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FAQs
Plasus plasma process control and diagnostics
Q1: In the demand of precise control for a plasma process, which tool is the right choice?
OES tool or RGA mass spectrometer?
A1: RGA mass spectrometer is mainly designed for the monitor of vacuum quality and easily
detect minute traces of particles in the low-pressure gas environment. No matter the plasma is
ignited or not, RGA mass spectrometer is not able to tell the instant variations of the particles
involved in the plasma reaction area. On the other hand, OES can easily monitor the actual
changes of the particles in the specific plasma reaction area for precise plasma process control,
but it's not sensitive to the environment change. In addition, OES tool has a much faster
response time than RGA mass spectrometer. The best way to contribute a precise control for a
plasma process is to combine both technologies,
- OES tool for plasma process controlling
- RGA mass spectrometer for the stabilization of the vacuum quality
OES tool or RGA mass spectrometer?
A1: RGA mass spectrometer is mainly designed for the monitor of vacuum quality and easily
detect minute traces of particles in the low-pressure gas environment. No matter the plasma is
ignited or not, RGA mass spectrometer is not able to tell the instant variations of the particles
involved in the plasma reaction area. On the other hand, OES can easily monitor the actual
changes of the particles in the specific plasma reaction area for precise plasma process control,
but it's not sensitive to the environment change. In addition, OES tool has a much faster
response time than RGA mass spectrometer. The best way to contribute a precise control for a
plasma process is to combine both technologies,
- OES tool for plasma process controlling
- RGA mass spectrometer for the stabilization of the vacuum quality
A2: Plasma Emission Monitor (PEM) has two main types, they are:
(a) filter type
(b) spectroscopic type
(a) In filter type PEM system, only one fixed emission wavelength is available. To switch to
another emission wavelength, the filter lens must be exchanged. The filter lens is a kind of
narrow band pass filter which has a fixed central wavelength and span the spectral range from
the central to longer and shorter with a few nanometers to form a complete optical filter. Due to
the narrow band pass filter, the spectral intensity is very weak. A high sensitivity PMT (Photo
Multiplier Tube) detector is used to acquire the emission intensity information and convert the
light information to electrical data.
(b) In spectroscopic type, an OES tool with an arrayed CCD spectrometer is used to acquire
spectral data from 200nm to 1100nm with optical resolution 1.4nm or 10 times higher with lower
light sensitivity. In the optics, an external quartz optical fiber, an opto-vacuum feedthrough, an
in-vacuum quartz optical fiber and an optical collimator with a honey comb coating protection
device are included to guide the plasma light from plasma zone to spectrometer. A grating
inside the spectrometer diffracts the incoming light onto the arrayed CCD to get the spectrums
mapping to the CCD pixels. Each CCD pixel has its own mapping spectrum which is the same
definition of the central peak wavelength of a narrow bandpass filter that filter type PEM is used.
Therefore, simply saying, a 2048 pixels CCD OES tool is equivalent to 2048 filter type PEM
systems. ---> 2048 x filter type PEM systems = 1 x CCD type OES PEM system
Q3: Can PEM (OES tool) improve the uniformity?
A3: PEM (OES tool) is not able to improve the coating uniformity in the long axis of magnetron
(or cathode), but it is a good process controlling tool to have a high quality of homogeneity in
the film growing direction. To improve the coating uniformity can be done by re-designing or
re-aligning the gas inlet positions or gas inlet hole dimension or layouts, even a
A3: PEM (OES tool) is not able to improve the coating uniformity in the long axis of magnetron
(or cathode), but it is a good process controlling tool to have a high quality of homogeneity in
the film growing direction. To improve the coating uniformity can be done by re-designing or
re-aligning the gas inlet positions or gas inlet hole dimension or layouts, even a
Q4: Ｗhy argon particle density on the target surface of a reactive sputtering process
decreases while the reactive gas oxygen flow increases?
A4: In the vicinity of target surface of a reactive sputtering process, the argon particle density
decreases while the oxygen density increases because of the effective particle density in this
fixed volume space must be kept in a constant under a constant pressure control condition.
Once the fraction of argon and oxygen reaches an acceptable value which has a good quality
(or properties) on the grown layer, the process can be applied by giving an EMICON setpoint to
reproduce the same result for an online quality control purpose.
decreases while the reactive gas oxygen flow increases?
A4: In the vicinity of target surface of a reactive sputtering process, the argon particle density
decreases while the oxygen density increases because of the effective particle density in this
fixed volume space must be kept in a constant under a constant pressure control condition.
Once the fraction of argon and oxygen reaches an acceptable value which has a good quality
(or properties) on the grown layer, the process can be applied by giving an EMICON setpoint to
reproduce the same result for an online quality control purpose.