Detecting Open Contacts in DRAM Using Electron Beam Pre-Charging
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Solution Overview
Problem
Conventional approaches using scanning electron microscopes (SEM) are ineffective in identifying open bit contacts during deep trench DRAM fabrication due to insensitivity and inefficiency in distinguishing between normal and defective contacts, particularly in the bit contact layer where the buried capacitor causes unbalanced connections.
Innovation Solution
A method and system that utilize a primary electron beam with proper landing energy to generate images, combined with pre-charging the gate contacts using an accessory beam to turn on the MOS devices, allowing for effective identification of open contacts by analyzing signal or image differences in voltage contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SEM approaches are used to scan bit contacts, then the inspection process is simple, but the detection precision of open contacts is insufficient due to insensitivity in distinguishing normal and open contacts
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate contacts with an accessory beam before the main inspection scan. This pre-charging step prepares the electrical state of the contacts, creating a detectable signal difference between normal and open contacts during subsequent scanning, thereby improving detection precision without requiring complex additional hardware
Solution Approach 2:
The patent introduces an accessory beam as an intermediary element that performs the pre-charging function. This intermediary beam prepares the electrical conditions necessary for detecting open contacts, acting as a mediator between the inspection system and the bit contacts to enable accurate defect identification
2Measurement precision
If the gate contacts are pre-charged to turn on the gate, then the detection accuracy of open contacts improves, but the inspection time increases due to additional scanning steps
Solution Approach 1:
The patent implements periodic action by performing the accessory beam scanning in repeated cycles before the main inspection. This periodic pre-charging approach ensures adequate charge accumulation on gate contacts while allowing optimization of the number of cycles to balance detection accuracy with inspection time requirements
3Measurement precision
If the primary electron beam landing energy is optimized for voltage contrast imaging, then the signal quality improves, but the system requires precise control of multiple parameters increasing operational complexity
Solution Approach 1:
The patent applies parameter changes by optimizing the primary electron beam landing energy to a specific range (1-5 keV) for voltage contrast imaging. This parameter optimization enhances signal quality and the contrast between normal and open contacts, providing clear detectable differences while establishing standardized operating conditions
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 enables efficient detection and review of open contacts by differentiating normal and defective contacts through controlled charging modes, improving the accuracy and sensitivity of SEM imaging in identifying electrical defects in semiconductor devices.
Implementation Method 1
pre-scanning or irradiating the wafer surface entirely or partially with an accessory beam, a plurality of times, to achieve positive charging to turn on the gate on the associated MOS devices
Implementation Method 2
scanning the at least a portion of the MOS devices with a primary electron beam of proper landing energy to generate images on the area of interest
Implementation Method 3
Advanced wafer inspection and review systems based on a Scanning Electron Microscope (SEM) system have been commonly used for detecting and reviewing electrical defects as a voltage contrast image
Implementation Method 4
an in-lens detector 107 arranged below a final aperture 106 to detect signal electrons 111 (including secondary electrons SE and/or backscattered electrons BSE) emanating from the specimen surface 113
Implementation Method 5
an in-lens detector 107 arranged below a final aperture 106 to detect signal electrons 111 (including secondary electrons SE and/or backscattered electrons BSE) emanating from the specimen surface 113
Data Source
AI summary
A method and system for detecting or reviewing defective contacts on a semiconductor device are disclosed. In a first embodiment, the method and system comprise providing a positive charge sufficient enough to turn on a gate of an associated MOS device and scanning an area of interest within the MOS device with a primary electron beam of proper landing energy to generate image. The method and system include analyzing the signal of contacts and identify the open contacts. In a second embodiment, the method and system comprises pre-scanning or irradiating the wafer surface defect with an accessory beam, a plurality of times, to achieve positive charged/sufficient to turn on the gate on the associated MOS devices of the wafer; and scanning the at least a portion of the device circuits with a primary electron beam of proper landing energy to generate images wafer or area of interest. The method and system include analyzing the signal and/or image of contacts and identify the open contacts.