JP2806240B2 - Reference mark for apparatus calibration of electron beam exposure apparatus and apparatus calibration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration reference mark used for calibrating an electron beam exposure apparatus.

[0002]

2. Description of the Related Art In an electron beam exposure apparatus for obtaining a desired pattern by using an electron beam exposure, the calibration of the electron beam exposure apparatus performed before the electron beam exposure has conventionally been performed as shown in FIG. A reference mark (3) for calibration of a heavy metal having a step on unevenness as shown in FIGS. 5 and 6, which is set on a stage (2) for moving a target wafer, reticle, etc. (1). Then, the reflected electron signal (5) obtained by scanning (deflecting) the incident electron beam (4) is detected by the detector (6). That is, this reference mark (3)
The stage position is measured from the reflected electron signal (5) obtained from the above, the deflection distortion calibration at the time of electron beam deflection necessary for actual exposure is performed, and the reflected electron signal (5) is used to calculate the incident electron beam. Was detected, and beam size calibration and the like were performed. However, when these calibration reference marks (3) are used, the reflected electron signal (5)
Since the ratio (S / N ratio) of the backscattered electron signal (5) from the flat portion is low, the accuracy of stage position detection, beam size detection, and the like is low, resulting in a disadvantage that the device calibration accuracy is deteriorated.

[0003]

FIG. 5 and FIG. 6 show the structure of an apparatus calibration reference mark used in a conventional electron beam exposure apparatus. In the case of the reference mark structure for device calibration shown in FIG. 5, since the material of the step portion (convex portion) (7) and the flat portion (8) are the same heavy metal such as W, Ta or the like (9), the flat portion (8) is used. ) Is detected to the same degree as the signal (5) of the step portion (7), the peak value of the first derivative waveform (10) of the reflected electron signal (5) is low, and the flat portion ( Since the reflected electron signal (5) from 8) becomes background noise, the S / N ratio becomes low.

A reference mark structure for device calibration as shown in FIG. 6 is known as a method for avoiding a decrease in peak value which is a drawback of the mark structure shown in FIG. This is not for device calibration, but is known as a reference mark for exposure position detection at the time of actual exposure, which is described in Japanese Patent Application Laid-Open No. 62-1011, entitled "Method of Manufacturing Integrated Device". However, Si, Al different from the step portion (7) which is a heavy metal (9) such as W, Ta, etc.
Since the light element (11) such as is used for the flat portion (8), the peak value intensity of the first-order differential waveform (10) is improved, but the reflected electron signal (5) from the flat portion (8) is shown in FIG. Since it is detected as background noise as in the case of the mark structure, a significant improvement in the S / N ratio cannot be expected.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a resist film provided on a semiconductor substrate or a thin film and absorbing and reacting to electron beam energy is exposed by using an electron beam. A reference mark for calibration used at the time of device calibration of an electron beam exposure apparatus for forming a desired pattern, wherein the reference mark is convex on a base substrate of a light element and a convex portion of a heavy metal material on the base substrate and around the convex portion. Is formed of a flat portion of the same heavy metal material as the portion, the thickness of the heavy metal material at the flat portion is smaller than the thickness of the heavy metal material at the convex portion, and the thickness of the heavy metal material at the flat portion is the maximum of the incident electrons in the heavy metal. This is a reference mark for device calibration, which is about 1/5 of the range distance. Further, the light element base substrate is Si or Al, and the heavy metal thin film is W or Ta. Further, electron beam exposure is performed using the calibration reference mark. An apparatus calibration method characterized by performing apparatus calibration of an apparatus.

[0006]

According to the present invention, the reference mark structure for calibrating the apparatus of the electron beam exposure apparatus comprises a base substrate made of a light element, a convex portion of the heavy metal material on the base substrate, and the same heavy metal material as the convex portion around the convex portion. The thickness of the heavy metal material at the flat portion is smaller than the thickness of the heavy metal material at the convex portion, and the thickness of the heavy metal material at the flat portion is about 1 of the maximum range of incident electrons in the heavy metal. / 5, that is, by coating a heavy metal film, which is the same material as the convex portion of the step having the optimum film thickness, on the flat portion, so that the flat noise causing the background noise is formed. The reflected electron signal from the section can be reduced, and the S / N ratio can be improved.

[0007]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of an apparatus calibration reference mark according to an embodiment of the present invention. When performing device calibration, incident electrons (4) are scanned (deflected) in the X-axis direction shown in FIG. 1, a reflected electron signal (5) is detected by a detector (6), and the reflected electron signal (5) is detected. The position of the center of the step is detected from the peak value of the primary differential waveform (10) of 5), and the beam size is detected from between the peak values. Then, based on these, the deflection distortion at the time of electron beam scanning (deflection) and the beam size of the incident electron beam (4) are quantified to calibrate the electron beam exposure apparatus.

In the present invention, a thin film of the same heavy metal (W, Ta, etc., (9) as the step portion (7)) is formed on a flat portion (8) on a base substrate (11), which is a light element such as Si or Al. Is formed with an optimum thickness (about 0.5 to 1.0 μm), so that the incident electrons (4) pass through the heavy metal thin film (9) and are injected into the underlying substrate (11) which is a light element. The incident electrons (4) injected into the base substrate (11) are scattered in the base substrate (11) and further scattered at the interface with the heavy metal thin film (9), so that the incident energy is lost. For this reason, the re-entry into the heavy metal thin film (9) and the reflected electron signal (5) detected from the surface of the flat portion (8) almost disappears.

That is, it is possible to reduce the reflected electron signal (5) from the flat portion (8) which causes the background noise, and to improve the S / N ratio. In other words, the use of the calibration reference mark having this structure enables highly accurate device calibration. here,
The optimum thickness of the heavy metal thin film (9) is determined by the acceleration voltage of the incident electrons (4), the film density of the heavy metal thin film (9), and the like. For example, if the acceleration voltage of the incident electron (4) is 50
kV, and when W is used for the heavy metal film (9), the maximum range of the incident electrons (4) into W is about 3.0 μm, and the incident electrons (4) Since the stationary probability distribution is usually represented by a Gaussian distribution, the optimal film thickness is about 1
If it is set to / 5, that is, 0.6 μm, about 90% or more of the electrons pass through the W film (9).

Next, a process for manufacturing the reference mark for device calibration according to the present invention will be described. FIG. 2 and FIG. 3 show an example of a production flow of the device calibration reference mark. In FIG. 2A,
A heavy metal such as W or Ta (9) is deposited on a substrate (11) such as a light element such as Si or Al by CVD or sputtering.
The film is formed with a sufficient film thickness. Next, etching is performed as shown in FIG. 2B using a resist or a mask of SiO ₂ (12). At this time, as shown in FIG. 2C, it is necessary to leave a heavy metal film having an optimum thickness on the flat portion. Although the heavy metals are described as W and Ta, other heavy metals may be used, and naturally, Mo and Cr may be used.

In the manufacturing example shown in FIG. 3, first, as shown in FIG. 3A, a heavy metal (9) is formed on an undersubstrate (11), which is a light element, with an optimum thickness by CVD or sputtering. I do.
Next, a film of (13) such as SiO ₂ or Si ₃ N ₄ is formed as shown in FIG.
It is formed by film formation and etching as shown in FIG. Finally, as shown in FIG. 3C, a heavy metal (9) is buried by selective CVD, sputtering, or the like, and finally SiO ₂ , Si ₃ N
_{4 The} film (13) is removed.

[0012]

As described above, according to the present invention,
By coating the flat part of the device calibration reference mark with a heavy metal film having the same optimum thickness as that of the step, the reflected electron signal from the step and the reflection from the flat part are maintained without reducing the intensity of the reflected electric signal. This has the effect of significantly improving the electron signal ratio (S / N ratio), and as a result, improving the position measurement accuracy and beam size detection accuracy by electron beam scanning (deflection) required when calibrating an electron beam exposure apparatus. Can be done. In other words, the use of this calibration reference mark has the effect of enabling highly accurate calibration of the electron beam exposure apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a calibration reference mark production process of the present invention.

FIG. 3 is a flowchart illustrating a process of producing a calibration reference mark according to the present invention.

FIG. 4 is an explanatory diagram of an apparatus calibration method for explaining a conventional example.

FIG. 5 illustrates a conventional example.

FIG. 6 illustrates a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Wafer, reticle, etc. 2 Stage 3 Device calibration reference mark 4 Incident electron 5 Reflected electron signal 6 Detector 7 Step portion of calibration reference mark 8 Flat portion of calibration reference mark 9 Heavy metal such as W, Ta 10 Reflected electron signal (5) the first-order differential waveform 11 Si, light element substrate 12 SiO ₂ such as Al, a resist such as a mask 13 SiO _2, Si ₃ N ₄ such as a mask of

Claims (4)

(57) [Claims] An electron beam exposure apparatus for exposing a resist film, which is provided on a semiconductor substrate or a thin film and absorbs and reacts to an electron beam energy, with an electron beam to form a desired pattern. In the fiducial mark, the fiducial mark is formed of a base substrate of a light element, a convex portion of the heavy metal material on the base substrate, and a flat portion of the same heavy metal material as the convex portion around the convex portion. The film thickness is smaller than the film thickness of the heavy metal material in the convex portion,
An apparatus calibration reference mark wherein the thickness of the heavy metal material at the flat portion is about 1/5 of the maximum range of incident electrons in the heavy metal. 2. The reference mark for device calibration according to claim 1, wherein the light element base substrate is Si or Al. 3. The reference mark according to claim 1, wherein the heavy metal thin film is W or Ta. 4. A method of calibrating an electron beam exposure apparatus using the calibration reference mark according to claim 1.