Optimization and Mechanism on Chemical Mechanical Planarization of Hafnium Oxide for RRAM Devices

Abstract

Chemical mechanical planarization (CMP) of hafnium oxide including chemical and mechanical factors has been investigated in this paper. We demonstrated that the introduction of sodium fluoroborate (NaBF4) into hafnium oxide CMP has efficiently improved the removal rate from 5 nm/min to 95.5 nm/min. According to the static etch rate and effects of down force and platen rotation rate on hafnium oxide CMP, the Preston equation RR = kPV was modified to RR = kPV + Rc which suggests that the hafnium oxide CMP is determined by the combination of chemical and mechanical process. Moreover, we proposed a possible mechanism that the reaction of introduced NaBF4 with hafnium oxide provides a softer surface layer, enabling hafnium oxide to be easily polished and removed. Therefore, the removal rate of hafnium oxide was substantially enhanced. Using this method, the hafnium oxide surface with sub-nanometric roughness (RMS) was achieved, which can provide the related planarization material and technology for hafnium oxide nano-devices.

Effect of Ultra Soft CMP Processing Parameters on Topography of HgCdTe Wafer Surfaces

“…It is known that an increase in the platen velocity leads to an increase in the relative velocity between the wafer-pad interfaces which, in turn, influenced the surface roughness. 24,25 Accordingly, in the present study when the platen velocity increases to 50, 60 and 70 rpm the relative velocity (with respect to the carrier) will also increase to 80, 90 and 100 rpm respectively. The higher relative velocity tends to distribute fresh slurry on the pad more efficiently and effectively remove the oxide residuals from the wafer surfaces.…”

“…To obtain good surface quality the rate of passivation/oxidation should match with the rate of material removal from the surfaces. 24,25 Therefore, an increase in R q at the relative velocities of 80 and 100 rpm could be attributed to the surface scratches produced by the unbalanced chemical and mechanical effects during the polishing process. Whereas, the observed significant decrease in R q with improved surface planarity of MCT surfaces at the relative velocity of 90 rpm could be attributed to the balanced mechanical action with the chemical effect.…”

Influence of Polishing Parameters on Abrasive Free Chemical Mechanical Planarization (AFCMP) of Non-Polar (11-20) and Semi-Polar (11-22) GaN Surfaces

“…At relatively higher pH, such as pH 3 in this case, the formation of surface layer may be too slow to match the abrasion by mechanical action of the pad, which results in a lower removal rate. 9 In other words, MRR decreases with increasing pH (pH3), when the thickness of the chemically modified layer is inadequate for mechanical removal. 27 In the CMP process, frictional heat is produced in the polishing interface between the wafer surface and the polishing pad, which can promote the surface reaction at a certain temperature.…”

“…Moreover, the increasing platen velocity also promotes delivery of the fresh slurry and transfer of the by-products, which enhances the passivation and dissolution of the passivated gallium oxide layer during polishing. 9 Beyond 90 rpm platen velocity, the Preston equation does not apply in case of (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and slightly hold good for (11-20) GaN AFCMP. At polishing condition of pressure −38 kPa, slurry pH-2 and 0.4 M concentration of KMnO 4 slurry, it is observed that at platen velocities of 90 rpm for non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and 100 rpm for semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN surface, the mechanical action is in balance with the chemical action and the MRR reaches a maximum value.…”

“…Chemical mechanical planarization (CMP) has been carried out in various forms to planarize different material surfaces aiming to get both local and global planarization. 9 CMP using different slurry chemistries and abrasive particles has been proven successful for preparing smooth GaN surfaces. [10][11][12][13][14] CMP of Ga polar (0001), N polar (000-1), and non-polar planes such as, a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and m-plane (1-100) GaN surfaces was reported by Hanser et al 15 For the non-polar (a-plane) surfaces, a RMS roughness of about <0.2 nm was achieved on a scan area of 5 μm z E-mail: ddse@uohyd.ernet.in × 5 μm.…”