Nanoscale x-ray imaging of circuit features without wafer etching

Abstract

Modern integrated circuits (ICs) employ a myriad of materials organized at nanoscale dimensions, and certain critical tolerances must be met for them to function. To understand departures from intended functionality, it is essential to examine ICs as manufactured so as to adjust design rules, ideally in a non-destructive way so that imaged structures can be correlated with electrical performance. Electron microscopes can do this on thin regions, or on exposed surfaces, but the required processing alters or even destroys functionality. Microscopy with multi-keV x-rays provides an alternative approach with greater penetration, but the spatial resolution of x-ray imaging lenses has not allowed one to see the required detail in the latest generation of ICs. X-ray ptychography provides a way to obtain images of ICs without lens-imposed resolution limits, with past work delivering 20–40 nm resolution on thinned ICs. We describe a simple model for estimating the required exposure, and use it to estimate the future potential for this technique. Here we show for the first time that this approach can be used to image circuit detail through an unprocessed 300 μm thick silicon wafer, with sub-20 nm detail clearly resolved after mechanical polishing to 240 μm thickness was used to eliminate image contrast caused by Si wafer surface scratches. By using continuous x-ray scanning, massively parallel computation, and a new generation of synchrotron light sources, this should enable entire non-etched ICs to be imaged to 10 nm resolution or better while maintaining their ability to function in electrical tests.

Arbitrary-path fly-scan ptychography

“…We believe that the A-fly method with continuous 2D trajectories will become an important tool for fast scanning in future high brightness 4th generation synchrotrons, where the positioning overhead of the classical step ptychography and even the line-to-line overhead will become a bottleneck [2] but at the same time the radiation damage caused by inefficient use of X-ray dose would lead to deteriorated imaging quality. Nowadays, the presented method is important mainly for ptychographic imaging with nanofocused beam [28][29][30], where the small beam diameter leads to very short exposure time per scan position and thus unacceptable overhead in the classical step-scan ptychography method. Additionally, the presented fly-scan experiments already required up to 400 Hz continuous framerate acquisition for a rather thin sample at the Swiss Light Source (SLS) that is a small 3rd generation synchrotron.…”

X‐Ray Topography—More than Nice Pictures

“…Such a high sensitivity allows the resolution of 20 nm sized details in integrated circuits. [113] But X-ray ptychography [114] and a variety of other high sophisticated X-ray microscopy and diffraction based imaging methods [115,116,117] are another story, which would go beyond the scope of this article.…”

3D x-ray imaging of continuous objects beyond the depth of focus limit

“…In x-ray ptychography experiments, this estimate has been found to agree within 20% of what is required for imaging integrated circuit features [14] and frozen hydrated biological specimens [56] using iterative phase retrieval algorithms. This indicates that the algorithms themselves can be robust to noise, and work at the limit of the minimally required photon exposure.…”

“…One can even reconstruct multiple probe function modes to account for x-ray beam partial coherence [8], sample vibration [9], and continuously moving illumination [10–13]. Ptychography has been used to image thin circuit layers through 300 μ m of silicon at 12 nm resolution [14], sub-10 nm resolution has been achieved with thinner specimens [15–17], and sub-wavelength resolution has been obtained using EUV light [18]. …”