Low-cost Parylene Thickness Sensor for More Accurate Deposition Systems
- Detailed Technology Description
- This simple, inexpensive sensor detects the end-point thickness during parylene deposition with greater accuracy than conventional methods. It reduces production costs and enables the use of parylene
- Countries
- United States
- Application No.
- 7445675
- *Abstract
-
This simple, inexpensive sensor detects the end-point thickness during parylene deposition with greater accuracy than conventional methods. It reduces production costs and enables the use of parylene coatings in applications that require a higher precision of thickness than is currently available. This disposable sensor is fabricated using a low-cost micromachining technology and can be easily implemented in commercial parylene deposition systems. Use of the sensor requires only the replacement of a viewport by a new flange with electrical feedthroughs and mechanical supports.
DESCRIPTION/DETAILS
How it Works
Parylene is the common name for a unique family of polymers, the basic member of which is poly-para-xylylene, or parylene-N. It is an organic material that is grown by chemical vapor deposition at room temperature and at a pressure of about 0.1 torr. No catalysts or solvents are required, and parylene coatings can be as thin as a few hundred angstroms or as thick as several mils. It is an exceptionally conformal coating material with very low pinhole density and has excellent properties as a low loss dielectric, a moisture barrier, and a coating that does not outgas. Due to its unique ability to seal and encapsulate, the material is useful in a wide array of industries such as electronics, aerospace, military, medical products, and more.
In recent years, Parylene has been used in the fabrication of microelectromechanical (MEM) devices such as microfluidic circuits, micro-injectors, and valves/pumps to name a few. Since the film in many MEMS applications is used to function as a mechanical structure, the thickness becomes an important parameter that determines the performance specifications of sensors and actuators. Consistently obtaining a desired thickness of parylene is difficult, making its use in certain applications, such as MEMS or those that require very thin coatings (<10 m), not feasible. Existing methods of controlling deposition thickness that are based on the amount of solid phase dimer used, typically provide an accuracy of 10% at best, which is problematic for some applications.
This new technology offers much better control of thickness tolerance with attainable accuracy levels within 3% of the target thickness, making possible a whole new array of applications for parylene coatings. This disposable sensor is fabricated using a low cost micromachining technology and can be easily implemented in commercial parylene deposition systems. Use of the sensor requires only the replacement of a viewport by a new flange with electrical feedthroughs and mechanical supports. (see Figure 1 attached) A schematic diagram of the Parylene sensor is shown in Figure 2 (attached). Each sensor consists of a heating element and a temperature sensor located at distal ends of two diving-board-type cantilever beams. The size of the gap, denoted d, between the distal ends of the two cantilever beams, is accurately defined using microlithography. The heater, made of thin-film metal coil, generates ohmic heating when an electrical current passes through. This heat may be transmitted to the sensor either through the gap or through the two cantilever beams and the supporting silicon substrate. Obviously, the latter heat transfer mode involves a much longer heat conduction path and greater thermal mass. When a sensor with an open gap is placed in a vacuum, the thermal conduction through the gap is negligible. As Parylene is deposited in a conformal fashion, the distance between the two distal ends of cantilevers is gradually reduced.
When the Parylene thickness reaches d/2, the two Parylene fronts will meet, filling the gap and completing a thermal conduction path. Heat from the heater now has a direct conduction path to reach the temperature sensor, causing the resistance of the temperature sensor to change very rapidly. The heat pulse travels directly across the gap bridged by parylene to the temperature sensor. This indicates the desired thickness has been reached and activates the signal to turn the deposition equipment off. An optical micrograph of a sensor before the gap is closed is shown in Figure 3 (attached). A scanning electron micrograph of an array of sensors with varying gap sizes is shown in Figure 4 (attached).
Each individual sensor is made to detect a particular thickness of parylene and may serve as a single end-point detector. Using an array like the one shown in Figure 4 (attached), it should be possible to monitor the growth rate and interpolate thickness values between sensor settings.
APPLICATIONS
Companies can license this parylene thickness monitoring technology for use in any application where parylene coatings are used, such as:
- Automotive: Sensors and protective coatings for electronics
- Aerospace: Protection for electronics and space exploration equipment
- Electronics: Strengthens wire bonds, provides a moisture barrier, and has potential application as an electronic device dielectric layer, such as a gate dielectric
- Medical: Biocompatible, protective coatings on devices and instruments (e.g., coronary stents, prosthesis, catheters, epidural probes, and bone growth stimulator components)
- Synthetic Rubber: Chemical barriers and low-friction coatings
- Microelectromechanical systems (MEMS): Anti-stiction coatings, micro fluidic systems, and tactile sensors
- Telecommunications: Dielectric coatings for ferrite cores used in modems and other telecommunications devices
- Simplifies process control: Provides users of parylene deposition systems with an easy to identify end-of-process indicator that is reliable and easily implemented in existing systems.
- Reduces material costs: The sensor saves material (dimer) by eliminating "overshooting" the target thickness. Unused dimer can be reclaimed and reused.
- Reduces time/costs: The sensor prevents runs from ending before the target thickness has been met, eliminating additional setup and rerunning time, thereby reducing costs.
- Enables new applications: Because many emerging applications require more accurate control of parylene thickness than existing methods can promise, this sensor will be instrumental in enabling those applications.
For more information about this technology, please contact the University of Illinois at Urbana-Champaign Office of Technology Management at otm@illinois.edu.
- *IP Issue Date
- None
- *IP Type
- Utility
- Country/Region
- USA
