How to identify vital signs of a plasma process

Exclusive blog on Plasma Health
Exclusive blog on Plasma Health
The human body is extraordinarily complex. Our physical and mental performance is dependent on the health and fitness of our major organs. As long as we keep our vital organs in good condition, we can work with optimum efficiency. We generally know how well our bodies are functioning. Occasionally, we feel under the weather and we may consult a GP for a diagnosis. The GP will want to check some or all of your vital signs; pulse rate, body temperature, respiration rate and blood pressure.

Admittedly, I am no GP, but I find an interesting analogy between the health of the human body and that of a plasma processing tool! Lets look at the vital signs with this analogy in mind.

Pulse rate and pulse shape (ECG) are critical indicators of our cardiovascular health. The heart really is the bodies main power supply. Modern plasma processes are also driven by pulsed RF power supplies. Just like the human body, the pulse rate and pulse shape are critical parameters to be monitored to determine the stability of the plasma process.

Our body temperature is extraordinarily well regulated. Almost every household on the planet has a thermometer to check body temperature and in times of illness a swing of +/- 5 degrees fahrenheit could be fatal. Similarly, every plasma has a vital sign known as the electron temperature. The electron temperature controls plasma chemistry and ion fluxes to the substrate. It is measured with a Langmuir probe, comparable to the body thermometer. When a plasma process issue occurs, one of the first parameters to be measured is often the electron temperature as it is so fundamental to the plasma condition. Changes in electron temperature are reflected in the plasma impedance.

Maintaining a healthy, stable, blood pressure is crucial for our well being. Similarly, a stable set point gas pressure is critical for plasma process performance. Gas pressure drift can have catastrophic impact on process outcome. The GP utilises a pressure monitor to check blood pressure, similarly, plasma process chambers are equipped with pressure gauges.

Finally, our respiration rate looks at the flow of air through the lungs. It increases and decreases in tandem with the type of process the body is carrying out. Every plasma process also has an associated gas flow rate. Stable gas flow is imperative for plasma process health. Respiration rate monitors are similiar to gas flow monitors used on every plasma reactor.

Now to the punch line! If we were to invent a single instrument that could measure all of the bodies vital signs simultaneously it would constitute a medical breakthrough. While we haven’t done this, we have developed a single instrument that can monitor all the vital signs of a plasma processing tool.

The vital sign levels for optimum functionality of the human body were established empirically. Healthy individuals were used to establish baselines over time. Control limits were set based on the natural variance between healthy individuals. An individual who reports with vital sign levels outside of the control limits are classified as unhealthy and a medical intervention may be recommended. We use a similar approach with our plasma process vital sign monitor i.e. the RF VI probe.

We establish baseline RF signatures for healthy processes i.e. processes that produce good quality product. Then, we use a design of experiment (DOE) approach to establish the limits for unhealthy processes through fault simulation. Live monitoring of a production tool over time while logging natural faults will serve the same process.

Thus, we establish the RF signatures that correlate with other vital sign faults such as pulse shape, gas pressure, gas flow, plasma impedance. If these fault signatures appear in a production run we can alert the user to take corrective action.

To summarise, plasma processing tools have a set of vital signs that are critical indicators of process health. We provide a single instrument that monitors for signatures of all vital sign faults. There are interesting analogies between process vital signs and the vital signs of the human body. You could say that Impedans are the GP for your unhealthy plasma processes. Isnt it time you made your next appointment?