Tungsten Film Formation for Low Resistivity and Surface Roughness
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Solution Overview
Problem
As semiconductor devices advance, the reduced line width, gate insulation film thickness, and junction depth make it difficult to achieve low gate resistance, and tungsten films face increased resistivity and surface roughness issues, leading to defects in subsequent processes.
Innovation Solution
A method involving the formation of a tungsten film in a stacked structure, where a low resistivity tungsten layer with an amorphous or β-phase nucleation layer is grown over a semiconductor substrate, followed by a physical vapor deposition process to create a second tungsten layer with a larger grain size, achieving low resistivity and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer tungsten film is formed by conventional methods, then the formation process is simple, but the film exhibits high resistivity and surface roughness
Solution Approach 1:
The tungsten film is divided into multiple layers with different phases and formation methods: a nucleation layer (amorphous or β-phase) formed by CVD/ALD, and overlying α-phase tungsten layers. This segmentation allows each layer to contribute different properties - the nucleation layer controls grain growth and resistivity, while subsequent layers provide structural integrity and low surface roughness.
Solution Approach 2:
The invention creates a composite tungsten film structure combining different crystalline phases (amorphous/β-phase nucleation layer with α-phase overlayers) and different deposition methodologies (CVD/ALD nucleation layer with PVD overlayers). This composite structure achieves superior electrical and surface properties that cannot be obtained with a single homogeneous layer.
2Productivity
If the gate critical dimension is reduced to increase integration, then device density increases, but gate resistance increases due to line width effects
Solution Approach 1:
The invention changes the physical and chemical parameters of the tungsten film by controlling the phase composition and grain structure through the multi-layer formation process. The nucleation layer is designed to promote large grain growth in the overlying α-phase tungsten, which reduces resistivity even when the gate dimensions are scaled down for higher integration density.
3Reliability
If a tungsten film with large grain size is formed to reduce resistivity, then electrical conductivity improves, but surface roughness increases causing defects in follow-up processes
Solution Approach 1:
The film is segmented into functional layers: the nucleation layer (formed by CVD/ALD) provides the grain growth template and resistivity control, while the subsequent α-phase tungsten layers (formed by PVD) provide a planarized surface with low roughness. This segmentation allows large grain size and smooth surface to coexist in different parts of the same film structure.
Solution Approach 2:
Different regions of the film structure have different qualities optimized for different functions: the nucleation layer has amorphous or β-phase structure optimized for grain growth control and low resistivity, while the overlying α-phase layers have crystalline structure optimized for surface planarity and mechanical stability.
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 method results in a tungsten film with low resistivity and improved surface roughness, enhancing the production yield and reliability of semiconductor devices by preventing defects in follow-up processes.
Implementation Method 1
The tungsten nucleation layer can be formed in a chemical vapor deposition process or an atomic layer deposition process
Implementation Method 2
The tungsten nucleation layer can be formed in a chemical vapor deposition process or an atomic layer deposition process
Implementation Method 3
forming a second tungsten layer over the first tungsten layer by a physical vapor deposition process
Data Source
AI summary
A method for forming a tungsten film includes forming a tungsten nucleation layer having an amorphous-phase or a β-phase over a semiconductor substrate. A first tungsten layer having a crystalline α-phase is then formed over the tungsten nucleation layer to form a low resistivity tungsten film. A second tungsten layer is formed over the first tungsten layer by a physical vapor deposition process, and the second tungsten layer has a large grain size similar to that of the low resistivity tungsten film. The tungsten film has both good surface roughness and low resistivity, thus enhancing the production yield and reliability of a semiconductor device.