Optical Semiconductor Device Resin Layer Thickness Control
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Solution Overview
Problem
The challenge in producing optical semiconductor devices, such as Mach-Zehnder modulators, lies in achieving uniformity in the thickness and etching rate of resin layers on semiconductor mesas, which affects the accuracy and reproducibility of electrode openings, leading to variations in device characteristics.
Innovation Solution
A method is developed to determine the in-plane distribution of resin layer thickness and etching rate, using a trench width map to adjust the trench structure, and applying a benzocyclobutene resin layer to ensure uniformity, involving steps like forming a mask pattern, etching the semiconductor layer, and applying the resin layer, with optional use of dummy semiconductor mesas to manage thermal expansion and capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin layer is applied onto a wafer with a semiconductor mesa formed, then the semiconductor mesa is buried and protected, but the resin layer thickness becomes non-uniform across the wafer plane, affecting opening formation accuracy
Solution Approach 1:
The patent applies different resin thicknesses to different regions of the wafer based on local requirements. By measuring the actual thickness distribution of the resin layer and adjusting the trench width locally, the patent ensures that each region achieves the desired opening uniformity while maintaining adequate protection of the semiconductor mesa. This local adaptation resolves the contradiction between providing uniform protection and achieving uniform opening formation.
Solution Approach 2:
The patent changes the trench width parameter in response to measured resin thickness variations. By determining a trench width map based on resin thickness measurements and using this map to adjust trench widths during device fabrication, the patent compensates for non-uniform resin thickness. This parameter adjustment allows the opening to be formed with high precision despite the inherent non-uniformity of the resin layer application process.
2Ease of manufacture
If an opening is formed by etching the resin layer, then the electrode can be electrically connected to the semiconductor mesa, but the etching rate exhibits in-plane distribution that affects opening shape and position variations
Solution Approach 1:
The patent implements a feedback mechanism where the actual resin thickness is measured and used to determine the required trench width. By measuring the resin layer thickness at multiple locations and using this information to adjust the trench width accordingly, the patent creates a closed-loop system that compensates for etching rate variations. This feedback approach ensures that openings are formed with high precision despite variations in etching rate across the wafer plane.
Solution Approach 2:
The patent performs preliminary measurements of resin thickness and determination of trench width maps before the actual device fabrication process. By preparing the trench width map in advance based on resin thickness measurements, the patent can then proceed with forming openings using pre-calculated trench dimensions. This preliminary action ensures that the opening formation process benefits from optimized parameters that account for resin thickness variations, thereby improving opening uniformity.
3Adaptability or versatility
If the mesa width is controlled to be several micrometers or less for single-mode waveguide operation, then the optical waveguide achieves single-mode operation, but the opening formation requires high accuracy and high reproducibility that is difficult to achieve
Solution Approach 1:
The patent changes the trench width parameter based on measured resin thickness to compensate for variations in opening formation. By determining a trench width map that accounts for local resin thickness variations, the patent can form openings with high precision even on narrow mesas. This parameter adjustment approach allows the opening to be formed with the required accuracy and reproducibility while maintaining the narrow mesa width necessary for single-mode waveguide operation.
Solution Approach 2:
The patent performs preliminary measurements and calculations to determine the optimal trench width before forming the opening. By measuring resin thickness and calculating the required trench width in advance, the patent can then proceed with opening formation using pre-determined parameters. This preliminary action ensures that the opening is formed with high accuracy on the narrow mesa, achieving both single-mode operation and high manufacturing precision.
Data Source
AI summary
A method for producing optical semiconductor devices includes: forming a stacked semiconductor layer on a device substrate to provide an epitaxial substrate having a size corresponding to a section arrangement; forming, on the epitaxial substrate, a mask having a pattern for a semiconductor mesa and for a trench of at least one optical semiconductor device, a width of the trench in the pattern being determined according to a trench width map in which trench width is based upon an in-plane distribution of the thickness of a resin layer of the at least one device, and upon a correlation between the thickness of the resin layer and the trench width; forming a trench structure including the semiconductor mesa and the trench by etching the stacked semiconductor layer using the mask; forming a resin layer on the trench structure; and forming an opening on the semiconductor mesa by etching the resin layer.