钴互连化学机械抛光浆料中的界面腐蚀行为研究

doi:10.13208/j.electrochem.210447

摘要/Abstract

摘要：

芯片互连层进行化学机械抛光（CMP）时,抛光液对互连金属的腐蚀问题是影响抛光后表面质量的重要因素。本文在含有氧化剂过硫酸钾（KPS）、络合剂甘氨酸（Gly）和缓蚀剂苯骈三氮唑（BTA）的抛光液体系中,对互连金属钴的界面腐蚀行为进行了研究。结果显示, 强氧化剂KPS在互连层抛光液中并不能使钴表面形成稳定钝化,需要进一步引入BTA以抑制过度腐蚀。静态腐蚀实验和扫描电子显微镜观察显示, BTA能有效地降低钴在抛光液中的腐蚀,提高表面质量,电化学测试计算出其缓蚀效率最高可达99.02%。电化学阻抗谱和X射线光电子能谱揭示了腐蚀过程机理： Gly的加入可以溶解钴表面的二价及三价氧化物,破坏KPS形成的钝化层,BTA的引入会大幅增加电化学腐蚀过程的电荷转移电阻,从而抑制抛光液对钴的腐蚀。

关键词: 钴互连, 化学机械抛光, 腐蚀, 甘氨酸, 苯骈三氮唑

Abstract:

Cobalt is widely regarded as the most promising interconnect material for 10 nm node and beyond. The development of a chemical mechanical planarization (CMP) slurry suitable for cobalt interconnect is a critical component for the application of cobalt interconnect. During CMP process of the interconnect layer, the achievement of high-quality surface after planarization is greatly challenged by the metal corrosion in CMP slurry. In this contribution, the corrosion behavior of cobalt in a slurry with potassium persulfate (KPS) as an oxidizer, glycine as a complexing agent, and benzotriazole (BTA) as an inhibitor was investigated. Static erosion rates (SER) of cobalt in the slurry at various pH values with and without the inhibitor were examined. The result showed that SER of cobalt increased slightly with increasing pH, whereas BTA clearly inhibited the corrosion of cobalt in the slurry. Scanning electronic Microscopic analysis revealed that BTA could improve the morphology of cobalt surface which was deteriorated due to corrosion in planarization slurry of pH = 9. Electrochemical corrosion measurements were conducted to further investigate the effects of BTA. The potentiodynamic polarization curves indicated that as the BTA concentration increased, the corrosion potential increased, while the corrosion current density decreased. The corrosion of cobalt was effectively inhibited by adding 0.4wt% BTA in the slurry, with an inhibition efficiency of 99.02%. The electrochemical impedance data showed that the Nyquist plots of cobalt contained two rings in the slurry without BTA. The high-frequency ring was formed by cobalt oxide, and the low-frequency ring was formed by double layers. While in the BTA-containing slurry, the Nyquist plots contained only one ring at a high frequency formed by double layers, with a significantly larger diameter than that in the slurry without BTA. It can be concluded that BTA is capable of preventing cobalt from forming an oxide layer, and thereby, reducing electrochemical corrosion. Finally, the X-ray photoelectron spectroscopy was implemented to quantitatively analyze the surface's valence composition of cobalt in various solutions. The results showed that when the KPS was added as an oxidizer, a double-layer of passivation was formed on the surface of cobalt, with a Co²⁺ rich inner layer and Co³⁺ rich outer layer. The addition of glycine resulted in the dissolution of the outer layer oxide, reducing the content of Co³⁺ in the passivation layer. The addition of BTA could suppress the oxidation of Co by KPS, and lowered the Co³⁺ content on the cobalt surface. It can be demonstrated that the CMP slurry developed in this work effectively inhibited the corrosion of cobalt in an acid solution, which may solve the problem of galvanic corrosion between the cobalt interconnect and barrier layer in CMP process.

Key words: cobalt interconnects, chemical mechanical planarization, corrosion, glycine, benzotriazole

秦凯旋, 常鹏飞, 黄钰林, 李明, 杭弢. 钴互连化学机械抛光浆料中的界面腐蚀行为研究[J]. 电化学（中英文）, 2022, 28(6): 2104471.

Kai-Xuan Qin, Peng-Fei Chang, Yu-Lin Huang, Ming Li, Tao Hang. An Investigation on the Interface Corrosion Behaviors of Cobalt Interconnects in Chemical Mechanical Polishing Slurry[J]. Journal of Electrochemistry, 2022, 28(6): 2104471.

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链接本文: https://electrochem.xmu.edu.cn/CN/10.13208/j.electrochem.210447

https://electrochem.xmu.edu.cn/CN/Y2022/V28/I6/2104471

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Composition	E_corr/V	i_corr/(μA·cm^-2）	η/%
0.25wt% KPS	0.105	393.46	-
0.25wt% KPS + 0.1 mol·L^-1 Gly	-0.438	398.84	-
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.1wt%BTA	-0.362	67.41	83.10
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.2wt% BTA	-0.346	24.34	93.90
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.3wt% BTA	-0.335	11.76	97.05
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.4wt% BTA	-0.321	3.89	99.02

R_sol(Ω·cm²)	R_ct(Ω·cm²)	R_c(Ω·cm²)	CPE_c		CPE_dl
R_sol(Ω·cm²)	R_ct(Ω·cm²)	R_c(Ω·cm²)	CPE-T (mF·cm^-2)	CPE-P	CPE-T (mF·cm^-2)	CPE-P
135.20	44.88	65.53	39.14	0.91	0.44	0.63

Composition	R_sol(Ω·cm²)	R_ct(Ω·cm²)	CPE
Composition	R_sol(Ω·cm²)	R_ct(Ω·cm²)	CPE-T (μF·cm^-2)	CPE-P
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.1wt% BTA	123.8	862.1	41.1	0.74
0.25wt% KPS + 0.2 mol·L^-1 Gly + 0.2wt% BTA	112.9	1998	32.5	0.79
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.3wt% BTA	90.77	6434	12.87	0.85
0.25wt% KPS + 0.1 mol·L^-1 Gly + 0.4wt% BTA	81.15	15354	14.91	0.81

Sample	Co (%)	Co²⁺ (%)	Co³⁺ (%)
A	11.45	6.01	82.54
B	16.45	19.78	63.77
C	10.14	19.21	70.65