Overlay Measurement Test Structures for Double Patterning
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Solution Overview
Problem
Current methods for measuring overlay error in multiple patterning on semiconductor wafers lack sufficient resolution and sensitivity, particularly as feature sizes decrease, making it challenging to accurately align patterns and correct errors.
Innovation Solution
The formation of special test structures in unused areas of the wafer, where the second pattern is shifted relative to the first pattern, such as by ½ pitch, to enhance the sensitivity of optical measurements, allowing for improved alignment error detection using scatterometry techniques without requiring complex calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photo-lithography is used for patterning, then the process is simple and well-established, but the resolution is limited to roughly 80 nanometers
Solution Approach 1:
The patterning process is divided into multiple sequential lithographic steps (first pattern exposure, second pattern exposure) to achieve higher resolution (60 nm) than single-step lithography can provide. Each step creates a subset of the final pattern, and the combination yields the desired fine pitch features.
Solution Approach 2:
The first pattern is formed and temporarily retained on the substrate before the second pattern is applied. This preliminary pattern serves as a reference or guide for the subsequent patterning step, enabling precise alignment and achieving the target resolution through cumulative patterning.
2Manufacturing precision
If double patterning techniques are used to achieve finer resolution, then the pattern density is doubled, but the overlay alignment error becomes more difficult to measure with sufficient sensitivity
Solution Approach 1:
A dedicated test structure is introduced as an intermediary measurement target. This test structure contains the first pattern and a shifted second pattern specifically designed for overlay measurement, allowing the measurement system to detect alignment errors with enhanced sensitivity without interfering with the production pattern measurement.
Solution Approach 2:
The second pattern in the test structure is intentionally shifted by a known amount (e.g., ½ pitch) relative to the first pattern. This parameter change creates a measurable offset that amplifies the overlay error signal, enabling the measurement system to detect and quantify alignment inaccuracies with greater precision.
3Manufacturing precision
If the second pattern is aligned exactly midway between first pattern features (at P/2 spacing), then the double patterning achieves the target pitch, but the overlay measurement sensitivity is reduced
Solution Approach 1:
Instead of symmetrically placing the second pattern exactly midway (P/2) between first pattern features, the test structure uses an asymmetric configuration where the second pattern is shifted by a different amount (e.g., ½ pitch offset). This asymmetry creates a more sensitive measurement signal that amplifies overlay errors, enabling better detection and correction of alignment inaccuracies.
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 increases the sensitivity of overlay error measurement, enabling more precise alignment and process adjustments to reduce errors, thereby improving the accuracy of pattern alignment and reducing measurement uncertainties.
Implementation Method 1
allowing for improved alignment error detection using scatterometry techniques
Data Source
AI summary
A multi-patterning method of manufacturing a patterned wafer provides test structures designed to enhance overlay error measurement sensitivity for monitoring and process control. One or more patterns are overlaid on a first pattern, each of a given pitch, with the elements interleaved. Test structure is formed with elements of the overlaid patterns spaced away from respective mid-positions more closely toward elements of the first pattern. In some embodiments, test structure elements of the second pattern are overlaid midway between mid-positions of elements of the first pattern and measured by scatterometry. In other embodiments, test structure elements of the second pattern are overlaid at a slightly different pitch than the elements of the first pattern and measured by reflectivity. Measurements are compared with library measurements to identify the error, which may be fed back to control the patterning process. The multi-patterning may be formed by LELE, LLE, LFLE, or other methods.