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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
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
Q2: What's the difference between lens filter type and spectroscopic type of Plasma Emission Monitor?
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
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
big change on the pumping position and layout is sometimes necessary.
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
big change on the pumping position and layout is sometimes necessary.
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.
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.