JPH0950780A - Scanning electron microscope - Google Patents

Abstract

(57) Abstract: An environment control type scanning electron microscope capable of suppressing a change in a sample image due to a change in the multiplication effect of secondary electrons. SOLUTION: Secondary electrons emitted from a sample 3 are multiplied in a multiplication region A adjusted to a low-vacuum gas atmosphere and taken into a secondary electron detection electrode 2 to which a positive voltage is applied, and the taken-in. In a scanning electron microscope that forms a sample image based on secondary electron signals, the multiplication environment detecting means 4 for detecting a physical quantity involved in the degree of multiplication of secondary electrons and the multiplication environment detecting means 4 A sample image adjusting means 11 for adjusting the formation state of the sample image based on the detection result is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environment control type scanning electron microscope which detects secondary electrons from a sample after multiplying them in a low vacuum gas atmosphere.

[0002]

2. Description of the Related Art Scanning electron microscopes (hereinafter sometimes abbreviated as SEMs) are used in a wide range of fields as means for microscopic morphological observation and analysis. When observing a sample with an SEM, the electron optical system and the secondary electron detection system require high vacuum, and therefore the sample must be placed in high vacuum. Therefore, the sample can be observed only in a dry state, not in a natural state. When the sample is an insulator, a conductive treatment such as metal coating on the surface of the sample is necessary to prevent the observation from being impossible due to charging. Recently, there has been an increasing demand for observing a sample in a "more natural state" and also in a "water-containing state" without drying the sample. Therefore, the saturated water vapor pressure at room temperature is 270
Environmentally controlled SEMs using a multiplication method capable of detecting secondary electrons even under an extremely low vacuum of 0 Pa are being widely used. In this environmentally controlled SEM, a gas (typically water vapor) having an electron multiplying effect is stored in the sample chamber at a maximum of 270.
While supplying up to 0 Pa, the sample is irradiated with an electron beam while applying a voltage of + several 100 V to the secondary electron detection electrode facing the sample (see, for example, JP-A-6-60841). The secondary electrons generated from the sample collide with gas molecules and are repeatedly ionized, amplified, and taken into the secondary electron detection electrode. The secondary electrons taken in are output to a predetermined signal processing circuit, where they are converted into a sample image. The sample image is displayed on a CRT for observation or photographed. The positive ions generated in the electron multiplication process are poured onto the sample, which neutralizes the charge of the sample. Therefore, even if it is an insulator, it is not necessary to conduct the conductive treatment, and it can be observed without treatment.

[0003]

In the environment-controlled SEM described above, the degree of vacuum (gas pressure) in the sample chamber and the voltage applied to the secondary electron detection electrode are set every time the sample to be observed is replaced. There is. However, a slight change in the applied voltage to the secondary electron detection electrode or the degree of vacuum in the sample chamber causes a large change in the intensity of the secondary electron signal. It will be appropriate. Therefore, every time the sample is replaced, the operator must manually adjust the applied voltage to the secondary electron detection electrode, the amplifier gain of the processing circuit of the secondary electron signal, the brightness level, etc. to adjust the brightness and contrast of the sample image. was there.

An object of the present invention is to provide an environment control type scanning electron microscope capable of suppressing a change in the sample image due to a change in the multiplication effect of secondary electrons.

[0005]

With reference to FIGS. 1 to 4 showing an embodiment of the present invention, the invention according to each claim for solving the above problems will be described. However, the present invention is not limited to the illustrated embodiment. Referring to FIGS. 1 and 2, the invention of claim 1 multiplies the secondary electrons emitted from the sample 3 in a multiplication region A adjusted to a low-vacuum gas atmosphere to obtain a positive voltage. In the secondary electron detection electrode 2 to which is applied, and a physical quantity related to the degree of multiplication of secondary electrons is detected in a scanning electron microscope that forms a sample image based on the captured secondary electron signal. Multiplication environment detection means 4
And the sample image adjusting means 11 for adjusting the formation state of the sample image based on the detection result of the multiplication environment detecting means 4 to achieve the above-mentioned object. According to a second aspect of the invention, in the scanning electron microscope according to the first aspect, the sample image adjusting means 11 adjusts the formation state of the sample image so that the value representative of the visibility of the sample image converges within the allowable range. To do. According to the invention of claim 3, in the scanning electron microscope according to claim 1,
The multiplication environment detecting means 4 detects the degree of vacuum in the multiplication area as the physical quantity. Then, the sample image adjusting means 11 adjusts the voltage applied to the secondary electron detection electrode 2 based on the detection result of the degree of vacuum. Explaining with reference to FIG. 4, in the invention of claim 4, in the scanning electron microscope according to claim 1, 2
It has signal processing circuits 14, 15 and 16 for forming a sample image based on the secondary electron signal detected by the secondary electron detection electrode 2, and the sample image adjusting means 24 has a multiplication environment detecting means 4 and 11.
Of the signal processing circuits 14, 15, 16 based on the detection result of
Adjust the processing conditions of. Referring to FIG. 1 and FIG. 2 again, the invention of claim 5 is such that 2 emitted from the sample 3
Multiplication area A in which the secondary electron is adjusted to a low vacuum gas atmosphere
A sample for evaluating the formation state of a sample image in a scanning electron microscope which is multiplied by and is taken into the secondary electron detection electrode 2 to which a positive voltage is applied, and a sample image is formed based on the taken secondary electron signal. Image evaluation means 18 and sample image evaluation means 18
Based on the evaluation result of 1., the multiplication environment adjusting means 18 for adjusting the physical quantity involved in the degree of the multiplication effect of the secondary electrons is provided to achieve the above-mentioned object. According to a sixth aspect of the invention, in the scanning electron microscope according to the fifth aspect, the multiplication environment adjusting means 18 adjusts the physical quantity so that the value representative of the visibility of the sample image converges within the allowable range. According to the invention of claim 7, in the scanning electron microscope according to claim 5,
Based on the evaluation result of the sample image evaluation means 18, the multiplication environment adjustment means 18 adjusts the voltage applied to the secondary electron detection electrode 2. According to the invention of claim 8, in the scanning electron microscope according to claim 2 or 6, the value representative of the visibility of the sample image is at least one of the brightness and the contrast of the sample image. According to a ninth aspect of the present invention, a secondary electron detection electrode 2 capable of detecting secondary electrons emitted from the sample 3, a voltage source 12 for applying a positive voltage to the secondary electron detection electrode 2, and an electron multiplication function are provided. A scanning electron microscope provided with a gas supply means 6 for supplying the contained gas to the multiplication area A between the sample 3 and the secondary electron detection electrode 2, and a vacuum exhaust means 8 for exhausting the multiplication area A into vacuum. In, the vacuum degree identifying means 4 for identifying the vacuum degree of the multiplication region A, and the voltage adjustment for adjusting the voltage applied from the voltage source 12 to the secondary electron detecting electrode 2 based on the identification result of the vacuum degree identifying means 4. Means 11 are provided to achieve the above-mentioned objects. According to a tenth aspect of the present invention, a secondary electron detection electrode 2 capable of detecting secondary electrons emitted from the sample 3, a voltage source 12 for applying a positive voltage to the secondary electron detection electrode 2, and an electron multiplication function are provided. The gas supply means 6 for supplying the gas contained therein to the multiplication area A between the sample 3 and the secondary electron detection electrode 2, the vacuum evacuation means 8 for evacuating the multiplication area A, and the secondary electron detection electrode 2 A sample image evaluating means 18 for evaluating the formation state of the sample image in a scanning electron microscope equipped with signal processing circuits 14, 15 and 16 for forming the sample image based on the detected secondary electron signal. The voltage adjustment means 18 for adjusting the voltage applied from the voltage source 12 to the secondary electron detection electrode 2 based on the evaluation result of the sample image evaluation means 18 is provided to achieve the above-mentioned object. According to the invention of claim 11, a secondary electron detection electrode 2 capable of detecting secondary electrons emitted from the sample 3, a voltage source 12 for applying a positive voltage to the secondary electron detection electrode 2, and an electron multiplication function are provided. The gas supply means 6 for supplying the gas contained therein to the multiplication area A between the sample 3 and the secondary electron detection electrode 2, the vacuum evacuation means 8 for evacuating the multiplication area A, and the secondary electron detection electrode 2 In the scanning electron microscope including the signal processing circuits 14, 15, 16 for forming the sample image based on the detected secondary electron signal, the vacuum degree identifying means 4 for identifying the vacuum degree in the multiplication region A. And a first voltage adjusting means 11 for adjusting the voltage applied from the voltage source 12 to the secondary electron detection electrode 2 based on the identification result of the vacuum degree identifying means 4, and a voltage by the first voltage adjusting means 11. Sample image evaluation means 1 for evaluating the formation state of the sample image after the adjustment of When the sample image evaluation means 1
Second voltage adjusting means 1 for adjusting the voltage applied from the voltage source 12 to the secondary electron detection electrode 2 based on the evaluation result of No. 8.
And 8 to achieve the above-mentioned object.

According to the first aspect of the invention, it is possible to always keep the sample image properly by reflecting the change of the physical quantity relating to the degree of the multiplication effect of the secondary electrons in the formation state of the sample image. According to the invention of claim 2, the visibility of the sample image is properly maintained.
According to the third aspect of the invention, the voltage applied to the secondary electron detection electrode 2 can be adjusted in accordance with the change in the degree of vacuum in the multiplication region A to properly maintain the sample image. In the invention of claim 4, it is possible to always keep the sample image properly by reflecting the change of the physical quantity related to the degree of the multiplication effect of the secondary electrons in the processing condition of the secondary electron signal. According to the invention of claim 5, it is possible to control the sample image in an appropriate state by adjusting the multiplication action of the secondary electrons according to the change of the sample image. In the invention of claim 6,
The visibility of the sample image is properly maintained. According to the invention of claim 7, the state of the finally formed sample image can be properly maintained by adjusting the voltage applied to the secondary electron detection electrode 2 according to the change of the sample image. According to the invention of claim 8, the brightness and the contrast of the sample image are appropriately maintained. According to the invention of claim 9, the sample image can be properly maintained by adjusting the voltage applied to the secondary electron detection electrode 2 in accordance with the change in the degree of vacuum in the multiplication region A. According to the tenth aspect of the present invention, the state of the finally formed sample image can be properly maintained by adjusting the voltage applied to the secondary electron detection electrode 2 according to the change of the sample image. According to the invention of claim 11, the voltage applied to the secondary electron detection electrode 2 is adjusted according to the change in the degree of vacuum in the multiplication region A to optimize the sample image, and further according to the state of the sample image. The sample image can be optimized by adjusting the voltage applied to the secondary electron detection electrode 2.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

—First Embodiment— A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a block diagram of an environment-controlled SEM according to this embodiment, where 1 is a sample chamber, 2 is a secondary electron detection electrode, and 3 is a sample. The secondary electron detection electrode 2 is attached to the lower end of a vacuum chamber 100 accommodating an electron gun (not shown), for example, via an insulator 101, as shown in FIG. An aperture 2a is formed to pass the electron beam emitted toward the aperture. A control power supply 12 and a preamplifier 14 are also connected to the secondary electron detection electrode 2. In FIG. 2, 102 is an objective lens that focuses the electron beam on the sample 3, and 103 is a vacuum pump that evacuates the vacuum chamber 100. The vacuum chamber 100 is divided into a plurality of chambers in the optical axis direction of the electron gun by an aperture (not shown), and each chamber is evacuated by a separate vacuum pump.

As shown in FIG. 1, the sample chamber 1 is connected to a gas supply source 6 via a valve 5 and a rotary pump 8 via a valve 7. Rotary pump 8
When the valve 7 is opened while driving, the sample chamber 1 is evacuated, and when the valve 5 is opened, a gas having an electron multiplying effect, for example, water vapor is supplied from the gas supply source 6. The vacuum degree (gas pressure) in the multiplication area A between the secondary electron detection electrode 2 and the sample 3 in the sample chamber 1 is detected by the vacuum gauge 4, and the detected value is input to the vacuum degree control circuit 9. To be done. The vacuum degree control circuit 9 controls opening and closing of the valves 5 and 7 so that the degree of vacuum detected by the vacuum gauge 4 matches the target degree of vacuum set by the vacuum degree setter 10. The target degree of vacuum is, for example, 10
It is set to 0 to 2700 Pa.

When the vacuum degree control circuit 9 controls the vacuum degree to a target value, the vacuum degree at that time is input to the arithmetic circuit 11. The arithmetic circuit 11 calculates an appropriate value + V _opt of the applied voltage of the secondary electron detection electrode 2 corresponding to the current degree of vacuum according to a given function, and instructs the control power supply 12 to the appropriate value + V _opt . The control power supply 12 applies the instructed positive voltage + V _opt to the secondary electron detection electrode 2. Proper value V
_opt corresponds to the applied voltage of the secondary electron detection electrode 2 required to keep the brightness and contrast of the sample image within the allowable range with respect to the current degree of vacuum. The function given to the arithmetic circuit 11 is illustrated in FIG. 3, for example. In this example, the lower the degree of vacuum (the higher the gas pressure) is, the more the collision frequency between the secondary electrons and the gas molecules is increased, and the electron multiplication action is increased.
In response to this, the applied voltage is lowered. Note that FIG.
The diagram of can be easily obtained by experiments and computer simulations.

Returning to FIG. 1, the description will be continued. When the vacuum degree of the multiplication region A in the sample chamber 1 is set to a target value and the voltage V _opt is applied to the secondary electron detection electrode 2, the sample 3 is irradiated with the electron beam. The secondary electrons generated from the sample 3 are gas-multiplied when passing through the multiplication region A, and the secondary electrons are detected.
Is taken into. 2 taken into the secondary electron detection electrode 2
The next electron signal is sequentially amplified by the preamplifier 14 and the main amplifier 15, and then converted into a digital image signal by the A / D converter 16. The image signal output from the A / D converter 16 is guided to a memory 17, a CRT 21 for observing a sample image, and a CRT 22 for photographing. Memory 1
A fine adjustment circuit 18 is connected to 7. Fine adjustment circuit 18
Refers to the image signal captured in the memory 17,
The optimum value V _opt output from the control power supply 12 is finely adjusted so that the brightness and contrast of the sample images displayed on the RTs 21 and 22 are optimized, and the D / A converter 2
The gain and DC level of the preamplifier 14 are finely adjusted via 0.

Reference numeral 19 denotes a mode indicator for instructing the fine adjustment circuit 18 to distinguish between the automatic follow-up mode and the single shot mode in response to the operation of the operator. When the automatic follow-up mode is instructed, the fine adjustment circuit 18 monitors based on the image signal in the memory 17 whether or not the brightness and contrast of the sample images of the CRTs 21 and 22 are kept in the optimum state. When the condition deviates from the optimum state, the output V _opt of the control power supply 12, the gain of the preamplifier 14 and the DC level are automatically adjusted. When the single shot mode is instructed, the fine adjustment circuit 18 performs the fine adjustment processing only when the adjustment start signal is output from the setting switch 23 in response to the operation of the operator.

In the above embodiment, the vacuum gauge 4 includes the multiplication environment detecting means and the vacuum degree identifying means, and the arithmetic circuit 11 includes the sample image adjusting means, the voltage adjusting means other than the tenth aspect, and the first voltage adjusting means. , The preamplifier 14, the main amplifier 15, and the A / D converter 16 constitute a signal processing circuit and a fine adjustment circuit 18
Are the sample image evaluation means, the multiplication environment adjusting means, the voltage adjusting means and the second voltage adjusting means of claim 10, the control power supply 12 is the voltage source, the gas supply source 6 is the gas supply means, and the rotary pump 8 is Each of the evacuation means is constituted.

-Second Embodiment- FIG. 4 shows a second embodiment of the present invention. In FIG. 4, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the configuration of FIG. 4, when the vacuum degree in the multiplication region A and the voltage of the secondary electron detection electrode 2 are controlled by the vacuum degree control circuit 9 and the arithmetic circuit 11, the values of the vacuum degree and the applied voltage at that time are It is output to the adjustment circuit 24. The adjustment circuit 24 specifies the gain and DC level setting values of the preamplifier 14 necessary for optimizing the brightness and contrast of the sample images displayed on the CRTs 21 and 22, based on the current degree of vacuum and the applied voltage. , The set values are given from the D / A converter 20 to the preamplifier 14.
The relationship between the degree of vacuum and the applied voltage and the amplifier gain and the DC level can be easily obtained by experiments or computer simulations, and these relationships may be tabulated and given to the adjustment circuit 24 in advance. Note that, also in this embodiment, an automatic tracking mode in which the sample image is automatically adjusted by operating the mode indicator 19 and the setting switch 23,
It is possible to switch to the single shot mode in which the sample image is adjusted according to the operation of the setting switch 23.

In the embodiment of FIG. 4, the vacuum gauge 4 and the arithmetic circuit 11 are multiplication environment detecting means, the adjusting circuit 24 is a sample image adjusting means, the preamplifier 14, the main amplifier 15 and the A / A.
The D converter 16 constitutes a signal processing circuit, the control power source 12 constitutes a voltage source, the gas supply source 6 constitutes a gas supply means, and the rotary pump 8 constitutes a vacuum exhaust means.

The present invention is not limited to the above embodiment. For example, the degree of vacuum of the sample chamber 1 and the voltage of the secondary electron detection electrode 2 may be manually set, and the gain and DC level of the preamplifier 14 may be automatically adjusted based on those set values.
The brightness and the contrast of the sample image after the manual setting may be automatically evaluated, and the voltage of the secondary electron detection electrode 2 may be automatically adjusted based on the evaluation result. In the configuration of FIG.
When the brightness and contrast of the sample image can be controlled to a practically sufficient degree only by controlling the voltage by the arithmetic circuit 11, the control by the fine adjustment circuit 18 may be omitted.

[0016]

As described above, according to the present invention, the multiplication environment and the processing condition of the secondary electron signal are changed according to the change of the physical quantity involved in the multiplication effect of the secondary electron and the change of the formation state of the sample image. Is adjusted so that the change of the sample image due to the change of the multiplication effect of the secondary electrons is suppressed and the sample image is always appropriate.
For example, a sample image whose brightness and contrast are properly adjusted,
Can be provided.

[Brief description of drawings]

FIG. 1 is an environment control type S according to a first embodiment of the present invention.
Block diagram of EM.

FIG. 2 is a diagram showing the configuration of the secondary electron detection electrode of FIG. 1 and its surroundings.

FIG. 3 is a diagram showing an example of a correspondence relationship between a degree of vacuum applied to the arithmetic circuit of FIG. 1 and an appropriate value of voltage.

FIG. 4 is an environment control type S according to a second embodiment of the present invention.
Block diagram of EM.

[Explanation of symbols] 1 sample chamber 2 secondary electron detection electrode 3 sample 4 vacuum gauge 5,7 valve 6 gas supply source 8 rotary pump 9 vacuum degree control circuit 10 vacuum degree setter 11 arithmetic circuit 12 control power supply 14 preamplifier 15 main Amplifier 16 A / D converter 17 Memory 18 Fine adjustment circuit 19 Mode indicator 20 D / A converter 21 CRT for observation 22 CRT for photography 23 Setting switch 24 Adjustment circuit

Claims (11)

[Claims] 1. A secondary electron emitted from a sample is multiplied in a multiplication region adjusted to a low-vacuum gas atmosphere, taken in to a secondary electron detection electrode to which a positive voltage is applied, and taken in. In a scanning electron microscope that forms a sample image based on a secondary electron signal, a multiplication environment detection unit that detects a physical quantity that is involved in the degree of multiplication of secondary electrons, and a detection result of the multiplication environment detection unit. And a sample image adjusting means for adjusting the formation state of the sample image based on the above. 2. The scanning electron microscope according to claim 1, wherein the sample image adjusting means adjusts the formation state of the sample image so that a value representative of the visibility of the sample image converges within its allowable range. A scanning electron microscope characterized by: 3. The scanning electron microscope according to claim 1, wherein the multiplication environment detecting means detects the degree of vacuum of the multiplication area as the physical quantity, and the sample image adjusting means detects the degree of vacuum. A scanning electron microscope, wherein the voltage applied to the secondary electron detection electrode is adjusted based on the result. 4. The scanning electron microscope according to claim 1, further comprising a signal processing circuit that forms the sample image based on a secondary electron signal detected by the secondary electron detection electrode, The scanning electron microscope, wherein the adjusting means adjusts the processing condition of the signal processing circuit based on the detection result of the multiplication environment detecting means. 5. The secondary electrons emitted from the sample are multiplied in a multiplication region adjusted to a low-vacuum gas atmosphere and taken into a secondary electron detection electrode to which a positive voltage is applied, and the taken-in 2 In a scanning electron microscope that forms a sample image based on a secondary electron signal, a sample image evaluation unit that evaluates a formation state of the sample image, and an increase in the secondary electrons based on an evaluation result of the sample image evaluation unit. A scanning electron microscope, comprising: a multiplication environment adjusting means for adjusting a physical quantity relating to the degree of doubling action. 6. The scanning electron microscope according to claim 5, wherein the multiplication environment adjusting means adjusts the physical quantity so that a value representative of the visibility of the sample image converges within its allowable range. Characteristic scanning electron microscope. 7. The scanning electron microscope according to claim 5, wherein the multiplication environment adjusting means adjusts a voltage applied to the secondary electron detection electrode based on an evaluation result of the sample image evaluating means. A scanning electron microscope. 8. The scanning electron microscope according to claim 2, wherein the value representing the visibility of the sample image is at least one of the brightness and the contrast of the sample image. electronic microscope. 9. A secondary electron detection electrode capable of detecting secondary electrons emitted from a sample, a voltage source for applying a positive voltage to the secondary electron detection electrode, and a gas having an electron multiplying effect on the sample. A gas supply means for supplying a multiplication region between the secondary electron detection electrode and the secondary electron detection electrode; and a vacuum evacuation means for evacuating the multiplication region, wherein a vacuum of the multiplication region is provided. A vacuum degree identifying means for identifying a degree, and a voltage adjusting means for adjusting a voltage applied from the voltage source to the secondary electron detection electrode based on an identification result of the vacuum degree identifying means. Scanning electron microscope. 10. A secondary electron detection electrode capable of detecting secondary electrons emitted from a sample, a voltage source for applying a positive voltage to the secondary electron detection electrode, and a gas having an electron multiplying effect on the sample. A gas supply means for supplying a multiplication region between the secondary electron detection electrode and the secondary electron detection electrode, a vacuum evacuation means for evacuating the multiplication region, and a secondary electron signal detected by the secondary electron detection electrode. In a scanning electron microscope equipped with a signal processing circuit for forming a sample image on the basis of the sample image evaluation means for evaluating the formation state of the sample image, based on the evaluation result of the sample image evaluation means, A scanning electron microscope, comprising: a voltage adjusting unit that adjusts a voltage applied from the voltage source to the secondary electron detection electrode. 11. A secondary electron detection electrode capable of detecting secondary electrons emitted from a sample, a voltage source for applying a positive voltage to the secondary electron detection electrode, and a gas having an electron multiplying effect on the sample. A gas supply means for supplying a multiplication region between the secondary electron detection electrode and the secondary electron detection electrode, a vacuum evacuation means for evacuating the multiplication region, and a secondary electron signal detected by the secondary electron detection electrode. A signal processing circuit for forming a sample image based on, in a scanning electron microscope comprising: vacuum degree identifying means for identifying the vacuum degree of the multiplication region, based on the identification result of the vacuum degree identifying means, First voltage adjusting means for adjusting the voltage applied from the voltage source to the secondary electron detection electrode, and evaluation of the formation state of the sample image after the voltage is adjusted by the first voltage adjusting means. Sample image evaluating means for performing the sample image Based on the evaluation results of the valence means, scanning electron microscope, characterized in that and a second voltage adjusting means for adjusting the voltage applied to the secondary electron detector electrode from the voltage source.