JPH0678999B2 - Electronic counter - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electron counting device that counts the number of electrons emitted from a sample upon irradiation with light energy.

(Prior Art) Conventionally, for example, as a method of measuring the film thickness of an oxide film or the like provided to cover the surface of a sample such as a semiconductor element, the sample surface is irradiated with light and the light is irradiated to pass through the thin film of the sample to the outside. A method is known in which emitted electrons are detected by an electron detector to measure the film thickness (Japanese Patent Application No. 59-118818, etc.).

(Problems to be Solved by the Invention) However, in such a conventional film thickness measuring apparatus using the electron detecting unit, the light from the light source device separately arranged with respect to the electron detecting unit is used as the electron detecting unit. Since the sample that is positioned relative to the detection window is irradiated from the oblique direction, the light source device must be arranged at a position where the sample surface can be irradiated with light from the oblique direction with respect to the electron detection section. In the case of scanning the surface, the light source device also has to be moved integrally, which causes a problem that the device configuration becomes complicated.

Furthermore, when measuring the film thickness of the semiconductor pattern part by irradiating the light from the light source with an optical system and irradiating a small beam spot on the sample surface, the beam spot is elliptical because the light is radiated from an oblique direction. It is difficult to make the spot diameter sufficiently small because it does not form a circular beam spot. The problem caused by irradiating light from such an oblique direction is not only in the case of irradiating a beam spot on a specific portion of the sample, but also in the case of enlarging the light from the light source to irradiate a specific portion of the sample There is also a problem that the irradiation range changes depending on the irradiation angle, the irradiation range cannot be set accurately, and the number of electrons emitted from a specific sample measurement portion cannot be accurately measured.

(Means for Solving Problems) The present invention has been made in view of such conventional problems, and the light source side is separately disposed with respect to the electron detection unit, so that the electron detection unit can be freely arranged. At the same time, it is an object of the present invention to provide an electron counting device capable of irradiating light from a direction orthogonal to the sample surface to measure the number of electrons more accurately.

In order to achieve this object, in the present invention, light is guided from a light source device separately arranged with respect to the electron detection section to the electron detection section by an optical fiber, and the optical fiber is arranged so as to penetrate the inner center of the electron detection section. The tip of the optical fiber is projected from the detection window of the electron detection unit facing the sample through the holder member made of an insulating member so that light is emitted from the direction orthogonal to the sample surface, and the anode in the electron detection unit has a horizontal ring structure. The optical fiber is arranged so as to be supported around the holder member and pass through the holder member which is the center of the horizontal ring structure, and the tip of the holder member extends beyond the fiber tip surface of the optical fiber to the sample side. An optical system that irradiates the sample surface with the light emitted from the optical fiber at a position apart from the fiber tip surface of the existing holder member by a predetermined distance. In which reflected light of light irradiated on the sample is acceptable to provide a shielding member that prevents incident on the electronic detection portion.

(Operation) According to such a configuration of the present invention, by making the anode of the electron detection unit a horizontal ring structure, the tip of the optical fiber is projected through the inside of the electron detection unit from the detection window to a position facing the sample, and is projected onto the sample surface. Light can be emitted from orthogonal directions, and an optical system such as a condenser lens or a magnifying lens can be arranged at a position close to the sample surface, which is a predetermined distance from the tip of the optical fiber protruding from the detection window of the electron detector. For,
It becomes possible to form a light spot of micron order or less on the sample surface or to irradiate a light spot with an expanded irradiation range to irradiate a specific portion of a wide sample surface with light.

Further, since a shielding member for preventing the reflected light from the sample surface from entering the electron detecting portion is arranged at a position apart from the fiber tip end surface by a predetermined distance, it is unnecessary for the reflected light to enter the electron detecting portion. It can prevent the emission of electrons and accurately count the number of electrons.

(Embodiment) FIG. 1 is an explanatory view showing an embodiment of the present invention.

First, the structure will be described. Reference numeral 1 denotes an electron detecting portion, which has a metal case 3 having a detection window 2 opened at the bottom, and the case 3 is grounded to serve as a cathode. A horizontal anode ring 4 having a horizontal ring structure is arranged in the case 3, and the horizontal anode ring 4 is connected to a high voltage power source 23 of 3.4 KV, for example.
Between the horizontal anode ring 4 and the case 3, a first grid electrode 5 to which a voltage of, for example, 100 V is applied, is installed, and further, the sample is arranged so as to face the first grid electrode 5 and the detection window 2 of the case 3. A second grid electrode 6 to which a voltage of 80 V, for example, is applied is installed between the second grid electrode 6 and the electrode 10.

On the other hand, 12 is a light source device separately arranged with respect to the electron detection unit 1. The light source device 12 includes a light source 13, a spectroscope 14 for monochromatic light from the light source 13, and slits arranged before and after the spectroscope 14.
15, 16 are provided, and monochromatic light from the spectroscope 14 whose light intensity is adjusted by the slits 15, 16 is incident on the optical fiber 18.

The tip side of the optical fiber 18 which receives the light incident from the light source device 12 passes through the cylindrical holder member 19 made of an insulating material which penetrates through the inner center of the electron detecting section 1 and the case 3
It is provided so as to project from the detection window 2 to the sample 10 side. Further, the horizontal anode ring 4 provided in the electron detector 1 is horizontally supported around the holder 19 by a conductive support wire 20, and passes through the holder 19 which is the center of the horizontal anode ring 4. The tip of the optical fiber 18 is arranged so as to project to the outside of the detection window 2 facing the sample 10.

Further, a small condenser lens 21 is arranged at a position separated from the fiber tip 18a of the optical fiber 18 protruding from the detection window 2 of the electron detector 1 by a predetermined distance.
The light from the light source device 12 emitted from
A light spot of micron order or less is formed on the surface of the sample by irradiation with light from a direction orthogonal to the sample surface. Further, in this embodiment, the tip of the holder 19 is the tip of the fiber as a supporting structure for installing the condenser lens 21 at a position apart from the fiber tip 18a by a predetermined distance.
The holder 19 that extends beyond 18a toward the sample 10
By fitting the condenser lens 21 into the inside of the sample, the condenser lens 21 can be supported at a position corresponding to the focal length capable of forming a minute light spot on the surface of the sample 10.

Furthermore, since the tip of the holder 19 extends to the sample 10 side beyond the position where the condenser lens 21 is arranged, the reflected light reflected by the surface of the sample 10 enters the electron detection section 1 from the detection window 2. The holder 19 has a function as a shielding member that prevents the light from entering the tip of the holder 19 so that the reflection angle θ of the reflected light from the surface of the sample is equal to or less than a predetermined reflection angle that deviates from the detection window 2. To the sample 10 side to realize the function as a shielding member.

On the other hand, the measuring circuit 30 includes the horizontal anode ring 4 of the electron detector 1.
An amplifier 31 connected to the first grid electrode 5 via a capacitor C, and a first pulse generator 32 is provided between the amplifier 31 and the first grid electrode 5.
Is provided. When a pulse voltage is generated in the horizontal anode ring 4, the first pulse generator 32 sends a rectangular wave pulse of 300 V to the first grid electrode 5 with a time width Te (5 ms), for example, and the voltage of the first grid electrode 5 is changed. Increase from 100V to 400V as shown in Fig. 2 (b). In addition, the amplifier 31 and the second grid electrode 6
A second pulse generator 33 is provided between the second pulse generator 33 and the second pulse generator 33. When a pulse voltage is generated in the horizontal anode ring 4, the second pulse generator 33 outputs a −110V rectangular wave pulse with a time width Te (5 ms), for example. It is supplied to the second grid electrode 6, and the voltage of the second grid electrode 6 is reduced from 80V to -30V as shown in FIG. 2 (c).
The time width Te and the peak voltage of the rectangular wave pulse generated by the first and second pulse generators 32 and 33 can be set arbitrarily.

34 is a counting means connected to the output of the amplifier 31, and this counting means 34 counts the number of pulse voltages generated in the horizontal anode ring 4. The output of the counting means 34 is given to the calculating means 35, and as the calculating means 35, for example, a microcomputer is used. The calculating function of the calculating means 35 is such that, when the counting number (counting rate) of the electron pulse per second in the counting means 34 is N, the output count number N of the counting means 34 is received and the thin film 10b of the sample 10 is processed. The film thickness T is calculated by the following equation.

logN = logN1-T / 2.30λ (1) where λ is the mean free path of electrons in the thin film (angstrom), and N1 is the number of counts (counting rate) when the film thickness is zero. The thickness T of the thin film 10b is, for example, CR
The film thickness T of the thin film 10b, which is sent to the display means 36 such as T or a printer and is the calculation result of the calculation means 35, is displayed on the display means 36.

Next, the film thickness measuring operation according to the embodiment of FIG. 1 will be described with reference to the signal waveform diagram of FIG.

First, taking a semiconductor integrated circuit as an example of the sample 10, a semiconductor integrated pattern having a thin film 10b made of silicon oxide is formed on the surface of a sample body 10a made of silicon, and the sample 10 made of such a semiconductor integrated circuit is formed. The sample table 9
Install on top of.

Next, from the high voltage power supply 23 provided in the measurement circuit 30, the electronic detection unit 1
A high voltage of 3.4 KV is applied to the horizontal anode ring 4 as shown in FIG. 2 (a). At the same time, the light from the light source 13 of the light source device 12 separately arranged with respect to the electron detector 1 is spectroscopically separated.
The light intensity is adjusted by the slits 15 and 16 while making it a monochromatic light by 14, and the sample 10 is irradiated with the light beam through the optical fiber 18.

Since the optical fiber 18 is arranged through the inside of the electron detector 1 for irradiating the sample 10 with the optical beam by the optical fiber 18, the light from the fiber tip 18a is irradiated from the direction orthogonal to the surface of the sample 10. Furthermore, since the condenser lens 21 is arranged at a position apart from the fiber tip 18a by a predetermined distance, the fiber tip 18a
The light emitted from the sample is narrowed down by the condenser lens 21, and is irradiated so as to form a minute light spot of 1 micron or less on the surface of the sample 10. Therefore, even when the semiconductor integrated circuit is measured as the sample 10, a light spot smaller than the oxide film pattern of the submicron order formed on the surface of the semiconductor integrated circuit can be formed, and the film thickness of the oxide film pattern can be measured. It will be possible.

Here, since the sample body 10a of the sample 10 is silicon and the thin film 10b is silicon oxide, the monochromatic light that gives energy to the sample 10 is equal to or higher than the photoelectric work function of the sample body 10a and the thin film 10b.
Ultraviolet light having an energy less than the photoelectric work function of is used.

The light spot of the monochromatic light irradiated on the sample 10 through the optical fiber 18 and the condenser lens 21 transmits the thin film 10b and then gives the light energy to the surface of the sample body 10a, and the low energy photoelectrons from the surface of the sample body 10a. To release. At this time, since the light energy of the monochromatic light is less than the photoelectric work function of the thin film 10b, no electrons are emitted from the thin film 10b.

Some of the electrons emitted from the sample body 10a pass through the thin film 10b and are emitted to the outside. That is, among the electrons emitted from the sample body 10a, those with small kinetic energy are thin films.
It loses energy in 10b and stays in the thin film 10b. On the other hand, those having a large kinetic energy pass through the thin film 10b and are emitted to the outside.

Here, the number of electrons that can pass through the thin film 10b gradually decreases as the film thickness increases, because more kinetic energy is taken from the electrons.

That is, if the energy applied to the sample body 10a is constant and the number of emitted electrons is constant, the number of electrons that can pass through the thin film 10b decreases as the thickness of the thin film 10b increases.
The functional relationship of the equation (1) holds between the film thickness and the number of electrons that can pass through. Further, since the average free path of electrons emitted from the sample body 10a in the thin film 10b is generally about several tens of angstroms, it is possible to measure an extremely thin film in the angstrom order.

Thus, the electrons that have passed through the thin film 10b and left outside the sample 10 enter the electron detection unit 1 through the detection window 2 and
It passes through the grid electrode 6 and the first grid electrode 5 and is attracted to the horizontal anode ring 4. When the emitted electrons approach the horizontal anode ring 4, a strong electric field is generated in the vicinity of the horizontal anode ring 4 due to the high voltage, and the electric field accelerates the electrons to cause a gas discharge phenomenon. As a result, the voltage applied to the horizontal anode ring 4 by the gas discharge is the second
As shown in FIG. 6A, the voltage drops and a voltage pulse is generated.

The voltage pulse generated in the horizontal anode ring 4 is amplified by the amplifier 31 and then given to the first pulse generator 32 and the second pulse generator 33 to generate rectangular wave pulses. That is, the first
The pulse generator 32 generates a rectangular wave pulse having a voltage of 300 V and a time width of Te and applies it to the first grid electrode 5,
Voltage is increased from 100V to 400V for Te time. As a result, the potential difference between the horizontal anode ring 4 and the first lattice electrode 5 is reduced by 300 V, and the secondary electrons due to light or cations generated by the gas discharge action cannot reach the discharge voltage. Avalanche discharge amplification is prevented.

On the other hand, the second pulse generator 32 has a time width of Te and a voltage of -110V.
Is applied to the second grid electrode 6 to reduce the voltage of the second grid electrode 6 from 80V to -30V. As a result, the cations generated by the gas discharge accompanied by the amplifying action are captured and neutralized by the second lattice electrode 6, whereby the cations reach the thin film 10b of the sample 10 and the sample body 10a, and the low-energy electrons are emitted. Prevents affecting the release action. In addition, it blocks electrons from the outside from entering the electron detector 1.

When Te time elapses due to such pulse generation, the first
Then, the voltages of the second lattice electrodes 5 and 6 are restored, and the electron detector 1 is again in a state where it can detect the emitted electrons from the sample 10, and the same operation is repeated every time the emitted electrons from the sample 10 are captured. .

On the other hand, the counting means 34 in the measuring circuit 30 is given a voltage pulse from the amplifier 31, and by counting the number of pulses, the number of electrons emitted from the sample body 10a and passing through the thin film 10b is counted. The counting result, for example, the counting rate is output to the calculating means 35. The calculation means 35 executes the calculation based on the equation (1) to obtain the film thickness T, and displays the film thickness T measured by the display means 36.

On the other hand, when a light spot is irradiated from the fiber tip 18a through the optical fiber 18 to the surface of the sample 10 through the condenser lens 21, the reflected light from the surface of the sample 10 is reflected to the electron detection unit 1 side as shown by an arrow A. However, the holder 19 containing the optical fiber 18 is passed over the condenser lens 21 and the sample 10
Since it extends to a position close to the surface of, the reflection angle θ from the sample 10 becomes the reflection angle determined by the tip of the holder 19,
The reflected light indicated by the arrow A is prevented from entering the inside of the electron detecting section 1 through the detection window 2.

That is, when the reflected light from the surface of the sample 10 enters the inside of the electron detection unit 1, the case 3 of the electron detection unit 1 which receives the reflected light similarly to the case where the sample 10 is irradiated with the light beam, and the first and second cases. Low energy electrons are emitted to the outside from the lattice electrodes 5 and 6, and low energy electrons emitted by this reflected light are attracted to the horizontal anode ring 4 to cause a gas discharge phenomenon, thereby generating an incorrect voltage pulse. In the embodiment shown in FIG. 1, since the tip of the holder 19 accommodating the optical fiber 18 is extended so that the reflected light from the sample surface does not enter the electron detector 1, the noise component due to the reflected light is reduced. As a result, electron emission can be prevented and the film thickness measurement accuracy can be improved.

FIG. 3 is an explanatory view showing another embodiment of the optical system arranged at a position separated from the tip end surface of the optical fiber by a predetermined distance. In this embodiment, the light emitted from the optical fiber 18 is held by the holder. Magnify the sample with the magnifying lens 40 provided in 19
It is characterized in that the surface of 10 is irradiated.

That is, when detecting scratches on the sample surface from changes in the number of emitted electrons due to light irradiation, it is necessary to irradiate light on a somewhat wide range of the sample surface. The light is spread by the magnifying lens 40 to be emitted.

Further, even in this embodiment, the tip of the holder 19 extends toward the sample 10 beyond the position of the magnifying lens 40.
The light reflected on the surface of is blocked by the tip of the holder 19 so as not to enter the electron detection unit 1.

As the shield member, in addition to extending the tip of the holder 19 as described above, a disc-shaped or umbrella-shaped shield member may be separately attached to the tip of the holder 19.

(Effects of the Invention) As described above, according to the present invention, the light from the light source device that is separately arranged with respect to the electron detection unit is guided to the electron detection unit by the optical fiber, and the optical fiber is guided to the inner center of the electron detection unit. It is arranged so that the tip of the optical fiber is projected from the detection window of the electron detection unit facing the sample through the holder member made of an insulating member penetratingly arranged so as to irradiate light from the direction orthogonal to the sample surface, and the anode in the electron detection unit Is supported around the holder member as a horizontal ring structure, the optical fiber is arranged so as to pass through the holder member that is the center of the horizontal ring structure, and the tip of the holder member is extended to the sample side beyond the fiber tip surface of the optical fiber. And irradiate the sample surface with the light emitted from the optical fiber at a position separated by a predetermined distance from the fiber tip surface of the extended holder member. Since an optical system for emitting light and a shielding member for preventing reflected light of the light irradiated on the sample from entering the electron detection unit are provided, even if the electron detection unit is arranged facing the sample, Light can be emitted from the direction orthogonal to the sample surface by the optical fiber that passes through the inside of the detection unit.
Since the light is emitted from the direction orthogonal to the sample surface, a light condensing lens is placed at a position a certain distance away from the tip of the fiber to focus the light beam, and a light spot of micron order or less on the sample surface. By forming such a minute light spot, it is possible to accurately measure the film thickness of the oxide film pattern or the like in the semiconductor integrated circuit in which the fine thin film pattern is formed. Also, when a magnifying lens is arranged as an optical system, the light emitted from the optical fiber can be enlarged and applied to the sample surface, and the optimum irradiation condition of light for detecting scratches on the sample surface can be created. .

Also, by horizontally mounting the anode provided in the electron detector as a horizontal ring structure, a structure is realized in which the optical fiber is arranged so that the sample surface can be irradiated with light through the center of the electron detector. The arrangement structure is not required for the optical system that irradiates light around the part from an oblique direction, and the size of the detection part can be reduced by integration with the electronic detection part. Furthermore, by making the anode ring a horizontal ring structure, the symmetry of the high electric field generated in the electron detector is obtained by the anode ring, and it is possible to reliably capture the sample emitted electrons and create a discharge state for electron measurement. You can

Furthermore, since a shielding member is provided at a position on the sample side that is a certain distance away from the tip of the optical fiber, it is possible to prevent reflected light from the surface of the sample from entering the electron detector, and reduce measurement noise due to reflected light. Thus, highly accurate electronic measurement can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, FIG. 2 is a waveform diagram of an operation signal of an electron detector, and FIG. 3 is another embodiment of an optical system arranged on the tip side of an optical fiber. It is explanatory drawing which took out and was shown. 1: Electron detection part 2: Detection window 3: Case 4: Horizontal anode ring 5: First grid electrode 6: Second grid electrode 9: Sample stage 10: Sample 10a: Sample body 10b: Thin film 12: Light source device 13: Light source 14: Spectrometer 15, 16: Slit 18: Optical fiber 18a: Fiber tip 19: Holder 20: Support line 21: Condenser lens 23: High voltage power supply 30: Measuring circuit 31: Amplifier 32: First pulse generator 33: Second Pulse generator 34: Counting means 35: Calculation means 36: Display means 40: Magnifying lens

Continuation of front page (56) Reference JP-A-59-195177 (JP, A) JP-A-60-93336 (JP, A) JP-A-62-145396 (JP, A)

Claims (1)

[Claims] 1. An electron counter which irradiates a sample with light and introduces electrons emitted from the sample into an electron detector to count the number of electrons, the electron counter being separated from the electron detector. The light from the light source device is guided to the electron detecting section by an optical fiber, and the optical fiber tip is detected from the detecting window of the electron detecting section facing the sample through a holder member made of an insulating member that is arranged to penetrate the inner center of the electron detecting section. Is arranged so as to project light from the direction orthogonal to the sample surface, and the anode in the electron detector is supported around the holder member as a horizontal ring structure, and a holder member serving as the center of the horizontal ring structure is formed. The optical fiber is arranged so as to pass therethrough, and further, the tip of the holder member extends toward the sample side beyond the fiber tip surface of the optical fiber, and the extended holder member An optical system that irradiates the sample surface with the light emitted from the optical fiber at a position apart from the fiber tip surface by a predetermined distance.
An electron counting device, comprising: a shield member that prevents reflected light of the light irradiated on the sample from entering the electron detection unit.