Spectroscopic Scatterometer with Oblique Higher-Order Detection
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Solution Overview
Problem
Current spectroscopic scatterometers are limited in measuring isolated features and pattern asymmetries, and they do not effectively utilize higher diffracted radiation, leading to challenges in resolving small features and accuracy in lithographic processes, while also facing issues with cross-talk between measurement targets due to the point spread function of illumination spots.
Innovation Solution
A spectroscopic scatterometer design that includes illumination optics for broadband radiation, zero order detection optics, and higher order detection optics, with the latter processing diffracted radiation in a separate plane due to an oblique orientation of the target grating, and a symmetrical diffraction grating to form symmetrical spectra, reducing sensitivity to defocus and allowing for simultaneous measurement of target properties with reduced cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional spectroscopic scatterometers are used to measure small features, then the hardware is relatively simple, but they cannot effectively measure very isolated features and pattern asymmetries
Solution Approach 1:
The detection system is segmented into multiple independent detection channels (zero-order detector, first-order detectors at different angles). Each detector captures specific diffraction order information, allowing the system to measure isolated features and asymmetries by analyzing combined data from all channels rather than relying on a single complex detection system
Solution Approach 2:
The system transitions from conventional single-plane detection to multi-dimensional detection by capturing diffraction patterns at multiple angles (including oblique angles) and combining zero-order and higher-order diffraction data. This dimensional expansion in detection space enables measurement of features that are invisible or ambiguous in conventional single-plane spectroscopic scatterometry
2Measurement precision
If higher diffracted radiation is utilized, then measurement accuracy of pattern asymmetries improves, but the optical system becomes more complex
Solution Approach 1:
The detection system is designed with multi-functionality where detectors capture multiple diffraction orders (zero-order and higher-orders) simultaneously. The same detection hardware processes both zero-order reflected radiation and higher-order diffracted radiation, eliminating the need for separate specialized systems for each measurement type
Solution Approach 2:
The system captures excessive diffraction information by detecting not only the zero-order reflection but also multiple higher-order diffraction patterns. This excessive data collection provides redundant information that improves asymmetry measurement accuracy while the data processing selectively extracts the necessary measurements from the abundant diffraction signals
3Device complexity
If conventional scatterometry is used, then the system is simpler, but cross-talk between measurement targets occurs due to point spread function
Solution Approach 1:
The system extracts and analyzes specific diffraction order signals (zero-order and higher-orders at particular angles) that are less susceptible to cross-talk contamination. By selecting and isolating these specific signal components from the total scattered radiation, the system reduces the impact of point spread function effects and adjacent target interference
Solution Approach 2:
The measurement approach combines multiple types of diffraction data (zero-order reflectivity and higher-order diffraction patterns at different angles) to create a composite measurement signal. This composite approach provides redundancy and cross-validation that reduces the impact of cross-talk and point spread function effects on individual measurement channels
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 design enhances the measurement accuracy of small features and pattern asymmetries, improves the utilization of higher diffracted radiation, and reduces cross-talk between measurement targets, enabling more precise metrology for current and next-generation lithographic processes.
Implementation Method 1
higher order detection optics for receiving radiation diffracted at one or more higher orders by the periodic grating in the target structure
Implementation Method 2
zero order detection optics for receiving radiation reflected from the target
Data Source
AI summary
A spectroscopic scatterometer detects both zero order and higher order radiation diffracted from an illuminated spot on a target grating. The apparatus forms and detects a spectrum of zero order (reflected) radiation, and separately forms and detects a spectrum of the higher order diffracted radiation. Each spectrum is formed using a symmetrical phase grating, so as to form and detect a symmetrical pair of spectra. The pair of spectra can be averaged to obtain a single spectrum with reduced focus sensitivity. Comparing the two spectra can yield information for improving height measurements in a subsequent lithographic step. The target grating is oriented obliquely so that the zero order and higher order radiation emanate from the spot in different planes. Two scatterometers can operate simultaneously, illuminating the target from different oblique directions. A radial transmission filter reduces sidelobes in the spot and reduces product crosstalk.