Particle detection on flat surfaces

Abstract

Since 2006 EUV Lithographic tools have been available for testing purposes giving a boost to the development of fab infrastructure for EUV masks. The absence of a pellicle makes the EUV reticles extremely vulnerable to particles. Therefore, the fab infrastructure for masks must meet very strict particle requirements. It is expected that all new equipment must be qualified on particles before it can be put into operation. This qualification requirement increases the need for a low cost method for particle detection on mask substrates.TNO developed its fourth generation particle scanner, the Rapid Nano. This scanner is capable of detecting nanometer sized particles on flat surfaces. The particle detection is based on dark field imaging techniques and fast image processing. The tool was designed for detection of a single added particle in a handling experiment over a reticle sized substrate. Therefore, the Rapid Nano is very suitable for the validation of particle cleanliness of equipment. During the measurement, the substrate is protected against particle contamination by placing it in a protective environment. This environment shields the substrate from all possible contamination source in the Nano Rapid (stages, elevator, cabling). The imaging takes place through a window in the protective cover. The geometry of the protective environment enables large flexibility in substrate shape and size. Particles can be detected on substrates varying from 152 x 152 mm mask substrates to wafers up to 200 mm. PSL particles of 50 nm were detected with signal noise ratio of 26. Larger particles had higher signal noise ratios. By individually linking particles in two measurements the addition of particles can be detected. These results show that the Rapid Nano is capable of detecting particles of 50 nm and larger of a full reticle substrate.

Radially Polarized Light for Detection and Nanolocalization of Dielectric Particles on a Planar Substrate

“…However, they still suffer from their complexity and lack of speed, since most of them utilize multiple beams and detectors and rely on correlations between them [8]. Moreover, in most cases the desired detection sensitivity is achieved only by using wavelengths shorter than Ultraviolet B (280-315 nm) [8] or high power [9], either of which are often harmful for organic substrates [10].…”

Investigating the intrinsic cleanliness of automated handling designed for EUV mask pod-in-pod systems

“…Both samples are shown in the RapidNano scan-box. Figure 3 (left photo) shows an image of the "wafer sample" inside the scan-box of the RapidNano [6,7] (defect detection system by TNO, see also chapter 2.2). Wafer level particle analysis was performed on the "wafer sample" using SEM and EDX in those cases where added particles detected were of a larger size.…”

“…The added PRP specification value is defined to 0.08 for particles larger 60nm (PSL equivalent) or less than 2 particles added for the 25 total handling paths in the InSync tool (see figure 4, qualification routing #4). These test cycles are were designed according to the principles of acceptance sampling [6,8,9]. In pre-qualification runs, the adder level of the manual transfer of the samples (hand carried in the Dual-Pod System) between the InSync tool and the RapidNano inspection system and the contribution of the Dual Pod and the measurement sequence itself was determined to result in a total adder PRP value of 0.05 (particle size larger 60nm PSL equivalent): This value was considered for the up-coming qualification experiments as the background particle adder level.…”

“…The RapidNano Particle Scanner is capable of detecting 1 added particle (>50nm) on a reticle sized substrate [6,9]. In a step and scan mode, dark field images are acquired of the entire reticle area.…”

Coherent Fourier scatterometry nanoparticle detection enhanced by synthetic optical holography

“…The dark-field technique is not limited by diffraction and background noise is avoided by selecting the angle of illumination that is different than the angle(s) of detection. However, if the particles are very small, the scattering signal is very low and, to achieve high signal-to-noise ratio (SNR), a high illumination power is often required [4]. This is particularly challenging in the detection of low scattering particles such as polystyrene latex (PSL) nanoparticles.…”