【作者】 孙禹辉；

【导师】 郭东明；

【作者基本信息】 大连理工大学 ， 机械制造及自动化， 2011， 博士

【摘要】 化学机械抛光(Chemical mechanical polishing, CMP)加工技术既能获得良好的加工表面全局,也能得到较好的局部平面度,因此在大规模集成电路和超大规模集成电路(ULSI)的制造过程中得到了广泛的应用。CMP技术既能在硅片制备过程中用于硅片上下表面的双片同时平坦化,也广泛应用在多层布线金属互连结构工艺的层间平坦化加工中。CMP过程中硅片表面材料去除非均匀性(non-uniformity of the material removal, NUMR)直接影响硅片最终的平坦化精度。但是,由于NUMR受抛光头和抛光盘转速、抛光压力、抛光垫特性、抛光液流量和粘度、抛光区域温度等诸多因素以及这些因素交互作用的影响,这给CMP过程的NUMR形成机理及控制方法等方面的研究带来很多困难,目前生产中在一定程度上还是通过经验或半经验的手段控制CMP过程的NUMR。集成电路(IC)制造技术的发展对CMP技术水平提出了很高要求,研究CMP材料去除非均匀性及其控制控制方法对于提高CMP技术水平具有重要理论意义和应用价值。本文在全面分析硅片CMP加工中NUMR问题研究现状的基础上,系统研究了影响硅片NUMR的因素及减小NUMR的方法进行了,主要研究工作如下：根据硅片CMP的特点,通过仿真计算分析了在硅片与抛光垫直接接触和混合接触两种形态下,压力分布、抛光盘及抛光头转速、抛光头摆动变量、偏心距等参数对硅片NUMR的影响规律,为揭示硅片CMP中NUMR的形成机理,研究减小NUMR的工艺方法以及设计开发CMP机床提供了理论依据。基于对NUMR的影响因素的分析,首先研究了采用保持环加压降低NUMR的方法。利用接触力学和边界润滑理论分别建立了硅片与抛光垫直接接触和混合接触两种形态下的接触应力和抛光液压力模型,分析了保持环的压力、宽度以及硅片和保持环之间间隙等参数对接触应力分布的影响。结果表明使用保持环可以有效降低硅片边缘过高的接触应力,减小硅片接触应力分布的非均匀性,在一定程度上改善硅片的NUMR。但由于采用保持环减小硅片中心区域接触应力分布的非均匀性作用有限,而且增加生产成本,保持环在降低NUMR上的应用有局限性。为克服保持环在降低NUMR方面的局限性,进而提出了通过分区域调整硅片背压降低硅片CMP过程中材料去除非均匀性的方法。根据Preston方程和弹性板理论建立了硅片与抛光垫在直接接触形态下的硅片背压补偿模型,根据流体润滑方程和接触力学理论建立了硅片与抛光垫在混合接触形态下的硅片背压补偿模型,分别得到了两种接触形态下的硅片多区域背压曲线,以此为依据研制了具有多区域压力调整功能的硅片夹持器,应用于改造的CMP试验台进行了硅片CMP试验验证。试验结果表明多区域背压调整夹持器可有效地降低硅片CMP中由于抛光压力分布不均匀所造成的NUMR。考虑实际生产中硅片抛光前的表面轮廓和厚度变化,为提高多区域背压调整夹持器对硅片的适应性,应用试验设计法(Design Of Experiment, DOE)，分别对多区域背压调整夹持器的各区域进行加压,进行抛光试验并测量抛光前后硅片厚度沿径向的变化,通过最小二乘法求出反映区域压力与硅片径向各点材料去除率关系的稳态增益矩阵,建立了改进的硅片背压补偿模型。针对硅片表面多层介质的层间CMP加工,为了在减小NUMR同时防止出现过抛光或抛光不足现象,开发了抛光垫温度在线测量系统,通过将抛光垫温度监测与硅片多区域背压调整相结合更好地监控CMP过程。更多还原

【Abstract】 Chemical mechanical polishing (CMP) is a main planarization technology of wafer in ultra large scale integrated circuit (ULSI) manufacturing, it is not only used to obtain the ultra-smooth surface in manufacturing silicon wafer, but also to achieve local and global planarization of wafer with the multi-layer interconnect structure. The non-uniformity of the material removal (NUMR) on wafer surface in CMP has direct influence on the flatness of silicon wafer. However, because the NUMR is affected by many factors, such as the rotational speed of carrier and polishing pad, the polishing pressure, the characteristics of polishing pad, the polishing temperature, etc., and their interactions, the formation mechanism of the NUMR and influence the process variable on the NUMR have not yet been understood completely, the NUMR of wafer in CMP process has been mainly controlled by the semi-empirical or empirical means in some extent. It is important and necessary to study the NUMR and its control methods in CMP for the improvement of CMP technology to meet the needs of fast development of integrated circuit (IC) technology.Based on the analysis of the research status on the NUMR, the influencing factors on the NUMR and the methods to reduce the NUMR are systematically studied in this thesis. The main research contents and conclusions are as follows:According to the characteristic of wafer CMP, the effects of the distribution of pressure, the rotational speed of the carrier and the platen, the oscillation variables of the carrier, and center distance between the carrier and the platen on the NUMR were analyzed by simulation in the cases of the solid contact and the boundary lubrication contact between wafer and polishing pad, which provided the theoretical basis for research on the formation mechanism of the NUMR, development of the techniques to reduce the NUMR and design of CMP equipment.Base on the analysis of the influencing factors on the NUMR, a method of reducing the NUMR by using the retaining ring was researched. Through application of the contact mechanics and the two-dimensional boundary lubrication theory, a contact stress model and a hydrodynamic pressure model in the cases of solid contact and the boundary lubrication contact between wafer and polishing pad were established respectively. The effects of the width and pressure of the retaining ring, the gap between the wafer and the retaining ring on the contact stress distribution were discussed. The results indicated that the using of retaining ring can effectively reduce the excessive contact stress near the wafer edge and the non-uniformity of the contact stress distribution, so as to decrease the NUMR in CMP at a certain extent. However, the limitation of application of the retaining ring to control the NUMR in CMP is obvious because the using of retaining ring is incapable of reducing the contact stress in the wafer central area, and capable of increasing the production cost.To overcome the limitation of the retaining ring in reducing NUMR, a new method for controlling the NUMR in CMP by adjusting the back-pressure of wafer in multi-zone was presented. The calculating model of wafer back pressure in the case of solid contact between wafer and polishing pad were established based on the Preston equation for material removal rate and the elastic plate theory, the calculating model of wafer back pressure in the case of boundary lubrication contact between wafer and polishing pad were established according to the fluid lubrication equation and contact mechanics theory, and the back pressure profiles in multi-zone were calculated respectively for both cases, based on which a wafer carrier with pressure adjustment function in multi-zone was developed. The wafer CMP experiments were performed on a developed CMP platform by using the multi-zone pressure adjustment carrier of wafer. The verification experimental results indicated that the NUMR of wafer in CMP caused by the non-uniformity of the polishing pressure distribution can be effectively reduced through adjusting the back pressure of wafer in multi-zone by using the developed carrier of wafer.According to the actual profile and thickness variation of silicon wafer before CMP, the calculating model of wafer back pressure was modified to enhance the applicability of the multi-zone pressure adjustment carrier by using Design of Experiment (DOE), in which CMP experiments were carried out when the multi-zone pressure adjustment carrier was pressurized independently in different zone, the wafer thickness variation along the radial direction were measured before and after CMP, and the steady-state gain matrix of the relationships between the material removal rate distribution along radial direction and the pressure of different zone were obtained by using the least square regression method.In order to reduce the NUMR and avoid the over-polishing or under-polishing in CMP of the interlayer dielectric and metal on wafer, a in-situ temperature measurement system of polishing pad was developed, by which CMP process could be better monitored and controlled through combining with the multi-zone back pressure adjustment method.更多还原