对通孔消失机理的研究以及相应的解决方案

通孔消失是困扰半导体生产的难点之一.它与产品的生产合格率息息相关,正因为如此这一问题一直摆在业界工程师面前.由于这一问题的成因较多,故在分析和解决问题上存在诸多困扰.本文实验并分析了多种通孔消失的实效模型,结合先进的缺陷测试手段对其给出了不同的解决方案.此外,对相应的光刻胶也进行了研究并将缺陷密度与光刻胶的分辨率相联系,通过研究发现较低的分辨率的光刻胶的缺陷密度也相应较低.

Missing Via Mechanism and Solutions

Missing via has been a defect in semiconductor manufacturing,especially of foundries. Its solution can be rather attractive in yield improvement for relatively mature technology since each percentage point improvement will mean significant profit margin enhancement. However,the root cause for the missing via defect is not easy to determine since many factors,such as,defocus,material re-deposition,and inadequate development,can lead to missing via defects. Therefore,knowing the exact cause for each defect type is the key.In this paper,we will present the analysis methodology used in our company. In the experiments,we have observed three types of missing vias. The first type consists of large areas,usually circular,of missing patterns,which are primarily located near the wafer edge.The second type consists of isolated sites with single partially opened vias or completely unopened vias.The third type consists of relatively small circular areas,within which the entire via pattern is missing.We have first tried the optimization of the developing recipe and found that the first type of missing via can be largely removed through the tuning of the rinse process,which improves the cleaning efficiency of the developing residue. However,this method does not remove missing via of the second and third type. We found that the second type of missing via is related to local defocus caused by topographical distribution. To resolve the third type of missing via defects,we have performed extensive experiments with different types of developer nozzles and different types of photomasks,and the result is that we have not found any distinct dependence of the defect density on either the nozzle or the mask types. Moreover,we have also studied the defect density from three resists with different resolution capability and found a correlation between the defect density and the resist resolution. It seems that,in general,lower resolution resists also have lower defect density.The results will be presented in the paper.