JP3292159B2 - Film thickness measuring device and film thickness measuring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus and a method for measuring the thickness of a thin film using an electron beam.

[0002]

2. Description of the Related Art Multiple reflection interferometry and polarization spectroscopy are generally used as methods for determining the thickness of a thin film. The multiple reflection interferometry is a method in which a monochromatic light is applied to a thin film to form an interference fringe using repetitive reflection interference of the monochromatic light, and a thickness is determined from a shift of the interference fringe. Polarization spectroscopy is a method of determining the thickness by applying polarized light to a thin film and observing the state of polarization of reflected light.

However, in the method utilizing the optical properties of a thin film, the diameter of a light beam incident on the thin film is as large as several tens of microns to several hundreds of microns, so that measurement cannot be performed when the area of the thin film to be measured is small. As a method for overcoming this, as disclosed in JP-A-63-9807,
A method of irradiating a thin film with an electron beam to collect secondary electrons emitted from the thin film and measuring the thickness of the thin film on the substrate from the correlation between the amount of collected secondary electrons and the thickness of the thin film is known. Are known.

FIG. 19 shows a conventional film thickness measuring apparatus. In this film thickness measuring device, an electron gun 191 for irradiating the thin film sample 194 with an electron beam 192 and a secondary electron detector (secondary electron detection) for collecting secondary electrons 195 emitted from the substrate 193 and the thin film sample 194 are provided. Means) 196, an amplification circuit 197 for amplifying the signal, a deflection electrode 198 for scanning an electron beam, a scanning circuit 199 for generating a scanning signal, and an A / D converter 200 for converting a signal from the amplifier into a digital signal. , A storage device 201 for storing the data, and a CPU 202 for performing control for automatically performing a series of processes.

[0005]

In recent years, the place where an ultra-thin film is formed is not necessarily a flat surface of a substrate due to the progress of semiconductor fine processing technology. In other words, there is an increasing need to measure the thickness of a silicon oxide film, a metal film, an organic film, or the like inside a contact hole having a very large aspect ratio. However, in the prior art, it is necessary to collect all the secondary electrons generated from the substrate surface, and it is difficult to accurately collect the secondary electrons generated at the bottom of the structure having a large aspect ratio.
There was a problem that it was impossible to measure.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can accurately measure the thickness of a thin film, particularly, the thickness of an ultrathin thin film, and has a thin film within a contact hole having a large aspect ratio. It is an object of the present invention to provide a film thickness measuring device and a film thickness measuring method capable of measuring the thickness and also measuring the film thickness of the outermost surface of a multilayer film composed of a plurality of films.

[0007]

To achieve the above object, the present invention employs the following constitution. The film thickness measuring device according to claim 1 applies a constant acceleration voltage and a constant voltage to the thin film on the substrate.
Irradiate a fixed amount of electron beam perpendicular to the thin film surface
An electron beam irradiating means, and an electron beam irradiating the thin film.
The amount of secondary electrons emitted by the thin film
Is the current value of the current flowing through the board.
The electrode through an electrode arranged in contact with the substrate.
A current detecting means for detecting a current, and a film thickness for converting the current detected by the current detecting means into a film thickness of the thin film from correlation data between the current and the film thickness for a standard sample of the same material as the thin film. Conversion means.

[0008]

According to a second aspect of the present invention, in the film thickness measuring apparatus according to the first aspect, the current detecting means includes a differential amplifier for removing an offset voltage due to a leakage current other than the current. It is characterized by having.

According to a third aspect of the present invention, there is provided a film thickness measuring apparatus according to the first or second aspect, wherein the electron beam scanning means for scanning the electron beam on the thin film; And a position current storage means for storing the current at the scanning position.

According to a fourth aspect of the present invention, in the film thickness measuring method, a constant acceleration voltage and a constant amount of an electron beam are applied to a thin film on a substrate.
Irradiated perpendicular to the thin film surface, the thin film was irradiated
From the electron beam amount, the secondary electrons emitted by the thin film
The value obtained by subtracting the emission amount is the current value of the current flowing through the substrate.
As before through an electrode arranged in contact with the substrate
The current is detected, and the current is converted into a film thickness of the thin film from correlation data between the current and the film thickness of a standard sample made of the same material as the thin film.

According to a fifth aspect of the present invention, there is provided a film thickness measuring method, wherein an electron beam is scanned on a thin film formed on a substrate, and a plurality of scanning positions of the electron beam are perpendicular to the thin film surface.
Emitted by the thin film from the amount of electron beam directly irradiated
The value obtained by subtracting the amount of secondary electron emission
The current value of the current
Detecting the current through the electrodes, and
The position information and the current in the memory are stored in association with each other, and each of the currents is converted into a film thickness from correlation data between the current and the film thickness for a standard sample of the same material as the thin film, and the film of the thin film is formed. It is characterized in that a thickness distribution is obtained.

[0013]

[0014]

The film thickness measuring apparatus and the film thickness measuring method of the present invention do not measure the secondary electrons jumping out of the substrate surface, but the electron beam penetrating the thin film to be measured and reaching the substrate in a completely reverse manner to the conventional one. It is characterized by measuring the amount. The amount of electrons that penetrate the thin film and reach the substrate is a function of the amount of electron beam applied to the sample and the secondary electrons that jump out of the substrate surface.
In contrast to the difficulty in collecting all secondary electrons diverging from the substrate surface in all directions, the through current is the aggregate of all electrons that have passed through the part to be measured, regardless of the shape of the object to be measured. , It is possible to quantitatively capture information on the thin film portion.

FIG. 17 shows the measurement principle of the present invention. In this principle diagram, a case where a silicon oxide film 172 on the order of nanometers is formed on a silicon substrate 171 will be described. First, an electron beam controlled from the electron gun so as to have a constant amount of electrons is applied to a thin film sample to be measured. Since the amount of secondary electrons emitted from the sample is affected by the inclination of the axis of the irradiated electron beam, the axis of the electron beam is adjusted to have a constant inclination with respect to the sample surface. Even when a wide range of measurement is performed, the electron beam is adjusted so as to have a constant inclination angle in that range. In general,
Since the electron beam 173 emitted from the electron gun into a vacuum has a very high impedance, once the control conditions such as the filament voltage and the acceleration voltage of the electron gun are determined, the amount of the electron beam is almost independent of the electric impedance of the object to be measured. It will be constant. The amount of the electron beam emitted from the electron gun needs to be known, but it can be measured in advance using a Faraday cup or the like, or measured from the intensity of the electromagnetic field generated near the beam, or injected into the electron gun. There are a method of directly measuring the current, a method of simultaneously measuring the through current and the secondary electrons, and a method of calculating the difference between the two by calculation. Since each value depends on the acceleration voltage, it is measured each time the control parameter of the electron gun is changed. The secondary electron emission amount I _s for a given electron beam injection current I _in is the secondary electron I _s (Si) emitted from the silicon film existing within the escape depth of the secondary electrons and the secondary electron emission _s from the silicon oxide film. And the sum of the secondary electrons I _s (O). The through current Ip is given by equation (1), where d is the thickness of the silicon oxide film provided on the supporting substrate. Here, the secondary electron emission ratio of silicon and silicon oxide film is SE
Let L be the escape depth of C (Si) and SEC (O) and secondary electrons.

(Equation 1)

As shown in FIG. 18, since the silicon oxide film 172 has a large secondary electron emission ratio, when the electrons are irradiated, more electrons than the injected electrons fly out of the surface of the silicon oxide film as secondary electrons. Despite the injection of the electron beam, the through current 174 gives an experimental result that electrons are sucked into the silicon substrate 171 from the current amplifier (current amplifier) 175. In FIG. 18, the case where electrons exit from the back surface of the silicon substrate toward the current amplifier is indicated as positive. When the thickness of the oxide film is 0,
A positive through current, in which electrons are substantially injected into the silicon substrate, is observed. When the thickness of the oxide film increases from 0, the amount of secondary electrons increases, so that the through current increases in the negative direction in proportion to the thickness d. On the other hand, when d is greater than the escape depth, the through-sample current is determined only by the secondary electron emission ratio of the silicon oxide film 172 within the escape depth, and therefore, the current value observed at a substantially constant value is determined. Saturates. Further, when the oxide film is very thick, the current becomes 0, and the current value is different from the places where the oxide film remains very thin and the places where the oxide film is left out, so that they are distinguished from each other. When the electron beam acceleration voltage is constant, the ratio of the through current to the thickness of the silicon oxide film is constant. Therefore, a calibration curve is created in advance, and the data is stored in the storage device 11 (see FIG. 1). After measuring the unknown measurement object by the same method, the two can be compared and converted to obtain the film thickness of the thin film on the sample surface from the current penetrating the sample. In general, the secondary electron emission ratio is a value specific to an element,
The secondary electron emission ratio for a specific acceleration voltage takes a different value for each element. Therefore, the kind of element can be estimated by measuring the through current of the same thin film sample while changing the acceleration voltage in various ways.

[0018]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and description thereof will be omitted.
FIG. 1 shows a first embodiment of the film thickness measuring apparatus of the present invention. In the first embodiment, an electron gun (electron beam irradiation means) 3 for injecting an electron beam 2 having a known acceleration voltage and a current amount into a thin film sample 1, and a contact arrangement below a substrate 4 on which the thin film sample is fixed. Electrode 5 and a current amplifier (current detecting means) for amplifying a very small current collected by the electrode 5
6, and a differential amplifier (current detecting means) 7 for removing the offset of the measuring device and stabilizing the measuring system;
A digital multimeter 8 for monitoring the result on the way, an A / D converter (current detecting means) 9 for enabling the output of the differential amplifier to be handled by a computer, and storing the converted digital data. Storage device (current detection means) 10, storage device (film thickness conversion means) 11 for storing calibration curve data measured using an existing standard sample, and a comparison device for comparing the data with measured data (Thickness conversion means) 12, a CPU 13 for automatically performing these operations, and a display 14 for displaying calculation results. Thin film sample 1
It is placed in a vacuum of ^-4 mb or less.

This device operates as follows. Electron gun 3
An electron beam of several picoamps to several microamps is emitted toward the sample. The emitted electron beam 2 reaches the substrate 4 through the thin film sample 1. When it hits a thin film on the substrate surface, it emits secondary electrons at a ratio determined by the secondary electron emission ratio specific to the thin film material. Of the irradiated electron beam,
The remaining part penetrates the thin film and reaches the substrate to form a through current, which is finally collected on the electrode 5. When the electron beam current to be irradiated is, for example, 100 pA, the through current is the same or about one digit larger. The collected current is amplified by the current amplifier 6 by a factor of about 10 7. Since the measured current is extremely small, there is also a leakage current between wirings other than the current penetrating the thin film to be measured. Therefore, the offset voltage which is input to the differential amplifier 7 having the offset adjusting function and is composed of the leakage current is removed, and the amplification is performed about 10 times. The offset voltage is corrected using the difference between the current when the electron beam is not irradiated and the current when the electron beam is irradiated. In general, a current amplifier is slow and easily oscillates. Therefore, when amplifying at a high magnification, the measurement system becomes stable when the current amplifier and a high-speed voltage amplifier that further amplifies the output voltage are amplified in two stages. . The amplification result is converted into a digital signal by the A / D converter 9 and stored in the storage device 10. On the other hand, the relationship between the thickness of the thin film and the through-current was determined in advance by using a standard sample having a thin film part of a known thickness made of the same constituent material as the thin film to be measured. Line data is stored in the storage device 11. The data stored in the storage device 10 and the comparison device 12 are compared with each other. By this comparison, the current data is converted into a thin film thickness. A series of these operations are performed by the CPU 13 and a control program 15 for instructing direct control in a high-level language such as C or a machine language for operating the CPU 13 and a conversion result is shown on the display 14.

FIG. 2 shows that the P.O.
A silicon oxide film having a thickness of 9 nm to 12 nm was provided and irradiated with an electron beam, and a through current generated at that time was measured. The thickness of the silicon oxide film is measured in advance using ellipsometry. As the thickness of the silicon oxide film increases from 0, the through current increases to the negative side.
Saturation is observed at about 10 nm, which is called the escape depth of the silicon oxide film. When the acceleration voltage is changed, the ratio between the thickness of the silicon oxide film and the through current changes. Since the escape depth is determined by the energy of the secondary electrons, the influence of the acceleration voltage is not so large. According to the experimental results, when the accelerating voltage is 1.2 kV than the accelerating voltage of 0.5 kV, a larger slope is obtained, the amount of change in current with respect to the change in film thickness is large, and the detection sensitivity is increased. From these measurement data, for example, the film thickness is calculated as the current amount x
Using an approximate expression such as a coefficient + constant or the like, the straight line portion is analytically treated as calibration curve data. From the calibration curve data, for example, if the penetration current observed when an unknown sample is irradiated with an electron beam of 1 kV is -3500 pA, the oxide film thickness of the sample is 6 nm.

3 to 15 show examples of measurement samples. FIG. 3 shows that a flat silicon substrate 31 has a thickness
This shows a sample on which a silicon oxide film 32 of 1 nm or less is formed. This structure is often seen after forming a gate oxide film on a transistor. An electron beam 33 having an acceleration voltage of about 1 kV applied from the silicon oxide film 32 side
Reaches the silicon substrate 31 through the silicon oxide film 32. As described above, the amount of secondary electrons emitted from the substrate surface includes both those derived from the silicon oxide film 32 and those derived from the silicon substrate 31. The silicon oxide film emits more secondary electrons than the silicon substrate. Since the ratio is large, the amount of secondary electrons emitted from the surface of the silicon oxide film increases in proportion to the thickness of the silicon oxide film, and as a result, the amount of current collected by the electrode through the silicon substrate decreases. .
Since this relationship is always constant, the thickness of the silicon oxide film 22 provided on the silicon substrate 21 can be known by measuring the amount of through current. If the electron beam is narrowed down to a small diameter, it is suitable for measuring the thickness of the silicon oxide film in a small area of 100 nm or less. If a field emission type electron gun is used, it is possible to narrow down to about several nm even with an acceleration voltage of about 1 kV, so that the thickness of the region can be known. Conversely, if the beam is expanded, the average film thickness over a wide range can be known. Even when the beam is expanded, the inclination of the electron beam of each part constituting the beam with respect to the sample surface is made the same.

FIG. 4 shows a case in which a hole 43 is provided in a silicon oxide film 42 provided on a silicon substrate 41, and the thickness of the silicon oxide film 44 at the bottom of the hole is measured. . This structure is very similar to the structure of a contact hole that takes a contact from a transistor provided on a silicon substrate in a DRAM or the like. The contact hole is formed by etching the silicon oxide film from the surface by RIE or the like. However, if the etching is insufficient for some reason, the silicon oxide film may remain at the bottom of the contact hole. This embodiment corresponds to a case where such a remaining silicon oxide film 44 is detected. In an apparatus such as an SEM that forms an image by qualitatively using a change in the amount of secondary electrons emitted from the substrate surface, it is only necessary to obtain contrast, so the tilt angle of the electron beam axis during electron beam irradiation is particularly constant. , And greatly differs depending on the location of the sample. For this reason, the electron beam is vertically incident at the center of the sample, but a considerably inclined electron beam is applied to the sample at the periphery of the sample. The present invention is characterized in that, unlike the related art, any part of the sample is irradiated with the electron beam vertically. If the beam has a slope as in the prior art, the incident electron beam collides with the side surface of the contact hole, generates secondary electrons and decelerates, and does not directly hit the bottom of the contact hole. In order to obtain a through current that is in good agreement with the calibration curve for the specific acceleration voltage electron beam, it is necessary for the irradiated electrons to directly hit the silicon oxide film at the bottom of the contact hole. Therefore, in this embodiment, the electron beam 45 is substantially perpendicularly incident into the hole 43 provided in the silicon oxide film 42. The normally incident electron beam does not hit the oxide film on the side, but directly hits the silicon oxide film 44 at the bottom of the hole. The electron beam hitting the silicon oxide film 44 at the bottom of the contact hole emits secondary electrons proportional to the thickness of the oxide film. The emitted electrons may go out of the hole or may be absorbed by the oxide film 42 forming the hole. In any case, however, the amount of the electron beam passing through the silicon oxide film 44 at the bottom of the hole becomes inversely proportional to the thickness of the oxide film at the bottom. The thickness of the film can be known.

FIG. 5 shows an example in which the thickness of the silicon oxide film 52 provided on the metal wiring 51 is measured.
The electron beam 53 penetrating through the silicon oxide film 52 reaches the metal wiring 51. Generally, a silicon oxide film has a thickness of 2 to 3 when irradiated with an electron beam having an acceleration voltage of about 1 kV.
, Whereas a metal film such as aluminum has a secondary electron emission ratio near 1. Therefore, when the electron beam is applied to the sample surface without silicon oxide film,
The through-current amount becomes almost zero, and as the thickness of the silicon oxide film on the outermost surface increases, a through-current proportional to the thickness can be obtained. By converting this current into a silicon oxide film thickness using a calibration curve, the thickness of the oxide film on the metal wiring can be known. Generally, secondary electrons emitted from the underlying material are detected as an offset current when there is no thin film on the outermost surface, and when the value is subtracted from the through current, the outermost surface that does not depend on the underlying material is almost always detected. A calibration curve of the material constituting the layer is obtained.

FIG. 6 shows a thin metal film 61 made of aluminum or the like.
A silicon oxide film 62 is provided thereon, and a hole 63
Are shown, and the thickness of the silicon oxide film 65 at the bottom of the hole is measured. The electron beam 64 vertically incident on the hole 63 is applied to the silicon oxide film 65 at the bottom of the hole.
Hit. The electron beam hitting the silicon oxide film emits secondary electrons in proportion to the thickness of the silicon oxide film. The emitted electrons may go out of the hole or may be absorbed by the silicon oxide film 62 forming the hole. However, in any case, the amount of the electron beam that has passed through the silicon oxide film 65 at the bottom of the hole is proportional to the thickness of the silicon oxide film at the bottom. The thickness of the silicon oxide film can be known.

FIG. 7 shows the reverse of the previous embodiment.
The measurement shows a case where a metal thin film 72 having a thickness on the order of nanometers is provided on a silicon oxide film 73 as an insulating film as on an I substrate. The electron beam penetrating the metal thin film 72 reaches the silicon oxide film 73. Since the silicon oxide film has a secondary electron emission ratio of 2 to 3, and the metal thin film 72 such as an aluminum film has a secondary electron emission ratio of around 1, the two secondary electron emission ratios are significantly different. Therefore, a through current proportional to the thickness of the metal film can be obtained. By converting this current using a calibration curve that converts the current to the thickness of the metal film, it is possible to know the thickness of the extremely thin metal thin film on the silicon oxide film. In general, since the secondary electron emission ratio of metal is smaller than that of silicon oxide film, this calibration curve is similar to the calibration curve that rises to the right where the amount of through current increases to the positive side as the thickness of the metal thin film increases. Become.

FIG. 8 shows that a metal (for example, aluminum) thin film 82 is provided on a silicon oxide film 83, and a hole 85 is formed in a part thereof, and a metal (for example, aluminum) thin film at the bottom of the hole is formed. 84 shows a case where the film thickness is measured. The normally incident electron beam 81 strikes the metal thin film 84 at the bottom of the hole. The electron beam hitting the metal thin film emits secondary electrons in proportion to the thickness of the metal film. The emitted electrons may go out of the hole or may be absorbed by the metal film forming the hole. However, in any case, the electron beam passing through the metal film at the bottom of the hole,
Since the amount is proportional to the thickness of the metal film at the bottom, the thickness of the metal film at the bottom of the hole can be known by measuring the value.

FIG. 9 shows a second embodiment of a film thickness measuring device and a film thickness measuring method for measuring the film thickness distribution of a pattern comprising a silicon oxide film 92 provided on a silicon substrate 91. The position of the measurement section 94 irradiated with the electron beam is changed by scanning the electron beam 93 itself or moving the substrate by a movable stage (electron beam scanning means) or the like. The position information (X, Y) of the measuring section and the through current 95 are stored in the storage device (position current storage means) 10 in association with each other. The amount of the through current is compared with the calibration curve data 11 by the comparator 12, and the through current is converted into the thickness of the silicon oxide film. In particular, since the calibration curve data has good linearity,
It is expressed by the following equation or quadratic equation, the coefficient is stored, and the required conversion value is calculated by an approximate equation. With this apparatus, the film thickness distribution of the silicon oxide film can be determined, and at the same time, the silicon oxide film pattern width 96 can be measured. If a thin film having non-constant constituent elements or a material having a different secondary electron emission ratio is contained in the thin film to be measured, they can be detected as different thickness regions.

FIG. 10 shows that a hole 103 is provided in a silicon oxide film 102 provided on a silicon substrate 101.
The case where the thickness profile of the silicon oxide film 104 in the hole is measured is shown. The electron beam is injected into the hole by using the electron beam 105 whose beam axis is vertically set so as to pass through the hole. The electron beam hitting the silicon oxide film 104 at the bottom of the hole emits secondary electrons proportional to the thickness of the silicon oxide film. The emitted electrons may go out of the hole 103 or may be absorbed by the silicon oxide film 102 forming the hole. However, in any case, the silicon oxide film 104
Since the amount of the electron beam passing through the hole becomes proportional to the thickness of the silicon oxide film at the bottom, the thickness of the silicon oxide film at the bottom of the hole can be known by measuring the value. The amount of the through current is compared with the calibration curve data by the comparator, and the through current is converted into the thickness of the silicon oxide film. Particularly, since the calibration curve data has good linearity, it is represented by a linear expression or a quadratic expression, and an intermediate value is calculated using an approximate expression. With this measurement method, the thickness of the silicon oxide film in the hole or groove can be determined, and at the same time, the width of the silicon oxide film pattern can be measured. In this case, it is not necessary that the entire electron beam is narrowed so as to enter the hole. If the beam shape is flat, the shape of the hole bottom is determined using the change in the amount of current caused by the movement of the beam edge. Can be requested. The figure shows the case where the oxide film remains, and the current is observed on the minus side, but in the region where the silicon film is exposed, the current is observed on the plus side, and the two are separated. As a specific application example, there is a measurement of a bottom shape of a contact hole after etching is completed. In a contact hole having a high aspect ratio, the size of the opening and the size of the bottom are generally different. In particular, it is important to know the size of the bottom of the contact hole where the silicon substrate is exposed. If this method is applied to contact holes, the shape of the contact hole bottom can be measured,
The width, area and shape of the silicon region at the bottom can be known.

FIG. 11 shows an eleventh embodiment of the present invention. In the present embodiment, a method is described in which an electron gun or an object to be measured is moved two-dimensionally and a two-dimensional film thickness distribution measurement is performed. The electron gun can be used when the sample is flat
Although not necessarily perpendicular to the surface to be measured, the electron beam is irradiated at the same angle to any part in the measurement range. When measuring the thickness of the thin film at the bottom of a hole or groove, the electron beam is kept vertical so that the electron beam reaches the bottom of the hole directly. Electron beam scanning does not apply a deflection voltage to the electron beam itself and does not bend it to the left or right.Electron beam irradiation scans the electron beam two-dimensionally so that the axis is vertical, or vertically sets the electron beam axis. Move the electron gun while keeping it. The sample may be moved two-dimensionally with the electron beam emission axis of the electron gun fixed. In the above state, while measuring the relationship between the two-dimensional coordinates 112 of the electron beam irradiation location and the through current 113, the measurement position is sequentially moved to measure the entire sample, and from the through current to the thickness of the silicon oxide film. Perform transformation to obtain two-dimensional coordinates 11
If the film thickness of the silicon oxide film is plotted on an axis perpendicular to 2, a two-dimensional film thickness distribution of the thin film can be obtained.

FIG. 12 shows a silicon oxide film 12 on the outermost surface.
Measurements of a multilayer film composed of a metal thin film such as aluminum 122 as the first and second layers and a supporting substrate such as a silicon substrate 123 thereunder are shown. When the electron beam 124 is irradiated from the sample surface with an electron beam accelerated at an acceleration voltage of about 1 kV, the electron beam reaches a depth of about 50 nm from the surface. However, as described above, what affects the through current is the secondary electron emission ratio of a substance within 10 nm from the surface. Since the silicon oxide film 121 and the aluminum 122 constituting the first and second layers have different secondary electron emission ratios from the surface, secondary electrons are emitted in proportion to the thickness of the first layer, and the through current changes accordingly. . However, if the distance from the surface to the third layer is 10 nm or more, the magnitude of the observed through current is not affected by the third layer.
The thickness of the silicon oxide film on the outermost surface can be known by using the calibration curve data reflecting the secondary electron emission effect of the silicon oxide film and aluminum constituting the layer and the second layer.

FIG. 13 shows that an aluminum wiring 132 provided on a silicon substrate 131 is further covered with a silicon oxide film 13.
3 is formed, a hole 134 is provided in a part thereof, and the thickness of the silicon oxide film 135 at the bottom is measured. The electron beam 136 is vertically incident on the hole 134. The electron beam hits the silicon oxide film at the bottom of the hole and emits secondary electrons in proportion to the thickness of the silicon oxide film. The emitted electrons may go out of the hole,
In some cases, it is absorbed by the silicon oxide film 133 forming the hole. However, in any case, the current that has passed through the silicon oxide film at the bottom of the hole has a thickness of 10
If the thickness is larger than nm, the silicon oxide film 13
Since the amount is proportional to the film thickness of No. 5, the thickness of the silicon oxide film at the bottom of the hole can be known by measuring the value. When the thickness of the metal wiring is thinner than 10 nm, secondary electron emission from the silicon substrate 131 below the wiring also affects the through current. In this case, the calibration curve including the silicon substrate 131 is used. The thickness of the silicon oxide film at the bottom of the hole can be accurately measured by forming the silicon oxide film in advance.

FIG. 14 shows a silicon oxide film 14 on the outermost surface.
A measurement of a multilayer film composed of a nitride film 142 as the first and second layers and a supporting substrate therebelow such as a silicon substrate 143 is shown. When the electron beam 144 is irradiated with an electron beam accelerated from the sample surface at an acceleration voltage of about 1 kV, 50
The electron beam reaches a depth of about nm. However, as mentioned above, the influence on the through current is from the surface
This is the secondary electron emission ratio of a substance within 10 nm. Since the silicon oxide film 141 and the nitride film 142 constituting the first and second layers have different secondary electron emission ratios from the surface, secondary electrons are emitted in proportion to the thickness of the first layer, and the through current changes accordingly. I do. However, if the distance from the surface to the third layer is 10 nm or more, the magnitude of the observed through current is not affected by the third layer, so that the silicon oxide film forming the first and second layers is not affected. By using the calibration curve data reflecting the secondary electron emission effect of the nitride film, the thickness of the silicon oxide film on the outermost surface can be known.

FIG. 15 shows that a silicon oxide film 153 is further formed on a nitride film 152 provided on a silicon substrate 151, a hole 154 is provided in a part thereof, and a silicon oxide film 155 on the bottom thereof is formed. The case where thickness is measured is shown. An electron beam 156 is vertically incident on the hole 154. The electron beam hits the silicon oxide film at the bottom of the hole and emits secondary electrons proportional to the thickness of the silicon oxide film. The emitted electrons may go out of the hole or may be absorbed by the silicon oxide film 153 forming the hole.
However, in any case, the current passing through the silicon oxide film at the bottom of the hole is proportional to the thickness of the silicon oxide film 155 at the bottom of the hole when the thickness of the nitride film 152 is greater than 10 nm. Therefore, the thickness of the silicon oxide film at the bottom of the hole can be known by measuring the value. If the thickness of the nitride film 152 is smaller than 10 nm, secondary electron emission from the silicon substrate 151 under the wiring also affects the through current.
By preparing a calibration curve including 1 in advance, the thickness of the silicon oxide film at the bottom of the hole can be accurately measured.

FIG. 16 shows a third embodiment of the present invention. The present embodiment is characterized in that the through current measurement and the secondary electron measurement are combined. In the configuration shown in FIG. 1, a secondary electron detector (secondary electron detecting means) 162 and an amplifier 161 for amplifying the signal are further added. As described above, when a specific substance is irradiated with a certain amount of electron beam, the irradiated electrons are separated into two, a secondary electron and a through current, and the relationship is given by equation (1). The degree of the separation is specific to the secondary electron emission ratio and the film thickness of the object to be measured. Therefore, if a calibration curve measuring both of them is used at the same time, the measurement parameters consisting of the amount of incident electron beam, the amount of secondary electron emission, and the amount of through current are uniquely determined, and the film thickness can be accurately determined rather than using only the through current. Can be measured. In this case, since the secondary electron emission ratio is accurately obtained, the material analysis can be performed if the secondary electron emission ratio of the material is accurately known in advance. On the other hand, an apparatus that measures the film thickness using secondary electrons is greatly affected by the potential near the substrate surface. Since the amount of secondary electrons to be performed changes or all the secondary electrons are not recovered by the secondary electron detector, a true quantitative measurement that can be compared with other data cannot be performed. However, the through current is measured in advance for a small number of samples, and then the secondary electron collection efficiency is calculated using the measured value to convert it into a true secondary electron emission amount. Measurement becomes possible.

[0035]

As described in detail above, the film thickness measuring apparatus or method according to the present invention has the following effects. It is possible to quantitatively measure the thickness of an ultrathin film on the order of nanometers, which was impossible in the past, with good reproducibility. Not only can you quantitatively know the thickness of the thin film that exists on a flat surface, but also the extremely thin film that exists in places such as the bottom of a contact hole that has an extremely high aspect ratio with an aspect ratio exceeding 5 The film thickness can also be measured. Even with a multilayer film composed of a plurality of films, only the thickness of the outermost surface can be measured. Also, by measuring the through current before forming the film and comparing it with the through current after forming the film, it is possible to know the film thickness of any number of films formed. In the measurement sample example, the description was made using only silicon, a silicon oxide film, and aluminum as materials. However, the present invention is not limited thereto, and W, Mo, Pt, Au, Cu, Ti,
It can be applied to the thickness measurement of any material such as silicide, nitride film, ferroelectric, polyimide, resist, fluorocarbon, carbon, protein, DNA and the like. The hole may have any opening shape as long as the electron beam having an accelerating voltage sufficient for secondary electron emission hits the location to be measured. As the acceleration voltage of the electron beam for irradiation, it is desirable to select a voltage at which the secondary electron emission ratio between the first layer and the second layer, which are the outermost surface of the measurement sample, can be maximized. If an insulating region exists below the measurement location, a higher acceleration voltage may be used to penetrate that region. Alternatively, the measurement may be performed while changing the acceleration voltage. Since it can be used to identify the contaminated material at a minute location and to know its film thickness, it can be used to determine whether or not cleaning has been completed. If the determination is made automatically using an appropriate threshold value, it can be used as an inspection device for inspecting whether or not etching has been performed satisfactorily. Although the present embodiment shows an example in which the through current of the thin film is extracted from the back surface of the substrate, an electrode for extracting the current penetrating to the back surface of the substrate may be provided on the front surface of the substrate. Further, the measurement method of the present invention can be used even if there is an insulating film on the back surface of the substrate.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a film thickness measuring apparatus according to the present invention.

FIG. 2 is a diagram showing a relationship between a thickness of a silicon oxide film and a through current.

FIG. 3 is an example of a sample that can be measured by the film thickness measuring device of the present invention.

FIG. 4 is an example of a sample that can be measured by the film thickness measuring apparatus of the present invention.

FIG. 5 is an example of a sample that can be measured by the film thickness measuring device of the present invention.

FIG. 6 is an example of a sample that can be measured by the film thickness measuring device of the present invention.

FIG. 7 is an example of a sample that can be measured by the film thickness measuring device of the present invention.

FIG. 8 is an example of a sample that can be measured by the film thickness measuring apparatus of the present invention.

FIG. 9 is a schematic diagram for explaining a second embodiment of a film thickness measuring apparatus according to the present invention, and an example of a sample that can be measured by the schematic diagram.

FIG. 10 is a schematic diagram for explaining a second embodiment of the film thickness measuring apparatus according to the present invention and an example of a sample that can be measured by the schematic diagram.

FIG. 11 is a schematic diagram for explaining a second embodiment of the film thickness measuring apparatus according to the present invention, and an example of a sample that can be measured by the schematic diagram.

FIG. 12 is an example of a sample measured by the film thickness measuring device of the present invention.

FIG. 13 is an example of a sample measured by the film thickness measuring device of the present invention.

FIG. 14 is an example of a sample measured by the film thickness measuring device of the present invention.

FIG. 15 is an example of a sample measured by the film thickness measuring apparatus of the present invention.

FIG. 16 is a schematic view showing a third embodiment of the film thickness measuring apparatus according to the present invention.

FIG. 17 is a diagram for explaining the principle of the present invention.

FIG. 18 is a diagram showing a relationship between a thickness of a silicon oxide film and a through current.

FIG. 19 is a view showing a conventional film thickness measuring device.

[Explanation of symbols]

 Reference Signs List 1 thin film sample (thin film) 2 electron beam 3 electron gun (electron beam irradiation means) 4 substrate 5 electrode 6 current amplifier (current detection means) 7 differential amplifier (current detection means) 9 A / D converter (current detection means) Reference Signs List 10 storage device (current detection means) 11 calibration curve data storage device (thickness conversion means) 12 comparison device (thickness conversion means) 95 penetration current 162 secondary electron detector (secondary electron detection means) 195 secondary electron 196 Secondary electron detector (secondary electron detection means)

Claims (5)

(57) [Claims] 1. A constant acceleration voltage and a constant voltage applied to a thin film on a substrate.
And <br/> electron beam irradiation means for irradiating perpendicularly the amount of the electron beam to the thin film surface, the amount of the electron beam irradiated to the thin film, the thin film
The value obtained by subtracting the amount of secondary electrons emitted from the substrate
As the current value of the current flowing through the substrate
Current detecting means for detecting the current through a selected electrode
And a film thickness conversion means for converting the current value detected by the current detection means into a film thickness of the thin film from correlation data between the current and the film thickness for a standard sample of the same material as the thin film. A film thickness measuring device, characterized in that: 2. The film thickness measuring apparatus according to claim 1, wherein said current detecting means includes a differential amplifier for removing an offset voltage due to a leakage current other than said current. apparatus. 3. The film thickness measuring device according to claim 1, wherein: an electron beam scanning unit for scanning the electron beam on the thin film; a scanning position of the electron beam on the thin film; And a position current storage unit for storing the current at a scanning position. 4. A constant acceleration voltage and a constant voltage applied to a thin film on a substrate.
Irradiating an amount of electron beam perpendicular to the thin film surface;
From the amount of electron beam applied to the thin film,
The value obtained by subtracting the amount of secondary electrons emitted from the substrate
As the current value of the current flowing through the substrate
Detecting the current through the electrode, and converting the current to a film thickness of the thin film from correlation data between the current and the film thickness for a standard sample of the same material as the thin film. Thickness measurement method. 5. A scanning electron beam on a thin film formed on a substrate, a plurality of scan positions of the electron beams, before
The amount of electron beam irradiated perpendicular to the thin film surface?
Subtract the amount of secondary electrons emitted by the thin film
The value obtained as the current value of the current flowing through the substrate is
Detects the current through electrodes placed in contact with the plate
And the position information and the current at the plurality of scanning positions are
The current is stored in association with each other, and each of the currents is converted into a film thickness from correlation data between the current and the film thickness of a standard sample of the same material as the thin film, thereby obtaining a film thickness distribution of the thin film. Thickness measurement method.