Query: Green chemical mechanical polishing of sapphire wafers using a novel slurry

Candidate papers:

abstract: Toxic and corrosive solutions are widely used in the preparation of abrasives and chemical mechanical polishing (CMP) of sapphire wafers, resulting in potential environmental pollution. Developing a novel green CMP technique to achieve light emitting diode sapphire wafers is a significant challenge. In this study, a novel green CMP slurry, consisting of silica, sorbitol, aminomethyl propanol, and deionized water was developed for sapphire wafers. After CMP, the sapphire wafers were cleaned with deionized water and dried with compressed air, which is a green process. After CMP, the surface roughness Ra of the sapphire wafer surface with an area of 5 x 5 mm2 was 0.098 nm, which is the lowest surface roughness reported to date for sapphire wafers. Tetrahydroxy coordinated Al(OH)4 ions were produced in the alkaline CMP slurry, and chelation occurred between sorbitol and these ions. The proposed green CMP has potential applications in the semiconductor and microelectronics industries.
author_names: Wenxiang Xie

Zhenyu J Zhang

Longxing Liao

Jia-wen Liu

Hongjiu Su

Shudong Wang

Dongming Guo
title: Green chemical mechanical polishing of sapphire wafers using a novel slurry.
venue: Nanoscale
year: 2020

abstract: Abstract At present, corrosive ingredients are widely employed in chemical mechanical polishing (CMP) of sapphire, bringing a potential threat to both people and environment. This results in high cost and long processing time on the treatment of CMP slurry of sapphire. It is a challenge to develop a novel green CMP for sapphire to meet the stringent requirements of high performance products. In this study, a novel green CMP is proposed for sapphire, consisting of silica nanoparticles of 50 nm, triethanolamine (TEA) sodium metasilicate nonahydrate, and deionized water. After green CMP, surface roughness Ra, root mean square (rms) and peak to valley (PV) are 0.11, 0.139, and 1.65 nm, respectively. Material removal rate is 3.31 mm/h during green CMP. To the best of our knowledge, surface roughness Ra and rms after green CMP developed are the lowest on a sapphire wafer, compared with those reported previously. The CMP mechanism is elucidated by X ray photoelectron spectroscopy (XPS) and infrared (IR) spectra. Sapphire formed Al(OH)4 ions in an alkaline environment, which was chelated by TEA, and removed from the surface of sapphire. These findings provide new insights to fabricate high performance devices of sapphire for the use in semiconductor and microelectronic industries.
author_names: Zhenyu J Zhang

Weibing Hu

Lezhen Zhang

Longxing Liao
title: Chemical mechanical polishing for sapphire wafers using a developed slurry
year: 2021

abstract: Silicon carbide (SiC) single crystals, along with sapphire and silicon, are one of most important substrates for high brightness LED fabrications. Owing to extremely high hardness (Mohs' scale of 9.5) and chemical inertness, the polishing rate of SiC with conventional chemical mechanical polishing (CMP) methods is not high, and surface scratches are also inevitable because of using slurry containing hard abrasives such as silica particles. Here artemisinin (Qinghaosu) crystals, very soft molecular solids, were found, for the first time to the best of our knowledge, to effectively polish SiC wafers even in pure water as demonstrated by proof of concept scratching experiments using atomic force microscopy (AFM) The underlying mechanism is attributed to activated oxidation of SiC by mechanically released reactive *OH free radicals from the endoperoxide bridges. The preliminary results reported here have important implications for developing novel alternative green and scratch free polishing methods for hard brittle substrates including SiC and others.
author_names: Yu-rong Zhu

Dan Zhang

Yang Gan

Feihu Zhang
title: Marrying Medicine and Materials: Artemisinin (Qinghaosu) Particle is Soft Enough for Scratching Hard SiC Wafer in Water
year: 2016

abstract: Non spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering (DLS) and the Focus Ion Beam (FIB) system. This kind of novel colloidal silica particles can be well used in chemical mechanical polishing (CMP) of sapphire wafer surface. And the polishing test proves that non spherical colloidal silica slurry shows much higher material removal rate (MRR) with higher coefficient of friction (COF) when compared to traditional large spherical colloidal silica slurry with particle size 80 nm by DLS. Besides, sapphire wafer polished by non spherical abrasive also has a good surface roughness of 0.460 6 nm. Therefore, non spherical colloidal silica has shown great potential in the CMP field because of its higher MRR and better surface roughness.
author_names: Huijun Kong

Dan Wang

Weili Liu

Zhitang Song
title: Preparation of Non spherical Colloidal Silica Nanoparticle and Its Application on Chemical Mechanical Polishing of Sapphire
venue: Journal of Wuhan University of Technology Mater. Sci. Ed.
year: 2019

abstract: Abstract In this paper, a novel non noble metal catalyst (Fe N x /C) is used to improve the removal mass of sapphire as well as obtain atomically smooth sapphire wafer surfaces. The results indicate that Fe N x /C shows good catalytic activity towards sapphire removal rate. And the material removal rates (MRRs) are found to vary with the catalyst content in the polishing fluid. Especially that when the polishing slurry mixes with 16 ppm Fe N x /C shows the maximum MRR and its removal mass of sapphire is 38.43 nm/min, more than 15.44% larger than traditional CMP using the colloidal silicon dioxide (SiO 2 without Fe N x /C. Catalyst assisted chemical mechanical polishing of sapphire is studied with X ray photoelectron spectroscopy (XPS) It is found that the formation of a soft hydration layer (boehmite, g AlOOH or g AlO(OH) on sapphire surface facilitates the material removal and achieving fine surface finish on basal plane. Abrasives (colloid silica together with magnetite, ingredient of Fe N x /C) with a hardness between boehmite and sapphire polish the c plane of sapphire with good surface finish and efficient removal. Fe 2 O 3 Fe 3 O 4 pyridinic N as well as pyrrolic N group would be the catalytical active sites and accelerate this process. Surface quality is characterized with atomic force microscopy (AFM) The optimum CMP removal by Fe N x /C also yields a superior surface finish of 0.078 nm the average roughness (Ra)
author_names: Li Xu

Chunli Zou

Xiaolei Shi

Guoshun Pan

Luo Guihai

Yan Zhou
title: Fe Nx/C assisted chemical mechanical polishing for improving the removal rate of sapphire
year: 2015

abstract: Recently, sapphire has been used in a wide range of applications including optics, consumer electronics, and especially the rapidly growing LED wafer manufacturing. This paper investigates effects of a novel compound slurry composed of micron scaled diamond abrasives and various nano platelets of graphene oxide (GO) for improving lapping performance of c plane single crystal aluminum oxide (Al2O3) sapphire wafers. Four kinds of graphenes including GO, reduced graphene oxide (RGO) ML RGO (laminate) and MF RGO (few layer) are added into the diamond slurry to achieve compound slurries. Those compound slurries have been prepared with various graphene weight fractions in the range of 0.3 to 2.0 wt% by LP (low power) or HP (high power) ultrasonication with different time spans in the range of 10 min to 48 h to adjust size of GOs. For the lapping process conducted by 10 min HP ultrasonicated GO (2.0 wt%/diamond slurry, combination of medium down force pressure and the highest platen rotation speed of 45 kPa/80 rpm results in highest material removal rate (MRR) of 926.73 nm/min, which is 324% higher than MRR by pure diamond slurry. It is caused by high reactivity of GOs with sapphire wafer. As lapped at pressure/speed of 45 kPa/70 rpm by ultrasonicated GO (0.5 wt%/diamond compound slurry, the average surface roughness Ra of wafer can reach 7.19 nm, which is 0.7% lower than 7.24 nm by pure diamond slurry. Experimental results demonstrate that the optimized planarization of sapphire wafer with high MRR and low surface roughness can be achieved using the GO compound slurry when the mechanical removal effect and the chemical reaction mechanism are in synergistic equilibrium. The XPS and EDS analyses clearly support the material removal model that a reactant aluminum carbonate layer and a residual carbon layer exist and both are efficiently removed by diamond abrasives. Results of this study can be applied to further explore high volume production of CMP of sapphire wafers.
author_names: Hsien-Kuang Liu

Chao-Chang A Chen

Wei-Chung Chen
title: Effects of compound diamond slurry with graphene for lapping of sapphire wafers
year: 2020

abstract: Abstract Chemical mechanical polishing of sapphire with a novel catalyst (SoFeIII) based colloidal silicon dioxide has been studied with high resolution transmission electron microscopy and X ray diffraction. It has been found that a polytype of aluminun trihydroxide is formed on the polished crystal surface when SoFeIII 80 degC catalyst is used, while aluminum silicate hydrate layer is found on the polished sapphire surface when burnished with catalyst free slurry. And the novel catalyst plays effective performance towards improving the removal rate of sapphire, and its removal rate is 7.21 mm/h, 1.66 times than the material removal rate obtained with catalyst free slurry. Additionally, the optimum CMP removal by SoFeIII 80 degC yielded an ultra smooth wafer surface with an average roughness of 0.0543 nm.
author_names: Li Xu

Xin Zhang

Chengxi Kang

Rongrong Wang

Chunli Zou

Yan Zhou

Guoshun Pan
title: Preparation of a novel catalyst (SoFe III and its catalytic performance towards the removal rate of sapphire substrate during CMP process
year: 2018

abstract: Abstract A novel semi empirical model was developed for predicting the material removal rate (MRR) during chemical mechanical polishing (CMP) based on the following assumptions: plastic contact at the wafer particle interface, elastic contact at the pad particle interface, a particle size distribution, and a randomly distributed surface roughness of the polishing pad. The proposed model incorporates the effects of particle size, concentration, and distribution, as well as the slurry flow rate, pad surface topography, material properties, and chemical reactions during the silicon dioxide (SiO 2 CMP. To obtain the unknown parameters and ensure the validity of the model, a SiO 2 CMP experiment was conducted by using various sized CMP slurries. The spatial distribution of the MRRs is expressed with respect to the normal contact stress distribution and the relative velocity distribution. The proposed MRR model can be used for the development of a CMP simulator, the optimization of CMP process parameters, and the design of next generation CMP machines.
author_names: H S Lee

Hae-do Jeong

David A Dornfeld
title: Semi empirical material removal rate distribution model for SiO2 chemical mechanical polishing (CMP) processes
year: 2013

abstract: To meet the stringent requirements of device integration and manufacture, surface defects and mechanical stresses that arise during chemical mechanic planarization (CMP) must be reduced. Towards this end, we have synthesized multiple hybrid and composite particles on micron length scales consisting of siloxane co polymers functionalized with inorganic nanoparticles. These particles can be easily tailored during synthesis, leading to softer or harder abrasion when desired. Upon using these particles for the planarization of silicon oxide wafers, we obtain smooth surfaces with reduced scratches and minimal particle deposition, which is an improvement from conventional abrasive materials like pure silica, ceria and alumina nanoparticle slurries. Tribological characteristics during polishing were examined using a bench top CMP tester to evaluate the in situ co efficient of friction. Characterization of the hybrid and composite particles has been done using infrared spectroscopy, dynamic light scattering, and electron microscopy. Surface roughness of the wafers was examined using atomic force and optical microscopy while removal rate measurements were conducted using ellipsometry at multiple angles.
author_names: Cecil A Coutinhoa

Subrahmanya R Mudhivarthib

A Kumarb

Vinay K Guptaa
title: Chemical Mechanical Polishing of Oxide Layers using Novel Ceria Polymer Microcomposites
year: 2008

abstract: In this study, the chemical mechanical polishing (CMP) of iridium and iridium oxide has been investigated. The results show that it is possible to polish this highly inert noble metal and its oxide with removal rates and selectivities that are satisfactory for damascene processes in semiconductor manufacturing. All slurries are based on commercially available abrasives and chemicals. Using blanket wafers, two particular slurry systems have been systematically studied. Concentration variations of abrasive as well as oxidizer and base have been investigated for iridium and iridium oxide, respectively. The dependence of the removal rate on polishing parameters such as time, pressure, and rotational speeds have been investigated. Iridium and iridium oxide removal rates up to 50 and 260 nm/min with selectivities to SiO 2 up to 30:1 and 50:1 could be reached, respectively. Based on the results obtained on planar wafers slurries with optimized parameters were applied to structured wafers. The dishing effect is very small <10 nm) both in small <1 mm) and larger (10 mm width) structures. Erosion of tetraethyl orthosilicate is in the range between 20 and 40 nm, and the surface roughness (root mean square 0.5 2 nm) measured by atomic force microscopy as well as the depth of scratches (5 15 nm) were comparable to those of copper CMP. Overall, the process performance demonstrated on planar and patterned wafers fully satisfies production requirements. Therefore, these novel polishing processes allow, for the first time, the implementation of noble metal damascene processes in semiconductor manufacturing.
author_names: Gerd Mainka

Gerhard A Beitel

Rainer Florian Schnabel

Annette Saenger

Christine Dehm
title: Chemical Mechanical Polishing of Iridium and Iridium Oxide for Damascene Processes
year: 2001