Covered Through-Substrate Via Fabrication Using Sacrificial Cap Layer
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Solution Overview
Problem
The existing methods for producing through-substrate vias in semiconductor substrates face challenges such as material sagging, contamination, and stress-induced cracks due to thermal expansion differences between the substrate and conductive materials, which complicate the deposition of passivation layers and increase processing costs.
Innovation Solution
A method involving a sacrificial cap layer that is thermally stable below a threshold temperature and decomposes at higher temperatures, allowing for temporary coverage and filling of substrate trenches, followed by decomposition and removal of the cap layer to prevent contamination and stress, enabling the deposition of passivation layers and conductive materials without cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a through-hole is formed in the substrate to create a through-substrate via, then electrical connection between first and second substrate sides is achieved, but material deposited on either side of the substrate sags into the hole and contamination occurs due to capillary action
Solution Approach 1:
A cap layer is deposited on the first substrate side before forming the through-hole, preliminarily covering the future via location. This preliminary action prevents material sagging and contamination by blocking the opening before subsequent processing steps occur.
Solution Approach 2:
The cap layer acts as an intermediary element between the substrate surface and the environment. It temporarily covers the via opening during processing, preventing harmful interactions between deposited materials and the via interior, then is selectively removed to allow via formation.
2Reliability
If conductive material is filled into the through-hole to form a through-substrate via, then electrical conductivity is improved, but stress is induced in the substrate due to thermal expansion differences during subsequent high-temperature processing
Solution Approach 1:
The cap layer is deposited before filling the via with conductive material. This preliminary coverage allows the via to be formed and filled while protecting the substrate from stress-induced cracking during subsequent high-temperature processing steps.
Solution Approach 2:
The cap layer provides beforehand cushioning by covering the via opening before high-temperature processing. This protective layer prevents stress concentration at the via-substrate interface that would otherwise lead to cracking during thermal expansion cycles.
3Ease of manufacture
If wet-chemical deposition is used to fill the through-hole, then ease of manufacture is improved, but contamination of the trench and completed via occurs due to capillary action
Solution Approach 1:
The cap layer serves as an intermediary barrier during wet-chemical deposition processes. It prevents deposition solutions from entering the via via capillary action, thereby avoiding contamination while allowing the deposition process to proceed on other substrate areas.
Solution Approach 2:
The harmful effect of capillary action is eliminated by taking out the opening from the system - the cap layer effectively removes the via opening from exposure to wet-chemical processes, preventing contamination while maintaining manufacturing simplicity.
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 allows for the production of covered through-substrate vias that facilitate the deposition of passivation layers and the use of better conductive materials, reducing stress and contamination, and enabling the integration of complex circuits and RF capacitors while maintaining a flat substrate surface for further processing.
Implementation Method 1
a sacrificial cap layer that is thermally stable below a threshold temperature and decomposes at temperatures higher than the threshold temperature
Implementation Method 2
The cap-layer material is removed by evaporation or sublimation
Implementation Method 3
In such treatments the metal in the through-substrate via expands more than the silicon substrate, leading to the stress
Data Source
AI summary
The present invention relates to a method for producing a substrate with at least one covered via that electrically and preferably also thermally connects a first substrate side with an opposite second substrate side. The processing involves forming a trench on a the first substrate side remains and covering the trench with a permanent layer on top of a temporary, sacrificial cap-layer, which is decomposed in a thermal process step. The method of the invention provides alternative ways to remove decomposition products of the sacrificial cap-layer material without remaining traces or contamination even in the presence of the permanent layer. This is, according to a first aspect of the invention, achieved by providing the substrate trench with an overcoat layer that has holes. The holes in the overcoat layer leave room for the removal of the decomposition products of the cap-layer material. According to the second aspect of the invention, opening the covered trench from the second substrate side and allowing the cap-layer material to be removed through that opening provides a solution. Both methods of the present invention are based on the common idea of using a temporary cap-layer even in a situation where the substrate opening is permanently covered before the removal of the temporary cap-layer.