SiC Substrate Alignment Mark Contour Stability
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Solution Overview
Problem
The conventional method of forming alignment marks on silicon carbide semiconductor substrates results in contour changes and positional deviations after epitaxial layer growth, leading to difficulties in reducing element size and increasing ON-resistance.
Innovation Solution
A fabrication method involving a silicon carbide substrate with a tilted c-axis, where a convex-shaped alignment mark is formed and covered by an epitaxial layer, ensuring the width of the alignment mark satisfies a specific relationship with the film thickness to prevent contour deformation and positional deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional alignment mark is formed by removing the oxide layer and substrate surface, then the alignment mark can be used for photomask alignment, but the alignment mark contour changes and positional deviation occurs after epitaxial layer growth
Solution Approach 1:
The patent applies preliminary action by forming a convex-shaped alignment mark that protrudes from the substrate surface before epitaxial layer growth. This pre-formed convex structure ensures that when the epitaxial layer is grown, it uniformly covers the alignment mark without causing contour changes or positional deviations, thus maintaining alignment mark recognition accuracy throughout the fabrication process.
Solution Approach 2:
The patent inverts the conventional approach by forming a convex alignment mark instead of a concave one. While conventional methods remove material to create凹-shaped marks, this patent creates凸-shaped marks that protrude from the surface. This inversion prevents the alignment mark contour from changing during epitaxial growth, eliminating positional deviation and maintaining manufacturing precision.
2Productivity
If the element size is reduced to increase device density, then productivity improves, but alignment mark recognition becomes difficult and ON-resistance increases
Solution Approach 1:
The patent applies asymmetry by designing a cross-shaped alignment mark with unequal arm lengths (first arm length different from second arm length). This asymmetric design creates a unique, easily recognizable pattern that maintains high measurement precision even when element sizes are reduced. The asymmetric cross shape allows photomasks to accurately recognize alignment marks in smaller devices, enabling increased device density without sacrificing alignment accuracy.
Solution Approach 2:
The patent transitions from traditional two-dimensional planar alignment marks to a three-dimensional convex-shaped alignment mark that protrudes from the substrate surface. This dimensional change creates a more prominent, easily recognizable feature that maintains alignment precision even when element sizes are reduced, thus supporting higher device density while preserving measurement accuracy.
3Manufacturing precision
If a convex-shaped alignment mark is formed and covered by epitaxial layer with specific width relationship, then contour stability is maintained, but the fabrication process becomes more complex
Solution Approach 1:
The patent applies parameter changes by establishing a specific mathematical relationship between the alignment mark width (W) and epitaxial layer thickness (T), where W ≥ 2T. By controlling these parameters to satisfy this relationship, the patent maintains alignment mark contour stability during epitaxial growth without requiring complex additional fabrication steps. This parameter-based approach simplifies the overall process while ensuring manufacturing precision.
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 method allows for accurate recognition of the alignment mark by photomasks, enabling reduced element size and lower ON-resistance by maintaining the alignment mark's contour and position, thus facilitating the production of smaller, more efficient silicon carbide semiconductor devices.
Implementation Method 1
growing an epitaxial layer on the principal surface of the silicon carbide substrate to cover the alignment mark
Data Source
AI summary
A (000-1) C-plane of an n− type silicon carbide substrate having an off-angle θ in a <11-20> direction is defined as a principal plane, and a periphery of a portion of this principal surface layer defined as an alignment mark is selectively removed to leave the convex-shaped alignment mark. The alignment mark has a cross-like plane shape such that two rectangles having longitudinal dimensions tilted by 45 degrees relative to the <11-20> direction are orthogonal to each other. When a film thickness of a p− type epitaxial layer is Y; a width of the alignment mark parallel to the principal surface of the n− type silicon carbide substrate is X; and an off-angle of the n− type silicon carbide substrate is θ, an epitaxial layer is formed on an upper surface of the alignment mark such that Y≧X·tan θ is satisfied.