Study of Test Structures for Use as Reference Materials for Optical Critical Dimension Applications

Abstract

Optical critical dimension (OCD) metrology has Since the edges of features made using the SCCDRM rapidly become an important technology in supporting the process are silicon lattice-planes, the dimensions of any worldwide semiconductor industry. OCD relies on a particular feature can be calibrated by using the known combination of measurement and modeling to extract the spacing of the silicon lattice (0.543 102 122(20) nm).34 In average dimensions of an array of parallel features, having addition, the geometry makes the SCCDRM excellent for use fixed pitch and drawn linwidth. This paper reports results of in atomic force microscopy (AFM) calibration and tip OCD measurements on arrays selected to serve as prototype cr iat iond reference structures. In addition, SEM CD measurements were characterization. made on several of these structures to verify line uniformity.Previous work focused on SCCDRM test structures with These prototypes are fabricated using the single-crystal CD isolated features; calibration ofthese isolated features was for reference materials (SCCDRM) process, which in prior work a single location on a particular feature. has been successfully applied to isolated feature reference OCD applications differ from conventional CD materials. The SCCDRM process provides features with measurements in two critical ways: known geometries, typically vertical sidewalls, defined by the * The CD is determined over a relatively large region: silicon lattice.typically a spot size of 20 ptm to 50 ptm.

Modeling and Analysis of Scatterometry Signatures for Optical Critical Dimension Reference Material Applications

“…In previous work, we have shown that the variation in w OCD for this target from repeated measurements was very small, with a standard deviation of w OCD over the data sets of only 0.4 nm. 3 We do not believe that the repeatability of the reflectance measurement is the only source of error in w OCD , however. There may be additional systematic components to σ i (θ j ).…”

“…Although we have refined the substrate model in this work compared to our previous effort and have generally improved the χ 2 r values of the reflectance fits, our earlier substrate description also gave nearunity slope and very little offset between w OCD and w SEM . 3 However, the precise value of w OCD for an individual target can vary for different substrate descriptions, particularly when χ 2 r for that target is large.…”

“…This allows us to parameterize the thicknesses and refractive indices of the SIMOX (separation by oxygen implantation) substrate used for the SCCDRM chips, where we refer to the silicon wafer, a mixed boundary layer (if present), and the buried oxide (BOX) layer as the substrate. While we recently reported on OCD measurements of a subset of the targets considered here, 3 the improved substrate description in the current work is a better match to substrate reflectance data, and improves the fits of the simulated optical signatures to measured signatures for the grating targets.…”

“…The perimeter of each target is a parallelogram such that all edges are aligned to the <112> lattice directions. 3 The targets used here measure 100 µm from top edge of the target to the bottom edge of the target. The design widths of the lines in the targets range from 350 nm to 1000 nm, and targets with a ratio of design linewidth to line space of 1:1 and 1:2 were used.…”

“…This was consistent with previous spectroscopic ellipsometry (SE) measurements on an unpatterned sample of SIMOX similar to that used for the SCCDRM chips, which showed that the oxide layer was not well described by a single layer of SiO 2 , but required the addition of a mixed oxide/silicon boundary layer. 3 The solid lines in Fig. 2 show the resulting best fit reflectance when n oxide was fixed at 1.462, the mixed boundary layer was taken to be a single Bruggeman effective medium layer 7 with a 50/50 mix of the oxide and silicon, and s and t were allowed to vary.…”