SF6 Etching of Silicon Substrates with Copper Oxide Protection
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Solution Overview
Problem
Conventional methods for thinning silicon substrates to expose through-silicon vias (TSVs) in 3D-stacking are inefficient, leading to inconsistent protrusion heights and microtrenching, and existing etch chemistries are slow and non-selective, causing copper sulfide formation which corrodes the TSVs.
Innovation Solution
The use of a sulfur hexafluoride (SF6)-containing etchant for selective removal of silicon substrates relative to copper features, with an initial oxidation step to form copper oxide that protects the copper from corrosion, allowing for faster and more controlled etching without forming copper sulfide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional etch chemistries (KOH, NH4OH, TMAH, HBr/O2, CF4, NF3) are used to remove silicon substrate, then the substrate can be thinned to expose TSV ends, but the etch rate is slow and the process is not selective to oxides
Solution Approach 1:
An oxide layer is formed on the copper-filled TSV before the etching process. This preliminary oxidation creates a protective barrier that prevents copper sulfide formation during SF6 etching, enabling faster etching rates while maintaining selectivity and preventing corrosion of the TSV structure
Solution Approach 2:
The patent changes the chemical parameters of the etching process by using SF6-based chemistry instead of conventional etchants. This parameter change enables significantly faster etch rates (up to 8 times faster) while the preliminary oxidation step maintains selectivity by protecting the copper from reacting with the sulfur-containing etchant
2Speed
If bias RF power is used to speed up the etch rate, then the etching process becomes faster, but microtrenching of the substrate material occurs along exposed features
Solution Approach 1:
The patent changes the etching chemistry from conventional methods to SF6-based chemistry, which enables faster etch rates without causing microtrenching. The combination of SF6 etchant with preliminary oxidation creates a protective oxide layer on copper features, allowing the use of higher RF power settings to accelerate etching while maintaining smooth substrate surfaces without microtrench defects
3Speed
If SF6-containing etchant is used to remove substrate at faster rate, then the etch rate increases significantly, but copper sulfide forms on the copper-filled TSV causing corrosion and connectivity issues
Solution Approach 1:
The key solution is to form an oxide layer on the copper-filled TSV before applying the SF6-containing etchant. This preliminary oxidation step creates a protective barrier that prevents the sulfur in the SF6 etchant from reacting with the copper, thereby eliminating copper sulfide formation while maintaining the fast etch rate benefits of SF6 chemistry
Solution Approach 2:
The oxide layer acts as an intermediary protective layer between the copper-filled TSV and the SF6-containing etchant. This intermediate oxide barrier prevents direct contact and harmful chemical reaction between sulfur and copper, allowing the etching process to proceed rapidly without generating copper sulfide corrosion products
4Manufacturing precision
If grinding or polishing is used to thin the substrate and expose TSV ends, then the TSV protrusion can be achieved, but the protrusion height is inconsistent (no more than a few hundred microns)
Solution Approach 1:
The patent replaces mechanical thinning processes (grinding, polishing) with a chemical etching process using SF6-based chemistry. This substitution enables precise control of substrate thinning to achieve consistent TSV protrusion heights while improving productivity through faster etch rates. The process provides better controllability and consistency in protrusion height compared to mechanical methods
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 enables faster and more selective etching of silicon substrates, preventing copper sulfide formation and improving the consistency and connectivity of TSVs in 3D-stacking, enhancing the performance of 3D-integrated circuits.
Implementation Method 1
oxidizing a semiconductor structure comprising a substrate and at least one copper feature
Implementation Method 2
A portion of the substrate is removed using an etchant comprising sulfur hexafluoride (SF6) without forming copper sulfide on the at least one copper feature
Data Source
AI summary
A method for selectively removing material from a substrate without damage to copper filling a via and extending at least partially through the substrate. The method comprises oxidizing a semiconductor structure comprising a substrate and at least one copper feature and removing a portion of the substrate using an etchant comprising SF6 without forming copper sulfide on the at least one copper feature. Additional methods are also disclosed, as well as semiconductor structures produced from such methods.