Micro Four-Point Probe based Metrology

For the past 5 decades, the semiconductor industry has followed a steady path of constantly shrinking device geometries and increasing circuit density. This has resulted in production of new technology nodes roughly every 2 years, which is a trend commonly referred to as "Moore's Law". As scaling and fundamental thermodynamic limits approach, new and advanced solutions must be found, for the current technology development rate to be maintained. In particular, the shrinking of device feature sizes and the transition from planar structures to three-dimensional ones, necessitates reliable and accurate characterization. Most metrologies are not geared for these new concepts and hence, it is of paramount importance to develop new characterization methods and the solution must be found by looking beyond state of the art metrologies.
The main objective of this project has been to develop new Micro Four-Point Probe (M4PP) based metrology methods suitable for characterising materials and devices intended for future technology nodes in the semiconductor industry.
The objective has been fulfilled in different ways. In the first part of the thesis, the Variable Probe Pitch (VPP) Micro Hall  Effect (MHE) method is presented. The method entails two ways of extracting key sample parameters, such as sheet resistance, R₀, Hall sheet carrier density, N_HS, and Hall mobility, μ_H, by relying either on the Hall signal or the resistance signal. Furthermore, the sensitivity of each method to position errors and electrical noise is explored. It is found that in presence of significant electrical noise, lower standard deviations are always obtained when the geometrical analysis is based on the resistance signals. The situation is more complicated when electrode position errors are dominant; in that case, the better method depends on the experimental conditions. The theoretical findings are verified with a set of experimental data measured on an ultrashallow junction silicon sample. Moreover, the VPP MHE method is used extensively in the pursuit of MHE measurements on test pad structures. Investigations of the effect of confinement on the measurement accuracy and precision are presented. Most notably, a Monte Carlo (MC) study of MHE measurements subjected to electrical noise and position errors is conducted on different test pad sizes. Here, it is found that the magnitudes of the relative standard deviations scale with the degree of confinement for the pad sizes investigated. A minimum test pad size is also found. Experimental MHE  measurements on test pad structures are performed and confirm the expected trend of increasing deviations on the extracted parameters, N_HS and μ_H for decreasing pad dimensions. In this way, the capabilities of the MHE method is pushed to include highly confined geometries, such as test pad structures. Furthermore, it is discussed that the carrier concentration of a sample can be assessed using the N_HS parameter, as long as caution is exerted in the presence of position errors and electrical noise.
In the second part of the thesis, a new method of using the M4PP technique for thermoelectric measurements is introduced. It is discussed that much like characterization of planar geometries is important, so is electrical characterization of non-planar structures, such as Fin Field-Effect Transistors (FinFETs). The principle of using a high current in an M4PP measurement to dissipate heat in a sample through Joule heating is presented. Furthermore, a Finite Element Method (FEM) model capable of simulating the temperature increase during a thermoelectric measurement is developed. Manually recorded proof-of-concept measurements on 500nm fins are shown and found to have low yield and troublesome identification. An automated lock-in technique produced by Capres A/S is used on 500nm and 300nm fins to record thermoelectric measurements. The data is inspected and found to behave according to expectation. Furthermore, a specific thermoelectric measurement on a 500nm fin is used together with the FEM model to calculate a Seebeck coefficient for a real sample. The Seebeck coefficient is then converted into an active carrier concentration for the fin and found to be smaller than expected, providing valuable information about the structure. In this way, a proposal on how to address the gap in metrology related to the active carrier concentration of fins is suggested and the capabilities of the M4PP technique pushed yet again, to include non-planar structures.