Edge Plate Voltage Control for Charged Particle Beam Inspection Accuracy
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Solution Overview
Problem
Charged particle beam inspection systems face image variation issues near substrate edges due to non-axial symmetrical electric field distributions, which cause image shifting, distortion, and defocus, and existing solutions like enlarged gaps with biased rings are impractical to implement due to control and insulation challenges.
Innovation Solution
A method and system that capture central and peripheral images of a substrate using a charged particle beam, apply a voltage between the substrate and an edge plate determined by the image differences, and use an edge effect eliminator to adjust the bias voltage and equipotential lines to minimize edge field effects, ensuring a uniform potential distribution and accurate imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bias voltage is applied between the substrate and objective lens to perform low energy inspection, then the charged particle beam can be focused properly, but the non-axial symmetrical electric field distribution at substrate edges causes image shifting, distortion and defocus
Solution Approach 1:
An edge plate is introduced as an intermediary component between the substrate and the inspection system. The edge plate is positioned close to the substrate edge and has a controllable potential that can be adjusted to compensate for the non-axial symmetrical electric field distribution, thereby reducing image shifting, distortion and defocus at substrate edges
2Object-affected harmful factors
If an insert ring with voltage is used to reduce edge effect by enlarging the gap, then the edge field effect can be reduced, but the height, shape and flatness control becomes too difficult and additional isolation is needed which may induce more severe problems
Solution Approach 1:
The invention extracts the edge field effect compensation function from the complex insert ring structure and implements it through a simpler edge plate positioned close to the substrate edge. This eliminates the need for difficult-to-control height, shape and flatness specifications while avoiding the insulation problems associated with enlarged gaps
Solution Approach 2:
The invention changes the control parameter from mechanical dimensions (height, shape, flatness of insert ring) to electrical parameter (potential of edge plate). By controlling the potential of the edge plate, the system achieves edge field effect reduction without the manufacturing and assembly difficulties of the insert ring approach
3Ease of manufacture
If the gap between substrate and chuck is increased to accommodate position accuracy tolerance, then assembly tolerance can be tolerated, but the non-uniform gap creates non-axial symmetrical electric field that distorts the primary beam
Solution Approach 1:
The edge plate acts as an intermediary that compensates for the non-uniform gap between substrate and chuck. By positioning the edge plate close to the substrate edge and controlling its potential, the system maintains beam positioning accuracy despite the presence of assembly tolerance in the gap
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 effectively reduces edge effects by compensating for image shifts, distortions, and defocus, providing accurate and non-defocused inspection images by planarizing the potential distribution near the substrate edge, thus enhancing the precision of defect inspection in semiconductor fabrication.
Implementation Method 1
The imaging practice is irradiating a charged particle beam 102, to the surface of the substrate 160 and detecting the backscattered and secondary charged particles emanating from the surface of substrate 160
Implementation Method 2
the objective lens 130 will focus the primary charged particle beam 102 on to the surface of the substrate 160
Implementation Method 3
a bias voltage is applied between the plate holding the substrate 160 and the objective lens 130. Since the substrate is not located in an area free of electrical fields, its material, shape and bias voltage may change the spatial electrical field distribution
Data Source
AI summary
An apparatus and method are introduced in this invention to reduce the edge effect of a substrate that causes image variation or distortion due to applied substrate bias. An edge plate with an edge effect eliminator are provided such that substrate is inspected by a charged particle beam can capture images without distortion at substrate edge.