROLITH simulation, and the structure of p ¼ 1:92λ=NA and pw ¼ 2p=3 proves to be with the highest sensitivity. The optimized Alt-PSM mark is used as a measurement mark to retrieve coma aberration from the projection optics in lithographic tools. In comparison with an ordinary Alt-PSM mark with its phase width being a half its pitch, the measurement accuracies of Z 7 and Z 14 apparently increase.

Translational-symmetry alternating phase shifting mask grating mark used in a linear measurement model of lithographic projection lens aberrations

“…An optimized Alt-PSM grating mark with phase width of 2=3 pitch is used to enhance the accuracy further [11]. As the Alt-PSM mark imaged by the projection lens, the transmission function is…”

“…The sensitivity variation range is simulated with different values of NA and σ. The accuracy of aberration measurement can be estimated by [11,16] …”

“…Except for the in situ aberration-measurement techniques based on the phase measurement interferometry (PMI) principles and ENZ diffraction theory, another kind of technique has been widely researched and developed for application for commercial lithographic tools [9][10][11][12][13][14][15][16]. This kind of technique is based on the following linear relationships between (a) coma and image placement error (IPE), with the abbreviation "Coma-IPE linearity"; (b) spherical aberration and best focus shift (BFS), with the abbreviation "Spherical-BFS linearity"; (c) astigmatism and relative best focus shift of horizontal and vertical grating images, with the abbreviation "Astigmatism-BFS hv linearity."…”

“…The dense lines binary intensity mask (BIM) mark and the isolated spaces mark are used to retrieve coma and spherical aberrations. Later, the techniques based on TAMIS are improved by use of an alternating phase shifting mask (Alt-PSM) grating mark [10] and an optimized Alt-PSM grating mark [11]. Nomura and Sato [12] and Nomura et al [13] worked on a three-beam interference-measurement technique based on the BIM grating marks and double-exposure bars-inbox marks.…”

“…Recently, a kind of Coma-IPE linearity model based on interference of AE1st order diffraction light has been used to measure coma aberration, and an optimized Alt-PSM grating mark is used to enhance the accuracy [11]. However, the linearity of Coma-IPE, Spherical-BFS, and Astigmatism-BFS hv has not been discussed seriously, and how the sensitivity is determined by the measurement mark's structure is still unknown.…”