Tungsten Gap Fill Stack for Low Stress and Low Resistivity
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Solution Overview
Problem
Current semiconductor technologies face challenges in achieving both low resistivity and low stress tungsten fill solutions with reasonable gap fill performance, as existing methods using chemical vapor deposition of tungsten are at their limits and result in high tensile stress and limited resistivity reduction.
Innovation Solution
The proposed method involves a physical vapor deposition of a tungsten liner, followed by an atomic layer deposition nucleation layer and a chemical vapor deposition bulk fill process, with a nitridation step and optional rapid thermal processing to reduce internal stresses and lower resistivity, using argon or krypton as ambient gases and optimizing temperature, pressure, and nitridation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chemical vapor deposition of tungsten is used, then tungsten fill can be achieved, but high tensile stress and limited resistivity reduction occur
Solution Approach 1:
The tungsten fill process is divided into multiple stages: PVD tungsten liner deposition, ALD nucleation layer formation, and CVD bulk fill deposition. This segmentation allows each stage to be optimized independently, with PVD providing low-stress liner and CVD providing bulk fill, achieving both low stress and good gap fill performance
Solution Approach 2:
The patent changes deposition parameters including using high ionization PVD with argon or krypton ambient gas, controlling deposition temperature between 20-500°C, and adjusting pressure between 5-300 Torr. These parameter changes optimize the tungsten fill process to achieve low stress and low resistivity simultaneously
2Stress or pressure
If rapid thermal processing is performed at high temperature, then internal stresses are reduced and resistivity is lowered, but process complexity increases
Solution Approach 1:
Rapid thermal processing utilizes controlled heating and cooling cycles to induce phase transitions in tungsten, reducing internal stress and resistivity. The quick heating to 700-900°C and controlled cooling creates beneficial microstructural changes without requiring prolonged high-temperature exposure
Solution Approach 2:
The PVD tungsten liner is deposited first with specific properties that prepare the structure for subsequent RTP. The liner's low stress characteristics and adhesion properties are established beforehand, making the RTP process more effective and reducing the need for additional process steps
3Stress or pressure
If physical vapor deposition with high ionization is used, then low stress and low resistivity are achieved, but adhesion issues may occur
Solution Approach 1:
An ALD nucleation layer is introduced as an intermediary between the PVD tungsten liner and the CVD bulk fill. This nucleation layer improves adhesion and provides a transition zone that maintains the low-stress, low-resistivity properties while ensuring good interfacial bonding
Solution Approach 2:
Different regions of the tungsten fill have different properties: the PVD liner region has low stress and low resistivity, while the ALD nucleation layer provides adhesion enhancement. This local differentiation of material properties allows simultaneous optimization of multiple competing requirements
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 approach effectively reduces internal stresses by 10-50% and resistivity by 30-45% compared to conventional methods, while maintaining high throughput and avoiding adhesion issues, and is suitable for high aspect ratio structures without void formation.
Implementation Method 1
depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process
Implementation Method 2
depositing a nucleation layer using an atomic layer deposition (ALD) process
Implementation Method 3
depositing bulk fill tungsten into the structure using a chemical vapor deposition (CVD) process
Implementation Method 4
treating the structure with a nitridation process
Implementation Method 5
performing a rapid thermal process (RTP) on the structure, wherein the RTP is configured to reduce internal stresses of the bulk fill tungsten and to lower resistivity of the bulk fill tungsten
Data Source
AI summary
Method for forming tungsten gap fill on a structure, including high aspect ratio structures includes depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process with high ionization and an ambient gas of argon or krypton. The PVD process is performed at a temperature of approximately 20 degrees Celsius to approximately 300 degrees Celsius. The method further includes treating the structure with a nitridation process and depositing bulk fill tungsten into the structure using a chemical vapor deposition (CVD) process to form a seam suppressed boron free tungsten fill. The CVD process is performed at a temperature of approximately 300 degrees Celsius to approximately 500 degrees Celsius and at a pressure of approximately 5 Torr to approximately 300 Torr.