DE1589906B2 - SCANNING ELECTRON MICROSCOPE - Google Patents

Description

the variation in the intensity of the electron beam. 2 is a block diagram showing the structure of a

on the other hand is guaranteed. Scanning electron microscope in accordance with the invention

According to the invention, the task at hand is there training and

solved by that to the pulse generator for Vari- ', Fig. 3 is a graphical representation of the waves the intensity of the object-scanned elec- 5 forms to illustrate the operation of the electron beam also has a phase-sensitive scanning electron demodulator designed according to the invention for modulating the intensity of the microscope.

Electron beam synchronous rectification of the parts shown in FIG. 1 shown known electron

the separation stage derived from the scanning signal microscope with object scanning has one of a

AC component is connected. io loading an electron beam emitting wire 1

The inventive design of a grid standing electron gun, a Wehnelt cylinder

electron microscope leads to a large number of the 2 and an anode 3. In addition, the elec-

Advantages of which only the following particularly electron microscope continues a condenser lens 4 for

are to be enumerated: the electron beam, a deflection device 5, the

1. The electron microscope can particularly 15 a deflectable electron beam 16 onto an object for the examination of objects, such as project 6 directed, a detector 7, such as. B. a photoconductor object, use as the scan image without a multiplier or a secondary electron multiplier can be observed while looking at the fan to determine backscattered or reflected Object a direct voltage as continuous pre-electrons and secondary electrons, a direct voltage is present, ao current amplifier 8, on and off switches 9, 10 and 14,

2. Any noise at frequencies other than a cathode ray oscilloscope 11, a deflection span -x of the pulse frequency of the electron beam modulating source 12 for the deflection device 5 and the j ling pulses, in particular any secondary oscilloscope 11 and a high voltage source 13 for

DC voltage noise as a result of thermospan the acceleration of the beam electrons. ^:

nings or the like, can be made by attaching 25 .. It is now assumed that the object 6,

Means, such as, for example, a matched version, can be scanned by the electron beam 16

stronger, completely suppress. is supposed to be a semiconductor device -which has a p-n-

3. Contains the possibility of a complete switch-off transition. Because in such a case the The processing of the noise leads to an improvement in the electron volta effect in the object 6 Sensitivity of the detection and enables the voltage generated depending on the voltage generated over a according to. a decrease in the. Electron beam bias source 15 applied to object 6 Stromes. As a result, it is possible to have an electrical bias that can be varied in detail inner beam with a smaller diameter than before for information about the structure of the p-n junction use, and thereby the resolving power to only successfully obtain when it is possible to use the enlarge and often with the measurement of the specific 35 type of change of the on the cathode ray oscilloscope Resistance of an object-related error scope 11 appearing scan image under Conditionunzu Reduce. .- ■ .... genes to be observed in which the preload remains

4. The previous requirement for a completely applied to the object 6. With regard to the shielding of the means of detecting the. that in the electron microscope with Objektab electrons such. B. of the photomultiplier, opposite 4o _; Sensing the previously known type of electrons using outside light is extremely difficult. In the case of the invention beam 16 has a constant intensity which, as the photomultiplier is already mentioned above, does not vary with time

J) is not adversely affected, since the Si to be recognized the object 6 generated voltage in the form of a

gnal has a pulsating waveform. 45 DC voltage and cannot be influenced by the as

5. The intensity modulation of the oscilloscope leaves bias applied to the p-n junction differ not only with a DC modulation DC voltage. It therefore prepares system, but also by an alternating current modulus caused by the electron voltalation system make what the build-up of the Inten effect in the object 6 generated voltage in the sub-intensity modulation system much simplified and 50 divisible way to determine. To overcome the system makes it very cheap. this difficulty has already been tried, the

In a preferred embodiment, for a voltage taken from the object, a DC voltage

according to the invention designed to superimpose scanning electron microvoltage in such a way that the portion

The scope contains the separation stage a filter to cut off the bias voltage and thus only the

cut a direct current component and a 55 going back to the electron volta effect

downstream tuned amplifier. Except voltage is tapped. However, it can be easily

an integrator can simulate the demodulator that the correct adjustment for a

be switchable, the the alternating current component of the suppression only the portion of the bias voltage

Scanning signal for generating the scanning image while at the same time continuously creating the pre

integrated, and a further development of the invention voltage to the object is technically very difficult

tion consists in the fact that the object can be reached in advance.

Voltage source can be connected. In addition, since the electron volts

To further explain the invention, reference is now made to the drawing, effect induced voltage in the order of magnitude; If this is 10 ~ ⁸ volts, an attempt is made to find this chip. 65 voltage with the help of the usual broadband direct current

F i g. 1 is a block diagram showing the structure of an amplifier 8 to amplify, often to a voltage

Electron microscope with object scanning in up-to-air level, which is below the noise level of the

previous design shows, amplifier 8 is so that it is impossible to

5 6

to determine the reduced voltage in a useful way. is borrowed, with regard to a high noise level Another difficulty arises in the fact that the amplifier has a high sensitivity to the expected strength stage, as in most cases, as has already been pointed out above. At the same time a thermoelectric voltage in the order of magnitude leads inevitably to every attempt to detect 10 ~ ⁶ volts. In such a situation, the sensitivity of an electron microscope to the demand for amplifier 8, even if the noise level of the previous type is increased, is below 10 ~ ^fi volts, impossible to increase the electron beam current, which makes it possible to decide whether the determined signal voltage in turn gives rise to an increase in the diameter of the induced voltage described above or the electron beam and thus represents a thermal voltage. io reduction in resolving power.

It is now assumed that the Detek-Wie F i g. 2, in which to denote the same parts gate 7 is in the form of a photomultiplier, so the same reference numerals are used as in FIG that the backscattered or reflected electrons F i g. 1, shows, possesses the inventive and secondary electrons emitted from the object 6-grain electron microscope with object scanning Never, to achieve a scan image for the object 15 an electron-emitting wire 1 existing ject 6 can be used. In a sol electron gun, a Wehnelt cylinder 2, a Chen case it turns out to be necessary, the rear anode 3, a condenser lens 4 for the electron beam or reflected electrons or secondary beam, a deflection device 5 for the electron final electrons to accelerate these electrons to beam for deflectable alignment of the electrons In the drawing, not shown fluorescent beam 16 on an object 6, a detector 7, such as to let the substance impinge to this sub- e.g. a photomultiplier or a secondary punch to shine, and that from the electron multiplier to detect backscattered fluorescent substance emitted light with the help of electrons and secondary electrons, on and off Photomultiplier switch to an electrical signal 9, 10, 14 ', 27 and 28 to select a cathode ray. In this case too, the oscilloscope 11 has a high voltage source 13 for the Radiation of the fluorescent substance obtained acceleration of the beam electrons and a pre-light signal a constant intensity which with time becomes voltage source 15. In the electron microscope does not vary, and even the entry of the common transformer 17 with the exit of the Detekringsten Part of the outside light is connected in the photomultiplier 7 and in this way serves as a sound box a useful signal detection device would be possible for separating a DC voltage component do. Recently, the signal determined by the detector 7 has been used instead of the component. Photomultiplier uses a p-n junction, but the transformer 17 can be through a Kondoch the situation remains the same as in the capacitor to be replaced. It also has an Elek trap signal recognition by the photomultiplier microscope, a tuned amplifier. In the same way, the previous marker 18, a phase-sensitive demodulator 19, method of detecting the flowing into the object 6 a pulse generator 20, a phase shifter 21, Electron flow unsatisfactory, since it is hardly possible to use a pulse transformer 22.

1 sheet of drawings

Supplementary sheet to interpretation document 15 89 9 0 6
Int. Cl. ² : HOlJ, 37/28

Date of publication: October 5, 1972

7 8

an additional bias source 23, a DC amplifier 24 to electrostatic deflection plates 5 '

Current amplifier 24 and a voltmeter 25. The trans- is applied. Of course, the distraction

formator 17, the tuned amplifier 18, the system 5 can also be constructed so that it can be used as a

phase-sensitive demodulator 19 and the phase electromagnetic deflection system using

slide valves 20 form part of the detector means; 15 formation of an electromagnetic deflection coil works,

however, the object 6 can of course also be scanned instead

use other components. It is also clear as soon as switches 9 and 27 are engaged

that the oscilloscope 11 in the electron microscope and the switch 14 'is in its grounding position

inside with a deflection voltage source 12 as taken. With this switch position

it is shown in Fig. 1, is equipped. 20 reflected electrons and secondary electrons that

As described above, the invention coming from the object 6 through the detector 7 is suitable according to electron microscope can be recognized with object scanning. As an alternative, the scarffor an operation with an electron beam, of which 9 and 27 are opened, and the switch 10 This intensity varies periodically. For this purpose can be inserted to an object stream or For example, square-wave pulses with a repetition frequency of 25 generate an electron flowing into the object 6 1 kHz from the pulse generator 20 to take off current. There is another possibility testifies and via the pulse transformer 22 to the fact that the switches 10 and 27 turned on who-WEHNELT-cylinder 2 created. This is of the and the switch 14 'is operated so that it is with the wire 1 is connected to a pulsating electron beam 16 from the bias voltage source 15 in order to given, but it goes without saying that the 30 induced one of the electron voltaic effect Pulse frequency does not decrease in any way to the above voltage.

given frequency of 1 kHz is limited and that it is assumed, for the sake of example, that the object instead of any other suitable frequency is a semiconductor device that can be freely selected. Likewise, the pulsating pn junction needs to have. Then the electron beam does not necessarily have a rectangular waveform, as above, an electron-volta effect whenever the transition occurs. scanned by the pulsating electron beam 16 If the pulsating electron beam, however, a pulsating voltage is induced and this form of a sine wave, the result is considerable pulsating voltage 18 as shown in FIG. 3 a is shown, which is fed completely freely 40, which amplifies only the pulse component with the Im of each alternating current component, since normal pulse frequency 1 kHz. In this case, the example has od a drift change. Like. In the output signal voltage induced a pulsating waveform, the pulse generator 20 and usually unavoidable whose amplitude due to the fact that it the bar g in a in F i. 3 b is superimposed on pre-DC voltage shown, varies. Since the stored direct current component E occurs. The on '45 tuned amplifier 18, however, the tuning circuit contact of such a DC component E leads at its input side, has merely the through Inevitably for generating a noise in-gear of an AC component allows, is due to thermal stresses as already described above, only one such AC component in which has been exposed . In order to push the rectification through the phase sensitive to the sine wave amplifier 18 and then a synchronously connected DC component, a DC bias must be subjected to reverse demodulator 19, which creates it as a pulsating polarity and emits it as a function of the signal. The for the modulation of the Elek change the sinusoidal voltage can be varied. In- tron beam used pulses from the impulse insofar as a rectangular waveform, as it is used in the generator 20, is shown in such a manner in FIG. synchronous rectification of the direct current component described without creating that from the pulses only a sinusoidal component can be made to zero by deriving the pre-shaped component and passing through the voltage only according to the change in phase shifter 21 to the phase-sensitive peak value E _{2 of} the rectangular waveform is passed on in demodulator 19. . adjusts appropriately. : 60 r With the above arrangement, the

Subsequently, the pulsating electron beam object 6 will completely switch off applied DC bias voltage on the 16 by the deflection device 5 synchronously with the detector side, and since the scanning on the oscilloscope 11 along two. The induced voltage is deflected by the sinusoidal component dimensions and in this way scans the component in the pulses for the strand modulation of an object 6 . The deflection device 5 is subjected to synchronous rectification and can be constructed in such a way that it operates as an electrical deflection system at the junction with a signal of the same polarity with which the deflection signal for the oscilloscope and the induced voltage are determined. After amplification by the direct current, the scope 11 can generate a scan image on the oscilloscope 11.

hold and the intended purpose can be achieved when the switch 28 is closed and that pulsating signal after it has been subjected to synchronous rectification to effect the intensity modulation for the oscilloscope 11 is used. The intensity modulation system for the oscilloscope 11 does not belong to the previously known type with direct current modulation, how they z. B. is described on page 1476 in "Japan Applied Physics", No. 36 from 1965, but to a type with alternating current modulation, as for example in the book by G. Parr and O. H. Davie "The Cathode-ray Tube and its Applications," published by Reinhold Publishing Corporation, New York, 1959, is described on page 222 as that of the synchronous Rectified signal at the switch 9 has a pulsating waveform with a Has a frequency of 1 kHz. In this way is a universal oscilloscope that used earlier in the art was common, sufficiently usable for the intended purpose.

The above description relates to the extraction of a sample image from one in the object voltage induced by the electron volta effect. Similarly, if the Determination of an object current or an electron current flowing into the object is based on the working method hit in such a way that only an alternating current component is picked out from the object current and then reinforced. In this mode of operation, noise can be heard at a different frequency than the signal frequency of 1 kHz completely, and the detection sensitivity can be can be significantly improved. In the case of a recognition of reflected electrons and secondary electrons a circuit of the same type as that described above in connection with the Use detector 7, which can be a photomultiplier, since its output is an AC signal is. An alternative arrangement can also be used in which the synchronous rectification is not used and other operations the detected AC signal is only rectified to a To obtain a direct current signal, and to achieve the intensity modulation for the oscilloscope 11 can a DC modulation system can be used. For this purpose, the operating system can be adapted. The solution to the intended purpose can be appropriately modified.

In connection with the above case, the diffusion potential can, for example, at a p-n junction can be eliminated by a forward bias voltage, which is caused by the electron volta effect to make induced voltage zero. This makes it possible to determine the diffusion potential on the basis of the value of such Measure preload. For this purpose, a DC bias can be used from the DC bias source 15 can be applied to the semiconductor object 6 in order to achieve the above-mentioned forward direction Generate bias voltage that can be read on the voltmeter 25. If at the same time the scanned image is observed on the oscilloscope 11 until the observation result on this scan image indicates that the induced voltage has been made zero, the voltmeter reading shows 25 at this moment the value of the diffusion potential, and in this way it can be Measure diffusion potential easily.

In the case of such a semiconductor object, its specific resistance can also be measured by the arrangement is made in such a way that only the induced voltage is determined without the above-mentioned one Pre-DC voltage is applied. As is well known, it is very important for improvement the properties and uniformity of a device such as one from Semiconductor material made transistor, its specific resistance and its distribution in to know the semiconductor material.

The induced voltage V, which appears on the sample 6 as a result of the electron-volta effect when the electron beam scans the sample in the direction of its ΛΓ-axis without the application of a DC bias, can be given by the equation

AV

express, in which I _{B is} the electron current, r is the resistance between the point of electron bombardment and a grounded point, and Δ V is the electromotive force developed from the electrons and holes generated by the bombardment in the semiconductor sample and is proportional to the distribution of the specific

Resistance ~~ - in the semiconductor sample. That's why

the relationship V ^ AV can be obtained if I _B alone can be made sufficiently small without reducing the radiation energy of the electron beam. It can thus be understood that a quantity proportional to the specific resistance ρ can be obtained by integrating the above value of V , and thereby the specific resistance of the semiconductor sample can be easily measured.

According to the invention, the electron beam is pulsed in the manner described above, and therefore any unfavorable influence of the thermal voltage resulting from the electron bombardment completely switched off. As a result, on the output side of the phase-sensitive demodulator 19 attach an interator 26, the switch 28 can be brought into its open position and the. Switch 29 closed to the output signal of the integrator 26 in the oscilloscope 11 to the To feed in intensity modulation. This mode of operation allows the distribution of the specific Resistance in the semiconductor sample 6 in two-dimensional Watch wise.

Claims (4)

1 2 gnal is always in the form of a direct current, with patent claims: afflicted with various inevitable defects. U.S. Patent 2,348,030 and pages 15-23 of the August 1942 ASTM Bulletin 1. Scanning electron microscope with an Im- 5 further described an electron microscope in which pulse generator for periodically varying the one electron source an electron beam from intensity one sends an object to be examined, the intensity of which is transmitted by one with the electrical end Electron beam, a square wave generator connected to an oscilloscope electron source phen for displaying the scan image of the object can be varied in time with its output signal. and a separation stage for feeding the oscilloscope. The electron graph arrives from the electron source with a beam derived from the scanning signal through a lens system at the rear that focuses it AC component, thereby through to a slide on which a with indicates that the object to be examined is sent to the pulse generator using the electron beam (20) to vary the intensity of the object located. The slide is attached to it through (6) scanning electron beam (16) also 15 engaging mechanical means perpendicular to the fixed phase-sensitive demodulator (19) displaceable to the stationary electron beam, so that to modulate the intensity of the electron beam, a relative movement of the object and the electron- (16) synchronous rectification of the radiation that results in a scanning of the object separation stage (17, 18) corresponds to the electron beam separated from the scanning signal. Furthermore is at AC component is connected. 20 the known electron microscope in the area of A scanning electron microscope according to claim 1, thereby triggered by the electron beam in the object characterized in that the separation stage a th secondary electrons arranged a device, Filter (17) for cutting off a direct current from these secondary electrons of the scanning component and a downstream disconnected object with the electron beam accordingly Contains correct amplifier (18). 25 electrical signals and these signals again 3. Scanning electron microscope according to claim 1 to a facsimile writer connected to it to- or 2, characterized in that the demodulator leads to a demodulator resulting from these signals (19) an integrator (26) can be switched to hold the tactile image. The mechanical feed device is which is the AC component of the scanning of the recording medium of the facsimile call signal integrated to generate the scan image. 30 bers is mechanically connected to the mechanical 4. Scanning electron microscope according to one of the means for moving the slide and thus Claims 1 to 3, characterized in that the object is connected to the electron beam the object (6) a bias source (15) so that the advancement of the recording medium is connectable. in the facsimile writer and the scanning of the object 35 take place synchronously with one another by the electron beam. - ,, -. ,, ·.: ' Such a mechanical type of synchronization with the help of circumferential. But cam disks remain even if, as with the well-known elec- 40 electron microscope; by ^: the. Activation of optical or electro-optical transmission elements in the form The invention relates to a scanning electro- of lamps and photo elements ^ at least from their internal microscope with a pulse generator for the strongest sources of friction, in any case odic variation of the intensity of a too unsatisfactory and imprecise, and also aggravatingly searching object. , scanning. Electron beam, 45 it is important that there is a mechanical displacement of the object with respect to a fixed object and a separation stage for feeding the stationary electron beam because of the low output of the oscilloscope with a measurement of the displacement movements from the scanning signal and the their conducted AC component. ... "Carrying out observable accuracy without an electron microscope with object scanning is associated with great difficulties. In addition, as is well known, a visible display of a scanning device is missing" in the known "electron micrograph of an object, when the object is examined with a scope because of the selected type to generate the electron beam is scanned and either back-scanning movement of the object and electron beam regscattered electrons or reflected on the object relative to each other at any coupling between or from this: emitted secondary electrons, or'55: this scanning movement on the one hand and the variation of the an object current or, on the other hand, one in the object as a result of the intensity of the electron beam ^5. This so-called "electron-volta effect", that is, the voltage that is produced in an undesirable manner on the electron bombardment determines the sharpness of the known electron microscope, like this example For example, in an attachment scope of the object to be examined, from _.T .. E. Eyerhart, OC Welks * and RK 60 to obtain scanning images. ν C; ji ΐ .ΐ ^ M a 11 a on pp. 929 to 936 of the »Journal qf Elec- The invention is therefore based on the object Trochemical Society ", Vol. 111 from 1964 describes a scanning electron microscope mentioned at the beginning. The type belonging to the known state of the art should be designed so that it can be seen with a purely electric electron microscope with object scanning or electromagnetic generation of the scanning with regard to the fact that the intensity 65 scanning movement of the electron beam compared to that of the scanning electron beam is constant - The object to be examined works and is also kept at th value, which does not vary with time, a synchronization between the iert, and therefore the Si scanning movement of the electron beam emanating from the object on the one hand and