Thick Copper Conductor Patterning With Multi-Step Isotropic Etching
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Solution Overview
Problem
Current low-cost copper patterning processes, such as isotropic copper wet etching, produce low-aspect ratio conductors due to undesirable lateral etch (undercut), which inhibits the scaling down of core pattern feature sizes and fails to meet future design rule forecasts for increased line-space resolution in large power conductors.
Innovation Solution
A multi-step subtractive isotropic etch (MSIEP) process is employed to form high-aspect ratio thick conductors by using a dual or multiple-step isotropic etching method with negative-tone and positive-tone photoresists to control lateral and vertical etch dimensions, allowing for precise formation of high-aspect ratio conductors without significant substrate copper thickness limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If isotropic copper wet etching is used for copper patterning, then the process is low-cost and simple, but lateral etch (undercut) occurs which limits aspect ratio and prevents scaling to finer line-space dimensions
Solution Approach 1:
The patent divides the single etching operation into multiple sequential etching steps (first isotropic etch, second isotropic etch, third isotropic etch) with different photoresist masking strategies. Each step removes a portion of the copper layer, progressively achieving the final high-aspect-ratio conductor pattern while minimizing lateral undercut through controlled masking at each stage.
Solution Approach 2:
The patent applies photoresist masks before each etching step to predefine the boundaries of the conductor patterns. The first photoresist is applied to protect areas where conductors should remain, the second photoresist is applied to protect sidewalls during the second etch, and the third photoresist is applied for the final etching step, ensuring precise dimensional control throughout the process.
2Quantity of substance
If copper thickness is increased to meet power conductor requirements, then current carrying capacity improves, but undercut becomes more significant due to isotropic etching nature
Solution Approach 1:
The multi-step etching process segments the removal of thick copper layers into controlled portions. Each etching step removes a specific thickness range with appropriate photoresist protection, enabling the formation of high-aspect-ratio conductors from thick copper foils (e.g., 35 microns or more) while maintaining precise dimensional control and minimizing cumulative lateral undercut.
Solution Approach 2:
The patent transitions from controlling etching in a single dimension to controlling etching across multiple dimensions through sequential steps. By applying photoresist masks at different stages and performing multiple etching operations, the process achieves precise control over both vertical depth and lateral dimensions, enabling high aspect ratios even with thick copper starting material.
3Productivity
If single-step isotropic etching is used, then the process is simple and fast, but line-space resolution cannot meet future design rule forecasts
Solution Approach 1:
The patent segments the etching process into multiple steps, each optimized for specific dimensional control. The first etching step creates initial cavities with protective photoresist, the second etching step refines the pattern with sidewall protection, and the third etching step achieves final precision. This segmentation maintains relatively high productivity while achieving the fine line-space resolution required for future design rules.
Solution Approach 2:
Photoresist masks are applied in advance before each etching step to pre-establish the conductor pattern boundaries. The first photoresist defines the initial pattern, the second photoresist protects sidewalls during refinement, and the third photoresist ensures final dimensional accuracy. This preliminary masking action enables the multi-step process to achieve high resolution without excessive complexity or time penalty.
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
The MSIEP process enables continuous scaling of power conductors to meet future design rules by achieving high-aspect ratio conductors with controlled dimensions, reducing undercut issues and enabling finer line widths and spacing, thus overcoming the limitations of existing isotropic etch processes.
Implementation Method 1
shallow cavities are formed by isotropic chemical etching of exposed copper within the openings in the negative photoresist etch mask
Implementation Method 2
A negative-tone photoresist is deposited over the copper layer and lithographically patterned with an array of openings
Implementation Method 3
The liquid photoresist is patterned by illuminating it with UV light through a second lithographically-patterned photomask to form openings in the liquid photoresist within the cavities
Data Source
AI summary
An integrated circuit device, comprising a substrate comprising a dielectric material and a conductor on or within the dielectric material of the substrate. The conductor comprises a first portion comprising a first sloped sidewall, wherein a first base width of the first portion is greater than a first top width of the first portion. The conductor also comprises a second portion over the first portion, the second portion comprising a second sloped sidewall, wherein a second base width of the upper portion is greater than both a second top width of the second portion and the first top width of the first portion.