SEM Charging and EFISH for Wafer Interface Trap Density
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Solution Overview
Problem
Current semiconductor wafer testing methods face challenges in non-invasively and non-destructively measuring electrical properties, such as dielectric properties and charge carrier lifetime, due to issues with charge distribution and surface contamination, which affect the accuracy and reliability of measurements.
Innovation Solution
The use of a scanning electron microscope (SEM) to deposit charge on the wafer surface and a pulsed laser for second harmonic generation (SHG) measurements, allowing for contactless and non-invasive determination of electrical properties by analyzing the SHG signal, while maintaining the wafer in a vacuum to minimize contamination and charge diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional contact-based measurement methods are used to determine electrical properties, then measurement accuracy can be improved, but the wafer surface becomes contaminated and charge distribution is disturbed
Solution Approach 1:
The patent replaces mechanical contact-based measurement systems with a non-contact optical system. A probe laser beam is directed at the wafer surface to induce second harmonic generation, and the reflected light is detected to determine electrical properties such as interface state density and charge carrier lifetime. This substitution eliminates physical contact, thereby preventing surface contamination and charge distribution disturbance while maintaining measurement accuracy.
Solution Approach 2:
The patent introduces light as an intermediary medium to transfer information from the wafer surface without direct contact. The probe laser beam interacts with the wafer surface to generate second harmonic signals that carry information about electrical properties. This intermediary approach allows measurement of electrical characteristics while avoiding the harmful effects of direct contact, including contamination and charge disturbance.
2Adaptability or versatility
If invasive scribing or grounding methods are used to enable measurement, then measurement capability is improved, but the wafer structure is damaged and processing complexity increases
Solution Approach 1:
The patent replaces invasive mechanical preparation methods (scribing, grounding) with non-contact optical measurement. The probe laser beam can measure electrical properties on intact wafer surfaces without requiring any physical modification. This eliminates the need for complex preparatory steps and preserves wafer structure, thereby reducing processing complexity while maintaining full measurement capability.
Solution Approach 2:
The patent performs measurement actions before any invasive preparation would be needed. By using non-contact optical measurement on the as-received wafer surface, the system obtains electrical property data without requiring subsequent scribing or grounding steps. This preliminary measurement approach eliminates the need for additional processing complexity and preserves wafer integrity.
3Ease of operation
If the wafer is exposed to ambient environment during measurement, then ease of operation is improved, but charge diffusion and measurement reliability deteriorate
Solution Approach 1:
The patent employs a vacuum environment as an inert atmosphere during measurement. The vacuum chamber prevents ambient air molecules from interacting with the wafer surface, thereby eliminating charge diffusion caused by air exposure. This controlled environment maintains charge distribution stability and measurement reliability while the non-contact optical method ensures ease of operation by requiring no special wafer preparation for vacuum compatibility.
Solution Approach 2:
The non-contact optical measurement system allows measurements to be performed through the vacuum chamber window without breaking vacuum. The probe laser beam and detection system can operate remotely, maintaining the vacuum environment throughout the measurement process. This substitution of contact-based methods with optical methods enables the vacuum environment to be maintained, ensuring charge stability while preserving operational ease.
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 method enables precise and accurate measurement of electrical properties without damaging the wafer, reducing measurement errors and allowing for in-line testing during front-end-of-line (FEOL) processing, with the ability to determine interface state density and charge distribution without invasive scribing or grounding.
Implementation Method 1
using a scanning electron microscope (SEM) or components typically used in an SEM (e.g., electron gun, anode, electron lenses, electron beam deflector) to deposit charge on a top surface of an insulator layer
Implementation Method 2
measuring an optical response of the semiconductor wafer. This optical response may comprise, for example, second harmonic generation (SHG) light having a frequency that is the second harmonic of the frequency of incident pulsed laser light
Implementation Method 3
in various implementations the Electric Field Induced Second Harmonic generation (EFISH) is measured in response to SHG laser stimulus with the addition of surface charge provided by an SEM or SEM components
Data Source
AI summary
A non-invasive semiconductor technique for measuring dielectric/semiconductor interface trap density can be performed by charging the dielectric by creating charges on the top surface of the dielectric layer over the wafer using Scanning Electron Microscope (SEM) charging. This charging can induce an accumulated, a depleted and/or an inverted semiconductor surface. The states of the semiconductor surface can subsequently be measured, identified, and/or quantified using Electric Field Induced Second Harmonic generation (EFISH). From the measured/acquired EFISH versus SEM charge curve, the interface state density (Dit) can be extracted. A large working distance provides the ability to create charge and measure the Second Harmonic Generation (SHG) at the same semiconductor surface spot without the needing to move the wafer.