JP2701764B2 - Apparatus and method for measuring size of charged particle beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for measuring the size of a charged particle beam.

[0002]

2. Description of the Related Art As a conventional example of electron beam dimension measurement, a single crystal Si knife edge method as described in Japanese Patent Application Laid-Open No. 2-254368 has been devised. The single crystal Si knife edge method is a method of performing wet etching of a Si wafer with an aqueous solution of potassium hydroxide or the like as shown in FIG. In this method, an edge portion where the surface 3 forms a taper angle of about 54 degrees is used to shield the electron beam 4. An electron beam measuring method according to a conventional example will be described with reference to FIG. When the electron beam 4 emitted from the electron source 5 is scanned at a constant speed in a direction perpendicular to the perpendicular or parallel side of the single crystal Si knife edge 1 at the height of the sample surface, the electron beam is not blocked by the edge. 4 is single crystal Si
It is detected by a Faraday cup 6 located below the knife edge 1. On the other hand, the electron beam 4 blocked by the single crystal Si knife edge 1 is reflected and does not reach the Faraday cup 6. Therefore, a current density distribution waveform as shown in FIG. The first derivative waveform of this waveform is as shown in FIG. 5B. For example, the interval determined by the slice level of 50% of the peak value is the beam size W. This method is called a threshold method. Furthermore, this 2
The next differential waveform is as shown in FIG. 5C, and there is a method in which the interval between zero crossings is used as the beam size W.

[0003]

By the way, in the electron beam size measuring apparatus as shown in the above-mentioned conventional example, when the acceleration voltage of the electron beam 4 is relatively low, 10 kV to 20 kV or less, a single crystal Si knife edge is used. All the electron beams 4 blocked by 1 are reflected and absorbed, and the Faraday cup 6
, And the obtained current density distribution waveform does not become dull.

However, when the size of the electron beam is obtained only from the signal detected from the Faraday cup 6, a part of the electron beam reaching the Faraday cup 6 is reflected there to become a reflected electron 12 or a secondary electron 11 And the S / N ratio is poor due to the generation of the dimensional error, which limits the accuracy of dimension measurement.

Further, in the electron beam lithography apparatus, an acceleration voltage of 10 k to 20 kV has conventionally been generally used. Acceleration voltages of 50 kV to 100 kV have been employed to reduce the proximity effect due to scattering and obtain high dimensional accuracy.

For example, an acceleration voltage of 50 k incident on Si
It is required by simulation that the electron beam of V penetrates to a depth of 20 μm. That is, the electron beam having a relatively high accelerating voltage is transmitted or scattered through the thin portion of the single-crystal Si knife edge 1, and a part of the electron beam reaches the Faraday cup 6, thereby dulling the detected current density distribution waveform. However, there is a disadvantage that accurate beam size measurement cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks, and to provide a charged particle beam size measuring apparatus and a measuring method capable of accurately measuring the charged particle beam size.

[0008]

According to the present invention, a charged particle source, a shield having an opening, a Faraday cup for capturing charged particles passing through the opening, and a shield having the opening And a signal processing unit that receives and processes signals from the shield, the Faraday cup, the reflected charged particle detector, and the secondary electron detector. A charged particle beam size measuring device having the same is obtained.

The shield having the opening is made of metal or silicon. In the case of silicon, an opening whose side wall angle is 80 degrees or more with respect to the surface is used.

According to the present invention, there is provided a method for measuring a beam size from a signal obtained by scanning a charged particle beam emitted from a charged particle source on a shield having an opening. Signal processing is performed using the obtained signal, the signal of the charged particle passing through the opening, the signal of the charged particle reflected from the shield, and the signal of the secondary electron emitted from the shield to determine the beam size. Thus, a method for measuring the size of a charged particle beam is obtained.

[0011]

Next, the present invention will be described with reference to the drawings. FIG. 1A is a configuration diagram of a charged particle beam size measuring apparatus according to a first embodiment of the present invention. In FIG. 1A, there is a 5 μm thick Cu aperture 7 for shielding an electron beam having an acceleration voltage of 50 kV, and an ammeter is connected.
The absorption current can be measured. The Faraday cup 6 is located below the Cu aperture 7. An ammeter is also connected to the Faraday cup 6. Above the Cu aperture 7, a reflected electron detector 8 and a secondary electron detector 9 are provided. Each signal is output to the signal processing unit 10 shown in FIG. In addition to Cu, a shield made of a metal such as Mo may be used.

Referring to FIG. 1, a method for obtaining the beam size will be described. The electron beam 4 scans the shield at a constant speed from left to right. The shield has a thickness enough to completely block the electron beam 4 having a high accelerating voltage over the entire area, and the electron beam 4 transmits through the shield or scatters the Faraday electron beam in the shield. It hardly reaches the cup 6. FIG. 2 shows a signal waveform obtained at this time. The signal detected by the Faraday cup 6 is I
₁ , the signal absorbed and detected by the shield is I ₂ , the signal detected by the backscattered electron detector 8 is I ₃ , and the signal detected by the secondary electron detector 9 is I ₄ . I ₁ , I ₂ , I
₃ and I ₄ are respectively increased and added or subtracted at an appropriate magnification by the signal processing unit 10 to obtain a current density distribution waveform having a higher S / N ratio. That is, at least one signal of I ₂ , I ₃ and I ₄ amplified to an appropriate magnification is subtracted from I ₁ . From the signal I ₅ obtained by treating seeking first derivative or second derivative waveform obtaining the beam size W by the aforementioned method.

FIG. 3 is a view showing a second embodiment of the present invention using Si as a shielding object. Since Si is a light metal, the shielding effect of the electron beam 4 is smaller than that of a heavy metal such as Cu. Therefore, an extremely thick film is required to completely shield the electron beam 4. For example, to shield an electron beam having an acceleration voltage of 50 kV, a 20 μm thick Si aperture is required. By the way, when the etching angle of the opening of the Si aperture 21 with respect to the surface is 90 degrees or less, as shown in FIG. 4, the electron beam may pass through a thin side surface or may be reflected on the side surface of the opening as described above. Signal S /
The N ratio becomes worse, the signal waveform becomes dull, and the accuracy of beam size measurement decreases. Therefore, a high etching angle is required. However, when Si is used as the aperture material, a conventional semiconductor manufacturing process can be used, and processing and manufacturing can be performed relatively easily. Therefore, 20μ
It is possible to etch at an angle nearly perpendicular to the surface over a depth of m. In a process using a current semiconductor manufacturing apparatus and a semiconductor device, it is possible to process at an angle of 80 ° or more with respect to the surface over a depth of 20 μm. Further, when a metal or alloy such as Au or Pt is formed on the Si surface to form the conductive layer 22, the thickness of Si can be reduced to about 10 μm.

[0014]

As described above, the present invention relates to an apparatus for measuring a beam size from a signal obtained by scanning a charged particle beam emitted from a charged particle source on a shield,
By performing signal processing using a plurality of signals to determine the beam size, a signal waveform having a high S / N ratio is obtained, and as a result, highly accurate measurement is possible. The present invention relates to the measurement of the size of an electron beam, but the same effect can be obtained even when charged particles other than the electron beam are used.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a first embodiment of the present invention,
(B) is a diagram showing the signal processing unit.

FIG. 2 is a diagram showing a current waveform of each part of the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a conventional example.

FIGS. 5A to 5C are diagrams showing a current waveform and a differential waveform thereof in a conventional example.

[Explanation of symbols]

 Reference Signs List 1 single crystal Si knife edge 2 [111] plane 3 [100] plane 4 electron beam 5 electron source 6 Faraday cup 7,22 aperture 8 reflected electron detector 9 secondary electron detector 10 signal processing unit 11 secondary electron 12 reflection Electron 22 conductive layer

Claims (4)

(57) [Claims] 1. A charged particle source, a shield having an opening, a Faraday cup for capturing charged particles passing through the opening, and a reflected charged particle detector disposed above the shield having the opening. An apparatus for measuring the size of a charged particle beam, comprising: a detector and a secondary electron detector; and a signal processing unit that receives and processes signals from the shield, the Faraday cup, the reflected charged particle detector, and the secondary electron detector. 2. The apparatus for measuring the size of a charged particle beam according to claim 1, wherein the shield having the opening is made of metal. 3. The charged particle beam size measuring apparatus according to claim 1, wherein the shield having the opening is made of silicon, and an angle of a side wall of the opening is 80 degrees or more with respect to a surface. 4. A method for measuring a beam size from a signal obtained by scanning a charged particle beam emitted from a charged particle source on a shield having an opening, wherein the signal obtained from the shield, Signal processing is performed by using a signal of a charged particle passing through an opening, a signal of a charged particle reflected from a shield, and a signal of a secondary electron emitted from the shield to obtain a beam size. A method for measuring the size of a particle beam.