TEM Sample Preparation for Semiconductor Defect Analysis
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Solution Overview
Problem
Existing methods for preparing TEM samples fail to distinguish lightly doped drain and source/drain regions from the silicon substrate, making it difficult to observe patterns and defects due to equal thickness, which is problematic for analyzing semiconductor devices, especially in deep submicron systems.
Innovation Solution
A TEM sample preparation method involving the use of a mixed acid solution for etching, comprising nitric acid, hydrofluoric acid, and copper sulfate, to differentially thin the lightly doped regions relative to the silicon substrate, allowing clearer distinction and observation of defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FIB milling is used to prepare TEM samples, then the sample can be thinned to observe cross sections, but the lightly doped drain and source/drain regions remain at the same thickness as the silicon substrate, making them difficult to distinguish
Solution Approach 1:
The patent applies chemical etching selectively to the lightly doped drain and source/drain regions, creating local thickness differences between these regions and the silicon substrate. This local quality change enables clear differentiation and observation of the doped regions in TEM, resolving the contradiction between sample thinning and region distinguishability.
2Productivity
If SIMS method is used for defect detection, then detection can be performed, but the detection speed is low and it cannot accurately represent defects in final products
Solution Approach 1:
The patent replaces the SIMS method with TEM observation of chemically etched samples. This substitution enables direct visual observation of defects in the actual device structure at high resolution, achieving both high productivity through rapid sample preparation and high measurement precision through direct imaging of the etched features that reflect actual device defects.
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
The method enables clear differentiation and observation of lightly doped drain and source/drain regions from the silicon substrate, facilitating defect analysis and improving the resolution of TEM samples.
Implementation Method 1
etching the first surface of the failure region with a mixed acid solution comprising nitrate acid, hydrofluoric acid, acetic acid, and copper sulfate
Implementation Method 2
milling the first surface of the failure region until the cross section of the semiconductor device is exposed
Implementation Method 3
the failure region is irradiated with an electron beam accelerated by a high voltage. The pattern of the failure region is magnified and projected onto a screen for analysis
Data Source
AI summary
A method for preparing TEM sample, comprising the following steps: providing a sample with two pits and a failure region between the two pits, the failure region comprising a semiconductor device; milling the first surface of the failure region, till the cross section of the semiconductor device is exposed; etching the first surface of the failure region; cleaning the sample; milling the second surface of the failure region, till the failure region can be passed by electron beam. A sample can be prepared for a high resolution TEM through above steps. When the sample is observed, it is easy to distinguish the lightly doped drain, source/drain regions from the silicon substrate and observe the pattern and defects in the lightly doped drain, source/drain regions clearly; in addition, it is easy to distinguish the BPSG from the non-doped silicon dioxide in the failure region.