High-density CD measurement technology with high-throughput and high-precision on the entire surface of a process wafer, capable of capturing randomly occurring CD defects

Abstract

In recent years, the number of manufacturing processes is increasing in pursuit of device pattern miniaturization. Complicated processes such as SAQP have been introduced, increasing the number of control parameters. Nevertheless, the demand for production yield enhancement is as high as ever. To detect CD changes, fixed-point measurement by using CD-SEM or scatterometry tools is typically performed, but these time-consuming measurement methods are not suitable for high-density, across-a-wafer measurement or for detecting CD anomalies that randomly occur. To address these issues, we have developed a technology that enables high-precision CD measurement of more than 100,000 points per wafer within a few minutes. It enables monitoring various CD defects in various processes such as holes and L/S patterns after photolithography, L/S patterns after SAQP/SADP, and fine hole diameters after etching. It can also measure CD imbalances after SAQP processes. In addition, it enables precisely obtaining intra-shot CD distribution based on the distribution over the entire surface of a wafer. We evaluated this technology using actual device wafers. CD imbalances of SAQP on DRAM process wafers were measured, within a few minutes across a wafer, at an accuracy of |X|+3σ<0.5 nm. CD changes at the outermost area of the wafer were captured by CD measurement of 27 nm hole patterns on a DRAM process wafer. Random CD defects were captured by CD measurement of 38 nm hole patterns on a DRAM process wafer. These defects affect device yield but were not detectable by using conventional inspection tools.

Technology for high density CD measurement of EUV-processed resist patterns across a wafer ensuring high throughput and precision

“…The CD measurement algorithm followed the method described in the previous study, 1 which estimates the CD by examining the correlation between the CD value and the intensity of optically captured images. The brief flow of the procedure of the CD measurement is shown in Figure 1.…”

“…We have developed a high-resolution, high-precision CD optical metrology technique that leverages the correlation between the CD and signals of optically captured images of the entire wafer at once. [1][2][3] The platform is the AMI5700, an automatic macro defect inspection system. This technique enables the acquisition of CD distribution data in just a few minutes, achieving a remarkable resolution of over 100,000 points across the wafer.…”

“…The correlation between CD values and image signals of diffracted or reflected light was used to perform highly accurate CD measurements of resist patterns in SAQP and SADP processes of DRAM process wafers. 1 However, as the pattern pitch becomes increasingly finer and surpasses the diffraction limit, a challenge can arise in obtaining enough intensity of the diffracted light to be correlated with CD.…”

“…To solve this problem, we have developed a CD measurement technology that enables high density measurement of more than 100,000 points on the wafer surface in a few minutes per wafer. 1 The CD value is calculated from the correlation between the diffracted light signal and CD.Despite the advantages this method provides, there still have been challenges. Measuring the critical dimensions of resist patterns of several tens of nanometers formed in EUV lithography across the entire wafer sometimes poses difficulties due to insufficient sensitivity with diffracted light, making high-precision CD measurement difficult.In this paper, we propose an enhanced measurement technique that quantifies the changes in the polarization state of diffracted light and reflected light from the wafer as Stokes parameters and calculates the CD based on the correlation between the obtained Stokes parameters and the CD value.…”

“…To solve this problem, we have developed a CD measurement technology that enables high density measurement of more than 100,000 points on the wafer surface in a few minutes per wafer. 1 The CD value is calculated from the correlation between the diffracted light signal and CD.…”