JPH05164537A - Apparatus and method for measuring length of electron beam - Google Patents

Abstract

PURPOSE:To achieve higher length measuring accuracy with a highly accurate calibration of a measuring system by forming an interference fringe directly on a sample to be measured with a pitch thereof determined accurately by the wavelength of a laser light to scan thereon by an electron beam. CONSTITUTION:A wafer 1 is irradiated with two laser lights 8a and 8c different in the length of the optical path thereof and scanned on the spot by an electron beam 3. An interference fringe 14 is generated at the place where the two laser lights 8a and 8c are irradiated. When it is set as this place where a silicon surface of the wafer 1 is exposed, a carrier density increases at the place subjected to the laser lights 8a and 8c to enhance the generation of secondary electrons. which produces the secondary electrons corresponding to the interference fringe 14. Since the pitch of the interference fringe 14 is determined accurately by the wavelength of the laser lights, accurate measurement of length is made possible by measuring the pitch of the interference fringe 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam length measuring apparatus and method, and more particularly to an apparatus and method for measuring a fine pattern width of an LSI or the like with high precision by electron beam scanning.

[0002]

2. Description of the Related Art As a means for measuring a pattern width of 1 μm or less of an LSI or the like, an apparatus and method using electron beam scanning are often used. FIG. 7 is an explanatory diagram showing the principle thereof, and FIG. 8 is an explanatory diagram showing a method of absolute dimension calibration. In these figures, 1 is a sample to be measured, for example, a wafer, 1a, 1c and 1d are measured patterns formed on the wafer 1, 1b is an edge portion of the pattern 1, and 2 is provided facing the wafer 1. An electron beam column 3 is an electron beam focused by the electron beam column 2, 4 is a deflector provided in the electron beam column 2 for deflecting the electron beam 3, and 5 and 5a are patterns 1a and 1c, respectively. , 1d is a secondary electron signal generated when the electron beam 3 scans.

First, the principle will be described with reference to FIG. The electron beam 3 is deflected by the deflector 4 and scans across the pattern 1 a formed on the wafer 1. At this time, secondary electrons are generated according to the pattern shape. A secondary electron signal 5 is obtained by detecting the secondary electrons with a detector (not shown) such as a scintillator and converting them into signals. Since a large amount of secondary electrons are generated at the edge portion 1b above the pattern, it corresponds to the peak of the secondary electron signal 5. The secondary electron signal 5 is detected by the detector, and the detection signal is compared with the electron beam scanning signal to obtain the width of the pattern by the arithmetic unit (not shown).

Next, the absolute value calibration of the length measurement by the conventional method will be described with reference to FIG. Electron beam scanning is performed on a plurality of patterns 1c and 1d with a known pitch p, and the measurement system is calibrated so that the pattern pitch obtained from the obtained secondary electron signal 5a is p. ..

[0005]

The calibration by this method includes an error when forming the patterns 1c and 1d, for example, an error based on a pattern position error of the photomask and a magnification error at the time of transferring the pattern. In addition, there is a problem that deformation due to pattern waviness and other errors due to chipping / adhesion occur due to the pattern formation process, and these errors during calibration deteriorate the length measurement accuracy.

The present invention has been made to solve such a problem, and an object of the present invention is to improve the length measurement accuracy by calibrating the measurement system with high accuracy.

[0007]

SUMMARY OF THE INVENTION An electron beam length measuring apparatus according to the present invention includes an electron beam lens barrel for focusing and deflecting an electron beam, and secondary electrons generated when a sample is scanned with the electron beam. Is provided with a detector for detecting the pattern width, a calculation unit for calculating the pattern width of the sample surface from the secondary electron signal and the electron beam scanning signal, and a laser optical system for forming interference fringes on the sample surface. Further, the electron beam length measuring apparatus according to the present invention is characterized by corrosive gas, organometallic gas,
Alternatively, it is provided with a mechanism for supplying a gas containing carbon. Further, the electron beam length measuring apparatus according to the present invention, when measuring the width of the pattern from the secondary electron signal indicating the secondary electrons generated by scanning the pattern of the length-measurable sample with the electron beam, Interference fringes obtained by interfering light are formed on the sample surface and used for absolute dimension calibration for length measurement. Further, in the present invention, a pn junction or a Schottky barrier is formed at the place where the dimension calibration is performed. Furthermore, when forming interference fringes on the sample surface, a corrosive gas, an organometallic gas, or a gas containing carbon is supplied to the sample surface to form an uneven pattern corresponding to the interference fringes. The pattern is used for absolute dimension calibration of length measurements.

[0008]

In the electron beam length measuring apparatus and method according to the present invention, the pitch of interference fringes is accurately determined by the wavelength of laser light, and it is formed directly on the length-measuring sample. Is scanned with an electron beam, and the pitch of the obtained secondary electron signal is made equal to the pitch of the interference fringes, whereby the accuracy of calibration can be improved.

[0009]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a basic configuration of calibration according to the present invention,
2 is a diagram showing the relationship between interference fringes and secondary electron intensity, FIG. 3 is a configuration diagram for generating the interference fringes, and FIG. 4 is a diagram showing the relationship between the path difference of laser light and the pitch of the interference fringes. FIG. 5 is a diagram showing an example of the layout of the reference area for performing the calibration. In each figure, 1 to 4 are the same as those described in FIGS. 7 and 8. 6 is a laser oscillator, 7 is a beam expander placed in front of the laser oscillator 6,
Reference numeral 8 is a laser beam generated from the beam expander 7, 9 is a half mirror placed obliquely to the laser beam 8, 10 is a mirror placed on the right and left sides of the half mirror 9, 11 Is an LSI chip, 12 is a dicing line drawn on the LSI chip 11, 13 is a calibration in the dicing line 12, location 14 is formed according to the interference fringes generated on the wafer 1, and 15 is formed according to the interference fringes. Indicates a grating.

As shown in FIG. 1, when the length measurement is calibrated, two laser beams 8a and 8c having different path lengths are applied to the wafer 1, and the position is scanned by the electron beam 3. In the place where the two laser beams 8a and 8c are irradiated,
Interference fringes as shown in FIG. 2 occur. If this place is taken as the place where the silicon surface of the wafer 1 is exposed, the laser light 8
The carrier density increases where a and 8c hit, and the generation of secondary electrons increases, so that a secondary electron signal corresponding to interference fringes can be obtained. Since the pitch of the interference stripe is accurately determined by the wavelength of the laser light as described later, accurate measurement calibration can be performed by measuring the pitch of the interference stripe.

According to FIG. 3 showing the configuration of the laser irradiation system,
The laser beam emitted from the laser oscillator 6 is expanded into a desired width by the beam expander 7, and then obliquely enters the half mirror 9. Then, a part of the laser beam passes through the half mirror 9 and travels to the right, and another part of the laser beam reflects and travels to the left, is reflected by the mirror 10 and is incident on the wafer 1, where interference is generated. Make 14

The principle of occurrence of interference stripes is shown in FIG. Let α be the incident angles of the laser beams 8a and 8b, and
The difference in the optical path lengths of b is d. In FIG. 3, laser light 8
c has the same optical path length as the laser beam 8b. Therefore, the difference between the optical path lengths of the laser beams 8a and 8c is d. From FIG. 4, the conditions for causing these two laser beams 8a and 8c to interfere with each other to cause interference fringes of the pitch p are as follows.

P = λ / 2sinα (1) Here, λ is the wavelength of the laser light. As an example, when the laser light is an argon laser (λ = 350 nm) and the incident angle α is 60 °, p = 0.202 μm.

FIG. 5 shows an example of a place where the above-described length measurement calibration is performed. In the timing line 12 of each LSI chip 11, an exposed portion of the silicon surface, that is, a calibration place 13 is provided. The size of the calibration place 13 is set to the same size as the maximum scanning width of the electron beam during length measurement, for example.

Example 2. In Example 1, the calibration location 13 on the sample uses a surface with exposed silicon,
If a Schottky barrier or a thin pn junction is formed in the calibration place 13, a difference in carrier density causes a potential difference on the surface, and a secondary electron signal with higher contrast can be obtained.

Embodiment 3. Although the length measurement is calibrated by using the carrier density distribution based on the intensity distribution of the laser light in the first embodiment, a pattern formed according to the interference fringes of the laser light may be used. An example thereof will be described with reference to FIG. Figure 6
In (a), the interference stripe 14 is 2 as described above.
It is generated by the irradiation of the laser light 8c, 8a of the book. If a corrosive gas such as XeF ₂ , Cl ₂ or the like is supplied to the sample surface while the interference stripes 14 are generated, the corrosive gas molecules adsorbed on the surface are excited by the laser beam and the sample surface is etched. As shown in FIG. 6B, it is possible to accurately form the etching pattern 15a corresponding to the interference stripe 14. Therefore, this etching pattern 15
The accuracy can be improved by using a for calibration of the length measurement. Also, instead of corrosive gas, W (CO)
₆ , organometallic gases such as WF ₆ and carbon C such as C ₂ H ₅
When a gas containing is used, the gas adsorbed on the sample surface is decomposed by the laser light, so that the deposition pattern 15b of metal or carbon corresponding to the interference stripe 14 can be accurately obtained as shown in FIG. 6 (c). Formed, which can also be used for length measurement calibration. Such an etching pattern 15
a and the deposition pattern 15b are made of S other than silicon.
Since it can be formed on the surface of iO ₂ , Al, etc.,
It is not necessary to expose the silicon surface at the calibration place 13 as in the first embodiment.

[0017]

As described above in detail, the electron beam length measuring apparatus according to the present invention is generated when the electron beam lens barrel for focusing and deflecting the electron beam and the sample is scanned with the electron beam. Since it has a detector for detecting secondary electrons, a calculation unit for calculating the pattern width of the sample surface from the secondary electron signal and the electron beam scanning signal, and a laser optical system for forming interference fringes on the sample surface. Further, the electron beam length measuring apparatus according to the present invention scans the length of the pattern to be measured with an electron beam by a converging / deflecting device, and measures the width of the pattern of the semiconductor element from the generated secondary electron signal. Interference stripes obtained by interfering light are formed on the surface of the sample to be measured and used for absolute dimension calibration of the length measurement.
When measuring the electron beam length, it is possible to calibrate the measurement system with high precision, and thus to perform the length measurement with high precision. Further, since the pn junction or the Schottky barrier is formed at the place where the dimension calibration is performed, a secondary electron signal having a higher contrast can be obtained, which in turn has the effect of increasing the measurement accuracy.
Furthermore, when forming interference fringes on the sample surface, a corrosive gas, an organometallic gas, or a gas containing carbon is supplied to the sample surface to form an uneven pattern corresponding to the interference fringes. Since the pattern is used for absolute dimension calibration for length measurement, the calibration accuracy is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of calibration according to the present invention.

FIG. 2 is a diagram showing a relationship between an interference stripe and a secondary electron signal.

FIG. 3 is a configuration diagram for generating an interference stripe.

FIG. 4 is a diagram showing the relationship between the path difference of laser light and the pitch of interference fringes.

FIG. 5 is a diagram showing an example of a layout of a region for performing calibration.

FIG. 6 is a diagram showing another embodiment for forming an etching pattern or a deposition pattern corresponding to interference fringes.

FIG. 7 is a principle diagram of an electron beam length measuring device.

FIG. 8 is a diagram for explaining an absolute value calibration method for length measurement according to a conventional method.

[Explanation of symbols]

 1 Wafer 2 Electron Beam Column 3 Electron Beam 4 Deflector 6 Laser Oscillator 7 Beam Expander 8 Laser Light 9 Half Mirror 10 Mirror 13 Calibration Place 14 Interference

Claims (5)

[Claims] 1. An electron beam lens barrel for focusing and deflecting an electron beam, and detection for detecting secondary electrons generated when the electron beam from the electron beam lens barrel scans a length-measurable sample. An operation unit for calculating the pattern width of the sample surface from the secondary electron signal detected by this detector and the scanning signal of the electron beam, and a laser optical system for forming interference fringes on the sample surface, An electron beam length measuring device comprising: 2. An electron beam lens barrel for focusing and deflecting an electron beam, and detection for detecting secondary electrons generated when the electron beam from the electron beam lens barrel scans a length-measurable sample. An operation unit for calculating the pattern width of the sample surface from the secondary electron signal detected by this detector and the scanning signal of the electron beam; a laser optical system for forming an interference fringe on the sample surface; An electron beam length measuring device comprising a mechanism for supplying a corrosive gas, an organometallic gas, or a gas containing carbon to the surface of the sample. 3. Interference obtained by interfering laser light when measuring the width of the pattern from a secondary electron signal indicating secondary electrons generated by scanning the pattern of the length-measurable sample with an electron beam. A method for measuring an electron beam, which comprises forming a stripe on a sample surface and using it for absolute dimension calibration of the length measurement. 4. The electron beam length measuring method according to claim 3, wherein a pn junction or a Schottky barrier is formed at a location where the dimension calibration is performed. 5. When forming interference fringes on the sample surface, a corrosive gas, an organometallic gas, or a gas containing carbon is supplied to the sample surface to form an uneven pattern corresponding to the interference fringes. The electron beam length measuring method according to claim 3, wherein the uneven pattern is used for absolute dimension calibration of length measurement.