PVD Chamber Switching to Prevent Aluminum Pad Oxide Regrowth
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Solution Overview
Problem
In semiconductor fabrication, particularly in BEOL processing, the regrowth of an oxide layer on aluminium pads during the transfer from a pre-cleaning module to a PVD deposition module leads to increased contact resistance, as existing methods are inadequate in preventing oxide regrowth and maintaining system productivity.
Innovation Solution
A PVD apparatus is operated in two modes: a cleaning mode with an RF bias and electrical signal to remove material from the substrate using ions, and a deposition mode with reduced or no RF bias and increased electrical power to the target, allowing for simultaneous cleaning and deposition, thereby minimizing oxide regrowth and reducing transfer time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the wafer is transferred from the pre-cleaning module to the PVD deposition module, then the cleaning process is completed and deposition can begin, but the transfer time allows oxide layer regrowth on the aluminium pads
Solution Approach 1:
The patent combines the pre-cleaning function and PVD deposition function into a single integrated module. The cleaning electrode and target are both located within the same vacuum chamber, allowing the wafer to be cleaned and then immediately deposited upon without physical transfer between separate modules. This eliminates the transfer time that previously caused oxide regrowth.
Solution Approach 2:
The single vacuum chamber is designed to perform multiple functions: it serves as both a pre-cleaning chamber (with cleaning electrode and inert gas inlet) and a PVD deposition chamber (with target and deposition gas inlet). This multi-functional design allows the same chamber to sequentially perform cleaning and deposition operations without requiring transfer to a different chamber.
2Ease of manufacture
If separate pre-cleaning and PVD deposition modules are used, then each module can be optimized for its specific function, but the wafer transfer between modules causes oxide regrowth and reduces productivity
Solution Approach 1:
The patent merges the pre-cleaning module and PVD deposition module into a single integrated unit. The cleaning electrode is positioned facing the target within the same chamber, allowing sequential operation of cleaning and deposition functions without wafer transfer. This eliminates the productivity loss associated with inter-module transfer while maintaining the functional capabilities of both processes.
3Device complexity
If the target is not sputtered during the cleaning step, then the cleaning process is simpler, but the target surface becomes contaminated and deposition quality deteriorates
Solution Approach 1:
The patent applies continuous low-power sputtering to the target during the cleaning step. While the cleaning electrode removes organic contaminants from the wafer surface using inert gas plasma, the target simultaneously undergoes gentle sputtering that maintains its surface cleanliness. This continuous action on both the wafer (cleaning) and target (conditioning) ensures that when deposition begins, both surfaces are in optimal condition.
Solution Approach 2:
The patent uses different power levels for the target during cleaning versus deposition. During cleaning, low power is applied to the target to provide gentle sputtering that cleans the surface without excessive material removal. During subsequent deposition, higher power is applied to achieve the required deposition rate. This parameter change allows the target to serve different functions at different stages of the process.
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 contact resistance by minimizing oxide regrowth and enhances productivity by allowing instantaneous switching between cleaning and deposition steps, maintaining a clean target surface and achieving deposition rates comparable to traditional processes.
Implementation Method 1
supplying an electrical signal having an associated electrical power to the target, wherein the RF bias and electrical power are sufficient to remove material from the electrically conductive feature predominantly by etching with ions of the inert gas while the target is simultaneously sputtered
Implementation Method 2
supplying an electrical signal having an associated electrical power to the target, wherein the RF bias, if present, and electrical power are sufficient to deposit an electrically conductive deposition material onto the electrically conductive feature by PVD
Data Source
Figure 1~2
Figure 3(a)~4(b)
Figure 5
AI summary
According to the invention there is provided a method of operating a PVD apparatus to perform a cleaning step and a deposition step on an electrically conductive feature formed on a semiconductor substrate comprising the steps of: providing a PVD apparatus comprising a chamber having a substrate support, a target, an RF bias signal supply for applying an RF bias to the substrate support and an electrical signal supply for supplying an electrical signal to the target; positioning the semiconductor substrate with the electrically conductive feature thereon on the substrate support; performing a cleaning step by introducing at least one inert gas into the chamber, applying an RF bias to the substrate support and supplying an electrical signal having an associated electrical power to the target, wherein the RF bias and electrical power are sufficient to remove material from the electrically conductive feature predominantly by etching with ions of the inert gas while the target is simultaneously sputtered ; and performing a deposition step by applying no RF bias to the substrate support or applying an RF bias which is less than the RF bias applied to the substrate support during the cleaning step and supplying an electrical signal having an associated electrical power to the target, wherein the RF bias, if present, and electrical power are sufficient to deposit an electrically conductive deposition material onto the electrically conductive feature by PVD.