Electrical characterization of single nanometer-wide Si fins in dense arrays

Abstract

This paper demonstrates the development of a methodology using the micro four-point probe (μ4PP) technique to electrically characterize single nanometer-wide fins arranged in dense arrays. We show that through the concept of carefully controlling the electrical contact formation process, the electrical measurement can be confined to one individual fin although the used measurement electrodes physically contact more than one fin. We demonstrate that we can precisely measure the resistance of individual ca. 20 nm wide fins and that we can correlate the measured variations in fin resistance with variations in their nanometric width. Due to the demonstrated high precision of the technique, this opens the prospect for the use of μ4PP in electrical critical dimension metrology.

Electrical Contact Formation in Micro Four‐Point Probe Measurements

“…Moreover, for phase 2, we propose a new method allowing for excellent control of the contact resistance of the created electrical contacts. Finally, we show that the electrical contact formation is similar on more confined structures such as fins, where the precise control of the electrical contact is needed for measuring single fins in dense arrays …”

“…Note that the measurement of R 1 and R 2 is done using the extra two electrodes 3 and 4 (not shown in Figure a) of our microprobes after forming the corrrespoding electrical contacts R 3 and R 4 with a high current (>500 μA; Figure b) to ensure a low contact resistance (i.e., R 3 , R 4 << R 1 , R 2 ). Here, because the Si sample is highly doped, R sample is much lower than the contact resistances (i.e., R sample << R 1 , R 2 , R 3 , R 4 ) and can thus be neglected, making that all contact resistances can be obtained using a series of independent two‐point measurements. For example, R 1 is extracted using R 1 = 0.5 × ( R 1–3 + R 1–4 − R 3–4 ), where R 1–3 is the two‐point measurements between electrodes 1 and 3.…”

“…Interestingly, with our proposed method of using a controlled current to lower the contact resistances, an excellent control of the electrical contact formation and the current during this process is achieved, which is required while trying to contact single fins in fin arrays with a pitch smaller than the electrode contact size. Indeed, it was shown that the maximum current during the electrical contact formation has to be carefully controlled to make sure that the electrical contacting remains isolated to a single fin …”

“…Ever since the transition from planar to 3D transistor architectures such as the fin field‐effect transistor (finFET), there has been a rising need for metrology solutions able to measure the electrical properties of nanometer‐wide conducting features . Recently, it has been shown that the micro four‐point probe (μ4pp) technique is able to measure the resistance in nanometer‐wide fins . To perform such measurements with a high precision, all four electrodes are required to form low‐resistance contacts with the sample under investigation .…”

Apparent size effects on dopant activation in nanometer-wide Si fins

“…2 Indeed, characterizing the electrical properties of these features, which can be impacted by their nanoscale dimensions via, e.g., size-dependent dopant activation, diffusion, and recrystallization, [3][4][5] often requires metrology that is able to probe variations in dopant/carrier concentration within a few nanometers and with high accuracy. 2,6 For example, while a width-dependent sheet resistance has been observed in B-implanted Si fins using the micro four-point probe (μ4PP) [7][8][9][10] technique, this technique alone is not sufficient to characterize the (local) electrical properties of these structures. Additionally, scanning spreading resistance microscopy (SSRM) 2,11,12 measurements are difficult to quantify for such nanometer scaled features, as the measured spreading resistance is easily impacted by parasitic series resistances.…”