JP2007066789A - Charge prevention device and charge prevention method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent charge of a sample in a scanning electron microscope. <P>SOLUTION: After a gas is ionized by an ion generator 11, the gas containing ions is introduced into a plane-scanned area on a sample by a gas introduction tube 16 while irradiating it with an electron beam. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charge prevention device and a charge for a scanning electron microscope that generates a picture by scanning a plane while squeezing an electron beam and irradiating a sample, and detecting emitted secondary electrons or reflected reflected electrons. It relates to a prevention method.

  Conventionally, an accelerated electron beam is narrowed down and scanned while irradiating a sample, and the secondary electrons emitted at that time and reflected backscattered electrons are detected to produce an image (secondary electron image, reflected electron image). Are generated and inspections such as measurement of the line width of the pattern, detection of foreign matter, and detection of defects are performed on the image.

  At this time, the sample to be inspected (for example, a sample such as a mask or a wafer for forming a semiconductor) is charged and the image drifts, making it difficult to accurately measure the pattern on the sample. In order to prevent this, gas was introduced into the vicinity of the plane scanning while irradiating the electron beam on the sample, and at the same time, ultraviolet rays were irradiated to neutralize the charge.

  However, as described above, the gas is introduced to neutralize the gas by irradiating with ultraviolet rays while the gas is introduced in the vicinity of the plane scanning while irradiating the electron beam on the sample. And a mechanism for introducing light from an ultraviolet lamp are required, which complicates the structure and makes it difficult to introduce strong ultraviolet light in the vicinity of the sample.

  In the present invention, in order to solve these problems, after ionizing a gas with an ion generator, a gas containing ions is introduced into an area where plane scanning is performed while irradiating an electron beam on the sample with an introduction tube. ing.

  In the present invention, after ionizing a gas with an ion generator, the gas containing the ions is introduced into a region to be scanned in a plane while irradiating the electron beam on the sample with an introduction tube, thereby charging (negative) with the electron beam. Alternatively, the positive charge) can be neutralized.

  In the present invention, after ionizing a gas with an ion generator, a gas containing ions is introduced into a region to be scanned in a plane while irradiating an electron beam on a sample with an introduction tube, and charged by the electron beam (negative or positive). ) Was neutralized.

  FIG. 1 shows a block diagram of an embodiment of the present invention. FIG. 1 schematically shows a main part of a column (lens barrel) 2 and a sample chamber 8 of an SEM (scanning electron microscope) 1.

  In FIG. 1, a column (barrel) 2 generates an electron beam 3 and is narrowed down to have various functions for performing planar scanning while irradiating on a sample (mask) 9. Then, the electron gun 4, the objective lens 5, the secondary electron detector 6, the reflected electron detector 7, and the like are configured.

  The electron beam 3 is generated by an electron gun 4, converged by a focusing lens (not shown), finely focused by an objective lens 5, and irradiated onto a sample 9 while performing planar scanning with a deflection system (not shown).

The electron gun 4 generates the electron beam 3.
The objective lens 5 focuses the electron beam 3 generated by the electron gun 4 with a focusing lens (not shown) and then squeezes it finely to irradiate the sample 9.

  The secondary electron detector 6 is for focusing and detecting the secondary electrons emitted when the sample 9 is irradiated with a finely focused electron beam, thereby generating a so-called secondary electron image.

  The backscattered electron detector 7 detects a backscattered electron that is reflected when the sample 9 is irradiated with a narrowed electron beam, and generates a so-called backscattered electron image.

The sample chamber 8 is a vacuum chamber for storing a sample (mask) 9 and the like.
The mask (sample) 9 is a sample to be observed, for example, a semiconductor mask.

The exhaust system 10 is a pump that evacuates the sample chamber 8.
The ion generator 11 ionizes the gas (see FIG. 4).

  Here, the UV light 12 is an excitation source (a lamp for UV light) for irradiating the gas in the ion generator 11 with UV light and ionizing the gas (positive ions, negative ions).

  The gas valve 13 adjusts the gas amount (gas inflow amount) supplied to the ion generator 11 to an appropriate amount.

  The ion extractor 14 applies a positive or negative tens to hundreds of volts DC voltage from the ion polarity control means 15, and desired ions (positive or negative) are generated from the positive or negative ions generated by the ion generator 11. Only negative ions) are extracted. The extracted gas containing positive or negative ions is injected to the vicinity of the observation region of the sample 9 via the gas introduction pipe 16. Here, when the surface of the sample (mask) 9 does not escape electrons when the sample (mask) 9 is scanned in plane while irradiating the sample with the electron beam 3, for example, if it is insulative, the incident electron beam 3 When the difference between the amount and the amount of charged particles such as secondary electrons, reflected electrons, and ions emitted is negative, the observation part of the sample (mask) 9 is negatively charged and the difference becomes positive Since the observation part of the sample (mask) is considered to be positively charged, either positive ions or gas containing negative ions is extracted and sprayed on the sample (mask) 9 to neutralize the charge. Like to do.

  The gas introduction tube 16 is for injecting a gas containing ions to the vicinity of the observation region of the sample 9 to neutralize the charge on the sample 9 and the charge in the vicinity thereof.

Next, the operation of the configuration of FIG. 1 will be described in detail according to the order of the flowchart of FIG.
FIG. 2 shows a flowchart for explaining the operation of the present invention.

  In FIG. 2, in S1, a sample (mask) 9 is set on the stage. This is because the sample (mask) 9 is preliminarily exhausted in a preliminary exhaust chamber (not shown in FIG. 1), a valve between the preliminary exhaust chamber and the sample chamber 8 is opened, and the sample (mask) 9 is opened by a robot arm (not shown). Is set on a stage (not shown) to obtain the state shown in FIG.

  In S2, an SEM image is observed. This is because, after setting the sample (mask) 9 in the state shown in S1, the electron beam 3 is narrowed down and irradiated on the observation region of the sample (mask) 9, and the surface is scanned by a deflection system not shown in the drawing. Here, secondary electrons emitted from the sample (mask) 9 are focused, detected and amplified by the secondary electron detector 6 here, and a secondary electron image (SEM image) is displayed on the screen of a display device (not shown). Is displayed, and the SEM image is observed, and an inspection such as measurement of the line width of the pattern on the SEM image is performed as necessary.

  In S3, it is determined whether the image is stable. This is to determine whether the image displayed on the display device in S2 is stable and no image movement due to charge such as drift occurs. In the case of YES, it is determined that there is no drift due to charging and that it is normal. On the other hand, in the case of NO in S3, since it has been found that drift or the like due to charging has occurred, the ion generator is turned on in S4. As a result, according to the flowchart of FIG. 3 described later, a gas containing ions is injected from the ion generator 11 of FIG. 4 to the vicinity of the observation region of the sample (mask) 9 from the gas introduction tube 16 and above or near the sample 9. It is possible to neutralize the charge and eliminate the drift caused by the charge. Then, S3 is repeated.

  As described above, the sample (mask) 9 is set on the stage, the surface scanning is performed while irradiating the sample with the electron beam 3, and the secondary electrons (or reflected reflected electrons) emitted at that time are detected by the detector. An image is detected and displayed, and when the image is found to drift due to drift or the like, the ion generator 11 is turned on, and a gas containing ionized ions is supplied from the gas introduction pipe 16 to the vicinity of the observation region of the sample 9 It is possible to neutralize the charge by spraying on and prevent image drift and the like.

  FIG. 3 is a flowchart for explaining the operation of the present invention (ion generation). This is a detailed description of the operation when the previously described ion generator of S4 in FIG. 2 is turned on.

  In FIG. 3, S11 introduces gas. This is done by opening the gas valve 13 in FIG. 1 to adjust the flow rate to a predetermined gas flow, and introducing a gas (for example, a gas such as nitrogen, oxygen, or argon as described on the right side) into the ion generator 11.

  In S12, the UV light is turned on. This is because, in FIG. 1, with the gas introduced into the ion generator 11 at a predetermined flow rate, the UV light is turned on (for example, the power of the lamp that emits UV light is turned on), The gas is excited to generate positive and negative ions.

  In S13, the ion (+-) polarity control means 15 is turned ON. This is because the ion polarity control means 15 of FIG. 1 is turned ON, and a voltage (from several tens of volts) for extracting a designated positive ion or negative ion out of the positive ions and negative ions generated by the ion generator 11. For example, when extracting positive ions, a positive voltage is applied to the ion extractor 14 (or further the ion generator 11) to form the ion extractor 14 or the like. A gas containing positive ions by removing negative ions is blown to the vicinity of the observation region of the sample 9 via the gas introduction pipe 16 of Fig. 1. A hole is formed in the center where the ion extractor 14 is formed. A negative voltage is applied to the extracted electrode to accelerate positive ions generated by the ion generator 11, while blocking negative ions and containing a gas containing positive ions passing through the extracted electrode. Via the introduction pipe 16 It may be blown to the vicinity of the observation region of the sample 9 Te.

  In step S14, it is determined whether the image drift is stationary. This is because the image drift due to the charge of the sample 9 or the vicinity of the sample 9 is eliminated (stationary) by blowing a gas containing positive or negative ions in the vicinity of the observation region of the sample 9 in S13. Determine. Image drift is determined by whether a specific pattern (or a pattern under observation) moves a predetermined distance or more in a certain time. In the case of YES, since there is no image drift, the process ends here. On the other hand, in the case of NO, since the drift of the image has not stopped even if a gas containing ions is blown in the vicinity of the observation region of the sample 9 in S13, the gas amount is increased in S15 (the gas inflow amount is reduced by the gas valve 13). Increase the predetermined amount (or increase the UV light, high frequency power (excitation source power) by a predetermined amount), repeat S14 and subsequent steps, to the amount of gas that can neutralize the charge (or the UV light of the excitation source, the amount of high frequency power) If the gas amount exceeds the specified flow rate (maximum gas amount) (or if UV light or high-frequency pattern exceeds the maximum power), it was found that the charge amount was too large to neutralize, so an error occurred. Message (for example, “The maximum gas flow (or maximum UV light, high frequency power supplied) cannot stop the image drift due to charging”) Shows, to stop the supply of gas (or power).

  As described above, when the image of the sample (mask) 9 is observed, when an image drift due to charging occurs (or when the operator manually instructs it), the ion generator 11 is turned on and a predetermined gas amount is set. And ionized by the ion generator 11 and extracted as necessary by a gas containing positive ions or negative ions (if the ion polarity control means 15 is not turned on, positive ions The gas (including both negative ions) is blown to the vicinity of the observation region of the sample (mask) 9 through the gas introduction tube 16 to neutralize the charge and eliminate image drift due to the charge. Is possible.

  FIG. 4 shows an ion generator 11 of the present invention. In FIG. 1, UV light (lamp that emits UV light) 12 is used as an excitation source of the ion generator 11, but here, another high-frequency power source (high-frequency voltage) and a resonator (ultra-high-frequency resonator) are used. Examples of use are shown in FIGS. 4A and 4B, respectively. Alternatively, the gas may be irradiated with soft X-rays to ionize the gas (positive ions, negative ions).

  FIG. 4A is a schematic diagram when a high-frequency power source (high-frequency voltage) is used as the excitation source of the ion generator 11. It is made into a cylindrical shape with an insulator (for example, heat-resistant glass) 21, and in the figure, gas is supplied from the right by adjusting the flow rate with the gas valve 15 of FIG. A cylindrical internal gas is excited to generate positive ions and negative ions, and a positive or negative voltage from the ion polarity control means 15 is applied to the left ion extractor 14 so that negative ions or positive ions are applied. Ions are extracted, and a gas containing the extracted ions is sprayed from the left side to the vicinity of the observation region of the sample 9 via the gas introduction pipe 16 of FIG. 1 to neutralize the sample 9 and the charge in the vicinity thereof. .

  FIG. 4B is a schematic diagram when a resonator (an ultrahigh frequency resonator such as a magnetron) is used as an excitation source of the ion generator 11.

  4 (b-1), the gas is supplied from the right to the resonator by adjusting the flow rate with the gas valve 15 in FIG. 1, and the internal gas is excited by the resonator to generate positive ions and negative ions. Ions are generated, a positive or negative voltage from the ion polarity control means 15 is applied to the left ion extractor 14 to extract negative ions or positive ions, and a gas containing the extracted ions is extracted from the left side. Further, it is sprayed to the vicinity of the observation region of the sample 9 via the gas introduction pipe 16 of FIG.

  (B-2) of FIG. 4 shows a state in which a gas containing ions generated by the ion generator 11 is blown to the vicinity of the observation region of the mask (sample) 9 through the gas introduction tube 15.

  In the present invention, after ionizing a gas with an ion generator, a gas containing ions is introduced into a region to be scanned in a plane while irradiating an electron beam on a sample with an introduction tube, and charged by the electron beam (negative or positive). Of charge) can be neutralized.

1 is a configuration diagram of one embodiment of the present invention. It is an operation | movement explanatory flowchart of this invention. It is operation | movement description flowchart (ion production | generation) of this invention. It is an ion generator of the present invention.

Explanation of symbols

1: SEM (scanning electron microscope)
2: Column 3: Electron beam 4: Electron gun 5: Objective lens 6: Secondary electron detector 7: Reflected electron detector 8: Sample chamber 9: Sample (mask)
10: exhaust system 11: ion generator 12: UV light 13: gas valve 14: ion extractor 15: ion polarity control means 16: gas introduction pipe 21: insulator 22: high frequency power supply 31: resonator

Claims (5)

In an anti-charge device for a scanning electron microscope that scans a plane while irradiating a sample with an electron beam narrowly narrowed and detects an emitted secondary electron or reflected reflected electron to generate an image,
An ion generator for ionizing a gas;
A charge preventing apparatus, comprising: a gas introduction pipe that blows a gas containing ions generated by the ion generator in the vicinity of a plane scanning while irradiating the sample with an electron beam of a sample narrowed down.   An ion extractor for applying a positive voltage or a negative voltage, which extracts either positive ions or negative ions generated by the ion generator, includes the extracted positive ions or negative ions. 2. The charge preventing apparatus according to claim 1, wherein gas is blown onto the sample by the gas introduction pipe.   The ionization of the gas is performed by irradiating the gas with UV light, soft X-rays, supplying high-frequency power to the gas, or introducing the gas into a resonator. 2. The charge prevention device according to 2.   Adjustment of the amount of ionized ions is adjusted by UV light, soft X-rays, high frequency power, power supplied to the resonator as the excitation source, or by adjusting the amount of gas supplied, or both. The charge prevention device according to claim 1, wherein the charge prevention device is a charge prevention device. In a method for preventing charge of a scanning electron microscope, which scans a plane while irradiating a sample with a finely focused electron beam, and detects an emitted secondary electron or reflected backscattered electron to generate an image,
An ion generator for ionizing a gas;
A gas introduction pipe for blowing a gas containing ions onto the sample;
A charge prevention method comprising neutralizing a charge by spraying a gas containing ions generated by the ion generator in the vicinity of plane scanning while irradiating and narrowing an electron beam with the gas introduction tube.

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