GB2170619A - Device for controlling the current of an electromagnetic lens - Google Patents
Device for controlling the current of an electromagnetic lens Download PDFInfo
- Publication number
- GB2170619A GB2170619A GB08601293A GB8601293A GB2170619A GB 2170619 A GB2170619 A GB 2170619A GB 08601293 A GB08601293 A GB 08601293A GB 8601293 A GB8601293 A GB 8601293A GB 2170619 A GB2170619 A GB 2170619A
- Authority
- GB
- United Kingdom
- Prior art keywords
- current
- electromagnetic lens
- output
- input
- digital
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
- G05B19/07—Programme control other than numerical control, i.e. in sequence controllers or logic controllers where the programme is defined in the fixed connection of electrical elements, e.g. potentiometers, counters, transistors
- G05B19/075—Programme control other than numerical control, i.e. in sequence controllers or logic controllers where the programme is defined in the fixed connection of electrical elements, e.g. potentiometers, counters, transistors for delivering a step function, a slope or a continuous function
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Automation & Control Theory (AREA)
- Feedback Control In General (AREA)
- Lens Barrels (AREA)
- Microscoopes, Condenser (AREA)
Abstract
A device for controlling the current of an electromagnetic lens comprising a pulse generator (1) connected in series with an electromagnetic lens current reversal unit (3) and a reversible pulse counter (4) having its less significant digits output connected to an input of a digital-to-analog converter (5) whose output is electrocally connected with the electromagnetic lens (2). To the other input of the converter (5) the output of a switching circuit (10) is connected, an input (11) of which being connected to the output of a permanent memory (9), an input (13) being connected to the output of a decoder (12) and an input (14) being connected to the output of the more significant digits output of the pulse counter (4). The inputs of the permanent memory (9) and the decoder (12) are connected to the output of a word address former (8). The device may be operated in manual or programmed mode with fine manual adjustment being possible during programmed operation. <IMAGE>
Description
SPECIFICATION
Device for controlling the current of an electromagnetic lens
The invention relates to the electron-beam technology, and more particularly, to a device for controlling the current of an electromagnetic lens used in general in electronic microscopes, electron-diffraction apparatuses and electron-beam devices for processing parts (welding in particular) as well as electron-beam lithography.
A device for controlling the current of an electromagnetic lens should meet the requirements based on the specific features of controlling a lens with an electron beam. These include the speed of the device and efficiency of its control. The speed here means the possibility to vary the lens current according to a pre-set program with the manual adjustment of current in a narrow range, storing the program when the power supply is switched off, the possibility of a rapid reprogramming depending on the parameters of an electromagnetic lens, the possibility of a rapid transition from a programmed mode to the manual adjustment of the electromagnetic lens current.
The control efficiency is determined by the possibility of the manual adjustment of the electromagnetic lens current in the range between zero and its maximum value as well as the digital indication of an actual value of the electromagnetic lens current.
Solving the problem concerning speed and control efficiency has become possible using elements of the computer technology. Thus the publications recently appeared describing devices for controlling the electromagnetic lens current which solve this problem to this or other extent.
Known in the art is a device for controlling the current of an electromagnetic lens (cf.
USSR Inventor's Certificate No. 1050009, C1.
H 01, J 37/14, publ. 1983) comprising a pulse generator, an electromagnetic lens current reversal unit, a reversible counter and a digital-to-analog converter connected in series, the output of the digital-to-analog converter being connected to an electromagnetic lens current amplifier. A parallel data exchange unit provided in the device makes it possible to record in a working memory current codes obtained at the output of the first digital-toanalog converter for the lens modes established during operation and to perform manual adjustment of current using a second digitalto-analog converter.
Thus using this device, the electromagnetic lens current can be set according to a program from the working memory, and the manual current adjustment can be performed in a narrow range. However, when the power supply is switched off, the current code information stored in the working memory is lost and when the power supply is switched on again the information is to be restored, much time being spent on establishing the desirable modes of lens operation and their rewriting in the working memory which results in a decrease in the device speed. Since there are two digital-to-analog converters, it is necessary to add the two analog signals obtained at their outputs in an adder which results in a more complicated circuitry and impairs reliability of the device as a whole.Since the digital indication of the current sent to the digital-toanalog converters is not provided, it is impossible to set the desired values of the electromagnetic lens current when it is manually adjusted, which impairs the efficiency of controlling the electromagnetic lens current.
Known in the art is also a device for controlling the current of an electromagnetic lens (cf. Japanese Patent No. 58-16745, C1. H 01
J 37/10, publ. April 1, 1983), comprising a pulse generator connected in series with an electromagnetic lens current reversal unit, a reversible pulse counter and a digital-to-analog converter having its output electrically connected with the electromagnetic lens. In addition to the counter, the device incorporates other reversible pulse counters, their total number corresponding to the possible number of modes of operation of the electromagnetic lens. The outputs of less and more significant digits of all counters are electrically connected with the digital-to-analog converter via a mode switch which connects a chosen reversible counter to the pulse generator and the digitalto-analog converter.The digital-to-analog converter consists of a reversible counter code decoder and a reference voltage switch controlled by the signals coming from the output of the code decoder. A control program is defined by a reference voltage taken from a resistor voltage divider, each output of the divider corresponding to one of the modes of operation and magnification produced by the electromagnetic lens.
Therefore this device impiements the possibility to vary the lens current according to a chosen program and to store the programs when the power supply is switched off since the lens current is controlled by the reference voltage resistor divider.
Storing a program when the power supply is switched off do not, however, permit the effective control of the electromagnetic lens current since current can only be adjusted according to a pre-set program and the manual adjustment cannot be performed not only in the entire range of the electromagnetic lens current variation but also in a narrow range.
Therefore, when the electromagnetic lens parameters are changed, much time is required to reprogram the device operation which essentially lowers the device speed.
In addition, the data from the reversible counter outputs arriving at the digital-to-analog converter do not correspond to the current flowing in the electromagnetic lens due to the presence of the reference voltage divider. It is therefore impossible to obtain information on the actual value of the current flowing in the electromagnetic lens which is necessary to choose a mode of operation of the lens.
It. is an object of the invention to provide a device for controlling the current of an electromagnetic lens having high speed and control efficiency.
The invention resides in that a device for controlling the current of an electromagnetic lens comprising a pulse. generator connected in series with an electromagnetic lens current reversal unit and a reversible pulse counter having its less significant digits output connected to an input of a digital-to-analog converter whose output is electrically connected with the electromagnetic lens, according to the invention, also comprises a word address former connected in series with a permanent memory and a switching circuit having its output connected to the other input of tHe digitalto-analog converter, end a decoderhaving its input connected to the output of the word former and its output connected to the re respective input of the switching circuit having its other input connected to the more significant digits output of the reversible pulse counter.
A device for current control preferably comprises an electromagnetic lens current digital indication unit having its inputs connected to the switching circuit output and the less sign!- ficant digits output of the reversible pulse counter.
Dividing the digital data concerning an actual value of the electromagnetic lens current obtained at the outputs of the pulse counter makes it possible to perform the manual adjustment of the electromagnetic lens current in a narrow range using a single digital-to-analog converter, which is necessary when working with an object with varying thickness. The current adjustment in a narrow range during the programmed operation of the electromagnetic lens is also necessary to correct timevarying parameters of the electromagnetic lens, e.g., when the value of clearance at the pole piece changes both during operation and as a result of the routine cleaning of the electromagnetic lens core elements.
The provision of a permanent memory in the device for controlling the current of the electromagnetic lens makes it possible to store the information concerning the modes of operation of the lens when the power supply of the whole device is switched off. Thus the device speed is increased since the electromagnetic lens is supplied in accordance with a pre-set mode immediately after it has been switched on.
The switching circuit used in the device provides for a rapid transition from the programmed modes of operation of the electromagnetic lens to the manual current control when the programmed modes of operation are suitable for test conditions, so as to allow, in the end, the apparatus time to be used more effectively, the productivity of an apparatus incorporating the electromagnetic lens being improved.
On the one hand, the visual digital indication of the current flowing in the electromagnetic lens improves labour conditions for an operator in a man-machine systeme. On other hand, during a free-mode operation, when the, electromagnetic lens current variation in the entire adjustment range is performed manually, the visual digital indication makes it possible to choose promptly desirable modes of operation of the electromagnetic lens and to put them into a control program, thus improving the control efficiency.
A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which shows a functional block-diagram of a device for controlling the current of an electromagnetic lens according to the invention.
A device for controlling the current of an electromagnetic lens comprises a pulse generator 1 having a pulse repetition rate variable in a wide range depending upon a desired rate of change of current in the electromagnetic lens 2. The output of the pulse generator 1 is connected to the input of an electromagnetic lens current reversal unit 3 which gates the pulses to an adding (+) or subtracting (-) input of a reversible pulse counter 4. The number of digits of the counter is determined by the required current variation steps of the electromagnetic lens 2. The output of less significant digits of the reversible pulse counter 4 whose number depends upon the range of the manual adjustment of current in the electromagnetic lens 2 is connected to a respective input of a digital-to-analog converter 5.The analog signal from the output of the digital-toanalog converter 5 goes to the control input of a regulated electromagnetic lens current stabilizer 6 whose output is connected to the electromagnetic lens 2. Series-connected with the electromagnetic lens 2 is a resistor 7 in a feedback ioop of the electromagnetic lens current stabilizer 6, the signal from the resistor being fed to the input of the feedback circuit of the stabilizer 6. The source of the reference voltage U of the digital-to-analog converter 5 and the resistor 7 in the feedback loop of the stabilizer 6 are chosen in such a manner that the current code applied to the inputs of the digital-to-analog converter 5 should correspond to the current flowing in the electromagnetic lens 2.
For operation in the programmed modes of the electromagnetic lens 2, the device comprises a word address former 8 connected in series with a permanent memory 9 and a switching circuit 10, the permanent memory 9 being connected to an input 11 of the switching circuit 10. The former 8 can be controlled both manually, with the help of a switch, and by a computer. The output of the former 8 is also connected to the input of a decoder 12 having- its output connected to an input 13 of the switching circuit 10.
When a word address is applied to the input of the permanent memory 9, the latter produces at its output a digital value of current in parallel codes, which corresponds to the chosen mode of operation and magnification produced by the electromagnetic lens 2.
By incrementing the contents of the permanent memory 9, one can realize any desired number of modes and magnifications obtained using the electromagnetic lens. The distingu- - ishing feature of the permanent memory 9 is the possibility of a long-term storage of the recorded information after the power supply is switched -off.
The more significant digits output of the reversible pulse counter 4 is connected to an input 14 of the switching circuit 10 having its output connected to the other input of the digital-to-analog converter 5. Depending on the signal fed from a decoder 12 to the input 13, the switching circuit 10 will connect the output of the permanent memory 9 or the more significant digits of the reversible pulse counter 4 to the respective input of the digital-to-analog converter 5, the connection of the more significant digits of the reversible counter 4 being effected if a digital code is generated at the input of the decoder 12.
which corresponds to a free-mode operation of the electromagnetic lens 2 so as to enable manual adjustment of-current in the electromagnetic lens 2 in the range between zero and its maximum value from the pulse generator 1.
For visual indication of current in the electromagnetic lens 2, the device comprises an electromagnetic lens current digital indication unit 15 having its inputs connected to the output of the switching circuit 10 and the less significant digits output of the reversible pulse counter 4.
The device for controlling the current of an electromagnetic lens functions as follows.
There are two basic modes of operation of the device: a free-mode operation in which current in the lens 2 is manually adjusted in the range between zero and its maximum value, and operation with programmed values of current in electromagnetic lens 2.
The free-mode operation is necessary, e.g., for the permanent memory 9 programming.
To choose this mode, at the output of the word address former 8 a free-mode code is produced and sent to the input of the decoder 12. If a free-mode code is received at the input of the decoder 12, the latter sends to the input 13 of the switching circuit 10 a signal resulting in connecting the more significant digits of the pulse counter 4 to the respective input of the digital-to-analog converter 5. After that, using the pulse generator 1, the current reversal unit 3 and the reversible pulse counter 4 the desired current in the electromagnetic lens 2 or the desired magnification produced by the electromagnetic lens 2 can be set, and, using the digital indication unit 15, the value of current flowing in the electromagnetic lens 2 with the given magnification can be defined.
The adjustment of current of the electromagnetic lens 2 is carried out as follows.
When a current code obtained at the outputs of the reversible pulse counter 4 and sent to the inputs of the digital-to-analog converter 5 changes, the voltage at the output of the digital-to-analog converter 5, which is a control voltage for the current stabilizer 6, will also change. The current stabilizer 6 starts changing the current flowing in the electromagnetic lens 2 and the feedback resistor 7 until the voltage applied to its other input, via the feedback resistor 7, becomes equal to the voltage from the digital-to-analog converter 5.Since the reference voltage U of the digital-to-analog converter 5 and the rating of the feedback resistor 7 are chosen in such a manner that a current code at the inputs of the digital-toanalog converter 5 should correspond to the value of the current flowing in the electromagnetic lens 2, the stabilizer 6 stops changing the current as soon as the current in the electromagnetic lens 2 reaches the value corresponding to the pre-set current code at the input of the digital-to-analog converter 5, and the desired current value is established in the electromagnetic lens 2. The digital information on the value of current of the electromagnetic lens 2 which corresponds to the pre-set magnification produced by the lens is read from the digital indication unit 15.On the basis of this information, the programming of the permanent memory 9 by the more significant digits of the digital information is carried out.
The code of the more significant digits current is written in the form of a word having an address and corresponding to a predetermined magnification produced by the electromagnetic lens 2.
The operation with the programmed values of current in the electromagnetic lens 2 consists in producing at the output of the word former 8 a word address previously recorded in the permanent memory 9 and corresponding to a chosen magnification produced by the electromagnetic lens 2. The decoder 12 sends to the input 13 of the switching circuit 10 a signal resulting in the output of the permanent memory 9 being connected to the respective input of the digital-to-analog converter 5.
Thus, a current code is formed at the inputs of the digital-to-analog converter 5, the more significant digits of the code coming from the permanent memory 9 and the less significant digits, from the pulse counter 4. Current adjustment due to code variation of the less significant digits of the pulse counter 4 is carried out similarly to the manual adjustment of current in the electromagnetic lens 2. Using the digital indication unit 15 in this mode, the operation of the permanent memory 9 can be supervised.
Use of the device for controlling the current of an electromagnetic lens due to its high speed and effective control makes it possible to considerably improve the efficiency of investigations when the device is employed in electronic microscopes as well as productivity of electron-beam devices.
Claims (3)
1. A device for controlling the current of an electromagnetic lens including a pulse generator connected in series with an electromagnetic lens current reversal unit and a reversible pulse counter having its less significant digits output connected to an input of a digital-toanalog converter whose output is electrically connected with the electromagnetic lens, a word address former connected in series with a permanent memory and a switching circuit having its output connected to the other input of the digital-to-analog converter and a decoder having its input connected to the output of the word address former and its output connected to the respective input of the switching circuit having its other input connected to the more significant digits output of the reversible pulse counter.
2. A device for controlling the current as claimed in claim 1, wherein an electromagnetic lens current digital indication unit is connected to the switching circuit output and to the less significant digits output of the reversible pulse counter.
3. A device for controlling the current of an electromagnetic lens substantially as hereinabove described with reference to, and as shown in the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SU853849367A SU1415270A1 (en) | 1985-01-31 | 1985-01-31 | Device for controlling the current of electromagnetic lens |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8601293D0 GB8601293D0 (en) | 1986-02-26 |
| GB2170619A true GB2170619A (en) | 1986-08-06 |
Family
ID=21160577
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08601293A Withdrawn GB2170619A (en) | 1985-01-31 | 1986-01-20 | Device for controlling the current of an electromagnetic lens |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS61198538A (en) |
| DE (1) | DE3602482A1 (en) |
| GB (1) | GB2170619A (en) |
| NL (1) | NL8600223A (en) |
| SU (1) | SU1415270A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2215947A (en) * | 1987-03-19 | 1989-09-27 | Jeol Ltd | Controlling an electron microscope |
-
1985
- 1985-01-31 SU SU853849367A patent/SU1415270A1/en active
-
1986
- 1986-01-20 GB GB08601293A patent/GB2170619A/en not_active Withdrawn
- 1986-01-28 DE DE19863602482 patent/DE3602482A1/en not_active Withdrawn
- 1986-01-30 NL NL8600223A patent/NL8600223A/en not_active Application Discontinuation
- 1986-01-30 JP JP1696886A patent/JPS61198538A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2215947A (en) * | 1987-03-19 | 1989-09-27 | Jeol Ltd | Controlling an electron microscope |
| GB2215947B (en) * | 1987-03-19 | 1992-11-04 | Jeol Ltd | Control system using an external computer for an electron microscope |
Also Published As
| Publication number | Publication date |
|---|---|
| NL8600223A (en) | 1986-08-18 |
| GB8601293D0 (en) | 1986-02-26 |
| JPS61198538A (en) | 1986-09-02 |
| SU1415270A1 (en) | 1988-08-07 |
| DE3602482A1 (en) | 1986-08-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |