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55mm 2.5D package used in an artificial This aids fast Ga FIB polishing times, it can be done in areas far away from the
intelligence application. The inset image and rapid results are further enabled by a desired target location. This reduces the risk
showing 25µm-diameter microbumps was streamlined single-instrument queue, rather of preparation artifacts, even in high-stress
acquired using 1.8µm/voxel. 3D XRM has than managing two queues of separate tools. packages containing advanced-node silicon
become standard in FA labs because of its The laser-integrated FIB-SEM (laserFIB) die with ultra-lowK dielectrics.
ability to image fully intact packages with represents a new class of FIB-SEM, The sloped walls produced by the fs-laser
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high spatial resolution [5], and state-of- optimized for imaging targeted features at ensure the Ga beam has a short milling
the-art 3D XRM has a spatial resolution nanoscale resolutions within SiP and 2.5/3D path in the z-dimension of this wedge-
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of 500nm with voxel sizes of 40nm [6]. packages. Table 1 shows it is well-suited shaped edge, enabling efficient local Ga
The XRM images are helpful to guide for removing cubic millimeters of material, FIB polishing and high-resolution imaging
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subsequent cross-sectional scanning unlike the Xe plasma FIB (PFIB). Using across areas of 100µm to 500µm wide
electron microscope (SEM) analysis. parameters for high-quality laser-processed and equal or greater depths. High imaging
Traditional mechanical cross-section surfaces, it takes four minutes for the fs- quality and low maintenance is ensured
techniques are under pressure to deliver laser to remove a half cubic millimeter of by segregating the laser from the FIB-
artifact-free results at high throughput [7]. silicon, compared to two days for a PFIB or SEM chamber to avoid contaminating the
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Focused ion beam (FIB) processing, while 15 days for a Ga FIB at published milling columns and detectors with ablated and
having adequate accuracy and quality for the rates [9]. recast material. Efficient transfer between
finest-pitch interconnects, lacks efficiency The time-consuming conventional chambers enables the repeated cycles of
for removing large volumes of packaging cross-section steps of epoxy embedding laserFIB processing and imaging that may
material to analyze buried features. To and mechanical polishing are not used in be required for new recipe set-up or for
address these deficiencies, a new instrument, the laserFIB workflow (Figure 2), and if analyzing multiple sites in a sample.
ZEISS Crossbeam laser, was recently downsizing of larger samples is required,

Figure 1: 3D XRM images from three scans of a 55mm x 55mm 2.5D package, showing multiple levels of interconnect, the smallest being 25µm-diameter Cu-pillar microbumps.
developed. It extends the nanoscale imaging
and process accuracy of FIB-SEM to
packages by enabling site-specific removal
of large volumes of packaging material. It
includes a fs-laser attached to the external
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load lock of a gallium ion (Ga ) FIB-SEM,
delivering an improved workflow for site-
specific cross-sectional imaging. Integration
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of a fs-laser and Ga FIB into a single
system ensures a streamlined “cut and look”
workflow for fastest time to results, as well
as a pristine sample that is not oxidized by
exposure to atmosphere, thereby enabling
accurate analysis. The fs-laser interaction is
essentially athermal [8], producing a laser
affected zone (LAZ) smaller than 1µm
under optimized processing conditions. Table 1: Technology timing comparisons for removal of up to one cubic millimeter of silicon.

40 Chip Scale Review May • June • 2020 [ChipScaleReview.com]
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