Fabrication and application of high quality diamond coated. CMP pad conditioners

Transcription

1 Fabrication and application of high quality diamond coated CMP pad conditioners Hua Wang 1,a, Fanghong Sun 1,b* 1 School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, , China a wanghuar@sjtu.edu.cn, b sunfanghong@sjtu.edu.cn Keywords: Diamond film, CMP pad conditioner, Si 3 N 4, Wear resistance, Lifetime Abstract. Continuous, homogeneous diamond films are deposited on the working surfaces of CMP pad conditioners with regularly patterned protrusions and well controlled pyramid shape, using the hot filament chemical vapor deposition (HFCVD) technique. After deposition, the fabricated diamond coated CMP pad conditioners are characterized by Field emission scanning electron microscopy (FESEM), Rockwell hardness tester and Raman spectroscopy. To evaluate further the dressing characteristics of diamond coated conditioners, comparative application tests for both diamond coated and uncoated CMP pad conditioners are conducted. The results exhibit that the hardness and wear resistance of the working surfaces after deposition of diamond films are improved. Therefore, diamond coated CMP pad conditioners have longer lifetime and better stability relative to the uncoated CMP pad conditioners. Introduction Due to the superior mechanical and tribological performances, such as high hardness and elastic modulus, good wear resistance, good corrosion resistance, low friction coefficient and high thermal conductivity, chemical vapor deposition (CVD) diamond films have enormous application prospects as surface coatings of oxidation-resistant and wear-resistant components such as cutting tools, compacting and drawing dies used in the metal processing industry [1,2]. Hot filament chemical vapor deposition (HFCVD) method is a very practical kind of CVD technologies because of its advantages such as geometrical simplification, operational convenience and low cost, especially the practicality on the complicated surfaces [3]. Hot filament chemical vapor deposition (HFCVD) diamond thin films have been widely used as abrasive resistant material [4,5]. Chemical mechanical polishing (CMP) is one of the most important processes in the fabrication of integrated circuits (IC). In CMP, as more and more wafers are polished, the pad planarity and surface roughness could be deteriorated by surface glazing resulting from pad wear and debris. This leads to a reduction in material removal rate (MRR) and poor wafer uniformity [6]. Therefore, pad conditioner is employed to dress the pad surface to restore pad planarity and surface asperity. The CMP process contains a large number of variables and interactions between the polishing pad, slurry and conditioners [7]. CMP pad conditioners play the most important role, and their structures are commonly very dexterous. Si3N4 is often used as the material of CMP pad conditioners. The conventional CMP diamond

2 pad conditioner, which is usually fabricated by electroplating or brazing, consists of numerous industrial diamond grits on the flat surface of substrates. Although the conventional pad conditioner contains regularly distributed diamond grits, the tips of the diamond grits are set at various heights. In addition, the diamond grits have various shapes and sizes, and their dressing efficiency and uniformity consequently differ from place to place [8]. Moreover, the scratches appear on polishing pads due to segregation of diamonds and contamination of the dissolved substrate grits. The conventional conditioners usually have poorer wear resistance, which extremely limits the working lifetime of them. This work consists of the evaluation of the hardness and wear resistance of diamond films deposited on CMP pad conditioners with regularly patterned protrusions. The surface morphology, thickness and quality of fabricated diamond films are examined by Field emission scanning electron microscopy (FESEM). The hardness and adhesion are characterized by the Rockwell hardness tester and the purity is evaluated by the Raman spectroscopy. Then we investigate the dressing characteristics of both diamond coated and uncoated CMP pad conditioners based on the application tests. The comparative results demonstrate that diamond coated CMP pad conditioners have longer lifetime, better stability compared with that of uncoated one. As deposited diamond film can improve obviously the wear resistance and extend the life time of conditioners. Experiments Fabrication of CVD Diamond Coated CMP Pad Conditioners. The CMP pad conditioners (ϕ14.4mm) with regularly patterned protrusions and well controlled pyramid shape are used as substrates, the tip to tip pitch of which is 0.64mm, as shown in Fig.1. The working surface of the conditioner is designed to be very coarse which contribute to higher dressing efficiency and accuracy. Before deposition, the working surfaces of substrates are polished slightly with diamond powders for 2 minutes to improve the deposition rate. The deposition processes are carried out with a home-made bias-enhanced HFCVD apparatus. Methane and excessive H2 are used as reaction gas, and there are six filaments during the deposition. Hot filaments are parallel to each other and the distances between them are 30mm.The filaments are dragged straightly by high-temperature resistance springs and the distance between filaments and substrates is 10mm during the deposition process, which can generate a uniform temperature distribution above the surfaces of CMP pad conditioners, as is shown in Fig.2. Fig.1 Specimen of CMP pad conditioner Fig.2 Sketch of depositiom The detailed deposition parameters are as the following. Methane and H2 flow rate are

3 respectively 50sccm and 1800sccm. The pressure in the reaction chamber is 4000Pa during the deposition. The filament temperature is C, and the deposition temperature is C. A direct current bias (3A) is applied between the filament and substrate to enhance the nucleation density. The deposition time is totally 6 hours. The fabricated diamond films are characterized by FESEM (Field emission scanning electron microscopy), Rockwell hardness tester, and Raman spectroscopy. Application Tests. In order to evaluate the dressing characteristics of fabricated CMP pad conditioners, comparative application tests are conducted for both diamond coated and uncoated CMP pad conditioners, as is demonstrated in Fig.3. The CMP pad conditioner is used to dress the polishing pad. The polishing pressure keeps stable, and the polishing slurry is enough during the application tests. The lifetime of both diamond coated and uncoated CMP pad conditioners and the wear resistance are compared eventually. Results and Discussions Fig.3 Sketch of application tests Characterization of Diamond Films Deposited on the Conditioners. FESEM is used to observe the surface morphologies and cross-section morphologies of diamond films exactly. Different parts of as-fabricated CMP pad conditioners are demonstrated as Fig.4. It can be found that a continuous and uniform layer of micro diamond film was deposited on different locations of conditioners. In the figures of surface morphologies, most MCD crystallites with grain size of 2-4um have sharp octahedral shape and exhibit <111> crystallographic orientations.from the cross-section morphologies of diamond films, it can be observed that the thickness of fabricated diamond film during 6 hours is about 10.3μm.

4 Fig.4 Surface morphologies and cross-section morphologies of diamond films at different locations of as-fabricated CMP pad conditioners The indentation experiments of diamond coated CMP pad conditioners are carried out to analyze the adhesion of the diamond coating deposited on the conditioners. The indentation morphologies during different periods are observed using FESEM, as is demonstrates in Fig.5. Three distinct failure modes, namely, plastic deformation, radial cracks and a detached annular area of coating around the indentation, are visible. The largest diameter of indentation dimensions is about 184.3μm.

5 Fig.5 Indentation experiments of diamond coated CMP pad conditioners by Rockwell hardness tester Raman spectra is frequently used to characterize the CVD diamond films, giving the ability of being sensitive to the different carbon phases [9]. The quality of diamond film fabricated on the working surface of the CMP pad conditioner is evaluated in Fig.6. The Raman spectra is deconvoluted and analyzed by multi-gaussian peak fitting and detailed Raman data are demonstrated in the range 1000~1800cm -1, which can offer corresponding information of different diamond deposits. The sharp peak corresponded to the sp 3 bonding of diamond is shown at about 1336cm -1. The frequency of this peak shift from the value of natural diamond ( cm 1 ), indicating the residual stress in the diamond films. There is no obvious peak at 1580cm -1, which suggests the high quality of as deposited diamond coatings. Another band at approximately 1477 cm -1, together with 1130 cm -1 is thought to be originated from sp 2 carbon. Besides,the 1550 cm -1 mode is well known as G peak characteristic of non-diamond carbon. Fig.6 Raman spectra of the diamond film deposited on the conditioner Results of Applicaton Tests on both Diamond Coated and Uncoated CMP Pad Conditioners. Based on the application tests, diamond coated CMP pad conditioners have longer lifetime and better stability compared with those of uncoated conditioners. It is turned out that as deposited diamond films can provide sufficient protecting effects on the working surfaces of conditioners to improve obviously the hardness and wear resistance of the conditioners. The results of comparative application tests are beneficial to further expand the

6 applications of diamond films. Summary Continuous, homogeneous, and high-quality diamond films are deposited on the working surfaces of CMP pad conditioners with regularly patterned protrusions and well controlled pyramid shape, the characterizations of which exhibit that the adhesion between the diamond film and Si3N4 substrate is strong. Besides, the diamond film can obviously improve the hardness of the working surfaces of CMP pad conditioners. In the application tests of diamond coated CMP pad conditioners, as-deposited diamond films can provide sufficient protecting effects on the working surfaces of conditioners. As a result, the diamond film presents an apparent increase in the wear resistance and extend life time of conditioners. Diamond films are promising to be the protecting coatings of CMP pad conditioners because of their high hardness, chemical inertness, low adhesion to many materials, low friction coefficient and the strong adhesive strength between them and substrate surfaces. Acknowledgements This research is supported by the National Natural Science Foundation of China (No ) References [1] Z. Zhang, H. Shen, F. Sun, X. He and Y. Wan, Fabrication and application of chemical vapor deposition diamond-coated drawing dies, Dia. Rel. Mat. 10(2001) [2] X. Wang, B. Shen, F. Sun, Z. Zhang, H. Shen and S. Guo, Deposition and application of CVD diamond films on the interior-hole surface of silicon carbide compacting dies, Key Eng. Mat. 499(2012) [3] C. Wolden, S. Mitra and K.K. Gleason, Radiative heat transfer in hot-filament chemical vapor deposition diamond reactors, J. Appl. Phys. 72(1992) [4] F. Sun, Z. Zhang, M. Chen and H. Shen, Improvement of adhesive strength and surface roughness of diamond films on Co-cemented tungsten carbide tools, Dia. Rel. Mat. 12(2003) [5] B. Shen, F. Sun, H. Xue, M. Chen and Z. Zhang, Study on fabrication and cutting performance of high quality diamond coated PCB milling tools with complicated geometries, Surf. Eng. 25(2009) [6] M.Y. Tsai, S.T. Chen, Y.S. Liao and J. Sung, Novel diamond conditioner dressing characteristics of CMP polishing pad, Int. J. Mach. Tool. Manuf. 49(2009) [7] A. Tan, Y. Cheng, Wear-corrosion properties of diamond conditioners in CMP slurry, Wear, 262(2007) [8] C. Sung, Y. Pai, CMP pad dresser: A diamond grid solution, Proceedings of Third Advances in Abrasive Technology, the Society of Grinding Engineers (SGE) in Japan, 2000, pp [9] S. Askari, G. Chen, F. Akhtar and F. Lu, Adherent and low friction nano-crystalline diamond film grown on titanium using microwave CVD plasma, Dia. Rel. Mat. 17(2008)