High frequency plasma power source and impedance matching device for supplying power to a semiconductor processing apparatus

• US 5,394,061 A
• Filed: 05/05/1993
• Issued: 02/28/1995
• Est. Priority Date: 01/14/1993
• Status: Expired due to Term

• Current Assignee: Adtec Plasma Technology Co., Ltd.
• Original Assignee: Adtec Servicos Rurais S/C LTDA EPP
• Inventors: Fujii, Syuitsu
• Primary Examiner(s): Pascal, Robert J.
• Assistant Examiner(s): Philogene, Haissa
• Application Number:
  US08/057,675
• Time in Patent Office: 664 Days
• Field of Search: 315/111.21, 315/111.31, 315/111.81, 315/219, 315/244, 330/301, 330/116, 330/117, 324/645
• US Class Current: 315/111.21
• CPC Class Codes: H01J 37/32183 Matching circuits
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance

Abstract

In a high frequency plasma power supply comprising a final stage push-pull amplifier 2 with each phase having a parallel combination of at least two FETs, an output transformer 5 having the connection of the phase outputs of the push-pull amplifier 2 to the opposite terminals of a primary winding with a neutral tap, and a low pass filler 6 allowing passage of substantially the fundamental frequency component from the secondary winding output of the output transformer 5, the high frequency power passing through the low pass filter being supplied between the electrodes of a plasma chamber 10 through an impedance matching circuit 9 having an impedance adjusting mechanism,

the dc voltage Vds to be applied between the drain and source of each FET of each phase of the push-pull amplifier is adjusted to not more than about 30% of the dc absolute rated value and the turn ratio of the output transformer is 1:4, thereby supplying the power having the level necessary for plasma reaction.

Claims

1. In a high frequency plasma power supply consisting of a final stage push-pull amplifier with each phase having a parallel combination of at least two FETs, an output transformer having the Connection of the phase outputs of said push-pull amplifier to the opposite terminals of a primary winding with a neutral tap, and a low pass filter allowing passage of substantially the fundamental frequency component from the secondary winging output of said output transformer, the high frequency power passing through said low pass filter being supplied between the electrodes of a plasma chamber through an impedance matching circuit having an impedance adjusting mechanism,

a high frequency plasma power supply and impedance matching device characterized in that the dc voltage Vds to be applied between the drain and source of each FET of each phase of said push-pull amplifier is adjusted to not more than about 30% of a dc rated voltage and the turn ratio of said output transformer is greater than the turn ratio which was adopted when said Vds was about 50% of the dc absolute rated value, so as to generate the same high frequency voltage on the secondary side as when said Vds was about 50%, thereby supplying the power necessary for plasma reaction, and

in that an arithmetic section comprising a CPU and a storage device is installed to compute the plasma ignition level of high frequency power supplied between the electrodes of said plasma chamber by using parameters set according to the kind, flow rate and temperature of raw gas to be fed to said plasma chamber or material to be plasma-processed,

thereby making it possible to compute and set the operation start position of said impedance adjusting mechanism in such a manner that in order to ensure that the high frequency power to be supplied between the electrodes of said plasma chamber is gradually elevated from the ignition level to the set power ignition level without providing the dark current sweep period extending from the zero level to the ignition level via the dark current level, the power output impedance including said impedance matching circuit is equal to the impedance of the plasma chamber at said ignition level.

2. A high frequency plasma power supply circuit comprising:

a final stage push-pull amplifier with each phase having a parallel combination of at least two FETs;

an output transformer having the connection of the phase outputs of said push-pull amplifier to opposite terminals of a primary winding with a neutral tap;

a low pass filter allowing passage of substantially the fundamental frequency component from a secondary winding output of said output transformer;

an impedance matching circuit positioned between said low pass filter and electrodes of a plasma chamber, said impedance matching circuit having an impedance adjusting mechanism, characterized in that a dc voltage Vds to be applied between drain and source of each FET of each phase of said push-pull amplifier is adjusted to not more than about 30% of a dc rated voltage assigned thereto and said output transformer has a turn ratio N1;

N2 where N1=1 and N2>

3, so as to generate substantially the same high frequency voltage on the secondary side as when said Vds was about 50%, thereby supplying the power necessary for plasma reaction; and

an arithmetic section comprising a CPU and a storage device to compute a plasma ignition level of high frequency power supplied to said plasma chamber by using parameters set according to the kind, flow rate and temperature of raw gas to be fed to said plasma chamber or material to be plasma-processed, thereby making it possible to compute and set an operation start position of said impedance adjusting mechanism in such a manner that in order to ensure that said high frequency power to said plasma chamber is initiated from said ignition level and gradually increased therefrom to a predetermined plasma power level without going through the dark current sweep from a zero level to said ignition level, power output impedance including said impedance matching circuit is equal to the impedance of said plasma chamber at said ignition level.

3. The circuit according to claim 2, wherein said output transformer has a turn ratio N1:

N2 where N1=1 and N2=4.