Shang Gao

Design and evaluation of soft abrasive grinding wheels for silicon wafers

The objective of this study is to design and evaluate soft abrasive wheels for silicon wafer grinding. In this study, CeO2, SiO2, Fe2O3 and MgO soft abrasives are used in the design of soft abrasive grinding wheels. The soft abrasive grinding wheels are then used to grind silicon wafers and compared with diamond wheel grinding and chemomechanical polishing. This study demonstrates that the newly designed soft abrasive grinding wheels are generally superior to diamond wheel grinding or chemomechanical polishing in terms of wafer surface/subsurface quality, wheel dressability, grinding ratio and material removal rate. This study further identifies the MgO soft abrasive grinding wheel as the best of the four soft abrasive grinding wheels. Discussion is provided to explore material removal mechanisms, wheel dressing characteristics and wafer surface finish and quality of the newly designed soft abrasive grinding wheels.

Study on the Subsurface Damage Distribution of the Silicon Wafer Ground by Diamond Wheel

Using the cross-section angle polishing microscopy, the subsurface damage of the silicon wafers (100) ground by the diamond wheels with different grain size were investigated, and subsurface damage distributions in different crystal orientations and radial locations of the silicon wafers (100) were analyzed. The experiment results showed that the grain size of diamond wheel has great influence on the subsurface damage depth of the ground wafer. On the ground wafer without spark-out process, the subsurface damage depth increased along the radical direction from the centre to the edge and the subsurface damage depth in <110> crystal orientation was larger than that in <100> crystal orientation; but on the ground wafer with spark-out process, the subsurface damage depth in different crystal orientations and radial locations become uniform.

Surface Integrity and Removal Mechanism in Grinding Sapphire Wafers with Novel Vitrified Bond Diamond Plates

ABSTRACT In order to improve machining efficiency of sapphire wafer machining using the conventional loose abrasive process, fixed-abrasive diamond plates are investigated in this study for sapphire wafer grinding. Four vitrified bond diamond plates of different grain sizes (40 µm, 20 µm, 7 µm, and 2.5 µm) are developed and evaluated for grinding performance including surface roughness, surface topography, surface and subsurface damage, and material removal rate (MRR) of sapphire wafers. The material removal mechanisms, wafer surface finish, and quality of the diamond plates are also compared and discussed. The experiment results demonstrate that the surface material is removed in brittle mode when sapphire wafers are ground by the diamond plates with a grain size of 40 µm and 20 µm, and in ductile mode when that are ground by the diamond plates of grain sizes of 7 µm and 2.5 µm. The highest MRR value of 145.7 µm/min is acquired with the diamond plate with an abrasive size of 40 µm and the lowest surface roughness values of 3.5 nm in Ra is achieved with the 2.5 µm size.

Study on Grinding Performance of Soft Abrasive Wheel for Silicon Wafer

With the development of IC manufacturing technology, the machining precision and surface quality of silicon wafer are proposed much higher, but now the planarization techniques of silicon wafer using free abrasive and bonded abrasive have the disadvantage of poor profile accuracy, environmental pollution, deep damage layer, etc. A soft abrasive wheel combining chemical and medical effect was developed in this paper, it could get super smooth, low damage wafer surface by utilizing mechanical friction of abrasives and chemical reaction among abrasives, additives, silicon. A comparison experiment between #3000 soft abrasive wheel and #3000 diamond abrasive wheel was given to study on the grinding performance of soft abrasive wheel. The results showed that: wafer surface roughness ground by soft abrasive wheel was sub-nanometer and its sub-surface damage was only 0.01µm amorphous layer, which were much better than silicon wafer ground by diamond abrasive wheel, but material removal rate and grinding ratio of soft abrasive wheel were lower than diamond wheel. The wafer surface ground by soft abrasive wheel included Ce4+, Ce3+, Si4+, Ca2+ and Si, which indicated that the chemical reaction really occurred during grinding process.

Surface Layer Damage of Silicon Wafers Sliced by Wire Saw Process

Wire saw process is widely used in the machining of hard and brittle materials with low surface damage and high efficiency. Cutting of silicon wafers in integrated circuit (IC), semiconductor and photovoltaic solar industries is also generally using wire saw process. However, the surface layer damage induced by wire saw process will seriously decrease the wafer quality and increase the process time and production costs of the post grinding and polishing. The surface layer qualities of the silicon wafers sawed by the different wire saw processes was investigated in this paper. The characteristics of surface roughness, surface topography and subsurface damage of silicon wafers sliced by the fixed abrasive and the loose abrasive wire sawing respectively were compared and the corresponding reasons were analyzed.

Change of Hydrophobicity on Silicone Rubber Modified by CF4 Capacitively Coupled Plasma and Inductively Coupled Plasma

Silicone rubber (SIR) samples are exposed to CF4 capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) at radio frequency (RF) power of 60–200 W for a treatment time up to 20 min, respectively. Static contact angle is employed to estimate the change of hydrophobicity of the silicone rubber modified by the two coupled types of CF4 RF plasma. A milder enlargement of static contact angle of SIR samples modified by ICP treatment is observed compared with that by CCP treatment. The hydrophobicity of the modified SIR surface by CCP treatment increases to a maximum, and further decreases toward the hydropholicity. The higher self-bias on the SIR samples being modified by CCP treatment than that by ICP treatment leads to the more dramatic physical and/or chemical reaction on the SIR surface, resulting in the competition between fluorination and ablation or etching.

Research on the Polishing Performance of CMP Slurry for the Sapphire Crystal

Aiming at the problems such as metal ionic contamination, poor dispersion property and low material removal rate (MRR) in the chemical mechanical polishing (CMP) process for sapphire crystal, a proper CMP slurry based on the organic basis was studied in this paper. Through the single-factor experiment, the effect of different abrasives, pH regulators, dispersants and active agents on the surface roughness and material removal rate (MRR) were studied and a fine CMP slurry was developed. The polishing performance of developed CMP slurry was also researched by comparing the MRR and the surface roughness of sapphire crystal with that polished using the KA-901 CMP slurry. The results show that the MRR and the surface roughness corresponding to the developed slurry were all better than KA-901 slurry, and the developed CMP slurry has a good application prospect.

Development of a Measuring Equipment for Silicon Wafer Warp

Larger diameter wafers are used to decrease the cost of IC manufacturing and the wafer thickness is decreasing for form factor and thermal power dissipation considerations. The larger wafer requires a large scanning area to inspect the warp, and warp measurement of large and thin silicon wafers is greatly affected by the gravity-induced deflection. In this paper the gravity-induced deflection was calculated using finite element method by supporting the wafer horizontally with three steel balls. A laser displacement sensor based on triangulation principle was used to measure the warp and an air bearing stage was developed to achieve high straightness. The shape of the wafer was obtained using the silicon wafer warp measuring equipment.

Grinding Performance Evaluation of the Developed Chemo-Mechanical Grinding (CMG) Tools for Sapphire Substrate

In order to improve the surface quality of sapphire substrates ground by diamond wheel, the chemo-mechanical grinding (CMG) tools for sapphire grinding was investigated in this paper. According to the processing principle of CMG, three CMG tools with different abrasives of SiO2, Fe2O3 and MgO were developed respectively. The compositions of the CMG tools were designed and optimized based on the physicochemical characteristics of sapphire. The grinding experiments were performed with the developed CMG tools and the grinding performance of three kind of tools were evaluated by comparing the surface roughness and the MRR of sapphire. The experiment results show that the grinding performance of SiO2 CMG tool was worst. The surface roughness and MRR corresponding to SiO2 CMG tool were all significantly poorer than Fe2O3 and MgO CMG tools. The highest MRR could be obtained by Fe2O3 CMG tool, but the best surface quality was obtained by MgO CMG tool.

Surface and Subsurface Damages of CdZnTe Substrates Ground by Diamond Grinding Wheel

Surface and subsurface damage affect the preparation of high-resolution HgCdTe and CdZnTe detectors. Grinding experiments were performed on CdZnTe substrates with the grinding wheels of different abrasive sizes. The surface topography and subsurface damages of CdZnTe substrates ground by diamond grinding wheels with different grit sizes were studied. The effects of the grit sizes of grinding wheels on the surface topography and subsurface damage of CdZnTe substrates were discussed. The surface roughness and subsurface damage layer depth of CdZnTe after grinding with #3000 diamond grinding wheel are only Ra 7 nm and 100 nm, proved that grinding is of great potential for CdZnTe substrate processing.