Preparation of Ni-Doped Colloidal Silica Abrasives and Their Chemical Mechanical Polishing Performances on Sapphire

Abstract

Chemical mechanical polishing (CMP) has become a widely accepted global planarization technology. Abrasive is one of the key elements in CMP process. In order to enhance material removal rate (MRR) and improve surface quality of sapphire substrate, a series of novel Ni-doped colloidal silica abrasives were prepared by seed-induced growth method. The CMP performances of composite abrasives on sapphire substrate were investigated using UNIPOL-1502 polishing equipment. The analyses on the surface of polished sapphire substrate indicate that slurries containing the Ni-doped colloidal silica composite abrasives achieve lower surface roughness and higher material removal rate than that of pure colloidal SiO 2 abrasive under the same experimental conditions. Furthermore, the acting mechanism of the Ni-doped colloidal silica abrasive on sapphire CMP was investigated. X-ray photoelectron spectroscopy analysis shows that solid-state chemical reactions between Ni-doped colloidal silica abrasive and sapphire surface occur during CMP process, which can promote the chemical effect in CMP and lead to the improvement of material removal rate.With the development of light emitting diodes (LEDs), substrate materials have been given more attention. Sapphire wafers with c (0001) orientation are used as lattice-mismatched substrate for gallium nitride (GaN) LED on account of its comparatively low cost, large diameter, high quality, chemical compatibility, optical transparency and high temperature stability etc. 1-5 It has been established that the crystal structure of epitaxial films is strongly influenced not only by the substrate material and its orientation, but to a great extent also by the surface preparation of the substrate. 6 The defects on the substrate surface could be replicated into the epilayer and impair the quality of epitaxy, 7 so the surface of sapphire is required to be super smooth and has little defect. As is known to all, the intrinsic nature of sapphire (great hardness and chemical inertness) poses great challenges to such machining. 8,9 To achieve the above-mentioned surface quality of sapphire, researchers put forward several polishing technologies. 10 Among which, chemical mechanical polishing (CMP) is almost only accepted global planarization technology for sapphire because of its simple operation, high processing efficiency and little or no surface and subsurface damage (such as scratch and microcrack). 11,12 In the CMP process, there are up to 16 variables that need to be controlled to achieve a stable process, and one of the major variables is related to slurry. 13 As the basic element of slurry, i.e. the hardness, size, and chemical properties of abrasives are crucial for a good CMP performance. 14 A series of inorganic abrasives were used to examine the sapphire CMP, such as silica, diamond, boron carbide, ceria and alumina. [15][16][17][18] And it is found that high material removal rate (MRR) and good surface quality is very difficult to be obtained at the same time. With limiting of production cost a...

Nanomaterials and Equipment for Chemical–Mechanical Polishing of Single-Crystal Sapphire Wafers

“…Table 4 demonstrates the influence of the composite abrasives on the polishing efficiency of sapphire [89][90][91][92][98][99][100]105]. Typically, in the work of Lei's research group, they doped metal ions such as Co/Fe/Cu/Ni/Zn in SiO 2 to form metal-doped SiO 2 composite abrasives, and found that solid chemical reactions occurred on the surface of sapphire during the grinding process of composite abrasives and sapphire [94][95][96][97][98]. The intermediate layer such as CoAl 2 O/AlFeO 3 /Al 2 CuO 4 /NiAl 2 O 4 / Al 2 ZnO 4 was formed and was easy to be removed.…”

Effect of Chitosan Oligosaccharide as a Complexing Agent on Chemical Mechanical Polishing Performance of C-, A-, and R-Plane Sapphire Substrate

“…14 Lei et al mixed some metal ions into the silica sol for C-plane sapphire CMP, such as La, Zn, Fe, Cu, and Ni ions, and found that AlLaO 3 , Al 2 ZnO 4 , AlFeO 3 , Al 2 CuO 4 , and NiAl 2 O 4 were easily formed and removed, which promoted the chemical reaction and improved the MRR. [15][16][17][18][19] Dai et al found that coating SiO 2 on the SiC surface significantly improved the polishing performance of the abrasive and increased the MRR of C-plane sapphire. 20 Lu et al found that the MRRs were improved and good surface morphology was obtained for C-, A-and R-plane sapphire by adding potassium persulfate (K 2 S 2 O 8 ) into the slurry.…”

Effect of ZnO-SiO2 Composite Abrasive on Sapphire Polishing Performance and Mechanism Analysis

“…), and found AlLaO 3 /CoAl 2 O/AlFeO 3 / NiAl 2 O 4 /Al 2 CuO 4 /Al 2 ZnO 4 which are softer and easier to remove were formed. [18][19][20][21][22][23] Yin et al confirmed that solid-solid reaction occurred and aluminum silicate was formed, which has lower hardness and can be removed easily than sapphire itself during the CMP process. 24 Through preliminary investigations, it is found that ZnO can react with Al 2 O 3 under certain conditions to form ZnAl 2 O 4 .…”