PVD Tungsten Film Deposition for Resistivity and Stress Control
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Solution Overview
Problem
Existing semiconductor device materials like Cu exhibit high resistivity as thickness decreases, necessitating the use of materials like tungsten (W) with lower resistivity, but current PVD processes struggle to control grain size and stress effectively.
Innovation Solution
A method involving a first deposition step at low power density, followed by RF bias treatment, and a second deposition step at higher power density, repeated 1 to 4 times, to enhance grain size and orientation of tungsten films, controlling stress and resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-step PVD deposition is performed at constant DC power, then the deposition process is simple and fast, but the grain size and orientation of the tungsten film cannot be effectively controlled
Solution Approach 1:
The deposition process is divided into multiple distinct steps: initial deposition at low DC power density (<0.5 W/cm²), followed by RF bias treatment, then additional deposition at higher DC power density (≥0.5 W/cm²). This segmentation allows each step to serve a specific function - the low power initial deposition promotes grain growth and orientation, while the subsequent high power deposition builds up the film thickness efficiently.
Solution Approach 2:
The process employs periodic alternation between deposition and plasma treatment cycles, repeated 1-4 times. Each cycle consists of initial low-power deposition, RF bias plasma treatment to modify the surface, and then additional deposition. This periodic action allows progressive improvement of grain structure and orientation through multiple cycles.
2Reliability
If Cu is used as wiring material, then low resistivity is achieved at larger thickness, but resistivity increases rapidly as thickness decreases
Solution Approach 1:
The process changes the power density parameter during deposition - starting with low DC power density (<0.5 W/cm²) to promote grain growth and orientation, then increasing to higher power density (≥0.5 W/cm²) for efficient film buildup. This parameter change enables the tungsten film to achieve low resistivity even at ultra-thin dimensions by controlling the microstructure development during deposition.
3Reliability
If repeated deposition and plasma treatment is performed, then grain size and orientation are improved and resistivity is reduced, but the process time increases
Solution Approach 1:
The process performs the complete deposition and plasma treatment cycle only 1-4 times, which is sufficient to achieve the desired grain size and orientation improvement without excessive process time. This partial repetition provides just enough cycles to achieve the necessary microstructure control while maintaining production efficiency.
4Manufacturing precision
If RF bias treatment is applied after tungsten deposition, then the surface is modified and grain structure is improved, but additional process steps are required
Solution Approach 1:
The RF bias treatment step is merged into the deposition sequence, combining the plasma treatment function with the deposition process flow. The RF bias treatment is performed immediately after initial deposition and before additional deposition, creating an integrated process that achieves both surface modification and film buildup in a unified sequence rather than as separate independent steps.
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 achieves tungsten films with improved grain size and orientation, reducing resistivity and allowing stress control, suitable for next-generation semiconductor devices.
Implementation Method 1
a) first deposition step of depositing a tungsten film on the semiconductor substrate using magnetron sputtering
Implementation Method 2
b) step of modifying a surface of the deposited tungsten by performing radio-frequency (RF) bias treatment under an inert gas atmosphere
Data Source
AI summary
The present invention relates to a method for forming a tungsten (W) film in a semiconductor device, by using a physical vapor deposition (PVD) sputtering method on a semiconductor substrate, the tungsten film forming method comprising: a) a first deposition step of depositing a tungsten film on the semiconductor substrate by using magnetron sputtering with a power density of less than 0.5 W/cm2; b) a step of modifying the surface of the deposited tungsten by performing RF bias processing under an inert gas atmosphere; and c) a second deposition step of additionally depositing a tungsten film on the deposited tungsten film by using magnetron sputtering of a power density of 0.5 W/cm2 or more.