Preparation and properties of intermetallic-bonded diamond grinding wheel for thinning SiC wafer
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摘要: 与Si基材料相比，SiC因其导热性好、击穿电场强度高和禁带宽度大等特性成为芯片制造的理想基底材料。但SiC晶片莫氏硬度高达9.5，磨削困难。实现SiC晶片的减薄加工，降低加工成本，提高SiC晶片的加工质量，成为半导体行业亟待解决的问题。采用Cu3Sn和Cu6Sn5金属间化合物为黏结剂，制备面向SiC晶片粗磨和精磨减薄的金刚石砂轮。结果表明：金刚石砂轮能够适用于SiC晶片的减薄加工，制备的M5/10金刚石粗磨砂轮减薄6英寸（15.24 cm）SiC晶片的磨耗比达1.0∶5.0，SiC晶片表面粗糙度为0.011 µm；制备的M1/2金刚石精磨砂轮减薄同种SiC晶片，其磨耗比为1.0∶0.6，SiC晶片表面粗糙度达2.076 nm，总厚度变化 RTTV＜ 3.00 µm。金刚石砂轮的减薄效果良好，可满足工业生产需要。Abstract: Objectives: Compared with Si-based materials, SiC has become an ideal substrate material for chip manufacturing due to its good thermal conductivity, high breakdown electric field strength, and large bandgap width. However, the Mohs hardness of SiC wafer is as high as 9.5, which makes it difficult to grind. The thinning process of SiC single crystal wafers, reducing processing costs, and improving the processing quality of SiC chips have become urgent problems to be solved in the semiconductor industry. This study uses Cu3Sn and Cu6Sn5 intermetallic compounds as bonders to prepare rough and fine grinding diamond wheels for thinning SiC wafers. Methods: On the basis of the research and development of intermetallic compound bonding agent superhard material grinding wheels proposed earlier, the M5/10 diamond grinding blocks and the M1/2 diamond grinding wheel teeth were prepared using raw materials such as diamond, Cu3Sn, Cu6Sn5, graphite, and pore-forming agent through a 450 ℃ hot pressing process. After grinding the upper and lower end faces of the diamond grinding wheel teeth flat, 34 pieces were selected and uniformly bonded to the aluminum substrate tooth groove with universal strong adhesive, and the diamond coarse grinding and fine grinding wheels for silicon carbide wafer thinning were obtained. At the same time, the processing load and wear ratio of the silicon carbide grinding wheel, and the roughness and RTTV (total thickness deviation) of the silicon carbide wafer were systematically characterized. Results: (1)The bending strength and the impact toughness of Cu3Sn material subjected to 450 ℃ hot pressing are 206.6 MPa and 0.45 J/cm2, respectively. The bending strength and the impact toughness of Cu6Sn5 material are 142.0 MPa and 0.31 J/cm2, respectively. (2)With the increase of pore-forming agent amount, the porosity of the grinding wheel teeth significantly increases, while its bending strength rapidly decreases. When the mass fraction of the added pore-forming agent is 20%, the porosity and the bending strength of the grinding wheel teeth are 35.0% and 42.5 MPa, respectively. (3)During the grinding process, the higher the bending strength of the grinding wheel teeth, the greater the holding force of the binder on the diamond, and the grinding wheel is prone to load alarms. However, too low bending strength of grinding wheel teeth will lead to excessive wear of the grinding wheel, easy edge breakage, and even broken teeth. (4) The wear ratio of M5/10 diamond rough grinding and thinning wheel with a mass fraction of 20% pore-forming agent for grinding 6-inch SiC chips reaches 1.0∶5.0, the surface smoothness of SiC chips reaches 0.011 µm, and the fragmentation rate is less than 0.2%. (5) When the mass fraction of the pore-forming agent added is 30%, the porosity and the bending strength of M1/2 fine grinding wheel teeth are 43.0% and 16.2 MPa , respectively. In addition, there are a large number of pores on the surface of the thinning grinding wheel, forming a honeycomb shape, ensuring that the grinding wheel has good chip holding and chip removal effects during the grinding process. At the same time, the wear ratio of the diamond wheel for grinding 6-inch SiC wafer is 1.0∶0.6, the surface smoothness of SiC wafer is 2.076 nm, and the RTTV is 2.55 µm. The process of grinding is smooth with a stable load. Conclusions: Cu3Sn material has high strength and can be used to prepare coarse grinding wheels for thinning SiC wafers. Cu6Sn5 material has good brittleness and can be used to prepare fine grinding wheels for thinning SiC wafers. During the grinding process, the pores in the grinding wheel can play a role in accommodating and removing chips, and can also accommodate failed and detached diamonds, thereby ensuring good surface quality of SiC wafers. The coarse and fine grinding diamond wheels prepared in this paper have obtained good grinding results. However, the diamond used in the grinding wheel for thinning SiC wafers is developing to M0/0.5 at present, which is hoped to achieve the better surface roughness and the lowest surface damage layer of SiC wafers, in order to reduce the processing amount of the CMP process. The follow-up work will further improve the brittleness of Cu6Sn5 material through ceramicization to enhance the sharpness of the grinding wheel, and carry out research on M0/0.5 diamond precision grinding and thinning grinding wheels.
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Key words:
- intermetallic compound /
- diamond grinding wheel /
- SiC wafer /
- grinding quality
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图 1 Cu-Sn相图、晶体结构示意图和晶格参数
Figure 1. Phase diagram, schematic diagram of crystal structure and lattice parameters of Cu-Sn
图 3 金刚石砂轮磨削过程示意图
Figure 3. Schematic diagram of diamond grinding wheel grinding process
图 4 造孔剂添加量对金刚石砂轮粗磨齿气孔率的影响
Figure 4. Effect of adding amount of pore-forming agent on porosity of rough grinding teeth of diamond grinding wheel
图 5 造孔剂添加量对金刚石砂轮粗磨齿抗弯强度的影响
Figure 5. Effect of adding amount of pore-forming agent on bending strength of rough grinding teeth of diamond grinding wheel
图 7 粗磨减薄后的SiC晶片表面形貌及粗糙度曲线
Figure 7. Surface morphology and roughness curve of SiC wafers after rough grinding and thinning
图 8 造孔剂添加量对金刚石砂轮精磨齿气孔率的影响
Figure 8. Effect of adding amount of pore forming agent on porosity of fine grinding teeth of diamond grinding wheel
图 9 造孔剂添加量对金刚石砂轮精磨齿抗弯强度的影响
Figure 9. Effect of adding amount of pore forming agent on bending strength of fine grinding teeth of diamond grinding wheel
表 1 Si和SiC指标参数
Table 1. Si and SiC index parameters
材料 禁带宽度
E1 / eV饱和电子
漂移率
μ / (cm·S−1)击穿场强 E2 /
(MV·cm−1)热导率 K /
[W·(cm.K)−1]莫氏硬度
HMSi 1.12 1 × 107 0.3 1.5 7.0 SiC 3.20 2 × 107 3.5 4.0 9.5 
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表 2 Cu3Sn和Cu6Sn5材料的基础性能
Table 2. Basic properties of Cu3Sn and Cu6Sn5 materials
金属间
化合物烧结温度
θ / ℃密度
ρ / (g·cm−3)抗弯强度
σ / MPa硬度 / HV 冲击韧性
KIC / (J·cm−2)Cu3Sn 450 8.89 206.6 389.0 0.45 Cu6Sn5 450 8.30 142.0 387.2 0.31
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表 3 粗磨金刚石砂轮化学组成（质量分数）
Table 3. Chemical compositions of rough diamond grinding wheels (mass fraction )
砂轮
编号金刚石
ω1 / %Cu3Sn
ω2 / %石墨
ω3 / %造孔剂
ω4 / %其他
ω5 / %A 10～20 70 5～10 10 3～6 B 10～20 65 5～10 15 3～6 C 10～20 60 5～10 20 3～6 D 10～20 55 5～10 25 3～6
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表 4 精磨金刚石砂轮化学组成（质量分数）
Table 4. Chemical compositions of fine diamond grinding wheels (mass fraction )
砂轮
编号金刚石
ω6 / %Cu6Sn5
ω7 / %造孔剂
ω8 / %其他
ω9 / %E 30～40 35 25 3～6 F 30～40 30 30 3～6 G 30～40 25 35 3～6 H 30～40 20 40 3～6
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表 5 金刚石砂轮C粗磨减薄SiC晶片时的批量使用效果
Table 5. Batch use effect of diamond grinding wheel C for rough grinding and thinning of SiC wafers
参数 类型或取值 粗磨砂轮 C 砂轮转速 n1 / (r·min−1) 2 000 进给速率 vw1 / (µm·s−1) 0.5 磨耗比 R1 1.0∶5.0 表面粗糙度 Ra1 / µm 0.011 磨床最大负载值 La1 / % 30～35 破片率 Rr / % ＜0.2
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表 6 精磨金刚石砂轮的使用效果
Table 6. Application effects of fine diamond grinding wheels
砂轮编号 造孔剂质量分数 ω8 / % 使用效果 E 25 负载报警 F 30 正常 G 35 砂轮齿崩边 H 40 断齿
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表 7 金刚石砂轮F精磨SiC晶片的实际效果
Table 7. Actual effect of fine grinding SiC wafer with diamond grinding wheel F
参数 类型或取值 精磨砂轮 F 砂轮转速 n2 / (r·min−1) 2 000 进给速率 vw2 / (µm·s−1) 0.3 磨耗比 R2 1.0∶0.6 表面粗糙度 Ra2 / nm 2.076 磨床最大负载值 La2 / % 35～40 RTTV / µm 2.55
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