Focused Ion Beam Milling of Single-Crystal Sapphire with A-, C-, and M-Orientations

Abstract

Sapphire substrates with different crystal orientations are widely used in optoelectronic applications. In this work, focused ion beam (FIB) milling of single-crystal sapphire with A-, C-, and M-orientations was performed. The material removal rate (MRR) and surface roughness (Sa) of sapphire with the three crystal orientations after FIB etching were derived. The experimental results show that: The MRR of A-plane sapphire is slightly higher than that of C-plane and M-plane sapphires; the Sa of A-plane sapphire after FIB treatment is the smallest among the three different crystal orientations. These results imply that A-plane sapphire allows easier material removal during FIB milling compared with C-plane and M-plane sapphires. Moreover, the surface quality of A-plane sapphire after FIB milling is better than that of C-plane and M-plane sapphires. The theoretical calculation results show that the removal energy of aluminum ions and oxygen ions per square nanometer on the outermost surface of A-plane sapphire is the smallest. This also implies that material is more easily removed from the surface of A-plane sapphire than the surface of C-plane and M-plane sapphires by FIB milling. In addition, it is also found that higher MRR leads to lower Sa and better surface quality of sapphire for FIB etching.

Fracture Behavior of Single-Crystal Sapphire in Different Crystal Orientations

“…In a perfect crystal, the plane of chipping must pass between these nets. In the basal plane with interchanging O-Al-Al-O-Al-O layers, there are no conditions for cleavage, whereas in the plane (10)(11)…”

“…where M is the crystal orientation of (10-10), C is the crystal orientation of (0001), and A is the crystal orientation of (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

“…Azhdari et al prepared notched samples of sapphire with different crystal orientations. Through the compression fracture test, it was found that most of the samples fractured along the weak cleavage plane, and the two weakest families of cleavage planes were (-1012) and (10)(11), especially, plane (-1102), plane (-1100) and plane were the preferred fracture planes [24]. Konstantiniuk et al used chemical vapor deposition to deposit single crystal and polycrystalline α-Al 2 O 3 coatings on sapphire substrates with different crystal orientations, and prepared unnotched and notched microcantilevers.…”

“…Konstantiniuk et al used chemical vapor deposition to deposit single crystal and polycrystalline α-Al 2 O 3 coatings on sapphire substrates with different crystal orientations, and prepared unnotched and notched microcantilevers. The (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) single crystalline coating which was aligned for fracture on the C-plane, exhibited the highest fracture stress and fracture toughness [25]. Graça et al used the SEVNB method to explore the fracture resistance of single-crystal sapphire with different crystal orientations prepared by two processes.…”

“…In this paper, the fracture toughness of single-crystal sapphire with different crystal orientations was tested by three-point bending tests. Single crystal sapphire samples were prepared by the single-edge V-notch beam (SEVNB) method, including C-plane (0001), A-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and M-plane (10-10) sapphires. In addition, this paper further considered the influence of the loaded surface during the three-point bending tests.…”