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Real time monitoring of thin film deposition and etch processes using in situ monitoring tools can improve yield and speed production, reducing total cost of ownership (TCO). This is especially true for low-volume, low-yield processes where each finished piece represents a relatively large investment in time, materials, and economic value-add. Denton offers a variety of different in situ monitoring tools, each with a different purpose and at a different price point.
Not every thin film or etch application needs real-time monitoring. For example, with high-volume, high-yield processes, it is often more cost-effective to handle the quality assurance (QA) process post-production using statistical sampling and other tools. But in the right circumstances, in situ monitoring can save time and money.
Such monitoring is particularly necessary when process precision or yield cannot be achieved by time-based control.
The in situ monitoring tools available for Denton’s thin film deposition and etch systems include:
- Residual Gas Analysis (RGA)
- Plasma Emission Monitoring (PEM)
- Optical Monitoring System (OMS)
- Quartz Crystal Monitoring (QMS), and
- Secondary Ion Mass Spectroscopy (SIMS)
Residual Gas Analysis (RGA) supports vacuum readiness and troubleshooting
Residual Gas Analysis (RGA) systems identify molecules present in vacuum systems during and after pump down. As such, it is less about monitoring the progress of thin film deposition than it is about isolating leaks and determining the achievement of a clean vacuum.
RGA can reduce pump down time. Many thin films don’t require total vacuum – it is only necessary to remove the contaminants that might interfere with the development of the film, perhaps oxygen, nitrogen, or other gasses found in air. RGA can determine when the specific problem contaminants have been removed, even if total vacuum hasn’t been achieved. Perhaps the thin film process isn’t sensitive to water – the water molecules therefore don’t need to be removed. This can save hours of pump down time and reduce pump down uncertainty.
If your process requires breaking vacuum frequently, an RGA system may pay for itself quickly in time savings.
Plasma Emission Monitor (PEM) enables high-rate magnetron sputtering without target poisoning
Plasma Emission Monitoring (PEM) is a closed-loop magnetron sputtering control system for transition mode, high-rate reactive sputtering of metal oxides and nitrides. As the name suggests, PEM involves managing reactive gas flow by monitoring plasma characteristics during the deposition of oxide and nitride films.
PEM improves throughput and yield, ensuring that performance-related properties do not fall outside of the desired setpoints. It prevents target poisoning by maintaining the reactive gas concentration at a constant setpoint, forming clean, stoichiometric films. PEM enables up to ten times higher deposition rates compared to RF sputtering, all with optimum film quality and performance.
Quartz Crystal Monitoring (QCM) provides cost-effective control of film thickness
Quartz Crystal Monitoring (QCM) is another option for real-time monitoring of thin film deposition. QCM involves indirect monitoring of a separate witness chip, not the actual substrate, so it requires calibration based on its position within the tool. The QCM uses a linear change in crystal frequency to signal the film thickness on the crystal.
QCM measurements are accurate within 3%, so it’s a cost-effective control that is best applied when there are broad specifications on the optical properties of metal and optical films. QCM is standard for e-beam evaporation systems, but can be used with other deposition methods.
Optical Monitoring Systems (OMS) for greater precision in thin film deposition
An Optical Monitoring System (OMS) measures optical thickness during thin film deposition, while a QMS measures physical thickness. Compared to QMS, OMS provides better precision for optical films, accurate to 0.3%, ten times more precise than QMS.
Typically, this monitoring is done using the reflection of, or transmission of, light through a substrate or witness chip.
Like PEM, an OMS helps maximize yield by controlling the deposition and improving repeatability. The result is higher production yields on precision multi-layer optics. OMS is well-suited for anti-reflectance and high-reflectance, laser facets, and filters, among other applications.
To further explore the accuracy and precision of OMS, Denton undertook a small study on the variation in precision using a fully automated OMS. Download the technical paper, “Considerations and Examples for Determining Precision of Indirect Optical Monitoring” to see the results of this research.
Secondary Ion Mass Spectroscopy (SIMS) for accurate whole-chip delayering
Unlike the other in situ controls offered by Denton – which are intended for use in film deposition – Secondary Ion Mass Spectroscopy (SIMS) monitors the etching process in Denton’s Infinity FA whole-chip delayering system.
The ever-smaller scale and ever-larger surface areas of today’s semiconductors make it increasingly difficult to delayer chips with commonly used delayering methods. The Kaufman-type broad ion beam etch used in Denton’s Infinity FA System can etch extremely large areas quickly and easily, making it ideal for whole-chip delayering, while the precision endpointing supported by SIMS enables both automated and operator-assisted processes.
As the beam etches through each layer, SIMS tracks the compositional changes in the ions sputtered off the surface, signaling the transition from one layer to the next, enabling the etch to be automatically or manually ended at the exact layer of interest.
Customer needs determine the right solution for real-time monitoring
While real-time monitoring with in situ controls is not universally required, in the right situation it can improve throughput, yield, and total cost of ownership. This is especially true in low-volume, low-yield processes. Selection of the right in situ control depends on process sensitivity, required precision, rate, vacuum condition, or endpoint control.
Talk to Denton today about your particular needs for real-time monitoring.