Abstract Wide variations in the dose enhancement factor observed when milling silicon using Focused Ion Beam (FIB) XeF2 Gas Assisted Etching (GAE) prompted the development of a simple model of the GAE process. The model accounts for three material removal mechanisms: regular sputtering; gas-assisted sputtering; and spontaneous chemical reactions. An expression linking the dose enhancement factor, εd, to the gas and milling parameters has been derived. Experiments show that εd behaves as predicted; good quantitative agreement is achieved over wide ranges of milling parameters for εd values between 20X and 2500X. Conditions required to minimize variations in d and maximize material removal rates, M, are derived. It is shown that if the dose per unit area per raster is below a threshold value then εd and M depend only on the average current density J (the area of the box divided by the beam current). A consideration of the J regimes used for front-side and back-side FIB work shows why changes in εd have not previously been a problem but are inevitable when milling the large trenches characteristics of Flip Chip circuit modification work. While εd changes dramatically there is a region of J values for which M is approximately constant.

Abstract This paper introduces a novel sample preparation method using plasma focused ion-beam (pFIB) milling at low grazing angle. Efficient and high precision preparation of site-specific cross-sectional samples with minimal alternation of device parameters can be achieved with this method. It offers the capability of acquiring a range of electrical characteristic signals from specific sites on the cross-section of devices, including imaging of junctions, Fins in the FinFETs and electrical probing of interconnect metal traces.

Abstract High speed FIB cross-sectioning of polyimide material was traditionally very difficult because of artifacts created by FIB on the cross section plane. Therefore we propose a simple method, which retains the high speed of the FIB process, but significantly improves the quality of the cross section plane. The method involves a hard mask positioned close to the intended place of the cross section using a precise manipulator. This then enables highly accurate and site-specific FIB cross-sectioning. Cross sections can be made very quickly and with the excellent quality in comparison to standard procedures based on gas-assisted deposition of a protection layer.

Abstract Ex situ lift out is fast, easy, and reproducible, and adds flexibility for either frontside or backside manipulation of focused ion beam milled specimens. ex situ lift out methods may be enhanced by eliminating electrostatic forces. In addition, optimizing the geometry of the specimen relative to the probe improves the Van der Waals forces responsible for the lift out and subsequent manipulation of focused ion beam prepared specimens.

Abstract We present application examples of site specific energy filtered transmission electron microscopy (EFTEM) analysis using advanced focused ion beam (FIB) specimen preparation techniques. Specifically, we address topics such as throughput and reliability enhancement by chemically assisted broad ion beam milling and on-line monitoring of the etch process. We discuss how integrated elemental analysis by EFTEM can be used to gain quantitative information on the broad variety of new material systems currently entering front end and back end of the IC manufacturing process line. The accelerating pace of device integration results in extreme demands for quantitative analysis in process development, yield ramp-up and process control with spatial resolution and elemental sensitivity at the very limits of currently available instrumentation. Historically, the high resolution performance of TEM analysis has been hampered by long turn around times for the required sample preparation. Meanwhile the routine use of FIB systems for “trench” and “lift-out” preparation techniques allows for an enormous increase in the efficiency of TEM analysis.

Abstract It has been reported that a sample prepared by ion beam milling has a sandwich structure with amorphous on two sidewalls and crystal in the middle. In this paper, the sandwich structure of such a single crystal TEM sample was studied experimentally. A novel sample and its fabrication process were reported. The sandwich structure can be observed directly in TEM with this sample. When the crystal layer in monocrystal silicon TEM sample is less than 18 nanometers, or when the sample is thinner than 64 nanometers, the sample will be observed as fully amorphous. Removal of the amorphous layer on the sample sidewalls is crucial to get TEM pictures of better quality.

Abstract FIB column performance can be difficult to evaluate, and the traditional metrics of imaging resolution and minimum spot size give little indication of how a FIB system will perform its intended daily tasks. A series of supplemental FIB performance tests is proposed to quantify “milling acuity” under real-world conditions. A quantitative measuring scheme for evaluating the quality of High Aspect Ratio (HAR) vias is proposed, and an example is shown in which the HAR measuring scheme can be used for process development.

Abstract In this paper the new Vion™ Plasma-FIB system, developed by FEI, is evaluated for cross sectioning of Cu filled Through Silicon Via (TSV) interconnects. The aim of the study presented in this paper is to evaluate and optimise different Plasma-FIB (P-FIB) milling strategies in terms of performance and cross section surface quality. The sufficient preservation of microstructures within cross sections is crucial for subsequent Electron Backscatter Diffraction (EBSD) grain structure analyses and a high resolution interface characterisation by TEM.

Abstract A new method and grid design is described for implementation of ex-situ lift-out of FIB prepared specimens. This technique negates all prior disadvantages to ex-situ liftout and provides a method for higher throughput and rethinning of ex-situ specimens. In particular, this method allows for easy, fast, and routine manipulation for subsequent backside FIB milling and analysis.

Abstract In this paper, crystal damage on TEM sample sidewalls induced by FIB milling during sample preparation was studied. A novel method was invented to prepare the sample, which facilitates the direct observation of amorphous layers on the sidewall. The ion beam acceleration voltage is the dominant factor that affects the damaged layer thickness. The measured amorphous thickness is about 23 nanometers at 30Kv and 10 nanometers at 10Kv. The damage layer thickness is constant with different beam currents over the range from 30pA to 1000pA. Amorphous layer thickness also stays constant with the sample tilt angle.

Abstract The ability to expose a huge kerf/PCM (Process Control Monitor) test structure at the same level is limited from top down finger polishing. Also, in Scanning Electron Microscopy (SEM) the electron beam (e-beam) shift for electron beam absorbed current (EBAC) analysis is not able to cover the whole structure. The recently implemented technique described herein combines the focus ion beam (FIB) chemical enhanced milling method with EBAC analysis to stop the polishing at the upper layer and split the EBAC analysis into portions from the test structure. These help to improve the area of interest (AOI) evenness and enable the extension of the EBAC analysis.

Abstract Fast and accurate examination from the bulk to the specific area of the defect in advanced semiconductor devices is critical in failure analysis. This work presents the use of Ar ion milling methods in combination with Ga focused ion beam (FIB) milling as a cutting-edge sample preparation technique from the bulk to specific areas by FIB lift-out without sample-preparation-induced artifacts. The result is an accurately delayered sample from which electron-transparent TEM specimens of less than 15 nm are obtained.

Abstract Transmission electron microscopy (TEM) specimens are typically prepared using the focused ion beam (FIB) due to its site specificity, and fast and accurate thinning capabilities. However, TEM and high-resolution TEM (HRTEM) analysis may be limited due to the resulting FIB-induced artifacts. This work identifies FIB artifacts and presents the use of argon ion milling for the removal of FIB-induced damage for reproducible TEM specimen preparation of current and future fin field effect transistor (FinFET) technologies. Subsequently, high-quality and electron-transparent TEM specimens of less than 20 nm are obtained.

Abstract Several methods are used to invert samples 180 deg in a dual beam focused ion beam (FIB) system for backside milling by a specific in-situ lift out system or stages. However, most of those methods occupied too much time on FIB systems or requires a specific in-situ lift out system. This paper provides a novel transmission electron microscopy (TEM) sample preparation method to eliminate the curtain effect completely by a combination of backside milling and sample dicing with low cost and less FIB time. The procedures of the TEM pre-thinned sample preparation method using a combination of sample dicing and backside milling are described step by step. From the analysis results, the method has applied successfully to eliminate the curtain effect of dual beam FIB TEM samples for both random and site specific addresses.

Abstract The semiconductor industry recently has been investigating new specimen preparation methods that can improve throughput while maintaining quality. The result has been a combination of focused ion beam (FIB) preparation and ex situ lift-out (EXLO) techniques. Unfortunately, the carbon support on the EXLO grid presents problems if the lamella needs to be thinned once it is on the grid. In this paper, we show how low-energy (< 1 keV), narrow-beam (< 1 μm diameter) Ar ion milling can be used to thin specimens and remove gallium from EXLO FIB specimens mounted on various support grids.

Abstract In this study, a comprehensive investigation of the Ag-Al bond degradation mechanism in an electrically failed module using the argon ion milling, scanning electron microscopy (SEM), dual beam focused ion beam-SEM, scanning transmission electron microscopy energy dispersive x-ray spectroscopy, and time-of-flight secondary ion mass spectrometry is reported. It is found that the bond degradation is due to the galvanic corrosion in the Ag-Al bonding area. Specific attention is given to the information of microstructures, elements, and corrosive ions in the degraded bond. In this study, it is believed that the Ag-Al bond degradation is highly related to the packaging designs.

Abstract The semiconductor industry is constantly investigating new methods that can improve both the quality of TEM lamella and the speed at which they can be created. To improve throughput, a combination of FIB-based preparation and ex situ lift-out (EXLO) techniques have been used. Unfortunately, the carbon support on the EXLO grid presents problems if the lamella needs to be thinned once it is on the grid. In this paper, we present low-energy (<1 keV), narrow-beam (<1 μm diameter), Ar+ ion milling as a method of preparing electron-transparent and gallium-free EXLO FIB specimens.

Abstract The sub-nanometer resolution that transmission electron microscopy (TEM) provides is critical to the development and fabrication of advanced integrated circuits. TEM specimens are usually prepared using the focused ion beam, which can cause gallium-induced artifacts and amorphization. This work presents the use of a concentrated argon ion beam for reproducible TEM specimen preparation using automatic milling termination and targeted ion milling of device features; the result is high-quality and electron-transparent specimens of less than 30 nm. Such work is relevant for semiconductor product development and failure analysis.

Abstract A technique to “graft” a FIB lift-out TEM sample onto a scrapped wedge polished sample was introduced. In this way, the sample can be ion milled with lower accelerating voltage to avoid FIB caused problems. This technique does not require special attachment for the FIB. Improved imaging quality and potential applications are discussed.

Abstract Scanning capacitance microscopy (SCM) has become a valuable tool for failure analysis in integrated circuit manufacture. The ability to perform two-dimensional dopant distribution analysis on small, specific structures has been hampered, however, by the imprecision of current polishing techniques. Utilization of focused ion beam (FIB) milling instrumentation to perform precise cross sectioning of specific structures is preferable to manual polishing, although SCM data has not been forthcoming, due in part at least to the thicker amorphous silicon layer. This work examines the thickness of the amorphous silicon layers generated by various sample preparation methods, including conventional polishing, FIB milling, and low-energy FIB milling. In addition, this work provides SCM comparisons of the low energy FIB milling preparation procedure and conventional polishing.