Scatterometer Pixel Selection for Microstructure Measurement
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Solution Overview
Problem
Existing scatterometry systems face challenges in accurately evaluating very small microstructures on semiconductor wafers due to limitations in locating small features, noise from large spot sizes, inadequate wavelength resolution for small dimensions, lengthy data processing times, and complex calibration requirements, especially when dealing with p- and s-polarized components over a wide range of angles.
Innovation Solution
A scatterometer system with a laser source, optics assembly, and detector that focuses a beam to a small spot size over a range of altitude and azimuth angles, using a single camera with a polarizing beam splitter to separate p- and s-polarized components, and a CMOS imager for efficient data collection, along with an auto-focus system and navigation system for precise positioning and calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large spot size is used to illuminate the workpiece, then the illumination covers a large area, but it generates reflections from surrounding areas that result in excessive noise
Solution Approach 1:
The patent segments the illumination area by using multiple smaller spot sizes that can be positioned at different locations on the workpiece. Instead of using one large spot, the system divides the illumination into multiple smaller spots, each contributing to the overall measurement while minimizing noise from surrounding areas. This is achieved through the controller coordinating multiple beam positions and the detector array capturing reflected light from each spot independently.
2Adaptability or versatility
If existing scatterometers are used to assess microstructures, then they can measure photometric and colorimetric properties, but they are not well-suited for assessing gratings or microstructures with much smaller dimensions
Solution Approach 1:
The patent changes key parameters of the scatterometer system to adapt it for measuring smaller microstructures. This includes using shorter wavelengths (blue and UV LEDs instead of just red), reducing spot sizes, and adjusting the angular ranges of the illumination and detection systems. These parameter changes enable the system to resolve and accurately measure microstructures with dimensions much smaller than what conventional display inspection scatterometers can handle.
3Illumination intensity
If relative long wavelengths are used to assess flat panel displays, then they are suitable for larger pixel areas, but they are not capable of assessing very small microstructures on microelectronic devices
Solution Approach 1:
The patent changes the wavelength parameter by employing blue LEDs (around 450 nm) and UV LEDs (around 375 nm) instead of the longer wavelengths (around 650 nm) typically used for flat panel display inspection. This wavelength reduction improves the resolution capability of the system, enabling it to detect and measure very small microstructures on semiconductor wafers with dimensions below 70 nm, while still maintaining the ability to assess larger features.
4Area of stationary object
If data is collected from all pixels of the sensor array, then comprehensive coverage is obtained, but it increases the amount of data that needs to be processed
Solution Approach 1:
The patent extracts and processes only the relevant data from the sensor array pixels. Instead of processing data from all pixels, the system identifies and processes only those pixels that correspond to the illuminated spot positions and contain meaningful signal information. The controller coordinates with the detector to read data selectively from specific pixels, thereby reducing the overall data processing burden while maintaining comprehensive measurement coverage across the workpiece.
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
Enables accurate and efficient evaluation of microstructures with improved precision and speed, reducing noise and processing time, and simplifying calibration, allowing for real-time assessment of submicron features on semiconductor wafers.
Implementation Method 1
an optics assembly configured to condition the beam and focus the beam to a spot size on the workpiece throughout a range of angles of incidence
Implementation Method 2
a beam splitter aligned with the illumination source, and a first lens between the beam splitter and the sample. The first lens focuses the light from the beam splitter to a spot size on the wafer throughout a large range of angles of incidence
Data Source
AI summary
Scatterometers and methods of using scatterometry to determine several parameters of periodic microstructures, pseudo-periodic structures, and other very small structures having features sizes as small as 100 nm or less. Several specific embodiments of the present invention are particularly useful in the semiconductor industry to determine the width, depth, line edge roughness, wall angle, film thickness, and many other parameters of the features formed in microprocessors, memory devices, and other semiconductor devices. The scatterometers and methods of the invention, however, are not limited to semiconductor applications and can be applied equally well in other applications.