Examining the Effect of Evaporation Field on Boron Measurements in SiGe: Insights into Improving the Relationship Between APT and SIMS Measurements of Boron

Abstract

Understanding and resolving discrepancies between atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) measurements of B dopants in Si-based materials has long been a problem for those in the semiconductor community who wish to measure B within the source/drain SiGe of a device. APT data collection of Si-based materials is typically optimized for Si, which is logical, but perhaps not ideal for field evaporation of B. Increasing the evaporation field well beyond the typically used 28Si2+:28Si+ ratio of approximately 10:1 up to a ratio of ~200:1 is demonstrated to improve B detection while retaining well-matched Si and Ge concentrations with respect to those measured by SIMS. A range of evaporation conditions are examined from a very low field with high laser energy to an extremely high field with extremely low laser energy demonstrating problems at both far ends of the spectrum and a sweet spot when the operating conditions used produce a 28Si2+:28Si+ ratio of approximately 200:1 (in terms of total counts of each ionization state), which is more than an order of magnitude higher than normally used conditions and results in nicely matched B, Si, and Ge APT measurements with those of SIMS.

Atom Probe Tomography Characterization of Dopant Distributions in Si FinFET: Challenges and Solutions

“…Therefore, we conclude that the dopants are mainly in the oxide side, which is consistent with TCAD simulation results. Though it is known that the change in local field resulting from the large variation of laser energy could affect the quantitatively measurement of B and Ga in semiconductors (Meisenkothen et al, 2015; Rigutti et al, 2018; Martin & Yatzor, 2019), with the evaporation fields of P and As in Si and SiO 2 unknown, it is difficult to comment on effect of laser energy used in this study on the quantitative measurement of n-type dopants without further experiments.…”

Quantification of dopant species using atom probe tomography for semiconductor application

“…It is of course important not to forget some of the disagreements might due to laser energy and evaporation field that have been proven to significantly affect the measured B profile. 11,20 It should be pointed out that higher laser energy will result in a larger underestimation of B concentration. The effect of laser energy on B concentration quantification is under investigation, and the data will be published elsewhere.…”

“…A big gap of deviation (46% deviation in B dose of 7e14 atom/cm 2 ) between these two species indicates that high deviation is dominated by the multi‐hit events. It is of course important not to forget some of the disagreements might due to laser energy and evaporation field that have been proven to significantly affect the measured B profile . It should be pointed out that higher laser energy will result in a larger underestimation of B concentration.…”

“…The most common dopant elements in the silicon semiconductors are B (for p‐doping) and P (for n‐doping). Although there are a few APT studies of B quantification, only Meisenkothen et al reported there is 20% to 36% B signal lost in B implanted (B dose of 1.5e15 atoms/cm 2 ) of Si standard sample. It is well understood that B determined by the APT is always smaller than the SIMS value, but the loading dependence on concentration is not established yet.…”

A scheme to correct for inaccuracies in the compositional analysis of SixGe1-x by Atom Probe Tomography

“…The choice of the experimental conditions has a significant impact on the elemental composition quantification of SixGe1-x, a reoccurring issue in the APT community when characterizing semiconductor alloys and compounds [Mar19,Cud20]. The charge state ratio (CSR) not only offers a measure for the apex electric field, but has been identified as a parameter to link and compare the APT elemental quantification between different experimental conditions [Man14].…”