Non-contact Metal Work Function Monitoring via Kelvin Probe
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Solution Overview
Problem
Monitoring metal effective work function (EWF) in semiconductor wafers is challenging due to its sensitivity to dielectric materials and fabrication processes, leading to deviations from intended specifications that can impact integrated circuit performance and yield.
Innovation Solution
A non-contact technique using Kelvin probes to measure surface voltage differences between dark and illuminated conditions, allowing for the quantification of semiconductor surface barrier voltage (VSB), which is proportional to the metal effective work function (EWF), enabling accurate monitoring and mapping of EWF on semiconductor wafers without contaminating the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-contact measurement techniques are used to monitor metal EWF, then device contamination is avoided and measurement speed is improved, but measurement precision and reliability are compromised due to the indirect nature of the measurement
Solution Approach 1:
The patent uses the semiconductor surface barrier voltage (VSB) as an intermediary parameter to indirectly measure the metal effective work function (EWF). The VSB is measured non-contactively using a Kelvin probe, and then EWF is calculated from VSB using the relationship EWF = φS - qVSB, where φS is the bulk work function of the semiconductor substrate. This intermediary approach enables non-contact measurement while maintaining measurement reliability.
Solution Approach 2:
The patent replaces direct electrical contact measurement methods with a non-contact Kelvin probe technique. Instead of physically contacting the metal gate to measure EWF, the system measures the surface voltage of the semiconductor substrate beneath the metal gate using a vibrating capacitor probe, thereby eliminating contact-related contamination and damage while obtaining the required electrical parameter information.
2Measurement precision
If conventional contact-based measurement methods are used, then direct EWF measurement is achieved, but device contamination and damage occur, impacting yield and requiring additional processing time
Solution Approach 1:
The patent measures the surface barrier voltage (VSB) of the semiconductor substrate as an intermediary parameter instead of directly measuring the metal EWF. The VSB is obtained through non-contact Kelvin probe measurements on the semiconductor surface beneath the metal gate, and then EWF is derived from VSB. This eliminates the need for direct contact with the metal gate, avoiding contamination and damage.
Solution Approach 2:
The patent substitutes direct electrical contact measurement with a non-contact optical/electrical field-based Kelvin probe technique. The vibrating capacitor probe measures surface voltage through capacitive coupling without physical contact, replacing mechanical/electrical contact methods that cause contamination and damage to the device structure.
3Reliability
If traditional EWF monitoring methods are employed, then comprehensive device testing is performed, but processing time increases and productivity decreases
Solution Approach 1:
The patent extracts only the essential information needed for EWF monitoring by measuring the surface barrier voltage (VSB) of the semiconductor substrate beneath the metal gate. Instead of performing comprehensive device testing, the method selectively measures the VSB parameter that directly correlates with EWF, using the relationship EWF = φS - qVSB. This extraction of critical information enables rapid monitoring without full device characterization, improving productivity while maintaining reliability.
Solution Approach 2:
The patent skips lengthy comprehensive device testing procedures by directly measuring the surface barrier voltage (VSB) using a non-contact Kelvin probe. The method rushes through to the essential measurement parameter (VSB) that provides the required EWF information, eliminating unnecessary testing steps and significantly reducing processing time while maintaining the ability to verify device performance.
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 provides fast and effective monitoring of metal EWF, shortening the metal gate development cycle, improving performance control, and increasing manufacturing yield by allowing non-contact measurements on product wafers, thus facilitating faster data feedback and better control over metal gate development.
Implementation Method 1
measurements of surface voltage on metal surface done in the dark, giving VDark and under illumination with strong light with photon energy larger than the energy gap of the semiconductor substrate, giving VLight
Data Source
AI summary
An example semiconductor wafer includes a semiconductor layer, a dielectric layer disposed on the semiconductor layer, and a layer of the metal disposed on the dielectric layer. An example method of determining an effective work function of a metal on the semiconductor wafer includes determining a surface barrier voltage of the semiconductor wafer, and determining a metal effective work function of the semiconductor wafer based, at least in part, on the surface barrier voltage.