Design of an integrated aerial image sensor

Abstract

The subject of this paper is a novel integrated aerial image sensor (IAIS) system suitable for integration within the surface of an autonomous test wafer. The IAIS could be used as a lithography processing monitor, affording a "wafer's eye view" of the process, and therefore facilitating advanced process control and diagnostics without integrating (and dedicating) the sensor to the processing equipment. The IAIS is composed of an aperture mask and an array of photodetectors. In order to retrieve nanometer scale resolution of the aerial image with a practical photo-detector pixel size, we propose a design of an aperture mask involving a series of spatial phase "moving" aperture groups. We demonstrate a design example aimed at the 65nm technology node through TEMPEST simulation. The optimized, key design parameters include an aperture width in the range of 30nm, aperture thickness in the range of 70nm, and offer a spatial resolution of about 5nm, all with comfortable fabrication tolerances. Our preliminary simulation work indicates the possibility of the IAIS being applied to the immersion lithography. A bench-top far-field experiment verifies that our approach of the spatial frequency down-shift through forming large Moiré patterns is feasible.

An Integrated Aerial Image Sensor for Lithography Diagnostics

“…Second, the noise tolerance of the DI must be significantly larger than the noise level of photo-detectors. The detailed design of the IAIS parameter is described in [7]. Figure 3 summarize the optimum design window for the 65nm technology node.…”

“…The signal acquisition process of the IAIS is described in [7], where we define that Detector Image (DI) is the Aerial Image (Al) passing through (interferes with) the aperture mask, right at the detector plane before collected by the photodetectors. Therefore the integrated intensity of DI can be expressed as:…”

“…Io(x)= +Wg Id(x')dx' (2) Wg Where, Id is the intensity distribution at the detector plane [7], and Io is proportional to the power incident on the photodetector surface of the area of the aperture groups. The variable x* signifies the lateral dimension at the bottom of the interference mask.…”

“…The projected periodic pattern is 292nm LIS, with wavelength 193nm, and NA 0.75, as shown in Figure 5. The aperture mask uses amorphous Si [7] with thickness 90nm and the width of the aperture "slit" is 50nm. The sampling group is 61.…”

“…The assembly technique with capillary force assisted alignment appears quite promising, and is expected to overcome the limitation from the thermal budget and the subsequent lithography steps of the IAIS fabrication. The fabrication details are shown in a previous presentation [6].…”