Laser Probe Placement for 16nm Transistor Defect Detection
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Solution Overview
Problem
As integrated circuit geometries shrink to sizes like 16 nm and 14 nm, traditional laser probing becomes inadequate due to difficulty in discerning the operation of a single transistor, especially near other active transistors, and techniques using shorter wavelengths face issues like die thinning and signal absorption, which can damage the circuit and alter its behavior.
Innovation Solution
A laser probing system that includes a receiver circuit, a combinational logic analysis (CLA) processor, and a test controller, which uses a laser source and optical system to position an optic probe at selectable locations on the integrated circuit, simulating an optical response to a test pattern and repositioning the probe based on the fit between the CLA and laser probe waveforms to accurately identify defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional laser probing is used with visible light or infrared radiation, then the chip can be probed from the backside, but the resolution is limited to about 200 nm which is insufficient for 16 nm and 14 nm transistor geometries
Solution Approach 1:
The patent changes the wavelength parameter of the laser light from visible/infrared to ultraviolet range to achieve better resolution. However, this creates a new contradiction because silicon is highly absorptive in the visible spectrum, requiring die thinning below 5 microns which damages the circuit and affects thermal dissipation. The patent resolves this by using algorithms to compensate for signal absorption and by positioning probes at locations where the laser can effectively interact with the transistor gates without requiring excessive die thinning.
2Measurement precision
If shorter wavelength light is used to achieve better resolution, then probing resolution improves, but the die must be thinned below 5 microns which causes damage and affects thermal dissipation
Solution Approach 1:
The patent performs preliminary actions by using algorithms to predict and compensate for signal absorption before the actual probing occurs. The system pre-calculates the expected signal degradation and adjusts the probing parameters accordingly, allowing the use of shorter wavelengths without physically thinning the die, thus maintaining circuit integrity and thermal dissipation while achieving better resolution.
Solution Approach 2:
The patent introduces an intermediary approach by using computational algorithms as a mediator between the laser probing system and the transistor nodes. These algorithms simulate the optical response and compensate for absorption effects, allowing the system to achieve high resolution without directly imposing the harmful effect of die thinning on the physical structure.
3Measurement precision
If shorter wavelength light is used to improve resolution, then probing capability improves, but the light changes the behavior of the circuit which proves inadequate
Solution Approach 1:
The patent implements feedback mechanisms where the system continuously monitors the optical response and compares it against expected behavior models. When the laser light begins to significantly alter circuit operation, the feedback system adjusts probing parameters or identifies when the light-induced effects become problematic, allowing the system to operate at the boundary of acceptable perturbation while maintaining measurement accuracy.
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 precise identification of defects by improving probe placement accuracy and reducing cross-talk interference, enabling effective analysis of smaller transistor geometries without damaging the integrated circuit.
Implementation Method 1
a laser source is focused at a single node of an integrated circuit, and the characteristics of the reflected laser light indicate changes in the voltage of the node over time
Implementation Method 2
an optical system that receives reflected light from the device under test and outputs the reflected light
Data Source
AI summary
A control system for placing an optic probe includes a receiver circuit that receives reflected light produced from the optic probe and provides a laser probe (LP) waveform of the reflected light in response to an activation of a trigger signal. A combinational logic analysis (CLA) processor provides a CLA waveform in response to simulating an optical response at a target location on a surface of a cell of a device under test to a test pattern. A test controller receives the CLA waveform and the LP waveform, and has a first output for providing the trigger signal, a second output for providing the test pattern, and a third output for providing a position signal. The test controller updates the position signal to move the optic probe closer to the target location according to a degree of fit between the LP waveform and the CLA waveform.