In this study, surface formation mechanism in micro-grinding of single crystal silicon is investigated based on analysis of undeformed chip thickness hm. A predicting model of grinding force considering crystallographic effects in micro-grinding of single crystal silicon is built. In this model, micro-grinding process of single crystal silicon is divided into two steps by one line on which hm of single grit equals to lattice constant. Two micro-grinding experiments with different ranges of cutting depths and feed rates have been designed and conducted on single crystal silicon to verify the model this paper proposes. The relationship between micro-grinding parameters and crack length lc is investigated and the empirical formula of lc is derived based on analysis of experiment results. Ductile-regime transitions in micro-grinding process of single crystal silicon have been revealed, 20 nm and 100 nm are turned out to be two critical conditions based on analysis of experiment results. It is found that the grinding force has a sudden change when micro-grinding process comes within material's crystal boundary in experiment. The force predicting model this paper proposes has well explained this phenomenon in micro-grinding of single cyrstal silicon. When micro-grinding undeformed chip thickness hm belows 0.5 nm, micro grinding force doesn't decrease with the decrease of cutting parameters but has a rising tendency, and these experimental measurements also provide a support to the result of model this paper proposes.

Experimental study of surface generation and force modeling in micro-grinding of single crystal silicon considering crystallographic effects

Precision is one of the most important aspects of manufacturing. High precision creates high quality, high performance, exchangeability, reliability, and added value for industrial products. Over the past decades, remarkable advances have been achieved in the area of high-precision manufacturing technologies, where the form accuracy is approaching the nanometer level and surface roughness the atomic level. These extremely high precision manufacturing technologies enable the development of high-performance optical elements, semiconductor substrates, biomedical parts, and so on, thereby enhancing the ability of human beings to explore the macro- and microscopic mysteries and potentialities of the natural world. In this paper, state-of-the-art high-precision material removal manufacturing technologies, especially ultraprecision cutting, grinding, deterministic form correction polishing, and supersmooth polishing, are reviewed and compared with insights into their principles, methodologies, and applications. The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.

https://iopscience.iop.org/article/10.1088/2631-7990/ab1ff1/pdf

Manufacturing technologies toward extreme precision

The increased concern for environment and sustainability are pushing machining operations towards the reduction or even complete elimination of cutting fluids. Grinding is not excluded from this objective, but greater difficulties appear due to the nature of the material removal mechanisms. In this work, two approaches aiming at the optimization of fluid application in grinding are presented. First, the influence of nozzle design on the development of velocity and pressure fields is studied using CFD tools. A new nozzle design that optimizes the characteristics of the jet is introduced, analyzed and manufactured. Grinding experiments show that improvements in wheel life and surface finish are possible using the new nozzle. Second, the performance of a new grinding technology that combines MQL with low-temperature CO 2 is evaluated trough industrial grinding tests. Results show an increased performance in terms of friction conditions and surface finish.

Strategies for optimal use of fluids in grinding

Chemo-mechanical magneto-rheological finishing (CMMRF) of silicon for microelectronics applications

This study investigates warping of silicon wafers in ultra-precision grinding-based back-thinning process. By analyzing the interactions between the wafer and the vacuum chuck, together with the machining stress distributions in damage layer of ground wafer, the study establishes a mathematical model to describe wafer warping during the thinning process using the elasticity theory. The model correlates wafer warping with machining stresses, wafer final thickness, damage layer thickness, and the mechanical properties of the monocrystalline silicon. The maximum warp and the warp profile are measured on the wafers thinned to various thicknesses under different grinding conditions, and are used to verify the modeling results.

Warping of silicon wafers subjected to back-grinding process

Elimination of surface scratch/texture on the surface of single crystal Si substrate in chemo-mechanical grinding (CMG) process

Grinding process on the Si wafer develops subsurface damage, which remarkably degrades deflective strength of the wafer and constitutes a barrier against producing a thin wafer for low-profile packaging. In this paper, the authors propose a new index for evaluation of the Degree of Subsurface Damage (DSD). Requiring no costly instrument, the new index is easily calculated via the external geometry of the ground wafer. With the new index, it is able to quantitatively evaluate the subsurface damage introduced by different processes (or wheel) and to estimate the minimally achievable thickness of the wafer by each process. Also, a novel fixed abrasive process of Chemo-Mechanical Grinding (CMG) has been proposed for stress relief. All results indicate that the subsurface damage after CMG is nearly zero.

Fabrication and evaluation for extremely thin Si wafer

Disclosed is a synthetic grinding stone used for polishing of silicon wafer, which is composed of a structure comprising cerium oxide fine particles as abrasive grain, a resin as a binder, a salt as a filler and a nano diamond as an additive. This synthetic grinding stone is characterized in that the purity of the cerium oxide is not less than 60% by weight, the content of the salt as a filler is not less than 1% but not more than 20%, the volume content of the nano diamond as an additive is not less than 0.1% but less than 20% relative to the total volume of the structure, and the porosity as the volume fraction relative to the total volume of the structure is less than 30%.

Synthetic grinding stone

This paper reports our recent results on the diamond grinding process of single crystallized sapphire wafers. It was found that the diamond grains were severely dislodged at the wheel/ workpiece interface and the material was removed by a mixed process of both grinding and lapping. Grinding governed the wafer center while lapping dominated its fringe. By increasing the wheel speed, it was able to shift the dominant process from lapping to grinding, and achieve a better surface roughness. Nine diamond wheels varying in both concentration and bond material were tested in surface grinding of 6 inch sapphire wafer, to investigate the dynamic behavior of diamond grain in the grinding process and its resultant surface quality and productivity.

Study on Grinding Processing of Sapphire Wafer

Chemo-mechanical grinding (CMG) process is a promising process for large-sized Si substrate fabrication at low cost. An encountered issue in current CMG process of Silicon (Si) wafers is metallic contaminations on ground Si wafer surface, which is attributed to the existence of sodium carbonate in wheel compounds. In this paper, four different CMG wheels were developed and grinding experiments were conducted to study the effects of exclusion of sodium carbonate and concentration of ceria abrasive on grinding performance. The grinding characteristics of the four wheels were analysized and discussed to reveal the effects of different compositions.

Yoshiaki Tashiro

Papers

Elimination of surface scratch/texture on the surface of single crystal Si substrate in chemo-mechanical grinding (CMG) process

Fabrication and evaluation for extremely thin Si wafer

Synthetic grinding stone

Study on Grinding Processing of Sapphire Wafer

Effects of Sodium Carbonate and Ceria Concentration on Chemo-Mechanical Grinding of Single Crystal Si Wafer