Figure 2

Mechanical profilometry measurements. (a) Schematic of a flip-chip bonded device without spacers indicating the scan direction of the mechanical profilometer stylus. (b) Raw profilometer data and (c) data after leveling, cropping to the top-chip region, and subtracting the mean height of the entire top-chip area. (d) Mechanical profilometer height maps of the modules bonded without spacers. The purple arrows in the rightmost panel (N4) indicate the trace presented in (c). (e) Schematic of a flip-chip bonded device with spacers and corresponding height maps (f). The height maps are approximately 11 mm by 11 mm in size. The colors represent the deviation from the mean top-chip height on each module while the number in the center of each sub-panel is the extracted average inter-chip spacing (measured value minus estimated top-chip substrate thickness; in μm). Light gray vertical lines are columns that have been removed from the data set due to a measurement artifact. Sample names are indicated by the gray text above each height map