Radio-frequency plasma generator RFPG-128

    Purpose: creation and continuous maintenance of high-density gas discharge plasma in working spaces of vacuum technological machines. RFPG-128 provides higher plasma densities (ion flux density up to 50 mA/cm2).

    Installation: into a view port flange or inside the vacuum chamber on a DU60 sliding seal both in new machines and when modernizing the existing ones. There are tested and tried procedures of using plasma generators in the majority of serially produced Russian plants.

    Application: processes of ion and plasmachemical etching, depositing of thin film deposition, ion-plasma surface treatment: polishing, nitriding and carbonization. The devices work with any gases that do not cause depositing of low-resistance layers on the protective screen surface. Depositing rate: up to 40 µm/min, capacity: up to 20 kW.

    Parameter

    RFPG-128

    Operating frequency, MHz

    13.56

    Maximum HF energy input, W

    3000

    Housing diameter, mm

    128

    Operating pressure range, Pa

    0.1..10

    Ion flux density at 1 kW power, mA/cm2  

    a) without accessories

     15

    b) with a specially configured magnetic system

    50


    RFPG-128 has a wide range of technnological applications. It was specially designed for installation on a conventional flange 128 mm in diameter, but it also may be mounted inside of a vacuum chamber through a sliding sealing. RFPG-128 is designated for dense plasma generation (1..2*1012 cm-3 on 13.56 MHz RF power of 1 kW) in various  gases and mixtures, the operation pressure vary between 70 mPa up to 100 Pa.

    RFPG–128 utilizes an inductively coupled plasma discharge in a weak external magnetic field. It has no any electrodes and generates dense plasma in a relatively large volume. It can be easily mounsted as a standard window flange, or it can replace the standard ion source “Radical” which is used in the 70th and 79th vacuum machines produces by Kalinigrad plant “Kvarts”.

     The plasma generator -inner chamber installation.  The plasma generator - Installation flange.

    The RFPG has a cylinder shaped body with a cap flange. The vacuum side of the generator is covered with a dielectric shield (quartz or sapphire). All inner elements of the generator are tuned fine with a precision of 0.1 mm. Water cooling is required, with the minimum water flow of 60 l/h. The advantage of this plasma generator’s design is that water is at ground potential and no additional isolation methods are required. The electro-magnetic coil for the external magnetic field generation, installed in alignment with the RFPG axis, and can be removed or replaced if necessary. This coil has resistance 10 Om and can be operated with dc current up to 3 A. The RFPG-128 can utilize any RF-power supply with an operational frequency of 13,56 MHz and an output power no less than 600 W. The matching device for RFPG-128 can be specified by a customer or it can be equipped with a standard one, also developed by our company. The RFPG-128 can operate at least 8 hours continuously with the input power 1000 W in any gases or gas mixtures.

    Design, installation and maitenance features: The radio frequency plasma generator can be installed either on a window flange(outside the vacuum chamber) or on the sliding vacuum feed-through (inside vacuum chamber). The length of the copper coaxial vacuum feed-through can be customized. Both possible installation capabilities are presented in figure 2. 

    Step by step operation guide: 

     1. The device is installed on a vacuum window. A standard elastomeric o-ring can be used for vacuum sealing.

     2. With the help of a specially designed bobbin an external magnetic field coil is installed on the RFPG-128 in alignment with its axis.

     3. A matching devise is installed on the RFPG-128.

     4. Cooling water tubes and power supply cables are connected to sockets.

     5. Vacuum chamber is pumped.

     6. Operating gas is inserted. The optimal operating pressure for different plasma assisted technological processes can be different.

     7. Power is supplied to the magnetic coil, matching device, and the RFPG-128.

    RFPG-128 can be turned on immediately after installation when desired pressure in a vacuum chamber is achieved. If the plasma generator comes along with an automatically matching device, the plasma will be ignited shortly after RF power is applied.

    In the argon plasma at gas pressure 0.1 Pa and input RF-power 1 kW, the 50 mA/cm2 ion saturation current on the -30 V biased 100 mm in diameter substrate was achieved. In the same conditions 30 mA/cm2 substrate ion saturation current was achieved on a 150 mm in diameter substrate. These current values were obtained on substrates which were situated 200 mm away from RFPG-128 surface; the axis of the substrates was aligned to the RFPG’s axis.

    RFPG-128 in operation is presented on the figure 1. One can see bright light emission prom argon plasma inside vacuum chamber. The RFPG-128 is installed on the top side of the vacuum chamber. An RF matching network is installed right on the RFPG. 

    Plasma generator on tests    

    RFPG-128 in operation regime inside the large vacuum chamber is shownon the figure 2. With the help of external magnetic fields the plasma can be easily controlled, compressed, or directed towards any specific location inside a vacuum chamber.

    RFPG-128 can be used in any plasma assisted technique: plasma chemical etching, thin film deposition, nitriding or reactive thin film deposition. It can be equipped with a Faraday shield to provide a long turn operation in the case of intensive process of conductive film deposition.

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