SOI Substrate Surface Flattening via Recessed Mask Oxide
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Solution Overview
Problem
Conventional methods for manufacturing Silicon-On-Insulator (SOI) substrates with buried oxide films face issues such as uneven surface topography, exposure of buried oxide film edges, and non-uniform oxidation, leading to substrate surface irregularities and potential defects in device fabrication.
Innovation Solution
The method involves forming a mask oxide film, implanting oxygen ions, and annealing to create a buried oxide film, with additional steps like forming recess portions, using buffer films, and adjusting mask oxide film thickness to ensure uniformity and prevent edge exposure, thereby achieving a flush substrate surface and consistent oxide film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If oxygen ions are implanted into the substrate surface to form a buried oxide film, then the oxide film is formed inside the substrate, but the edge area of the buried oxide film becomes exposed on the substrate surface due to expansion during annealing
Solution Approach 1:
A recess portion is formed in advance at the edge area of the substrate surface before oxygen ion implantation. This preliminary action compensates for the expected expansion of the buried oxide film during annealing, preventing the film edge from exposing on the substrate surface and maintaining surface flatness.
Solution Approach 2:
The recess portion acts as a preliminary countermeasure against the harmful effect of oxide film expansion. By creating a depression in advance, the method anticipates and neutralizes the surface elevation that would otherwise occur when the oxide film expands during annealing.
2Reliability
If the substrate is annealed at high temperature to form the buried oxide film, then oxidation occurs to create the oxide film, but uneven oxidation and non-uniform oxide film thickness result
Solution Approach 1:
Different regions of the substrate are treated differently: the edge area has a recess portion while the central area maintains the original surface level. This local differentiation ensures uniform oxidation conditions across the substrate, as the recess portion compensates for edge effects during annealing, resulting in uniform oxide film thickness throughout.
3Productivity
If conventional photolithography is performed on substrates with uneven surfaces, then device fabrication proceeds, but focus shift occurs and photolithography accuracy deteriorates
Solution Approach 1:
The recess portion is formed in advance to pre-compensate for surface unevenness. This preliminary surface preparation ensures that when photolithography is subsequently performed, the substrate surface is sufficiently flat to maintain focus and achieve accurate patterning, preventing focus shift and maintaining photolithography accuracy.
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 allows for the accurate flattening of SOI substrate surfaces, prevents edge exposure of buried oxide films, and ensures uniform oxide film thickness, reducing defects and improving the reliability of subsequent photolithography processes.
Implementation Method 1
implanting oxygen ions, and annealing to create a buried oxide film
Implementation Method 2
annealing to create a buried oxide film
Implementation Method 3
annealing to create a buried oxide film
Data Source
AI summary
To easily and accurately flush a substrate surface serving an SOI area with a substrate surface serving as a bulk area, make a buried oxide film, and prevent an oxide film from being exposed on substrate surface. After partially forming a mask oxide film 23 on the surface of a substrate 12 constituted of single crystal silicon, oxygen ions 16 are implanted into the surface of the substrate through the mask oxide film, and the substrate is annealed to form an buried oxide film 13 inside the substrate. Further included is a step of forming a predetermined-depth concave portion 12c deeper than substrate surface 12b serving as a bulk area on which the mask oxide film is formed on the substrate surface 12a serving as an SOI area by forming a thermally grown oxide film 21 on the substrate surface 12a serving as an SOI area on which the mask oxide film is not formed between the step of forming the mask oxide film and the step of implanting oxygen ions.