Backside Optical Carrier Injection for High-Resolution IC Imaging
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Solution Overview
Problem
Existing optical carrier injection methods for ICs face challenges such as substrate light absorption, time-consuming imaging processes, and limited spatial resolution due to mechanical translation stage limitations, especially when using backside illumination with comparable or lower bandgap materials.
Innovation Solution
Employing a focused optical beam with photon energy below the substrate bandgap for backside injection, utilizing nonlinear optical interactions like two-photon absorption, and combining electronic beam steering to acquire and stitch 2D image tiles for high-resolution imaging without substrate thinning or polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If backside optical carrier injection is used to avoid interference from metallization traces, then imaging quality is improved, but substrate light absorption occurs when substrate bandgap is comparable to or smaller than active layer bandgap
Solution Approach 1:
The patent changes the photon energy parameter of the optical beam to be below the substrate bandgap but above the active layer bandgap, allowing the beam to pass through the substrate without being absorbed while still enabling carrier injection in the active layer. This parameter optimization resolves the contradiction between avoiding substrate absorption and achieving effective carrier injection.
Solution Approach 2:
The patent uses the substrate as an optical window or mediator that transmits the optical beam from the backside to the active layer. By selecting appropriate optical wavelengths and materials, the substrate acts as a transparent intermediary that enables backside illumination without significant absorption, thus improving imaging quality while minimizing energy loss.
2Area of stationary object
If mechanical translation stage is used for beam positioning, then scanning coverage is achieved, but spatial resolution is limited by mechanical tolerance
Solution Approach 1:
The patent segments the imaging process into two stages: coarse positioning using mechanical translation stage to cover the entire wafer area, and fine positioning using electronic beam steering (galvanometer mirrors) to achieve high spatial resolution. This segmentation allows each subsystem to optimize for its specific function without compromising the other.
Solution Approach 2:
The patent replaces pure mechanical positioning with a hybrid system that uses electronic beam steering (galvanometer mirrors) to achieve fine spatial resolution. This substitution of mechanical control with electronic control for the fine positioning task eliminates mechanical tolerance limitations while maintaining the mechanical stage's advantage in providing broad scanning coverage.
3Loss of energy
If substrate is thinned or removed to reduce light absorption, then optical transmission is improved, but destructive processing is required which alters IC functional behavior
Solution Approach 1:
Instead of changing the physical thickness of the substrate, the patent changes the optical parameters (wavelength, photon energy) to optimize transmission. By selecting wavelengths below the substrate bandgap, the substrate naturally becomes transparent without requiring mechanical thinning or chemical removal, thus avoiding destructive processing while improving optical transmission.
4Measurement precision
If frontside optical carrier injection is used to achieve tight focal point, then spatial resolution is improved, but interference from metallization traces and insulating layers occurs
Solution Approach 1:
The patent inverts the conventional approach by applying optical illumination from the backside of the substrate rather than the frontside. This inversion allows the optical beam to reach the active layer without being blocked or scattered by metallization traces and insulating layers that are present on the frontside, thus eliminating interference while maintaining tight focal point capability through proper optical focusing.
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
Achieves high spatial resolution imaging of ICs without substrate alteration, reducing imaging time and overcoming mechanical translation limitations, while avoiding destructive processing.
Implementation Method 1
the backside illumination used for optical carrier injection has photon energy higher than the bandgap of the substrate. Hence, the illumination will be absorbed by the substrate before it can reach and be absorbed by the active layer
Implementation Method 2
utilizing nonlinear optical interactions like two-photon absorption
Data Source
AI summary
In an imaging method, a focal point of a focused optical beam is sequentially mechanically positioned at coarse locations in or on an integrated circuit (IC) wafer or chip. At each coarse location, a two-dimensional (2D) image or mapping tile is acquired by steering the focal point to fine locations on or in the IC wafer or chip using electronic beam steering and, with the focal point positioned at each fine location, acquiring an output signal produced in response to an electrical charge that is optically injected into the IC wafer or chip at the fine location by the focused optical beam. The 2D image or mapping tiles are combined, including stitching together overlapping 2D image or mapping tiles, to generate an image or mapping of the IC wafer or chip. The electronic beam steering may be performed using a galvo mirror. The set of coarse locations may span a three-dimensional (3D) volume.