Vacuum Plasma Generator

• US 20080143260A1
• Filed: 03/01/2006
• Published: 06/19/2008
• Est. Priority Date: 03/24/2005
• Status: Active Grant

• Current Assignee: Oerlikon Surface Solutions Ag, PfAffikon (OC Oerlikon Corporation AG)
• Original Assignee: Oerlikon Trading, Ltd.
• Inventors: Lendi, Daniel, Ramm, Jurgen, Tuymer, Gerhard
• Granted Patent: US 7,455,755 B2
• Time in Patent Office: Days
• US Class Current: 315/111.21
• CPC Class Codes: H01J 37/32091 the radio frequency energy being capacitively coupled to the plasma
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H02M 7/10 arranged for operation in series, e.g. for multiplication of voltage

Abstract

The invention relates to a vacuum plasma generator for providing a plasma discharge (10) for treating work pieces (5) by way of a pulsed plasma process in a vacuum chamber (2). Said vacuum plasma generator comprises a generator output (9, 9′) having an AC mains supply (6a), an AC/DC mains rectifier system (6) for rectifying the AC mains voltage to a DC voltage, a filter capacitor (6b), a first stage as clocked DC/DC voltage converter (7) with means for adjusting the DC output voltage which produces an intermediate circuit voltage (Uz), comprising a controlled power switch (7a) which feeds the primary winding of a transformer (14) and the secondary winding of which is connected to a rectifier (15) and a downstream intermediate capacitor (12) and configures a floating transformer secondary circuit (23). Said secondary circuit is connected to a downstream second stage which is a pulse output stage (8) and is connected to the generator output (9, 9′). The DC/DC voltage converter (7) has at least two floating transformer secondary circuits (23) and comprises a switch-over device (20) with a switch controller (22) for optionally switching the floating transformer secondary circuits (23) in parallel or in series.

Claims

1. :

Vacuum plasma generator with a generator output (9, 9′

) for feeding a plasma discharge (10) for the treatment of workpieces (5) in a vacuum chamber (2) with an AC voltage mains connection (6a), a mains rectifier configuration (6) for the conversion of the mains AC voltage into a DC voltage, a smoothing capacitor (6b), a first stage as a clocked DC/DC voltage converter (7) with means for setting the DC output voltage which forms an intermediate circuit voltage (Uz), comprising a controlled power switch (7a) which feeds the primary winding of a transformer (14) and whose secondary winding is connected to a rectifier (15) and a downstream intermediate circuit capacitor (12) and forms a floating transformer secondary circuit (23), wherein this circuit is connected with a downstream second stage which forms a pulse output stage (8) and this output stage is connected to the generator output (9, 9′

), characterized in that the DC-DC voltage converter (7) comprises at least two floating transformer secondary circuits (23) and includes a change-over device (20) with a switch control (22) for the optional parallel or serial connection of the floating transformer secondary circuits (23).

2. :

Generator as claimed in claim 1, characterized in that as means for setting the intermediate circuit voltage (Uz) the power switches (7) are pulse-width controlled and that with the switchable transformer secondary circuits (23) the intermediate circuit voltage is additionally doubled or multiplied in steps as required for the expansion of the voltage setting range of the DC/DC converter.

3. :

Generator as claimed in claim 1, characterized in that the change-over device (20) includes switching diodes (D) and controlled switches (21).

4. :

Generator as claimed in claim 1, characterized in that the change-over device (20) includes controlled electronic switches (21), preferably mechanical switches (21).

5. :

Generator as claimed in claim 1, characterized in that three transformer secondary circuits (23) are provided with change-over devices (20).

6. :

Generator as claimed in claim 1, characterized in that the pulse output stage (8) is implemented as a voltage converter with additionally settable pulse width control for the generation of pulses with specified pulse amplitude, pulse width and pulse frequency.

7. :

Generator as claimed in claim 1, characterized in that the voltage converter (7) and/or the pulse output stage (8) can be operated with time gapped pulses.

8. :

Generator as claimed in claim 1, characterized in that the configuration at the output terminals (9) covers several plasma impedance ranges for feeding a multiplicity of plasma modes, such as glow discharge, abnormal glow discharge, spark evaporation or “

diffused discharge”

.

9. :

Generator as claimed in claim 8, characterized in that the plasma impedance ranges include 0.05 Ohm to 1.0 Ohm and 0.2 Ohm to 3.0 Ohm.

10. :

Generator as claimed in claim 9, characterized in that the plasma impedance ranges include additionally 10 Ohm to 100 Ohm.

11. :

Generator as claimed in claim 8, characterized in that the plasma impedance ranges include additionally 50 Ohm to 500 Ohm.

12. :

Generator as claimed in claim 8, characterized in that the plasma impedance ranges include additionally 50 Ohm to 5000 Ohm

13. :

Generator as claimed in claim 1, characterized in that the configuration at the output terminals (9) maintains an edge steepness of the pulses which is steeper than 0. V/ns, preferably steeper than 1.0 V/ns.

14. :

Generator as claimed in claim 1, characterized in that the generator at the output (9, 9′

) provides unipolar and/or bipolar pulses.

15. :

Generator as claimed in claim 14, characterized in that the bipolar pulses have unequal pulse lengths, in particular with the connection to the workpiece (5) for bias operation the negative pulse is longer than the positive pulse, preferably the pulse length of the positive pulse is less than 5%, preferably less than 2%, of the negative pulse duration.

16. :

Generator as claimed in claim 1, characterized in that the generator output (9, 9′

) is connected to a change-over device which optionally connects at least two, preferably several, plasma sources (10), preferably sequentially.

17. :

Generator as claimed in claim 16, characterized in that the generator with the change-over device connects plasma sources (10) with different plasma impedances.

18. :

Generator as claimed in claim 1, characterized in that the generator output (9, 9′

) is connected to a filter, preferably comprising diodes, for the electrical decoupling of the generator (1) from a connected superimposed DC feed

19. :

Generator as claimed in claim 14, characterized in that the bipolar pulse lengths are different and that the voltage pulse amplitudes adjust accordingly to the connected load impedance and that the pulse widths can be varied.