Inspection Pattern Structure for Non-Destructive Lateral Etch Measurement
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Solution Overview
Problem
The accuracy of etching processing in compound semiconductor devices is compromised by lateral etching, which is difficult to measure non-destructively due to variations in etching conditions and the presence of upper layers obstructing visibility, affecting device characteristics such as optical loss, parasitic capacitance, and dark current.
Innovation Solution
An inspection pattern and method that includes an inspection pattern portion and an inspection layer portion with a thinner thickness than the actual upper layer, allowing non-destructive evaluation of etching states by observing the difference in shapes from the side of the inspection layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-section observation by FIB processing is used to measure lateral etching amount, then measurement precision is improved, but the inspection becomes destructive and cannot be applied to each wafer in mass production
Solution Approach 1:
The invention divides the semiconductor structure into two segments: the actual element with thick upper layers that cannot be observed, and an inspection pattern with deliberately thinner upper layers that can be observed. This segmentation allows non-destructive measurement of lateral etching in the inspection pattern while preserving the actual element for production.
Solution Approach 2:
The inspection pattern serves as a copy or replica of the actual element's etching structure. By creating this copy with modified observability characteristics (thinner upper layers), the lateral etching amount can be measured without destroying the actual production elements.
2Ease of manufacture
If observation from upper surface with optical microscope is used, then non-destructive inspection is achieved, but the state of pattern below electrode or passivation film cannot be observed
Solution Approach 1:
The invention applies local quality by creating a specific region (inspection pattern) with different structural properties than the actual element. The inspection pattern has thinner upper layers specifically at the etched portion, making it locally observable while the actual element maintains its original structure with thick protective layers.
3Manufacturing precision
If lateral etching amount is managed by advance etching measurement, then etching accuracy can be controlled, but the measured value does not necessarily coincide with mass production etching
Solution Approach 1:
The inspection pattern is prepared in advance together with the actual element during the same etching process. This preliminary preparation ensures that both the inspection pattern and actual element undergo identical etching conditions, making the measurement representative of mass production results.
Data Source
AI summary
In the inspection pattern T for inspecting a processing state of a mesa (monitoring a fabrication accuracy against the expected pattern of a mesa) used for an actual element M, the actual element M includes a mesa formed by etching a substrate, and an electrode formed on the mesa, the inspection pattern T includes a mesa formed by etching the substrate, and a thin film that is formed at least on an upper surface of the inspection pattern portion T and has a thickness smaller than the thickness of the electrode, an etching state of the mesa is evaluated on the basis of a difference between the shape of the inspection pattern portion T and the shape of the thin film, and a lateral etching amount at the time of etching is quantitatively and accurately evaluated with a non-destructive inspection.