TSV Tungsten Cap Layer for Copper Protection
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Solution Overview
Problem
Existing through-silicon via (TSV) technologies face challenges in achieving reliable electrical connections and structural integrity for stacked chips, particularly in the integration of conductive materials and insulation layers, which can lead to performance issues and damage during processing.
Innovation Solution
A TSV structure is developed with a semiconductor substrate, inter-metal dielectric layers, a cap layer, a conductive layer extending through the substrate, a tungsten film capping the conductive layer, and interconnect features within the IMD layers, utilizing selective tungsten chemical vapor deposition and copper damascene processes to enhance electrical performance and minimize damage during processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional TSV fabrication processes are used, then through-vias can be formed to connect stacked chips, but damage occurs during processing and electrical performance deteriorates due to indirect contact between conductive materials and tungsten surfaces
Solution Approach 1:
A tungsten film is deposited over the conductive layer (copper) before back-grinding, creating a protective cap that prevents direct exposure and damage to the copper during subsequent processing steps. This preliminary protective action eliminates the need for copper to be directly contact with grinding tools and prevents oxidation and contamination.
Solution Approach 2:
The tungsten film serves as an intermediary protective layer between the copper conductive material and the external environment during back-grinding. This intermediary layer allows the copper to maintain its integrity while still enabling electrical connection through the tungsten cap to the upper chip's TSV.
2Productivity
If back-grinding is performed to expose TSVs, then chips can be stacked and connected, but the copper conductive layer is exposed to damage and oxidation
Solution Approach 1:
The tungsten film is deposited beforehand to create a protective cap over the copper layer before back-grinding occurs. This preliminary action ensures that when the substrate is ground to expose the TSV, the copper remains protected while the tungsten is selectively removed or exposed to create the electrical connection interface.
Solution Approach 2:
The selective removal of tungsten cap material through etching or selective grinding changes the material composition at the TSV opening, allowing copper to be exposed only where needed for electrical connection while maintaining protection in other areas. This parameter change enables controlled exposure for connectivity while preserving integrity.
3Reliability
If copper is used as the conductive material in TSV, then electrical conductivity is improved, but copper is vulnerable to damage during back-grinding and processing
Solution Approach 1:
The TSV structure uses a composite material system combining copper (for high electrical conductivity) with a tungsten cap layer (for mechanical strength and protection). This composite structure leverages the advantages of both materials: copper provides superior electrical performance while the tungsten cap provides the mechanical strength needed to withstand back-grinding and processing.
Solution Approach 2:
The tungsten cap acts as an intermediary protective layer that shields the soft, vulnerable copper from mechanical damage during back-grinding. The tungsten's high hardness and strength properties protect the copper underneath while allowing the copper to maintain its electrical functionality.
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 solution improves the electrical performance of copper interconnects by ensuring direct contact with tungsten surfaces and reduces damage from processing steps, resulting in a robust and efficient connection method for stacked chips.
Implementation Method 1
utilizing selective tungsten chemical vapor deposition
Implementation Method 2
a metal is filled into the vertical hole through an electroplating process to form a TSV
Data Source
AI summary
A through silicon via (TSV) structure including a semiconductor substrate; a first inter-metal dielectric (IMD) layer on the semiconductor substrate; a cap layer overlying the IMD layer; a conductive layer extending through the cap layer, the first IMD layer and into the semiconductor substrate; a tungsten film capping a top surface of the conductive layer; a second IMD layer overlying the cap layer and covering the tungsten film; and an interconnect feature in the second IMD layer.