JP4054525B2 - Output control device for ion source having cathode heated indirectly - Google Patents

Description

[0001]
The present invention relates to an output control device for controlling a power source of an ion source having a cathode that is indirectly heated.
[0002]
Hot cathode ion sources are well known and include, for example, so-called Freeman ion sources and so-called Bernas ion sources. These ion sources contain a filament cathode that is heated directly by energizing the filament from a filament power source. The ion source includes an arc chamber containing a filament, and gas or vaporized material is supplied to the arc chamber. Once the cathode filament is sufficiently heated by the filament current, thermionic electrons are emitted from the cathode. If the cathode is held at a sufficiently negative potential with respect to the anode in the arc chamber, plasma is generated in the arc chamber by the arc current flowing between the cathode and anode. Usually, the cathode is actually formed by the wall of the arc chamber.
[0003]
In the plasma thus generated in the arc chamber, the source gas or vapor molecules are ionized, and these cations are apertured by the extraction electrode held at a negative potential relative to the arc chamber. Through the arc chamber. The extracted ions can be used to generate an ion beam that can be used in many applications. One important application is ion beam implantation, in which an ion beam of a desired impurity element material is implanted into a semiconductor substrate (wafer) for the purpose of implanting the impurity element into the semiconductor in order to provide a desired conductivity condition. is there.
[0004]
One freeman ion source, particularly for an ion beam implanter, is disclosed in US-A-4578589. The Freeman ion source includes a filament power source that supplies a heating current through a cathode filament and an arc power source. US-A-4754200 discloses a method for controlling a power supply to optimize the performance of an ion source, particularly when applied to an ion implanter.
[0005]
US-A-5262652 discloses an example of a Bernas type ion source for ion implanter applications. Here again, the Bernas ion source is connected to a filament power supply for supplying a heating current via the filament, and has a cathode filament that is directly heated, and separately between the filament and the anode or arc chamber body. An arc power source for applying a desired arc potential is provided.
[0006]
US-A-4754200 described above discloses a circuit for controlling the power source of an ion source. Thus, it is known to provide a constant arc voltage between the filament and the arc chamber body (or anode) and then adjust the filament power supply to obtain the desired arc current. In addition, it is known to control the filament power supply by the power demand signal, that is, to obtain output power from the filament power supply in response to the input power demand signal, while the filament input power demand keeps the arc current constant, Derived from arc voltage error.
[0007]
US-A-5497006 discloses an ion source with a cathode which is of the Bernas type but indirectly heated. In this configuration, the cathode in the source arc chamber is formed of a conductive button-like member, which is behind the button attached to the opposite side of the main plasma chamber of the ion source. Heated indirectly from another filament. The power source includes not only an arc power source and a filament power source, but also a cathode bias power source for applying a necessary bias potential between the filament and the cathode button. In operation, since the filament is negatively biased with respect to the cathode button, the thermoelectrons emitted by the filament are accelerated and impinge on the back of the button, thereby heating the button cathode, so that the cathode is then Electrons for initiating or maintaining the plasma arc of the ion source are emitted into the plasma chamber.
[0008]
This arrangement with the indirectly heated cathode in the ion source greatly extends the lifetime of the ion source until it is necessary to replace the cathode itself or the cathode heating filament. The above-described form of the ion source with the indirectly heated cathode will be referred to hereinafter as an indirectly heated cathode type ion source, as described above.
[0009]
US-A-5497006 discloses an ion source having a filament power supply unit, a cathode bias power supply unit, and an arc power supply unit, and an output control device for controlling these power supply units. In this US specification, a programmable power supply unit is used for each of these power supplies. The arc power supply unit is controlled to apply the output arc voltage according to the input voltage demand level. The bias voltage applied between the cathode button and the filament by the cathode bias power supply unit minimizes this difference depending on the difference between the desired arc current and the current that is passed through and measured by the arc power supply. Is set as follows. In this way, when the arc current is below the demand value, the cathode bias supply voltage is increased to increase the heating energy delivered to the cathode button, thereby reducing the impedance of the plasma in the arc chamber and consequently Increase arc current. The filament power supply in US-A-5497006 is then controlled to keep the current supplied by the cathode bias power supply equal to the desired current level. In this way, the current from the cathode bias power supply is maintained at the required demand level by increasing or decreasing the voltage applied to the filament by the filament power supply.
[0010]
The present invention provides a method for controlling various power sources of an indirectly heated cathode ion source to improve stability, maximize the lifetime of the source, and obtain a fast response speed, particularly by controlling the plasma arc of the power source. It is intended to improve.
[0011]
According to one aspect of the invention, It has a cathode bias power supply unit, an arc power supply unit, and a filament power supply unit Of the indirectly heated cathode ion source defined above. Control power The output control device for the arc power supply Output voltage or output current In response to the difference between the parameter and the demand value of the parameter, a bias power demand signal is generated that is representative of the output power of the cathode bias power supply unit necessary to minimize the difference and is responsive to the bias power demand signal. And a bias supply controller for maintaining the output power of the cathode bias power supply unit at the required output power.
[0012]
The bias supply controller operates to maintain the output power of the cathode bias power supply unit at the required level, so that the power delivered to the cathode is the impedance of the cathode bias load, i.e., in the region between the filament and the indirectly heated cathode itself. Unaffected by changes in impedance of electron flow. Such an impedance change may occur due to, for example, a chemical change in a substance, a change in gas pressure, or a physical change in this region.
[0013]
For example, in prior art controllers where the output voltage of the cathode bias power supply is directly controlled, a change in the cathode bias load impedance will cause a change in the cathode bias current, and thus will be sent from the cathode bias power supply unit to the cathode. Cause a change in the power generated. In the prior art configuration disclosed in US-A-5497006, this change in cathode bias power must be compensated by adjusting the filament power supply to return the cathode bias current to the required value. In the configuration of the present invention, the output of the cathode bias power supply unit is directly controlled to match the demand value, so that the change in the bias load impedance is applied from the outside in order to keep the power sent to the bias load at the demand value. No compensation is required.
[0014]
The arc power supply parameter used to generate the bias power demand signal is either the output voltage or output current of the arc power supply unit, depending on whether the main control input to the arc power supply is an arc current demand signal or an arc voltage demand signal. sell. The output control device is preferably used together with a cathode bias power supply unit, and the cathode bias power supply unit includes a bias voltage feedback signal representing an output voltage of the power supply unit and a bias representing an output current of the power supply unit. A bias feedback controller for deriving a bias power feedback signal from a product of the bias voltage feedback signal and the bias current feedback signal; and the bias power feedback signal and the bias power demand signal. A bias power comparator for deriving a bias power error signal from the difference; adjusting the bias power error signal for application as an output control signal to the cathode bias power supply unit; and Controlling the output of the power supply unit so as to reduce the issue, and a bias power error adjustment filter including a multiplier. In this way, a relatively fast bias power control loop is formed to ensure that the output power supplied by the cathode bias power supply unit is maintained at a level determined by the bias power demand signal.
[0015]
The bias supply controller also includes an arc parameter comparator that derives an arc parameter error signal from the difference between the arc power supply parameter and the demand value of the parameter; and the arc parameter error to provide the bias power demand signal. An arc parameter error adjustment filter including an integrator for adjusting the signal is preferably included.
[0016]
The present invention also includes: It has a cathode bias power supply unit, an arc power supply unit, and a filament power supply unit Control the power source of the indirectly heated cathode ion source output A control device is provided, which device preferably comprises a filament supply controller, the filament supply controller comprising: Bias power supply Bias power supply for desired value of parameter Load impedance In response to a parameter error, a filament power demand signal representative of the output of the filament power supply unit required to minimize the error is generated and in response to the filament power demand signal, the output of the filament power supply unit The power is maintained at the required power.
[0017]
This filament power supply controller can be used together or independently with the bias supply controller described above. The filament supply controller described above has the advantage of ensuring that the power delivered to the filament is directly controlled and is therefore independent of changes in filament impedance that tend to increase during the life of the filament.
[0018]
In the prior art example described in US-A-5497006, only the output voltage of the filament power supply unit is controlled. As a result, an increase in filament impedance causes a decrease in filament current and a corresponding decrease in power delivered to the filament. There is no provision for internal compensation for this change in filament impedance to maintain filament power. Instead, in the prior art U.S. specification, a decrease in filament power will likely result in an increase in cathode bias impedance resulting in a decrease in cathode bias current, and a voltage demand signal applied to substantially compensate the filament power supply. Bring about an increase. However, the control loop disclosed in the prior art of the US patent requires a reduction in the cathode bias current and hence the delivery of power to the cathode, which can affect the plasma arc in the main arc chamber of the ion source. is there.
[0019]
The above-described apparatus is preferably used with a filament power supply unit, and the filament power supply unit includes a filament voltage feedback signal representing an output voltage of the filament power supply unit and a filament current feedback signal representing an output current of the filament power supply unit. A filament multiplier that derives a filament power feedback signal from a product of the filament voltage feedback signal and the filament current feedback signal; and a filament power error from a difference between the filament power feedback signal and the filament power demand signal. A filament power comparator for deriving a signal, and adjusting the filament power error signal to provide the filament power error signal By controlling the output of the filament power supply unit so as to reduce, it applied as an output control signal to said filament power supply unit, and a filament power adjustment filter including a multiplier. In this way, an inner control loop is provided that ensures that the output power of the filament power supply is maintained at the required level.
[0020]
The filament supply controller preferably includes a bias parameter error adjustment filter including an accumulator that adjusts the bias parameter error signal to provide the filament power demand signal.
[0021]
The bias power parameter used above may be the output voltage of the cathode bias power unit, in which case the error is the difference between the output voltage and the desired value of the output voltage. Alternatively, the bias power supply parameter may be the output current of the cathode bias power supply unit, in which case the error is the difference between the desired value of the output current and the output current.
[0022]
However, the bias power parameter is preferably an impedance of a load supplied by the cathode bias power unit.
[0023]
In a further aspect of the invention, It has a cathode bias power supply unit, an arc power supply unit, and a filament power supply unit For controlling the power supply of an indirectly heated cathode ion source output A control device is provided, preferably the device is responsive to a signal representative of the impedance of the load supplied by the cathode bias power supply unit to maintain the bias load impedance at a desired value. Adjusting the power supply unit for Filament supply controller I have. This filament supply controller may be used in combination or independently with the bias supply controller.
[0024]
By controlling the filament power supply to maintain the cathode bias load impedance constant, no separate cathode command signal from the outside is required to control the cathode bias load impedance. By maintaining the cathode bias load impedance substantially constant, the gain in the power control loop for the cathode bias power supply can be kept more constant for the required arc power changes. The gain control and the stability of the cathode bias power supply unit can be maintained up to the maximum output of the cathode bias power supply. In practice, the controlled impedance value of the cathode bias load can be selected according to the maximum output performance of the voltage and current of the cathode bias power supply unit, so that the output performance of the power supply can be maximized. Can do.
[0025]
Thus, the above apparatus may be used with a cathode bias power supply unit that produces a voltage feedback signal that is directly proportional to the output voltage for the load and a current feedback signal that is directly proportional to the output current for the load. In this case, the direct proportional relationship is such that when the value of the feedback voltage signal is equal to the value of the feedback current signal, the ratio of the output voltage to the output current is equal to the desired value of the bias load impedance. The filament supply controller may then respond to minimize the difference between the hoodback voltage and the current signal value. Thus, the filament supply controller may include an impedance comparator that derives a bias load impedance error signal from the difference between the voltage feedback signal and the current feedback signal from the cathode bias power supply unit.
[0026]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an indirect heating cathode ion source having separate filament power supply unit, cathode bias power supply unit and arc power supply unit, and bias supply controller and filament supply controller for them, according to an embodiment of the present invention. Will be described below.
[0027]
Referring to the figure, an ion source 10 is schematically represented. The ion source 10 may be in the form of an indirectly heated cathode type ion source as disclosed in the above-mentioned US-A-5497006. Accordingly, the ion source 10 is comprised of an arc chamber 11 that provides a conductive inner surface, an indirectly heated cathode element 12 and a separate filament 13.
[0028]
The arc power supply unit 14 applies an arc potential between the cathode element 12 and the wall 11 of the arc chamber, and the cathode element 12 is negatively biased with respect to the wall of the arc chamber 11. The cathode bias power supply unit 15 is connected to apply a cathode bias between the cathode element 12 and the filament 13, and the filament 13 is negatively biased with respect to the cathode element 12. The filament power supply unit 16 supplies a DC heating current through the filament 13.
[0029]
The cathode element 12 can be configured as a cylinder 17 that extends through an aperture 18 in the wall of the arc chamber 11, which is closed at its inner end by a “button” 19. Filament 13 is positioned near button 19 but spaced from its inner surface.
[0030]
In operation, the entire structure of the ion source 10 is in the exhaust region. A desired source gas is supplied into the arc chamber 11. The filament power supply unit 16 is controlled such that sufficient power is supplied to the filament 13, which emits thermal electrons. The cathode bias power supply unit 15 is controlled so as to accelerate these emitted electrons and to transmit energy by impacting the adjacent surface of the button 19 of the cathode element 12. This energy flowing to the button 19 effectively heats the button of the cathode element 12. The heating power transmitted to the cathode element 12 mainly depends on the power supplied by the bias power supply unit 15.
[0031]
The cathode element 12 is then heated sufficiently to emit electrons into the arc chamber. These emitted electrons are then accelerated by the electric field created by the arc power supply unit 14. Collisions that occur between these accelerated electrons and source gas molecules in the arc chamber 11 tend to ionize these molecules, increasing the number of available electrons and generating an arc plasma in the ion chamber 11. The arc power supply unit 14 controls the current flowing through the plasma in the arc chamber 11.
[0032]
In practice, a magnetic field is generated in the arc chamber 11 to concentrate the plasma in the central region of the arc chamber. Configurations for this purpose are well known in the art.
[0033]
In order to function as an ion source, the arc chamber 11 has an aperture, and ions generated in the plasma in the arc chamber are extracted by an extraction electrode having a negative potential with respect to the potential of the arc chamber 11. Configurations for extracting ions from the arc chamber and generating the required ion beam are also well known in the art and will not be described further here.
[0034]
The configuration described so far is similar to the configuration disclosed in US-A-5497006.
[0035]
Each power supply unit 14, 15 and 16 is a programmable power supply having voltage demand inputs 20, 21, 22 which can be set to control the maximum output voltage of the respective power supply unit. Each power supply unit also has a corresponding current demand input 23, 24, 25, which can be controlled to set the maximum output current of the corresponding power supply unit. Thus, each power supply unit responds to voltage demand and current demand signals at its respective inputs and provides an output voltage corresponding to the voltage demand input as long as the output current does not exceed the current demand input. In practice, the programmable power supply units 14, 15 and 16 are typically used in either a controlled current mode or a controlled voltage mode. In the accompanying drawings, the power supplies are shown as operating in a controlled current mode, with each power supply having a corresponding voltage demand input set to the highest possible input level. In this mode, each power supply operates to set an output voltage sufficient to deliver the required input current.
[0036]
The voltage demand and current demand input signals to each power supply unit can vary from zero volts appropriately corresponding to zero output voltage or current to 5 volts corresponding to maximum output voltage or current. In this embodiment, the arc power supply unit has an output voltage range of zero to 150 volts with an output current range of zero to 7 amps, and the cathode bias power supply unit 15 has an output voltage range of zero to 600 volts. With an output current range of zero to 2 amps, the filament power supply unit 16 has an output voltage range of 0 to 7.5 volts and an output current range of zero to 80 amps.
[0037]
Each power supply unit 14, 15 and 16 also provides a voltage feedback signal on each line 26, 27, 28 and a current feedback signal on each line 29, 30 and 31. These feedback signals also have a voltage range between 0 and 5 volts corresponding to the maximum range of power supply output voltage and output current. Thus, when the cathode bias power supply unit 15 passes an output voltage of 600 volts and an output current of 2 amps, the voltage feedback signal and the current feedback signals 27 and 30 are 5 volts representing the maximum.
[0038]
The arc power supply unit 14 is controlled by an arc current demand signal (arc I demand) of the current control input 23. The voltage control input 20 is set to a maximum (5 volts). The cathode bias power supply unit 15 receives a current demand signal from the bias supply controller 32 at its current control input 24. The voltage control input 21 of the cathode bias power supply unit 15 is set to the maximum (5 volts). The current control input 25 of the filament power supply unit 16 receives a current demand signal from the filament supply controller 33. The voltage control input 22 of the filament power supply unit 16 is held at the maximum (5 volts).
[0039]
Bias supply controller 32 receives a control input consisting of an arc voltage demand signal (arc V demand) on line 34 and a voltage feedback signal from arc power supply unit 14 on line 26. Filament supply controller 33 receives a control input consisting of a voltage feedback signal 27 from cathode bias power supply unit 15 to line 35 and a current feedback signal 30 from bias power supply unit 15 to line 36.
[0040]
In the illustrated configuration, the only external control signals received by the system are the arc voltage demand on line 34 and the arc current demand on input 23.
[0041]
The bias supply controller 32 issues power demand control to the cathode bias power supply unit 15. As described above, the arc power supply unit 14 is required to produce this arc current in order to produce an output current corresponding to the required current represented by the arc I demand in response to the arc current demand at the input 23. As long as the correct voltage is lower than the maximum output voltage of the power supply unit, here 150 volts, a sufficient output voltage is output from the power supply unit.
[0042]
Assuming that the ion source is operating with a plasma generated in the arc chamber 11, an arc current can flow and the required arc voltage depends on the impedance of the plasma. This output arc voltage on line 26 is compared in a comparator 37 with the required arc voltage represented by the arc V demand on line 34. If there is any difference between the actual arc voltage and the required arc voltage, an error signal adjusted by a three-term (Proportional Integral Derivative-PID) filter 39 is output to the line 38. The PID filter 39 includes an integral term and provides a signal on line 40 that functions as a power demand signal for the cathode bias power supply unit 15.
[0043]
The current demand signal at the control input 24 of the cathode bias power supply unit 15 controls the power supply so that the filament 13 and cathode in the ion source as long as the required output voltage of the bias power supply unit does not exceed the maximum output voltage, here 600 volts. An output voltage sufficient to output a required output current between the elements 12 is output. The output voltage value and the output current value output from the cathode bias power supply unit 15 are a line connected to a multiplier 41 that outputs a signal representing the product of the output voltage and the output current, that is, the output power of the cathode bias power supply unit 15 to the line 42. 27 and 30 are represented by feedback signals. This power signal on line 42 is compared in comparator 43 with the power demand signal on line 40. The bias power error signal to the line 44 corresponds to the difference between the power actually supplied by the power supply unit 15 and the required power represented by the signal on the line 40. This error signal is then adjusted with another PID filter 45 that also incorporates an integrator to provide a current demand signal that is supplied to the current control input 24 of the power supply unit 15.
[0044]
The feedback loop shown in the bias supply controller 32 causes the output power of the cathode bias power supply unit 15 to depend on the difference between the required arc voltage and the actual arc voltage delivered by the arc power supply unit 14 to the required power on the line 40. And act to maintain substantially the same. As can be seen, the cathode bias power supply unit 15 converts the power supplied to the cathode bias load by the bias power supply unit 15 into a chemical change in the arc chamber of the ion source, a change in gas pressure, or a physical change in the cathode structure. It has an inner power control loop that contributes to keep it substantially constant regardless of the impedance change of the load, which may occur.
[0045]
The PID filter 45 in the power control loop of the bias supply controller 32 gives a very fast response because the cathode bias load formed by the electron flow between the filament 13 and the button 19 of the cathode element 12 does not have much thermal inertia. be able to. As a result, the power control loop of the bias supply controller 32 allows the effective power delivered to the cathode to be very high for both changes in cathode bias load impedance resulting from changes in arc parameters and changes in power demand on line 40. Ensure that you respond quickly.
[0046]
In this way, the arc in the plasma chamber (between the cathode element 12 and the plasma chamber 11 wall) can be accurately controlled with a very short time constant.
[0047]
As described above, various changes in the ion source cause changes in the cathode bias load impedance. Filament supply controller 33 operates to control the power delivered to filament 13 so that such changes in cathode bias load impedance can be minimized. However, due to the thermal inertia of the filament 13, the filament supply controller 33 operates to maintain a relatively slow response to maintain stability.
[0048]
In the embodiment described above, the cathode bias power supply unit 15 is such that the maximum output voltage of the supply unit divided by the maximum output current of the supply unit is equal to the desired cathode load impedance corresponding to 300 ohms in this example. It is structured. Since the voltage and current feedback signals to the lines 27 and 30 from the cathode bias power supply unit 15 have a maximum value of 5 volts corresponding to the maximum voltage and current values, the voltage feedback signal to the line 27 is the line 30. It can be seen that the load impedance to the cathode bias power supply unit is always 300 ohms.
[0049]
These current and voltage feedback signals are supplied to the comparator 46 of the filament supply controller 33 by lines 35 and 36. The error signal on line 47 corresponds to the difference between these current and voltage feedback signals, so when this impedance is different from 300 ohms (in this embodiment), it will result in an error in the load impedance of the cathode bias power supply unit 15. Equivalent to. This error signal to line 47 is further fed to a PID filter 48 that incorporates an integrator and provides a filament power demand signal to line 49.
[0050]
The filament voltage feedback signal to the line 28 and the filament current feedback signal to the line 31 are supplied to the multiplier unit 50 in the filament controller 33, and the product of the output voltage and the output current of the filament power supply unit 16, that is, the power supply unit 16. A signal representing the power output of This power signal on line 51 is compared with the power demand signal on line 49 in comparator 52. A signal representing the difference between the actual power and the required power of the filament power supply unit 16 is a further PID including an integrator that provides a current demand signal for supply to the current control input 25 of the filament power supply unit 16 via line 53. Supplied to the filter.
[0051]
In this way, the current supplied by the power supply unit 16 is adjusted so that the total power from the filament power supply unit 16 corresponds to the required power to the line 49. Conversely, this required power to line 49 is such that the cathode bias load impedance is maintained at a predetermined constant value (here 300 ohms).
[0052]
As described above, the PID filters 48 and 54 in the filament supply controller 33 are arranged to react relatively slowly to match the time constant of the filament 13 due to the thermal inertia of the filament.
[0053]
Importantly, any change in the impedance of the filament 13 is automatically compensated by the inner power control loop of the filament supply controller 33.
[0054]
Furthermore, by controlling the filament power to keep the cathode bias impedance constant, the cathode bias power supply unit 15 can operate in a wide output power range without saturating.
[0055]
It is also important that no external control signals are required for the supply controller other than the arc V demand and arc I demand.
[0056]
The above embodiments of the present invention have been described with reference to individual components such as comparators, PID filters and multipliers. However, the functions of both the bias supply controller 32 and the filament supply controller 33 can be embodied as a digital signal processing apparatus that is appropriately programmed to provide the required functions as described above.
[0057]
In the embodiment described above, the arc power supply unit 14 receives the arc current demand signal at the current control input 23 and the resulting arc voltage is then compared with the arc voltage demand signal in the bias supply controller comparator 37, although these The two operations can be reversed. Thus, the arc voltage demand can be supplied directly to the voltage control input 20 to the arc power supply unit 14 while keeping the current control input 23 at a maximum of 5 volts. The current feedback signal on line 29 is then compared to the arc current demand to control the cathode bias power supply unit 15.
[0058]
Similarly, the embodiment described above has the current control input 24 of the cathode bias power supply unit 15 controlled by the bias supply controller 32 and the voltage control input 21 is held at a maximum of 5 volts. If the two controls are reversed, the current control input is held at 5 volts, and the control input from the bias supply controller 32 is supplied to the voltage control input 21.
[0059]
Again, the control inputs 22, 25 of the filament power unit 16 can be reversed.
[Brief description of the drawings]
FIG. 1 is a schematic view of an ion source 10. FIG.

Claims (13)

An output control device for controlling a power source of an indirectly heated cathode ion source having a cathode bias power source unit, an arc power source unit, and a filament power source unit , the parameter being an output voltage or an output current of an arc power source, and the parameter In response to a difference from the demand value of the parameter, a bias power demand signal representing the output power of the cathode bias power supply unit necessary to minimize the difference is generated, and in response to the bias power demand signal, An output control device comprising a bias supply controller that maintains the output power of the cathode bias power supply unit at the required output power.   The apparatus of claim 1, wherein the arc power supply parameter is an output voltage of the arc power supply unit.   The apparatus of claim 1, wherein the arc power supply parameter is an output current of the arc power supply unit. The bias supply controller is adapted for use with a cathode bias power supply unit, the cathode bias power supply unit representing a bias voltage feedback signal representative of an output voltage of the cathode bias power supply unit and an output current of the cathode bias power supply unit. A bias current feedback signal, the bias supply controller deriving a bias power feedback signal from a product of the bias voltage feedback signal and the bias current feedback signal; the bias power feedback signal and the bias power demand signal; A bias power comparator for deriving a bias power error signal from the difference between the bias power error signal and the bias power error signal for application as an output control signal to the cathode bias power supply unit. While settling, the includes a bias power error adjustment filter including a multiplier for controlling an output of the power supply unit so as to reduce the bias power error signal, according to claim 1 apparatus.   The bias supply controller includes an arc parameter comparator that derives an arc parameter error signal from the difference between a parameter of the arc power supply and the demand value of the parameter, and the arc parameter error signal to provide the bias power demand signal. The apparatus according to claim 1, further comprising an arc parameter error adjustment filter including an integrator for adjusting. Further comprising a filament supply controller, the filament supply controller, in response to the error parameter is the load impedance of the bias power to the desired value of the parameter of the bias power supply, filament power supply units required to minimize the error The filament power demand signal representing the output of the filament power is output, and the output power of the filament power supply unit is maintained at the required power in response to the filament power demand signal. Equipment. An output control device for controlling the power supply of an indirectly heated cathode ion source having a cathode bias power supply unit, an arc power supply unit, and a filament power supply unit , the device comprising a bias for a desired value of a bias power supply parameter In response to an error in a parameter that is a load impedance of the power supply, a filament power demand signal representing an output of the filament power supply unit necessary to minimize the error is generated, and in response to the filament power demand signal, An apparatus comprising a filament supply controller that maintains the output power of the filament power supply unit at the required power. The filament supply controller is adapted for use with a filament power supply unit , the filament power supply unit including a filament voltage feedback signal representative of an output voltage of the filament power supply unit and a filament current feedback representative of an output current of the filament power supply unit. With a signal ,
The filament supply controller includes a filament multiplier that derives a filament power feedback signal from a product of the filament voltage feedback signal and the filament current feedback signal, and a filament power error signal from a difference between the filament power feedback signal and the filament power demand signal. a filament power comparator to derive, by adjusting the filament power error signal controls the output of the filament power supply unit so as to reduce the filament power error signal, for application as an output control signal to said filament power supply unit The apparatus according to claim 6, further comprising a filament power adjustment filter including an integrator. The filament supply controller includes a bias parameter error adjustment filter including an accumulator that adjusts a bias parameter error signal that represents an error in the bias power supply parameter to generate the filament power demand signal. The apparatus of any one of -8.   2. A filament supply controller that adjusts the filament power supply unit to maintain the bias load impedance at a desired value in response to a signal representative of an impedance of a load supplied by the cathode bias power supply unit. The apparatus of any one of -5. An output control device for controlling the power supply of an indirectly heated cathode ion source having a cathode bias power supply unit, an arc power supply unit, and a filament power supply unit, the device being supplied by the cathode bias power supply unit An apparatus having a filament supply controller for adjusting the filament power supply unit to maintain the bias load impedance at a desired value in response to a signal representative of a load impedance. The bias supply controller is adapted for use with a cathode bias power supply unit , the cathode bias power supply unit for a voltage feedback signal having a first direct relationship with an output voltage for the load and an output current for the load. It issues a current feedback signal having a second directly proportional relationship, wherein the first directly proportional relationship, and the second directly proportional relationship, when the voltage value of the voltage feedback signal becomes equal to the voltage value of the current feedback signal, output being adapted to the ratio of voltage and the output current becomes equal to the desired value of the bias load impedance, the filament supply controller, minimizing the difference between the voltage value of the voltage value and the current feedback signal of said voltage feedback signal claim responds to reduction 6-1 Apparatus according to any one of. The apparatus of claim 12 , wherein the filament supply controller includes an impedance comparator that derives a bias load impedance error signal from a difference between the voltage feedback signal and the current feedback signal from the cathode bias power supply unit.

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