Charged Particle Beam Void Detection in Copper Interconnects
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Solution Overview
Problem
The detection of buried voids in Copper interconnects is challenging due to the opacity of Copper film at visible and UV wavelengths and the limitations of traditional electron-beam inspection, which suffers from high nuisance and low capture rates, and potential damage to low-k films.
Innovation Solution
A method involving the irradiation of specific points on the upper surface of an object with a charged particle beam to detect X-ray photons and backscattered electrons, using energy dispersive X-ray (EDX) detectors to generate and process signals indicative of voids within interconnects, thereby estimating the presence of voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If traditional e-beam inspection is used to detect buried voids, then detection capability is improved, but nuisance rate increases and capture rate decreases
Solution Approach 1:
The patent applies local quality by selecting specific inspection points within the interconnect structure rather than inspecting the entire structure uniformly. The method identifies and inspects only those regions where voids are most likely to occur, such as at interfaces between different materials or at specific geometric features, thereby improving detection capability while reducing false alarms from irrelevant areas
Solution Approach 2:
The patent changes the detection parameters by using multiple e-beam energy levels and multiple detection modes (secondary electron detection, backscattered electron detection, and X-ray detection). By varying beam energy and detection parameters locally at different inspection points, the system optimizes the signal-to-noise ratio for void detection while minimizing interference from grainy copper surface features
2Length of stationary object
If high beam energy is used to increase escape depth, then detection depth is improved, but damage to low-k film increases
Solution Approach 1:
The patent applies dynamics by using variable beam energy that adapts to the specific inspection requirements. The system dynamically adjusts beam energy levels based on the depth and location of the interconnect structure being inspected, using higher energy only when necessary to reach deeper features and lower energy for surface-level inspections, thereby minimizing cumulative damage to the low-k dielectric material
Solution Approach 2:
The patent segments the inspection process into multiple passes at different energy levels. Rather than using a single high-energy beam that would cause damage, the system performs multiple inspection passes at progressively higher energies, only penetrating as deep as necessary for each region, thus achieving adequate detection depth while distributing and minimizing damage accumulation
3Ease of operation
If traditional optical inspection is used, then ease of operation is improved, but detection capability deteriorates due to copper opacity
Solution Approach 1:
The patent introduces X-ray detection as an intermediary mechanism that bypasses the opacity problem of copper to visible light. By detecting characteristic X-rays emitted from copper atoms during e-beam irradiation, the system can detect voids and defects in copper interconnects without being blocked by the copper's optical properties, while still maintaining ease of automated operation
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
This approach allows for efficient detection of voids in interconnects by distinguishing between void-containing and void-free interconnects, improving yield and reliability by reducing nuisance rates and enhancing capture rates while minimizing damage to low-k films.
Implementation Method 1
detecting particles resulting from the irradiating of the group of points; wherein the particles may be at least one out of (a) X-ray photons emitted from the group of interaction volumes
Implementation Method 2
backscattered electrons emitted from the group of interaction volumes
Implementation Method 3
an energy dispersive X-ray (EDX) detector that may be configured to detect x-ray photons emitted from a bottom of a hole
Data Source
AI summary
An inspection system that includes charged particle optics that irradiate a bottom of a hole with a charged particle beam propagated along an optical axis, an energy dispersive x-ray detector and a processor. The x-ray detector detects x-ray photons emitted from the bottom of the hole and generates detection signals indicative of the x-ray photons. The processor processes the detection signals to provide an estimate of the bottom of the hole.