先进硬脆材料的椭圆超声辅助固结磨粒化学机械抛光研究

得益于其优异的光学、电学、磁学性能，以先进陶瓷、光学玻璃以及新型半导体材料为代表的硬脆性材料被广泛应用于先进光电行业。然而，其内部原子主要通过共价键或离子键连接，材料对外呈现出极高的硬度和低的断裂韧性，为磨粒加工带来了极大的困难。无论是传统的金刚石磨削或者基于游离磨粒的化学机械抛光都无法同时兼顾加工效率和表面质量的要求。近年来，随着三维封装技术的不断发展，器件集成度越来越高，对超薄硅晶圆和高导热氮化铝陶瓷的需求也日益剧增。在这一背景下，亟需针对这两种典型硬脆性材料开发一种新型高效环保的平坦化方法用来取代金刚石磨削和化学机械抛光。 本文通过选择适当的结合剂将软质磨粒固结成块来实现固结磨粒干式化学机械抛光。这种方法一方面能获得较高的材料去除速率，同时还可以有效避免碱性磨浆的环境污染。与传统的金刚石磨削相比，使用可以与工件发生化学反应的软磨粒还可以大大减少亚表面损伤。椭圆超声振动也被引入干式加工过程用以解决排屑困难的问题，有助于进一步提高了材料去除效率和加工质量。 针对这种新型的椭圆超声辅助固结磨粒化学机械抛光方法，本文以压电陶瓷材料的逆压电效应为原理，设计制作了一款椭圆超声振子，并在此基础上搭建了四轴专用椭圆超声抛光平台。此外，本文还指明了软质磨粒和工件材料在摩擦学能量作用下发生的黏着磨损和摩擦化学反应磨损为主要的材料去除机理，椭圆超声振动的存在可以使磨粒运动轨迹呈规律的空间螺旋线，进一步有助于材料的去除。 本文以单晶硅和氮化铝陶瓷为加工对象，从有利于促进摩擦化学反应发生的角度为两种材料选定了固结磨粒磨头配方，进而开展椭圆超声振动辅助固结磨粒抛光实验。加工实验结果表明：与金刚石磨粒砂轮相比，软质磨粒磨头可以大幅度改善工件的表面质量，但材料去除速率较低，固结磨粒磨头的损耗也比较严重。而椭圆超声的存在明显提高了工件的表面粗糙度和材料去除率，改善了排屑效率，减轻了固结磨粒磨头的损耗。

Benefit from its excellent optical, electrical and magnetic properties, hard and brittle materials represented by advanced ceramics, optical glass and new semiconductor materials are widely used in the optoelectronic industry. However, the internal atoms are mainly connected by covalent bonds or ionic bonds, and the material exhibits extremely high hardness and low fracture toughness, which brings great difficulty to the processing of abrasive grains. Whether traditional diamond grinding or chemical mechanical polishing based on free abrasive particles is impossible to balance the processing efficiency and surface quality. In recent years, with the continuous development of 3D packaging technology, the integration of devices has become higher and higher, and the demand for ultra-thin silicon wafers and high thermal conductivity aluminum nitride ceramics substrate has also increased rapidly. In this context, a new, more efficient and environmentally-friendly planarization method for these two typical hard and brittle materials is strongly required to replace diamond grinding and chemical mechanical polishing. In this work, a bonded abrasive pellet containing soft grains was employed to realize the fixed-abrasive dry CMP. With this method, higher material removal rate can be obtained and the environmental pollution of alkaline slurry can be effectively avoided. The use of soft abrasives also greatly reduced the subsurface damage under the assistance of chemical reaction compared to the traditional fixed abrasive method like diamond grinding. However, the chip discharge problem still exist which limits the further improvement of processing efficiency. Consequently, an elliptic ultrasonic vibration was applied to the abrasive pellet during dry CMP. In order to perform the proposed novel method, we designed and fabricated an elliptical ultrasonic vibrator based on the inverse piezoelectric effect of piezoelectric ceramic, and built a four-axis dedicated polishing platform. In addition, we also pointed out that the adhesion and tribochemical reaction between soft abrasive particles and workpiece materials under tribological energy was the main material removal mechanism. The existence of elliptical ultrasonic vibration can make the abrasive trajectory of the abrasive grain a regular spatial spiral, which further contributed to the material removal. In this paper, single crystal silicon and aluminum nitride ceramics were selected as processing targets, and the detailed fixed abrasive pellet formulation was determined for these two materials from the perspective of facilitating the occurrence of tribochemical reaction. The processing results showed that compared with the diamond abrasive grinding, the soft abrasive pellet can greatly improve the surface quality of the workpiece, but the material removal rate was lower and the wear of the grinding pellet was also more serious. The presence of elliptical ultrasonic vibration significantly improved the surface roughness and material removal rate. It also improved the chip removal efficiency and reduced the wear of the grinding pellet.