Implementing registration measurements on photomasks at the Nanometer Comparator

Abstract

Due to the introduction of double patterning schemes in the production processes of the semiconductor industry and the corresponding stringent specifications of the placement errors of the optical images of mask features (1.2 nm (3σ)) in the lithographic projection process, significant improvements of the registration measurements on photomasks are required. The Nanometer Comparator of the PTB, a one-dimensional vacuum-interference length comparator, has already demonstrated measurement reproducibility at this level on line scales and linear encoders, and therefore this comparator should also be applied for placement metrology on photomasks. Because a photomask is a relatively thin plate which is supported almost at its ends, the bending influence is much larger than for line scales and precautions had to be taken to reduce the influence of the sample support on the measurements results. A new sample mount was built, which exhibits mechanical alignment aids. In addition the position deviations caused by the mask bending were corrected by means of finite element calculations. Measurements performed with the Nanometer Comparator on a high-quality mask showed a maximum deviation of measured feature positions from the common mean of below 0.5 nm and a reproducibility of 0.2 nm. These results suggest that the use of a one-dimensional calibration of mask measuring machines allows us to perform traceable registration measurements with sufficient accuracy.

Improved measurement performance of the Physikalisch-Technische Bundesanstalt nanometer comparator by integration of a new Zerodur sample carriage

“…The repeatability σ ¼ 0.6 nm could be significantly reduced in comparison to the former value σ ¼ 0.9 nm. 7, they indicate that here at least the same performance level has been reached again. 7 shows the results of line position measurements on photomasks in two different orientations.…”

“…5,6,7 Measurement uncertainties in the nm range and with a reproducibility in the sub-nm range were realized. Consequently, the PTB developed a one dimensional (1-D) vacuum length reference comparator, the so-called nanometer comparator, in cooperation with partners from industry.…”

“…7 shows new results of repeated measurements on a 280 mm quartz line scale by means of the improved nanometer comparator. 7. In addition, the right diagram of Fig.…”

Challenges in nanometrology: high precision measurement of position and size

“…3. It remains below 0.5 nm and exhibits a 1σ standard deviation of 0.2 nm [3]. The measurement uncertainty for line positions on high quality 6'' photomasks (chrome on quartz or MoSi) currently is 2 nm.…”

Ultra-präzise Lageregelung mittels interferometrischer Positionsdetektion und Tauchspulenantrieb

“…Hierzu wird an der PTB ein Längenkomparator mit Vakuuminterferometern betrieben, der Nanometerkomparator (NMK). Diese Maschine, dargestellt in Abbildung 1, erlaubt die Charakterisierung von Inkrementalgebern sowie anderen Wegsensoren, Maẞstäben und Photomasken mit Reproduzierbarkeiten bis in den SubNanometerbereich über einen Verfahrbereich von bis zu 540 mm [1].…”