Removal of Ga Implantation on FIB-prepared Atom Probe Specimens Using Small Beam and Low Energy Ar+ Milling

Abstract

Atom probe tomography (APT) is a powerful characterization technique for obtaining three-dimensional structure and materials composition at the near atomic scale. It is also a complementary with other analysis techniques, such as transmission electron microscopy (TEM). In tandem, the two techniques provide a detailed characterization of structure and chemistry. APT specimens are typically prepared using a dual beam focused ion beam (DB-FIB), which is an efficient tool for removing a substantial amount of material, and in situ electron beam imaging allows more control when shaping the APT specimen tip [1]. However, Ga-induced damage and implantation from FIB milling can result in ambiguous results, especially for Al/Al alloys [2] and Ga containing materials [3]. Low energy (< 1 keV) Ar + milling has been shown to improve TEM specimen quality by removing Ga damage and implantation from FIB preparation [4][5]. Here, we present the use of small beam (< 1 μm), low energy Ar + milling for the removal of FIB-induced damage from APT specimens.Si and Al APT specimens were prepared on a Si half-grid with multiple needle carriers. The needles were prepared in a FIB system [Thermo Fisher] using standard lift-out methods and annular milling at 30 kV [1]. Final cleaning steps were performed using an Ar + milling system [Fischione Instruments] prior to APT acquisition using a LEAP 5000 XR [CAMECA Instruments]. Ar + ions were rastered within a defined area and directed longitudinally at the needle at decreasing milling energies (900 and 500 eV). The protective Pt cap on the needle was removed by the ion milling system; its back-scattered electron detector was used to monitor the needle shape and size in situ. TEM, energy dispersive X-ray spectroscopy, and APT characterization were performed before and after ion milling to determine the removal of FIB-induced damage.

The Trends of In Situ Focused Ion Beam Technology: Toward Preparing Transmission Electron Microscopy Lamella and Devices at the Atomic Scale

“…The acceleration voltage of the Ga + is gradually reduced during the TEM sample thinning process from 30 keV (for a thickness < 150 nm) to 5 and 2 keV (for the final target thickness). [62][63][64][65][66] For the last step, considering that lower energy Ga + leads to thinner amorphization, the 2 keV beam energy is used to minimize the amorphous layer. [64] Refer to Table 3 for the parameter settings of the FIB-SEM in each step of the sample preparation.…”

Optimal Specimen Preparation for Correlative Atom Probe Tomography and Electron Microscopy of Environmentally Sensitive Materials

“…The fast surface transformations that occur upon exposure to ambient conditions can be significantly suppressed by protecting the specimen's environment during the transfer from specimen preparation to characterization. Our previous work showed that concentrated ion beam (< 1 μm), low-energy Ar ion milling improves TEM and APT specimen quality by removing surface oxides and Ga damage caused by focused ion beam (FIB) preparation [1,2,3]. Here, we present specimen preparation using Ar ion milling techniques for subsequent atomic-scale characterization by TEM and APT under controlled environments.…”

Raman Spectroscopy and Electron Microscopy Studies of Ga FIB and Post-FIB Ar Ion Milling's Impact on Si TEM Specimens

“…However, even using low energies in the final FIB polishing step, Ga implantation and amorphous damage [2] are still present. Alternatively, post-FIB concentrated Ar ion beam (CIB) milling at low energies (< 2 keV) removes FIBinduced damage (both amorphous damage and Ga implantation) [3,4]. Here, we use Raman spectroscopy to characterize not only the damage layers, but also residual strain on Si specimens prepared by Ga FIB and post-FIB Ar ion milling.…”