DRIE Sidewall Smoothing via Intermediate Oxygen Plasma Cleaning
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Solution Overview
Problem
Deep Reactive Ion Etching (DRIE) processes for producing through-substrate vias often result in sidewall defects like undulation and vertical striations, leading to electrical shorts and increased leakage currents due to the buildup of passivation layers and polymer deposition.
Innovation Solution
The method involves interrupting the etching and passivating cycles with an additional etching step using a different etchant, such as oxygen plasma, to selectively remove the passivation layer from the sidewall, thereby reducing defects and achieving smoother sidewalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If deep reactive ion etching with alternating etching and passivation cycles is performed, then deep openings can be etched through the substrate, but the sidewall becomes undulated with striations and roughness
Solution Approach 1:
The patent applies periodic action by introducing intermediate cleaning cycles at specific intervals (after 50-200 cycles) during the deep reactive ion etching process. These cleaning cycles use oxygen plasma to periodically remove polymer deposits from sidewalls, interrupting the continuous build-up of undulations while maintaining the overall periodic etching-passivation cycle structure needed for deep etching
Solution Approach 2:
The patent changes process parameters by switching between different gas chemistries (SF6 for etching, C4F8 for passivation, and O2 for cleaning) and adjusting cycle timings. The intermediate cleaning step introduces a new parameter dimension (oxygen plasma exposure) that modifies the sidewall condition without significantly affecting the overall etch depth or rate
2Productivity
If the etching cycle continues without interruption, then the etching rate is maintained, but polymer deposits accumulate on the sidewall causing pocketing defects
Solution Approach 1:
The patent applies the skipping principle by rapidly performing intermediate cleaning steps at strategically chosen intervals to remove accumulating polymer deposits before they can cause pocketing defects. This brief interruption skips the harmful accumulation phase while maintaining overall high productivity through efficient cycle management
Solution Approach 2:
The oxygen plasma cleaning step acts as an intermediary process between the SF6 etching cycles. It temporarily removes polymer deposits that would otherwise accumulate and cause defects, serving as a mediating step that protects the sidewall integrity without significantly disrupting the overall etching progress
3Manufacturing precision
If short etching cycles are used, then smoother sidewalls are achieved, but the total process time increases significantly
Solution Approach 1:
The patent uses periodic action by implementing intermediate cleaning cycles at optimized intervals (after 50-200 etching cycles) rather than after every single cycle. This periodic intervention maintains sidewall smoothness comparable to short-cycle processing while dramatically reducing the total number of cleaning steps needed, thus avoiding excessive process time extension
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 significantly reduces sidewall defects and improves the yield of semiconductor devices by eliminating or minimizing 'pocketing' issues, resulting in reduced leakage currents and smoother sidewalls, with a demonstrated improvement in production efficiency.
Implementation Method 1
The passivation layer is typically formed from a polymer former contained in the plasma and may comprise C4F8, octafluorocyclobutane, for instance. The passivation layer is formed by polymerization.
Implementation Method 2
Silicon is removed by plasma etching using a reactive etching gas. A standard, essentially isotropic plasma etching is performed to etch a deep opening in silicon. The plasma may comprise SF6, sulfur hexafluoride, for instance.
Implementation Method 3
an oxygen plasma is employed in the additional etching
Data Source
AI summary
An opening (17) is etched from a main surface (10) of a substrate (1) of semiconductor material by deep reactive ion etching comprising a plurality of cycles, each of the cycles including a deposition of a passivation in the opening and an application of an etchant. An additional etching is performed between two consecutive cycles by an application of a further etchant that is different from the etchant. The passivation layer (9) is thus etched above a sidewall (7) of the opening to remove undesired protrusions.