MTJ Cell Redeposition Inspection Using Grayscale Wafer Imaging
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Solution Overview
Problem
The dry etching process used in the manufacture of integrated circuits (ICs) is uncontrollable, leading to redeposition of etched material on sidewalls of magnetic tunnel junctions (MTJs), which results in high leakage and yield degradation.
Innovation Solution
A non-destructive inspection method using grayscale imaging and image processing to quantify etch redeposition on sidewalls of MTJs, allowing for real-time assessment and decision-making on whether to rework the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching is performed to form MTJ cells, then the cells are formed with high aspect ratios and anisotropic profiles, but etched material redeposits on sidewalls causing leakage and yield degradation
Solution Approach 1:
A cap layer is deposited over the MTJ cell before the etch process to prevent redeposition of etched material on sidewalls. This preliminary protective action eliminates the harmful redeposition effect while maintaining the desired anisotropic etch profile and high aspect ratio cell structure
Solution Approach 2:
The cap layer acts as an intermediary barrier between the etched material and the MTJ cell sidewalls. This intermediate layer captures the redeposited material, preventing it from adhering to the cell structure and causing leakage, thereby resolving the contradiction between achieving precise cell profiles and avoiding harmful redeposition
2Measurement precision
If traditional inspection methods are used to assess etch redeposition, then detailed analysis is possible, but the process is destructive and time-consuming
Solution Approach 1:
The mechanical and chemical processes of traditional inspection (wafer slicing, mounting, imaging) are replaced with an optical/electrical impedance-based measurement system. This substitution enables rapid, non-destructive assessment of etch redeposition with sufficient precision to guide process decisions, eliminating time-consuming destructive analysis while maintaining measurement accuracy
Solution Approach 2:
Instead of physically examining the actual MTJ cell structure through destructive cross-sectioning, the invention creates an electrical copy or proxy measurement through impedance analysis. This copying approach provides sufficient information about redeposition levels without requiring time-consuming physical preparation and examination of actual cell structures
3Productivity
If wafers with etch redeposition are processed further, then manufacturing throughput is maintained, but yield degradation occurs due to high leakage
Solution Approach 1:
An inspection step with impedance measurement is introduced into the manufacturing process to provide feedback about etch redeposition levels. This feedback mechanism enables real-time assessment of cell quality, allowing the process to identify and address redeposition issues before they cause yield degradation, thereby maintaining both throughput and reliability through informed process control
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for non-destructive inspection of cell etch redeposition. In some embodiments of the method, a grayscale image of a plurality of cells on a wafer is captured. The grayscale image provides a top down view of the cells and, in some embodiments, is captured in situ after etching to form the cells. The cells are identified in the grayscale image to determine non-region of interest (non-ROI) pixels corresponding to the cells. The non-ROI pixels are subtracted from the grayscale image to determine ROI pixels. The ROI pixels are remaining pixels after the subtracting and correspond to material on sidewalls of, and in recesses between, the cells. An amount of etch redeposition on the sidewalls and in the recesses is then scored based on gray levels of the ROI pixels. Further, the wafer is processed based on the score.