Backside Silicon Milling Endpoint Detection via FET Power Draw
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Solution Overview
Problem
Existing semiconductor failure analysis methods require backside silicon removal, which lacks in-situ endpoint detection, leading to high risks of device destruction due to overmilling or mechanical stress.
Innovation Solution
An assembly and method using a piezoelectric mechanism to monitor power draw of field effect transistors during backside milling, detecting endpoint changes in power draw to prevent irreversible damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside silicon removal is performed to enable optical imaging and failure analysis, then imaging capability is improved, but device integrity deteriorates due to risk of overmilling and mechanical stress
Solution Approach 1:
The patent implements real-time feedback by monitoring power draw changes of field effect transistors during backside milling. The system continuously measures electrical characteristics and uses these measurements to detect when the milling process approaches the endpoint, providing feedback control to prevent overmilling and device damage.
Solution Approach 2:
The patent replaces mechanical measurement methods (physical contact, direct thickness measurement) with electrical field-based detection. By monitoring power draw changes caused by strain-induced electron mobility variations in FETs, the system substitutes mechanical endpoint detection with electrical field sensing, enabling non-contact, real-time monitoring.
2Measurement precision
If continuous monitoring during milling is implemented, then endpoint detection accuracy is improved, but system complexity increases
Solution Approach 1:
The patent makes the device under test serve its own monitoring function. The field effect transistors within the device itself provide the sensing mechanism through their power draw characteristics, eliminating the need for separate external sensors or complex monitoring apparatus. The device's own electrical characteristics become the measurement signal.
Solution Approach 2:
The patent monitors changes in electrical parameters (power draw, current consumption) of the field effect transistors as indicators of mechanical strain. By tracking parameter variations rather than direct physical measurements, the system achieves precise endpoint detection through electrical field changes that occur naturally during the milling process.
3Manufacturing precision
If frequent pauses for thickness measurement are made, then milling precision is improved, but productivity decreases
Solution Approach 1:
The patent enables continuous milling operation by implementing real-time electrical monitoring that eliminates the need for periodic pauses. The power draw monitoring continues uninterrupted during the milling process, allowing the milling operation to proceed continuously while endpoint detection is performed in real-time, thereby maintaining precision without sacrificing productivity.
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 safe and accurate in-situ endpoint detection, reducing the risk of device destruction during backside milling by monitoring strain-induced power changes in integrated circuits.
Implementation Method 1
An assembly and method using a piezoelectric mechanism to monitor power draw of field effect transistors during backside milling, detecting endpoint changes in power draw
Data Source
AI summary
An assembly for monitoring a semiconductor device under test comprising a mill configured to mill the device, a sensor configured to measure an electrical characteristic of the device, and a computer configured to determine the amount of strain in the device from the electrical characteristic when the mill is milling the device and detect an endpoint of milling at a circuit within the device. In use the endpoints of the milling process of the semiconductor device are detected measuring an electrical characteristic of the device with a sensor during milling determining the amount of strain in the device from the electrical characteristic and detecting an endpoint of the milling process within the device based on the amount of strain.