TEM Sample Preparation Using FIB Marking for Precise Localization
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Solution Overview
Problem
Existing TEM sample preparation methods face challenges in accurately locating target positions due to different etch rates caused by varying materials, leading to a 'curtain effect' and difficulty in exposing minor failure points, especially when analyzing metal gates with repeated structures.
Innovation Solution
A method involving first-time FIB cutting to remove the top pattern layer, forming a FIB mark pattern on the target pattern layer, and then performing second-time FIB cutting based on this mark to create a TEM sample, ensuring accurate localization without generating a curtain effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If auxiliary localization of target position is performed according to upper layer structure layout, then target position can be located, but different materials above target cause different etch rates leading to curtain effect
Solution Approach 1:
The patent segments the FIB cutting process into two distinct stages: first-time cutting to remove top pattern layer and expose target pattern layer, then second-time cutting to form final TEM sample. This segmentation allows the curtain effect to occur only in the removed top layer rather than affecting the final sample cross-section, thereby resolving the contradiction between localization accuracy and cross-section flatness.
Solution Approach 2:
The patent performs preliminary action by forming a FIB mark pattern on the target pattern layer before the second-time cutting. This mark pattern serves as a precise localization reference that enables accurate target position identification without relying solely on upper layer structure layout, thus achieving both accurate localization and avoiding curtain effect in the final sample.
2Volume of moving object
If FIB cutting is performed directly through multiple layers to prepare TEM sample, then sample thickness can be reduced, but curtain effect affects sample thickness and makes it difficult to expose minor failure points
Solution Approach 1:
The patent divides the thickness reduction process into two stages: first-time cutting removes the top pattern layer to expose the target pattern layer, and second-time cutting reduces the thickness of the final TEM sample. By segmenting the cutting process, the curtain effect is confined to the removed top layer and does not affect the thickness uniformity of the final sample, thereby resolving the contradiction between achieving sufficient thickness reduction and maintaining thickness uniformity.
3Measurement precision
If localization is performed based on upper layer structure layout, then target position can be identified, but repeated metal line structures make accurate localization difficult
Solution Approach 1:
The patent performs preliminary action by creating a unique FIB mark pattern directly on the target pattern layer before final cutting. This mark pattern serves as an unambiguous localization reference that is not affected by the repetition complexity of upper layer metal structures, enabling accurate target position identification even in devices with repeated metal line patterns.
Solution Approach 2:
The patent introduces an intermediary element - the FIB mark pattern - that mediates between the complex repeated upper layer structures and the target position identification. This intermediary provides a unique, easily identifiable reference that simplifies localization despite the complexity of repeated metal gate structures above.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise localization of the TEM sample, eliminating the curtain effect and facilitating effective failure analysis by accurately defining the target position, particularly for complex structures like metal gates.
Implementation Method 1
performing first-time FIB cutting on the chip sample using a FIB, to remove the top pattern layer and to expose a top surface of the target pattern layer
Implementation Method 2
etching the top surface of the target pattern layer using a FIB, to form a FIB mark pattern that defines a target position of the TEM sample
Data Source
AI summary
The present disclosure discloses a method for preparing a TEM sample, including: fixing a chip sample on a sample stage of a FIB system, where the chip sample includes a semiconductor substrate, a target pattern layer, and a top pattern layer. The chip sample has a cuboid structure and includes a first side and a second side opposite each other and composed of a length and a height. A first protective layer is formed on one of the first side and the second side. First-time FIB cutting is performed to remove the top pattern layer. A top surface of the target pattern layer is etched to form a FIB mark pattern. A second protective layer is formed on the top surface of the target pattern layer. Based on localization of the FIB mark pattern, second-time FIB cutting is performed to form the TEM sample.