JP2007149449A - Device and method for preventing charged contamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for preventing charge contamination wherein a mechanism to generate ions for preventing charge and a mechanism to generate plasma for removing contamination are provided, the ions or the plasma are/is selectively discharged from the device and irradiated on an object to be measured, and thereby, charge prevention and the contamination removal of the object to be measured are easily carried out by using this simple device. <P>SOLUTION: This device for preventing charge contamination is composed of an ion generating means to generate positive ions and negative ions by irradiating gas with UV light or an X-ray, a plasma generating means to convert the gas into plasma, and a means to extract and discharge the ions and the plasma generated by the ion generating means or the plasma generating means toward a sample to be measured or the vicinity of the sample to be measured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a device for preventing electrostatic contamination of a scanning electron microscope that scans a plane while squeezing an electron beam and irradiating a sample, and detects emitted secondary electrons or reflected reflected electrons to generate an image. The present invention relates to a method for preventing electrostatic contamination.

  Conventionally, when an object to be measured by a CD-SEM is electrically insulating, negative charges are accumulated (charged) by scanning with an electron beam. When this charge accumulation phenomenon occurs, the secondary electron image and the reflected electron image of the object to be measured are deteriorated in image quality, and the accumulated negative charge affects the path of the electron beam, causing the image to be distorted or the pattern image. The whole moves.

  In order to prevent such image degradation, conventionally, the charge accumulation is neutralized by irradiating UV light, for example, UV light (for example, 160 nm to 400 nm) from a deuterium lamp to the site of the object to be measured. It was. It is considered that the ion generation process at this time is performed as follows.

  (1) In a ground state in which gas atoms / molecules are neutral and stable, electrons exist on orbits having the lowest energy level.

  (2) When one photon is irradiated and absorbed, one electron moves (excites) on the outer orbit. In this state, it is electrically neutral but unstable. For example, in about 1 to 2 seconds, this state returns to the ground state.

  (3) When another photon hits and absorbs energy before returning to the ground state, the excited electron gains more energy, so that the electron jumps out of the orbit and is completely released from atomic and molecular constraints. (Ionized) generates positive ions and electrons (bonded to other neutral molecules in a single time to become negative ions).

  As described above, neutral light atoms and molecules cannot be ionized by only one photon energy, and UV light is ionized by the energy of two photons (E = h × frequency, h is Planck's constant).

  On the other hand, if a nitride or a compound of sulfur element adheres to the object to be measured while acquiring an image by scanning the object while irradiating the object with an electron beam with an SEM, a foreign substance film is formed using these as a nucleus. In this case, since the quality of the image is deteriorated or the pattern size on the object to be measured is measured differently, it is adversely affected.

  As described above, in a device such as a conventional CD-SEM, when charging the sample to be measured, UV light is irradiated to generate positive ions and negative ions to remove the charge of the sample to be measured. On the other hand, when a foreign substance film is formed on the sample to be measured, it has been decomposed and removed by plasma treatment in order to remove it, and thus there is a problem that it is necessary to mount two different types of apparatuses.

  In order to solve these problems, the present invention provides a mechanism for generating antistatic ions and a mechanism for generating plasma for decontamination in the apparatus, and selectively releases ions or plasma from the apparatus. Antistatic and decontamination of the object to be measured are performed.

  The present invention is provided with a mechanism for generating antistatic ions and a mechanism for generating plasma for decontamination within the apparatus, and selectively irradiates ions or plasma from the apparatus to irradiate the object to be measured. Accordingly, it is possible to easily prevent the object to be measured and the like and remove the contamination with a simple apparatus.

  The present invention provides a mechanism for generating antistatic ions and a mechanism for generating decontamination plasma in the apparatus, and selectively emits ions or plasma from the apparatus to irradiate the object to be measured. We realized simple equipment and easy antistatic and contamination removal of measured objects.

FIG. 1 shows a structural diagram of one embodiment of the present invention.
FIG. 1A shows an example of the overall structure.

  In FIG. 1 (a), the antistatic contamination device 1 is according to the present invention, and here is mounted on the SEM, and an electron beam of the sample 2 to be measured is attached by attaching an introduction tube 21 to the tip. Ions or plasma is irradiated so as to blow on the scanning portion of the beam 13 to neutralize the charge of the sample 2 to be measured, to prevent or remove contamination, or to discharge the entire sample chamber 11 to the sample chamber. 11 is neutralized, and the contamination is prevented and removed.

  The sample 2 to be measured is a target to be measured by generating an image by scanning the electron beam 13 in a plane and detecting secondary electrons, reflected reflected electrons, or absorbed electrons emitted at that time. Sample (eg, mask, LSI, etc.).

  The stage 3 is a stage on which the sample 2 to be measured is mounted and moved (for example, X, Y, Z, θ).

  The sample chamber 11 is a chamber that is evacuated by a vacuum evacuation system (not shown) for holding the sample 2 to be measured mounted on the stage 3 in a vacuum.

  The electron optical system 12 planarly scans the sample 13 to be measured with a finely focused electron beam 13 and detects emitted secondary electrons, reflected reflected electrons, absorbed electrons, etc., and displays an image not shown. It is a well-known thing displayed on the display apparatus.

  The electron beam 13 is a narrowly focused electron beam beam generated by a known electron optical system 12, and here scans the sample to be measured 13 (for example, a semiconductor mask) in a plane.

  The introduction tube 21 is for emitting ions and plasma emitted from the electrostatic contamination prevention device 1 toward the irradiation position of the electron beam 13 of the sample 2 to be measured.

  FIG. 1B shows a structural diagram of the main part. This shows an example of a main part structure of the anti-static device 1 shown in FIG.

  In FIG. 1B, a UV lamp 22 is turned on by supplying power from a power source 25, irradiates UV light to nitrogen or the like introduced from a gas inlet 24, and emits ions (positive ions and negative ions). Is to be generated. Instead of the UV lamp, soft X-rays may be irradiated from the X-ray generator to nitrogen or the like introduced from the gas inlet 24 to generate ions.

  The coil 23 supplies high-frequency power from a high-frequency power source (not shown), and efficiently generates plasma by exciting ions (positive ions and negative ions) generated by irradiating the UV light from the UV lamp 22 with nitrogen gas. Is for.

  The gas inlet 24 is an inlet for introducing a gas (an inert gas such as nitrogen gas or argon gas, a gas such as oxygen or clean air) from a cylinder (not shown) at a predetermined flow rate (predetermined pressure). The gas introduction is performed so that the inside of the container of the anti-static device 1 is maintained at a predetermined pressure between the atmosphere and the vacuum of the sample chamber 11 (or to the extent that the charge of the sample 2 to be measured is removed). A gas flow rate introduced by a needle valve (not shown) attached to the port 24 is adjusted.

  The ion extraction electrode 26 extracts ions or plasma from ions (positive ions and negative ions) generated by irradiating the UV light from the UV lamp 22 to nitrogen gas or the like or generated plasma, and irradiates the sample 2 to be measured. It is for doing. Note that, without providing the ion extraction electrode 26, the vacuum of the sample chamber 11 may be used to attract ions or plasma and gas together.

  The ion or plasma 27 is ions or plasma that is extracted from the ion extraction electrode 26 (or without the ion extraction electrode 26) and released. The extracted ions or plasma are ejected to a portion of the sample 2 to be measured which is scanned by the electron beam 13 or ejected to the entire sample chamber 11. The charge (charging) on the surface of the sample 2 to be measured is neutralized by ions. The plasma prevents the surface contamination of the observed sample 2 or the like, or removes the attached contamination.

  1 (b) having the above structure is attached to the sample chamber 11 of FIG. 1, and an introduction tube 21 is attached below the ion extraction electrode 26 to thereby measure the electron beam of the sample 2 to be measured. The beam 13 is sprayed onto the plane-scanned portion, and the charge of the portion is neutralized (neutralized by ions), and contamination is prevented and removed (prevented and removed by plasma), which is easily switched. It becomes possible. 1 is attached to the sample chamber 11 shown in FIG. 1 to release ions or plasma into the sample chamber 11 so that the sample 2 to be measured in the sample chamber 11 and the like can be obtained. It is possible to easily switch between neutralizing the surface charge (neutralized by ions), preventing contamination, and removing (preventing and removing by plasma).

  Next, in accordance with the order of the flowcharts of FIGS. 2 and 3, the operation of preventing charging, preventing contamination and removing under the structure of FIG. 1 will be sequentially described in detail.

FIG. 2 is a flowchart for explaining the operation of the present invention (part 1).
FIG. 2A shows a flowchart in the case of decontamination.

In FIG. 2A, S1 evacuates the sample chamber 11 to a vacuum. This is to operate a vacuum exhaust system (not shown) of the sample chamber 11 in FIG. 1A to exhaust the sample chamber 11 to a vacuum (for example, exhaust to 10 ⁻⁶ Torr or less).

  In S2, contamination occurs. In this state, the sample chamber 11 in FIG. 1A is evacuated to a vacuum by an unillustrated evacuation system, and contaminants flow in when the sample 2 to be measured is taken in and out and adhere to the inside of the sample chamber 11. As a result, contamination occurs, or contamination, gas, or the like attached to the sample 2 to be measured is released and attached to cause contamination. Further, a gas (organic gas or the like) floating in the sample chamber 11 by the irradiation of the electron beam 13 is decomposed and adhered to the sample 2 to be observed or its vicinity, thereby causing contamination.

  In S3, the apparatus is turned on. This is performed by turning on the power supply of the above-described charging contamination preventing apparatus 1 of FIG. 1 to introduce plasma into the sample chamber 11 to prevent or remove the occurrence of contamination.

  In S4, a sample is introduced. In this case, the sample 2 to be measured is introduced into the sample chamber 11 of FIG. 1 from the outside via the preliminary exhaust chamber and mounted on the stage 3 shown in the figure.

  S5 removes contamination. In S3, the power supply of the anti-static device 1 is turned on, and plasma is blown to the inside of the sample chamber 11 and the surface of the sample 2 to be measured introduced in S4 to remove the attached contaminants.

In S6, it is determined whether a predetermined time has elapsed. This is because the antistatic device 1 is turned on and a predetermined time elapses (a suitable time is obtained by experiment) for removing contamination by blowing plasma on the inside of the sample chamber 11 and the surface of the sample 2 to be measured. To determine whether sufficient decontamination has been completed.
In the case of YES, the apparatus is turned off, the contamination of the sample chamber 11 and the sample 2 to be measured is terminated, and the measurement is started. If NO, repeat S5 and continue removing contamination.

  As described above, in a state where the sample chamber 11 is evacuated, the charging contamination prevention apparatus 1 is turned on periodically or whenever the sample 2 to be observed is put into the sample chamber 11, and plasma is supplied to the sample chamber 11 and the sample 2 to be observed. By spraying on the surface of the surface to remove the contamination, a high-quality image of the sample 2 to be observed is generated in a state where the contamination is removed, and measurement is performed with high accuracy and stability (for example, precise measurement of the shape and dimensions of the mask pattern). It becomes possible to do.

FIG. 2 (b) shows a detailed flowchart for decontamination.
In FIG. 2B, S11 turns on UV.

S12 introduces gas.
S13 excites.

S14 turns on the high frequency.
In S15, a large amount of ionization is performed using the excited ions as seeds. In steps S11 to S15, the power of the UV lamp 22 in FIG. 1B constituting the charging contamination preventing apparatus 1 in FIG. 1 is turned on (S11), and a gas (for example, nitrogen gas) is introduced from the gas inlet 24. (S12) Irradiating and exciting the gas introduced with UV light to generate ions (positive ions and negative ions) (S13), and then turning on the high-frequency power supply to supply high-frequency power to the coil 23 (S14) Then, a large amount of ionization is performed using the generated ions as seeds to generate plasma (S15).

S16 is pulled out by an electric field.
S17 irradiates the object. In S16 and S17, the plasma generated in S15 is efficiently extracted by applying a voltage (for example, a voltage of about −10 V to −300 V) to the ion extraction electrode 26 in FIG. Irradiate the inside of the chamber 11 and the surface of the sample 2 to be measured to remove contamination on the surface.

  1 is turned on, and the generated plasma can be irradiated to the inside of the sample chamber 11 and the surface of the sample 2 to be measured to remove the contamination. .

  FIG. 3 shows a flowchart (part 2) for explaining the operation of the present invention. This shows a flowchart for explaining the operation when neutralizing the charge and removing the contamination.

  In FIG. 3, S21 is evacuated to a vacuum. This evacuates the sample chamber 11 of FIG. 1 by operating a vacuum exhaust system (not shown) in a vacuum.

  In S 22, the sample is put into the sample chamber 11. In this state, the sample 2 to be measured is placed in the sample chamber 11 via a preliminary exhaust chamber (not shown) in the state where the sample chamber 11 is evacuated in S21 and mounted on the stage 3.

  In S23, it is determined whether the measurement is started. This is because the measurement sample 2 mounted on the stage 3 in the sample chamber 11 starts measurement (generates an image and starts measuring the dimension of the pattern on the image), or the image moves during measurement and charges up. Is detected. In the case of YES, it is determined that the measurement is started, or the image is moved during the measurement and it is determined that charge-up (charging) is detected, and the process proceeds to S24. If NO, repeat S23 and wait.

  S24 introduces gas. This turns on the power supply of the anti-static device 1 in FIG. 1 and starts introducing gas from the gas inlet 24 at a predetermined flow rate.

  In S25, ions are irradiated to remove the charge. This is because, with the gas introduced from the gas inlet 24 at a predetermined flow rate in S24, the UV lamp is turned on and the introduced gas (for example, nitrogen gas) is irradiated to generate ions (positive ions and negative ions). The generated ions are irradiated to the scanning portion of the electron beam 13 of the sample 2 to be observed to neutralize and remove the charge.

  In S26, plasma is irradiated to remove contamination. This is a state in which a gas is introduced from the gas introduction port 24 at a predetermined flow rate in S24, a UV lamp is turned on, and the introduced gas (for example, nitrogen gas) is irradiated to generate ions (positive ions and negative ions). Furthermore, a high frequency power is supplied to the coil 23, a large amount of ionization is performed using the generated ions as seeds to generate plasma, and the generated plasma is irradiated onto the scanning portion of the electron beam 13 of the sample 2 to be observed. , Remove contamination.

  In step S27, it is determined whether a predetermined time has elapsed. This is to determine whether the predetermined time has elapsed for each of S25 and S26, the charge has been sufficiently removed (neutralized), and the contamination has been sufficiently removed. If YES, the process ends. In the case of NO, S25 and subsequent steps are repeated.

  As described above, when the sample 2 to be measured is mounted on the stage 3 of the sample chamber 11 (or when the charge is detected by moving the image during measurement), the power supply of the anti-static device 1 shown in FIG. The ions (positive ions, negative ions) generated by irradiating the gas introduced with UV light are irradiated to the scanning portion of the electron beam 13 of the sample 2 to be measured to neutralize and remove the charge (charging), Further, high frequency power is supplied to the coil 23 to generate plasma, and the plasma is irradiated into the sample 2 and the sample chamber 11 to remove contamination, or the operation of one electrification contamination prevention device 1 is switched. It is possible to easily remove (prevent) charge and remove (prevent) contamination.

  In addition, when an image moves during measurement and a charge phenomenon is detected, the charge is neutralized and removed by ions, and further, it is difficult to generate charges by irradiating ions before the image moves. It may be prevented (suppressed). Similarly, if the occurrence of contamination is detected due to a decrease in the contrast of the image being measured, the contamination is removed by irradiating with plasma, or contamination is performed by irradiating the plasma before the image contrast decreases. It is also possible to prevent (suppress) the occurrence of this.

  The present invention provides a mechanism for generating antistatic ions and a mechanism for generating decontamination plasma in the apparatus, and selectively emits ions or plasma from the apparatus to irradiate the object to be measured. It is possible to easily prevent and charge the object to be measured and remove contamination with a simple apparatus.

1 is a structural diagram of an embodiment of the present invention. It is operation | movement explanatory flowchart (the 1) of this invention. It is operation | movement description flowchart (the 2) of this invention.

Explanation of symbols

1: Antistatic contamination device 2: Sample to be measured 3: Stage 11: Sample chamber 12: Electron optical system 13: Electron beam 21: Introducing tube 22: UV lamp 23: Coil 24: Gas inlet 25: Power supply 26: Ion Extraction electrode 27: ion or plasma

Claims (4)

In the anti-electrostatic contamination apparatus of the scanning electron microscope that scans the surface while irradiating the sample with a narrowed electron beam and detects the emitted secondary electrons or reflected reflected electrons to generate an image,
Ion generating means for generating positive ions and negative ions by irradiating a gas with UV light or X-rays;
Plasma generating means for converting gas into plasma;
And a means for taking out the ions or plasma generated by the ion generating means or the plasma generating means and discharging the ions or plasma toward the sample to be measured or in the vicinity of the sample to be measured.   2. The apparatus for preventing charge contamination according to claim 1, wherein the ion generation means or the plasma generation means is electrically switched to take out ions or plasma from either one.   3. A charging contamination preventing apparatus according to claim 1, wherein plasma is generated by using ions generated by the ion generating means. In the anti-electrostatic contamination apparatus of the scanning electron microscope that scans the surface while irradiating the sample with a narrowed electron beam and detects the emitted secondary electrons or reflected reflected electrons to generate an image,
Ion generating means for generating positive ions and negative ions by irradiating a gas with UV light or X-rays;
Plasma generating means for converting gas into plasma;
A means for taking out the ions or plasma generated by the ion generating means or the plasma generating means and discharging the ions or the plasma toward the sample to be measured or in the vicinity of the sample to be measured;
Irradiating or irradiating the sample to be measured with ions or plasma generated by the ion generating unit or the plasma generating unit, or preventing or removing contamination from the sample to be measured. A characteristic antistatic method.

Images