Evaluation of the Electric Field above a Specimen Surface during SIMS Analysis

Abstract

Secondary ion mass spectrometry (SIMS) has been a central analytical technique for the microelectronics industry. More precise analysis has become important along with the development and process monitoring of integrated circuits (ICs) production. The level of quantitative analysis is influenced by random and systematic uncertainties. The origin of these uncertainties in SIMS have been well documented by Werner. 1 A number of authors have reported measurement techniques to minimize the contribution of uncertainties to the analytical results. [2][3][4][5][6][7][8][9][10] One of the error factors is related to the specimen holder, itself. It has been reported that the obtained secondary ion intensities are different from those among the windows of the specimen holder, 8,11 or from the tilted holder to the electric field of the extraction space. 6,8 Also, the ion intensities fall off as the analysis location approaches the edge of the holder window. 6,13,14 These detrimental phenomena are attributed to the deviation of secondary ion trajectories by a distortion of the electric field, which is commonly applied above the sample surface in order to effectively collect the emitted secondary ions. It has been accepted that the distortion is caused by warping of the holder faceplate due to pressure from the mounting springs. 9 Besides, it has been demonstrated by a computer simulation that a non-uniform electric field exists near to the window edge of the holder. 14 In the Cameca IMS-type SIMS instrument, a high extraction field, typically 1.0 kV/mm, is used between the sample and a grounded extraction plate (immersion lens cover); therefore, the effect of the specimen holder is more sensitive than for other types of instruments. There are no investigations mentioned in the literature concerning a distorted electric field above various types of specimen holders.In this work, we investigated the distortion area of the electric field near to the edge of the specimen holder window as a function of the faceplate thickness of the specimen holder by a computer simulation after confirming that the computed results was in good agreement with the SIMS experimental results. We also demonstrated the advantage of a specimen holder with a tapered-edge faceplate. ExperimentalThe experiments were conducted using a Cameca IMS-4f ion microscope. A Cs + primary ion beam with an impact energy of 14.5 keV was used. The primary ion current was 100 nA and the raster size was 250 × 250 µm 2 . In the IMS-4f, the specimen holder was biased to -4.5 kV for the detection of negative secondary ions. The distance between the surface of the specimen holder and the grounded extraction plate (immersion lens cover) was 4.5 mm. Thus, an electric field of 1.0 kV/mm was applied above the surface of the specimen holder. 28 Sisecondary ions were detected using a Faraday-cup detector. The diameter of the analyzed area in the center of the crater bottom was 60 µm. The types of specimen holders used in this experiment are summarized in Table 1. The type-B holde...

Atomic Spectrometry Update. Atomic mass spectrometry

“…Becker et al 139 addressed the problem of quantification in the determination of long-lived radionuclides by LA-ICP-MS, for which no suitable standard RMs were available. Their approach was to make synthetic standards by doping a graphite or concrete matrix with long-lived radionuclides, such as 237 Np, 99 Tc, 232 Th, 233 U, 235 U or 238 U. Two calibration procedures were considered: the correction of analytical results with experimentally determined relative sensitivity coefficients; and the use of calibration curves and solution calibration by coupling LA-ICP-MS to an ultrasonic nebulizer.…”

“…Two calibration procedures were considered: the correction of analytical results with experimentally determined relative sensitivity coefficients; and the use of calibration curves and solution calibration by coupling LA-ICP-MS to an ultrasonic nebulizer. The LOD of long-lived radionuclides investigated in a concrete matrix were determined in the pg g 21 range, for example 50 pg g 21 for 237 Np by quadrupole LA-ICP-MS and 1.3 pg g 21 for 233 U by double-focusing magnetic sector LA-ICP-MS. Furthermore, LA-ICP-MS allowed precise and accurate isotope ratio measurements of Th and U in solid samples.…”

“…Two quadrupole and two double-focusing magnetic-sector [one single detector and one multiple collector (MC)] instruments were compared. The same samples of the IRMM-072 series of RMs were used under routine conditions to measure 233 U : 235 U and 233 U : 238 U ratios, which varied by over almost three orders of magnitude from 1 to 2610 3 . Within expanded (k~2) uncertainties, good agreement was observed between the certified values and the data internally corrected for massdiscrimination effects.…”

“…Within expanded (k~2) uncertainties, good agreement was observed between the certified values and the data internally corrected for massdiscrimination effects. For the MC instrument, expanded uncertainties varied from ¡0.04% to ¡0.24% for the 233 U : 235 U ratio, and from ¡0.08% to ¡0.27% for the 233 U : 238 U ratio. They were 1-5 times larger for the single detector instrument, and 10-25 times larger with both quadrupole instruments.…”