Multi-Layer Alignment Mark Structure for Wafer Processing
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Solution Overview
Problem
Existing alignment mark structures on semiconductor wafers are compromised by processes like chemical mechanical polishing, leading to reduced detectability due to low reflectivity and step height, causing interference with additional layers and inefficient alignment during circuit pattern formation.
Innovation Solution
A novel alignment mark arrangement featuring a first alignment pattern with smaller dimensions and a second pattern overlapping it, where each second stripe has a larger dimension than the first, with a transparent layer allowing improved light passage and a reflective layer for enhanced detection by stepper systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical polishing is applied to the wafer, then the wafer surface is flattened and circuit patterns are formed, but the alignment mark integrity is compromised and step height is reduced
Solution Approach 1:
The alignment mark structure is segmented into multiple layers: a bottom reflective layer formed before polishing, a transparent intermediate layer, and a top alignment pattern layer. This segmentation allows the reflective layer to remain intact after CMP while the upper layers provide alignment functionality.
Solution Approach 2:
The bottom reflective layer is formed in advance before the chemical mechanical polishing process. This preliminary formation ensures that the reflective layer is already in place and protected during subsequent polishing operations, preventing damage to the alignment mark's reflective properties.
2Productivity
If additional layers are deposited on the alignment mark, then circuit patterns are formed, but the reading of the alignment mark is interfered with
Solution Approach 1:
A transparent intermediate layer is introduced between the bottom reflective layer and the top alignment pattern layer. This intermediary layer allows laser light to pass through the upper circuit pattern layers and reach the reflective layer, enabling alignment mark detection even when additional layers are present.
Solution Approach 2:
The transparent layer is specifically designed to be optically transparent at the laser wavelength used for alignment detection. This optical property allows the alignment mark signal to pass through the layer without significant attenuation, maintaining detectability despite the presence of additional deposited layers.
3Manufacturing precision
If the alignment mark step height is reduced, then the wafer undergoes processing, but the alignment contrast and detection quality deteriorate
Solution Approach 1:
The solution moves from relying solely on vertical step height to utilizing a multi-layer structural arrangement. The bottom reflective layer provides a consistent reflective base, while the transparent layer and top pattern layer provide optical contrast through their structural arrangement rather than just height difference.
Solution Approach 2:
The alignment mark structure uses composite materials with different optical properties: a reflective material for the bottom layer, a transparent material for the intermediate layer, and patterned material for the top layer. This composite structure maintains detection quality by combining the reflective properties of the bottom layer with the optical transparency of the intermediate layer.
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 arrangement enhances alignment contrast and accuracy by maintaining detectability even after wafer processing, reducing wasted space and improving image contrast, thus facilitating precise circuit pattern alignment.
Implementation Method 1
each of the first stripes comprises a reflective layer
Implementation Method 2
a transparent layer allowing improved light passage
Implementation Method 3
The light from the laser beam is diffracted by the alignment marks, and the diffraction pattern is detected
Data Source
AI summary
An alignment mark arrangement includes: a first alignment pattern comprising a plurality of parallel first stripes on a substrate, wherein each of the first stripes includes a first dimension; and a second alignment pattern positioned directly above and overlapping with the first alignment pattern, the second alignment pattern including a plurality of parallel second stripes, wherein each of the second stripes of the second alignment pattern has a second dimension that is larger than the first dimension of each of the first stripes of the first alignment pattern.