Chemical Mechanical Polishing Mechanism for BK7 Optical Glass

YIN Xincheng; ZHOU Yuhang; WANG Youliang; WANG Zikai

doi:10.16490/j.cnki.issn.1001-3660.2026.01.004

PDF(9981 KB)

Surface Technology ›› 2026, Vol. 55 ›› Issue (1) : 43-57. DOI: 10.16490/j.cnki.issn.1001-3660.2026.01.004

Precision and Ultra-precision Machining

Chemical Mechanical Polishing Mechanism for BK7 Optical Glass

YIN Xincheng^1,2, ZHOU Yuhang^1,2, WANG Youliang^1,2, WANG Zikai¹

Author information +

History +

Abstract

BK7 optical glass is an excellent material in the optical industry due to its low dispersion and high transmittance. However, its surface polishing still remains a serious challenge. BK7 optical glass is a typical hard-brittle material with high hardness, high brittleness, low fracture toughness, and good chemical stability. Traditional mechanical processing methods are difficult to meet the technical requirements of modern industry. CMP (Chemical Mechanical Polishing) can achieve an extremely low roughness on the surface of BK7 glass while causing minimal surface and subsurface damage. The work aims to explore the effect of various factors during the chemical mechanical polishing (CMP) process on the removal rate (MRR) and surface roughness (Ra) of BK7 optical glass materials, to reveal the chemical mechanical polishing mechanism of BK7 optical glass in a polishing liquid containing nano-scale cerium dioxide (CeO₂) abrasive particles, and improve the efficiency and achieve low-damage surface polishing of BK7 optical glass.
By the single-factor experimental method, CMP experiments were conducted on BK7 optical glass to compare the polishing effects under different polishing time, platen speed, CeO₂ contents, slurry pH values, and citric acid contents, to analyze the effect of these conditions on the polishing performance of BK7 optical glass, and the optimal parameter combination was determined through orthogonal experiments. The variations in the concentration of Ce³⁺ on the surface of CeO₂ abrasive particles were investigated through energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), as well as the aggregation and adsorption behavior of CeO₂ under different conditions.
Through orthogonal experimental design, the optimal combination of polishing parameters was determined: the polishing time of 50 min, the polishing disc speed of 60 r/min, the slurry pH value of 6, the CeO₂ abrasive concentration of 0.5%, and the citric acid concentration of 2%. Under these conditions, the best MRR of 139.6 µm/h and a Ra of 2 nm were achieved, with a 99.6% reduction in surface roughness. No obvious abrasive residues were observed on the polished surface of the BK7 optical glass. Based on the characterization results obtained from X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), and nanoindentation testing, the material removal mechanism of BK7 optical glass during CMP was proposed. Citric acid acted as a reducing agent, reduced Ce⁴⁺ ions on the surface of CeO₂ abrasive particles to Ce³⁺. This reduction process increased the surface concentration of Ce³⁺ on the CeO₂ particles, forming oxygen vacancies. With the increase in Ce³⁺ concentration, the chemical adsorption between CeO₂ abrasive particles and silicate ions increased, forming Ce—O—Si bonds. Meanwhile, free electrons in Ce³⁺ migrated to the surface of SiO₂, which promoted the breaking of Si—O bonds. This facilitated the mechanical removal of the softened layer on the polished surface of BK7 optical glass by CeO₂ abrasives, thereby improving the polishing efficiency.
Compared with the chemical mechanical polishing method that prepares complex CeO₂ core-shell structures and adds low-valent metal ions to CeO₂ abrasive particles, this study employs the addition of citric acid to enhance the surface concentration of Ce³⁺ on CeO₂ abrasive particles. This method accelerates the reaction rate between CeO₂ abrasives and the polished surface of BK7 optical glass, thereby facilitating the cleavage of Si—O bonds and significantly improving the polishing efficiency of BK7 optical glass surfaces. It can also be applied to ultra-precision machining with high accuracy, which provides guidance for optimizing polishing process parameters and elucidating the material removal mechanism to achieve high-quality surfaces on BK7 optical glass.

Key words

BK7 optical glass / chemical mechanical polishing / CeO₂ / material removal mechanism / pH / material removal rate

Cite this article

EndNote

Ris (Procite)

Bibtex

Download Citations

YIN Xincheng, ZHOU Yuhang, WANG Youliang, WANG Zikai. Chemical Mechanical Polishing Mechanism for BK7 Optical Glass[J]. Surface Technology. 2026, 55(1): 43-57

References

[1] LI C, HU Y X, WEI Z Z, et al.Damage Evolution and Removal Behaviors of GaN Crystals Involved in Double- Grits Grinding[J]. International Journal of Extreme Manufacturing, 2024, 6(2): 025103.
[2] 梁赢东, 牛俊开, 张超, 等. 超声振动辅助抛光BK7过程中聚氨酯抛光垫磨损行为[J]. 东北大学学报(自然科学版), 2023, 44(1): 82-88.
LIANG Y D, NIU J K, ZHANG C, et al.Wear Behavior of Polyurethane Polishing Pads Used in BK7 Ultrasonic Vibration-Assisted Polishing[J]. Journal of Northeastern University (Natural Science), 2023, 44(1): 82-88.
[3] GUO Y F, YIN S H, OHMORI H, et al.A Novel High Efficiency Magnetorheological Polishing Process Excited by Halbach Array Magnetic Field[J]. Precision Engineering, 2022, 74: 175-185.
[4] 白倩, 马浩, 殷景飞. 基于偏振激光共聚焦的研磨石英玻璃亚表面损伤检测[J]. 光学精密工程, 2021, 29(8): 1795-1803.
BAI Q, MA H, YIN J F.Polarized Laser Confocal Technique for Subsurface Damage of Lapped Quartz Glass[J]. Optics and Precision Engineering, 2021, 29(8): 1795-1803.
[5] LEE H, KIM H, JEONG H.Approaches to Sustainability in Chemical Mechanical Polishing (CMP): A Review[J]. International Journal of Precision Engineering and Manufacturing-Green Technology, 2022, 9(1): 349-367.
[6] LI W, XIN Q, FAN B, et al.A Review of Emerging Technologies in Ultra-Smooth Surface Processing for Optical Components[J]. Micromachines, 2024, 15(2): 178.
[7] 朱子俊, 刘顺, 韩冰, 等. 超声振动复合研磨K9光学玻璃工艺研究[J]. 表面技术, 2020, 49(4): 74-80.
ZHU Z J, LIU S, HAN B, et al.Study on Hybrid Technology of Ultrasonic Vibration Assisted Abrasive Lapping K9 Optical Glass[J]. Surface Technology, 2020, 49(4): 74-80.
[8] QI H, SHI L W, TENG Q, et al.Subsurface Damage Evaluation in the Single Abrasive Scratching of BK7 Glass by Considering Coupling Effect of Strain Rate and Temperature[J]. Ceramics International, 2022, 48(6): 8661-8670.
[9] HUANG Y H, WANG M C, LI J M, et al.Effect of Abrasive Particle Shape on the Development of Silicon Substrate during Nano-Grinding[J]. Computational Materials Science, 2021, 193: 110420.
[10] CUI X X, ZHANG Z Y, SHI C J, et al.Atomic Surface Induced by Novel Green Chemical Mechanical Polishing for Aspheric Thin-Walled Crucibles with Large Diameters[J]. Journal of Manufacturing Processes, 2024, 117: 59-70.
[11] STREY N F, SCANDIAN C.Abrasive Polishing Load Effect on Surface Roughness and Material Removal Rate of Al₂O₃, ZTA and SiC[J]. Wear, 2021, 477: 203787.
[12] KENCHAPPA N B, POPURI R, CHOCKKALINGAM A, et al.Soft Chemical Mechanical Polishing Pad for Oxide CMP Applications[J]. ECS Journal of Solid State Science and Technology, 2021, 10(1): 014008.
[13] 余青, 刘德福, 陈涛. 单晶蓝宝石衬底晶片的化学机械抛光工艺研究[J]. 表面技术, 2017, 46(3): 253-261.
YU Q, LIU D F, CHEN T.Chemico-Mechanical Polishing Technique of Monocrystal Sapphire Substrate Wafer[J]. Surface Technology, 2017, 46(3): 253-261.
[14] 许宁, 马家辉, 刘琦. CeO₂基磨粒在化学机械抛光中的研究进展[J]. 中国稀土学报, 2022, 40(2): 181-193.
XU N, MA J H, LIU Q.Research Progress of CeO₂-Based Abrasive Particles in Chemical Mechanical Polishing[J]. Journal of the Chinese Society of Rare Earths, 2022, 40(2): 181-193.
[15] XIAN W H, ZHANG B G, LIU S T, et al.The Mechanism of Ceria Slurry on Chemical Mechanical Polishing Efficiency and Surface Quality of Gallium Nitride[J]. Materials Science in Semiconductor Processing, 2025, 188: 109208.
[16] 程佳宝, 石芸慧, 牛新环, 等. CMP抛光液中SiO₂磨料分散稳定性的研究进展[J]. 微纳电子技术, 2024, 61(2): 31-41.
CHENG J B, SHI Y H, NIU X H, et al.Research Progress on Dispersion Stability of SiO₂ Abrasive in CMP Slurry[J]. Micronanoelectronic Technology, 2024, 61(2): 31-41.
[17] 朱玉广, 王子睿, 马服辉, 等. pH条件对铝合金化学机械抛光过程中纳米摩擦化学行为的影响[J]. 表面技术, 2025, 54(2): 173-181.
ZHU Y G, WANG Z R, MA F H, et al.Effect of pH on Nano-Tribochemical Behavior in Chemical Mechanical Polishing of Aluminum Alloy[J]. Surface Technology, 2025, 54(2): 173-181.
[18] 贾慧灵, 徐阳, 吴锦绣, 等. 制备条件对二氧化铈稀土抛光粉性能的影响[J]. 稀土, 2022, 43(4): 37-45.
JIA H L, XU Y, WU J X, et al.Effect of Preparation Conditions on the Properties of Cerium Oxide Polishing Powder[J]. Chinese Rare Earths, 2022, 43(4): 37-45.
[19] MA J H, XU N, HU J R, et al.Doping Strategy on Properties and Chemical Mechanical Polishing Performance of CeO₂ Abrasives: A DFT Assisted Experimental Study[J]. Applied Surface Science, 2023, 623: 156997.
[20] 王旭, 李鑫, 邱名健, 等. 纳米CeO₂磨料在化学机械抛光中的研究进展[J]. 有色金属材料与工程, 2025, 46(2): 1-8.
WANG X, LI X, QIU M J, et al.Research Progress on Nano-CeO₂ Abrasive in Chemical Mechanical Polishing[J]. Nonferrous Metal Materials and Engineering, 2025, 46(2): 1-8.
[21] SEO J, KIM K, KANG H, et al.Perspective - Recent Advances and Thoughts on Ceria Particle Applications in Chemical Mechanical Planarization[J]. ECS Journal of Solid State Science and Technology, 2022, 11(8): 084003.
[22] 姜峰, 钱善华, 屈克松, 等. 不同粒径氧化铈磨料对K9玻璃化学机械平坦化性能的影响[J]. 中国表面工程, 2025, 38(5): 107-118.
JIANG F, QIAN S H, QU K S, et al.Effect of Cerium Oxide Abrasives with Different Particle Sizes on the Chemical Mechanical Planarization Performance of K9 Glass[J]. China Surface Engineering, 2025, 38(5): 107-118.
[23] MA J H, XU N, LUO Y X, et al.Enhancing the Polishing Efficiency of CeO₂ Abrasives on the SiO₂ Substrates by Improving the Ce³+ Concentration on Their Surface[J]. ACS Applied Electronic Materials, 2023, 5(1): 526-536.
[24] BRUGNOLI L, MIYATANI K, AKAJI M, et al.New Atomistic Insights on the Chemical Mechanical Polishing of Silica Glass with Ceria Nanoparticles[J]. Langmuir, 2023, 39(15): 5527-5541.
[25] FAN Y Y, JIAO J, ZHAO L, et al.Nd-Doped Porous CeO₂ Abrasives for Chemical Mechanical Polishing of SiO₂ Films[J]. Materials Science in Semiconductor Processing, 2024, 175: 108265.
[26] ZHANG Y S, LEI H, ZHANG J H, et al.Dual Impact of Nd³+ Doping on CeO₂ Abrasives: Enhancing Chemical and Mechanical Effects in Chemical-Mechanical Polishing[J]. Surface Science and Technology, 2025, 3(1): 6.
[27] KIM K, YI D K, PAIK U.Increase in Ce³+Concentration of Ceria Nanoparticles for High Removal Rate of SiO₂ in Chemical Mechanical Planarization[J]. ECS Journal of Solid State Science and Technology, 2017, 6(9): 681-685.
[28] ZHU C Z, WANG Y T, JIANG Z F, et al.CeO₂ Nanocrystal-Modified Layered MoS₂/g-C₃N₄ as 0D/2D Ternary Composite for Visible-Light Photocatalytic Hydrogen Evolution: Interfacial Consecutive Multi-Step Electron Transfer and Enhanced H₂O Reactant Adsorption[J]. Applied Catalysis B: Environmental, 2019, 259: 118072.
[29] HANCOCK M L, YOKEL R A, BECK M J, et al.The Characterization of Purified Citrate-Coated Cerium Oxide Nanoparticles Prepared via Hydrothermal Synthesis[J]. Applied Surface Science, 2021, 535: 147681.
[30] KONG J J, XIANG Z W, LI G Y, et al.Introduce Oxygen Vacancies into CeO₂ Catalyst for Enhanced Coke Resistance during Photothermocatalytic Oxidation of Typical VOCs[J]. Applied Catalysis B: Environmental, 2020, 269: 118755.
[31] JIANG F, WANG S S, LIU B, et al.Insights into the Influence of CeO₂Crystal Facet on CO₂Hydrogenation to Methanol over Pd/CeO₂Catalysts[J]. ACS Catalysis, 2020, 10(19): 11493-11509.
[32] BARTH C, LAFFON C, OLBRICH R, et al.A Perfectly Stoichiometric and Flat CeO₂(111) Surface on a Bulk-Like Ceria Film[J]. Scientific Reports, 2016, 6: 21165.
[33] YE J H, YU J X, HE H T, et al.Effect of Water on Wear of Phosphate Laser Glass and BK7 Glass[J]. Wear, 2017, 376: 393-402.
[34] VOSKRESENSKAYA O O, SKORIK N A.Thermodynamics of the Formation of Intermediate Complexes in the Oxidation of Citric Acid with Cerium(IV) and the Kinetics of Their Intramolecular Redox Decomposition[J]. Russian Journal of Physical Chemistry A, 2023, 97(4): 663-671.
[35] VOSKRESENSKAYA O O, SKORIK N A.The Kinetics of Cerium(IV) Sulfate Reaction with Citrate and the Thermodynamic Characteristics of Formation of Intermediate Complexes[J]. Russian Journal of Physical Chemistry A, 2009, 83(6): 945-950.

Funding

National Natural Science Foundation of China (52265056); Natural Science Foundation of Gansu Province (23JRRA776); Lanzhou Youth Talent Project (2023-QN-38); Scientific Research Project of Wenzhou City ( G20240035)