Backside Optical Carrier Injection Without Substrate Thinning
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Solution Overview
Problem
Backside optical carrier injection in microelectronic devices is impractical when the substrate and active layer have similar or reversed bandgap energies, leading to substrate absorption of the optical beam, and traditional thinning methods are destructive and time-consuming, while imaging processes are slow due to mechanical translation limitations.
Innovation Solution
Employing a pulsed optical beam with photon energy below the substrate and active layer bandgaps for backside injection using nonlinear optical interactions, and utilizing a fiber laser doped with ytterbium and/or erbium to focus the beam at a focal point in the active layer, avoiding substrate absorption and enabling precise carrier injection without substrate thinning, and using electronic beam steering for faster and higher-resolution imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If backside optical carrier injection is used to avoid interference from metallization traces, then spatial resolution is improved, but substrate absorption of the optical beam occurs when photon energy exceeds substrate bandgap
Solution Approach 1:
The patent changes the energy parameter of the optical beam by using two-photon absorption with photons having energy below the substrate bandgap (e.g., 1550 nm wavelength photons with 0.8 eV energy for silicon substrate with 1.1 eV bandgap). This allows the optical beam to pass through the substrate without absorption while still achieving carrier injection through nonlinear two-photon absorption at the focal point in the active layer.
Solution Approach 2:
The patent employs pulsed optical excitation instead of continuous wave illumination. The pulsed nature allows accumulation of carriers during the pulse duration while minimizing thermal effects and substrate heating between pulses, enabling precise carrier injection through two-photon absorption without excessive energy deposition in the substrate.
2Loss of energy
If substrate thinning or removal is performed to enable backside optical injection, then optical beam transmission is improved, but the process is destructive and time-consuming
Solution Approach 1:
The patent changes the approach from physical substrate modification to optical parameter optimization. By selecting photon energies below the substrate bandgap and using two-photon absorption mechanics, the method achieves effective optical transmission through the intact substrate without requiring mechanical thinning or chemical etching processes.
Solution Approach 2:
The patent replaces the mechanical/chemical substrate thinning process with an optical solution. Instead of physically removing or thinning the substrate to enable optical transmission, the method uses appropriate wavelength selection and two-photon absorption physics to achieve the same effect with the complete substrate intact.
3Area of stationary object
If mechanical translation stage is used for scanning optical carrier injection across IC wafer, then imaging coverage is improved, but imaging speed is reduced
Solution Approach 1:
The patent replaces the mechanical translation stage with an acousto-optic beam steering system. Acousto-optic deflectors use sound waves in a crystal to modulate the refractive index and steer the optical beam electronically, eliminating mechanical moving parts and enabling much faster scanning speeds for imaging across the IC wafer.
Solution Approach 2:
The patent uses acousto-optic modulation which operates through periodic sound wave excitation in the deflecting crystal. This allows rapid, electronically controlled beam steering without mechanical inertia limitations, significantly increasing imaging productivity while maintaining full wafer coverage.
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 allows for efficient carrier injection into microelectronic devices without substrate thinning, reducing heating risks through short pulses, and enables faster, higher-resolution imaging by electronically steering the optical beam, overcoming the limitations of mechanical translation stages.
Implementation Method 1
Photons of the optical beam are absorbed at the focal point in the active layer by nonlinear optical interactions to inject carriers at the focal point in the active layer
Implementation Method 2
A pulsed optical beam having pulse duration of 900 femtoseconds or lower is applied on a backside of a substrate... Photons of the optical beam are absorbed at the focal point in the active layer by nonlinear optical interactions
Implementation Method 3
an objective arranged to focus the pulsed optical beam at a focal point in the active layer disposed on the frontside of the substrate
Implementation Method 4
The pulsed optical beam is applied using a fiber laser in which the fiber is doped with ytterbium and/or erbium
Implementation Method 5
a fiber laser in which the fiber is doped with ytterbium and/or erbium
Implementation Method 6
the optical beam is applied on the backside of the substrate and travels through the substrate to reach the active layer disposed on the frontside of the substrate
Data Source
AI summary
In an optical carrier injection method, a pulsed optical beam having pulse duration of 900 fs or lower is applied on a backside of a substrate of an integrated circuit (IC) wafer or chip, and is focused at a focal point in an active layer on a frontside of the substrate. Photons of the optical beam are absorbed at the focal point by nonlinear optical interaction(s) to inject carriers. The pulsed optical beam may be applied using a fiber laser in which the fiber is doped with Yb and/or Er. An output signal may be measured, comprising an electrical signal or a light output signal produced by the IC wafer or chip in response to the injected carriers. By repeating the applying, focusing, and measuring over a grid of focal points in the active layer, an image of the IC wafer or chip may be generated.