Optical Semiconductor Etching for Electrode Depth Control
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Solution Overview
Problem
In manufacturing optical semiconductor devices with high-mesa-shaped semiconductor optical waveguides embedded in resin, forming electrodes with different depths requires precise etching to avoid connection failures, particularly in creating openings in the buried layer for electrodes on both the upper surface of the mesa structure and the substrate, where existing methods struggle to achieve the necessary depth and width variations effectively.
Innovation Solution
A method involving multiple etching steps with resist masks and controlled gas mixing ratios of CF4 and O2 in reactive ion etching to form first and second openings with distinct depths and widths, allowing for the formation of electrodes connected to both the mesa structure and the substrate, with the second opening being deeper and wider than the first, and using the same photomask with varying exposure amounts to create resist masks with appropriate opening widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single etching process is used to form openings in the buried layer, then the manufacturing process is simple, but it is impossible to form openings with different depths required for electrodes on mesa structure and substrate
Solution Approach 1:
The single etching process is segmented into multiple etching steps with different resist masks. The first etching step forms a first opening to the mesa structure upper surface, and the second etching step forms a second opening deeper to the substrate principal surface. This segmentation allows each etching step to target specific depth requirements independently.
Solution Approach 2:
The first opening is formed in advance before forming the second opening. The first resist mask is applied and etched to create the first opening, then removed. Subsequently, the second resist mask is applied to form the second opening. This preliminary action ensures that the shallower opening is established before the deeper etching occurs.
2Manufacturing precision
If the second opening is made deeper to reach the substrate, then electrode connection to substrate is achieved, but the opening width becomes insufficient for proper electrode formation
Solution Approach 1:
The etching process parameters are dynamically adjusted between steps. The first etching step uses parameters optimized for creating an opening of appropriate width to the mesa surface. The second etching step uses different parameters to extend the opening depth to the substrate while maintaining sufficient width for electrode formation.
Solution Approach 2:
Etching parameters such as gas mixing ratios of CF4 and O2 are changed between the first and second etching steps. These parameter changes control the etching rate and selectivity, allowing the second opening to be formed deeper while maintaining adequate opening width for proper electrode connection.
3Manufacturing precision
If different resist masks are used for first and second etching steps, then openings with different depths and widths are achieved, but the manufacturing process complexity increases
Solution Approach 1:
The resist masking process is segmented into two separate steps, each with its own resist mask application, exposure, and removal. The first resist mask controls the first opening dimensions, and the second resist mask controls the second opening dimensions. This segmentation enables precise control over opening depth and width for each electrode type.
Solution Approach 2:
The first resist mask is applied and processed in advance to define the first opening. After removal, the second resist mask is applied to define the second opening. This preliminary action sequence allows each resist mask to be optimized for its specific opening requirements without interference from the other.
4Reliability
If the buried layer is etched deeply to connect to the substrate, then substrate electrode connection is achieved, but connection failures may occur due to improper opening dimensions
Solution Approach 1:
The etching process incorporates feedback control through careful sequencing. The first etching step creates a controlled opening to the mesa surface, and only after this is complete and the first resist mask is removed does the second etching step proceed to the substrate. This feedback-based sequencing ensures each opening is properly formed before the next step, preventing connection failures.
Solution Approach 2:
The process cushions against connection failures by forming the first opening and removing the first resist mask before proceeding to the second etching step. This intermediate step acts as a cushion, allowing verification and preparation before the critical second etching that creates the deeper substrate connection, thereby preventing premature or improper etching that could cause connection failures.
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 ensures reliable connection of electrodes by controlling etching rates and resist mask behavior, preventing connection failures and improving the frequency characteristics of optical semiconductor devices like Mach-Zehnder modulators by embedding mesa structures in low dielectric constant resins like benzocyclobutene.
Implementation Method 1
controlled gas mixing ratios of CF4 and O2 in reactive ion etching to form first and second openings with distinct depths and widths
Implementation Method 2
using the same photomask with varying exposure amounts to create resist masks with appropriate opening widths
Data Source
AI summary
A method for manufacturing an optical semiconductor device includes the steps of preparing a substrate product including a semiconductor layer, a mesa structure, and a protective layer; forming a buried layer composed of a resin on the substrate product; forming a first opening in the buried layer on the mesa structure; forming a second opening in the buried layer on the semiconductor layer; exposing the mesa structure and the semiconductor layer by etching the protective layer; forming a first electrode in the first opening; and forming a second electrode in the second opening. The step of forming the second opening includes a first etching step including etching the buried layer using a first resist mask for forming a recess and a second etching step including etching the buried layer using a second resist mask having an opening pattern which has an opening width not smaller than that of the recess.