ScAlN Etch Mask for High Selectivity DRIE
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Solution Overview
Problem
Current etch masks for deep reactive ion etching (DRIE) in semiconductor fabrication face challenges with micromasking and low etch mask selectivity, particularly in fluorine-based chemistries, leading to undesired artifacts and increased wafer bowing due to high sputtering rates and micromasking effects.
Innovation Solution
The use of ScAlN as an etch mask material, which is chemically nonvolatile in fluorine-based etch chemistries and has a low sputter yield, providing high etch mask selectivity relative to silicon and other semiconductor materials, thereby reducing micromasking and wafer bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etch masks (Cr, Ni, Al, Ga, Al2O3) are used in fluorine-based DRIE, then etch mask selectivity is improved, but micromasking and sputtering artifacts increase due to nonvolatile reaction products
Solution Approach 1:
The patent changes the material composition parameter by introducing ScAlN (scandium aluminum nitride) as the etch mask material. This material composition has unique properties: it is chemically nonvolatile in fluorine-based etch chemistries and exhibits low sputter yield, thereby resolving the contradiction between maintaining high etch mask selectivity and avoiding micromasking artifacts
Solution Approach 2:
The patent uses ScAlN, a composite material consisting of scandium, aluminum, and nitrogen in specific ratios. This composite material combines the benefits of chemical inertness with low sputter yield, achieving both high etch mask selectivity and minimal micromasking effects that conventional single materials cannot provide
2Manufacturing precision
If thicker etch mask films are used to improve selectivity, then etch mask selectivity increases, but wafer bow induced by film stress increases and deposition time increases
Solution Approach 1:
The patent changes the material property parameter by selecting ScAlN with inherently low sputter yield and appropriate stress characteristics. This allows the use of thinner etch mask films (reducing wafer bow and deposition time) while maintaining high etch mask selectivity, thus resolving the contradiction between selectivity and film thickness
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
ScAlN etch masks significantly improve etch mask selectivity and reduce micromasking, enabling deeper and higher aspect ratio structures with lower sputtering rates, resulting in higher fidelity feature transfer and reduced wafer bowing, thus enhancing semiconductor fabrication processes.
Implementation Method 1
Etch mask selectivity is typically controlled by two major etching mechanisms in plasma etch techniques: chemical etching and physical sputtering. For nonreactive etch mask materials, neutrals and radicals in the etching processes are less important to etch mask selectivity than ion impingement.
Implementation Method 2
Etch masks which do not chemically react with fluorine, such as Cr, Ni, Al, Ga, and Al2O3, have higher selectivity to silicon than those that can react with fluorine to produce volatile compounds. ScAlN etch mask material is chemically nonvolatile in fluorine-based etch chemistries.
Implementation Method 3
silicon and germanium are energetically favorable to react with fluorine to produce volatile silicon tetrafluoride (SiF4) and germanium tetrafluoride (GeF4)
Implementation Method 4
Etch mask selectivity is typically controlled by two major etching mechanisms in plasma etch techniques: chemical etching and physical sputtering.
Data Source
AI summary
A fabrication process employing the use of ScAlN as an etch mask is disclosed. The ScAlN etch mask is chemically nonvolatile in fluorine-based etch chemistries and has a low sputter yield, resulting in greater etch mask selectivity and reduced surface roughness for silicon and other semiconductor materials. The ScAlN etch mask has an etch mask selectivity of greater than 200,000:1 relative to silicon compared to an etch mask selectivity of less than 40,000:1 for a prior art AlN etch mask relative to silicon. Further, due to reduced sputtering of the ScAlN etch mask, and thus reduced micromasking, the ScAlN etch mask yielded a surface roughness of 0.6 μm compared to a surface roughness of 2.8 μm for an AlN etch mask.