We have developed a high speed, miniature scanning probe microscope (MSPM) integrated with a Positioning Unit (PU) for accurately positioning the MSPM on a large substrate. This combination enables simultaneous, parallel operation of many units on a large sample for high throughput measurements. The size of the MSPM is 19 × 45 × 70 mm(3). It contains a one-dimensional flexure stage with counter-balanced actuation for vertical scanning with a bandwidth of 50 kHz and a z-travel range of more than 2 μm. This stage is mechanically decoupled from the rest of the MSPM by suspending it on specific dynamically determined points. The motion of the probe, which is mounted on top of the flexure stage is measured by a very compact optical beam deflection (OBD). Thermal noise spectrum measurements of short cantilevers show a bandwidth of 2 MHz and a noise of less than 15 fm/Hz(1/2). A fast approach and engagement of the probe to the substrate surface have been achieved by integrating a small stepper actuator and direct monitoring of the cantilever response to the approaching surface. The PU has the same width as the MSPM, 45 mm and can position the MSPM to a pre-chosen position within an area of 275×30 mm(2) to within 100 nm accuracy within a few seconds. During scanning, the MSPM is detached from the PU which is essential to eliminate mechanical vibration and drift from the relatively low-resonance frequency and low-stiffness structure of the PU. Although the specific implementation of the MSPM we describe here has been developed as an atomic force microscope, the general architecture is applicable to any form of SPM. This high speed MSPM is now being used in a parallel SPM architecture for inspection and metrology of large samples such as semiconductor wafers and masks.
With the device dimensions moving towards the 1X node, the semiconductor industry is rapidly approaching the point where 10 nm defects become critical. Therefore, new methods for improving the yield are emerging, including inspection and review methods with sufficient resolution and throughput. Existing industrial tools cannot anymore fulfill these requirements for upcoming smaller and 3D features, since they are performing at the edge of their performance. Scanning probe microscopy (SPM) has the ability to accurately measure dimensions in the micrometer to nanometer scale. Examples of applications are surface roughness, channel height and width measurement, defect inspection in wafers, masks and flat panel displays. In most of these applications, the target area is very large, and, therefore, the throughput of the measurement plays an important role in the final production cost. Single SPM has never been able to compete with other inspection systems in terms of measurement speed, thus has not fulfilled the industry needs in throughput and cost. Further increase of the speed of the single SPM helps, but it still is far from the required throughput and, therefore, insufficient for high-volume manufacturing. Over the past three years, we have developed a revolutionary concept for a multiple miniaturized SPM heads system, which can inspect and measure many sites in parallel. The very high speed of each miniaturized SPM unit allow the user to scan many areas, each with the size of tens of micrometers, in a few seconds. This paper presents an overview of the technical developments and experimental results of the parallel SPM system for wafer and mask inspection.
Scanning probe microscopy (SPM) is a promising candidate for accurate assessment of metrology and defects on wafers and masks, however it has traditionally been too slow for high-throughput applications, although recent developments have significantly pushed the speed of SPM [1,2]. In this paper we present new results obtained with our previously presented high-throughput parallel SPM system [3,4] that showcase two key advances that are required for a successful deployment of SPM in high-throughput metrology, defect and mask inspection. The first is a very fast (up to 40 lines/s) image acquisition and a comparison of the image quality as function of speed. Secondly, a fast approach method: measurements of the scan-head approaching the sample from 0.2 and 1.0 mm distance in under 1.4 and 6 seconds respectively.
Applying aspherical and freeform optics in high-end optical systems can improve system performance while decreasing the system mass, size and number of required components. The NANOMEFOS measurement machine is capable of universal non-contact and fast measurement of aspherical and freeform optics up to ∅500 mm, with an uncertainty of 30 nm (2σ). In this machine, the surface is placed on a continuously rotating air bearing spindle, while a specially developed optical probe is positioned over it by a motion system. A separate metrology system measures the probe and product position relative to a metrology frame.The prototype realization, including custom electronics and software, has been completed. The noise level at standstill is 0.88 nm rms. A reference flat was measured with 13 µm and 0.73 mm tilt. Both measurements show an rms flatness of about 8 nm rms, which correspond to the NMi measurement. A hemisphere has also been measured up to 50° slope, and placed 0.2 mm eccentric on the spindle. These measurements reproduce to about 5 nm rms. Calibration and software are currently being improved and the machine is applied in TNO aspherical and freeform optics production.
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